A little more than a week ago scientists discovered a gamma ray burst from outer space lasting 10 seconds with a redshift of 8,2. It is calculated that the source is more than 13 billion lightyears away, probably an explosion of a star. Because of the finite speed of light, observing a lightsource 13 billion lightyears away also means observing an explosion that happened 13 billion years ago, only about 600 million years after the birth of the universe (according to the big bang theory).
At first i just thought it was cool that we are able to observe this kind of stuff. After a while I gave it some more thought: How is it that we are able to observe light from an explosion that happened more than 13 billion years ago? To answer this question, assuming the most popular theories of physics (and my knowledge of it) and the method of measurements are correct, I thought of the following:
During the first couple of million years the universe had to be expanding at a rate tremendously faster than the speed of light. If this wasn’t the case then the light of the explosion would have passed our location in the universe a couple of billion years ago (because of the limited side of the universe at an age of 600 million years) and we never would have been able to see it. After a while the expansion rate had to slow down, or the light wouldn’t be able to catch up to us, and we again wouldn’t be able to see it. Recent observations show that the galaxies surrounding us are moving away from us at an increasing rate, indicating that the expansion of the universe is accelerating again?
I don’t know if what I’m saying is correct, cause I don’t have a background in physics. But I think this observation can cause more interesting thoughts and a nice discussion. And maybe a person with a background in physics can shed some light onto this.
What this means to us, is that its completely impossible to reach the expanding end of the universe, because it expands faster than the speed of light, therefore when we got there so much more would be created already
We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.
If i'm understanding you correctly this might be related to how the expansion of the universe works. IIRC the universes expansion doesn't work "outwardly" per se. It's not related to outwards motion, but instead the expansion of space itself. As such, the percieved "speed" at which we move away from other objects in the universe is greater the further away from it we are since space "expands" equally everywhere. I might be terribly wrong about this tho. If i am, someone please correct me : ]
On May 06 2009 18:25 omninmo wrote: "the birth of the universe" ... humans are so vain. animals are born. existences is and never was not. you want cosmic? learn about 大道
I think he was just referring to the big bang as a birth, which it was in a way. Even if existence has always been, this last 14 billion years was the product of one big bang. Sounds like a birth to me.
On May 06 2009 18:10 D10 wrote: What this means to us, is that its completely impossible to reach the expanding end of the universe, because it expands faster than the speed of light, therefore when we got there so much more would be created already
That's why scientists are no longer trying to achieve the speed of light per se because travelling anywhere with just the speed of light will still have a journey that outlasts human lifespan.That's why they are now more curious on faster than light theories and time warp/worm hole theories.
On May 06 2009 18:10 D10 wrote: What this means to us, is that its completely impossible to reach the expanding end of the universe, because it expands faster than the speed of light, therefore when we got there so much more would be created already
That's why scientists are no longer trying to achieve the speed of light per se because travelling anywhere with just the speed of light will still have a journey that outlasts human lifespan.That's why they are now more curious on faster than light theories and time warp/worm hole theories.
Actually because of timedilatation you can travel a great distance during a human lifetime. If you have a powersource that manages to let you accelerate with 1 g during your whole lifetime, you can travel more than 13 billion lightyears.
Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
An infinitely dense singularity counts as "nothing"?
Define "infinitely dense singularity."
How the fuck could he define that? The world's best scientist can only approach this subject from a theoretical standpoint, nobody knows what's actually 'there' (at the heart of a black hole for example)
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
i would recommend you reading "the elegant universe" by brian greene. i didnt finish it yet but i've read like 3/4 and thought it was a great book up to now. there's also a second book by him which i havent read yet. the english title is "The Fabric of the Cosmos" i think
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
That's a great book and his latest, "The best of all possible worlds" is also very good. He is actually based in my university which is very cool and I see him all the time but I dare not ask him the great questions about the universe.
During the first couple of million years the universe had to be expanding at a rate tremendously faster than the speed of light. If this wasn’t the case then the light of the explosion would have passed our location in the universe a couple of billion years ago (because of the limited side of the universe at an age of 600 million years) and we never would have been able to see it. After a while the expansion rate had to slow down, or the light wouldn’t be able to catch up to us, and we again wouldn’t be able to see it.
Not for a couple of million years, but, most of the more recent models of the early universe do include a brief period called the inflationary period where the universe was expanding much more rapidly than the speed of light.
to quote hyperphysics: "Triggered by the symmetry breaking that separates off the strong force, models suggest an extraordinary inflationary phase in the era 10^-36 seconds to 10^-32 seconds. More expansion is presumed to have occurred in this instant than in the entire period ( 14 billion years?) since."
Not that i know wtf i am talking about, but from what I've learn I thought that the universe was not really expanding faster then light. It was just that at the time of the big bang. When gravity, the strong/weak nuclear, and electromagnetism were combined. The laws of faster then light travel were not in place yet. So matter expanded like super quick in that small amount of time just before those 4 forces broke away from each other. I don't know its all confusing but that's what I always understood.
That sounds like quantum mechanics... but I could've sworn I read something about traveling faster than light... nearing the speed of light things turn purplish. Reading a few articles on light speed I know theres nothing that exceeds it (that we know about I'm sure theres something) but I have this personal theory that somewhere out there physics/math doesn't hold up.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
That's a great book and his latest, "The best of all possible worlds" is also very good. He is actually based in my university which is very cool and I see him all the time but I dare not ask him the great questions about the universe.
Both of his books that I've read were quite good and explained the concepts to anyone with even very limited knowledge of physics. These are the two that I have read, I didn't know he had a third and I'll definitely have to pick that up.
Not that i know wtf i am talking about, but from what I've learn I thought that the universe was not really expanding faster then light. It was just that at the time of the big bang. When gravity, the strong/weak nuclear, and electromagnetism were combined. The laws of faster then light travel were not in place yet. So matter expanded like super quick in that small amount of time just before those 4 forces broke away from each other. I don't know its all confusing but that's what I always understood.
No, the period where the forces were unified came first, and lasted for only like 10^-43 seconds. It's a period we basically know nothing about, though. The inflationary phase of faster-than-light expansion came afterwards.
Of course inflation has only recently started to gain wide acceptance, and it's still very much under debate, so no one can give a firm answer for exactly how and why it happened.
On May 07 2009 04:55 Xenixx wrote: That sounds like quantum mechanics... but I could've sworn I read something about traveling faster than light... nearing the speed of light things turn purplish. Reading a few articles on light speed I know theres nothing that exceeds it (that we know about I'm sure theres something) but I have this personal theory that somewhere out there physics/math doesn't hold up.
Usually when you talk about things going faster than light speed, what it means is that the light wasn't in a vacuum (light goes slower through matter than it does through a vacuum). But if you really want to "break the speed of light", in other words to have something faster than light, in a vacuum, in the same reference frame, you'd pretty much need to prove that the theory of relativity is wrong, because the theory is quite clear about that (as speed goes to C, energy increases to infinitiy, so you'd need an infinite amount of energy to get to light speed. Interestingly the mathematics DO allow for something which is already traveling faster than light speed, and which could never slow down below C. But that wouldn't really make much sense). Anyway I wouldn't bank on relativity being wrong since it's been tested countless times and it's ALWAYS help up perfectly.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
That's a great book and his latest, "The best of all possible worlds" is also very good. He is actually based in my university which is very cool and I see him all the time but I dare not ask him the great questions about the universe.
Both of his books that I've read were quite good and explained the concepts to anyone with even very limited knowledge of physics. These are the two that I have read, I didn't know he had a third and I'll definitely have to pick that up.
Makhno is referring to "the best of all possible worlds" by ulf danielsson, not brian greene. I've found that the english version is also called "the best of worlds"
And Makhno, that is really cool that hes at your university. Did you ever attended any of his lectures? I'll see if i can find his newest book you talked about, the reviews i've found show that it's an interesting read.
PS- The universe expands really fast because its like a balloon that doesn't pop. I'm sure you've all seen the experiment. Take a slightly inflated balloon and place a few dots on it and random places. Fill it up with air and watch as the dots spread apart. Now imagine that balloon expanding bigger and bigger. From the center standpoint it seems like the dots are traveling at huge speeds away from you but in reality they are all just riding the plane together. It is the SPACE itself which is expanding/spreading not the actual objects moving. Just like how a buoyant object moves up when the water rises.
We already see the background radiation, and although it may not count as an "object", it´s definitely farther out than any "object" scientists discovered now.
Time seems finite, while we cannot be sure about space. There can be galaxies which are so far away, that their light can never reach us due to the expansion of the universe.
Space itself expands, and "recession velocities" greater than the speed of light do not violate general relativity at all, since there is no real movement, just the space between to objects expanding. That´s why it is a mistake to use the relativistic Doppler formula for cosmological redshifts. edit: time seems finite as in there seems to be a beginning; that´s maybe more astonishing than infinities
edit: oops some mistakes, I shouldn´t type my thoughts in a hurry
PS- The universe expands really fast because its like a balloon that doesn't pop. I'm sure you've all seen the experiment. Take a slightly inflated balloon and place a few dots on it and random places. Fill it up with air and watch as the dots spread apart. Now imagine that balloon expanding bigger and bigger. From the center standpoint it seems like the dots are traveling at huge speeds away from you but in reality they are all just riding the plane together. It is the SPACE itself which is expanding/spreading not the actual objects moving. Just like how a buoyant object moves up when the water rises.
according to that guy (very basically) our universe began with a star in an already-existent universe exploding and creating a black hole
On May 06 2009 17:44 Thats_The_Spirit wrote: A little more than a week ago scientists discovered a gamma ray burst from outer space lasting 10 seconds with a redshift of 8,2. It is calculated that the source is more than 13 billion lightyears away, probably an explosion of a star. Because of the finite speed of light, observing a lightsource 13 billion lightyears away also means observing an explosion that happened 13 billion years ago, only about 600 million years after the birth of the universe (according to the big bang theory).
At first i just thought it was cool that we are able to observe this kind of stuff. After a while I gave it some more thought: How is it that we are able to observe light from an explosion that happened more than 13 billion years ago? To answer this question, assuming the most popular theories of physics (and my knowledge of it) and the method of measurements are correct, I thought of the following:
During the first couple of million years the universe had to be expanding at a rate tremendously faster than the speed of light. If this wasn’t the case then the light of the explosion would have passed our location in the universe a couple of billion years ago (because of the limited side of the universe at an age of 600 million years) and we never would have been able to see it. After a while the expansion rate had to slow down, or the light wouldn’t be able to catch up to us, and we again wouldn’t be able to see it.
ok. Thing here is that you shouldn't have the image of the universe as a pancake that grows, but rather an image of an inflating balloon as proposed by other posters. So light passing us first time will not go on and hit the "end of the universe" (no such thing exists), but it will rather continue around the balloon and could possibly hit us on the second passing, or third etc.
Recent observations show that the galaxies surrounding us are moving away from us at an increasing rate, indicating that the expansion of the universe is accelerating again?
If you trust this observation (WMAP satellite iirc), then yes, the expansion of the universe is accelerating. There have recently been some doubts on this experiment though, but i'm not sure about the details. You would have to research that further if you want an up to date view of that.
I don’t know if what I’m saying is correct, cause I don’t have a background in physics. But I think this observation can cause more interesting thoughts and a nice discussion. And maybe a person with a background in physics can shed some light onto this.
That'd be me.
Let me also comment on this "faster than light expansion". As many pointed out, the relativity bound of "impossible to go faster than light" cannot be used here. Reason is that what we actually measure is not only the relative speed between the earth and a distant star in an instance (this is bounded by light speed), but we measure also how fast the space grows in between us (this comes from the increased redshift while the photons are traveling). The rate with which extra space is created between us is not limited by light speed, since it cannot be seen as a relative speed between two objects, and special relativity do not apply.
What people normally mean when they talk about the universe expanding faster than light is the following: Let's talk about the inflating balloon again. Place an ant at a certain point on the balloon, and let it start moving towards an other point on the balloon. As it moves, it will come closer to the other point, but the point will also get more distant as the balloon inflates. If the balloon is inflated fast enough, the ant will never reach the other point.
Now replace the balloon with the universe, the ant with a beam of light, and you will understand what is meant with the universe growing faster/slower than light. As has also been said already, during inflation in the first fraction of the second of the universe, the universe expanded (much) faster than light in this sense, but by the time stars were formed, it had since long slowed down below light speed.
ok, I hope I contributed with something, back to work now for me. hf guys.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
Lol cool. Stars and falling apples is used as the course literature at my university for a summer course called "physics for philosophers" which is basically a short popular scientific explanation of the field of physics. Ulf Danielsson is a professor here and is the one holding the course
On May 06 2009 17:44 Thats_The_Spirit wrote: A little more than a week ago scientists discovered a gamma ray burst from outer space lasting 10 seconds with a redshift of 8,2. It is calculated that the source is more than 13 billion lightyears away, probably an explosion of a star. Because of the finite speed of light, observing a lightsource 13 billion lightyears away also means observing an explosion that happened 13 billion years ago, only about 600 million years after the birth of the universe (according to the big bang theory).
At first i just thought it was cool that we are able to observe this kind of stuff. After a while I gave it some more thought: How is it that we are able to observe light from an explosion that happened more than 13 billion years ago? To answer this question, assuming the most popular theories of physics (and my knowledge of it) and the method of measurements are correct, I thought of the following:
During the first couple of million years the universe had to be expanding at a rate tremendously faster than the speed of light. If this wasn’t the case then the light of the explosion would have passed our location in the universe a couple of billion years ago (because of the limited side of the universe at an age of 600 million years) and we never would have been able to see it. After a while the expansion rate had to slow down, or the light wouldn’t be able to catch up to us, and we again wouldn’t be able to see it.
ok. Thing here is that you shouldn't have the image of the universe as a pancake that grows, but rather an image of an inflating balloon as proposed by other posters. So light passing us first time will not go on and hit the "end of the universe" (no such thing exists), but it will rather continue around the balloon and could possibly hit us on the second passing, or third etc.
Recent observations show that the galaxies surrounding us are moving away from us at an increasing rate, indicating that the expansion of the universe is accelerating again?
If you trust this observation (WMAP satellite iirc), then yes, the expansion of the universe is accelerating. There have recently been some doubts on this experiment though, but i'm not sure about the details. You would have to research that further if you want an up to date view of that.
I don’t know if what I’m saying is correct, cause I don’t have a background in physics. But I think this observation can cause more interesting thoughts and a nice discussion. And maybe a person with a background in physics can shed some light onto this.
That'd be me.
Let me also comment on this "faster than light expansion". As many pointed out, the relativity bound of "impossible to go faster than light" cannot be used here. Reason is that what we actually measure is not only the relative speed between the earth and a distant star in an instance (this is bounded by light speed), but we measure also how fast the space grows in between us (this comes from the increased redshift while the photons are traveling). The rate with which extra space is created between us is not limited by light speed, since it cannot be seen as a relative speed between two objects, and special relativity do not apply.
What people normally mean when they talk about the universe expanding faster than light is the following: Let's talk about the inflating balloon again. Place an ant at a certain point on the balloon, and let it start moving towards an other point on the balloon. As it moves, it will come closer to the other point, but the point will also get more distant as the balloon inflates. If the balloon is inflated fast enough, the ant will never reach the other point.
Now replace the balloon with the universe, the ant with a beam of light, and you will understand what is meant with the universe growing faster/slower than light. As has also been said already, during inflation in the first fraction of the second of the universe, the universe expanded (much) faster than light in this sense, but by the time stars were formed, it had since long slowed down below light speed.
ok, I hope I contributed with something, back to work now for me. hf guys.
Ah thanks for the nice explanation. The one with the ant on the balloon made it really clear for me. Only i find it hard to grasp the idea of a beam of light hitting us on the 2nd or 3rd passing. Would this mean that if we were able to keep accelerating to one direction, we would eventually come back to the same location as we started? (and a couple million years into the future because of time dilatation?). And would this also mean that if we calculate the distance using redshift of a ray of light that has reached us the 2nd time around, wouldn't we get a much greater distance than it actually is?
Usually when you talk about things going faster than light speed, what it means is that the light wasn't in a vacuum (light goes slower through matter than it does through a vacuum). But if you really want to "break the speed of light", in other words to have something faster than light, in a vacuum, in the same reference frame, you'd pretty much need to prove that the theory of relativity is wrong, because the theory is quite clear about that (as speed goes to C, energy increases to infinitiy, so you'd need an infinite amount of energy to get to light speed. Interestingly the mathematics DO allow for something which is already traveling faster than light speed, and which could never slow down below C. But that wouldn't really make much sense). Anyway I wouldn't bank on relativity being wrong since it's been tested countless times and it's ALWAYS help up perfectly.
But nobody likes theoretical particles, just stirring the pot...
On May 07 2009 18:35 Cascade wrote: As has also been said already, during inflation in the first fraction of the second of the universe, the universe expanded (much) faster than light in this sense, but by the time stars were formed, it had since long slowed down below light speed
I am pretty sure that the universe is still ever-expanding faster than light, and in fact increasing in speed, hence theories explaining the massive amounts of energy furthering this acceleration (like http://en.wikipedia.org/wiki/Dark_matter )
As the Universe expands, the density of dark matter declines more quickly than the density of dark energy (see equation of state) and, eventually, the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant for a cosmological constant).
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
That's a great book and his latest, "The best of all possible worlds" is also very good. He is actually based in my university which is very cool and I see him all the time but I dare not ask him the great questions about the universe.
Both of his books that I've read were quite good and explained the concepts to anyone with even very limited knowledge of physics. These are the two that I have read, I didn't know he had a third and I'll definitely have to pick that up.
Makhno is referring to "the best of all possible worlds" by ulf danielsson, not brian greene. I've found that the english version is also called "the best of worlds"
And Makhno, that is really cool that hes at your university. Did you ever attended any of his lectures? I'll see if i can find his newest book you talked about, the reviews i've found show that it's an interesting read.
Uhh not sure how I misread that conversation thread. I feel retarded.
I still I can't find this book though, under either name.
On May 06 2009 19:05 yejin wrote: Could anyone recommend me some good books about these theories (string theories, multiple universes), serious and "easy" enough for a beginner ? I'd really like to learn more about that eventho my physic background is rather weak.
I second this.
I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples. Also i liked "a brief history of time", by stephen hawking
That's a great book and his latest, "The best of all possible worlds" is also very good. He is actually based in my university which is very cool and I see him all the time but I dare not ask him the great questions about the universe.
Both of his books that I've read were quite good and explained the concepts to anyone with even very limited knowledge of physics. These are the two that I have read, I didn't know he had a third and I'll definitely have to pick that up.
Makhno is referring to "the best of all possible worlds" by ulf danielsson, not brian greene. I've found that the english version is also called "the best of worlds"
And Makhno, that is really cool that hes at your university. Did you ever attended any of his lectures? I'll see if i can find his newest book you talked about, the reviews i've found show that it's an interesting read.
Uhh not sure how I misread that conversation thread. I feel retarded.
I still I can't find this book though, under either name.
EPT
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