Is It true that matter cannot be created or destroyed?

  • #26
Drakkith
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lets try another angle

So the only way to really "destroy" or "convert" ordinary matter is to pair it with the same amount of antimatter so that their "matterness" cancels out—but in practice there is almost no antimatter generally available in the universe (see baryon asymmetry and leptogenesis) with which to do so

As I explained a few posts back, the annihilation of heavy particles like protons creates a number of different particles, not just photons (what most people think of as 'pure energy'). But this process is not unique to matter-antimatter annihilations. Proton-proton collisions in the LHC result in the destruction of protons and the creation of large numbers of other particles too, as does any high-energy collision.
 
  • #27
Dale
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but in practice there is almost no antimatter generally available in the universe
So what? That doesn’t change the fact that matter can indeed be destroyed.
 
  • #28
PeterDonis
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Whether matter can be destroyed depends on what you mean by "matter" and what you mean by "destroyed". This whole thread looks to me like people talking past each other because they're using those words with different meanings.

If a proton and an antiproton collide in the LHC and turn into gamma rays (and other stuff that's not protons or antiprotons), has "matter" been "destroyed"? Energy is conserved; so are electric charge, baryon number, lepton number, etc. What exactly got "destroyed"?

More importantly, who cares? What matters is what specific interactions took place and how the experimental data about those interactions matches the theoretical predictions that are being tested.
 
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  • #29
PeterDonis
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In 2004 Hawking himself conceded a bet he had made, agreeing that black hole evaporation does in fact preserve information.

His bet was theoretical, not experimental. Nobody has any experimental data on black hole evaporation.

In any case, @jbriggs444 is correct that this is a very different scenario from particle collisions in the LHC; there is no useful comparison between them. So talking about BHs is really off topic for this thread.
 
  • #30
Dale
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Whether matter can be destroyed depends on what you mean by "matter" and what you mean by "destroyed".
By “matter” I mean the fermions of the Standard Model and by destroyed I mean that the Feynman diagrams for the interaction has the fermion entering but not leaving.
 
  • #31
PeterDonis
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By “matter” I mean the fermions of the Standard Model and by destroyed I mean that the Feynman diagrams for the interaction has the fermion entering but not leaving.

This is a good precise definition, yes.
 
  • #33
Vanadium 50
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By “matter” I mean the fermions of the Standard Model and by destroyed I mean that the Feynman diagrams for the interaction has the fermion entering but not leaving.

A fine definition. But note that conservation of angular momentum prevents the sort of processes you are describing.
 
  • #34
PeterDonis
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conservation of angular momentum prevents the sort of processes you are describing.

?? A QED diagram with two entering fermion lines (electron and positron) and two exiting photon lines is perfectly consistent; it just has to have two vertices (at lowest order).
 
  • #35
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You're right. I was thinking about something else entirely: N fermions in, N-1 fermions out.
 
  • #36
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Whether matter can be destroyed depends on what you mean by "matter" and what you mean by "destroyed".

Agreed. They are almost weasel words when exact context is not nailed down.
 
  • #37
PeterDonis
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They are almost weasel words when exact context is not nailed down

I think "weasel words" is a bit strong; the terms do have well-established meanings. They just don't have unique well-established meanings. But I agree that nailing down exact context is a good thing.
 

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