Let's Talk Physics

A stochasticly updated blog about interesting topics in Physics & Astronomy

The First Few Minutes

My apologies for missing last week. I was in Turkey and had no way to post this article (which was totally finished by then). Also, next week I’ll probably be late as I will be somewhere in the middle of the Outback, so see you in 2 weeks! – Mark


The last few weeks, I’ve built up a few fundamental concepts in physics – the 4th state of matter, how particles have the ability to annihilate and how photons interact with electrons. So now it’s time to talk about how these 3 concepts link together – at the start of all things!

The Universe (supposedly) began with the Big Bang. I’m not going to talk about what caused it, but today I’m going to talk about the direct aftermath of the Big Bang.

What we’re talking about is up to roughly between the 1 second and the 300 thousand year mark.

After the Big Bang, the Universe was a chaotic place. Everything in the Universe (all of the galaxies, nebula and clusters that we see today) didn’t exist yet. Instead, the entire Universe existed as a plasma, and the Universe would have been smaller than our solar system (kind of. Talking about distances during this period is a bit…finiky). So, the Universe was literally a soup of protons, electrons, anti-protons and anti-electrons, which weren’t bound to each other. And all of the energy that wasn’t a proton or an electron (or an anti-particle) yet was a photon. So, here’s what was happening.

Firstly, the photons that were flying around would spontaneously split into a proton/anti-proton pair (or electron/anti-electron pair). Then, there was a chance that the particle produced by this decay would randomly hit its anti-particle formed by another photon decaying. This particles would annihilate and form yet another photon – this would happen millions of times per second in a continuous feedback loop! Now, while these photons were doing their stuff, the protons and electrons that weren’t annihilate would try to couple together to form hydrogen. But, whenever hydrogen formed, it wouldn’t last. Why? Because the photons that were flying around would interact with the electrons and decouple them from the protons via the photoelectric effect! Which meant the Universe was stuck in a plasma state, where no atoms could form.

Example of what might happen when a photon decays into a proton and anti-proton pair. What we're left with is a plasma state, where the electron and proton are decoupled from each other

Example of what might happen when a photon decays into a proton and anti-proton pair. What we’re left with is a plasma state, where the electron and proton are decoupled from each other (click for larger image)

And that’s it. That’s how the Universe behaved for roughly the first 378,000 years (ok, a bit longer than 5 minutes, but it’s a good approximation). After that…well, I’ll leave that for 2 weeks time.



About irishphysicist

I'm a PhD student with the Departments of Physics in University College Cork, Ireland and University of Notre Dame, Indiana. I want to try and bring astrophysics to the public, and also would like world domination. But that's a story for another day.

4 comments on “The First Few Minutes

  1. Edward
    July 2, 2013

    “After the Big Bang it was a chaotic place.”

    In reference to entropy in thermodynamics, if that was chaotic, where are we now? lol 😀

    I’m a first year high school student I don’t understand much here but it’s all very interesting; I like to blog about physics too.

    • irishphysicist
      July 6, 2013

      Interesting question – entropy of a system must approach a constant value as the temperature of that system tends to absolute 0. Which means, as the Universe cools (which is is), the entropy of the Universe is approaching this constant value. Might try tackle this in a blog post soon! Thanks Ed!

    • Thomas Kelly
      July 30, 2013

      Here is a brief discussion on entropy and its relevance when discussing the beginning of the universe.

    • Thomas Kelly
      July 30, 2013

      Ooops, forgot the link

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This entry was posted on July 1, 2013 by in Astrophysics and tagged , , , , , , , , .
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