5 ms·

Well for one, if the laws of physics are not time invariant (i.e. the laws of physics are not the same at all points in time) then energy can be created or dest

• itishappy 3y ago
  Doesn't dark energy do exactly that? 70% of the energy of the universe doesn't seem to want to play by our rules!
  • digging 3y ago
    Yes, but my understanding is that dark energy doesn't play by the same rules, it's an exception. I certainly can't explain why but also it may not be known exactly why, given dark energy is an unexplained phenomenon.
    • cygx 3y ago
      The party line is that energy is not conserved at cosmological scales. However, it's more of a semantic question: We can tell you exactly by how much it gets violated (that's basically the first Friedmann equation), and if you prefer, you can attribute the missing energy to the gravitational field. A lot of physicists don't like that approach as it isn't possible to write down a corresponding stress-energy tensor, ie gravitational energy cannot be properly localized.
• explaininjs 3y ago
  Do you think the current amount of energy in the universe is 0? If not, how was it created?
  • baq 3y ago
    That's a completely different question, to which the answer is 'we don't know'.
    • explaininjs 3y ago
      It's really not. If there is nonzero energy, and our current models don't allow for energy to be created, either we need new models that do allow for energy to be created (time-variant physics, for instance), or we need the existing models to propose a way it was initialized. Without that there's a gaping hole in the model the size of all of the energy in the universe. Certainly you can't 1) have a model where energy is constant 2) believe there is nonzero energy in the universe and 3) dismiss any model where energy can change as bogus out of hand because you believe it should be constant, without counter-proposing how it even got here.
      • mrguyorama 3y ago
        >or we need the existing models to propose a way it was initialized. We have that, it's the big bang.
        • explaininjs 3y ago
          How remarkably unsatisfactory. The argument being: You can't propose physics ever changed, that'd mean energy could have been created at some point! Energy was created at some point, wouldn't it be nice to know when? Everything created at the Big Bang exactly as it is now, stop asking questions.
          • baq 3y ago
            Nobody argues it wouldn't be nice. Physics argues we can't ever know. It's a rather significant difference and if this gets proven wrong, you'll find that physicists are the ones partying the hardest.
          • orra 3y ago
            You're asking to go too far back in time. The difficulty is we don't know what happened in the first planck second after the big bang, let alone before the big bang (if that's meaningful). We haven't unified quantum mechanics and relativity. Hence we can't be certain that singularities exist, or that the universe started off in a singularity.
• hnfong 3y ago
  Saying "X is true because otherwise, it would be quite a shocker" isn't really a proof. It's almost an appeal to common sense. (which, admittedly, is often the best argument we have). IMHO there's often a bit of over-confidence among scientists about the universe being 13 billion years old and what happened during the Big Bang, if it just relies on such a common sense argument. I know it's unscientific to suggest maybe laws of physics are not time invariant across such scales, because until we have a time machine we can't test this theory, but then flipping the argument (that laws of physics are definitely time invariant) is also technically unscientific -- we're basically assuming this without strong evidence. This goes back to the old debate on the problem of induction in science, (see David Hume, Karl Popper, etc.) and I think it isn't emphasized enough in modern discussions that, perhaps, there's a small chance that these foundational concepts in physics could be invalid.
  • Veserv 3y ago
    I did not present proof. They asked what it would mean and a consequence of physical laws not being time invariant would be that energy does not need to be conserved. To the extent that relates to epistemology that would be more like anti-proof I guess? It does not prove that the laws are time invariant, rather it raises the bar to demonstrate that the laws are not time invariant because that means energy need not be conserved. You can not get one without the other without attacking even deeper fundamentals of modern scientific models. So you must either demonstrate the linked claims, which are pretty foundational themselves, or you must overturn basically everything; both of which demand very robust evidence.