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Looking Back in Time

  1. May 7, 2004 #1
    Guys,

    I have a question about looking back in time to the beginning of the big bang.

    If you assume the universe is infinite and expanding, then i don't understand how we can see light from 500 million years before the big bang.

    When the big bang occured (save for an event horizon that may have occured when there is a singularity) light would be travelling at the constant speed that it does.. therefore:

    a. how come the light wasn't lost
    b. does this mean the universe is expanding faster than the speed of light.

    If you could place at yourselt next to the big bang, then after 1 sec the light would have travelled hte usual 186,000miles, therefore if the universe was not that big wouldn't the light have been lost forever.

    Additionally, in an infinite space there is no centre, then how can we know to look in the right direction, i mean, if we look left and see cosmic radation 18 billion years old and see the same if we look right how does that work.

    Cheers

    Gary (Newbie)
     
  2. jcsd
  3. May 8, 2004 #2

    selfAdjoint

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    Where did you get the idea that we can see light from before the big bang? Have you read your sources right? The earliest radiation we can perceive is the cosmic microwave background (CMB) which dates from the period when the universe became transparent, a short time AFTER the big bang.
     
  4. May 8, 2004 #3
    Isn't electromagnetic radiation, always the leading edge of the universe as it expands. Doesn't the leading edge define the universe in its progress? That is why "nothing" goes beyond the speed of light, since nothing would be beyond the leading edge of the light of the universe? Ohhhh nothingness is so attractive.
     
  5. May 8, 2004 #4

    selfAdjoint

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    Well, not exactly.

    May I suggest Lineweaver's account of cosmology, which will explain the different "horizons" we find in the electromagnetic phenomena available to us.
     
  6. May 9, 2004 #5
    Looking Back again

    I am not implying we can see before the big bang at all.

    What I am saying is this.

    Say the dot one the next line is the big bang

    .

    As this universe expands after say 1 second the dot will be here

    .

    Now if this expansion is less than the speed of light after that same 1 second if would look like this

    . x

    Where the . is the expansion of the universe (say at 10000kps) and x is the distance that the first photons of light have travelled to.

    Therefore, how can we ever see back to anywhere near the big bang, my point being that unless the universe is expanding faster than the speed of light the the light will have been long lost (beyond the known universe),

    Additionally, if there was a big bang it would imply that this was the beginning of centre of the universe, unless if was infinite in size which makes no sense, therefore you should only be able to see it in one direction. If i look left and see 18 billion year old light i shouldn't be able to see the same from the right.
    Well actually, that may not be true, i may be able to see light from both sides, however this would not be representative of the big bang, this would be light from 18billions years ago which would not be the big bang - it couldn't have happened in two places at once.

    Look at the following
    x x
    x . x
    x x

    If the . is eath and we are searching for old cosmic radiation, then we shouldn't be able to see the same aged light in all directions of X.
    Surely if we could then this would mean that this light is all say 18 billion years old and therefore had to exist in that state 18 billion years ago (i.e not as part of the big bang) as the points to look at would be much smaller and all in the same direction?

    Cheers

    Gary
     
  7. May 9, 2004 #6
    If tachyons exist as physical objects, causality is no longer invariant. Different observers will see different causal sequences. This effect requires only special relativity (not GR), and follows from the fact that for any spacelike trajectory, reference frames can be found in which the particle moves backward or forward in time. This is illustrated by the pair of spacetime diagrams below. One must be careful about what is actually observed; a particle moving backward in time is observed to be a forward moving anti-particle, so no observer interprets this as time

    http://math.ucr.edu/home/baez/physics/Relativity/GR/time_travel.html

    If we consider time. What distance can a photon travel, and not be seen from, in a dimensional perspective? Could it become lost, in the gravitational field (Calabi Yau string determination), and like gravitational lensing, speak to the illusion we see and at some point loose sight of, in that same dimensional aspect?

    Any one want to speak to this?
     
  8. May 9, 2004 #7

    selfAdjoint

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    Additionally, if there was a big bang it would imply that this was the beginning of centre of the universe, unless if was infinite in size which makes no sense, therefore you should only be able to see it in one direction. If i look left and see 18 billion year old light i shouldn't be able to see the same from the right.
    Well actually, that may not be true, i may be able to see light from both sides, however this would not be representative of the big bang, this would be light from 18billions years ago which would not be the big bang - it couldn't have happened in two places at once.


    This is a misunderstanding. At the big bang, the singularity (single point) was all the universe there was; it was the ancestor of every subsequent point. There is no center.

    Light we can see goes back to a period after the BB. I think you got your age figure 18Gy from an older source. It is only with the analysis of the data from recent monitoring of the CMB that we have determined the age to be 13.5Gy. So no light really comes from before the BB, it is just a case of improving estimates.
     
  9. May 9, 2004 #8
    Still Looking Back

    Guys,

    I think everyone is missing the point of the question,(which still hasn't been answered).

    Regardless of the age of the universe of the time of the big bang, after the big bang physical laws follow.

    Therefore if after 1min after the big bang the light caused by the big bang has travelled 1 light minute, if the rate of expansion is 1/2 the speed of light then the universe has expanded by 1/2 a light minute, therefore the light from the big bang should have been lost forever - i.e it would be outside the known scope of our universe.

    Therefore howcome we can see back this far.

    Sure if the Earth or any arbitary view point X is looking at the universe expansion i understand how we can see, however looking back before the view point existed baffles me

    X . |

    Say X is the view point, . is the point you are viewing and | is the universe expanding, then sure the light from . can travel towards X, however if the point you are viewing occured before X how can we see that, by the time X is created by the expansion of the universe then the light from the viewing point would have long passed by the view point.

    Thanks

    Gary
     
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