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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hello,
If I understood it correctly...
The maximum energy a photon can ever have is Planck energy, because at this energy half of wavelength would be smaller than planck length, and ultimately would not be able to exist anymore as nothing smaller than Planck length can be probed.
This is how I understood the event horizon of black holes: - gravitational blue shift which increases energy of infalling photons up to planck energy limit, up to the spot where their 1/2 wavelength is smaller than Planck length and they degenerate, adding their energy to the black hole.
In any case Planck length seems to be what fundamentally represents a limit for blue shift, but I didn't find an explanation how exactly.
But when thinking of normal Doppler shift, things become confusing.
Say I have a source of radiation, emitting photons with energy very close to Planck energy - If I start moving towards that source at some low velocity, but high enough that photon energy surpasses Planck energy for my frame of reference, what happens?
Looking back at gravitational blue shift, would I create some sort of event horizon relative to that source, would the photons disappear from my frame of reference and in that case where would the energy go?
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi Marco, this is known as a limit of a blue shift... A bit explained here and here
But your questions persist...
I think, that the situation you describe means that the Doppler effect do not work anymore, it is simply the highest freq. which stay constant, no matter how fast you approach to the source. But, it would be funny in case your idea about “disappearing†would be correct. It would mean that we can see only the back of some things...Or in other words, part of the universe becomes apparent only after we passes it
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
hi,
I'm aware of wikipedia articles for long time - but is there any site with some more through information about this?
I don't think if what I mentioned regarding black holes makes sense either.
As I see from equations nor gravitational nor doppler blue shift depend on frequency of the radiation thus there's no way event horizon could be the same for any arbitrary frequency.
I'm also sure blue shift can't just ''stop'' at some point because that would violate conservation of energy. Degeneration would be logically expected but I'm confused.
Question is now: for a number of photons with different frequencies entering a black hole, what will be their final frequency at point when they are at event horizon?
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Hi Marko, those wikipedia entries definitely smelled like bulls***, ahh, pseudoscience to me, so I took the liberty of editing them. I think all the stuff about Planck times, Planck lengths etc. is speculation at best. Because no experiments can be performed at this scale, and therefore any theory has to be considered tentative. There is no _proof_ that space turns into a foam, or becomes discrete, or contains little pink bunny rabbits at some scale, right?
Black holes are a lot more tangible though, and there is a lot more actual research about them. Therefore I expect there is an accepted answer to that part of your question at least. There may be a simple way to avoid the problem in the first place though: Above a certain energy, which is far below what you are talking about here, the vacuum essentially becomes opaque to radiation. See Therefore a photon would be scattered long before it could reach these energies.
Gee, I have no clue about high energy physics, someone else has to be able to clear this up! Have you tried posting to the usenet physics group where John Baez and his pals hang out? They should be able to give you all the answers to really make your head spin!
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The highest possible frequency of electromagnetic radiation
