21 Jul 09
3 edits
Something I have had a hard time getting my head around is the size of the Universe and how long it has existed. If we look at a distant galaxy about 10 billion light years away, we find new galaxies that are just forming. That makes sense. If intelligent life exists there and the stars have gone through several generations by now, they can look at our early galaxy before we exist. This makes sense to me too. How did the galaxies get that far apart in 10 billion years if the universe is expanding at a faster rate with time, but not even close to the speed of light? If we are in fact seeing the universe at a time close to its beggining when looking that far away, what accounts for the huge
distance.
http://www.sciencedaily.com/releases/2008/02/080212095443.htm
In this case the gallaxy is thought to be 13 billion light years away but they guesstimate we see it as it was only 700 million years after the beggining of the universe. Something just doesn't add up for me.
21 Jul 09
Originally posted by joe beyser…How did the galaxies get that far apart in 10 billion years if the universe is expanding at a faster rate with time, but not even close to the speed of light?
Something I have had a hard time getting my head around is the size of the Universe and how long it has existed. If we look at a distant galaxy about 10 billion light years away, we find new galaxies that are just forming. That makes sense. If intelligent life exists there and the stars have gone through several generations by now, they can look at our ea ...[text shortened]... ly 700 million years after the beggining of the universe. Something just doesn't add up for me.
….
I am not sure but I don’t think the ‘speed of light’ applies to space itself expanding for this would beg the question “speed” relative to what? (remember that all speed is relative)
-I mean, I don’t think it would make any sense to think “speed relative to space” because that would mean speed is not relative even though it is relative -I hope that makes some kind of sense.
21 Jul 09
I think the distance calculation gets really complicated because the space in between us and the other object is continually expanding. Whether this is equivalent to us moving away from each other I am not sure but some things will be the same. The galaxy will appear to be further away from us than it actually was at the time, and it will now be further away from us than it currently appears.
21 Jul 09
Originally posted by Andrew HamiltonJust to add to that:
I am not sure but I don’t think the ‘speed of light’ applies to space itself expanding for this would beg the question “speed” relative to what? (remember that all speed is relative)
-I mean, I don’t think it would make any sense to think “speed relative to space” because that would mean speed is not relative even though it is relative -I hope that makes some kind of sense.
If space is expanding uniformly, then the further apart two objects are then the faster they are moving away from each other. It is actually possible that the universe is big enough that the edges are moving away from each other at greater than the speed of light.
21 Jul 09
Originally posted by twhitehead…It is actually possible that the universe is big enough that the edges are moving away from each other at greater than the speed of light.
Just to add to that:
If space is expanding uniformly, then the further apart two objects are then the faster they are moving away from each other. It is actually possible that the universe is big enough that the edges are moving away from each other at greater than the speed of light.
….
I am not sure if I am thinking clearly here but wouldn’t that mean that that would be an exception to Einstein’s “nothing can go over the speed of light” rule? -if so, I find it a curious exception.
21 Jul 09
Originally posted by Andrew HamiltonWe see the red shift getting redder over time indicating acceleration of expansion of distant galaxies. As space itself expands, wouldn't the light have to travel further to reach us in the next instant? If space was expanding to where the distance between the galaxies increased as though we are moving away from each other faster than light, wouldn't there be more than a red shift effect? I think they use a realitive brightness of stars to determine the distance. If we are seeing light from that galaxie as it was only 700 million years after the beggining of the Universe and it traveled 13 billion light years to get to us now, the expansion of space had to have had an effect on it, so why isn't there much more than a red shift? Maybe it gives the illusion of the speed of light slowing down relative to us but the dopler effect is only minimal.
[b]…How did the galaxies get that far apart in 10 billion years if the universe is expanding at a faster rate with time, but not even close to the speed of light?
….
I am not sure but I don’t think the ‘speed of light’ applies to space itself expanding for this would beg the question “speed” relative to what? (remember that all speed is relat ...[text shortened]... uld mean speed is not relative even though it is relative -I hope that makes some kind of sense.[/b]
21 Jul 09
Originally posted by Andrew HamiltonIt is an exception even though it doesn't technically violate relativity. It also has other implications: if the universe is expanding and as we currently believe that expansion is accelerating, then we will definitely reach a point when distant areas are moving away from each other at faster than the speed of light and that will result in them becoming isolated from each other. Our local area of space will have (if it doesn't already) an event horizon beyond which we can never receive information from.
I am not sure if I am thinking clearly here but wouldn’t that mean that that would be an exception to Einstein’s “nothing can go over the speed of light” rule? -if so, I find it a curious exception.
21 Jul 09
Originally posted by twhiteheadI read about that. That adds an extra dimension to the questions I have about it. What I read was that once the galaxies are traveling away from each other faster than light they are then unobservable. We can see these distant galaxies though. I have a hard time thinking that expanding space effects the relative brightness of stars and there is only a red shift if things are traveling apart that fast. I bet they have a hell of a time mapping the universe. For all we know, many galaxies may be unobservable now.
Just to add to that:
If space is expanding uniformly, then the further apart two objects are then the faster they are moving away from each other. It is actually possible that the universe is big enough that the edges are moving away from each other at greater than the speed of light.
21 Jul 09
1 edit
Originally posted by joe beyser…Maybe it gives the illusion of the speed of light slowing down relative to us
We see the red shift getting redder over time indicating acceleration of expansion of distant galaxies. As space itself expands, wouldn't the light have to travel further to reach us in the next instant? If space was expanding to where the distance between the galaxies increased as though we are moving away from each other faster than light, wouldn't ther sion of the speed of light slowing down relative to us but the dopler effect is only minimal.
….
But there is no such illusion because the speed of light (in a vacuum) is constant for all observers.
We see the speed of light from those distant galaxies having the same speed as the speed of light from all other sources -the fact that those distant galaxies are moving away from us and the space expands while that light travels to reach us has no effect on that speed.
…but the Doppler effect is only minimal.
...
Not sure what you mean by that: the Doppler effect is so great as to push all those wavelengths of visible light from those most distant galaxies to the radio wavelengths.
21 Jul 09
Originally posted by joe beyserActually redshift is not caused by the dopler effect alone but also by the fact that the space it travels through is stretching. As the light travels it is slowly stretched out causing redshift.
Maybe it gives the illusion of the speed of light slowing down relative to us but the dopler effect is only minimal.
21 Jul 09
What would happen if I travel toward a distant galaxy faster than the speed of light? Would I arrive
in its past of current state? 'Cause if I would arrive in the past, that would be awesome? I could then
travel back and forth between galaxies? Until I arrive in the milky way? Some ten thousand years
ago? And I could create a civilisation? And be a God? And have all the beautiful women all to myself?
And then when I grow older? I can put my ship on autopilot? And it could go back and forth between
galaxies? Until it reaches my past again? And then my past me can get on the ship? And return to my
future? And my conciousness could be transferred to it? And I can live forever?
Niiiiice.
21 Jul 09
Originally posted by twhiteheadI'm no expert on relativity, but I think this would violate relativity. Remember that two photons moving in opposite directions actually have a speed of c with respect to each other (and not 2c).
It is actually possible that the universe is big enough that the edges are moving away from each other at greater than the speed of light.
21 Jul 09
Originally posted by JigtieAll that is well and good except for the part where you can't go even the SPEED of light much less past it. The speed of light in space and the expansion of space are two different phenomena, Space does not have a speed limit, in fact during the big bang, in the inflation stage, space was expanding something like 22 orders of magnitude greater than the speed of light so a photon for all intents and purposes stood still while space expanded around it. Think of a photon occupying some point in space during the inflation period of the big bang. That photon would not have a chance to even have gone its own distance before space around it had gone to macro size. Even after the inflation period when the expansion slowed down, that expansion was STILL going several times greater than the speed of light and that is why physicists think the universe is actually about 50 billion light years across and why we can only see about 14 billion light years of it and will never see more than that even if we get a telescope the size of our galaxy because photons beyond that distance are out of our reach, physically and observationally.
What would happen if I travel toward a distant galaxy faster than the speed of light? Would I arrive
in its past of current state? 'Cause if I would arrive in the past, that would be awesome? I could then
travel back and forth between galaxies? Until I arrive in the milky way? Some ten thousand years
ago? And I could create a civilisation? And be a God? ...[text shortened]...
future? And my conciousness could be transferred to it? And I can live forever?
Niiiiice.
21 Jul 09
1 edit
Originally posted by KazetNagorra…two photons moving in opposite directions actually have a speed of c with respect to each other (and not 2c).
I'm no expert on relativity, but I think this would violate relativity. Remember that two photons moving in opposite directions actually have a speed of c with respect to each other (and not 2c).
….
Yes -because if they are moving away from each other then one would appear to be frozen in time and motionless to the other and visa versa.
-but I don’t think space expanding faster than the speed of light would violate relativity -but I am no expert.
22 Jul 09
Originally posted by Andrew HamiltonCould it be that the astronomers have it wrong? What if there is no expansion of space. Instead of one big bang maybe there were many smaller bangs and they formed the galaxies. I do know that in every direction the distant galaxies are moving away from us, but we are not the center of the universe. That gives expanding space some creedence.
[b]…two photons moving in opposite directions actually have a speed of c with respect to each other (and not 2c).
….
Yes -because if they are moving away from each other then one would appear to be frozen in time and motionless to the other and visa versa.
-but I don’t think space expanding faster than the speed of light would violate relativity -but I am no expert.[/b]