# Is it true?

#### Schrodinger's Dog

I was reading that apparently antimatter travels back in time according to Feynman(OK on the internet admittedly)

What implications does this have for QM?

More important is this actually factual or internet jabber.

Was Feynman correct in his assertion, and what is the current thinking about such strange ideas?

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#### cristo

Staff Emeritus
I was reading that apparently antimatter travels back in time according to Feynman(OK on the internet admittedly)
Feynman pointed out that the desription of a positron moving forward in time is identical to that of an electron moving backward in time, however I doubt he ever said "antimatter travels back in time."

#### AlphaNumeric

Though this is pretty slap dash, I think a decent way to think about it is to consider the fourier components of the electron field. The 'matter' components have a term $$e^{-ip.x} = e^{i(Et - \mathbf{p.x})}$$ while the 'antimatter' components have $$e^{ip.x} = e^{i(-Et+ \mathbf{p.x})}$$ instead. There's a change in the sign of the 'iEt' term in the exponent. You can either interpret this as '-E' going in the +t direction (antimatter moving forward in time) or '+E' going in the '-t' direction (matter going backwards in time).

It's not very rigorous and I half expect someone will come along and set me right, but I think it's a fairly simple way of seeing how such an interpretation can come about.

#### Schrodinger's Dog

Ok that sounds much more reasonable, the usual half stated half baked ideas you find on the web I guess. Interesting but not quite Earth shattering. Thanks guys

#### Severian

This is called the Feynman-Stuckelberg Interpretation, and is used to get around having negative energy solutions of the wave equations.

#### Schrodinger's Dog

This is called the Feynman-Stuckelberg Interpretation, and is used to get around having negative energy solutions of the wave equations.
Yeah I looked it up, thanks.

http://en.wikipedia.org/wiki/Antiparticle

The Feynman-Stueckelberg interpretation

Observer 1 sees two particles, one propagating inside the light cone, the other outside the light cone. Observer 2, moving at a uniform velocity with respect to the first observer, could then see the second particle as moving back in time, and with reversed charge: hence as an antiparticle. However, the mass and lifetime of such a particle would remain unchanged, as a consequence of relativity.By considering the propagation of the positive energy half of the electron field backward in time, Richard Feynman showed that causality is violated unless some particles are allowed to travel faster than light. However, if a particle is moving faster than light, another inertial observer would observe that the particle was travelling backward in time with the opposite charge.

Hence Feynman reached a pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q. This allowed him to rewrite perturbation theory precisely in the form of diagrams, called Feynman diagrams, of particles propagating back and forth in time. This technique now is the most widespread method of computing amplitudes in quantum field theory.

This picture was independently developed by Ernst Stueckelberg, and has been called the Feynman-Stueckelberg interpretation of antiparticles.

I know how everyone hates wikipedia but it does have some relevant information, and seeing as the reference is Feynman should be fairly accurate..