3 ms·
It is pretty well understood, but the answer is the opposite (following from special relativity). You can take an ordinary low frequency photon, and just observ
by srl 6y ago
It is pretty well understood, but the answer is the opposite (following from special relativity). You can take an ordinary low frequency photon, and just observe it while moving arbitrarily close to the speed of light, and the frequency of the photon will appear arbitrarily large.
Pair production won't happen until two photons collide, with a large /relative/ momentum. So if they have the same frequency and are traveling in the same direction, no pair production.
But, you're absolutely correct in the case of /astrophysical/ photons. A high-energy astrophysical photon will have to pass through, among other things, the background of CMB radiation, and that gives plenty of opportunities to pair-produce, so there is in fact a cutoff to the spectrum of photons we expect from far-away events.
- seiferteric 6y agoWould a high enough energy photon also turn into a black hole?
- jfengel 6y agoPrecisely. That's what the Planck length is: the wavelength of a photon that would be its own black hole. We can't know what happens there without applying both general relativity and quantum mechanics simultaneously, but when you try, you get divide-by-zero errors (singularities). So it's not a limit of the universe, exactly, but it is a limit to what we can know about the universe with our current theories.