[phkahler]

>> Antimatter just has the opposite electrical charge.

We don't know that. It may have the regular charge but after computing the force it may experience the opposite behavior via F=ma since the mass is negative.

We don't really know if the charge is opposite or the mass. Blindly using the equations you may get similar results depending where you stick the negative.

Also, I seem to recall Dirac predicting the existence of antimatter because some solution to an equation had an m^2 term and when you take a square root to solve for m there are two solutions. Then the positron came along and this was forgotten and people just assumed it had positive charge rather than negative mass.

[thfuran]

Antimatter isn't some unobserved theoretical thing. It's produced daily at most large hospitals. We absolutely know that its electric charge is opposite that of the normal matter counterpart.

[fooker]

>. We absolutely know that its electric charge is opposite that of the normal matter counterpart.

Here is a contrived example calculating a hypothetical quantity X = m * Y.

Suppose we observe that X is always negative.

By your logic, we would then assume that Y is always negative.

This is true if m is never negative, but it is somewhat possible that we would eventually find a situation where m is negative and Y is positive.

[thfuran]

I'm not sure what you're trying to say.

[phkahler]

How do we know that? Because of how it behaves in electric and magnetic fields. In particular, how it accelerates. It obviously has a negative sign in it somewhere. My point is that we don't know if that sign flip is in charge or mass. A lot of the math behaves in accordance with observation whether we flip the charge or the mass.

[tiborsaas]

Recent experiment at CERN: https://www.space.com/matter-antimatter-same-response-to-gra...

[thfuran]

>How do we know that

Both theory and experimental validation. Their interaction with electric fields, their interaction with gravity, conservation laws, and so on.

[m_dupont]

Unfortunately this isnt correct. We know it has the opposite charge. This is due to conservation laws which include, among other things, the conservation of charge.

In a given interaction, charge is always conserved. So we see interactions where an electron and a positron collide they produce a chargeless photon. So it must have the opposite charge to an electron

[phkahler]

Thank you. That's the first thing anyone has said that disambiguation it for me. My first thought was "but what if mass is concerned and the positive and negative mass cancel out?" But I quickly remembered the photons have the mass-equivalent energy, so the mass doesn't cancel, it gets "converted".

Is there energy in an electric field? If so it must be signed or it wouldn't cancel out.

[LegionMammal978]

> Is there energy in an electric field? If so it must be signed or it wouldn't cancel out.

The energy contained in the electromagnetic field is nonnegative: as I understand it, within a given volume, it's simply the sum of the photon energy of all of the photons.

Meanwhile, electrons and positrons exist in their own particle field, and have both positive mass energy and nonnegative kinetic energy. When an electron and positron annihilate and produce photons, they convert their combined mass energy into kinetic energy in the photons. The only thing that gets "canceled out" is the positive and negative electric charge.