Very futuristic and esoteric energy sources

There are problems with the word "already", which appears to assume a global clock and an event horizon that can be shown to exist at some finite time (to a remote observer). My claim is that at all times, to a remote observer, all matter (and energy) appears to be behaving according to general relativity without any event horizon. This is a substantial generalisation from facts about what happens as matter approaches an event horizon.  My physical and mathematical intuition says it is highly plausible, but this is open to attempts at disproof by calculation.

Black hole physics is a bit strange..., if we have to say that the event horizon doesn't actually exist from our perspective...  Do you think its possible that some black holes be composed of antimatter?  Would that change anything as we see it, or would it still behave the same from our view?

The only reason that there may not be any black holes made of antimatter is that our universe appears to have very little antimatter in it, and probably no quantities large enough to form a black hole. If a forming black hole made of antimatter did exist, it would appear very like an ordinary forming black hole unless some matter came into contact with the antimatter, when obviously there would be annihilation and a violent explosion with a lot of gamma rays being produced.

I would like to see what would happen if an antimatter blackhole and a normal black hole did the dance of death!

Elroch, can you give us some calculations on that?

Just use E=mc^2 and you'll get the big picture.

Or if you want a detailed simulation of what happens when two very dense objects made of matter and antimatter collide, a supercomputer and some fancy software will be needed. This sort of thing has been done for colliding galaxies made of matter with big black holes at their centres.

Hehe.. I tried doing a simulation of the scenario but all MATLAB came up with was a warning that said:

"Gone fishing"

And Maple ... well, Maple was just plain rude!

Maybe Octave well accomodate me..

I added a link to a nice simulation to my last post.

Hey, I'm impressed by all the math engines. I enjoyed using Mathematica in the distant past, but recall finding Matlab more useful for the things I actually needed to do. Also reminds me of the more distant past (over 25 years) when I tried to simulate the solar system on my Sinclair spectrum (with 16 bit integer arithmetic -lol). Taught me how how small errors add up very quickly!

Found a superb video on large black holes. Highly recommended.

I enjoyed the link about the large black holes, 18 billion solar masses... thats a lot.  One thing though, around the 13th minute, they said something about the black hole's weight.  If I know what I'm talking about this time, isn't weight a force, and mass would be the more appropriate term?  Other than that, the images were really nice, and its interesting to know why matter shoots out of two sides of a black hole in a beam.

 But how exactly do we know that matter outnumbers anti-matter in the universe?  Is it possible to know that Andromeda is made of matter and not antimatter?  All we get from neighboring galaxies is light, and the anti-particle of a photon is itself.

Also, it just occurred to me -- in a black hole, theoretically, everything gets torn up and destroyed, down to the quarks and further.  Since the only difference between antimatter and matter is spin, if everything is torn apart, that would mean there's no more spin.  So, would that mean there is no such thing as matter and anti-matter when considering a black hole?  Then we'd need to rethink Hawking radiation, but it's possible that black holes are just lots and lots of mass, right?

Great questions!

Yes, you are right about the weight. A careless error by the script writer.

The argument against antimatter galaxies is that if there were substantial amounts of antimatter in the universe at some place there would have to be a boundary somewhere between a region of antimatter and a region of matter where they would come into contact. Even if this was very tenuous (say an atom per cubic metre), it would produce an powerful gamma ray signal for a long time. No such signal has ever been seen. Hence there is not much antimatter around.

Actually the laws of physics are not the same for antimatter as for matter (it's not just about opposite spin). There were some major discoveries in the 60s that surprised people by showing that the universe had a "handedness", which is linked to the direction of time. If you wanted to transform the laws of physics for matter to the laws of physics for antimatter, you would need to change the signs on charges, flip space through a mirror and then change the sign on time. This is called CPT symmetry. Feynman realised that antimatter behaves exactly like matter travelling backwards in time. Anyhow the net result is that physics in an antimatter galaxy would not be quite the same as in a matter galaxy. Specifically, the weak force would not be the same. This would affect the way stars would behave, as the weak interaction is vital to nuclear fusion. What the effects would be, and how it would affect the appearance of an antimatter star or galaxy, I don't know, but my guess is that the weak interaction is so important, they would be very different. Someone might be able to use this to tell a galaxy was made of matter.

The story about losing the properties of matter in a black hole has caused physicists some headaches. The standard view is that in the end, a black hole has nothing but mass, angular momentum and charge. So yes, it would "forget" if matter or antimatter had made it. This caused much unhappiness as it was not meant to happen. But they managed to find a way to fix it, but leaving a sort of ghost of the source material on the black hole. See a wikipedia article. I am not satisfied they have made the problem go away, but my eccentric view about black holes dodges the problem entirely, because there is no problem within finite time. [but need to check this is true from the point of view of someone falling in as well ...]

Elroch wrote:

Even if this was very tenuous (say an atom per cubic metre), it would produce an powerful gamma ray signal for a long time. No such signal has ever been seen. Hence there is not much antimatter around.

I think that you are misusing the rules of logic there .. =) .. A more correct expression would be that it is highly unlikely that much antimatter is around ..

Hmm. I agree. But you could probably argue about the phrasing of most scientific statements on similar grounds.

I have spotted a possible chink in my non-standard view of black holes. There is no problem in a classical world, but we live in a quantum world. The issue is that in quantum mechanics you have a wave function that is not localised - i.e. spread across space - in some formulations, or an infinite number of possible paths for a particle in other formulations. Could this influence the possibilities for a particle that remained outside of a black hole if the wave function went past the event horizon, but the particle did not fall in?

Actually with the path integral formulation, it would appear at first sight not, as if you knew a particle had started at A and ended at B (both outside a black hole), you could infer that it had never been to C (past the event horizon) because if it had it could not have got out again! This would be fine, except I am aware that Hawking came up with some surprising conclusions about what happens around the event horizon, so what is obvious may not be true.  But his ideas do not actually involve any information getting out of the black hole, just black body radiation from near the event horizon.

Would that be like quantum tunneling outside of a black hole?  The particle cloud goes past the event horizon, even from within the black hole, so it can find a way out of the black hole?  Or is it like we see a particle go from point A to B, its just that the cloud goes past the event horizon, and there is a probability that it was at point C, even if we didn't see it?  But once it's at point C (if it tunneled there), shouldn't the cloud also change location?  Could a particle cloud from point C reach point B?

Because the potential barrier to get out of the black hole is infinite, I infer there is zero chance of tunnelling out.

By "particle cloud" do you mean the spread out wave function? Having asked this, I realise this may be an unfair question, as it requires a course in Schroedinger's formulation of quantum mechanics to make sense.

Given the inadequacy of my answer about why people strongly believe almost everything in the universe is made of matter, I was pleased to find a thesis on this very topic:

How do we know antimatter is absent?

I'll take the unusual step of replying to my own earlier post, as I realised when I was reading about this stuff later that it was an incorrect generalisation. It is true that the simplest type of black hole (spherically symmetric and non-rotating) emits no gravitational waves. I think this is also true for larger class of nice symmetric black holes. But in other cases this is not true. People have studied what happens when two black holes collide and coalesce, and in this case a lot of energy is emitted as gravitational waves.

"all of space jiggles like a bowl of Jell-O as gravitational waves race out from the collision at light speed. "

That's an interesting quote...

So a gravitational wave is a fluctuation in the strength of gravity?

"These mergers are by far the most powerful events occurring in the universe, with each one generating more energy than all of the stars in the universe combined.

Wouldn't that mean that if two black holes merged, then they'd lose a lot of (more than half) of their original mass upon becoming one?

By "particle cloud" do you mean the spread out wave function?

I think so -- the particle cloud is the locus of places where the particle could possibly be "now".

I think a reasonable analogy to a gravitational wave is to a physical one. If space is like a smooth water surface and a wave passes across that surface, then it becomes temporarily distorted, in a way which distorts the usual geometry and temporarily distorts distances and things on the surface are perturbed as the wave passes. People are trying to measure tiny changes in distances due to gravitational waves (less than a proton width). You can find loose analogies to non-rotating and rotating black holes as well, if you like. This analogy is loose, because space and time are separate, whereas they are not in relativity.

Oops. Was just thinking that I said "negative mass was fictional", a long way back. While this is true for all real particles, it is not true for virtual particles. These can have any mass, positive or negative (I am told). Even a virtual photon can have negative mass. People describe virtual particles as being "off mass shell" because of their freedom to have any mass.

[virtual, fictional, shmirtual, schmictional ... ]