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Timeline of Natural History - Part 1

June 4, 2008 on 9:49 am | In big bang, cosmology |

Sometimes people ask me what I do, and if I’m being completely honest, I’ll tell them I’m a cosmologist. When they ask for more details (because it isn’t hair, nails, and makeup), I tell them that I study the Universe, and try to figure out and understand the story of how we came to live in the world we live in here and now. Then they either smirk and ask, “Is that all,” or tell me that we already know this, and they saw it on PBS.

But I think you might enjoy hearing the most up-to-date version of the story that we have. So, dear readers, I present to you the most accurate timeline ever composed of what has happened in the Universe to bring us to the present day, and telling you the age of the Universe at that time. I’ll do this in three parts, and so today I bring you part 1, from inflation to the first stars:

  1. 10-35 seconds: The Universe expands exponentially fast, stretching space to make it flat and giving it the same properties everywhere. We call this inflation.

  2. 10-30 seconds: Inflation ends, and all the energy that was stored in space, causing the exponential expansion now becomes an incredibly dense bath of hot particles of matter, anti-matter, and radiation. The birth of all the energy in what we know as our Universe is what we call the Big Bang.

  3. Somewhere between 10-30 and 10-10 seconds: natural processes create slightly more matter than anti-matter in the Universe. Even though there is only one extra matter particle for every one billion pairs of matter-antimatter particles, that’s enough to explain all the matter in the Universe today. We call this process baryogenesis.

  4. 3 minutes: After all the antimatter annihilates away with the matter, there’s a little bit of matter left over in a sea of radiation. At three minutes, the Universe cools enough so that protons and neutrons can fuse together to form heavier nuclei without being blasted apart. This is where nearly all the hydrogen, deuterium, helium, and lithium in the Universe is created. (Most of it is hydrogen, about 75%, and most of the rest is helium, about 25%. The rest is less than 0.01%.) We call this part Big Bang Nucleosynthesis.

  5. 380,000 years: The first neutral atoms form. Up until this point, all of the radiation energy in the Universe has been too cold to blast the nuclei of atoms apart, but that energy has also been too hot to allow neutral atoms to form. It takes almost 400,000 years for the Universe to expand and cool enough for the leftover radiation from the Big Bang to chill out. Finally, at this point, electrons and nuclei can meet to form neutral atoms. When this happens, that leftover radiation simply flies off in all directions; this is what we see as the Cosmic Microwave Background.

  6. 50 Million Years: The first stars in the Universe begin to form. It takes about 50 million years for gravity to collapse matter into volumes that are dense enough and massive enough to ignite nuclear fusion. These first stars are huge, hundreds or even thousands of times as massive as our Sun, and are responsible for creating many of the heavy elements and metals that our Universe has today. These stars will all die as supernovae or even hypernovae, and will blast their remnants all over the Universe.

Come back tomorrow for Part 2, where we’ll walk through the formation of galaxies to the creation of Earth and our Solar System!


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  1. What happened to 10^-43 seconds? Cosmology can at least say that gravity was combined with the other three forces[sic] up to that point in a quantum gravity era(or Planck epoch).

    Comment by mark a. thomas — June 4, 2008 #

  2. Awesome! I can’t wait for part two….. Ethan, your the best!

    Comment by dan w. — June 4, 2008 #

  3. Can I use the comment section to ask questions? At 10 -35 seconds you say the universe expanded to become flat. I hear the term “flat” in many articles on cosmology and astronomy in general, but haven’t seen an explanation of what is meant by it. Certainly, we don’t mean 2-dimensional. By flat, do we mean to say time only goes one direction or that expansion continues without reversal?
    Also, nice differentiation between expansion and big bang!

    Comment by Kendall — June 4, 2008 #

  4. Thanks for the fast comments, guys!

    Dan, Part 2 is coming tomorrow.

    Mark, 10-43 seconds assumes that we can say something sensible about what happened before inflation. While we can speculate that energies and densities were even higher than the inflationary scale, there’s simply no way to know for sure.

    Kendall, always you can ask questions here! When a cosmologist says “flat” we mean that space could have been curved, either like the surface of a sphere (we call that positive curvature) or like the surface of a cowboy saddle (negative curvature). Instead, we find that it’s really flat. Here’s a simple way to measure which one you have. Take those three surfaces and draw a triangle on each one. Now, measure the three angles on each surface and add them up. On the flat surface, they add up to 180 degrees, just like you expect. But on the sphere, the number you get is more than 180 degrees, and on the saddle, it’s less! That’s what we mean by flat: if I took three points in space and connected them to make a triangle, and measured the angles between them, it would be exactly 180 degrees.

    Comment by ethan — June 4, 2008 #

  5. Hi Ethan,
    I think I see what you are saying. In a sense you are using the 10^-35 seconds as a starting point for a classical big-bang with inflation. Pre-bang conditions are still veiled even when using purely theoretical constructs (looking for a measure of correctness, aka best fit speculation). So the classical big-bang has possible experimental immediacy whereas the pure theory at the top perhaps does not. So cosmological inflation in this case is stating; “We are not so sure about up to the Planck time and do not have much to say about this, but we have a very good theoretical model after the Planck time about the flattening of spatial directions and exponential growth of this space and we can go from there”. Or something to that order.

    Comment by mark a. thomas — June 4, 2008 #

  6. Mark,
    That is indeed what I’m saying. Before we had inflation, it only made sense to trace the energies and densities back as far as we could, i.e., the Planck scale. But inflation, which happens some 4-10 (depending on the model) orders of magnitude of energy below that, obscures whatever came before.
    I still think examining the physics of higher energies is incredibly interesting, but as far as our Universe goes, I am taking inflation as the present starting point. But yes, we are certainly not so sure what happens before it!

    Comment by ethan — June 4, 2008 #

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  9. I can see that my understanding of ‘flat’ is correct, but what I’m having trouble understanding is why Inflation is needed to get that flatness.

    I mean, couldn’t space have expanded to the same size and flatness with just regular old expansion?

    Comment by Sili — June 16, 2008 #

  10. Sili,

    It could have, but there’s no reason for it to be flat. Inflation forces you to be flat, but in principle space could have started out curved like a sphere or curved like a saddle; instead it’s flat like a sheet of paper. If I take a sphere or a saddle and I increase its size by billions and billions of times, and then I look at a small area, it looks flat to me. But if there’s no inflation, I need some compelling reason to make my Universe flat. A sphere or saddle with regular expansion would still look like a sphere or saddle; but that’s not what we see.


    Comment by ethan — June 16, 2008 #

  11. I think I need to (re)study more geometry …

    I honestly still don’t follow. I do get the how Inflation explains how otherwise non-causally connected parts of the Universe are in thermal equilibrium, and how quantum fluctuations seed the macrostructure, but …

    ” If I take a sphere or a saddle and I increase its size by billions and billions of times, and then I look at a small area, it looks flat to me.”

    That’s exactly what thought! So is the problem that regular expansion hasn’t progressed enough? I really appreciate your answering me, but I can’t seem to bend my head round how Inflation differs from regular expansion in this regard. I’m sure it’s just down to an inability to think four (or three) dimensionally. Or perhaps I’m suffering some unstated misconception that’s blocking my enlightenment.

    Thank you.

    Comment by Sili — June 16, 2008 #

  12. Inflation expands things in a different fashion than you’re used to. In a “normal” Universe, with matter and radiation, the size of the Universe expands as a power law with time, so that R ~ t^(some power). For a Universe with radiation, that power is 1/2, for a Universe with matter, that power is 2/3, and for a Universe with the mix we currently have, that power is 1.

    But in an inflating Universe, the expansion rate is R ~ e^Ht; meaning that in just a tiny fraction of a second, the Universe can expand by a factor of billions and billions of times its original size. Plot y=e^x and y=x on your graphing calculator, for example, and the difference between those two graphs is the difference between how inflation works and how regular expansion works.

    Comment by ethan — June 16, 2008 #

  13. Ah! Thank you. That helps a lot, yes. I think I’m closer to getting it now. At least I think I have the right imagery in my head.

    (I’m too old to have a graphing calculator and never learned to actually use Maple.)

    Onward to part 2 and 3!

    Comment by Sili — June 16, 2008 #

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    Comment by MIKE ROE — June 24, 2009 #

  16. I just came across your article and I am not as proficient in science as you are. I’m sure I’m missing a critical part in the thought process, so I am just wondering: if the Big Bang created all the energy in the universe, then how could the bang have occurred prior to the existence of energy? How could there be inflation or expansion of any kind?

    Comment by Kendle — November 28, 2010 #

  17. Praise God!

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  18. Fuck that shit!!!!! Your fuckin stupid. U need to read the bible man there’s a man called GOD. That’s how all this got created.

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