# Simple E=mc^2 question

So, I know that E=mc^2. I’m happy with that in a I-hope-they-don’t-ask-me-about-it sort of way.

What about antimatter though? Does E=antimatter*c^2?

I’m trying to understand the period immediately after the big bang. Specifically, if the energy release from a matter/antimatter explosion would be just as likely to later form matter as antimatter (assuming that that’s what happens).

Antimatter has opposite charge but positive mass. No need to muck about with the equation.

Yes, E=mc[sup]2[/sup] applies equally to matter and antimatter. In fact, when matter and antimatter annihilate each other, the energy produced is exactly as you would expect: The mass of the matter and antimatter times the speed of light squared.

The m stands for mass, not matter.

Thanks guys. It the negative charge (as opposed to negative mass) part that I was missing. All makes sense now.

Except, I just started thinking about electrons. Is that antimatter charge the same type of negative as the charge on an electron, or are they different?

If not, why does antimatter and matter go boom whereas protons and electrons don’t?

Not negative charge, opposite charge. An anti-matter electron (positron) is similar to an electron but positively charged.

The antimatter equivalent of the electron is called a positron. It has the same mass, but opposite charge. In both cases, the electic charge is carried by photons.

All particles have anti particles that have an opposite electrical charge. So you could have anti-hydrogen made up of a negative proton and positive electron. In fact , I believe that anti-hydrogen has been produced in small quantities.

Post Big Bang you had particles smashing about, the kinetic energy of the respective particles was too great to allow proton/electron producing hydrogen. Now if a proton and its antimatter mate approached each other they would be attracted to each other through their differing electrical charges. Then they would smash into each other annihilating themselves.

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Now why do you get a complete anihiliation? When electrons get captured by protons you get a neutron and neutrino right? When protons merge you get a neutron, proton, electron and a neutrino.

What is it about particle/anti-particle collisions that results in a complete conversion to energy?
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I’m not sure how it would work with an electron-positron pair, but in many solids you can have bound electron-hole pairs (called excitons). If you imagine the charge-carrying electrons in a solid (e.g. a metal) as a fluid sloshing around in the material, a hole is like a bubble in that fluid. It can be modelled as an electron with a positive charge. The electron and hole attract each other and remain bound for short while.

So, I expect an electron and positron could be bound together for a finite time interval (before annihilating each other). Actually, in a strong magnetic the pair might last a while if their spin states were properly prepared.

Hmm, this post is probably too technical for most readers, and the physics is probably too simplified for those who know better. Oh, well.

But in that case the hole is an absence of electrical charge in a sea of negativity. In the electron/positron question both physically exist.

I would expect you could bind an electron around a positron “nucleus”, but I’m not sure that explains why the meeting of the two results in annihilation by default.

Like that’s ever stopped us before.

Ooops! I’m continuing to hijack the OP. Sorry Bromley. I’ll maybe open my own OP if I can get around to it later.

10 years ago no anti-hydrogen had been produced. Since the electrical forces are a couple orders of magnitude stronger than gravitational forces, scientists back then were eager to create anti-hydrogen to show with an experiment that anti-matter behaves the same way as matter in the gravitational field (I personally thought / think otherwise for a few reasons, but that’s too long a story).

I haven’t followed the development though, so if you should happen to have a link or recall where you have heard that anti-hydrogen has been successfully produced, I’d be interested in reading up on that.

Here’s a Nature article on 50,000 atoms worth of the stuff whipped up at CERN.

According to this page, antiprotons were first produced at Fermilab in 1985. An antiproton is an antihydrogen nucleus.

An electron and a positron orbiting each other form an unstable atom called positronium.

Of course. But an “antihydrogen nucleus” still has got a charge of -e, so you cannot really observe the effect of the gravitational field. In order to do so, you need antihydrogen atoms, meaning you need to have an antiproton “orbited” by a positron, making the whole thing neutral in charge. That was what I was looking for and in 1994 the magazines I read at school mentioned that they didn’t manage to create anti hydrogen back then. Again, I’m not talking about anti-protons or about positrons. I’ll check out Grey’s link though: It’s definitely possible that they managed to do so in the meantime, so that’d be interesting.

Congratulations, you’ve just stumbled upon one of the great unsolved problems in physics: the seeming matter-antimatter asymmetry in the Universe. A simplistic intepretation of physics as we know it would imply that there should have been equal amounts of matter & antimatter created at the big bang, and it should have (almost) all annihilated in the earliest minutes of the Universe. There are some good ideas out there about how to explain this discrepancy, but it hasn’t been worked out in full yet. See here for more details.

Probably a dumb question, but how do they know that some of the stars/galaxies aren’t made entirely of anti-matter?

For one thing, I don’t think there’s any reason to think they would be. “Don’t multiply entities beyond necessity” and all that.

For another, if an antimatter asteroid left an antimatter galaxy and slammed into a matter planet, the resulting explosion would be immense. Beyond comprehension. Hand of God-type stuff. The point is, we’d see it. I don’t think we’ve seen any massive explosions that weren’t connected to stars going nova. Absence of evidence isn’t evidence of absence, but it argues strongly a certain way.

So, to put things strictly, we don’t know. We don’t know a lot of things. But we can put forth working hypotheses, and one working hypothesis we’ve not had to seriously reconsider is that the Universe we can see is overwhelmingly made of matter.