
#1
Apr2804, 08:33 PM

P: 26

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?




#2
Apr2804, 08:42 PM

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PF Gold
P: 10,424

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 



#3
Apr2904, 04:08 AM

P: 653

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




#4
Apr2904, 04:12 AM

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PF Gold
P: 10,424

anti photons
There is no such thing as a negative energy photon.
 Warren 



#5
Apr2904, 04:17 AM

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#6
Apr2904, 04:19 AM

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



#7
Apr2904, 07:43 AM

P: 653

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 . 



#8
Apr2904, 12:29 PM

PF Gold
P: 2,884

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).




#9
Apr2904, 02:06 PM

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#10
Apr2904, 05:58 PM

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PF Gold
P: 5,540

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. 



#11
Apr2904, 06:33 PM

Mentor
P: 28,838

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/phz...ecture_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. 



#12
Jun2205, 04:25 AM

P: 2

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, AntiParticles, and a story, but... Photons are particles, correct? And it doesn't make much sense to me to be your own antiparticle; if you are, you can't be annihalated. So, isn't it possible, by some weird anomaly, that antiphotons are not oppositely charged to Photons, but, rather, have the opposite gravitational pull?




#13
Jun2205, 04:38 AM

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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 [itex] \pi^{0} [/itex] meson. Daniel. 



#14
Jun2205, 04:56 AM

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[tex]\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 [/tex] for arbitrary spin massive particles and [tex] \hat{P}^{0}\vec{p},\lambda\rangle =\mbox{sign}\left(p^{0}\right) \sqrt{\vec{p}^{2}} \vec{p},\lambda\rangle [/tex] 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 [itex] \hat{P}^{\mu} [/itex] belongs to the closed future light cone [itex] \bar{V}^{+} [/itex]." ,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. 



#15
Jun2205, 06:26 AM

P: 219

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. 



#16
Jun2205, 09:02 AM

P: 1,017

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 welllike, one is saddlelike 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. 



#17
Jun2205, 01:28 PM

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Daniel. 


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