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proberecall
United States104 Posts
My question is: what happens if they both carry a cellphone and they keep in constant communication? My guess is that since the waves travel at the speed of light, the signal would be discrete and would frequently break, until it gets to a point where the Earth twin dies and no longer sends a signal. Am I right or too far with this? | ||
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Jombozeus
China1014 Posts
In other words, its probably just not going to reach him within his lifetime after 2 days if hes traveling at 99% speed of light. Just do the math. | ||
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AmericanUmlaut
Germany2577 Posts
I guess I don't understand the point of the thought experiment, though. What about the situation is changed in an interesting way by having the two individuals in contact? | ||
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Nawyria
Netherlands140 Posts
Name the twin that stays on earth twin A and the travelling one twin B; assume further that they communicate by way of a continuous stream of light that varies mildly in wavelength around 550 nanometres (yellow). 1B) As twin B moves away from the earth at high speed, the relativistic doppler-effect redshifts the light signal, the signals he receives are in the red or infrared. He will also receive the signals at a lower pace due to the fact the light signals have to catch up to him, and thus the intensity will be much lower and the transmitted message plays very slowly. 2B) Just after twin B reverses his direction of travel (which we will assume he does instantly), all the signals he has been travelling ahead of will catch up to him in a very short amount of time. Since twin B is now travelling towards earth, the signals will be blueshifted and the signals he receives are in the blue, ultraviolet or beyond. He will now receive the signals at a much much higher pace, so the intensity will be much higher and the transmitted message plays extremely fast. 3B) After this short burst has passed and twin B is travelling back towards the earth, we are in the inverse of situation 1B. The light signals are blueshifted (as in 2B), the intensity is higher (though not as high in 2B) and the message players faster (though not as fast as in 2B). 1A) After twin A says his farewell to twin B, he will receive messages at a very slow pace, with the same redshift, intensity and message speed as in 1B. 2A) As twin B nears earth, all the messages that he has sent since turning around will reach earth in a very short fashion, much like what happens in 2B, only the intensity will be even higher. Edit: Assuming the distances are vast enough for twin A to die as twin B is travelling, it depends on the speed of twin B whether he receives words of twin A's death as he is travelling or soon after he turns around. The faster twin B travels, the less messages he will receive before turning around, thus increasing the chance he will hear of it after he turns around. | ||
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iNSiPiD1
United States140 Posts
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nam nam
Sweden4672 Posts
On July 22 2011 01:03 iNSiPiD1 wrote: If you assumed that they were actually able to keep in touch in real-time, which as others have pointed out is not possible with a cell phone, then yes, the twin on the spaceship would simply listen to the twin on earth die way before he dies. What if the twin on earth get hit by a car? | ||
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skunk_works
United States109 Posts
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japro
172 Posts
Aside from that I don't see why it wouldn't be possible to communicate with any kind of radio transmission (like a cell phone). Relativistic corrections have to be taken into account even at way lower velocities/acceleration differences. GPS satellites for example are essentially clocks and their signal has to be corrected for relativistic effects to obtain correct coordinates. So there is no "physical" reason why you shouldn't be able to communicate. A cellphone just wouldn't work for technical reasons. | ||
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oxidized
United States324 Posts
On July 22 2011 01:07 skunk_works wrote: This is from Einstein's theory of relativity. You can read about it.how does traveling at the speed of light keep you from getting old? | ||
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iNSiPiD1
United States140 Posts
If the twin on earth gets hit by a car then the twin on earth gets hit by a car. I think that answer the question? | ||
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AmericanUmlaut
Germany2577 Posts
Serves him right if he's talking on his cell phone instead of paying attention... | ||
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Stropheum
United States1124 Posts
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KimJongChill
United States6429 Posts
On July 22 2011 01:02 Nawyria wrote: The Lorentz transformation in flat space-time is a continuous transformation, so the signal will not be discrete; however, the signal will be distorted due to the relativistic doppler-effect. Name the twin that stays on earth twin A and the travelling one twin B; assume further that they communicate by way of a continuous stream of light that varies mildly in wavelength around 550 nanometres (yellow). 1B) As twin B moves away from the earth at high speed, the relativistic doppler-effect redshifts the light signal, the signals he receives are in the red or infrared. He will also receive the signals at a lower pace due to the fact the light signals have to catch up to him, and thus the intensity will be much lower and the transmitted message plays very slowly. 2B) Just after twin B reverses his direction of travel (which we will assume he does instantly), all the signals he has been travelling ahead of will catch up to him in a very short amount of time. Since twin B is now travelling towards earth, the signals will be blueshifted and the signals he receives are in the blue, ultraviolet or beyond. He will now receive the signals at a much much higher pace, so the intensity will be much higher and the transmitted message plays extremely fast. 3B) After this short burst has passed and twin B is travelling back towards the earth, we are in the inverse of situation 1B. The light signals are blueshifted (as in 2B), the intensity is higher (though not as high in 2B) and the message players faster (though not as fast as in 2B). 1A) After twin A says his farewell to twin B, he will receive messages at a very slow pace, with the same redshift, intensity and message speed as in 1B. 2A) As twin B nears earth, all the messages that he has sent since turning around will reach earth in a very short fashion, much like what happens in 2B, only the intensity will be even higher. Edit: Assuming the distances are vast enough for twin A to die as twin B is travelling, it depends on the speed of twin B whether he receives words of twin A's death as he is travelling or soon after he turns around. The faster twin B travels, the less messages he will receive before turning around, thus increasing the chance he will hear of it after he turns around. Wow, are you an astrophysicist? | ||
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Wonderballs
Canada253 Posts
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Nawyria
Netherlands140 Posts
Not an astrophysicist, but just a physicist. Einstein's Theory of Relativity has interested my for the larger part of my life; I wrote a paper on visualising relativity some time ago. | ||
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proberecall
United States104 Posts
So I understand that cell phone wouldn't work. Does your explanation also apply for any other radio signal or any other way of keeping in communication ? Also. Now that I see the signals are continued, if they keep talking at all times... at what point does the time difference start to notice ? meaning when does travelling twin start noticing Earth twin is growing older? | ||
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Sbrubbles
Brazil5776 Posts
On July 22 2011 01:15 AmericanUmlaut wrote: Serves him right if he's talking on his cell phone instead of paying attention... Which leads me to the conclusion that, if you have a twin in outer space traveling at close to the speed of light, you shouldn't buy a cell phone. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 01:47 proberecall wrote: Nawria, thank you So I understand that cell phone wouldn't work. Does your explanation also apply for any other radio signal or any other way of keeping in communication ? The reason cell phones wouldn't work is because the transmitters inside the phones or the large antennae we use to communicate on earth wouldn't do us any good over the vast distances involved in the twin paradox. Still, cell phones, radio's, skype calls etc. all work by means of sending electromagnatic waves, which travel at the speed of light. As long as the signal is strong enough to travel the distance without getting drowned out by background noise, the same reasoning holds as I gave for the yellow light signals. However most messages we send through our cell phones, for example, are encoded and a doppler-shift in the wavelength of the signal may not correspond 1-to-1 with a voice message being played at a higher or lower frequency or speed. The reason I used the example of yellow light signals to communicate is so that the similarity between the doppler-shifted light and the doppler-shift we frequently hear when an ambulance speeds past us is maintained. | ||
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Blazinghand
United States25551 Posts
On July 22 2011 01:47 proberecall wrote: Nawria, thank you So I understand that cell phone wouldn't work. Does your explanation also apply for any other radio signal or any other way of keeping in communication ? Also. Now that I see the signals are continued, if they keep talking at all times... at what point does the time difference start to notice ? meaning when does travelling twin start noticing Earth twin is growing older? They won't be able to keep talking due to the relatavistic "bend/stretch." Imagine, if you would, a train or car going past. It goes "wweeeeeeeee-ooooooooh", with the sound being high pitched as it approaches and low pitched as it passes away. This is because of the frequency of the sound being emitted sounding different to you due to the motion of the car. A similar, but somewhat different effect happens with "time dilation" where if I communicate, say, through a series of pulses, each pulse and the gap between each pulse becomes shorter and shorter as my reference frame moves faster and faster. This would make the establishment of some sort of communications standard very difficult, since anything using frequency would be out the window, or extremely hard to calculate. The traveling twin would immediately start noticing the earth twin is growing older, the instant his journey had been underway, because the earth twin will be a second or two older, etc, very quickly. This sort of thing has been done with atomic clocks and it doesn't take long for them to become desynced. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 01:58 Blazinghand wrote: They won't be able to keep talking due to the relatavistic "bend/stretch." Imagine, if you would, a train or car going past. It goes "wweeeeeeeee-ooooooooh", with the sound being high pitched as it approaches and low pitched as it passes away. This is because of the frequency of the sound being emitted sounding different to you due to the motion of the car. A similar, but somewhat different effect happens with "time dilation" where if I communicate, say, through a series of pulses, each pulse and the gap between each pulse becomes shorter and shorter as my reference frame moves faster and faster. This would make the establishment of some sort of communications standard very difficult, since anything using frequency would be out the window, or extremely hard to calculate. When considering though experiments like these, I usually idealise things and assume that communication is possible. However, practical issues do present a new variety of interesting problems as it all depends on the velocity of the travelling twin. At, say, 0.95c or 0.99c the associated γ-factor is 3.2 and 7.1 respectively and should be well within our capacity to handle. But you are more and more right when we continue adding 9's, seeing as 0.999c corresponds to γ=22.3, 0.9999c to 70.7 and it only gets much worse from there. | ||
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nihlon
Sweden5581 Posts
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mcc
Czech Republic4646 Posts
On July 22 2011 01:07 skunk_works wrote: how does traveling at the speed of light keep you from getting old? I assume you meant close to the speed of light as object with stationary mass traveling at the speed of light is iffy concept. With that assumption in mind : it does not. Just from a point of view of someone on Earth you will be aging slower. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 02:07 nihlon wrote: Are you people just assuming the rate of aging or is this a part of the theory? The rate of aging is part of the theory. Intertial observers travelling at different velocities have different notions of time. This is what's at the core of the Twin Paradox, the travelling twin experiences less time passing by a factor of 1 / sqrt( 1 - v²/c²) where v is his speed and c is the speed of light. This factor is also called the gamma-factor (often denoted by γ) and pops up a lot in the various formulae of the Theory of Special Relativity. | ||
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Capook
United States122 Posts
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XxDefexX
Denmark19 Posts
On July 22 2011 01:02 Nawyria wrote: The Lorentz transformation in flat space-time is a continuous transformation, so the signal will not be discrete; however, the signal will be distorted due to the relativistic doppler-effect. Name the twin that stays on earth twin A and the travelling one twin B; assume further that they communicate by way of a continuous stream of light that varies mildly in wavelength around 550 nanometres (yellow). 1B) As twin B moves away from the earth at high speed, the relativistic doppler-effect redshifts the light signal, the signals he receives are in the red or infrared. He will also receive the signals at a lower pace due to the fact the light signals have to catch up to him, and thus the intensity will be much lower and the transmitted message plays very slowly. 2B) Just after twin B reverses his direction of travel (which we will assume he does instantly), all the signals he has been travelling ahead of will catch up to him in a very short amount of time. Since twin B is now travelling towards earth, the signals will be blueshifted and the signals he receives are in the blue, ultraviolet or beyond. He will now receive the signals at a much much higher pace, so the intensity will be much higher and the transmitted message plays extremely fast. 3B) After this short burst has passed and twin B is travelling back towards the earth, we are in the inverse of situation 1B. The light signals are blueshifted (as in 2B), the intensity is higher (though not as high in 2B) and the message players faster (though not as fast as in 2B). 1A) After twin A says his farewell to twin B, he will receive messages at a very slow pace, with the same redshift, intensity and message speed as in 1B. 2A) As twin B nears earth, all the messages that he has sent since turning around will reach earth in a very short fashion, much like what happens in 2B, only the intensity will be even higher. Edit: Assuming the distances are vast enough for twin A to die as twin B is travelling, it depends on the speed of twin B whether he receives words of twin A's death as he is travelling or soon after he turns around. The faster twin B travels, the less messages he will receive before turning around, thus increasing the chance he will hear of it after he turns around. According to 2A (I guess A means, we watch it from A's perspective?), the messages sent after the turning point will arrive "in a very short fashion". The thing interesting me here is: If they were to do so, looking at the situation from A's perspective, the messages would have to travel faster than the speed of light. I mean, assuming B travelling as close to the speed of light as possible, it would take almost as long for B to return to Earth as it takes for the messages - since they of course can't travel faster than c. Therefore, the speed of the messages, B has sent after turning around, will not be that higher than the speed of B, and they will not reach Earth as fast as you claim? You could say, that looking from A's perspective (as I do in order to claim this), the time dillation kicks in and makes the "time of the messages" go at a slower pace. But according to B travelling nearly as fast, B's time would go almost as slow and therefore the messages shouldn't arrive "in a very short fashion"? Even if we turn the perspective, the distance to Earth (seen from the perspective of the messages) would be relatively short, due to the high speed, but so would the distance to Earth for our twin B. So unless I misunderstood something, which I probably did :D, the messages B sends after turning around, shouldn't arrive in a very short fashion, since you obviously can't just add the speed of B and the speed of light and get the speed of the messages  . | ||
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mcc
Czech Republic4646 Posts
On July 22 2011 02:07 nihlon wrote: Are you people just assuming the rate of aging or is this a part of the theory? I am not exactly familiar with the math, but the rate should depend on the velocities in question, or at least acceleration (as the acceleration and deceleration is in actuality what makes the paradox work as someone already noted). | ||
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JinDesu
United States3990 Posts
On July 22 2011 02:13 mcc wrote: I am not exactly familiar with the math, but the rate should depend on the velocities in question, or at least acceleration (as the acceleration and deceleration is in actuality what makes the paradox work as someone already noted). It's dependent on the velocity/ | ||
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mcc
Czech Republic4646 Posts
So the acceleration is there just to make it asymetrical situation(non-inertial frame) and the actual values have no bearing on the resulting age difference ? | ||
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JinDesu
United States3990 Posts
It would have bearing, since to achieve velocity, you have to have some form of acceleration for a duration of time. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 02:12 XxDefexX wrote: According to 2A (I guess A means, we watch it from A's perspective?), the messages sent after the turning point will arrive "in a very short fashion". The thing interesting me here is: If they were to do so, looking at the situation from A's perspective, the messages would have to travel faster than the speed of light. I mean, assuming B travelling as close to the speed of light as possible, it would take almost as long for B to return to Earth as it takes for the messages - since they of course can't travel faster than c. Therefore, the speed of the messages, B has sent after turning around, will not be that higher than the speed of B, and they will not reach Earth as fast as you claim? You could say, that looking from A's perspective (as I do in order to claim this), the time dillation kicks in and makes the "time of the messages" go at a slower pace. But according to B travelling nearly as fast, B's time would go almost as slow and therefore the messages shouldn't arrive "in a very short fashion"? Even if we turn the perspective, the distance to Earth (seen from the perspective of the messages) would be relatively short, due to the high speed, but so would the distance to Earth for our twin B. So unless I misunderstood something, which I probably did :D, the messages B sends after turning around, shouldn't arrive in a very short fashion, since you obviously can't just add the speed of B and the speed of light and get the speed of the messages .I'm not really sure what your question is, but I'll try to help anyhow. They say a pictures says a thousand words, so I hope these are worth at least two thousand. The idea here is that the observers are emitting messages at fixed intervals according to their own perception of time. Twin A's messages You can see clearly that most of A's messages arrive after B has turned around. Thinking about it, I may have been wrong in my initial post in that 2B doesn't happen when twin B turns around instantaneously, but is in fact due to him having to decelerate. + Show Spoiler [picture] + ![[image loading]](http://i.imgur.com/FVqPk.jpg) Twin B's messages You can see that A receives all of B's messages after he has turned around in the short amount of time before B's arrival. The messages do not actually travel faster than light, but the fact that they arrive quickly after one another is because each messages is sent from a position that is closer to earth than the previous. + Show Spoiler [picture] + ![[image loading]](http://i.imgur.com/Bm0YN.jpg) I'd be glad to answer any more questions you might have. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 02:36 JinDesu wrote: The acceleration would increase (or decrease) the rate of aging, or rather, increase or decrease the time dilation. It would have bearing, since to achieve velocity, you have to have some form of acceleration for a duration of time. The process of deceleration/acceleration itself isn't actually what causes the twin paradox to occur. The Lorentz-transformation has a directional bias and as long as the velocity of the travelling twin flips direction, the twin's time and space axes will shift to accommodate the lack of aging. | ||
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kellymilkies
Singapore1393 Posts
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XxDefexX
Denmark19 Posts
. The problem was, that I understood your post as if Twin B's messages sent after the turning point would arrive way faster than B (which is not what was meant - clearly seen by the picture.Good luck with your studies . And btw, I'm drinking coke atm., but filled the glass too much. Why didn't it run over the top and out on my desktop? (sorry for off-topic :D) | ||
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Blazinghand
United States25551 Posts
On July 22 2011 02:42 kellymilkies wrote: Where can I find more about this subject? http://en.wikipedia.org/wiki/Twin_paradox or the chinese translation these both have pretty good information on it. You might want to read up on spacetime diagrams as well, because they are also cool. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 02:42 kellymilkies wrote: Where can I find more about this subject? The wikipedia page for the Twin paradox is pretty good. Another few links that I can recommend: Through Einstein's Eyes The C-Ship: Aberration of light Cool videos: Relativistic Aberration Intensity Effects Relativistic Tram Relativistic Rollercoaster must watch | ||
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Maenander
Germany4926 Posts
On July 22 2011 02:40 Nawyria wrote: The process of deceleration/acceleration itself isn't actually what causes the twin paradox to occur. The Lorentz-transformation has a directional bias and as long as the velocity of the travelling twin flips direction, the twin's time and space axes will shift to accommodate the lack of aging. I see your point, but without deceleration/acceleration one couldn't actually decide which twin flipped direction, i.e. who is in the inertial frame. | ||
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wherebugsgo
Japan10647 Posts
On July 22 2011 02:12 XxDefexX wrote: According to 2A (I guess A means, we watch it from A's perspective?), the messages sent after the turning point will arrive "in a very short fashion". The thing interesting me here is: If they were to do so, looking at the situation from A's perspective, the messages would have to travel faster than the speed of light. I mean, assuming B travelling as close to the speed of light as possible, it would take almost as long for B to return to Earth as it takes for the messages - since they of course can't travel faster than c. Therefore, the speed of the messages, B has sent after turning around, will not be that higher than the speed of B, and they will not reach Earth as fast as you claim? You could say, that looking from A's perspective (as I do in order to claim this), the time dillation kicks in and makes the "time of the messages" go at a slower pace. But according to B travelling nearly as fast, B's time would go almost as slow and therefore the messages shouldn't arrive "in a very short fashion"? Even if we turn the perspective, the distance to Earth (seen from the perspective of the messages) would be relatively short, due to the high speed, but so would the distance to Earth for our twin B. So unless I misunderstood something, which I probably did :D, the messages B sends after turning around, shouldn't arrive in a very short fashion, since you obviously can't just add the speed of B and the speed of light and get the speed of the messages .I think you did misunderstand it. The reason the messages arrive faster/slower is not because the speed is added. It's because the point of propagation of the waves keeps changing. Look at it this way: when the spaceship is traveling away from Earth, with every passing unit of time the spaceship sends a signal, but from a position that is constantly changing and constantly getting further away from Earth. Let's take a few example wave pulses to demonstrate this, and say that the total distance to the alien planet is 10 light years. When the spaceship initially leaves, let's say 10 seconds after departure it sends a message, Earth will receive it a little bit less than 10 seconds later, while the spaceship has traveled roughly double the distance of where it was to begin with. If the spaceship sends a message from 5 light years away, it'll take 5 light years for the Earth to receive it. Regardless, on the way there it'll take longer for the messages to reach Earth while the spaceship travels away. Each message will therefore be received further and further apart. On the way back, let's start at 10 light years away. The spaceship sends a pulse while coming back, and it'll take 10 years to hit Earth. Call this message 1. Message 2 is sent at 9 light years away (a tiny bit more than a year later) and it takes 9 light years to get to Earth, etc etc. If you notice, at the end of the journey the receiver on Earth will receive almost every message from the ship that was made on the journey back within a very short span of time, almost immediately before the ship arrives. | ||
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hytonight
303 Posts
On July 22 2011 01:15 AmericanUmlaut wrote: Serves him right if he's talking on his cell phone instead of paying attention... what if it was a drunk driver that crashed into his house? | ||
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XxDefexX
Denmark19 Posts
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Nawyria
Netherlands140 Posts
On July 22 2011 02:49 Maenander wrote: I see your point, but without deceleration/acceleration one couldn't actually decide which twin flipped direction, i.e. who is in the inertial frame. You are entirely correct, sir. On July 22 2011 02:47 XxDefexX wrote: Thanks a lot, they did say at least two thousand words . The problem was, that I understood your post as if Twin B's messages sent after the turning point would arrive way faster than B (which is not what was meant - clearly seen by the picture.Good luck with your studies . And btw, I'm drinking coke atm., but filled the glass too much. Why didn't it run over the top and out on my desktop? (sorry for off-topic :D)This is because of surface tension. There are basically three forces at work here. 1) Water likes to be near water. Water molecules form so-called hydrogen bonds among each other, which makes it energetically favourable for water molecules to be clustered. 2) A body of water "pays energy" for its boundary. Basically, the larger the boundary between a body of water and the outside, the less energetically favourable the situation is. Therefore water will try to minimize its surface area. 3) There is gravity that attempts to pull the water molecules down and spill it over your glass. The lower the water molecules are, the more energetically favourable. What happens to your glass of coke is exactly what happens to a drop of water on your desk. The drop of water attempts to make its state as energetically favourable as it can. Clearly, going by gravity alone, the most energetically favourable state is for it to be as flat as possible, since then the water molecules are as close to the ground as they can be without spilling over your desk. However, the flatter the drop becomes, the larger its surface area will be (this costs energy) and the less clustered the drop becomes (this too costs energy). Therefore, the water droplet will become slightly flattened, but still retain a drop-like shape; this is simply the most favourable state considering the above three factors. In your case, if the water were to spill over the side of the glass, its surface area would increase dramatically and the gravitational energy is not sufficient to compensate for it. However if you were to pour a little more coke into the glass, you would surpass a critical point beyond which it is more favourable for the liquid to spill over and incur the penalty of a larger surface area, and your glass will spill. | ||
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XxDefexX
Denmark19 Posts
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Nawyria
Netherlands140 Posts
On July 22 2011 03:07 XxDefexX wrote: Cool!! Thanks a lot for the explanation. Say we were to make a glass with very small holes in it. Given the right proportions, the water would actually stay in the glass and thereby stay close to the other water molecules, instead of leaving the glass? Probably not. Part of the reason why water doesn't spill over the side of a glass is that only the water at the top of the glass goes into an gravitationally more favourable state by spilling. If you would have, say, a small hole in the middle of the glass, then any bit of water spilling out makes the water above able to take its place, so in essence spilling out puts an entire column of water above the spilling point in a gravitationally more favourable state, rather than just the bit that spilled. | ||
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JinDesu
United States3990 Posts
On July 22 2011 03:07 XxDefexX wrote: Cool!! Thanks a lot for the explanation. Say we were to make a glass with very small holes in it. Given the right proportions, the water would actually stay in the glass and thereby stay close to the other water molecules, instead of leaving the glass? I forget the name of the fabric, but there is a fabric that can hold water because of surface tension phenomenon. If I can remember the name of the fabric, I'll find links to it. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 03:13 JinDesu wrote: I forget the name of the fabric, but there is a fabric that can hold water because of surface tension phenomenon. If I can remember the name of the fabric, I'll find links to it. Good man, I forgot the name of the phenomenon. | ||
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XxDefexX
Denmark19 Posts
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Mafs
Canada458 Posts
I think this is what happens for what OP is asking. Just watch from 3 minutes to 4 minutes. Its a cool demonstration of time dilation. | ||
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JinDesu
United States3990 Posts
On July 22 2011 03:15 XxDefexX wrote: I see, it would be nice though. Say I ragequit a 1v1 game and accidently hit my glass of coke, a little hole occurs but it doesn't spill on my computer cause of surface tension, so I can keep 1v1-ing :D. Please let me know, if you find the link I'm not quite sure that would be how it works lol.. I believe the fabric is cheesecloth, as looking on the web, lots of videos are showing how you can wrap cheesecloth on a bottle (or jar) full of water and turn it upside down, and the water remains inside. However, if enough pressure is applied, the water will still go through (of course). | ||
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Sabin010
United States1892 Posts
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Reborn8u
United States1761 Posts
Here is something else to wrap your mind around. It takes 8 minutes for light to travel from the sun to the earth. If you had 1 long chain or rope and it stretched from the earth to the sun. When you pulled one end it would take 8 minutes for the other end to move. | ||
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MangoTango
United States3670 Posts
On July 22 2011 01:07 skunk_works wrote: how does traveling at the speed of light keep you from getting old? It doesn't. Outside observers will observe you aging very slowly. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 05:06 Sabin010 wrote: The real question is what if the twins kept in contact via morse code through entagled particles? If twin A measures his entangled particle on one end, he knows the wavefunction of twin B's particle on the other hand. However, when twin B measured the particle on his end, he has no way of knowing whether the result he gets came from a wavefunction that collapsed because twin A measured the other particle. Entangled particles cannot actually transmit information. | ||
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Igakusei
United States610 Posts
http://www.youtube.com/user/ozmoroid | ||
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Najda
United States3765 Posts
On July 22 2011 01:02 Nawyria wrote: The Lorentz transformation in flat space-time is a continuous transformation, so the signal will not be discrete; however, the signal will be distorted due to the relativistic doppler-effect. Name the twin that stays on earth twin A and the travelling one twin B; assume further that they communicate by way of a continuous stream of light that varies mildly in wavelength around 550 nanometres (yellow). 1B) As twin B moves away from the earth at high speed, the relativistic doppler-effect redshifts the light signal, the signals he receives are in the red or infrared. He will also receive the signals at a lower pace due to the fact the light signals have to catch up to him, and thus the intensity will be much lower and the transmitted message plays very slowly. 2B) Just after twin B reverses his direction of travel (which we will assume he does instantly), all the signals he has been travelling ahead of will catch up to him in a very short amount of time. Since twin B is now travelling towards earth, the signals will be blueshifted and the signals he receives are in the blue, ultraviolet or beyond. He will now receive the signals at a much much higher pace, so the intensity will be much higher and the transmitted message plays extremely fast. 3B) After this short burst has passed and twin B is travelling back towards the earth, we are in the inverse of situation 1B. The light signals are blueshifted (as in 2B), the intensity is higher (though not as high in 2B) and the message players faster (though not as fast as in 2B). 1A) After twin A says his farewell to twin B, he will receive messages at a very slow pace, with the same redshift, intensity and message speed as in 1B. 2A) As twin B nears earth, all the messages that he has sent since turning around will reach earth in a very short fashion, much like what happens in 2B, only the intensity will be even higher. Edit: Assuming the distances are vast enough for twin A to die as twin B is travelling, it depends on the speed of twin B whether he receives words of twin A's death as he is travelling or soon after he turns around. The faster twin B travels, the less messages he will receive before turning around, thus increasing the chance he will hear of it after he turns around. What if the twin traveling in the spaceship traveled in an arc-shaped fashion that allowed him to always be equidistant from his twin so he is never going towards or away from his twin but closer to perpendicular? | ||
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Blazinghand
United States25551 Posts
On July 22 2011 05:14 Reborn8u wrote: Time is relative to the individual. The twin traveling would experience time in slow motion. So if you could talk via communication hypothetically, the twin traveling might take an hour to say one word, as it was observed by the twin here on earth. But to the twin in space time would feel normal, and when the twin on earth spoke it would probably sound like it was on fast forward. Here is something else to wrap your mind around. It takes 8 minutes for light to travel from the sun to the earth. If you had 1 long chain or rope and it stretched from the earth to the sun. When you pulled one end it would take 8 minutes for the other end to move. Instead of using light waves, you're using sound waves transferred via the E-M interactions of particles in the chain. It would take substantially longer than 8 minutes. On July 22 2011 05:06 Sabin010 wrote: The real question is what if the twins kept in contact via morse code through entagled particles? Not possible. Entangled particles don't transfer classical information, but rather, are entangled qubits, which work quite differently. In order to transfer information, one twin needs to use a 2nd qubit and produce 2 bits from his 2 qubits, then send that information via conventional means to the other twin at slower-than-light speeds. | ||
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Zirith
Canada403 Posts
On July 22 2011 00:49 Jombozeus wrote: Well, your signal would take a near-infinite amount of time to reach your twin if hes traveling at near the speed of light. In other words, its probably just not going to reach him within his lifetime after 2 days if hes traveling at 99% speed of light. Just do the math. pretty much this, It has been years since I covered this topic in physics but there would just be a massive delay, depending on the speed of the phone waves. The twin in the space ship ages slower because he is moving faster, relative to our plain on existence, so for him we are all just moving slower ie he lives longer because everything he does is wayyyyy faster in comparison. I remember doing a question with some sort of particle that enters the earths atmosphere, it is moving so fast that it's normal half life of say(for example not accurate at all) is 2 seconds, since it is moving at like .8c it actually takes 5 of our seconds for it do finish 1 half life. Again the math behind this is all made up because I don't remember the formula or the numbers but that is basically how I remember it to work. Essentially what I'm trying to say is normal time from the person moving fast seems slower than their time and they age based off the the same time scale which is now slower! | ||
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Quanticfograw
United States2053 Posts
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Frigo
Hungary1023 Posts
On July 22 2011 01:58 Blazinghand wrote: A similar, but somewhat different effect happens with "time dilation" where if I communicate, say, through a series of pulses, each pulse and the gap between each pulse becomes shorter and shorter as my reference frame moves faster and faster. This would make the establishment of some sort of communications standard very difficult, since anything using frequency would be out the window, or extremely hard to calculate. There are self clocking signals that would make this kind of communication possible, provided you have a means to intercept shifted frequencies properly. I'm not sure about the latter tho, signal to noise ratio of time dilated signals might be pretty bad to make any kind of receiver impossible. You need to have a receiver capable of receiving very high frequencies, that's for sure. It would be certainly interesting to look into this matter. | ||
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Kira__
Sweden2672 Posts
On July 22 2011 01:07 skunk_works wrote: how does traveling at the speed of light keep you from getting old? it doesnt | ||
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Blazinghand
United States25551 Posts
On July 22 2011 05:38 Frigo wrote: There are self clocking signals that would make this kind of communication possible, provided you have a means to intercept shifted frequencies properly. I'm not sure about the latter tho, signal to noise ratio of time dilated signals might be pretty bad to make any kind of receiver impossible. You need to have a receiver capable of receiving very high frequencies, that's for sure. It would be certainly interesting to look into this matter. I never said that establishing a communications standard would be impossible, just that it was "very difficult". Assuming, of course, that you can move at .99c, instead of firing lights you could just launch projectiles at .99c towards home, and which projectile you launch could be code for the message. | ||
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Frigo
Hungary1023 Posts
On July 22 2011 05:43 Blazinghand wrote: I never said that establishing a communications standard would be impossible, just that it was "very difficult". Assuming, of course, that you can move at .99c, instead of firing lights you could just launch projectiles at .99c towards home, and which projectile you launch could be code for the message. Yeah, that would be the space age equivalent of dogs with CDs everyone keeps hearing in Computer Networks class :D | ||
]343[
United States10328 Posts
On July 22 2011 05:18 Nawyria wrote: If twin A measures his entangled particle on one end, he knows the wavefunction of twin B's particle on the other hand. However, when twin B measured the particle on his end, he has no way of knowing whether the result he gets came from a wavefunction that collapsed because twin A measured the other particle. Entangled particles cannot actually transmit information. WHOA thanks I was wondering about this! But enough pairs of entangled particles could transmit information with high probability, no? | ||
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Chilling5pr33
Germany518 Posts
If u take the speed resulting from earth rotation, add the speed of the earth (around the sun) add the speed the sun drifts inside the galaxie add the speed of the galixy drifting away from other galaxys. You already get something very close to the speed of light ^^. | ||
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Blazinghand
United States25551 Posts
On July 22 2011 06:01 Chilling5pr33 wrote: Theres something funny i discovered wich really messes my head... If u take the speed resulting from earth rotation, add the speed of the earth (around the sun) add the speed the sun drifts inside the galaxie add the speed of the galixy drifting away from other galaxys. You already get something very close to the speed of light ^^. Another thing that's interesting: if you take the speed of the earth relative to an arbitrary velocity vector, you can get something very close to the speed of light. There's no fixed reference frame in the classical sense-- each reference frame travels with itself, and "fixed" just means... not really fixed. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 05:53 ]343[ wrote: WHOA thanks I was wondering about this! But enough pairs of entangled particles could transmit information with high probability, no? The "information" transmitted is the wavefunction of the particles, which determines the probability with which a particular result will be found when measured. So in this way measuring the particle on one side impacts the measurement on the other side. However, there is no way of telling whether a measurement was conducted on one side, so you can never tell if the outcome of a particular measurement was due to random chance, or due to the collapse of a wavefunction. | ||
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lurked
Canada918 Posts
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Frigo
Hungary1023 Posts
On July 22 2011 06:01 Chilling5pr33 wrote: Theres something funny i discovered wich really messes my head... If u take the speed resulting from earth rotation, add the speed of the earth (around the sun) add the speed the sun drifts inside the galaxie add the speed of the galixy drifting away from other galaxys. You already get something very close to the speed of light ^^. It only matters in comparison to other physical entities. There is no absolute frame of reference, all motion is relative. For all we know, "everything" might be speeding at high speed to the same direction, but it would be no different than standing still. Of course this doesn't save us from colliding with something that moves in our direction extremely fast... | ||
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phyren
United States1067 Posts
On July 22 2011 05:53 ]343[ wrote: WHOA thanks I was wondering about this! But enough pairs of entangled particles could transmit information with high probability, no? http://en.wikipedia.org/wiki/EPR_paradox In short, no. You can read the wikipedia page for their explanation, which includes the no cloning theorem and which I mostly skimmed over. Based on some Quantum Field Theory lectures, I recall the crux of the issue being that there is a difference between local operators and causality. The EPR paradox about entangled particles suggests that entanglement allows information to be transmitted faster than the speed of light. There are different ways of tackling this issue, but the QFT lectures I'm remembering talked about the idea that quantum operators may in fact depend on regions of spacetime that cannot be causally connected. However, the physical observables that can be constructed must not. In this way, they can be non local without violating causality. I think the op's question has been answered in this thread, but I would add that Jackson's E&M (a famous and extremely frustrating text) contains a couple chapters on relativity and has a problem about what would happen if the twins were to exchange photos of themselves constantly. It discusses how the frequency at which the photos are received changes. It's a homework problem, but I'm sure you could find the solution online in a number of places. I can link it if you can't. | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 05:20 Najda wrote: What if the twin traveling in the spaceship traveled in an arc-shaped fashion that allowed him to always be equidistant from his twin so he is never going towards or away from his twin but closer to perpendicular? Interesting situation. Since there is no relative speed between the twins, their signals are not red- or blueshifted. However, they are still subject to time dilatation, meaning that they receive signals more slowly than they transmit them and the signals will seem to be stretched out. Also, due to Relativistic Aberration, the spiralling twin will perceive the signals as coming from a more forwards angle. I'm not particularly sure if any one twin would age more/faster than the other without having to calculate (which I'm currently not able to). | ||
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scorch-
United States816 Posts
On July 22 2011 06:01 Chilling5pr33 wrote: Theres something funny i discovered wich really messes my head... If u take the speed resulting from earth rotation, add the speed of the earth (around the sun) add the speed the sun drifts inside the galaxie add the speed of the galixy drifting away from other galaxys. You already get something very close to the speed of light ^^. Hence, the theory of special relativity. a question for those who know: if you sent a spaceship by Earth at constant velocity relative to earth and synchronized its clock with a clock on Earth at the exact point that it passed Earth, at some time in the future an observer on earth would read the clock on the spaceship as lagging behind the Earth clock, while an observer on the spaceship would read the clock on Earth as lagging behind the clock on the spaceship. can someone explain to me how this is true or false? | ||
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scorch-
United States816 Posts
On July 22 2011 06:16 Nawyria wrote: Interesting situation. Since there is no relative speed between the twins, their signals are not red- or blueshifted. However, they are still subject to time dilatation, meaning that they receive signals more slowly than they transmit them and the signals will seem to be stretched out. Also, due to Relativistic Aberration, the spiralling twin will perceive the signals as coming from a more forwards angle. I'm not particularly sure if any one twin would age more/faster than the other without having to calculate (which I'm currently not able to). That's not an inertial reference frame, so the theory of special relativity must be supplemented by the additional framework of general relativity. edit: I actually have no idea whether what you just said includes general relativistic considerations. | ||
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CatNzHat
United States1599 Posts
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Nawyria
Netherlands140 Posts
On July 22 2011 06:19 scorch- wrote: That's not an inertial reference frame, so the theory of special relativity must be supplemented by the additional framework of general relativity. Which makes it a lot harder than the twin paradox. | ||
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scorch-
United States816 Posts
On July 22 2011 06:20 Nawyria wrote: Which makes it a lot harder than the twin paradox. I don't think anyone would argue that, haha. | ||
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]343[
United States10328 Posts
On July 22 2011 06:06 Nawyria wrote: The "information" transmitted is the wavefunction of the particles, which determines the probability with which a particular result will be found when measured. So in this way measuring the particle on one side impacts the measurement on the other side. However, there is no way of telling whether a measurement was conducted on one side, so you can never tell if the outcome of a particular measurement was due to random chance, or due to the collapse of a wavefunction. Say you agree to send each signal (spin state or whatever) 1000 times beforehand. ... Oh I guess the chance of up or down is still 50/50 lol... Cool, thanks! Not totally comprehending what the other guy said about causality... Haven't taken enough relativity/quantum to understand all of it yet xD | ||
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Nawyria
Netherlands140 Posts
On July 22 2011 06:23 ]343[ wrote: Say you agree to send each signal (spin state or whatever) 1000 times beforehand. ... Oh I guess the chance of up or down is still 50/50 lol... Cool, thanks! It's exactly this what kills your ability to transfer information. Also, not entirely off-topic: http://xkcd.com/465/ | ||
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Dagon
Romania264 Posts
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scorch-
United States816 Posts
On July 22 2011 05:14 Reborn8u wrote: Time is relative to the individual. The twin traveling would experience time in slow motion. So if you could talk via communication hypothetically, the twin traveling might take an hour to say one word, as it was observed by the twin here on earth. But to the twin in space time would feel normal, and when the twin on earth spoke it would probably sound like it was on fast forward. There are no absolute frames of reference in a relativistic environment. To the twin on the spaceship, he is still and the twin on earth is moving away from him at a high velocity. Why would you expect their observations of the other twin's speech to differ? | ||
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scorch-
United States816 Posts
On July 22 2011 06:38 Dagon wrote: I am not sure if I undestand this correctly, but if some way of instant comunication is possible (think on the lines of thelepathy), neither twin would notice the other aging faster/slower, right? time dilation is not a construct like centrifugal force. it is a physical result which has been verified by experiment. it is not a result of the travel time of communication instruments. | ||
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Blazinghand
United States25551 Posts
On July 22 2011 06:38 Dagon wrote: I am not sure if I undestand this correctly, but if some way of instant comunication is possible (think on the lines of thelepathy), neither twin would notice the other aging faster/slower, right? If instant communication was possible, the laws of physics as we know it would have to be rewritten. Everything we know about Special Relativity would be false. The paradox of the twins would be as irrelevant an idea under that physics as the question of how to cast "expelliarmus" is under current physics. | ||
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Dagon
Romania264 Posts
On July 22 2011 06:50 Blazinghand wrote: If instant communication was possible, the laws of physics as we know it would have to be rewritten. Everything we know about Special Relativity would be false. The paradox of the twins would be as irrelevant an idea under that physics as the question of how to cast "expelliarmus" is under current physics. I am definetly not a physicist, but are there no forces that act faster than the speed of light? For example gravity. Does it not manifest itself instantaneous? | ||
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Blazinghand
United States25551 Posts
On July 22 2011 06:58 Dagon wrote: I am definetly not a physicist, but are there no forces that act faster than the speed of light? For example gravity. Does it not manifest itself instantaneous? I am a physicist. There are no forces that act faster than the speed of light. Gravity does not manifest instantaneously. http://en.wikipedia.org/wiki/Speed_of_gravity | ||
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Dagon
Romania264 Posts
On July 22 2011 07:02 Blazinghand wrote: I am a physicist. There are no forces that act faster than the speed of light. Gravity does not manifest instantaneously. http://en.wikipedia.org/wiki/Speed_of_gravity Did not know that. But still.. It says that the speed of gravitational wave is equal to the speed of light in vacuum. So, let's assume the twin in the spaceship has a device witch can detect gravitational pull ( I don't think that's unresonable). And the twin on earth had a device with witch he can create gravitational forces. Wouldn't they still be able to communicate in some kind of morse code, seeing that the messages would be at the speed of light? (so allmost instantaneous in comparison to the velocity of the spaceship) | ||
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mcc
Czech Republic4646 Posts
On July 22 2011 07:19 Dagon wrote: Did not know that. But still.. It says that the speed of gravitational wave is equal to the speed of light in vacuum. So, let's assume the twin in the spaceship has a device witch can detect gravitational pull ( I don't think that's unresonable). And the twin on earth had a device with witch he can create gravitational forces. Wouldn't they still be able to communicate in some kind of morse code, seeing that the messages would be at the speed of light? (so allmost instantaneous in comparison to the velocity of the spaceship) Nope, in the experiment the ship is moving close to the speed of light for the effects to be noticeable. Also you are complicating things, you can just use radio waves to communicate as they move at the speed of light No need to use gravity | ||
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Blazinghand
United States25551 Posts
On July 22 2011 07:19 Dagon wrote: Did not know that. But still.. It says that the speed of gravitational wave is equal to the speed of light in vacuum. So, let's assume the twin in the spaceship has a device witch can detect gravitational pull ( I don't think that's unresonable). And the twin on earth had a device with witch he can create gravitational forces. Wouldn't they still be able to communicate in some kind of morse code, seeing that the messages would be at the speed of light? (so allmost instantaneous in comparison to the velocity of the spaceship) Um, yes, but not any better than if they used lasers or radios, which also travel at the speed of light. Also, remember we're talking about a situation where you can travel at >.99c. They could as easily communicate by writing letters and strapping them onto rockets. | ||
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Dagon
Romania264 Posts
This whole paradox sounds to me the same as asking yourself in 200 AD: "what happens when you reach the end of the world?". And trying to answer this question basing your judgement on the "at the time" logical ideea that the earth is flat and has an end. | ||
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Blazinghand
United States25551 Posts
On July 22 2011 07:35 Dagon wrote: Hmm.. I do have one question though. Isn't all this just speculation based on some premises? Has it actually been proven that the speed of light is the fastest interaction in the universe? Because the whole theory of relativity is based on this premise. This whole paradox sounds to me the same as asking yourself in 200 AD: "what happens when you reach the end of the world?". And trying to answer this question basing your judgement on the "at the time" logical ideea that the earth is flat and has an end. You don't have to reach the end of the world to know that it's not flat. In the 5th century BC scholars knew the earth was round. http://en.wikipedia.org/wiki/Eratosthenes#Eratosthenes.27_measurement_of_the_Earth.27s_circumference You know why? Because you can use evidence to find the truth. Science doesn't make assumptions it draws conclusions. We used to think that some things were faster than the speed of light, or that the concept of "instantaneous" existed. We were wrong. We learned. We used evidence. It's not a premise, it's a conclusion. edited for typos | ||
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mcc
Czech Republic4646 Posts
On July 22 2011 07:35 Dagon wrote: Hmm.. I do have one question though. Isn't all this just speculation based on some premises? Has it actually been proven that the speed of light is the fastest interaction in the universe? Because the whole theory of relativity is based on this premise. This whole paradox sounds to me the same as asking yourself in 200 AD: "what happens when you reach the end of the world?". And trying to answer this question basing your judgement on the "at the time" logical ideea that the earth is flat and has an end. It is actually one of the better "proven" things in science. But as always in science no absolutes and no proofs, just evidence and testing theories. EDIT: especially since even I can generate at home things moving at relativistic speeds | ||
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scorch-
United States816 Posts
On July 22 2011 07:41 mcc wrote: It is actually one of the better "proven" things in science. But as always in science no absolutes and no proofs, just evidence and testing theories. EDIT: especially since even I can generate at home things moving at relativistic speeds High five for being a world class fart artist! | ||
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Dagon
Romania264 Posts
On July 22 2011 07:38 Blazinghand wrote: You don't have to reach the end of the world to know that it's not flat. In the 5th century BC scholars knew the earth was round. http://en.wikipedia.org/wiki/Eratosthenes#Eratosthenes.27_measurement_of_the_Earth.27s_circumference You know why? Because you can use evidence to find the truth. Science doesn't make assumptions it draws conclusions. We used to think that some things were faster than the speed of light, or that the concept of "instantaneous" existed. We were wrong. We learned. We used evidence. It's not a premise, it's a conclusion. edited for typos You say that, but dosen't modern physics atribute every universal law to a not yet understood probabilistic table? That's what quantum physics was all about, wasn't it? Also the string theory. It can certanly explain gravity at a quantum level, but can not be proven in the least. (or disproven for that matter) Premises are made in physics. There are not only conclusions. | ||
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scorch-
United States816 Posts
On July 22 2011 07:57 Dagon wrote: You say that, but dosen't modern physics atribute every universal law to a not yet understood probabilistic table? That's what quantum physics was all about, wasn't it? Also the string theory. It can certanly explain gravity at a quantum level, but can not be proven in the least. (or disproven for that matter) Premises are made in physics. There are not only conclusions. string theories and the corresponding n-dimensional realities they presuppose are a little bit different than the 4-dimensional space-time of einstein's relativity when it comes to confidence in its axioms. | ||
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Blazinghand
United States25551 Posts
On July 22 2011 07:57 Dagon wrote: You say that, but dosen't modern physics atribute every universal law to a not yet understood probabilistic table? That's what quantum physics was all about, wasn't it? Also the string theory. It can certanly explain gravity at a quantum level, but can not be proven in the least. (or disproven for that matter) Premises are made in physics. There are not only conclusions. Nope. You don't "attribute" laws and theories to anything. They're just patterns that have been observed. And if there is new data that changes the way those patterns work, it is evaluated, reproduced, and factored into the model. Are you arguing that there's no gravity? I mean, as far as theories as to WHY gravity works, those are still in progress. The theories as to HOW/WHAT gravity does are pretty well fleshed out. Which of these are you questioning? | ||
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Ender985
Spain910 Posts
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Simberto
Germany11507 Posts
On July 22 2011 07:41 mcc wrote: It is actually one of the better "proven" things in science. But as always in science no absolutes and no proofs, just evidence and testing theories. EDIT: especially since even I can generate at home things moving at relativistic speeds Exactly. Science works the way that you make a theory that explains all data that is known up to that point. If it is a good theory, you can usually deduct some other things from that (If you can't, it is a useless theory). Then, you think up experiments to check whether those things are actually the way they should be according to your theory. If they are, they strengthen your theory. If they are not, you need a new theory. In the case of special relativity, as far as i know Einstein basically thought about "what if the speed of light is constant in all inertial system?" (Inertial System = any nonaccelerated system, but the velocity of the system can be whatever). If you go from that basic premisse, everything else in special relativity like time delation, length contraction, mass distortion and the idea that nothing can be faster then the speed of light directly follows. So far, any experiment made is absolutely in line with those predictions, and as a result this idea is generally acceoted as correct. However, it is not dogma, so if someone comes up with an experiment that follows the scientific guidelines of reproducability and is contrary to that theory, it will have to be changed.But so far that has not happened. In contrary, every single experiment continues to deliver exactly the data that is expected in special relativity. Here are some experiments which strengthen the theory of special relativity: http://en.wikipedia.org/wiki/Tests_of_special_relativity Edit: On July 22 2011 08:05 Blazinghand wrote: Nope. You don't "attribute" laws and theories to anything. They're just patterns that have been observed. And if there is new data that changes the way those patterns work, it is evaluated, reproduced, and factored into the model. Are you arguing that there's no gravity? I mean, as far as theories as to WHY gravity works, those are still in progress. The theories as to HOW/WHAT gravity does are pretty well fleshed out. Which of these are you questioning? I support this. To go even further, science does fundamentally not answer "why?" questions. That is a common misconception. Science only tries to interpretate HOW stuff works, and thus to predict what will happen under specific circumstances without actually having to observe those specific conditions beforehand. A good scientific theory will deliver predictions for a lot of things by trying to generalise specific data. All the "whys" are just helpful constructs, and don't necessarily need to have direct scientific reality. No matter where you start, if you ask "why" often enough, you will reach a point where you won't get an answer. The reason is not that you don't have enough science to get that answer, you will always reach that point at some time. Because those answers to why-question that you think science delivers are not actually what you think they are, they are just part of a theory that explains hows, and not actual whys. But that is not a flaw in science. Science is not supposed to tell you why something happens, it is supposed to determine how it happens. Which is all that is necessary. "Why" is not a question that needs to be answered for anything other than ease of mind. If you want answers to whys, you will need to look somewhere else, but those are generally only speculation anyways, no matter if they come from religion or philosophy. | ||
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Simberto
Germany11507 Posts
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Nawyria
Netherlands140 Posts
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Xtasis
Canada14 Posts
Though I'd like to read something that doesn't require me to be a physicist to understand also ps: thanks for your explanations throughout the thread | ||
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AmericanUmlaut
Germany2577 Posts
On July 22 2011 09:52 Nawyria wrote: I am so in love with this thread. We should do a monthly science discussion thread! Seconded. This is a pretty interesting discussion. | ||
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arbitrageur
Australia1202 Posts
A real n body system, in any possible configuration, can maintain orbit until t->infinite without the system collapsing on itself or the planets going out into space. Say there's water on one. You could put an electricity generator in this water, and as the gravity of other bodies pulls and pushes on the water it will move through the turbine and electricity will be generated. As t->infinite and the system does not collapse, you gather infinite energy with a finite amount of matter (i.e. a never-ending supply of energy). ? Ty | ||
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yoshi_yoshi
United States440 Posts
On July 22 2011 06:06 Nawyria wrote: The "information" transmitted is the wavefunction of the particles, which determines the probability with which a particular result will be found when measured. So in this way measuring the particle on one side impacts the measurement on the other side. However, there is no way of telling whether a measurement was conducted on one side, so you can never tell if the outcome of a particular measurement was due to random chance, or due to the collapse of a wavefunction. Dumb question: How are entangled particles going to be more useful than just giving two people pieces of paper saying "YES" and "NO". Then when each of them look at their paper they know what the other one got. | ||
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lithiumdeuteride
96 Posts
On July 23 2011 01:33 arbitrageur wrote: A real n body system, in any possible configuration, can maintain orbit until t->infinite without the system collapsing on itself or the planets going out into space. If two objects orbit each other with zero eccentricity (circles), and both bodies are tidally locked to the other, then they can remain exactly as they are for t->infinity. + Show Spoiler + On July 23 2011 01:33 arbitrageur wrote: Say there's water on one. You could put an electricity generator in this water, and as the gravity of other bodies pulls and pushes on the water it will move through the turbine and electricity will be generated. As t->infinite and the system does not collapse, you gather infinite energy with a finite amount of matter (i.e. a never-ending supply of energy). If the bodies rotate relative to one another, or the orbits are eccentric, then an oceanic tide is possible. Friction will dissipate this motion, as will a generator running off the shifting of water. This will gradually change the orbits, removing the relative rotation between the objects, and transferring that angular momentum of rotation into orbital angular momentum. This would increase or decrease orbital radius, depending on whether the relative rotation was in the prograde or retrograde direction. | ||
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arbitrageur
Australia1202 Posts
On July 22 2011 06:06 Nawyria wrote: The "information" transmitted is the wavefunction of the particles, which determines the probability with which a particular result will be found when measured. So in this way measuring the particle on one side impacts the measurement on the other side. However, there is no way of telling whether a measurement was conducted on one side, so you can never tell if the outcome of a particular measurement was due to random chance, or due to the collapse of a wavefunction. Can't you thermally isolate one entangled partner such that it doesn't decohere, then cause a reduction of this wavefunction by "measuring" its coupled partner, which would not have otherwise otherwise occured due to near abs zero temperatures. The probability distribution of this waveicle after it has "spread out" again will then be altered from what you originally had? You sure you can't transmit information FAPP ftl using this? Noob question ty. Obv answer is no given the consensus of physicists on this question... but I'd like to know why | ||
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Blazinghand
United States25551 Posts
On July 23 2011 01:33 arbitrageur wrote: Nawyria, answer this. I'm no physicist, but I'm thinking there might be a flaw in the following claim: A real n body system, in any possible configuration, can maintain orbit until t->infinite without the system collapsing on itself or the planets going out into space. Say there's water on one. You could put an electricity generator in this water, and as the gravity of other bodies pulls and pushes on the water it will move through the turbine and electricity will be generated. As t->infinite and the system does not collapse, you gather infinite energy with a finite amount of matter (i.e. a never-ending supply of energy). ? Ty Doesn't work. The system you describe initially can maintain orbit. The system you describe in the last paragraph is not the same system, since it has a generator turbine in it, and one of the bodies has water, as well. I see no reason why every quality of the first system should be necessarily present in the second, or why the absence of any quality of the first system on the second system is meaningful to the first system. For example: A bicycle, unattended, falls over. But a bicycle with a kickstand does not fall over. Sounds like a paradox! How could this be a bicycle and ALSO NOT FALL OVER? The answer is, of course, something was added to the system. | ||
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lolsixtynine
United States600 Posts
On July 22 2011 01:07 skunk_works wrote: how does traveling at the speed of light keep you from getting old? It doesn't. It just makes your frame of reference for time slower and therefore to someone with a faster frame of reference (i.e. not moving), it looks like you're moving and aging more slowly. | ||
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arbitrageur
Australia1202 Posts
On July 23 2011 01:55 Blazinghand wrote: Doesn't work. The system you describe initially can maintain orbit. The system you describe in the last paragraph is not the same system, since it has a generator turbine in it, and one of the bodies has water, as well. I see no reason why every quality of the first system should be necessarily present in the second, or why the absence of any quality of the first system on the second system is meaningful to the first system. For example: A bicycle, unattended, falls over. But a bicycle with a kickstand does not fall over. Sounds like a paradox! How could this be a bicycle and ALSO NOT FALL OVER? The answer is, of course, something was added to the system. It's meant to convey a point. The keyword I'm trying to use is real, meaning uneven with dirt and crap and crusts on it. If we take away the turbine & water, then wouldn't whatever causes THAT n-body system to decay (the system with water/turbine) ALSO cause the n-body system of dirt rocks to decay, hence meaning that no real n-body system can maintain orbit for t->infinite? | ||
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Diks
Belgium1880 Posts
They will talk like instant telepathy during the travel time. The perception of time for the traveling twin will be different on the way back to earth. Time will feel like it goes slower for him, he'll feel like an hour last a bit longer and when his twin on earth will instantaneously talk to him, he'll feel like his twin is talking slower than usual. When he'll land to earth, there won't be any weird moment of "how can you be there ? You told me 1 minute ago that you were coming back in 2 years" The key is not the mesure of time, but the perception. I bet clock will feel like turning slower in a fast space travel. I'm curious but seriously lack of physical education on the subject, can anyone help clarify this ? | ||
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Simberto
Germany11507 Posts
You always simplify. In the first system, you simplify that there is no energy lost to anything, which in a real system obviously is not the case. (The energy is not literally "lost", it just gets transfered to something else that does not effect the rotation) Thus, as a result, if you have any those effects, you obviously can not retain the same motion for infinity. | ||
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Simberto
Germany11507 Posts
On July 23 2011 02:29 Diks wrote: I want to complicate the OP a bit and let's imagine we have a theorical instantaneous conversation with the twins (This is not physically possible, this is just a brain fuck scenario). They will talk like instant telepathy during the travel time. The perception of time for the traveling twin will be different on the way back to earth. Time will feel like it goes slower for him, he'll feel like an hour last a bit longer and when his twin on earth will instantaneously talk to him, he'll feel like his twin is talking slower than usual. When he'll land to earth, there won't be any weird moment of "how can you be there ? You told me 1 minute ago that you were coming back in 2 years" The key is not the mesure of time, but the perception. I bet clock will feel like turning slower in a fast space travel. I'm curious but seriously lack of physical education on the subject, can anyone help clarify this ? No, the clock won't "feel like turning slower". The clock is turning slower because time in its frame of reference passes slower. The clock thinks it turns as fast as always. But it thinks that any clock in a different frame of reference is turning at a different speed than it should be. But all clocks by themselves turn at the exact speed they are supposed to. Thus, as you said, in your supposed case of instanteneous communication, the earthward twin would experience the Spacetwin to talk slower, and the spacetwin would experience the earthtwin to talk faster than he is supposed to. But both feel like they are talking at the usual speed. | ||
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MangoTango
United States3670 Posts
On July 23 2011 02:29 Diks wrote: I want to complicate the OP a bit and let's imagine we have a theorical instantaneous conversation with the twins (This is not physically possible, this is just a brain fuck scenario). They will talk like instant telepathy during the travel time. The perception of time for the traveling twin will be different on the way back to earth. Time will feel like it goes slower for him, he'll feel like an hour last a bit longer and when his twin on earth will instantaneously talk to him, he'll feel like his twin is talking slower than usual. When he'll land to earth, there won't be any weird moment of "how can you be there ? You told me 1 minute ago that you were coming back in 2 years" The key is not the mesure of time, but the perception. I bet clock will feel like turning slower in a fast space travel. I'm curious but seriously lack of physical education on the subject, can anyone help clarify this ? The perception of time will be exactly the same for both people. Your premise is flawed. | ||
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Blazinghand
United States25551 Posts
On July 23 2011 01:57 arbitrageur wrote: It's meant to convey a point. The keyword I'm trying to use is real, meaning uneven with dirt and crap and crusts on it. If we take away the turbine & water, then wouldn't whatever causes THAT n-body system to decay (the system with water/turbine) ALSO cause the n-body system of dirt rocks to decay, hence meaning that no real n-body system can maintain orbit for t->infinite? If you define "real" as "sufficiently uneven that it can't maintain orbit", then yes, obviously. I'm not really sure what you're trying to get at, here. Are you noting that physical models hold certain variables constant and ignore others to make their calculations? This is correct. For example, non-universal projectile motion models use equations that work best when you're standing at about sea level. As you climb in elevation, gravity is ever-so-slightly weaker, meaning that the equations are ever-so-slightly less accurate. Also, since these equations don't account for wind or air resistance, despite being accurate most of the time, for projectiles shaped like feathers or parachutes, you'll lose some accuracy. On July 23 2011 02:41 MangoTango wrote: The perception of time will be exactly the same for both people. Your premise is flawed. If instantaneous communication was possible, special relativity and physics as we know it would have to be rewritten. The "Paradox of the Twins" wouldn't exist because time dilation wouldn't exist because time would no longer be relative. The fundamental laws of nature would have to be rewritten for instantaneous communication to be possible. At the very least, we'd find our understanding of the universe to be enormously flawed until we created a new physics. Asking about the Paradox in that situation, where the physics are fundamentally different, is about as relevant as asking how to cast Expelliarmus in our physics situation. | ||
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arbitrageur
Australia1202 Posts
On July 23 2011 02:53 Blazinghand wrote: If you define "real" as "sufficiently uneven that it can't maintain orbit", then yes, obviously. I'm not really sure what you're trying to get at, here. Are you noting that physical models hold certain variables constant and ignore others to make their calculations? This is correct. For example, non-universal projectile motion models use equations that work best when you're standing at about sea level. As you climb in elevation, gravity is ever-so-slightly weaker, meaning that the equations are ever-so-slightly less accurate. Also, since these equations don't account for wind or air resistance, despite being accurate most of the time, for projectiles shaped like feathers or parachutes, you'll lose some accuracy. What I'm saying is that, possibly, this thought experiment means that you can't have a real n-body planetary system that maintains orbit no matter the configuration of said bodies.. even in principle. Am I being confusing? | ||
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Blazinghand
United States25551 Posts
On July 23 2011 02:55 arbitrageur wrote: What I'm saying is that, possibly, this thought experiment means that you can't have a real n-body planetary system that maintains orbit no matter the configuration of said bodies.. even in principle. Am I being confusing? Yeah I'm confused about the part where you have a "real n-body planetary system... in principle" (emphasis mine). Does the system exist in reality, or in principle? If It's in principle, then the math functions, and if it's an "in reality" one, as you have described, then it is A) not in principle and B) not the same system that's being described anyways since it's made out of crappy crusty watery rocks rather than spherical rocks. | ||
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Nawyria
Netherlands140 Posts
On July 23 2011 01:33 arbitrageur wrote: Nawyria, answer this. I'm no physicist, but I'm thinking there might be a flaw in the following claim: A real n body system, in any possible configuration, can maintain orbit until t->infinite without the system collapsing on itself or the planets going out into space. Say there's water on one. You could put an electricity generator in this water, and as the gravity of other bodies pulls and pushes on the water it will move through the turbine and electricity will be generated. As t->infinite and the system does not collapse, you gather infinite energy with a finite amount of matter (i.e. a never-ending supply of energy). In general, an ideal n-body system of point masses is not solvable analytically for N>2. As far as I know, these systems are in general not stable for infinite time. Making the masses realistic only complicates this problem. Regardless, going on to the second point: Assuming the water on your planet is subject to friction, heat will be generated out of the gravitational push and pull of other planets. As the thermal energy increases, the kinetic energy of the system decreases and therefore the total mechanical (kinetic + gravitational) energy decreases. In the case of a two-body system, this means that the planets will creep closer together. For t large enough, eventually enough of the mechanical energy of the system will be transformed into thermal energy that the orbits of one or more planets intersect and collapse. Even if the water was frictionless and you somehow managed to build a turbine that generated electricity, the same process would occur. In this sense, Tidal power isn't quite a sustainable energy source, as we're basically tapping into the mechanical energy of the earth-moon system. An interesting point you've brought up. EDIT: As the matter of fact, a difference in gravitational pull on one side of the planet's centre of mass and the other side of the planet's centre of mass stretches and compresses the material the planet is made of, which causes heat generation. Therefore, in general, no 'real' n-body system will be stable as mechanical energy is dissipated through the motion of the planets. | ||
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Nawyria
Netherlands140 Posts
On July 23 2011 01:48 yoshi_yoshi wrote: Dumb question: How are entangled particles going to be more useful than just giving two people pieces of paper saying "YES" and "NO". Then when each of them look at their paper they know what the other one got. A completely valid question, and you are right. This is exactly what a system of entangled particles does, with a minor difference. If I look now and see I have "NO", I could look again in a second or two and see that I have "YES". | ||
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Blazinghand
United States25551 Posts
On July 23 2011 03:37 Nawyria wrote: A completely valid question, and you are right. This is exactly what a system of entangled particles does, with a minor difference. If I look now and see I have "NO", I could look again in a second or two and see that I have "YES". The reason that this is possible is that the data transmitted, instead of being a bit (1 or 0) is a qubit (a probability waveform made out of both |1> and |0>). This means that instead of being in a binary state, it's in a superposition of two binary states, with both |1> and |0> totally going on. | ||
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Nawyria
Netherlands140 Posts
On July 23 2011 02:29 Diks wrote: I want to complicate the OP a bit and let's imagine we have a theorical instantaneous conversation with the twins (This is not physically possible, this is just a brain fuck scenario). They will talk like instant telepathy during the travel time. The perception of time for the traveling twin will be different on the way back to earth. Time will feel like it goes slower for him, he'll feel like an hour last a bit longer and when his twin on earth will instantaneously talk to him, he'll feel like his twin is talking slower than usual. When he'll land to earth, there won't be any weird moment of "how can you be there ? You told me 1 minute ago that you were coming back in 2 years" The key is not the mesure of time, but the perception. I bet clock will feel like turning slower in a fast space travel. I'm curious but seriously lack of physical education on the subject, can anyone help clarify this ? The question I ask you then, is instantaneous to whose eyes? A big part of the Theory of Special Relativity is that simultaneity is in the eye of the beholder. Two events that occur simultaneous to you, may not occur simultaneous to me. Since all inertial systems are equal (this a fundamental postulate), there is no system we can point to and say "This observer has the correct notion of simultaneous". The only way we can work our way around this is to say "The signal travels instantaneously according to my perception of time". However, this generates an unresolvable paradox as below: Paradox + Show Spoiler [picture] + ![[image loading]](http://i.imgur.com/zjysk.jpg) 1) Twin A sends Twin B an instantaneous question according to his perception of simultaneous. 2) Twin B sends Twin A an instantaneous answer according to his perception of simultaneous. 3) Twin A receives Twin B's answer before he ever asked the question. | ||
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Trainrunnef
United States599 Posts
Why would one twin hear the communication of the other as slowed. Wouldn't there just be a delay in the communication due to the time it took for the light to reach twin a/b. IIRC the speed of light is constant, and redshift/blueshift is due to an accelleration either towards or away from the reciever of the signal. So with this in mind the communications would be heard by both twins with a normal speech pattern just a long pause. | ||
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Diks
Belgium1880 Posts
On July 23 2011 03:51 Nawyria wrote: The question I ask you then, is instantaneous to whose eyes? A big part of the Theory of Special Relativity is that simultaneity is in the eye of the beholder. Two events that occur simultaneous to you, may not occur simultaneous to me. Since all inertial systems are equal (this a fundamental postulate), there is no system we can point to and say "This observer has the correct notion of simultaneous". The only way we can work our way around this is to say "The signal travels instantaneously according to my perception of time". However, this generates an unresolvable paradox as below: Paradox + Show Spoiler [picture] + 1) Twin A sends Twin B an instantaneous question according to his perception of simultaneous. 2) Twin B sends Twin A an instantaneous answer according to his perception of simultaneous. 3) Twin A receives Twin B's answer before he ever asked the question. Thank you for your enlightment, I know realise my question didn't really make sens. I have something that still tickle me about "two events that occur simultaneous to you, may not occur simultaneous to me." So if I get this right; time and space are undissociable. When I see the mathematics model, the time/location is always refered as a dot, but we, human have a body that covers an area. Can I legitimately say that my right leg lives in the past and my left leg in the future ? (even by fractions of ns) Do we have some sort of "referencial center of the time/space perception" inside our brain ? I'm sorry for my questions that may have no sense one again :/ | ||
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KimJongChill
United States6429 Posts
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Nawyria
Netherlands140 Posts
On July 23 2011 04:23 Trainrunnef wrote: Question... Why would one twin hear the communication of the other as slowed. Wouldn't there just be a delay in the communication due to the time it took for the light to reach twin a/b. IIRC the speed of light is constant, and redshift/blueshift is due to an accelleration either towards or away from the reciever of the signal. So with this in mind the communications would be heard by both twins with a normal speech pattern just a long pause. This is partly because of time dilatation. That is to say, two observers with a relative speed between observe each other's clocks as running slower. This is because our notion of what space and time shifts as the speed between two inertial frames becomes of order c. Another way to think about it is this: If I'm travelling at some reasonable fraction of the speed of light away from you (say, 50%) and I say a sentence to you that takes me 10 seconds to say, then by the time I've finished speaking I'll be 5 lightseconds further away from you relative to where I was when I started speaking and the end of the message will take 5 seconds longer to reach you than the start of the message. This means that you'll receive my original 10-second message smeared out over 15 seconds and thus I'll appear to be talking in slow-motion. Edited for mistakes | ||
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Trainrunnef
United States599 Posts
On July 23 2011 04:55 Nawyria wrote: This is partly because of time dilatation. That is to say, when the two twins travel away from each other they observe each other's clocks as running slower; when the two twins travel towards each other, they observe each other's clocks as running faster. This is because our notion of what space and time shifts as the speed between two inertial frames becomes of order c. Another way to think about it is this: If I'm travelling at some reasonable fraction of the speed of light away from you (say, 50%) and I say a sentence to you that takes me 10 seconds to say, then by the time I've finished speaking I'll be 5 lightseconds further away from you relative to where I was when I started speaking and the end of the message will take 5 seconds longer to reach you than the start of the message. This means that you'll receive my original 10-second message smeared out over 15 seconds and thus I'll appear to be talking in slow-motion. Thanks.... i always forget to carry the time dilation | ||
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Nawyria
Netherlands140 Posts
On July 23 2011 04:52 Diks wrote: + Show Spoiler + On July 23 2011 03:51 Nawyria wrote: The question I ask you then, is instantaneous to whose eyes? A big part of the Theory of Special Relativity is that simultaneity is in the eye of the beholder. Two events that occur simultaneous to you, may not occur simultaneous to me. Since all inertial systems are equal (this a fundamental postulate), there is no system we can point to and say "This observer has the correct notion of simultaneous". The only way we can work our way around this is to say "The signal travels instantaneously according to my perception of time". However, this generates an unresolvable paradox as below: Paradox + Show Spoiler [picture] + 1) Twin A sends Twin B an instantaneous question according to his perception of simultaneous. 2) Twin B sends Twin A an instantaneous answer according to his perception of simultaneous. 3) Twin A receives Twin B's answer before he ever asked the question. Thank you for your enlightment, I know realise my question didn't really make sens. I have something that still tickle me about "two events that occur simultaneous to you, may not occur simultaneous to me." So if I get this right; time and space are undissociable. Time and space are not fixed quantities, but they represent "choices of axes" in what we call space-time. Within space-time, we can dissociate between three distinct regions, the timelike, the lightlike and the spacelike regions. To understand this, consider the picture below: + Show Spoiler [picture 1] + ![[image loading]](http://i.imgur.com/j4qbT.jpg) I've drawn 3 sets of space-time axes and the paths of 2 light signals that all pass through the same origin. As relative speeds get closer and closer to the speed of light, you can see that the space and time axes "bend towards" the rightbound light signal. However, since nothing that has any mass can go at the speed of light, the time-axis will always lie above this signal and the space-axis will always lie below this signal. + Show Spoiler [picture 2] + ![[image loading]](http://i.imgur.com/9nx05.jpg) This brings me to the subdivision mentioned earlier: 1) Timelike: the points of the lightcone that could be occupied by the time-axis of an observer passing through the same origin. Incidentally, these are the points in space-time that will ever be able to send a message to or receive a message from the origin through means of communication slower than the speed of light. 2) Lightlike: the points of the lightcone that could be occupied by any light signal passing through the same origin. Incidentally, these are the points in space-time that will ever be able to send a message to or receive a message from the origin through means of communication at the speed of light. 3) Spacelike: the points of the lightcone that could be occupied by the space-axis of an observer passing through the same origin. Incidentally, these are the points in space-time that will never be able to send a message to or receive a message from the origin. I hope this clarifies it a bit. When I see the mathematics model, the time/location is always refered as a dot, but we, human have a body that covers an area. Can I legitimately say that my right leg lives in the past and my left leg in the future ? (even by fractions of ns) Do we have some sort of "center of the time/space perception" inside our brain ? I'm sorry for my questions that may have no sense one again :/ Techically speaking, we would have to describe our body as the collection of molecules, the dealings of which are guided by chemical interactions and mechanical interactions. But then molecules are made out of atoms, atoms are made out of electrons and a nucleus of protons and neutrons. But then protons and neutrons are nothing but their constituent confined quarks, but these are delocalised and hard to measure and.. WWWAAAGGGHHHH. Things get very, very complicated when we try to describe objects that consist of large amounts of smaller objects to the point where it is very impractical to even use computers to attempt to simulate this. However, there is a whole field of study dedicated to doing exactly this: namely Thermal Physics, which can be used to model, say, a balloon. However, the methods we use do their utmost best to avoid having to describe the balloon as the collection of molecules inside the balloon, but instead we talk about larger so-called "macroscopic" properties such as temperature, pressure, volume etcetera. In practice, we generally approach describing complex objects as (in order of increasing complexity)
As for the leg-question, the notion of "living in the past" is a bit vacuous in relativity. Technically speaking though, if you've swung your right leg more often than your left leg then it is younger by an immeasurably minute amount. However, remember that no single atom you had in your body when your were born is in your body right now; and no atom you have in your body right now is likely to be there in a decade. This raises the interesting philosophical questions of "How is a 'leg' defined?" and "How is my 'body' defined?", but these fall outside of the purview of physics I'm afraid. As for the brain part. I suppose the way it works is that our brains receive information through the nervous system and than processes this is some way that allows you to perceive what you perceive. Exactly how the brain processes this information and deals with concepts such as space and time are big, BIG unanswered questions in neurology. If only we knew... Keep the questions coming! Edit: missed a part of your question. | ||
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Diks
Belgium1880 Posts
On July 23 2011 05:30 Nawyria wrote: Time and space are not fixed quantities, but they represent "choices of axes" in what we call space-time. Within space-time, we can dissociate between three distinct regions, the timelike, the lightlike and the spacelike regions. To understand this, consider the picture below: + Show Spoiler [picture 1] + I've drawn 3 sets of space-time axes and the paths of 2 light signals that all pass through the same origin. As relative speeds get closer and closer to the speed of light, you can see that the space and time axes "bend towards" the rightbound light signal. However, since nothing that has any mass can go at the speed of light, the time-axis will always lie above this signal and the space-axis will always lie below this signal. + Show Spoiler [picture 2] + This brings me to the subdivision mentioned earlier: 1) Timelike: the points of the lightcone that could be occupied by the time-axis of an observer passing through the same origin. Incidentally, these are the points in space-time that will ever be able to send a message to or receive a message from the origin through means of communication slower than the speed of light. 2) Lightlike: the points of the lightcone that could be occupied by any light signal passing through the same origin. Incidentally, these are the points in space-time that will ever be able to send a message to or receive a message from the origin through means of communication at the speed of light. 3) Spacelike: the points of the lightcone that could be occupied by the space-axis of an observer passing through the same origin. Incidentally, these are the points in space-time that will never be able to send a message to or receive a message from the origin. I hope this clarifies it a bit. Techically speaking, we would have to describe our body as the collection of molecules, the dealings of which are guided by chemical interactions and mechanical interactions. But then molecules are made out of atoms, atoms are made out of electrons and a nucleus of protons and neutrons. But then protons and neutrons are nothing but their constituent confined quarks, but these are delocalised and hard to measure and.. WWWAAAGGGHHHH. Things get very, very complicated when we try to describe objects that consist of large amounts of smaller objects to the point where it is very impractical to even use computers to attempt to simulate this. However, there is a whole field of study dedicated to doing exactly this: namely Thermal Physics, which can be used to model, say, a balloon. However, the methods we use do their utmost best to avoid having to describe the balloon as the collection of molecules inside the balloon, but instead we talk about larger so-called "macroscopic" properties such as temperature, pressure, volume etcetera. In practice, we generally approach describing complex objects as (in order of increasing complexity)
As for the leg-question, the notion of "living in the past" is a bit vacuous in relativity. Technically speaking though, if you've swung your right leg more often than your left leg then it is younger by an immeasurably minute amount. However, remember that no single atom you had in your body when your were born is in your body right now; and no atom you have in your body right now is likely to be there in a decade. This raises the interesting philosophical questions of "How is a 'leg' defined?" and "How is my 'body' defined?", but these fall outside of the purview of physics I'm afraid. As for the brain part. I suppose the way it works is that our brains receive information through the nervous system and than processes this is some way that allows you to perceive what you perceive. Exactly how the brain processes this information and deals with concepts such as space and time are big, BIG unanswered questions in neurology. If only we knew... Keep the questions coming! Edit: missed a part of your question. Wow, thank you, you are amazing. I was about to talk about an imaginary giant so big that the distance between his 2 eyes would be the distance earth-sun. The giant would be spinning and traveling at near lightspeed. I would be curious to know how his brain could process 2 very distinct timelines. What I'm curious is that what could be observed in small scale should apply in larger scale. So the giant traveling at light speed is just an exageration of a human standing on the moving earth. This is not solvable yet I guess. I don't see how we can possibly pretend to be in a space/time moment when our body actually are in an near infinite space-time moments. I guess we should have at least one molecule that we refere to be the center of perception or that our brain accept some sort of tolerance in what he assume to be the present (as we are pretty small and all our body travel at same velocity, so the reference could agree to have this 1/1000000 margin of error) in wich case the flying giant could not exist. I've always been passionated by those subjects and I regret to not have continue my studies in physics. | ||
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Blazinghand
United States25551 Posts
On July 23 2011 05:52 Diks wrote: Wow, thank you, you are amazing. I was about to talk about an imaginary giant so big that the distance between his 2 eyes would the distance earth-sun. The giant would be spinning and traveling at near lightspeed. I would be curious to know how his brain could process 2 very distinct timelines. What I'm curious is that what could be observed in small scale should apply in larger scale. So the giant traveling at light speed is just an exageration of a human standing on the moving earth. This is not solvable yet I guess. I don't see how we can possibly pretend to be in a space/time moment when our body actually are in an near infinite space-time moments. I guess we should have at least one molecule that we refere to be the center of perception or that our brain accept some sort of tolerance in what he assume to be the present (as we are pretty small and all our body travel at same velocity, so the reference could agree to have this 1/1000000 margin of error) in wich case the flying giant could not exist. I've always been passionated by those subjects and I regret to not have continue my studies in physics. The giant's brain would be effected by having parts of it moving at light speed and parts of it not moving at light speed; the physical layout of the brain and the dendrites connecting the nerves, along with the speed and direction of the impulses, would all be negative factors for brain function at varying near-light speeds. His glial cells that were closer or further from the axis of rotation would feed the neurons at different rates, killing them through starvation or flooding them with nutrients. He would die almost immediately, and would have next to no brain function while alive due to the inability of parts of his brain in different reference frames to communicate with each other.  | ||
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Diks
Belgium1880 Posts
On July 23 2011 05:55 Blazinghand wrote: The giant's brain would be effected by having parts of it moving at light speed and parts of it not moving at light speed; the physical layout of the brain and the dendrites connecting the nerves, along with the speed and direction of the impulses, would all be negative factors for brain function at varying near-light speeds. His glial cells that were closer or further from the axis of rotation would feed the neurons at different rates, killing them through starvation or flooding them with nutrients. He would die almost immediately, and would have next to no brain function while alive due to the inability of parts of his brain in different reference frames to communicate with each other. Shit, I just killed the giant :/ | ||
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Blazinghand
United States25551 Posts
Dude, he was a one of a kind, how could you ((but yeah the main thing is that the communication between the eyes and the brain is not instantaneous, it works just like, say, 2 radio operators with radios moving and relativistic speed would. | ||
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Nawyria
Netherlands140 Posts
Dude, he was a one of a kind, how could you ((but yeah the main thing is that the communication between the eyes and the brain is not instantaneous, it works just like, say, 2 radio operators with radios moving and relativistic speed would. That is to say, not very good ^^ | ||
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CptCutter
United Kingdom370 Posts
On July 22 2011 00:49 Jombozeus wrote: Well, your signal would take a near-infinite amount of time to reach your twin if hes traveling at near the speed of light. In other words, its probably just not going to reach him within his lifetime after 2 days if hes traveling at 99% speed of light. Just do the math. what the hell are you talking about? traveling at the speed of light in one direction does not mean that light coming from you travelling in the opposite direction essentially stops, thats just insane thinking, how did you manage that? thats like saying multiple galaxys out there should be doing this sort of thing since there are some that move at almost the speed of light. i dont know why anybody thinks that travelling faster than the speed of light would slow time down, the speed of light is just a speed limit placed on the universe, it has no other affect on it. it may not even be a limit, and if it wasnt, most of our physics/science up till this point will need a total rethink. | ||
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Diks
Belgium1880 Posts
The scale matters a lot as the proportional relativity changes from the unvariable constants like lightspeed. The size of a living body is determined by those unvariable composants and there may be a size-cap for a living being. If we take into account that what we see is past (because of light+nerves travel speed). All our thoughts and perceptions take time to travel through our body at different length and speedrate. But yet, we account that multiple past time lines to be our present and the present, a very close future. From thoses asomptions, a very small being like a fly would live closer to the actual present he's in than us (due to his size and scale compared to the constants like nerves and light speed.) if you wondered why you never able to catch flies, I guess we have our answer ! | ||
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scorch-
United States816 Posts
On July 23 2011 04:55 Nawyria wrote: This is partly because of time dilatation. That is to say, when the two twins travel away from each other they observe each other's clocks as running slower; when the two twins travel towards each other, they observe each other's clocks as running faster. This is because our notion of what space and time shifts as the speed between two inertial frames becomes of order c. Another way to think about it is this: If I'm travelling at some reasonable fraction of the speed of light away from you (say, 50%) and I say a sentence to you that takes me 10 seconds to say, then by the time I've finished speaking I'll be 5 lightseconds further away from you relative to where I was when I started speaking and the end of the message will take 5 seconds longer to reach you than the start of the message. This means that you'll receive my original 10-second message smeared out over 15 seconds and thus I'll appear to be talking in slow-motion. This is kind of a funky way of saying this. The direction of travel isn't relevant to a discussion of time dilation, but is relevant to the waveshift. To be precise, I mean to say that when A is traveling towards B, B is aware of A's velocity. While B may observe A's clock to read a difference of 1.1 seconds after one second of travel, he is aware that A is moving towards him and that the light has originated at a distance that is closer by some non-trivial amount. Because B and A are both aware of time dilation and they know their relative velocities, B will still deduce that A's clock is moving more slowly than B's, and A will still deduce B's clock to be moving more slowly than B's. Correct? | ||
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Simberto
Germany11507 Posts
On July 23 2011 06:20 CptCutter wrote: what the hell are you talking about? traveling at the speed of light in one direction does not mean that light coming from you travelling in the opposite direction essentially stops, thats just insane thinking, how did you manage that? thats like saying multiple galaxys out there should be doing this sort of thing since there are some that move at almost the speed of light. i dont know why anybody thinks that travelling faster than the speed of light would slow time down, the speed of light is just a speed limit placed on the universe, it has no other affect on it. it may not even be a limit, and if it wasnt, most of our physics/science up till this point will need a total rethink. Actually, it is quite intuitional thinking. If i stand on a train, and throw a stone backwards, it will be by the trains speed slower then if i had thrown it standing on solid ground. It is remarkable and unintuitive that that does not apply to light. You seem to accept that the speed of light is constant no matter the frame of reference. This can only yield consistent observations in each inertial system if time slows down more the nearer you get to the speed of light. Since from observation the speed of light does not seem to be affected by your own velocity, almost all physicists accept special relativity and as a result time delation on faster moving objects. So far, special relativity has resisted every attempt to disprove it, and as long as that stays the case, there is no problem in using it. Also, that was not even his point. His point was that If someone is travelling away from you at 0.99c, if you send a signal 2 days after he started it will reach him only after 200 days in your frame of reference. | ||
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Nawyria
Netherlands140 Posts
On July 23 2011 06:51 scorch- wrote: This is kind of a funky way of saying this. The direction of travel isn't relevant to a discussion of time dilation, but is relevant to the waveshift. To be precise, I mean to say that when A is traveling towards B, B is aware of A's velocity. While B may observe A's clock to read a difference of 1.1 seconds after one second of travel, he is aware that A is moving towards him and that the light has originated at a distance that is closer by some non-trivial amount. Because B and A are both aware of time dilation and they know their relative velocities, B will still deduce that A's clock is moving more slowly than B's, and A will still deduce B's clock to be moving more slowly than B's. Correct? Hmm, you are correct indeed. Time dilatation does not care about direction, only about the absolute speed; the visual impression of objects does. It seems I stand corrected. | ||
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zodde
Sweden1908 Posts
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GamerSyneX
United Kingdom64 Posts
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Nawyria
Netherlands140 Posts
On July 23 2011 07:04 GamerSyneX wrote: if the person travelling at the speed of light constantly was talking to the person on a cell phone, surely the sound wouldnt ever reach the person traveling at the speed of light? or am i missing something The point is that the travelling twin can never truly travel at the speed of light, but could reach any speed just below the speed of light. While it is true that the faster he goes, the longer it takes for the message to reach him; but given enough time, messages will reach him. | ||
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scorch-
United States816 Posts
On July 23 2011 07:04 GamerSyneX wrote: if the person travelling at the speed of light constantly was talking to the person on a cell phone, surely the sound wouldnt ever reach the person traveling at the speed of light? or am i missing something According to our understanding of our universe, no person can travel at the speed of light. So, if the person was travelling at the speed of light, our laws of physics break down and we have no idea what would happen. If the person was travelling very close to the speed of light, it would reach him eventually. The length of time it took depends on the frame of reference. | ||
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