I lack the knowledge to understand this but prima facie this seems more sensible than DM being some sort of phlogiston. The article mentions that no detections have been made by LIGO, but are these black holes below detectable mass? As ever, falsifiability is key. so how could this theory be proved or disproved?
nm
Shine a laser at some, if it comes out the other side then it wasn’t a black hole
Doesn’t work. These mini black holes would be minuscule and the amount of light they would absorb would be undetectable.
How you’d detect them would depend on how big they are. There’s no one measurement that could conclusively rule out all possibilities. We know that they can’t be too small, because then there would have to be a lot of them, and we’d be noticing them (for instance) within our own Solar System (get small enough, and the Hawking radiation would be hot enough to see). And we know that they can’t be too large, because if they were, then we’d have detected them from microlensing. But there is still some room in between those bounds.
Of note, though, for this to work the black holes must be primordial. Not only is there not enough baryonic matter in the Universe now, but there never was enough, so black holes formed from the collapse of baryonic matter are ruled out as dark matter.
What do you mean by “phlogiston”? The typical proposals are for some sort of subatomic particle. Said particle hasn’t yet been discovered, but there’s nothing remarkable or surprising about the sorts of properties such a particle would have. In fact, the most common proposals are for types of particles that the particle physicists expect to exist anyway, for reasons completely unrelated to cosmology.
Revisiting, rather than starting a new topic.
I was just watching a PBS video on youtube about this:
‘https://www.youtube.com/watch?v=srVKjWn26AQ’
It seems theoretically possible that there may be a size limit below which a black hole can’t decay?
Because the photon it would have to emit carries more energy than the mass-energy of the hole itself.
I’d actually thought of this myself quite a few years ago, and a few back-of-the-envelope calculations (with Wolfram Alpha doing the heavy lifting) suggests that this might be on the order of the Planck mass.
There’s an Occam’s Razor attraction to this idea: we don’t need to postulate any new dark matter particle.
But as noted: how could we test this? They’re not emitting Hawking (or any other) radiation, by definition.
And there wouldn’t have to be a large density of them, as mentioned in the video.
Is there any way to rule this out as a hypothesis?
The answer to this, as with anything involving the Planck scale, is that we don’t know. We can be absolutely certain that what we know of physics must be inadequate by the time you get to Planck: There must be some quantum theory of gravity that takes over at some point before then. But what that quantum theory of gravity would predict, nobody knows (some folks have guesses, but as yet we have no way to test the guesses).
All that said, I don’t think dark matter consists of Planck-mass black holes. While we don’t know exactly what the properties of a Planck-mass black hole would be, they’d probably have some interesting properties, and they’d be common enough that we’d expect to notice those interesting properties, whatever they are.
They might have interesting properties, but I’m not sure how we might notice them?
I haven’t checked the math of the youtube poster, but it seems there wouldn’t need to be a large density of them (if they have Planck mass) to add up to dark matter, so maybe not that common?
Comes back to: is there any observational test we could do?
Of course, the same could have been said for neutrinos several decades ago!
I just wonder if this has been seriously considered by Real Scientists (as opposed to us amateur afficionados)… 
How would you distinguish such a beast from an elementary particle?
I don’t know.
Like I said, what observational test(s) might be possible?
The Planck mass is actually not that insignificant, so one could probably envision some sort of detector which would register if something of that size flew past it closely enough.
Sort of great-great-grandson of the Cavendish experiment.
But as the youtube poster points out, it wouldn’t require a large density of such objects to add up to the assumed amount of dark matter, so the chances of such a flyby may be remote.
A bit like the search for magnetic monopoles, in a way.
I don’t know of any such experiments?
I’m also wondering about two issues:
One, has anyone who is really qualified to calculate such things expressed an opinion about the theoretical possibility of such ‘irreducible’ black holes?
Two: are there any analyses of observed evidence (or convincing computer simulations) which would support or contradict the possibility of them? Large-scale behavior of galaxies, for example?
Really, it would be an elementary particle. But it’d be, by far, the most massive elementary particle, closer to us in mass than to most elementary particles.
Well, as I said earlier, we really don’t know how a black hole close to the Planck mass would behave. But yes, the possibility that sufficiently-small black holes are stable is definitely one that’s taken seriously. And in fact, at least some of those appropriately-sized black holes would be magnetic monopoles, and if there aren’t any other magnetic monopoles, we’re almost certain that those black-hole-monopoles would be stable.
I don’t think there are any astronomical observations that could distinguish Planck black hole dark matter from other sorts of dark matter. But those monopole ones would be detectable. The experiment to detect magnetic monopoles is fairly simple, and has been done, by many different groups, over a long period of time, and in that time, we’ve only had one thing that looks like a detection, and that one was probably a glitch in the equipment of some sort.
Sheesh! learn to spellcheck! It’s monopolY- and I don’t care if it’s magnetic, regular or Star Wars edition, it’s a boring game.
On a serious note- Fascinating discussion. What’s the Cavendish experiment? How would you detect magnetic monopoles? Is the following a good analogy for dark matter- You know somebody who’s always covered in dog hair. You go their house and there are dog hair and paw prints everywhere. They have dog bowls in the kitchen. The only reasonable explanation is that they had a dog or until very recently had one. That dog is dark matter. We can’t observe it directly. But, if it didn exist our other observations would be wrong and our assumptions would be all screwed up.
I agree, Monopoly can get to be a excruciatingly boring game. Round and round it goes, will it never end?
The other topics: I really don’t want to be the asshole who responds to everything by saying “Read the F—ing manual”, but Wikipedia does have some fairly good introductory stuff on those.
I say this honestly and not out of laziness- I like the answers I get on the SDMB better. Plus, they often anticipate my next questions.
Dogs…black holes…Sirius inquiries…there’s got to be a joke around here, somewhere.
Right, that is almost a legend in the field, I think!
Is anyone still running any detectors, I wonder?
I rather gather that the possibility of magnetic monopoles has fallen out of favor with real physicists nowadays on theoretical grounds.
As my advisor put it, we know for certain that magnetic monopoles exist. There just might be a very low number of them, like zero. That is to say, they’re a real sort of particle, that would come into existence under the right conditions, but those conditions might be so rare and extreme that they haven’t come up anywhere in the observable universe.
As for the Cavendish experiment, it was an experiment to determine the value of Newton’s constant, G (and therefore, to indirectly determine the mass of the Earth). Basically, you take a couple of big metal balls (but not so big that you can’t weigh them or fit them in a lab), put them very close to each other, and measure the gravitational force between them. It’s a difficult experiment, and even with modern versions, G remains the fundamental constant with the most uncertainty in its value, but it can be done.
Ah, the Dirac argument! It’s elegent: if we believe angular momentum is quantized, then if there is even one magnetic monopole in the universe, then charge has to be quantized too. I really thought that was fun when I heard about it.
That’s not the argument that my advisor used. Rather, it was the black hole argument: Even if there are no other monopoles, charge (electric or magnetic) is one of the few properties black holes are allowed to have, and a sufficiently-strong magnetic field (where the phrase “sufficiently-strong” is doing a lot of work) would therefore produce pairs of magnetically-charged black holes, in the same way that a sufficiently-strong electric field produces electron-positron pairs.