7 ms·

Here's what I understand of this, correct me if I'm wrong. If 1 kg of matter and 1 kg of antimatter annihilate each other, their entire mass is converted into

Here's what I understand of this, correct me if I'm wrong. If 1 kg of matter and 1 kg of antimatter annihilate each other, their entire mass is converted into photons, which are massless. If said photons are entirely absorbed by a black hole, the mass of the black hole will increase by 2 kg, and so will the gravitational pull of the black hole. In that case, wouldn't it be safe to assume that photons, even if they're massless, create a gravitational field equivalent to their energy level?

monocasa 2y ago
Yep https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
dustingetz 2y ago
iiuc the photons need to be confined (e.g. by a mirror box) for the box-photon system to exhibit mass greater than the sum of its constitutents
- mitthrowaway2 2y ago
  What better box is there than a black hole event horizon?
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.
- hughesjj 2y ago
  Possibly during the big bang era?
  - pixl97 2y ago
    Depends if primordial black holes are a thing or not and how early they formed if they are.
- mitthrowaway2 2y ago
  Is 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 ago
    It'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 ago
      Interesting! 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.
fsmv 2y ago
Einstein's equation includes all forms of energy not just rest mass. Photons have 0 rest mass not 0 energy.
zackmorris 2y ago
Yes, the effective mass of a photon is determined by E=mc^2 even though it has no mass, but it's sort of by definition because nothing with mass can reach the speed of light. Also anything moving at the speed of light doesn't perceive the passage of time, because from its perspective we're so time-dilated that the universe comes and goes in an instant as it crosses that expanse. So an argument could be made that only one photon exists, forming a frozen 4D crystal with the shape of every photon's path through the universe. A black hole's average density decreases by increasing radius. So theoretically a black hole could be formed from a gas like air, and in fact IRAS 20100-4156 with a mass of 3.8 billion suns and a diameter of about 10 billion km (according to the video below) has the same density as air: https://www.youtube.com/watch?v=71eUes30gwc https://www.youtube.com/watch?v=71eUes30gwc Also from the video, if we take the average density of the universe and consider it a uniformly distributed gas, we find that it fits within a black hole 10 times larger than the radius of the visible universe, which is 45 billion light years. So I believe that we're inside of a giant black hole and that the expansion of the universe is driven by Hawking radiation at the event horizon causing it to evaporate, which lowers the radius, which from our perspective looks like galaxies slipping away from us faster than the speed of light as they pass that velocity due to the Hubble constant multiplied by that distance. So technically a black hole could be created by just photons with a mass energy equivalence similar to air. It would be curious to see what the radius of a black hole filled with the cosmic background radiation would be, and how that correlates to the ~5 hydrogen atoms per cubic meter from the video. It wouldn't surprise me if they're equivalent or correlated so that the background radiation represents how much matter is inside the universe, not just its age since the Big Bang. In the first 4 minutes of this video, Neil deGrasse Tyson is worried about the end of the universe trillions of years from now, when the last galaxies have slipped outside the observable radius, so that future life will think that the Milky Way galaxy is the entire universe: https://www.youtube.com/watch?v=rFVdueuDD_o https://www.youtube.com/watch?v=rFVdueuDD_o But I think that the inward rush of the universe's event horizon will continue forever and that even our galaxy won't be spared, even though right now it looks gravitationally bound. Eventually everything will be pulled apart in a big pop as even the force between nucleons won't be enough to resist Hawking radiation within a small enough black hole. Also the universal black hole will catch up to the Sagittarius A* supermassive black hole at the center of our galaxy, pulling even it apart. So eventually everything pops back out into the surrounding universe. So probably the universe can be thought of as perhaps an infinitely wide nested swiss cheese of black holes. There may be one principle formula that states how that shape comes from quantum mechanics where the long tail of probabilities leads to energy and particles arising (I'm speculating since my studies didn't take me that far), or maybe the physics of the child black holes can vary from their parent universes because they're separated by an event horizon so that our universe evolved physics favorable for life to observe its own existence. Which takes us back to the Anthropic Principle which doesn't really tell us much. TMI I realize, but hey, it's Sunday. - Edit: I forgot to add why I was writing this. At large scales, the universe forms bubbles with matter along the surfaces where they meet, and large voids in between. Which suggests that something caused matter to be attracted to those boundaries. I wonder if this is similar to how something like dark matter causes galaxies to rotate faster than they should for how much mass is at their perimeters. It suggests that space is moving there without having an attractor. As if space itself can acquire momentum without mass. This is sort of how space looks to us as it flows into Earth, causing us to perceive an accelerating reference frame which we feel as gravity. If the ground disappeared and we began falling, then we would no longer perceive gravity or its associated time dilation (except from tidal forces as we approach the center). Which suggests that someone falling into a black hole would remain weightless and stay synchronized with our frame of reference, even as they passed the speed of light from our reference frame and appeared close to frozen to us. So it might be possible to travel from outer to inner black hole. Although the speed of expansion by Hawking is so large that probably the falling observer would become suspended at the equilibrium point where expansion matches inward acceleration. So in a very real way, the amount of space within a black hole could be much larger than its apparent radius from our frame of reference. Giving some credibility to the idea that child universes exist within black holes. Also I don't know if there is a gravitational lens effect on photons arriving to us as they cross the heavier space at the edge of galaxies: A) If there is, then the mass exists there in the form of dark matter, neutrinos, WIMPs, etc. B) If there isn't, then space appears to be moving without an attractor, meaning that something like a Hubble constant might be missing from our relativity equations or work something like MOND, or that sci fi stuff like warp drives might be possible. I like to think that our universe evolved the conditions for sci fi, and that stuff like dark matter is a wink to us so we can figure out how to do it through something like electrogravitics.
ars 2y ago
People really need to stop writing that gravity is caused by mass!!! Gravity is caused by energy of which mass is just one form. And note this includes relativistic mass (which is just energy)!
xhrpost 2y ago
https://physics.stackexchange.com/questions/22876/does-a-photon-exert-a-gravitational-pull https://physics.stackexchange.com/questions/22876/does-a-pho...
yoav 2y ago
So the speed of light is really “the fastest the universe can fold on a crease in the direction of the trajectory of a photon”

monocasa 2y ago

Yep https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)

dustingetz 2y ago

iiuc the photons need to be confined (e.g. by a mirror box) for the box-photon system to exhibit mass greater than the sum of its constitutents

mitthrowaway2 2y ago
What better box is there than a black hole event horizon?

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.

hughesjj 2y ago
Possibly during the big bang era?
- pixl97 2y ago
  Depends if primordial black holes are a thing or not and how early they formed if they are.
mitthrowaway2 2y ago
Is 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 ago
  It'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 ago
    Interesting! 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.

fsmv 2y ago

Einstein's equation includes all forms of energy not just rest mass. Photons have 0 rest mass not 0 energy.

zackmorris 2y ago

Yes, the effective mass of a photon is determined by E=mc^2 even though it has no mass, but it's sort of by definition because nothing with mass can reach the speed of light. Also anything moving at the speed of light doesn't perceive the passage of time, because from its perspective we're so time-dilated that the universe comes and goes in an instant as it crosses that expanse. So an argument could be made that only one photon exists, forming a frozen 4D crystal with the shape of every photon's path through the universe. A black hole's average density decreases by increasing radius. So theoretically a black hole could be formed from a gas like air, and in fact IRAS 20100-4156 with a mass of 3.8 billion suns and a diameter of about 10 billion km (according to the video below) has the same density as air: https://www.youtube.com/watch?v=71eUes30gwc https://www.youtube.com/watch?v=71eUes30gwc Also from the video, if we take the average density of the universe and consider it a uniformly distributed gas, we find that it fits within a black hole 10 times larger than the radius of the visible universe, which is 45 billion light years. So I believe that we're inside of a giant black hole and that the expansion of the universe is driven by Hawking radiation at the event horizon causing it to evaporate, which lowers the radius, which from our perspective looks like galaxies slipping away from us faster than the speed of light as they pass that velocity due to the Hubble constant multiplied by that distance. So technically a black hole could be created by just photons with a mass energy equivalence similar to air. It would be curious to see what the radius of a black hole filled with the cosmic background radiation would be, and how that correlates to the ~5 hydrogen atoms per cubic meter from the video. It wouldn't surprise me if they're equivalent or correlated so that the background radiation represents how much matter is inside the universe, not just its age since the Big Bang. In the first 4 minutes of this video, Neil deGrasse Tyson is worried about the end of the universe trillions of years from now, when the last galaxies have slipped outside the observable radius, so that future life will think that the Milky Way galaxy is the entire universe: https://www.youtube.com/watch?v=rFVdueuDD_o https://www.youtube.com/watch?v=rFVdueuDD_o But I think that the inward rush of the universe's event horizon will continue forever and that even our galaxy won't be spared, even though right now it looks gravitationally bound. Eventually everything will be pulled apart in a big pop as even the force between nucleons won't be enough to resist Hawking radiation within a small enough black hole. Also the universal black hole will catch up to the Sagittarius A* supermassive black hole at the center of our galaxy, pulling even it apart. So eventually everything pops back out into the surrounding universe. So probably the universe can be thought of as perhaps an infinitely wide nested swiss cheese of black holes. There may be one principle formula that states how that shape comes from quantum mechanics where the long tail of probabilities leads to energy and particles arising (I'm speculating since my studies didn't take me that far), or maybe the physics of the child black holes can vary from their parent universes because they're separated by an event horizon so that our universe evolved physics favorable for life to observe its own existence. Which takes us back to the Anthropic Principle which doesn't really tell us much. TMI I realize, but hey, it's Sunday. - Edit: I forgot to add why I was writing this. At large scales, the universe forms bubbles with matter along the surfaces where they meet, and large voids in between. Which suggests that something caused matter to be attracted to those boundaries. I wonder if this is similar to how something like dark matter causes galaxies to rotate faster than they should for how much mass is at their perimeters. It suggests that space is moving there without having an attractor. As if space itself can acquire momentum without mass. This is sort of how space looks to us as it flows into Earth, causing us to perceive an accelerating reference frame which we feel as gravity. If the ground disappeared and we began falling, then we would no longer perceive gravity or its associated time dilation (except from tidal forces as we approach the center). Which suggests that someone falling into a black hole would remain weightless and stay synchronized with our frame of reference, even as they passed the speed of light from our reference frame and appeared close to frozen to us. So it might be possible to travel from outer to inner black hole. Although the speed of expansion by Hawking is so large that probably the falling observer would become suspended at the equilibrium point where expansion matches inward acceleration. So in a very real way, the amount of space within a black hole could be much larger than its apparent radius from our frame of reference. Giving some credibility to the idea that child universes exist within black holes. Also I don't know if there is a gravitational lens effect on photons arriving to us as they cross the heavier space at the edge of galaxies: A) If there is, then the mass exists there in the form of dark matter, neutrinos, WIMPs, etc. B) If there isn't, then space appears to be moving without an attractor, meaning that something like a Hubble constant might be missing from our relativity equations or work something like MOND, or that sci fi stuff like warp drives might be possible. I like to think that our universe evolved the conditions for sci fi, and that stuff like dark matter is a wink to us so we can figure out how to do it through something like electrogravitics.

ars 2y ago

People really need to stop writing that gravity is caused by mass!!! Gravity is caused by energy of which mass is just one form. And note this includes relativistic mass (which is just energy)!

xhrpost 2y ago

https://physics.stackexchange.com/questions/22876/does-a-photon-exert-a-gravitational-pull https://physics.stackexchange.com/questions/22876/does-a-pho...

yoav 2y ago

So the speed of light is really “the fastest the universe can fold on a crease in the direction of the trajectory of a photon”