SWaB: Ask Ethan: Why does nature obey laws at all?

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notFritzArgelander
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SWaB: Ask Ethan: Why does nature obey laws at all?

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Post by notFritzArgelander »


https://bigthink.com/starts-with-a-bang ... paign=swab

The question "Why does nature obey laws at all?" is fine bait for a category error, which Ethan skillfully sidesteps by examining how a lawless universe is contradicted by what we observe. However he trips up at this point:

It happens in the discussion of Noether's Theorem.
You might think that there are deeper reasons why such variations in the laws of physics, either through space or over time, are ruled out. After all, we have some fundamental symmetries and conservation laws in the Universe, and the existence of one arises as a consequence of the other: that’s what Noether’s theorem proved more than 100 years ago.

But that’s only an “if-then” sort of theorem. You no longer need to conserve (or keep constant) the quantities and entities that your perfect symmetries imply if you’re willing to violate the underlying symmetry. Even a slight, tiny violation can give you the wiggle-room you need to defy these conserved quantities.

You can violate spatial translation invariance (i.e., you can have things be different from place-to-place), and then momentum is no longer necessarily conserved.
You can violate rotational invariance (things can be different in different directions), and then angular momentum is no longer conserved.
You can violate time translation invariance (things can be different from moment-to-moment), and then energy is no longer conserved.

Although all of these conservation laws appear to be good for any particle properties we’ve been able to measure in the lab, we’re certain that the last one is not obeyed on a cosmic scale. In the expanding Universe, because cosmic distances vary from moment-to-moment between gravitationally unbound objects, even something as fundamental as energy is not strictly conserved.
No, the expanding universe does not violate conservation of energy. The universe can expand (or contract!) as a consequence of the laws of physics being time invariant. This is becoming a tediously common error in cosmological circles recently. It is linked to the old misunderstandings how to express energy conservation in GR via the Landau-Lifschitz stress energy pseudo tensor.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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