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Inflation Help

  1. Nov 16, 2009 #1
    I am stuck on a few cosmological points I could use some help on.

    The first being "redshift" as an indication of inflation. To me red shift just seems like it's a result of the degradation of light quanta over long distances. Since light slows down in environments close to absolute zero, its fairly straight forward that the fluctuations in speed over vast stellar distances would have this effect. Why is this wrong ?

    The second point I have trouble with in regards to modern cosmology is in regard to the impact of quantum theory on the standard model. It seems to me that if quantum mechanics is accurate, the universe is potentially just a set of all outcomes relative to an observer at a given point of reference. So that we live in a universe where all "possible" outcomes are equally real. In other words anything that could exist does exist, we just unfold the universe we experience based on local actions. If this viewpoint has so much support, then why isn't more credence given to cosmological theories that support this notion, rather than continuing to hunt for things like dark matter to save the anthropomorphic standard model?
  2. jcsd
  3. Nov 16, 2009 #2


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    Inflation is not the same as an expanding universe. Inflation (in cosmology) refers to a specific era in the very early universe when the universe expanded in size exponentially for a short period. This is before there were any stars or galaxies (or even any stable matter) and so we can't make any direct measurements of this.
    Redshifts are used to measure the expansion of the universe since then.

    Not quite - you can slow the speed of light in clouds of atoms at very low temperatures but not in empty space. The main argument that redshifts are due to expansion and not any absorption effect is that the same rule applies across all wavelengths we can measure - tis isn't the case for most other ways of slowing light,
  4. Nov 16, 2009 #3
    Light has no fluctuations in speed in vacuum. In fact, light slows down in some medium due to the fact that photons are being absorbed and re-emitted. Redshift is not indication of inflation, but expansion of universe.

    It is a very tricky question, but it can be helpful if you try to comprehend that there is no "future" in physical existence. All we can experience and measure is now, and "now" when plotted over distance has a shape of a cone, with observer at the top. There is no you when you are 90 years old (except, if you are now 90 years old).
    Last edited: Nov 16, 2009
  5. Nov 17, 2009 #4


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    Well, the evidence of inflation isn't found in the redshifts of objects around us. Inflation happened too early in the history of our universe for that.

    Inflation occurred in the earliest stages of our universe, long before the emission of the CMB. Because the universe prior to the emission of the CMB was opaque, we can't directly see inflation. Instead, we see its imprint on the later universe.

    In particular, inflation makes some very specific predictions for the sound waves that would have propagated in our early universe, sound waves that we see imprinted on the CMB. In particular, it predicts a very specific interference pattern that should appear, and does. This is currently our strongest evidence for inflation.

    Well, not quite. I have made this mistake in thinking a few times myself (that quantum mechanics = everything happens). But this aspect of quantum theory just guarantees that many things will happen, not that all things must. Also, when you're talking about cosmology, this particular aspect of quantum mechanics has remarkably little to say, for the simple reason that our universe is quite big enough to ensure almost pure classicality.

    That said, dark matter isn't currently accepted because it "saves" the standard model. Instead, it is supported by multiple pieces of mutually-corroborating evidence. Dark energy is still largely an unknown. The simplest proposals are but small extensions to the standard model, though we don't yet know what the right answer is. With dark matter, we have more than ample evidence to demonstrate that it very much exists. All that remains is determining exactly what type of particle it is.
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