Matter & Antimatter

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cadbrowser
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Matter & Antimatter

Post by cadbrowser »

Exerpt from a book I was reading last night (I'll post the name of the book tomorrow):
When matter and antimater come together they annihilate each other in the form of pure energy.
I'm confused. Isn't any form of energy essentially composed of fundamental particles?

Please don't beat me over the head too hard...just for some reason my brain locked up when I read that passage.

:banghead:

I understand that the antimatter and matter particle are annihilated...I am just confused by what the author means as "pure energy".
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Eternal_Freedom
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Re: Matter & Antimatter

Post by Eternal_Freedom »

As I understand it, they mean "pure energy" in the sense that ALL of the energy is thrown out in the form of gamma/x rays and other forms of light, unlike, say, nuclear reactions where a good chunk of the energy is lost propelling subatomic fragments away from each other.

In other words, pure energy = just EM stuff, no particles.
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Re: Matter & Antimatter

Post by Shadow6 »

Not necessarily. For instance, baryon-antibaryon (particles comprised of three quarks) annihilation produces mesons (quark/antiquark pairs) which eventually decay to give a net product of photons, electrons, positrons and neutrinos.
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Re: Matter & Antimatter

Post by MrDakka »

This is all assuming that each particle will meet its antimatter counterpart. However in all likelihood, not all of the matter will annihilate with the antimatter due to the blast wave generated. I always though this was rather a large problem for antimatter warheads.

Doubtless someone will engineer a clever way to reduce this or perhaps eliminate the problem altogether.
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Re: Matter & Antimatter

Post by cadbrowser »

Ahhhh, OK...that is what I was thinking, but wanted to make sure that I was comprehending it. Oh the book is named "The Elegant Universe" by Brian Green.

Thanks so much!
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Re: Matter & Antimatter

Post by someone_else »

yeah, antimatter is much more useful to rad-kill stuff than to blow it up or produce energy/thrust.
In a proton-antiproton annihilation you get something like 1/3 of the output in fucking high energy gamma rays.

The detail that at least 1/3 of that goes away as neutrinos (not "pure energy" at all, the kind of particle less likely to interact even if it flies through light years of lead) and that most other stuff decays into neutrinos shortly thereafter leaves you with a power-conversion efficiency that sucks balls.

a paper that goes more in depth, Comparison of fusion antiproton propulsion systems for interplanetary travel
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cadbrowser
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Re: Matter & Antimatter

Post by cadbrowser »

Thanks someone_else, looking at the paper now.

Edit: Ok...no I'm not. That site is ALSO blocked by my employer. UGH!
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Re: Matter & Antimatter

Post by HMS Conqueror »

Strictly it's a nonsense statement; photons aren't "purer energy" than massive particles. However that is not how people without much physics education perceive it.

It just means that the mass-energy of the particles is converted to gamma rays.
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Re: Matter & Antimatter

Post by Simon_Jester »

cadbrowser wrote:Exerpt from a book I was reading last night (I'll post the name of the book tomorrow):
When matter and antimater come together they annihilate each other in the form of pure energy.
I'm confused. Isn't any form of energy essentially composed of fundamental particles?

Please don't beat me over the head too hard...just for some reason my brain locked up when I read that passage.

:banghead:

I understand that the antimatter and matter particle are annihilated...I am just confused by what the author means as "pure energy".
It's a common rhetorical term for an interaction that leaves behind only light, basically.
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Re: Matter & Antimatter

Post by MrDakka »

someone_else wrote: a paper that goes more in depth, Comparison of fusion antiproton propulsion systems for interplanetary travel
Antimatter beam core rocket FTW
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