[DoctorBeaver (OP)]

I've seen it said in a few places that photons never expire. Is there any proof of that?
As I'm not a physicist or mathematician I don't understand the intricacies of the equations involved, but is the lifespan of a particle related to its energy?

[gsmollin]

quote:Originally posted by DoctorBeaver

I've seen it said in a few places that photons never expire. Is there any proof of that?
As I'm not a physicist or mathematician I don't understand the intricacies of the equations involved, but is the lifespan of a particle related to its energy?

I think the standard model shows photons are stable. Time dilation for the photon means it does not age, since it moves at c. Now the second question is more complicated, and yes, there is an upper limit for photon size, where it is supposed to decay. I think there is an issue with cosmic rays on this point.

[DoctorBeaver (OP)]

quote:there is an upper limit for photon size

Do you mean that photons can be of different sizes or that all photons are the same size but cannot be larger than that max?

[gsmollin]

quote:Originally posted by DoctorBeaver

quote:there is an upper limit for photon size

Do you mean that photons can be of different sizes or that all photons are the same size but cannot be larger than that max?

I meant energy "size". There is a limit to the amount of energy a photon can carry and remain stable. I think there is some point where charged particles are supposed to materialize and carry the energy away. It around 10^20 eV. Don't quote me on that though, I'm just remembering something about cosmic rays.

[DoctorBeaver (OP)]

OK, I understand it now. Thanks

[ukmicky]

Where did gsmollin go ,mr beaver you didnt scare him off did you.

[DoctorBeaver (OP)]

I don't know where he went. I was wondering about "expired" members the other day. gsmollin & sharkeyandgeorge were 2 who sprang to mind.

[ukmicky]

what does this mean ,posted at the bottom of gsmollins post

"F = ma, E = mc^2, and you can't push a string."

[DoctorBeaver (OP)]

F=ma is force=mass x acceleration (Newton's 2nd law) and we all know what E=mc² is.

Anyway, he's wrong about not being able to push a string. I just tried it & managed it.

[ukmicky]

I know what F=ma is and E=mc2 .

But how does the pushing a bit of string come into it.

[DoctorBeaver (OP)]

It's probably something to do with string theory akin to the "black holes have no hair" saying.

[syhprum]

I have heard that there is an upper limit of 10^20 Ev for cosmic rays due to their interaction with the CMBR,
Surely photons can come to an end in at least two ways, modest energy ones can be adsorbed by atoms and bump electrons up to a higher level, and high energy ones can transmute into into Electron Positron pairs

[maff]

The lifespan of a Photon is infinate unless effected by other energy. The Photon velocity is zero in any situation.
..maff

[lightarrow]

The lifespan of a Photon is infinate unless effected by other energy. The Photon velocity is zero in any situation.
..maff

Please?