Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 01/06/2005 21:48:50

Title: Photon life span
Post by: DoctorBeaver on 01/06/2005 21:48:50
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?
Title: Re: Photon life span
Post by: gsmollin on 02/06/2005 14:10:41
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.
Title: Re: Photon life span
Post by: DoctorBeaver on 02/06/2005 14:26:06
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?
Title: Re: Photon life span
Post by: gsmollin on 02/06/2005 18:58:48
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.
Title: Re: Photon life span
Post by: DoctorBeaver on 03/06/2005 13:15:03
OK, I understand it now. Thanks
Title: Photon life span
Post by: ukmicky on 21/06/2007 15:34:09
Where did gsmollin go ,mr beaver you didnt scare him off did you.
Title: Photon life span
Post by: DoctorBeaver on 21/06/2007 15:38:27
I don't know where he went. I was wondering about "expired" members the other day. gsmollin & sharkeyandgeorge were 2 who sprang to mind.
Title: Photon life span
Post by: ukmicky on 21/06/2007 15:41:29
what does this mean ,posted at the bottom of gsmollins post

"F = ma, E = mc^2, and you can't push a string."
Title: Photon life span
Post by: DoctorBeaver on 21/06/2007 15:49:19
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.
Title: Photon life span
Post by: ukmicky on 21/06/2007 15:53:36
I know what F=ma is and E=mc2 .

But how does the pushing a bit of string come into it.
Title: Photon life span
Post by: DoctorBeaver on 21/06/2007 15:55:07
It's probably something to do with string theory akin to the "black holes have no hair" saying.
Title: Photon life span
Post by: syhprum on 21/06/2007 16:32:52
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
Title: Photon life span
Post by: maff on 22/06/2007 00:02:53
The lifespan of a Photon is infinate unless effected by other energy. The Photon velocity is zero in any situation.
..maff
Title: Photon life span
Post by: lightarrow on 22/06/2007 18:57:00
Quote from: maff on 22/06/2007 00:02:53
The lifespan of a Photon is infinate unless effected by other energy. The Photon velocity is zero in any situation.
..maff

Please?