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How do we know everything in the universe is made of atoms?

  1. Sep 15, 2011 #1
    We know everything on Earth is made up of atoms and molecules, and most likely everything in the solar system, but how do we know everything in the universe uses them, and not something else? The Big Bang would cause things to have similarities, but different parts of the universe could still be very different.
  2. jcsd
  3. Sep 15, 2011 #2


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    The answer has to do with the Copernican principle. Basically, we make the assumption that we are in a fairly typical, normal part of the universe, and any other random place looks more or less the same. (Obviously this isn't strictly true -- we're confined to this nice Earth with water and habitability for carbon based life forms, but from an elementary physics point of view, it seems like a rather reasonable assumption). So on one level, we are simply assuming that the physics which works here is the same physics which works elsewhere. If this were not the case, physics would somehow be a local phenomenon, which simply seems wrong.

    (Caveat: You can have scenarios in which the fundamental constants are different in different parts of the universe. For example, in an inflationary cosmos where small parts of a pre-existing universe undergo periods of rapid expansion to effectively become separate universes, the values for the various fundamental constants which control the shape and fate of our universe may be different. The key point here is that the LAWS themselves remain the same)

    On a more empirical level, though, we can explain a lot of what we see out in the universe with the known laws of physics. We see the same chemical reactions taking place billions of light years away which take place here on the Earth -- which gives us good confirmation that the above mentioned hypothesis is indeed correct.
  4. Sep 15, 2011 #3
    EXCELLENT answer. And I am not referring to you with this comment. But as science has always been my passion, the one scar on the profession IMO is the fact that when theories are developed. They are fact. Until one rolls along that makes more sense.
    That is not how facts are learned or developed. (and I am not talking about all scientists or research. I just think that before we say something like "dark energy" is expanding the universe, we need to have proof of the "dark energy" first.
    I will get on a soapbox if I continue, so I will stop. lol.
  5. Sep 15, 2011 #4


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    No they're not. They're theories.

    The strength with which they are accepted is proportional to
    a] the amount of previous research that is also pointing in this direction,
    b] the amount of evidence that supports it,
    c] how well they explain the evidence compared to competing theories.

    What you may be seeing is that, often, one theory is dramatically better at the above than others. It is the front-runner for the most part unless another theory can explain the evidence better.

    But that doesn't make it fact. It simply means that, if you're going to insist on touting a competing theory, it had better darn well be better than the best one so far.
  6. Sep 16, 2011 #5
  7. Sep 16, 2011 #6
    Universe contains much more than atoms or molecules.
    There are particles which are not part of atoms. Also universe refers to space, time, matter, energy, and everything that exists.

    The fact that different parts of the universe are similar is supported by observation and by Inflation and Big Bang theories. These are the theories trying to explain how the universe was born.
  8. Sep 16, 2011 #7


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    It is not true that everything in Solar system is build of atoms, even if you restrict to a "matter" in common meaning of that word. Actually, vast majority of Solar system mass comes from an non-atomic matter. Solar core is built of plasma of protons, small nuclei and electrons.
    Actually no (large enough) astrophysical objects are build of atoms. Most stars are made of plasma, neutron stars are made of neutron matter.
  9. Sep 16, 2011 #8


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    Let us assume that the OP is also asking about subatomic particles as well, as they are what comprise atoms.

    TechEpicness, everywhere we look in the Universe and everywhere we have gone seem to work exactly the same. Stars far away from Earth have nearly identical measurable properties that our own Sun does and we can observe some of them here in a laboratory. One example is the emission spectrum from a star. These are dim lines that appear whenever we send the stars light through a prism like object and are the result of atoms or molecules existing in the stars outer layers and absorbing certain wavelengths of light. These lines directly correspond to identical lines we see when we send white light through ordinary gases in the lab.

    It is this and many other observations that tell us that the universe is made up of the same things that we are here on Earth.
  10. Sep 16, 2011 #9


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    Actually, this is wrong.

    Electrons are not made up of "atoms". Protons are not made up of atoms. Mesons are not made up of atoms. Light is not made up of atoms.

    I will rephrase your question in the hope that you might want to look up these things a little bit more as part of your education. What you probably meant to ask was "How do we know everything in the universe is made up of elementary particles within the Standard Model of particle physics?"

    Now that may be a bit more complicated for you to understand, but it is a good excuse to first of all figure out why your original question is different than my version, and why it makes a whole lot of difference.

  11. Sep 16, 2011 #10
    Sorry, that's what I meant.
  12. Sep 17, 2011 #11
    The present universe is made up of electrons, protons, neutrons, photons and neutrinos.
    The protons and neutrons form nuclei, free neutrons decay. Electrons and nuclei combine into atoms if their temperature is low enough.
  13. Sep 17, 2011 #12


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    True, but Neutrons and Protons themselves are composed of Quarks.
  14. Sep 17, 2011 #13
    The vast majority of the universe is currently thought to be made up of Dark Energy (Einstein showed us that matter and energy are tied together) & Dark Matter. The vast minority of the make-up is matter & antimatter. So it would seem the OP's question is built on false premises.
  15. Sep 17, 2011 #14


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    Perhaps, but as far as we know dark energy is exactly the same here as it is 13 billion light years from Earth. And I think we can give the OP a break, as dark energy is not matter and doesn't form objects.
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