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B Are the Laws of Physics consistant and universal?

  1. Jan 1, 2018 #1
    Was just curious if there are any holes in the major laws of physics making them not consistent.
    Or could they change over time?
    And are they universal, as in, are they the same in all regions of the universe?
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  3. Jan 1, 2018 #2
    Cosmological theories generally make the assumption that the Universe is homogeneous and isotropic,
    (On the large scale it is the same everywhere in time and space, and the same laws of physics apply)
    This is called the cosmological principle.

    If we don't start with that assumption then all bets are off, anything could happen anywhere.
    Physics would be a pointless exercise if say tomorrow we could find that electricity no longer behaves the way it does today.
  4. Jan 1, 2018 #3


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    General Relativity seem to explain things like gravity, the motion of planets and the expansion of the universe and Quantum Mechanics explains the other forces and how atoms behave. The problem is the two theories are very different/incompatible. Lot of work is being done to try and make one new theory cover both realms - a so called theory of everything.
  5. Jan 1, 2018 #4


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  6. Jan 1, 2018 #5


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    There are some things that we call "laws" which can change in time. For example, Hubble's law which relates the speed of a galaxy with the distance, but we know this to be changing. We have more complete theories which include the time evolution of the universe (see FLRW universe) but these extrapolate from known data and could be wrong.
  7. Jan 1, 2018 #6


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    People would probably have said that about the same conditions producing the same results, but the probabilities at the quantum level have been absorbed and the physics continues.

    If we found the universe wasn't homogeneous, then we would have to develop the physics that modelled how it changed with time and/or location.

    But, in a way, it doesn't really matter how things actually work, the laws themselves would simply be the things that we can say and that are true. To take an example. If, say, the gravitational constant reduced with time. We wouldn't say that the law of gravitation is changing every day. We would have a time parameter in the law of gravitation.

    Or if EM changed, then the way it changed would be part of the law of EM.

    However the universe works, the laws are really just the things we can say about it. By definition, therefore, the laws themselves are bound to be universal. Even if they were a bit stranger than the ones we have.
  8. Jan 1, 2018 #7


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    Not as far as we know so far.
    It's possible, and if we were ever to find experimental evidence suggesting that it is in fact happening we would (as @PeroK suggested above) reformulate the laws to include the necessary time dependence. However, there's currently no evidence suggesting that such a thing might exist, and that includes looking in the places where you'd expect time dependence to show up. For example, if we observe a galaxy a billion light years away we're seeing how it looked one billion years ago, and everything we see is consistent with it following the same laws of physics back then that we have today. (There are old threads on this topic, if you can find them).
    Same answer: It's possible that they are not the same everywhere, but so far there is no reason to think so.

    If we do find observations that suggest such inconsistencies, we'd consider that to be evidence that we've gotten one or more of the laws wrong, and we'd go looking for a way of reformulating them to fix the problem. For example, in 1863 Maxwell discovered the laws of electricity and magnetism, and it soon became clear that at high speeds (in this context "high" means not small compared with the speed of light, so things like ICBMs and SR-71s are considered "slow", along with snails and continental drift) these laws were not consistent with Newtonian physics. This hole was the great unsolved problem of 19th-century physics, and many of the physicists of that era nibbled away at this problem until Einstein discovered the corrections to Newtonian/Galilean physics that filled that hole.
  9. Jan 2, 2018 #8

    Mister T

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    They all have limits of validity, none of them are universally valid.
  10. Jan 2, 2018 #9


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    @CWatters seems to have given the best explanation for your answer. We have two theories each observing the macroscopic and microscopic respectively, but can't work well together. Depending on your level of education, you might want to read a few books regarding finding a theory of everything. I would recommend following Brian Greene's work, if you are interested. His book, the elegant universe, is good read for someone curious in the holes in modern physics.
  11. Jan 2, 2018 #10


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    We can never be totally certain about this, of course but there is some comforting evidence to support the universality of things. We can see the spectra of light from very distant sources and they exhibits the same patterns (absorption spectra) as we can see from local atoms. Red shift just moves all the frequencies down by the same amount. That strongly implies that the same physics is going on within those distant atoms so basic Quantum Mechanics is almost certainly the same wherever we see it at work.
  12. Jan 2, 2018 #11
    It's Hubble's constant that changes, not Hubble's Law.

    We suspect that General Relativity is incomplete because it yields nonsense answers under certain extreme conditions.
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