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Seeing light from early Universe

  1. Nov 9, 2005 #1
    Can anybody explain to me how our telescopes are able to capture images/light from the early universe (just after the big bang)?

    Every time there is an article that claims this, I scratch my head. I'd like to hear if someone has a "simple" explanation to this. Because I think the light from the big bang should have been absorbed a long time ago by matter. It shouldn't be floating around space.

    http://www.universetoday.com/am/publish/first_light_universe.html?2112005
     
  2. jcsd
  3. Nov 9, 2005 #2

    mathman

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    Let's start by being more precise. The earliest radiation which can be observed is the microwave radiation background, which dates from about 300,000 years after the big bang. Stars, galaxies, etc. which date from the early universe can be observed, but they are significantly later (several million? years). In any case, the universe was sufficiently spread out that radiation is going through mostly empty space.
     
  4. Nov 9, 2005 #3

    How can stars be observed several million years after the big bang? They don't exist anymore and we didn't exist when they existed.

    Are you saying that their light has been circling the universe for billions of years and all of a sudden we captured it? That is exactly what my professor at the University said, but I thought he was crazy.
     
  5. Nov 9, 2005 #4
    Ok, picture this

    one object is 10 light years away from another object.

    Someone who is lets say 9 years old, can view the object, even though whatever (s)he sees happened before (s)he was born obviously.


    It takes time for light to travel....

    Now, increase this distance to several billion light years, and realize that it takes that long for the light to simply reach us.
     
  6. Nov 9, 2005 #5
    Ok but here's where I get confused:

    If light travels at different speeds in different mediums (which I think it does), wouldn't some light from Event A reach a given point sooner (or later) than other light from the same Event A?

    If this is the case, couldn't we have a chance of yet observing still earlier light, etc?
     
  7. Nov 9, 2005 #6
    Light travels at c in a vacuum (space) no faster, no slower. There are events that occur beyond our 'cosmic horizon' which I believe I am right in saying is due to the expansion of space occuring at c+ and so the light can never reach us.
     
  8. Nov 10, 2005 #7

    Chronos

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    The intergalactic medium is too diffuse to have any measurable effect on the speed of light. As moose noted, the speed of light is finite, hence we see distant objects as they were in our past. Here is a useful analogy. When you view a distant lightning strike, you see the flash before you hear the thunder. The flash is [for all practical purposes] the 'now' position of the lightning bolt. The thunder, while emitted at the same time, arrives much later because the distance to the lightning bolt is much greater than the speed of sound. Because the distance to other galaxies is much greater than the speed of light, their 'now' position is like the flash and the image we see is the thunder.
     
  9. Nov 10, 2005 #8
    Yes - it was the portion about the intergalactic medium being too small that was my question. But even though the average medium is too diffuse to cause slowness in light, what if between Event A and Event B (us) there happened to be, say, several black holes and other large gravitational field causers which the light must negotiate (assuming it isn't stopped by them), wouldn't there be some slowdown?
     
  10. Nov 10, 2005 #9

    Chronos

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    Indeed. When light passes by [or through] locally dense regions, there are observational consequences - e.g., gravitational lensing and the SZ effect.
     
  11. Nov 10, 2005 #10

    SpaceTiger

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    As Chronos said, early-universe light rays do encounter things that deviate their path, but for the vast majority, these are very tiny deviations. The chances of a particular beam of light passing very close to multiple black holes is virtually nil.
     
  12. Nov 10, 2005 #11

    turbo

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    Some people will tell you that the speed of light in a vacuum is constant, and move on, perhaps leading you to believe that this is all settled. It is not all that settled, however. There are Loop Quantum Gravity researchers (Google on Fotini and Glast) that believe we will find frequency-dependent effects of the small-scale texture of the vacuum on light passing through it.

    There are others studying the nature of vacuum who believe that the density of the vacuum is not necessarily constant everywhere and that light might travel faster through more diffuse regions. This is called the Scharnhorst Effect. Despite expectations that the Scharnhorst Effect is too small to be detected in the lab, it might already have been detected and quantified in the longest-baseline laboratory we could have ever have devised - the Pioneer probes. The probes showed an anomalous shortening in the expected signal return times, which has been interpreted as a Sunward acceleration. It is possible that the probes are behaving just as they should, but that EM travels faster through more diffuse vacuum (farther and farther from the Sun) than we believed.
     
  13. Nov 11, 2005 #12

    Chronos

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    More diffuse vacuum? Energy interacts with mass, not the empty space [aether] between masses, last time I checked.
     
  14. Nov 11, 2005 #13

    turbo

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    Check again. According to GR, mass distorts space-time (the ether, the vacuum, call it what you will) and EM interacts with the distorted space-time (ether, vacuum), producing the optical effects that we see. EM waves are not bent by interaction with the mass embedded in the vacuum. That is action-at-a-distance gravitation, which Eintstein firmly rejected.
     
  15. Nov 11, 2005 #14

    Phobos

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    Correct me if I'm wrong, but spacetime, ether, and vacuum are not interchangeable terms. Ether was proposed (and rejected based on measurements of the aberration of starlight, IIRC) as a medium of EM propogation within spacetime (not as spacetime itself).
     
  16. Nov 11, 2005 #15

    turbo

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    In his Leyden address and in his later 1924 article "On the Ether" Einstein stated unequivocably that curved space-time was the ether of GR. He stated that the vacuum has physical properties that are necessary for the transmission of EM, and that the interaction of matter with the vacuum is the source of gravitation and inertia. He was in his 40's in this period and was at the height of his intellectual powers. It is unfortunate that so many people manage to dismiss his later work while embracing the earlier work (SR, GR) that he felt was incomplete.

    Depending on your preconceptions of vacuum, ether, and spacetime, these words may not be interchangeable to you. To Einstein, they were interchangeable, and he worked very hard to differentiate the GR ether from the ether of Newton so that preconceptions of Newtonian ether would not contaminate people's perception of the GR ether. He was not entire successful in this endeavor. I will be pleased to supply references....
     
  17. Nov 11, 2005 #16

    Danger

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    Hang on a sec... do you mean that the vacuum itself has some kind of structure, or that EM propogation is dependent upon quantum fluctuations such as virtual particles? :confused:
    Also, can you provide a link to the Pioneer stuff that you mentioned?
     
  18. Nov 12, 2005 #17

    turbo

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    Yes, the vacuum has physical properties:

    Einstein was far more explicit in his 1924 paper "On the Ether", but I cannot find an on-line translation to quote for you. The paper constitutes Chapter 1 of "the Philosopy of Vacuum" by Saunders and Brown, and you should see if you can find a copy at a library or school near you. At about $120, the book is a bit pricey. I'm tempted to spring for a copy, though, after reading the first page of Chapter 2 "The Mass of the Classical Vacuum" by Roger Penrose.
    I do not believe that you will find any published paper describing the Pioneer anomaly in terms of the Scharnhorst effect. It is a logical consequence of my model of ZPE gravitation, which can no longer be discussed on this board.

    Just Google on the "Scharnhorst Effect" or similar and you will find papers describing the effect. In essence, the ZPE electromagnetic field can be rarified by physically excluding some frequencies of the field. This occurs between the plates of a Casimir device. EM will cross this gap at a speed faster than the speed of light in an equivalent non-rarified vacuum. This is the Scharnhorst effect. The effect is widely believed to be undetectable at the sensitivites of current experimental apparatus. We do have a HUGE laboratory, however, with apparatus with a baseline of approximately the diameter of the Solar System. This apparatus consists of the Pioneer probes and their Earth-based telemetry station. If the vacuum (Einstein's GR ether) is densified by the presence of matter, we should expect it to be less dense the farther we move from the embedded matter (the Sun, in this case). The Scharnhorst effect predicts that EM will travel faster through the rarified vacuum. This is exactly what we see in the Pioneer telemetry data. The signals returned faster than expected, and the gap between the anticipated return time and the actual return time grew smoothly the farther the probes got from the Sun. If we believe that the speed of light in a vacuum is a constant, we must then explain why both probes seem to be slowing down with a constant smooth anomalous Sunward acceleration. In actuality, the probes are not slowing down - they are behaving normally. It is our insistence on the constancy of the speed of light in a vacuum that is causing the misunderstanding. The Scharnhorst effect is offering us the opportunity to quantify vacuum polarization in our solar system.

    This is a new idea, and because it is coming from an optician and not a cosmologist or astrophysicist, many here will reject it out-of-hand. I cannot help that. I ask only that you consider the observations (Pioneer data) and consider the simplest explanation: that the probes are behaving as they should (no perfectly coordinated sunward acceleration) and that somehow the probes' signals arrived sooner than expected the farther they got from the Sun.
     
    Last edited: Nov 12, 2005
  19. Nov 12, 2005 #18

    Danger

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    Thanks, turbo-1. I remember reading some stuff about the Casimer effect somewhere in this site a few months ago, but never quite got into it. It seemed quite contentious at the time, if I recall. I'll try digging into it again to see just what's up.
     
  20. Nov 12, 2005 #19

    turbo

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    Hi, Danger. Was it this one?

    https://www.physicsforums.com/showthread.php?t=86691

    It did get contentious at times. Few people seem to want to believe that Einstein required an ether, so he could extend GR and come up with a model of gravity that could be reconciled with electromagnetism. Einstein also required that the ether be dynamical. The few individuals brave enough to offer something like "OK, in a sense there might be a metric that you can call an ether" seemed a bit quick to follow up with statements to the effect that the ether could not have any properties.

    So much for Einstein's career. His mathematical model of GR gravitation as massive bodies following geodesics in curved space-time had been elevated to a "reality" that he rejected, and his later work toward grand unification is belittled and treated as if he was making a bad joke. By the mid-1920s, he had rejected all action-at-a-distance explanations for gravitation, inertia, etc and absolutely demanded that these arise as local interactions between matter and the ether in which it is embedded. Those who dare to point out this inconvenient truth are called cranks or worse.
     
    Last edited: Nov 12, 2005
  21. Nov 12, 2005 #20

    Danger

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    I think that it's the one I was recalling. I'll have to check back over it when I have more time.
     
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