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United States10328 Posts
On July 22 2011 05:18 Nawyria wrote:Show nested quote +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.
WHOA thanks I was wondering about this! But enough pairs of entangled particles could transmit information with high probability, no?
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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 ^^.
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Blazinghand
United States25563 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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Netherlands140 Posts
On July 22 2011 05:53 ]343[ wrote:Show nested quote +On July 22 2011 05:18 Nawyria wrote: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. 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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Edit: Didnt notice the 4 pages already in the thread, sorry for breaking the conversation... -_-
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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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On July 22 2011 05:53 ]343[ wrote:Show nested quote +On July 22 2011 05:18 Nawyria wrote: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. 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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Netherlands140 Posts
On July 22 2011 05:20 Najda wrote:Show nested quote +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?
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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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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On July 22 2011 06:16 Nawyria wrote:Show nested quote +On July 22 2011 05:20 Najda wrote: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? 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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The signal would be delayed, just like any other form of communication, it can only go as fast as light
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Netherlands140 Posts
On July 22 2011 06:19 scorch- wrote:Show nested quote +On July 22 2011 06:16 Nawyria wrote:On July 22 2011 05:20 Najda wrote: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? 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.
Which makes it a lot harder than the twin paradox.
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On July 22 2011 06:20 Nawyria wrote:Show nested quote +On July 22 2011 06:19 scorch- wrote:On July 22 2011 06:16 Nawyria wrote:On July 22 2011 05:20 Najda wrote: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? 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. Which makes it a lot harder than the twin paradox.
I don't think anyone would argue that, haha.
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United States10328 Posts
On July 22 2011 06:06 Nawyria wrote:Show nested quote +On July 22 2011 05:53 ]343[ wrote:On July 22 2011 05:18 Nawyria wrote: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. 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.
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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Netherlands140 Posts
On July 22 2011 06:23 ]343[ wrote:Show nested quote +On July 22 2011 06:06 Nawyria wrote:On July 22 2011 05:53 ]343[ wrote:On July 22 2011 05:18 Nawyria wrote: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. 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. 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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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?
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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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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 States25563 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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On July 22 2011 06:50 Blazinghand wrote:Show nested quote +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.
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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EPT
