The Big Bang theory explained chronologically in 7 steps


The Big Bang was the event which led to the formation of the universe, according to the prevailing cosmological theory of the universe’s early development (known as the Big Bang theory or Big Bang model).

According to the Big Bang model, the universe, originally in an extremely hot and dense state that expanded rapidly, has since cooled by expanding to the present diluted state, and continues to expand today. (The expansion of the universe was formulated by Edwin Hubble through his equation: the Hubble’s law).

The earliest phases of the Big Bang are subject to much speculation. In the most common models, the Universe was filled homogeneously and isotropically with an incredibly high energy density, huge temperatures and pressures, and was very rapidly expanding and cooling.

The Universe expansion timeline

This is an artist's concept of the Universe expansion, where space (including hypothetical non-observable portions of the Universe) is represented at each time by the circular sections. Note on the left the dramatic expansion (not to scale) occurring in the inflationary epoch, and at the center the expansion acceleration. The scheme is decorated with WMAP images on the left and with the representation of stars at the appropriate level of development. Image from WMAP press release, 2006.


Big Bang

1- (10^{-43} seconds) The universe is small, hot and dense.

2- (10^{-35} seconds) It is beginning to create particles such as quarks and antiquarks.

3- (10^{-4} seconds) Quarks make up protons and neutrons. The antiquarks make up antiprotons and antineutrons.

4- (1 second) Appear the earliest electrons and positrons.

5- (3 minutes) Protons and neutrons combined to form helium nuclei.

6- (300,000 years) The electrons and nuclei combined into atoms (mostly hydrogen).

7- (13,700,000 years) The current universe full of stars and planets. All of this cosmic evolution after the inflationary epoch can be rigorously described and modeled by the ΛCDM model of cosmology, which uses the independent frameworks of quantum mechanics and Einstein’s General Relativity.


You may also be interested in: Hubble's law and expansion of the universe


  1. Leo says:

    You need to exponentiate -43, -35, and -4 in your items 1, 2, and 3. Otherwise this makes no sense.

    Also this is terribly oversimplified and a bit inaccurate. Nothing is understood as early as 10^{-43} seconds. Maybe 10^{-33}, but definitely not 10^{-43}.

    The universe was in a thermal state at early times, so 1 second was definitely not the “first appearance” of electrons. That was around the time of the freeze-out of the reaction e+ + e- -> 2gamma. There were actually many _more_ electrons before this time.

    Protons and neutrons combined to make Deuterium, He-3, He-4, some Lithium and that’s about it (most protons are free; almost every neutron is bound up in a nucleus).

    Lambda CDM plus inflation describes almost the whole thing, not just stuff after big bang nucleosynthesis or after the surface of last scattering.

    • admin says:

      Thank you, Leo. In fact, these numbers appeared me as exponents into the edition menu. So since now I write these numbers using the method simpliest “10^{-33}”.

      Why can not to be 10^{-43}? I see I have some obsolete data. If I put -33, the second point is wrong. How can I fix it?

      Thank you for your very interesting and important comment! ;)

  2. Alan Andrew says:

    Am I missing something very basic in this? I have a well-rounded educ. but only first or second yr science.
    How do we know when “0″ is, in time?
    You say, “1- (10^{-43} seconds) The universe is small, hot and dense.”
    This is, in my logic, impossible. Do you mean that this is the point, AFTER ZERO, that the “explosion” happened? It’s confusing. Never mind how long the infinitely small state was present prior to the bang.
    My pet theory (completely untested, of course) is that for infinite time, there has been a “yo-yo” effect: expansion-contraction-expansion-contraction.
    But I’d still like to understand your point 1.

    • admin says:

      Point 1 is an hypothesis. Theoretically, if the current universe has “x” mass that which was created by the Big Bang (regardless of what came before the Big Bang, for example expansion-contraction), this mass should be concentrate at a point we do not know. Perhaps between the last contraction and the current expansion (in an exact moment that we can not calculate).

      Very interesting aportation, Alan. In fact, I am not a physicist, so I appreciate your comments.

      Thank you and greetings :)

  3. Latricia Carloni says:

    Wow, marvelous blog layout! How long have you been blogging for? you make blogging look easy. The overall look of your website is wonderful, let alone the content!

  4. Conor Brice says:

    UMMMMMM, so confused, Any tricks how to learn this fast. I need to know this for my Year 10 Physics Exam HAHAHAHA. FML

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