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What if antimatter, for some reason, clumped together more easily (weaker electric repulsion?). Wouldn't that cause more "anti-black holes" to form during the e

What if antimatter, for some reason, clumped together more easily (weaker electric repulsion?). Wouldn't that cause more "anti-black holes" to form during the early period of the universe, explaining both matter/antimatter imbalance and part of the dark matter in the process? And now I wonder the same as holler: firstly, can you differentiate a black hole made of matter from one made of antimatter? The resulting energy couldn't leave it, AFAIK? Secondly, if there is any difference, what would happen to Earth in case of a collision?

jdmichal 6y ago
I think being able to tell the difference would have to be answered by solving the information loss problem. Because otherwise, every property is either dependent on or constrained only by the mass. And yes, even if they were antimatter black holes eating matter, it wouldn't matter because all the energy from the resulting annihilation would just stay in the black hole and due to mass-energy equivalence nothing would be different to the outside observer.
- Aerroon 6y ago
  Couldn't the accretion disk of a black hole give us a clue though? Likely not all of the material would've been beyond the event horizon. Some of it would've stayed outside of it in the accretion disk. It's likely that the antimatter that stayed out would at some point interact with the regular matter that falls towards the black hole, but even that might give us a clue based on how energetic the accretion disk is (how much it radiates for example). But I'm just guessing here.
  - MayeulC 6y ago
    Well, probably not if we consider primordial black holes? Those can be quite light, and may have "cleared their orbit" a long time ago.
Aerroon 6y ago
I'm interested in antimatter too. There should be a lot of antimatter out there, but we can't seem to find it. It's possible that antimatter does interact gravitationally at a smaller magnitude with matter and/or other antimatter. As far as I know, we haven't even experimentally confirmed whether antimatter has the same sign for gravitational effects as regular matter (ie whether it's repulsive or attractive), but it seems very likely that it's the same as regular matter. The magnitude could be different though.
- frob 6y ago
  Keep an eye on ALPHA at CERN. It is designed to answer this exact question by producing anti-hydrogen atoms. https://home.cern/news/news/physics/alpha-collaboration-cern-reports-first-measurements-certain-quantum-effects https://home.cern/news/news/physics/alpha-collaboration-cern.... Their initial results a few years back were consistent with matter and antimatter acting the same under gravity, but their error bars were large enough to warrant a more precise measurement, which they're up to now.
  - Aerroon 6y ago
    Thank you. I had read about their previous experiment but didn't know about what was going on now.
yummypaint 6y ago
I have also wondered about these kinds of large scale local asymmetries. I.e. "how do we know distant galaxies aren't made of antimatter?" There is a paper by prokhorov published in physical review D in 2015 which was able to set some limits based on signatures of proton-antiproton annihilation. They claim no such asymmetries over a 20 megaparsec distance scale.
- vagab0nd 6y ago
  > "how do we know distant galaxies aren't made of antimatter?" I'm not an expert, but isn't that because we don't observe gamma rays from matter-antimatter annihilation in between the galaxies?
hhjinks 6y ago
Would an antimatter black hole shrink when absorbing regular matter, or is the mass of the photons from the annihilation process the same as the mass of the annihilated particles? How would that work? Would annihilation even happen under such extreme conditions?
- hpoe 6y ago
  When anti-matter enters a black hole it shrinks the mass of the black hole. This is how blackholes emit Hawking radiation.
  - bashinator 6y ago
    You're confusing antimatter with virtual particle pairs.
- marcosdumay 6y ago
  Matter annihilation conserves the energy (and as consequence, the mass) of the particles that were destroyed.
- kadoban 6y ago
  Adding antimatter to a matter black hole (don't think it matters actually, but this seems to be the case in question) should increase the mass and size, not decrease. Correct, the photons produced from annihilation should match the inputs. To decrease you'd need to add negative mass or negative energy, which aren't things we've found to exist yet. We don't actually know _what_ will happen in the singularity of a black hole, to answer the question of if annihilation will happen there. As far as I know we don't have any model of what happens in a singularity.
pavel_lishin 6y ago
> can you differentiate a black hole made of matter from one made of antimatter? Not as far as I'm aware. A black hole is defined solely by its mass, charge and spin. What goes into it becomes irrelevant once it crosses the event horizon, except for those three factors. (Though one does wonder, what happens if an object with negative mass enters a blackhole? But negative mass may not even exist.) > Secondly, if there is any difference, what would happen to Earth in case of a collision? None in practical terms.
- marcosdumay 6y ago
  AFAIK (but I'm no physicist), a black hole has a quantum number of every single kind predicted by the Standard Model. So they'll have a baryonic number that can be zero or negative just as well as positive.

jdmichal 6y ago

I think being able to tell the difference would have to be answered by solving the information loss problem. Because otherwise, every property is either dependent on or constrained only by the mass. And yes, even if they were antimatter black holes eating matter, it wouldn't matter because all the energy from the resulting annihilation would just stay in the black hole and due to mass-energy equivalence nothing would be different to the outside observer.

Aerroon 6y ago
Couldn't the accretion disk of a black hole give us a clue though? Likely not all of the material would've been beyond the event horizon. Some of it would've stayed outside of it in the accretion disk. It's likely that the antimatter that stayed out would at some point interact with the regular matter that falls towards the black hole, but even that might give us a clue based on how energetic the accretion disk is (how much it radiates for example). But I'm just guessing here.
- MayeulC 6y ago
  Well, probably not if we consider primordial black holes? Those can be quite light, and may have "cleared their orbit" a long time ago.

Aerroon 6y ago

I'm interested in antimatter too. There should be a lot of antimatter out there, but we can't seem to find it. It's possible that antimatter does interact gravitationally at a smaller magnitude with matter and/or other antimatter. As far as I know, we haven't even experimentally confirmed whether antimatter has the same sign for gravitational effects as regular matter (ie whether it's repulsive or attractive), but it seems very likely that it's the same as regular matter. The magnitude could be different though.

frob 6y ago
Keep an eye on ALPHA at CERN. It is designed to answer this exact question by producing anti-hydrogen atoms. https://home.cern/news/news/physics/alpha-collaboration-cern-reports-first-measurements-certain-quantum-effects https://home.cern/news/news/physics/alpha-collaboration-cern.... Their initial results a few years back were consistent with matter and antimatter acting the same under gravity, but their error bars were large enough to warrant a more precise measurement, which they're up to now.
- Aerroon 6y ago
  Thank you. I had read about their previous experiment but didn't know about what was going on now.

yummypaint 6y ago

I have also wondered about these kinds of large scale local asymmetries. I.e. "how do we know distant galaxies aren't made of antimatter?" There is a paper by prokhorov published in physical review D in 2015 which was able to set some limits based on signatures of proton-antiproton annihilation. They claim no such asymmetries over a 20 megaparsec distance scale.

vagab0nd 6y ago
> "how do we know distant galaxies aren't made of antimatter?" I'm not an expert, but isn't that because we don't observe gamma rays from matter-antimatter annihilation in between the galaxies?

hhjinks 6y ago

Would an antimatter black hole shrink when absorbing regular matter, or is the mass of the photons from the annihilation process the same as the mass of the annihilated particles? How would that work? Would annihilation even happen under such extreme conditions?

hpoe 6y ago
When anti-matter enters a black hole it shrinks the mass of the black hole. This is how blackholes emit Hawking radiation.
- bashinator 6y ago
  You're confusing antimatter with virtual particle pairs.
marcosdumay 6y ago
Matter annihilation conserves the energy (and as consequence, the mass) of the particles that were destroyed.
kadoban 6y ago
Adding antimatter to a matter black hole (don't think it matters actually, but this seems to be the case in question) should increase the mass and size, not decrease. Correct, the photons produced from annihilation should match the inputs. To decrease you'd need to add negative mass or negative energy, which aren't things we've found to exist yet. We don't actually know _what_ will happen in the singularity of a black hole, to answer the question of if annihilation will happen there. As far as I know we don't have any model of what happens in a singularity.

pavel_lishin 6y ago

> can you differentiate a black hole made of matter from one made of antimatter? Not as far as I'm aware. A black hole is defined solely by its mass, charge and spin. What goes into it becomes irrelevant once it crosses the event horizon, except for those three factors. (Though one does wonder, what happens if an object with negative mass enters a blackhole? But negative mass may not even exist.) > Secondly, if there is any difference, what would happen to Earth in case of a collision? None in practical terms.

marcosdumay 6y ago
AFAIK (but I'm no physicist), a black hole has a quantum number of every single kind predicted by the Standard Model. So they'll have a baryonic number that can be zero or negative just as well as positive.