# Does antimatter 'shine'

1. ### benk99nenm312

302
Hey. I was wondering, can we 'see' antimatter? By this, I mean, does a positron ever emit photons, or can we shine a light on antimatter and see what it gives off? Are we limited to 'seeing' antimatter by other means, such as annhilation, or charge?

From my understanding, antimatter travels backwards in time. We see things that move forwards in time. However, I am uncertain as to whether photon emissions are a common property of antimatter.

2. ### Bob S

Fermilab produces, accelerates, and stores antiprotons. They go the same way as protons if the magnetic field is reversed, the opposite way if it isn't. Protons and amtiprotons sometimes travel in the same vacuum chamber at the same time, in opposite directions. Antiprotons sometimes collide with protons, but they always go forward in time.

3. ### ZapperZ

30,440
Staff Emeritus
Antimatter behaves the same way as the matter counterpart.

When the Advanced Photon Source first came online, it used positrons to go around the synchrotron ring to generate light. They now use electrons in much the same way.

Zz.

4. ### Phrak

Antimatter emmits antiphotons. These are, of course, just photons. So, yeah, antimatter shines.

(Things move in time? When did that start happening?)

5. ### benk99nenm312

302
Thanks.

I assume you meant backwards in time, which is a principal of Quantum Electro-Dynamics. I am not familiar with any notion or theory that disclaims this principal, but it seems that a number of people know about a different way of looking at antimatter.

Quantum states of a particle and an antiparticle can be interchanged by applying the charge conjugation (C), parity (P), and time reversal (T) operators. This is the familiar CPT conjugation. Time is clearly a conjugate, so I am confused as to why so many think antimatter travels forwards in time. Maybe it's something I don't know.

6. ### Phrak

'Motion in time' is one of my pet peeves, I guess. When something moves in space, at one time it occupies one spatial position, and at a later time it occupies anther spatical position.

Now, reapply this meaning to time by replacing all instantiations of "space" with "time":

"When something moves in time, at one time it occupies one temporal postion, and at a later time it occupies another temporal postion."

It is a gramatically vacuous. Things do not move in time anymore than a line moves on a graph.

Last edited: May 11, 2009
7. ### malawi_glenn

4,726
This is the ugly popular science description again, trying to make particle physics as spooky as possible :-)

The antiparticles propagates (we don't like travel as a concept in particle physics) forward in time, but their state propagates backwards. It is a bit tricky to explain without going into the deep math.

I really don't understand the logic that we see things that move forward in time, we see things (with our eyes) things whos photons reaches our eyes.

Photon interactions are possible for every particle that interact with the electromagnetic-force. And what differs from a proton and an antiproton is just that they have opposite quantum numbers.

One example of antiparticles that DO NOT participate in the electromagnetic is the anti-neutrino, since it's particle counterpart, the neutrino, does not do so.

8. ### malawi_glenn

4,726
Pick up any book on relativistic quantum mechanics and study =)

9. ### benk99nenm312

302
A change in the position of space means a change in the position of time. You have said it yourself. If an object is here, and then it is there... there is a chronological advancement in the position of time.

Time is a dimension. We can move around in it, accelerating, decelerating, but not stopping. If things didn't move in time, then we would all be frozen solid, our very atoms and molecules at a stand still. Time is necessary to consider.

10. ### benk99nenm312

302
Thanks. I think I'm starting to get it. But, aren't the particles determined by their states. If their states move backwards in time, why not the particles themselves? (It's okay to give me a little math.)

11. ### hamster143

986
Question 1. There's a high-voltage power line that connects Austin, Texas, and San Antonio, Texas. San Antonio is 100 miles southwest of Austin.

Which way does the power line run?

a) South and west
b) North and east
c) Depends whether it's made of matter or antimatter
d) The question is vacuous

Question 2. A particle is in Austin, Texas, today and an identical particle is in San Antonio, Texas, tomorrow.

Which way did the particle propagate?

a) Forwards in time and to the southwest
b) Backwards in time and to the northeast
c) Depends whether its a particle or an antiparticle
d) The question is vacuous

Last edited: May 11, 2009
12. ### George Jones

6,480
Staff Emeritus
The modern way .

I can't resist quoting a passage from Zee's Quantum Field Theory in a Nutshell. The last section, Poetic but confusing metaphors, of Chapter II.2, Quantizing the Dirac Field, reads:

"In this closing chapter let me ask you some rhetorical questions. Did I speak of an electron going backward in time? Did I mumble something about a sea of negative energy electrons? This metaphorical language, when used by brilliant minds, the likes of Dirac and Feynman, was evocative and inspirational, but unfortunately confused generations of physics students and physicists. The presentation given here is in the modern spirit, which seeks to avoid these potentially confusing metaphors."

13. ### malawi_glenn

4,726
A physical positron propagating forward in time is the state electron propagating backward in time.

14. ### Bob_for_short

Yes, it is already in the far past. We may safely forget it. Less of worries :)

I was a joke. Let us admit that there is no antimatter but differently charged particles. (Some of them were discovered earlier, some later.) Then there will be no problem in understanding their dynamics.

Bob.

Last edited: May 11, 2009
15. ### Phrak

Measurable motion in space is velocity; $\Delta X / \Delta T$. What are the units and measure of motion in time?

Motion in space is a physically measurable with units of velocity. How would you measure motion in time and what would be its units? Physics is an experimental science; it ain't philosophy.

16. ### Phrak

Hey, malawi. It's been a while. Particles and antiparticles, as far as we know, are arbitary under relabeling--unless things have changed recently--aren't they?

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

Last edited: May 11, 2009
17. ### benk99nenm312

302
What are the units and measure of motion in time? How about seconds, or miliseconds, or even planck time intervals. These are simple measures of chronological advancement.

"Motion in space is physically measurable with units of velocity." And so motion in time is equal to Delta X / Velocity. Velocity is real, right?:uhh:

Even better is this. E=mc^2. So, c=(E/m)^1/2 . c = the speed of light, which involves a measure of time. A measure of simply time can be found by simplifying the dimensional analysis product of that equation.

The very notion of Delta T indicates that a measure of time is necessary. If I throw a baseball, is it flying through the air and in my palm? Obviously not. The baseball has to move somewhere in time. This is not philisophical by any means. How do you explain Special and General Relativity?

Last edited: May 11, 2009

Mia copa.

19. ### benk99nenm312

302
No Problemo.

I do that sometimes too.

20. ### malawi_glenn

4,726
A physical antiparticle propagating forward in time, is the state of a particle propagating backward in time

(since the negative frequency solutions to KG and Dirac has as Green's function G(t'-t) whereas the positive frequency solutions to KG and Dirac has Green's function G(t-t') )

The flow of fermion number and charge of the antifermion is thus opposite to the fermion.

By the way, Physics has clearly many philosophical claims and elements. The statement that Physics is a experimental science is in fact a philosophical statement ;-)