# Is antimatter matter going backwards through time?

1. Dec 8, 2011

The title kind of says it all. I've heard conflicting things about this one, so here goes: Is a positron really an electron going backwards in time? I've been thinking things out in my head, and it doesn't seem that that would result in a positive charge. Am I doing it all wrong? Would an electron going backwards through time really be the same as a positron? I'm just a high school student, so please don't make it too complicated! Thanks!

2. Dec 8, 2011

### e.bar.goum

It's not "really" an electron going backwards in time, but that's what the maths looks like, yes!

If you reverse the direction of time, you switch signs in your equations, which is the same as switching the sign of the charge on the particle.

If you want to know more, you could look into CPT (charge-parity-time) symmetry.

(You can blame Feynman (in part) for the whole "backwards in time" thing. Indeed, in Feynman diagrams, we draw an antiparticle going in the opposite direction in time to a particle)

3. Dec 8, 2011

### PSz

It is not. At least as long as we don't accept faulty logic coming from philosophers dealing with particle physics and Faynman diagrams.

4. Dec 8, 2011

### e.bar.goum

PSz, I wouldn't call it "faulty logic" - it's exactly what the equations look like! It might not be true in "reality", but in the models, they are equivalent. And I've yet to meet a philosopher who deals in Feynman diagrams, heh.

5. Dec 8, 2011

### PatrickPowers

Dirac and Feynman thought so. The idea has never caught on, though.

My view is, tell me how I can determine whether a particle is or is not going backward in time. Until then the question doesn't interest me.

6. Dec 9, 2011

Thanks for clearing things up! Does antimatter respond the same way to gravity and the strong force as regular matter?

7. Dec 9, 2011

### kmarinas86

That doesn't make sense. If you reverse time for an orbit based on attracting matter, you still have attraction. Forces do not change sign when you the reverse the motion. Only the displacements reverse. However, antimatter has the opposite charge as corresponding matter. With that, you expect the electromagnetic forces for antimatter to be reverse that of matter. That already implies something other than "time reversal". In addition, force reversal does not translate into reversing the displacement. Instead of an orbit, you would have a hyperbolic bounce. So there is no way that antimatter is simply matter traveling backwards through time.

8. Dec 9, 2011

### kmarinas86

I would also like to add that the idea that antimatter is somehow matter traveling backwards in time is a misinterpretation of what the equations say. The correct interpretation is that if you reverse the parity of a system, reverse the charge signs of the system, and reverse the momenta of the system, you have converted from a "matter" system to an "antimatter" system whose motions are a mirror opposite of the "matter" system. However, if this is not a isolated system we are speaking of (i.e. if we do not change the parity, charge, and momenta of all other systems influencing this system), then there is no way this could be regarded as a time reversal because it would lead to force reversals (i.e. attractive to unattractive and unattractive to attractive), which, as I pointed out above, are inconsistent with any "time reversal". On top of that, due to the change in parity relative to other systems, it would also lead to position reversals relative to other systems. That has nothing to do with a concept of true time reversal. Finally, time and momentum are simply not the same thing, so CPT-symmetry should be renamed CPM-symmetry.