E=mc^2 / Antimatter querry

[Feil]

Perhaps a month ago, I was engaged in a brief debate with someone over the potential yield of matter-antimatter annihilation in comparison to nuclear weapons.

Citing a degree in a related field (one which I find rather suspect), he claimed that "most of the calculations of the destructive/potential energy power of anti-matter were refined in the last few years. IDK what other schools are using, the old wave or new wave calculations, but MIT has instructed me using the new calculations. Since anti-matter isn't energy or matter, the old e=mc^2 calculation isn't very accurate."

This was in response to my attack on his claim that "Anti-matter the size of a dime would create a new Gulf of Mexico."

(Whereas, if e=mc^2 applies, it [approximately 2 grams of antimatter] might create a small pond and a whole lot of heat, but nothing terribly exciting.)

After restating my position and addressing some of the other bits of what seemed very like idiocy (for instance his apparent lack of understanding that for any forseeable estimate of space-space weaponry, you don't have a chance in hell of actually bringing a warhead in direct physical contact with the target) I requested/demanded that he support his claims, whereupon he conceeded, saying that

"I don't want to argue with you. The calculations I'd have to show are not the kind of thing I enjoy discussing in my freetime. However, I find your insistance that an "understanding of physics and sci-fi" [he's misquoting me slightly here, but no matter] is enough to debate this highly amusing. Before I entered into my specialty in weapons I would've agreed with you on all your points. However, now I know. If you are this interested in it, I suggest you pursue a degree in a related field."

It sure looks like classic backpedalling bullshit to me. Anyhow, I accepted his concession and that was that.

However, recent readings have brought antimatter back into my mind, so I'm asking here:
does E=mc^2 accurately describe matter-antimatter annihilation; and if not, why; and what does?

[kheegster]

Well, the energy released would be E = 2mc^2 since you'd have to consider the rest masses of the matter and anti-matter being annihilated, but you've grasped the point that E = mc^2 is still a valid description of the energy released.

His claims to have a degree in a related field sounds like bullshit. I am in a place where there are professors with really far-out ideas, and I've never heard of any such thing.

[Admiral Valdemar]

Yes, it describes the energy you'd get from a unit of matter being turned into pure energy, but for M/AM reactions, remember they are never 100% efficient. You will get some of that AM and some of that M flying off as the initial batch mass detonates, plus remember, you need half the mass of the bomb to be normal matter else you get no bang.

[Darth Wong]

Notice how he doesn't actually describe these "new wave calculations", nor does he explain what principles he's talking about, nor does he produce the calculations. Smells like bullshit to me.

Nothing but vague appeals to his claims of being an MIT student. Hell, he could be taking "political science" at MIT for all you know, if he's attending that school at all. Remember Revprez?

[Admiral Valdemar]

RevPrez said science was "bullshit" anyway, so he'd not even bother trying to explain anything. For you see, science hates him.

[Gil Hamilton]

Is he doubting that E = mc² or that it applies to antimatter?

[Ender]

e=mc^2 isn't really accurate for AM reactions. It does equate the total mass-energy released, yes, but the amount of usable energy is much lower. Admiral Valdemar is corrrect about reaction efficiency, but there is also the products to consider. For example, only 30% of proton/antiproton annihilation is in the form of gamma rays, the rest is released in the form of charged pions, which rapidly decay into neutrinos.

Said gamma rays are extremely high energy, and thus will be extremely penetrative and go a considerable distance before dumping all their energy into a local moderator (eg air or water). Pions could interact with the moderator to dump some of their energy, but the first ones doing that and the gamma rays would cause thermal bloom which would reduce the subsequent energy absorbtion prior to decay.

[Mad]

Since anti-matter isn't energy or matter

That's a blatant lie, antimatter is most definitely matter, and so E=mc^2 applies (as mentioned, there's a few things to factor in, but this stuff isn't going to cause the number to go up as he's claiming).

[Darth Wong]

I didn't even read his bullshit carefully, so I didn't notice (until Mad pointed it out) that he was claiming M/AM makes more than mc^2, not less. Having taken note of that fact, it's pretty obvious that he's nothing more than a liar, an idiot, and an asshole. He's not even anywhere near as smart as your average dipshit science poser.

[Ryushikaze]

Why do people so often overplay Antimatter? Recently someone on another board claimed you could blast the atmosphere off a planet with a softball's mass of antimatter. No math, no sources, nada.

[Feil]

Righto. I assumed as much when he refused to provide evidence for his claims, but it's nice to have a nice pile of masters-degree holders too vindicate my position .

Of course, as Admiral Valdimir and Ender pointed out, M/AM annihilation is far from 100% efficient in converting rest mass to heat, but that is neither here nor there.

I'm suspecting he drew his conclusions either from his posterior region or from the theory that matter/antimatter annihilation might be able to replace fission as the trigger for fusion reactions in thermonuclear weapons.

Anyhow, thanks.

[GrandMasterTerwynn]

e=mc^2 isn't really accurate for AM reactions. It does equate the total mass-energy released, yes, but the amount of usable energy is much lower. Admiral Valdemar is corrrect about reaction efficiency, but there is also the products to consider. For example, only 30% of proton/antiproton annihilation is in the form of gamma rays, the rest is released in the form of charged pions, which rapidly decay into neutrinos.

Said gamma rays are extremely high energy, and thus will be extremely penetrative and go a considerable distance before dumping all their energy into a local moderator (eg air or water). Pions could interact with the moderator to dump some of their energy, but the first ones doing that and the gamma rays would cause thermal bloom which would reduce the subsequent energy absorbtion prior to decay.

Yes, a proton-antiproton collision generates three flavors of pi-mesons (pions); positive, negative, and neutral. A third of them, as you said, are neutral pi-mesons, which immediately decay into high-energy gamma rays.

Second on the list are positively-charged pi-mesons, which immediately decay into mu-mesons (muons,) and neutrinos. The neutrinos sail off uselessly into the void, while the positively charged muons linger for a few microseconds before further decaying into positrons and yet more neutrinos.

The final flavor are the negatively-chaged pi-mesons, which decay into still more neutrinos and negatively charged mesons. These mesons last yet another few microseconds before they decay into electrons and still more neutrinos.

Then, provided you've done a good job of confining the intermediate charged reaction products . . . the positrons and electrons then interact to form high-energy gamma rays.

So, for an antimatter bomb, you get somewhere between 30% and 50% of your energy in terms of useful high-energy gamma rays, the rest being carried off in neutrinos and positrons and electrons flying off too fast to contribute meaningfully to the energy output.

[OmegaGuy]

Why do people so often overplay Antimatter? Recently someone on another board claimed you could blast the atmosphere off a planet with a softball's mass of antimatter. No math, no sources, nada.

I bet I know his source.

http://memory-alpha.org/en/wiki/Obsession

[Ryushikaze]

Given the boy's track record in all things scientific, It would not surprise me in the slightest. Of course, he also thought you could pull a BDZ-type event with the world's current complement of nukes, at least "the real high end fusion stuff".

[OmegaGuy]

Well that last one is somewhat excusable, due to all the propaganda and widespread exaggeration of the capabilities of nuclear warheads.

[Patrick Degan]

Why do people so often overplay Antimatter? Recently someone on another board claimed you could blast the atmosphere off a planet with a softball's mass of antimatter. No math, no sources, nada.

That's what happens when you take Star Trek seriously as a source of scientific education.

That one about a planet's atmosphere being blasted off with a small handful of antimatter comes right from the TOS episode "Obsession".

[drachefly]

So, for an antimatter bomb, you get somewhere between 30% and 50% of your energy in terms of useful high-energy gamma rays, the rest being carried off in neutrinos and positrons and electrons flying off too fast to contribute meaningfully to the energy output.

Seems to me that the electrons and positrons would be able to contribute substantially, so long as your target is more than a few meters across.

Sure, you're losing some to the rest mass of the electrons so created; but that's not going to be much.

Neutrinos, yeah, they're a drain.

[GrandMasterTerwynn]

So, for an antimatter bomb, you get somewhere between 30% and 50% of your energy in terms of useful high-energy gamma rays, the rest being carried off in neutrinos and positrons and electrons flying off too fast to contribute meaningfully to the energy output.

Seems to me that the electrons and positrons would be able to contribute substantially, so long as your target is more than a few meters across.

Sure, you're losing some to the rest mass of the electrons so created; but that's not going to be much.

Neutrinos, yeah, they're a drain.

Well, the charged muons which decay into electrons and positrons tend to have a mean free path which can apparently measure several kilometers in length. To keep them within your target requires a fairly strong method of confinement. Something that you can get on an antimatter rocket or antimatter power generator, but not an antimatter bomb.