[phkahler]

Yeah I've never looked at collisions. But if you blindly plug a negative mass into newtonian gravity F=GM1M2/r*2. And then use F=ma or a=F/m you get a=GM/r*2 where M is the other mass, and a is our acceleration toward that mass. Positive masses attract everything where negative masses repel everything. One of each held at constant separation should accelerate together.

This is why I want to know if antimatter falls up. Or I guess it might fall down but repel regular matter in which case it'll be very hard to detect.

[p1mrx]

"the BASE collaboration has shown, within strict boundaries, that antimatter does in fact respond to gravity in the same way as matter"

https://www.riken.jp/en/news_pubs/research_news/pr/2022/2022...

[lambdasquirrel]

That’s negative charge though, not negative mass. We haven’t been able to experiment with negative mass. No particle physics experiment has produced any evidence it exists.

[phkahler]

No, that doesn't cover the correct situation WRT gravity.

[Dylan16807]

Antimatter just has the opposite electrical charge. It doesn't do anything weird at all with gravity.

[monocasa]

IIRC, we don't actually know that for sure yet. I've seen some proposals for for experiments that use the relative stability and neutral charge of the exotic atoms muonium and anti-muonium to validate that anti muons don't have negative mass as well as flipped charge.

[sycren]

Since it focuses on electrical charge, would it be worth renaming it to Anti-charged-matter

Are there other types of Antimatter that focus on different properties?

[mayoff]

Antimatter also has anti-color-charge. Quarks have a ‘color charge’ (unrelated to visible colors) which is ‘red’, ‘green’, or ‘blue’. An antiquark is antired, antigreen, or antiblue (and has the opposite electrical charge from its corresponding normal quark).

https://en.wikipedia.org/wiki/Color_charge

[phkahler]

Could anti-quarks behavior be explained by them having negative mass instead?

[KMag]

That would require a re-formulation of conservation of color charge. You could probably come up with an alternative formulation where everything is consistent, but all of the formulas would almost certainly be more complicated. The most obvious way would end up replacing color by the sign of mass times color everywhere, but then you've just renamed ant-red, anti-blue, and anti-green, with no obvious benefit.

[monocasa]

I don't believe so; color charge isn't a scalar like mass is.

[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.