In a nutshell: a magnetic monopole is a theoretical elementary particle which has a north or south pole only, unlike any known magnetic material.
There were some speculative physics theories a few decades ago which suggested that these might have been produced in the Big Bang and might still be around.
Some experiments were done to see if any of these could be detected (they would induce a current if they passed through conducting loop). And one of the earliest apparently detected one almost as soon as the experiment was started.
But nobody has ever seen another one, and the general concensus is that it was probably an experimental glitch. Plus I think (I am not a professional physicist) that the theory predicting them has rather fallen out of favour these days?
It’s when you hold a Geiger Counter up to a banana.
Would a planck-mass black hole interact with matter in an interesting way, or is it too small to think that it could come into contact with fundamental particles?
If it has a charge (which it certainly might), it would interact with other fundamental particles that way.
Other than that, we’d really need to know quantum gravity to answer. It probably could interact with other particles by swallowing them, but then, if there’s some minimum possible mass for a black hole that prevents Hawking radiation, it’d now be above that mass, and would promptly re-emit a particle. How often would that happen? That’s the part we can’t answer with what we know. I wouldn’t be surprised if it were very, very rare, because such a black hole would have a very, very small event horizon, but event horizon size need not be the same thing as interaction cross-section.
I guess a quantum black hole could collide with another one now and then, and the result might emit Hawking radiation because it’s now above the threshold.
But as you say, this would probably be very - even astonishingly - rare?
Low cross section, plus probably a rare population (doesn’t need to be a large density of these to add up to dark matter).
I did once wonder if this might be an explanation for some Gamma ray bursts, but of course that doesn’t work.
But that’s the thing: We don’t know that it would be low cross section. The cross section could be the size of the event horizon, or it could be infinite. Or, probably, anything in between.
Well, true. It seems unlikely that something very small might have a large interaction cross-section, but we’re speculating in the absence of any useful theory here?
By the way, what do you think about Jonathan Oppenheim’s recent stuff? Interesting, or just another flash in the pan? We’ve been waiting for a long time for something that might make a testable prediction… string theory is starting to look more and more like navel-gazing…?
At one time there was a (maybe only semi-serious?) idea that the gravitational energy and mass-energy of the universe cancel out, so the universe “came from nothing”, or to put it another way, the universe is a black hole.
But I think that’s gone out of the window with the discovery of dark matter and energy.
That’s an observation, not a fundamental principle. If magnetic monopoles are so rare that we’ve never observed one, then we would always observe that the divergence of B is zero. But that doesn’t mean that there are no magnetic monopoles, just that we’ve never seen one.
One does sometimes wonder what Maxwell (or Archimedes etc…) would have made of current mathematical physics. Would they have picked it up and run with it… or were they in some sense products of their era?
But that’s a topic for an entirely different thread…
Well, they would certainly need some remedial education on what’s happened since their time. But both of them were friggin’ geniuses, and once they caught up, they’d still be geniuses. I’d give it a year or two before Maxwell was able to keep up with modern physics PhDs, and ten years tops for Archimedes (maybe less, if we can arrange for his classes to be in Doric Greek and translate his results for him-- Languages are harder for adults to learn).
I’ve said before about Maxwell, that it’s kind of a tragedy that the fourth-most-brilliant physicist in history got eclipsed just a few decades later by the third.
We need to get the flux capacitor working, and assemble the Eternal Academy of geniuses plucked from past time.
Of course the one we really need was born in Africa a couple of centuries ago in a rural village.
They made fun of her because she was thinking about stuff rather than hunting or gathering etc, died rather young.
Given access to current knowledge, she would have said: quantum gravity? That’s not hard at all, look, here are the equations.
