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I have read an answer on this site regarding the change of laws over time . However a physisct told me that the laws did evolve at planck era and then stopped evolving after it , is that true even in case of a TOE ( namingly as the best candidate string theory )

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could you link to the specific answer you reference? –  Jim Jun 17 '13 at 13:07
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physics.stackexchange.com/q/10078 –  Jasmine Jun 17 '13 at 13:12
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The point of Ted Bunn's answer to the question you link is that when physicists call something a law, e.g. Newton's laws or the Coulomb law, we mean that it is an approximate law. For example Newton's laws are a low speed, low density approximation, and in situations where speeds and densities are high we have to use an improved description i.e. general relativity.

If you wind time backwards the universe gets denser and hotter (hotter basically means things move faster) so laws that are low speed and low density approximations will not apply. However this does not mean that the laws of physics have changed. It just means that some low energy approximations are not valid. We expect that there is some (probably very complicated) law that applies right back to the Big Bang, and this law of physics does not change with time, not even at the Planck era.

However, we have little idea what this ultimate law looks like, so neither we nor the physicist you were talking to can do more than guess at what happens.

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So if i understood you correctly , you mean that the ultimate laws of physics ( TOE )or the most fundamental will be laws applied since t=0 (i.e start of the bigbang ) and these laws would be the same or immutable since then (i.e at planck area after few seconds of bigbang and now ) –  Jasmine Jun 17 '13 at 19:21
    
Yes. The laws we know about are approximations. –  John Rennie Jun 17 '13 at 19:24
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