How can something be created from nothing?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Cragzop, Oct 3, 2016.

  1. exchemist Valued Senior Member

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    Yes. It seems to me the honest answer to these questions is that we do not know. Science can only lead us as far as our powers of observation justify. Our observations justify our theory of the Big Bang but tell us noting about what led to it. Indeed, as I understand it, spacetime had no extent before the Big Bang so asking what was "before" it risks assuming that time and space existed before it, when they may not have.

    Local entropy decreases occur all the time during physical and chemical change (e.g. formation of a crystal from a liquid). What one never sees in any spontaneous change is an overall decrease in entropy, i.e. when the entropy change in the environment is also taken into account.
     
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  3. James R Just this guy, you know? Staff Member

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    Yazata:

    Of course we can't know if any laws of physics hold universally. But we do know that we haven't observed any distant (or close!) regions of the universe that show any evidence of having different physical laws.

    There are only 4 so-called Laws of Thermodynamics, numbered zero to three.

    The Zeroth law is a postulate that says that if object A is at the same temperature as object B, and A is at the same temperature as C, then B is at the same temperature as C. Sounds obvious, doesn't it? But it's an unprovable assumption.

    The First Law in the law of conservation of energy. This is an empirical law, based on the observation that no isolated, closed physical system has ever been observed that breaks the "law". Since the universe as a whole is an isolated, closed system, the first law is assumed to hold in the universe as a whole. Of course, the First Law rests on our definition of energy, which in turn is derived from mechanics.

    The Second Law is the complicated one about entropy. Roughly speaking, entropy is a measure of the amount of disorder in a given physical system, and the Second Law says that, on average, this tends to increase over time. The Second Law can actually be proved using arguments from statistical mechanics. Statistical mechanics itself rests, of course, on basic mechanics, which comes down to how particles and fields and things behave.

    The Third Law merely asserts that there is a lowest possible temperature, which we call "absolute zero". This one, too, is susceptible to rigorous proof.

    The Laws of Thermodynamics are not so much simplifying assumptions as they are general principles that summarise important aspects of our understanding of the physical world. Like all laws in science, they are ultimately only justifiable because they correspond with what we observe in the world/universe.

    There are various "multiverse" ideas in which universes like ours (and unlikely ours, perhaps) spawn in various ways, but end up causally disconnected from any other universes. In such theories, our universe did not come from "nothing". Of course, we then get back to the metaphysical question of why a multiverse exists instead of nothing.

    I don't think so. I think he's just making the point that there needn't have been any "stuff" "before" in order to make the universe that we see, where "stuff" means matter and/or energy.

    Again, we can push the explanation back a level. Multiverse ideas suggest, for example, that different universes pop in and out of existence with different sets of physical laws (or at least different sets of fundamental physical constants). However, there would still need to be a separate set of laws that govern the multiverse, so we don't in that sense have creation of universes from "nothing".

    From memory, he doesn't really look at the most complete philosophical version of the first cause argument. Necessarily that is very tricky to discuss, because it must be done so in the context of a multiverse in which concepts such as time do not really apply. Therefore, discussing ideas of "causation" at all requires a lot of intellectual gymnastics.

    The important take-away message from modern science is that science shows no necessity for a God to create things like light and matter and life, as described in various religious texts such as the bible and the Qur'an. This still leaves the metaphysical "something from nothing" argument unresolved, as it probably always will be.
     
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  5. James R Just this guy, you know? Staff Member

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    Fraggle Rocker:

    We've been through this before but...

    If you take a closed, isolated system, A, and regard it instead as two connected systems B and C, then the entropy of B at any time can decrease at the expense of the entropy of C, but the combined entropy of A(=B+C) will tend to increase. This is not exactly a "reversal" of entropy.

    With the big bang, we have the universe in an initial state of low entropy, which then increases as the universe expands.

    If you want to posit a "reversal" of entropy, you really need to specify some system A that consists of the universe (B) and something else that the universe can "exchange" entropy with (C). The problem is, there doesn't seem to be a C (unless you can suggest one).

    Without a C, the entropy of the universe as a whole cannot decrease, so there seems to be no way to produce a big bang from an already-existing universe.*

    Here you are saying, essentially, that we have system A = bear (B) plus mouse (C). Bear's entropy can decrease at the expense of mouse's entropy.

    Including the environment (the forest, the air, the water etc.) as part of "the system" along with the bear and the mouse is more realistic, and actually necessary if we want to look at the second law properly, because we require a closed, isolated system to talk about entropy. If we do that, we of course find that the entropy of the entire system increases appreciably when the bear eats the mouse (or, in fact, when the bear or the mouse do anything at all).

    ----
    * If you have read Hawking's A brief history of time, you'll know that there are various arguments about thermodynamic arrows of time and big crunches and other stuff, which rather complicate matters.
     
    Last edited: Jan 4, 2017
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  7. river Valued Senior Member

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    Interesting

    I have the book , I'll look it up .
     
  8. exchemist Valued Senior Member

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    James, I thought that the conservation of energy was nowadays considered to be founded on Noether's Theorem, not just on empirical evidence. Have I misunderstood?
     
  9. James R Just this guy, you know? Staff Member

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    Most people give up at some point when they read that book - often at the point where Hawking starts talking about imaginary time and other similar stuff.
     
  10. James R Just this guy, you know? Staff Member

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    No, you're right. Thanks for reminding me.

    For the benefit of others who may not be familiar with it: Noether's theorem says that for every symmetry in physics there is a corresponding conserved quantity. It turns out that energy conservation follows from the time-symmetric nature of the laws of physics.
     
  11. Q-reeus Valued Senior Member

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    Not correct. It's supposedly a consequence of the time invariant nature of physical laws (which is broken in most gravity theories). Time symmetry is evidently broken in certain electro-weak processes - but it does not imply violation of conservation of energy: https://www.slac.stanford.edu/pubs/slacpubs/13500/slac-pub-13518.pdf
    See Conclusion for a synopsis.
     
  12. James R Just this guy, you know? Staff Member

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    Yes. Thanks for the correction.
    That's two mistakes from me in the same thread, in quick succession.
     
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  13. SimonsCat Registered Member

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    The conservation principle doesn't actually hold for a universe: The problem is that general relativity cannot actually conserve energy because it lacks a clear definition of time. Moreover, general relativity doesn't even need time to generate a time evolution, for its evolution naturally arises from diffeomorphism invariance.
     
  14. Q-reeus Valued Senior Member

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    Is this some kind of appeal to 'Block Universe' notion?
     
  15. SimonsCat Registered Member

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    Block universe? Is this the concept that reality is one single entity and time is an illusion?

    Maybe related but certainly not an appeal to it.
     

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