The actual size of the universe

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Saint, Jul 26, 2023.

  1. gmilam Valued Senior Member

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    Or, more likely, it IS non-existent.
     
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  3. Saint Valued Senior Member

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    Do not limit your mind to what you can only see.
     
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  5. James R Just this guy, you know? Staff Member

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    So your claim is that somebody just made up a random number, then, is it? Interesting. Why that particular number, then?
     
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  7. James R Just this guy, you know? Staff Member

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    Back in the 1960s, the possibility that the universe is closed was more plausible than it is today. Closed means what you say: that if you jumped in your spaceship and travelled continuously in one direction, you'd eventually come back to where you started. The other possibility is an open universe, in which you could travel forever in one direction and never return.

    Theoretical cosmological models allow for closed universes and open universes and "flat" universes, with "flat" being a sort of borderline version between the two, although a flat universe looks more "open" than "closed".

    In the 1960s, it was thought that whether the universe was open or closed would be determined mainly by the average density of mass and energy in the universe. With enough mass, the universe would have to be closed; not enough mass and the universe is open. The mass density also determines the long-term fate of the universe. Closed universes are destined to slow their expansion over time, and then start collapsing again, eventually ending in a "big crunch". Open universes (and flat ones), on the other hand, expand forever.

    Observations of the mass density in our universe actually show that out universe is so close to being "flat" than we can't be sure if it is open or closed (or actually flat).

    However, recently a huge spanner has been thrown into the works. We discovered that our universe is not just expanding, but that the expansion is accelerating. In mass-only models of the universe, such behaviour is impossible. However, Einstein's equations from back in the 1910s allow for the possibility of a cosmological constant in the relevant gravitational equations. For most of the 20th century, it was thought that the cosmological constant of our universe was probably zero; this is what Einstein himself guessed. But a non-zero cosmological constant would produce the sort of accelerating expansion of the universe than we have observed.

    The question then becomes: what causes a non-zero cosmological constant? The current answer is: we don't know. The place-holder name that is given to the cause, these days, is "dark energy". To match observations, dark energy must make up about 75% of our universe, and we don't know what it is yet. However, there don't seem to be many other viable candidate theories that can explain the apparent accelerating expansion of our universe.

    There's work still to be done in cosmology, clearly.
     
  8. James R Just this guy, you know? Staff Member

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    Energy is really just a sort of accounting system used in science. Energy isn't a substance. Nothing is made of energy. Also, since energy is really just a number we can calculate for a given system, it doesn't have any properties other than the properties numbers have. In particular, it makes no sense to talk about the "frequency" of some energy. Waves of various kinds have frequencies, but energy is not a wave.
    Interesting. Why do you believe that? What evidence do you have that supports your belief?
    Are you talking about life after death? Or just "invisible" (undetectable) consciousnesses? If they are undetectable, why do you believe they exist?
    That's consistent with standard ideas in astronomy. After all, light has only had the opportunity to travel in the universe for 13 billion years or so, so we can't see anything further away than 13 billion light years.*

    ----
    * Actually, it's not quite that simple, because space itself has expanded since the big bang, but there's still a furthest distance we can receive any information from.
     
  9. exchemist Valued Senior Member

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    Aha, now I begin to understand your internet handle. I was wondering what "zero point native" could possibly refer to.

    A lot of your post isn't science but some kind of personal metaphysics. As James points out, this energy and "vibrations" stuff is risky and sounds like woo: you know, "it's all vibrations, man". There is a sense in which that is kind of true-ish, in that quantum mechanics, and in particular quantum field theory (QFT), deals with apparently wavelike behaviour of matter - and even of fields (in the physics sense). But I think it would be better to speak of "waves, man" rather than "vibrations, man" - and actually they are not really waves either, just wavelike in certain respects.

    If you are interested in the zero point energy of the vacuum and its relation to cosmology, there quite a nice article here on the subject, which dispels a few myths: https://www.scientificamerican.com/article/follow-up-what-is-the-zer/

    In this article, Baez sounds to me right in what he says. The materials scientist, burbling about a "seething cauldron of energy" is I think speaking ex ano.

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    (I should say here that I'm just a chemist with some knowledge of quantum chemistry. I am not a quantum physicist, and I have not studied QFT. So I just have to go on what I have read, with the advantage of understanding some of the QM concepts that are used.)
     
    Last edited: Aug 14, 2023
  10. Pinball1970 Registered Senior Member

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    I don’t. I limit my mind to that which can be tested experimentally.

    I cannot see gravity, quarks or EM fields but I know they are there.

    If one cannot do that, then we can just imagine anything we want and claim it is thing with zero evidence.


    I don’t think that gets us very far.
     
  11. Zero Point Native Registered Member

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    Ya caught me.

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    I based my handle on that point where energy is in its native state - unobserved and unadulterated pure native energy.
     
  12. exchemist Valued Senior Member

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    Haha. But do me a favour and never, please, talk of pure energy. That is Star Trek and not science.

    As James says, energy is not stuff: you can't have a bottle of energy. Energy is a calculated property of a physical system. It has no independent existence, any more than temperature has, or momentum.
     
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  13. ThazzarBaal Registered Senior Member

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    Yeah, I think a man or woman needs to have some spirit inside themselves for there to be life, whether physical aspects of life or spiritual. I get emotional ... Call me sensitive.
     

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