“The only reason for time is so that everything doesn’t happen at once.” -Albert Einstein

And yet, this is a very good reason! We need things to happen in stages: you can’t form human beings before you form planets (that would be bad); you can’t form stars before you form atoms (also bad); you can’t form atomic nuclei before you get rid of antimatter (still bad).

Image credit: Addison Wesley.

Image credit: Addison Wesley.

But somehow, despite having very little direct evidence for what happened in the early Universe, we tend to give timelines of precisely when various events happened. For this week’s Ask Ethan, we take a look at how well we actually know these pieces of information, and why we think we can state any of this with confidence.

Image credit: wiseGEEK, © 2003–2014 Conjecture Corporation, viahttp://www.wisegeek.com/what-is-cosmology.htm#; original fromShutterstock / DesignUA.

Image credit: wiseGEEK, © 2003–2014 Conjecture Corporation, viahttp://www.wisegeek.com/what-is-cosmology.htm#; original fromShutterstock / DesignUA.

Go take a read. You’ll be glad you did, and you’ll also get an appreciation for our (often-unsaid) uncertainties!

Comments

  1. #1 Henry Norman
    Philippines
    January 23, 2015

    You wrote:

    “combined with our (measured) understanding of what the original fluctuations were that the Universe started off with”

    How could the “original fluctuations” have been measured at the time the Universe “started off”?

  2. #2 Michael Kelsey
    SLAC National Accelerator Laboratory
    January 23, 2015

    @Henry Norman #1: The small-scale variations in the cosmic microwave background (that blue and green speckled oval which is always used to show the CMB) are what Ethan is alluding to here. With both the WMAP and Planck satellites, we can determine the magnitude of fluctuations down to very small angular scales.

  3. #3 Torbjörn Larsson
    January 25, 2015

    Time is so that everything doesn’t happen today, and space is so that everything happening today doesn’t happen to me.

    “There is no way to have them be empirically confirmed, and yet they are given to extreme degrees of accuracy (and with confidence).”

    Better tell the cosmologists that, since it is obvious the observation in the last part conflicts with the hypothesis of the first. =D

    But not only do cosmologists makes these observations as we write, they have witnesses of these times (elementary particles, nucleosynthesis isotopes, cosmic microwave background, …), relic fossils as it were. Reminds me of the similar question on the solar system age, where some radioactive isotopes were witnesses at the time.

  4. #4 xlsdx
    America
    January 26, 2015

    “We understand how the Universe expanded, and hence, what its physical size-and-scale is as a function of time.
    We understand how the temperature (and hence, energy) of the particles in the Universe depends on the expansion history.
    We understand — to varying degrees — the physical processes that determine each of these steps, and how they evolve.

    I disagree that we understand any of these things. We may have some primitive theories and models about them, but that is a far cry from “understanding”. There are a LOT of assumptions that go into extrapolating across time, in either direction, and you can never truly understand something that you have made blind assumptions about.

  5. #5 Pramendra Srivastava
    Indonesia
    May 20, 2016

    Good Morning All,
    I’m trying to locate Addison Wesly, to seek their permission in using one of their Big bang image in my first book, but unable to get any response or contacts whatsoever i tried. Mr Ethan and others, can some one help me contact Addison Wesly for their Big bang image. I am a Engineer turned spiritual author and I am authoring my first Book Sankhyayog Srimad Bhagwad Gita. A book which hides several scientific mentions including Big bang theories. In this regard, We request you to allow us to use Some of the Astro images especially the one on your home page Big bang image. Kindly Assist us and allow us the permission to use the image in order to explain the write up better. I am not very professional on such issues and do not know the right way to get such permissions. Please respond asap.

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