Matter and anti matter

[devrimci_kürt]

Can antimatter be used to destroy matter ?

[insane_alien]

yes.

[devrimci_kürt]

well, but..

we learned, matter is neither created nor destroyed

[ajb]

well, but..

we learned, matter is neither created nor destroyed

 

As an axiom of classical mechanics.

 

Your question is a quantum one.

[insane_alien]

only in non-nuclear reactions.

 

the correct conservation number is energy cannot be created or destroyed.

 

if an electron annihilates with a positron(an anti-electron) then you get 2 512keV photons. the matter is destroyed but the energy remains.

[GDG]

well, but..

we learned, matter is neither created nor destroyed

 

It is: this is what makes the Sun shine. Hydrogen is fused to make helium, and a small amount of the mass is converted into energy. The total amount of mass and energy together is conserved.

[timo]

only in non-nuclear reactions.

Assuming you meant "matter is conserved only in non-nuclear reactions": The example you provided (electron + positron) is a non-nuclear reaction as there is no atom's nucleus involved. In the sense of my understanding of conservation of matter (see below) this would of course still be somewhat true as electron+positron does conserve the amount of matter . But then, I wouldn't know of any nuclear reaction violating it, either.

 

The correct conservation number is energy cannot be created or destroyed.

There is quite a few other conservation numbers existing, some depending on context some being conserved in all known processes. Conservation of fermion number seems to be the most appropriate to the question for me. Particle physicists usually call something matter when it contains fermions - to my surprise I've found the same definition of matter in Atkins: Physical Chemistry, btw. If in that spirit you'd take the fermion number as a measure for the amount of matter and anti-particles are given the negative fermion number of their respective particle partners (1), then

1) The total amount of matter is conserved in all known processes (2).

2) Matter can in principle be destroyed by anti-matter.

 

(*): This is according to the Standard Model of particle physics. As far as I understand neutrinos being their own anti-particles (Majorana spinors) is at least being considered. In that case, you could probably not give them a (non-zero) fermion number. I could imagine processes like tau -> tau-neutrino + quark + anti-quark being possible. This would then violate fermion number and hence conservation of matter in the sense I talked about.

(**): I am not familiar with qft bound states so strictly speaking I can only talk about processes involving free elementary particles.

 

Summary: I think a sensible definition of the amount of matter (if you wanted to count it) is the number of fermions. Since anti-particles are given negative fermion numbers and fermion number is conserved, I think that matter is indeed conserved, then. Alternative measures of the amount of matter already mentioned are the amount of energy which is also conserved, or the amount of mass (which can be a bit delicate) which might not be conserved (depending on how one exactly counts mass).

[Mr Skeptic]

Can antimatter be used to destroy matter ?

 

I would say convert to energy, though the particle anti-particle pair are indeed destroyed. However, the matter does not simply vanish; it is converted to energy. Also, the count of that particle type remains unchanged (the antiparticle counts for -1, the particle for +1).

[devrimci_kürt]

atheist

 

I didn't understand(what is the relationship between fermion and matter )

[timo]

atheist

 

I didn't understand(what is the relationship between fermion and matter )

What's the definition of matter? One relatively common definition is "stuff that contains fermions". So you could say that the number of fermions contained is the amount of matter.

Edited October 11, 2009 by timo

[Severian]

Conservation of fermion number seems to be the most appropriate to the question for me.

 

Conservation of fermion number is probably a bit besides the point though, since it is just conservation of angular momentum. A more appropriate conservation for this thread would be conservation of lepton and baryon number.

[Edtharan]

To put is in the simplest way. It is not that matter can't be created or destroyed, but that Matter/Energy can't be created or destroyed.

 

Just as you can turn one type of energy into another type of energy (chemical energy in the petrol/gas in your car into kinetic energy of the car moving), you can also turn energy into matter (in the form of an Electron/Positron pair) and back again (when they annihilate).

[timo]

Conservation of fermion number is probably a bit besides the point though, since it is just conservation of angular momentum. A more appropriate conservation for this thread would be conservation of lepton and baryon number.

Agreed.

 

As a general comment on other posts: Do not confuse "matter" with "mass". That's two different things.

Edited October 11, 2009 by timo

[GDG]

atheist

 

I didn't understand(what is the relationship between fermion and matter )

 

Fermions are particles that have a spin of N/2, where N is an odd number. Electrons, quarks, protons, and neutrons are all spin 1/2 fermions. In other words, all of the fundamental particles that make up matter are fermions.

 

The other category is "baryons", which are particles that have 0 spin or an integer spin N, where N is an integer. Photons are baryons.

[timo]

The other category is "baryons", which are particles that have 0 spin or an integer spin N, where N is an integer. Photons are baryons.

Bosons, not Baryons. Baryons, which Severian mentioned above, are something different: The baryon number is basically the count of quarks in a given substance (divided by three). The lepton number is the number of leptons (usually electrons) in a given substance.

[ajb]

Would a better definition of matter be that it transforms under the fundamental representation of the gauge group and forces transform under the adjoint representation? Is that sufficient? Where would this place a Higgs boson? (remind me of the representation, been a while since I have studied "real particle physics".)

 

I am just thinking about how SUSY mixes the idea of matter and forces.

[Severian]

Would a better definition of matter be that it transforms under the fundamental representation of the gauge group and forces transform under the adjoint representation? Is that sufficient? Where would this place a Higgs boson? (remind me of the representation, been a while since I have studied "real particle physics".)

 

That would make the Higgs matter then, since the doublet is a fundamental representation of SU(2).

 

I am just thinking about how SUSY mixes the idea of matter and forces.

 

Yes, and for this reason I don't like the distinction.

 

Also, it has always bemused me a little that we say that the Standard Model includes 3 forces (QCD, weak and electromagnetism), and we never consider the Yukawa interactions as a force (ie. exchanging Higgs bosons). Although it has a very different origin, it is an interaction of fermions with bosons which allows you to exchange said bosons, resulting in a change of momentum for the fermions. Isn't that a force, by any definition?

[ajb]

Thanks for the reply.

 

I appreciate your last statement. The only thing that jumps to my mind is the representations.

 

Is it somehow not considered "fundamental"?

[GDG]

Bosons, not Baryons. Baryons, which Severian mentioned above, are something different: The baryon number is basically the count of quarks in a given substance (divided by three). The lepton number is the number of leptons (usually electrons) in a given substance.

 

Duh, from Bose-Einstein statistics.

[walsh155]

if antimatter touches a form of any matter it will be the most massive explosion ever the mas production of antimatter is 2.5 million dollars per gram that is the most expensive thing in the world.

[insane_alien]

probably closer to 2.5 trillion US dollars per gram.

 

and the explosion is not necessarily massive. 1kg of antimatter reacting with 1kg of matter would produce an explosion 43MT in yeild. the most power man made bomb that has been detonated was 50MT(scaled back from a potential 100MT)

 

as it stands antimatter contacts matter everyday. it is the basis for a PET scan which means they actually purposely do this within your body for diagnostic reasons.

 

as we do not here of hospitals erupting in a nuclear fireball daily i thin it is same to assume that no, it will not produce the biggest explosion ever.

[kanyalsingh]

I think a sensible definition of the amount of matter (if you wanted to count it) is the number of fermions. Since anti-particles are given negative fermion numbers and fermion number is conserved, I think that matter is indeed conserved, then. Alternative measures of the amount of matter already mentioned are the amount of energy which is also conserved, or the amount of mass

Edited November 4, 2009 by swansont
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[Severian]

Fermion number conservation is just angular momentum conservation though, so it is not a terribly useful additional quantum number. Lepton and baryon number are better. Also, mass is not conserved.