If the universe is expanding at an ever-increasing pace, and according to relativity?

Question

If the universe is expanding at an ever-increasing pace, and according to Einsteins theory of relativity traveling faster than the speed of light would cause moving backward in time (BTW i dont fully believe that part of relativity), then do you think that eventually the universe could accellerate to and beyond the speed of light, causing the universe to just keep bouncing back and forth in time, neverending?

**The main thing that i believe that would actually happen if traveling faster than light speed, is that there would be an illusion of time travel. If you are looking at something located 5 light years away, and you travel toward it at, say, 2 times the speed of light, you will visually see that object change from 5 years ago to 2.5 years ago after half the distance was travelled, appearing to travel into the future. If you were looking back at earth while taking this trip, earth would appear to move back in time, because you have caught up to and passed light that came from earth years before.

PHYSICS DUDE: So what about the matter contained in the universe? Would it be could it be moving backwards in time? Just going back and forth between the times when it wasnt traveling faster than light and the times when it was moving faster than 186,000 mps?

But abhinav: because of dark energy, the universes expansion has been accellerating ever since 9 billion years ago, and shows no sign of slowing down. If it continues (gravity cant stop it), it will keep increasing its acceleration of expansion for all eternity, correct?

Answer 1

You misunderstand Einstein's Theory of Special Relativity. It doesn't say that you can't have something move faster than the speed of light. Only "information" can NOT move faster than the speed of light. By information, I mean any "signal", like electromagnetic waves (which includes light, radio waves, etc. etc.). Any material object within the Universe are also restricted by Special Relativity, since material objects also carry "information".

For the Universe or the fabric of spacetime to be expanding faster than the speed of light is NOT a violation of Special Relativity, and the Universe will not be moving backwards in time.

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Edit - Ok, here let me clarify why I said that Special Relativity (SR) does NOT apply to the expansion of the Universe:

Velocity of something depends on which definition of distance we use. So, if we assume that the distance of an object at time t is the distance from our position at time t to the object's position at time t measured by a set of observers moving with the expansion of the Universe, and all making their observations when they see the Universe as having age t, then the velocity (change in D per change in t) can definitely be larger than the speed of light. This is not a contradiction of special relativity because this "distance" is not the same as the spatial distance used in SR, and the age of the Universe is not the same as the time used in SR.

In the special case of the "empty Universe", where one can show the model in both special relativistic and cosmological coordinates, the velocity defined by change in cosmological distance per unit cosmic time is given by v = c ln(1+z), where z is the redshift, which clearly goes to infinity as the redshift goes to infinity, and is larger than c for z > 1.718.

For the "critical density Universe", this velocity is given by v = 2c[1-(1/sqrt(1+z))], which is larger than c for z > 3.

For the "concordance model" based on CMB data and the acceleration of the expansion measured using supernovae, a flat Universe with Omega = 0.27 (this would be our Universe), the velocity is greater than c for z > 1.407

All this just means that for any expanding universe, there will be a value of z (i.e., redshift or cosmological distance) that will give the appearance of galaxies moving at velocities greater than c.

Answer 2

Physics Dude has said it far better than I could.

Another thing to ponder...
All this evidence that the expansion of the Universe is accelerating is based on the observations of distant supernovae. This is based on the assumption that they're standard candles, and that they obey the Chandrasekhar limit.
About two weeks ago it was announced that astronomers had found a supernovae of the type used in the dark energy observations that violated the Chandrasekhar limit. This calls into question the validity of the study.

Answer 3

Well I'm not a big bang denier, but relativity is most certainly not wrong. Even the little GPS device in your car wouldn't work properly if engineers didn't account for the fact that time moved at a different rate to satellites than it does to you in your car. Without relativity, GPS would go out of wack for everyone.

Answer 4

According to relativity nothing can travel faster than light through space. The reason some galaxies appear to move away from us faster than light has more to do with the expansion of space itself than it does with the galaxies' motions through space.

Answer 5

i don't think that universe can ever expand at the velocity of light because the equation according to which we state this fact becomes indeterminate if we put this velocity in that. moreover certain particles called TACHYONS have been proposed to be associated with the cosmic ray which are thought to travel with a speed greater than the speed of light and they do carry information.

Answer 6

Is it expanding? Even theoretically, it's not measurable since the measuring ruler would be also be expanding.

All we know is that there is a red shift.

And, like Albert says in "Saturday Night and Sunday Morning" --

All the rest is Propaganda.

;-)