Maximun energy of a photon

Jul30-03, 03:55 PM

Please explain the error in this logic (if any):

E = hc / λ

Where
h = Planck Constant = 6.62606876 x 10-34 Js
c = Speed of light = 299792458 m/s
λ = Wavelength

The wavelenght can't possibly be smaller than Planck Length (1.6160 x 10-35 m) yields:

Maximun Energy = 12292360398.7464 J
Maximun Energy = 7.6722887211823E+28 ev

Is this valid? Is there a limit on how much energy an photon can carry? I've never heard of that...

**AndersHermansson** · Jul30-03, 04:53 PM

Woops

**jcsd** · Jul30-03, 06:29 PM

What's you argument for a phton's wavelength not being smaller than the Planck length? I mean the compton wavelength of a flea is about the same as the Planck length. Are you saying that a photon with a wavelength of the pPlanck length would be unable to escape it's own gravitaional field, cos I believe that's been theorized, but I'm unsure.

Jul31-03, 10:08 AM

Originally posted by jcsd
What's you argument for a phton's wavelength not being smaller than the Planck length? I mean the compton wavelength of a flea is about the same as the Planck length. Are you saying that a photon with a wavelength of the pPlanck length would be unable to escape it's own gravitaional field, cos I believe that's been theorized, but I'm unsure.

Actually I was just wondering if there is a minumum wavelength for EM radiation and if so if it is the Planck Lenght? This would mean that there is a limit to the energy of a photon can carry.

**jcsd** · Jul31-03, 10:17 AM

All I can say is probably not, the idea that a photon will collapse under it's own graviational field is fallacious (it forgets blue-shifting), unless there's something I'm unware of I don't see why a photon can't have a wavelength > the Planck length, though such a photon would be unstable with any interaction probably forming an electron-positron pair. Infact Isaac Asimov (I don't like quoiting sci-fi authors but anyway) said that the maximum energy of a photon was the energy of the cosmos and the minimum energy was the enrgy corresponding to a photon with a wavelength the same as the size of the cosmos.

**russ_watters** · Jul31-03, 01:05 PM

I'm not sure what gravity has to do with this, jcsd - JAL din't mention it. Planck's constant is the "size" of quantum uncertainty. I don't think a photon can have a wavelength shorter than that.

**Brad_Ad23** · Jul31-03, 01:11 PM

Well I would suggest doing some simple quantum calculations with escape velocity as well.

However, it does seem that a photon of that small wavelength would be extremely energetic for a photon, and hence would be very unstable.

**jcsd** · Jul31-03, 05:56 PM

Originally posted by russ_watters
I'm not sure what gravity has to do with this, jcsd - JAL din't mention it. Planck's constant is the "size" of quantum uncertainty. I don't think a photon can have a wavelength shorter than that.

Yep, but it has been suggested in a physics report that the Planck length is the maximum length for a virtual photon as any photon with a wavelength greater than this would collapse in it's own graviational field like a black hole. This logic is obviously fallacious as from a different reference frame the photon's wavelength would be blue-shifted above the Planck wavelength so following this logic it wouldn't collapse in this reference frame, so we must reject it collapsing in a refernce frame where it's wavelength is below the Planck length.

Macroscopic objects, including yourself, generally have Compton wavelengths below the Planck length, why not a photon? There is no comopelling reason to think that photons with wavelengths smaller than the Planck length could at exist in theory.

**wimms** · Aug1-03, 09:15 AM

Originally posted by jcsd
Yep, but it has been suggested in a physics report that the Planck length is the maximum length for a virtual photon as any photon with a wavelength greater than this would collapse in it's own graviational field like a black hole. This logic is obviously fallacious as from a different reference frame the photon's wavelength would be blue-shifted above the Planck wavelength so following this logic it wouldn't collapse in this reference frame, so we must reject it collapsing in a refernce frame where it's wavelength is below the Planck length.

confused. Did you mean that photon with wavelength 'shorter' than planck's would collapse, and that redshift would 'avoid' that? Shouldn't frame of photon be the only one that matters (if such q makes sense)?

There is no comopelling reason to think that photons with wavelengths smaller than the Planck length could at exist in theory.

Photon at planck length would have mass of 1.5E+23 Me. Shouldn't such 'thing' condense into matter?

**drag** · Aug1-03, 01:07 PM

SST says the photon will grow instead of becoming
smaller, I think. [t)]

Live long and prosper.

**jcsd** · Aug1-03, 02:11 PM

Originally posted by wimms
confused. Did you mean that photon with wavelength 'shorter' than planck's would collapse, and that redshift would 'avoid' that? Shouldn't frame of photon be the only one that matters (if such q makes sense)?

Photon at planck length would have mass of 1.5E+23 Me. Shouldn't such 'thing' condense into matter?

No, as I said before the premise behind it is faulty, as considering a differen refrence frames the wavelength would be different.

Photons don't have mass, but yes, such a high energy phton is unstable and would after nearly any interaction change into massive particles.

**russ_watters** · Aug1-03, 03:03 PM

Originally posted by jcsd
Macroscopic objects, including yourself, generally have Compton wavelengths below the Planck length, why not a photon?

Isn't that just a mathematical average? Analagous to the idea of light "slowing down" when traveling through a medium?

There is no comopelling reason to think that photons with wavelengths smaller than the Planck length could at exist in theory.

You mean could NOT exist, right? There is no compelling reason to think they could NOT exist? I still think HUP is a pretty compelling reason (not that I necessarily understand it all that well).

Aug1-03, 03:08 PM

Originally posted by russ_watters
You mean could NOT exist, right? There is no compelling reason to think they could NOT exist? I still think HUP is a pretty compelling reason (not that I necessarily understand it all that well).

What is HUP?

Aug1-03, 03:28 PM

Question answered by an High Energy Astronomer at:

http://imagine.gsfc.nasa.gov/docs/as...s/970412e.html

**Integral** · Aug1-03, 06:09 PM

HUP=Heisenberg Uncertiantiy Priciple.

**jcsd** · Aug1-03, 06:14 PM

Originally posted by JAL
Question answered by an High Energy Astronomer at:

http://imagine.gsfc.nasa.gov/docs/as...s/970412e.html

For some reason I can't open that page, could you quote the relevant sections?