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You can even theoretically make a black hole out of nothing but photons, though I don't think there's any plausible process that would ever put enough photons i
by thfuran 2y ago
You can even theoretically make a black hole out of nothing but photons, though I don't think there's any plausible process that would ever put enough photons in one place to form a kugelblitz.
- mitthrowaway2 2y agoIs there a theoretical reason that a sufficiently-gigantic ultrafast pulse laser with a sufficiently-massive lens couldn't put enough photons at the focal point?
- ben_w 2y agoIt's a practical constraint rather than a theoretical one. If your photons are 1 nm wavelength, you're making a black hole of at least 3.37e17 kg: http://www.wolframalpha.com/input/?i=0.5nm%20%2A%20c%5E2%20%2F%202G http://www.wolframalpha.com/input/?i=0.5nm%20%2A%20c%5E2%20%... Which is about 3e34 joules, or the total energy output of our sun over 2.5 years. The longer the wavelength, the more energy you need. You have to also make sure they're timed precisely enough to all be within the (target) horizon at the same time. IIRC there's also a quantum mechanical limit on energy density distributions (I have a lower confidence feeling that this is Heisenburg uncertainty?), but I don't know enough about it to get Wolfram Alpha to calculate it for me.
- mitthrowaway2 2y agoInteresting! I didn't have a good intuition for how rapidly the density of a black hole grows as its event horizon shrinks. Now I do! Clearly nano-black-holes are much, much heavier than I thought.
- hughesjj 2y agoPossibly during the big bang era?
- pixl97 2y agoDepends if primordial black holes are a thing or not and how early they formed if they are.