anti photons

[cangus]

Since an anti photon is a photon travelling backwards in time, is the max speed of an anti photon 186,000miles/sec, or is it -186,000?

[chroot]

Actually, the photon is its own antiparticle. A photon and an antiphoton are exactly the same thing. Further, the concept of time really has no meaning for a photon, since it always travels the speed of light.

Also, a negative velocity has the same meaning as a positive velocity -- it just means the object is moving in the opposite direction.

- Warren

[kurious]

What about a negative energy photon - does that have momentum in the same direction as it is moving?

[chroot]

There is no such thing as a negative energy photon.

- Warren

[LURCH]

There is no such thing as a negative energy photon.

- Warren

You know, it's never occurred to me before that I've never heard of a negative energy photon. Is negative energy not considered to be quantized?

[chroot]

I'm not really sure I understand lurch; I've never really heard of any "negative energy" particle.

- Warren

[kurious]

Negative energy could account for the attraction of masses by carrying momentum in the opposite direction to which it is moving and also it could be causing the acceleration of the universe because negative energy would repel positive masses whereas normal positive energy would deccelerate masses.
For more on this issue go to theory development - the mechanism of gravity .

[arivero]

Actually the attractive/repulsive character of a carrier has a lot of its spin. 0 and 2 are attractive, 1 is repulsive (for equal charges, this is).

[LURCH]

I'm not really sure I understand lurch; I've never really heard of any "negative energy" particle.

- Warren

I haven't either, that's what I find so strange. Negative energy is known to exist, and I've done a little bit of research into it (though not very much, I'm afraid). It is only in the context of this discussion that I came to realize that I have never heard of a negative energy particle. In fact, I have never heard of negative energy being discussed in any quantized form.

[Tom Mattson]

You know, it's never occurred to me before that I've never heard of a negative energy photon.


There are no negative energy photons because photon energies are differences in atomic energy states. The absolute values of atomic energy states have no significance in and of themselves, but their differences do. Since photons are only emitted in transitions from higher states to lower states, you are bound to get a positive photon energy. Of course, you can always adopt the point of view that absorbed photons (those that promote electrons from lower states to higher states) are actually negative energy photons that move backwards in time.


Is negative energy not considered to be quantized?


No, the energy levels of the hydrogen atom are En=(-13.6eV)/n2, where n=1,2,3,...

As I said, that's just a matter of convention, and we can just as easily define the states to have positive energies, but there's something appealing about having the zero of energy at n-->infinity. That way, we associate negative energies with bound states, and nonnegative energies with free states.

[ZapperZ]

Maybe this is way too obvious to mention, but in case anyone forgets, the relativistic Schrodinger equation, as solved by Dirac, contains both positive and negative energy eigenvalues. When Dirac solve this, he still had fermions, but with these negative energies. This was the first indication of antiparticles that was verified later.

http://www.phys.ufl.edu/~korytov/phz5354/lecture_D06.pdf

So yes, there can be particles with "negative" energies. It is interesting to note that in condensed matter, these antiparticles correspond to the "holes" in the fermi sea below the vacuum state. So these holes also have negative energies.

Zz.

[Solasis]

Okay, this is probably going to sound idiotic, but it's 3:30 in the morning, I'm tired, and my mind is mixed up in Nemesis Theory, Evolutionism, Anti-Particles, and a story, but... Photons are particles, correct? And it doesn't make much sense to me to be your own anti-particle; if you are, you can't be annihalated. So, isn't it possible, by some weird anomaly, that anti-photons are not oppositely charged to Photons, but, rather, have the opposite gravitational pull?

[dextercioby]

Nope.In particle physics whe have a clear distinction of "antiparticle" and we have a clear rule of what might actually happens to the quantum field operators in order that that particle coincides with its own antiparticle.

The photon is its own antiparticle,just like the \pi^{0} meson.

Daniel.

[dextercioby]

I'm not really sure I understand lurch; I've never really heard of any "negative energy" particle.

- Warren

According to the famous analysis of the irreducible unitary representations of the Poincaré group by E.P.Wigner who published an article [1] in 1939,QFT can accomodate,basically for any value of spin and mass,negative energy particles.

\hat{P}^{0}|\vec{p},s_{3}\rangle =\mbox{sign}\left(p^{0}\right) \sqrt{\vec{p}^{2}+m^{2}} |\vec{p},s_{3}\rangle

for arbitrary spin massive particles and

\hat{P}^{0}|\vec{p},\lambda\rangle =\mbox{sign}\left(p^{0}\right) \sqrt{\vec{p}^{2}} |\vec{p},\lambda\rangle

for arbitary spin massless particles.

Upon reading more from [2],i realize that the third axiom of QFT (axiom III.a from [2]) states

"The spectrum of the energy momentum operator \hat{P}^{\mu} belongs to the closed future light cone \bar{V}^{+} ."

,therefore all negative energy unitary irreds of the restricted Poincaré group do not lead to physical states.

Daniel.

[1]E.P.Wigner (1939),"On Unitary Representations of the Inhomogeneous Lorentz Group",Ann.Math.,40,149.
[2]N.N.Bogolubov,A.A.Logunov,I.T.Todorov,"Introdiction to Axiomatic Quantum Field Theory",Benjamin/Cummings,NY,1975.

[Kruger]

I have the following definition problem (maybe it's just my teacher's problem):

He said in radioactivity decay (beta+ decay) the positron that gets free isn't an antiparticle. Is that true? In my mind not.

[El Hombre Invisible]

I've heard of negative energy in two contexts:

1) the curvature of space - positive energy curves space one way, negative the other... one is well-like, one is saddle-like but I can't remember which way round it is;

2) Hawking radiation, in which a pair of positive and negative energy particles are created on the event horizon of a black hole and separated by its gravity - the negative energy particle is pulled into the hole and reduces its mass and the positive energy particle is expelled away from it. I believe this might be what the OP is referring to, since as I recall it should appear as if the positive particle has come from inside the black hole.

If this 'negative energy' particle is indeed travelling backwards in time, then if it were to be absorbed it would look, forward in time, exactly like a positive energy particle being emitted. This, I guess, demonstrates why the photon is its own antiparticle: a 'negative' photon being absorbed is indistinguishible from a 'positive' photon being emitted and vice versa. So as Tom said, you could talk in terms of emission events being absorption of negative energies and absorption events being the emission of negative energies - convention and everyday experience dictate otherwise.

[dextercioby]

I have the following definition problem (maybe it's just my teacher's problem):

He said in radioactivity decay (beta+ decay) the positron that gets free isn't an antiparticle. Is that true? In my mind not.

The positron is a particle,the quanta of the positronic quantum field.It's the electron's antiparticle.Under any possible circumstances.

Daniel.

[Adrian Baker]

I have the following definition problem (maybe it's just my teacher's problem):

He said in radioactivity decay (beta+ decay) the positron that gets free isn't an antiparticle. Is that true? In my mind not.

The positron IS an antiparticle - the antiparticle of the electron. Are you getting positrons and photons mixed up?

[Kruger]

The positron is a particle,the quanta of the positronic quantum field.It's the electron's antiparticle.Under any possible circumstances

My teacher is doctor in Physics. So, might be he is wrong.

[El Hombre Invisible]

The positron is a particle,the quanta of the positronic quantum field.It's the electron's antiparticle.Under any possible circumstances.

Daniel.
Don't ask me why I looked at this thread again, but what is the positronic quantum field? I just googled it and got exactly zero matches.

[jtbell]

The positron IS an antiparticle - the antiparticle of the electron.

And the electron is the antiparticle of the positron. "Antiparticle" is a relative term, strictly speaking, not an absolute one. We tend to think of electrons as "particles" and positrons as "antiparticles", but that's mainly because there are a lot more electrons than positrons. With pions, on the other hand, I don't think I've ever seen anyone associate positive/negative with particle/antiparticle one way or the other.

[Kruger]

Don't ask me why I looked at this thread again, but what is the positronic quantum field? I just googled it and got exactly zero matches.

Might be better you look for "fermionic quantum field".

[El Hombre Invisible]

Might be better you look for "fermionic quantum field".
Groovy. Thanks.

[Lance McKenzi]

I think there is something missing here.You haven't stated the origin of an anti photon. If a photon is its own anti photon, then it would be capable of wave propagation backwards in time. This would have a different source to that of generating a photon, as well as have to remove energy from the present.
Therefore photons and anti photons must be able to interact in a manner similar to wave-particle duality; in that it will act as either when necassary.

[DaveC426913]

I think there is something missing here.
Yes. About four and a half years of conversation... :biggrin:

[Lance McKenzi]

Yes. About four and a half years of conversation... :biggrin:

Just decided now to find physics forums in my spare time at uni.

[DaveC426913]

Just decided now to find physics forums in my spare time at uni.

Welcome! :smile:

[haushofer]

I have the following definition problem (maybe it's just my teacher's problem):

He said in radioactivity decay (beta+ decay) the positron that gets free isn't an antiparticle. Is that true? In my mind not.
That's silly, because a positron is per definition the antiparticle of the electron.