There are probably no natural antistars, for example.
And if there are, we don’t know how to identify them from far away, do we?
BTW, can there be antimatter black holes? My limited understanding of physics is that matter/antimatter falling into a black hole passes the event horizon before it can interact with anything that fell into the hole in the past; and once it passes the event horizon, even if it mutually annihilates with something already in the black hole, the results can’t escape outside. So from the outside there’s no difference between matter, antimatter, and mixed black holes.
So from the outside there’s no difference between matter, antimatter, and mixed black holes.
I saw this and immediately thought of the no hair theorem, which says that the only distinguishing (reference frame-independent) characteristics of black holes are their mass, their charge and their angular momentum. Turns out that Wikipedia uses matter v. antimatter black holes as an example of the theorem’s implications!
Suppose two black holes have the same masses, electrical charges, and angular momenta, but the first black hole is made out of ordinary matter whereas the second is made out of antimatter, then they will be completely indistinguishable to an observer outside the event horizon.
So if I find a natural antimatter star, and I’m afraid someone will use it as a weapon, the safest thing to do is to throw it into a black hole.
Suppose two black holes have the same masses, electrical charges, and angular momenta, but the first black hole is made out of ordinary matter whereas the second is made out of antimatter, then they will be completely indistinguishable to an observer outside the event horizon.
In other words, even if we collide a matter black hole and an antimatter black hole, we won’t see any evidence of mutual annihilation—we’ll just get a double-size black hole. Cool.
So if I find a natural antimatter star, and I’m afraid someone will use it as a weapon, the safest thing to do is to throw it into a black hole.
I’m sorry if I’m explaining the joke, but the rule of thumb is that this only saves you an order of magnitude of violence; 10% of the mass is released as radiation.
In fact, “throw it into a black hole” seems like a better answer to Liron’s question than “collide it with equally much antimatter.” It’s not as efficient, but it’s a lot easier to find black holes than antimatter. It may be easier in the annihilation case to actually use the energy, but I’m not sure.
So if I find a natural antimatter star, and I’m afraid someone will use it as a weapon, the safest thing to do is to throw it into a black hole.
I’m sorry if I’m explaining the joke, but the rule of thumb is that this only saves you an order of magnitude of violence; 10% of the mass is released as radiation.
In fact, “throw it into a black hole” seems like a better answer to Liron’s question than “collide it with equally much antimatter.” It’s not as efficient, but it’s a lot easier to find black holes than antimatter. It may be easier in the annihilation case to actually use the energy, but I’m not sure.
So if I find a natural antimatter star, and I’m afraid someone will use it as a weapon, the safest thing to do is to throw it into a black hole.
If an antimatter star (of one solar mass) was thrown at a matter star how far away would they need to be for the ecosystem on earth not to be seriously damaged?
If throwing antimatter stars around is difficult we may be able to resort to playing ‘asteroids’. That is, throw actual asteroids at it, resulting in smaller blasts of annhialiation and probably in the star being fragmented, allowing further asteroids to finish the clean up process.
That is, throw actual asteroids at it, resulting in smaller blasts of annhialiation and probably in the star being fragmented, allowing further asteroids to finish the clean up process.
Wouldn’t we need asteroids of total mass comparable to the anti-star? Where would you we enough? Any planets or asteroid belts around that star would be antimatter too, almost certainly.
Wouldn’t we need asteroids of total mass comparable to the anti-star? Where would you we enough? Any planets or asteroid belts around that star would be antimatter too, almost certainly.
Yes, you would need that much matter to be annihilated. But finding one system’s worth of mass is a (relatively) trivial part of the problem. It is a whole order of plausibility easier than trying to throw an antimatter star into a black hole. Taking apart the nearby systems and throwing the planets and asteriods at the offending star is just an engineering problem once you have that sort of tech. I could probably do it myself if you gave me 30,000 years to work out the finer details. You either push on the asteroid while standing on something bigger or you launch tiny things off the asteroid at large fractions of the speed of light in a suitable direction.
Throwing a whole antimatter star into a suitable black hole? I can’t even do that one in principle (within 2 minutes of thought). Apart from being really big and too hot to put propulsion devices on… it’s made out of F@#% antimatter. The obvious options for accelerating it are gravity and photons, neither of which care about the ‘matter/antimatter’ distinction. If you have enough gravity hanging about in the vicinity then the star is probably already falling into the black hole. And if you are planning on pushing a star about using only photons.… well, you may end up using more than just one star worth of matter to pull that off.
Then there is the problem of finding a suitably large black hole to throw it at. They tend to have stuff in their orbit (often the rest of the galaxy). Navigating an antimatter star to the black hole without it annihilating itself of the way there would be tricky. It isn’t easy to steer these things.
What may be easier is to dedicate a year or two run time on a Jupiter Brain to work out just the right size rock to throw at just the right time at just the right place. The resulting explosion would be chosen to knock the star in the right direction, or in the right pieces in the right directions, or whatever it is that antimatter stars do when you throw rocks at them. Then most of the destruction would be from it hitting the other stars that you aimed for. You would dispose of the weapon by triggering it in a controlled manner.
I saw this and immediately thought of the no hair theorem, which says that the only distinguishing (reference frame-independent) characteristics of black holes are their mass, their charge and their angular momentum.
Wait… black holes keep their electrical charge? As in… if I shoot enough electrons at a black hole it will start to repel any negatively charged matter rather than attract it? No, that’d allow me to scout out information past the event horizon. Hmmm...
… Apparently charged black holes have two horizons, an event horizon and a Chauchy horizon. But I am still not sure what would happen in the case of a constant stream of electrons. Could someone with physics knowledge fill me in? What does happen when the black hole reaches a critical charge?
two different black holes I can make them actually repel each other rather than attract? Hmmm. And reject No, that lets me get information
As in… if I shoot enough electrons at a black hole it will start to repel any negatively charged matter rather than attract it? No, that’d allow me to scout out information past the event horizon.
(Disclaimer: I’m not a physicist, so this may be BS.) This might not be a problem. If a black hole repels negative charges, all that tells you is the black hole’s position and net charge, and AFAIK that kind of information is allowed to ‘escape’ the black hole: position is OK because that’s frame-dependent, and the no-hair theorem says it’s OK to know the net charge.
If a black hole can be charged sufficiently that it repels an electron rather than attracts via gravity then:
There will be a point at which the gravity is perfectly balanced by the repulsion of the negative charges.
Just after that point there there will be a point where the electron is subject to a slight acceleration away from the center of the black hole.
If I shoot an electron at a suitable speed at such a black hole the electron will slow down and reverse in direction at a point determined by the initial speed and the acceleration. This point could be below the event horizon.
If such an election hit something inside the event horizon it would not return to me.
This tells me something about things inside the event horizon.
The teacher says I am not allowed to discover things about the inside of the event horizon.
Something in the above scenario must not be right.
I think you will find that the charge repulsion never exceeds the gravitational attraction in this way. The mass of a black hole places a bound on how much charge it can have; if the bound is exceeded, you get a naked singularity. You may actually be rediscovering this!
ETA: The two horizons you mentioned earlier merge when this bound is reached. I suppose this means that if you try to shoot a charge into one of these “extremal” black holes, the charge will be repelled outside the event horizon. That would be a consistent way for everything to work out, so that the bound can never be violated. But I will have to check.
I suppose this means that if you try to shoot a charge into one of these “extremal” black holes, the charge will be repelled outside the event horizon.
You could be right, but how? I inject enough electrons into the black hole to maintain it at as high a charge as possible. Then I launch more electrons from a platform that is doing a slighshot pass right by the event horizon. And I dedicate the energy from a nearby star to shooting photons at it to force the extra particles in...
And even forgetting extreme options. Just why? If the black hole is not charged to a level that will repel electrons it will attract them. Add more and they will just hover there without accelerating. Add more still and they will be repelled. This works unless weird math comes in to play.
Red suggests discharge via Hawking radiation. I would not be able to rule out some sort of asymptotic increase in Hawking Radiation discharge toward my electron input rate. (Basically because I don’t know how Hawking Radiation works.)
I had never heard the term before but that is just where my thoughts were leading me.
Looking a bit more closely it would seem that ‘strong’ forces would ensure there is always at least a tiny horizon at which even electrons couldn’t escape no matter what the charge. (And if there wasn’t the thing would fall apart). It just doesn’t matter how big you make the charge. ‘Squared’ just doesn’t cut it. So while the electrons would return from where even photons could not escape they would still get stuck if they went deep enough. But I don’t know where things like strong forces start to break down...
And if there are, we don’t know how to identify them from far away, do we?
Yes. Not from the star itself but rather by the interstellar dust (hydrogen atoms floating about, etc). We would detect emissions from interactions at the boundary between ‘mostly empty but with bits of matter’ and ‘mostly empty but with bits of antimatter’.
And if there are, we don’t know how to identify them from far away, do we?
BTW, can there be antimatter black holes? My limited understanding of physics is that matter/antimatter falling into a black hole passes the event horizon before it can interact with anything that fell into the hole in the past; and once it passes the event horizon, even if it mutually annihilates with something already in the black hole, the results can’t escape outside. So from the outside there’s no difference between matter, antimatter, and mixed black holes.
I saw this and immediately thought of the no hair theorem, which says that the only distinguishing (reference frame-independent) characteristics of black holes are their mass, their charge and their angular momentum. Turns out that Wikipedia uses matter v. antimatter black holes as an example of the theorem’s implications!
So if I find a natural antimatter star, and I’m afraid someone will use it as a weapon, the safest thing to do is to throw it into a black hole.
In other words, even if we collide a matter black hole and an antimatter black hole, we won’t see any evidence of mutual annihilation—we’ll just get a double-size black hole. Cool.
I’m sorry if I’m explaining the joke, but the rule of thumb is that this only saves you an order of magnitude of violence; 10% of the mass is released as radiation.
In fact, “throw it into a black hole” seems like a better answer to Liron’s question than “collide it with equally much antimatter.” It’s not as efficient, but it’s a lot easier to find black holes than antimatter. It may be easier in the annihilation case to actually use the energy, but I’m not sure.
Probably. If nothing else, for a given amount of energy released you will probably be able to stand closer to collect it in the antimatter case.
I’m sorry if I’m explaining the joke, but the rule of thumb is that this only saves you an order of magnitude of violence; 10% of the mass is released as radiation.
In fact, “throw it into a black hole” seems like a better answer to Liron’s question than “collide it with equally much antimatter.” It’s not as efficient, but it’s a lot easier to find black holes than antimatter. It may be easier in the annihilation case to actually use the energy, but I’m not sure.
If an antimatter star (of one solar mass) was thrown at a matter star how far away would they need to be for the ecosystem on earth not to be seriously damaged?
If throwing antimatter stars around is difficult we may be able to resort to playing ‘asteroids’. That is, throw actual asteroids at it, resulting in smaller blasts of annhialiation and probably in the star being fragmented, allowing further asteroids to finish the clean up process.
Wouldn’t we need asteroids of total mass comparable to the anti-star? Where would you we enough? Any planets or asteroid belts around that star would be antimatter too, almost certainly.
Yes, you would need that much matter to be annihilated. But finding one system’s worth of mass is a (relatively) trivial part of the problem. It is a whole order of plausibility easier than trying to throw an antimatter star into a black hole. Taking apart the nearby systems and throwing the planets and asteriods at the offending star is just an engineering problem once you have that sort of tech. I could probably do it myself if you gave me 30,000 years to work out the finer details. You either push on the asteroid while standing on something bigger or you launch tiny things off the asteroid at large fractions of the speed of light in a suitable direction.
Throwing a whole antimatter star into a suitable black hole? I can’t even do that one in principle (within 2 minutes of thought). Apart from being really big and too hot to put propulsion devices on… it’s made out of F@#% antimatter. The obvious options for accelerating it are gravity and photons, neither of which care about the ‘matter/antimatter’ distinction. If you have enough gravity hanging about in the vicinity then the star is probably already falling into the black hole. And if you are planning on pushing a star about using only photons.… well, you may end up using more than just one star worth of matter to pull that off.
Then there is the problem of finding a suitably large black hole to throw it at. They tend to have stuff in their orbit (often the rest of the galaxy). Navigating an antimatter star to the black hole without it annihilating itself of the way there would be tricky. It isn’t easy to steer these things.
What may be easier is to dedicate a year or two run time on a Jupiter Brain to work out just the right size rock to throw at just the right time at just the right place. The resulting explosion would be chosen to knock the star in the right direction, or in the right pieces in the right directions, or whatever it is that antimatter stars do when you throw rocks at them. Then most of the destruction would be from it hitting the other stars that you aimed for. You would dispose of the weapon by triggering it in a controlled manner.
Wait… black holes keep their electrical charge? As in… if I shoot enough electrons at a black hole it will start to repel any negatively charged matter rather than attract it? No, that’d allow me to scout out information past the event horizon. Hmmm...
… Apparently charged black holes have two horizons, an event horizon and a Chauchy horizon. But I am still not sure what would happen in the case of a constant stream of electrons. Could someone with physics knowledge fill me in? What does happen when the black hole reaches a critical charge?
two different black holes I can make them actually repel each other rather than attract? Hmmm. And reject No, that lets me get information
(Disclaimer: I’m not a physicist, so this may be BS.) This might not be a problem. If a black hole repels negative charges, all that tells you is the black hole’s position and net charge, and AFAIK that kind of information is allowed to ‘escape’ the black hole: position is OK because that’s frame-dependent, and the no-hair theorem says it’s OK to know the net charge.
I am just speaking BS too but:
If a black hole can be charged sufficiently that it repels an electron rather than attracts via gravity then:
There will be a point at which the gravity is perfectly balanced by the repulsion of the negative charges.
Just after that point there there will be a point where the electron is subject to a slight acceleration away from the center of the black hole.
If I shoot an electron at a suitable speed at such a black hole the electron will slow down and reverse in direction at a point determined by the initial speed and the acceleration. This point could be below the event horizon.
If such an election hit something inside the event horizon it would not return to me.
This tells me something about things inside the event horizon.
The teacher says I am not allowed to discover things about the inside of the event horizon.
Something in the above scenario must not be right.
I think you will find that the charge repulsion never exceeds the gravitational attraction in this way. The mass of a black hole places a bound on how much charge it can have; if the bound is exceeded, you get a naked singularity. You may actually be rediscovering this!
ETA: The two horizons you mentioned earlier merge when this bound is reached. I suppose this means that if you try to shoot a charge into one of these “extremal” black holes, the charge will be repelled outside the event horizon. That would be a consistent way for everything to work out, so that the bound can never be violated. But I will have to check.
You could be right, but how? I inject enough electrons into the black hole to maintain it at as high a charge as possible. Then I launch more electrons from a platform that is doing a slighshot pass right by the event horizon. And I dedicate the energy from a nearby star to shooting photons at it to force the extra particles in...
And even forgetting extreme options. Just why? If the black hole is not charged to a level that will repel electrons it will attract them. Add more and they will just hover there without accelerating. Add more still and they will be repelled. This works unless weird math comes in to play.
Red suggests discharge via Hawking radiation. I would not be able to rule out some sort of asymptotic increase in Hawking Radiation discharge toward my electron input rate. (Basically because I don’t know how Hawking Radiation works.)
I had never heard the term before but that is just where my thoughts were leading me.
Looking a bit more closely it would seem that ‘strong’ forces would ensure there is always at least a tiny horizon at which even electrons couldn’t escape no matter what the charge. (And if there wasn’t the thing would fall apart). It just doesn’t matter how big you make the charge. ‘Squared’ just doesn’t cut it. So while the electrons would return from where even photons could not escape they would still get stuck if they went deep enough. But I don’t know where things like strong forces start to break down...
BTW, it seems that charged black hole will discharge via Hawking radiation.
Yes. Not from the star itself but rather by the interstellar dust (hydrogen atoms floating about, etc). We would detect emissions from interactions at the boundary between ‘mostly empty but with bits of matter’ and ‘mostly empty but with bits of antimatter’.