# Constructing an artificial blackhole

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1. Jun 8, 2014

### putongren

I have this crazy and goofy dream to construct an artificial black hole. Not a crude analogue, but the actual astronomical object. Would that entail using a particle accelerator to accelerate particles to huge velocities, gaining mass, and then smashing together and then turning into a black hole. I realize that normal particle accelerator technology would require the actual instrument to be extremely big. Would table top accelerator technology, once it matures, be able to smash particles until it is massive/dense enough to turn into a black hole.

I read somewhere that the LHC was once thought to might be able to create mini-black holes due to certain theories, but was not able to create any.

2. Jun 8, 2014

### UltrafastPED

Won't work. Black holes are invariant geometric objects in spacetime - that is, they appear as black holes in all possible reference frames.

Thus higher relative speeds cannot form a black hole.

The supposed process for micro black holes at particle accelerators would be due to the energy density at the point of a collision; the original worry was at Brookhaven. But of course if this were possible it would already be seen in the much more energetic particle collisions that are available with cosmic radiation ... and this mechanism doesn't occur naturally, so there was something wrong with the analysis.

3. Jun 8, 2014

### putongren

UltrafastPED, thanks for your response. Can you explain the fact that they are invariant geometric objects in spacetime would make it unable for particles to turn into black holes?

I'm really weak in the concept of frames of reference.

If creating an artificial black hole the way I suggested is impossible, can you think of a way? Or is the only way is just to have an extremely massive star run of fuel and implode?

4. Jun 8, 2014

### putongren

I'm watching a youtube video on black holes and near the end it tells about how the people at Brookhaven mentioned were unable to create a black hole.

They also mentioned how other theories mention the possibility of creating black holes.

Last edited by a moderator: Sep 25, 2014
5. Jun 8, 2014

### UltrafastPED

The so-called relativistic mass, which is "acquired" by a body moving faster and faster actually depends upon how fast you are moving, and in which direction. It is not a real increase in mass, it is simply an old fashioned way to write the kinetic energy of the object.

Thus it has nothing to do with the mass of the object if you were standing on it; it does not increase the local gravitational field.

"Frames of reference" are simply a way to describe a laboratory - it might be down the hall, or in orbit, or on a fast moving space ship. As long as it is not accelerating it makes a perfectly good inertial reference system, and if you describe some coordinates for it, a reference frame. There are an unlimited number of possible reference frames, some co-moving, some moving wrt each other, in all possible orientations and directions.

According to Special Relativity these are all equivalent for framing the laws of physics, and all physical experiments should yield equivalent results. But looking from one to another you might see things a bit differently ... this is where things often become confusing, and I refer you to the text books - I like Taylor & Wheeler's "Spacetime Physics", perfectly adequate for beginners, and requires nothing beyond algebra.

It is this "equivalent result" that dashes the possibility of a black hole from simply going faster - in some frames (co-moving frames - your space ship is keeping up with the object) the object is standing still, and hence it is what it was all along. If you analyze its relativistic invariants - see Taylor & Wheeler - the physical attributes that are seen as identical between all reference frames - it will always appear as it does to the co-moving frame.

To get the invariants from observations in a moving frame there are some calculations, fairly simple, but you must only use observations from a single moving frame, and combine them using the correct relativistic formulas ... and that gives the particular invariant. In this case, the invariant, or rest mass.

The Brookhaven hypothesis was not that they were moving fast, but that you could smash together two fast moving, heavy particles - gold nuclei, IIRC - then you obtain a quite high energy density in the center-of-mass frame. This density will be a relativistic invariant (because the rest frame invariants are easy to calculate!) ... so now the question becomes:

"What are the conditions for forming a micro black hole?"

And "Do micro black holes exist?"

Hawking, who came up with the black hole evaporation concept, calculated the life times for black holes of various sizes. It turns out that any that were created during the Big Bang - which had extreme conditions of the most extreme sort - would all have evaporated long ago; thus there can be no observation of them today, and there doesn't seem to be any astronomical evidence that they ever existed.

The usual way to form a black hole is for a massive star to die - when it's internal heat engine no longer produces enough pressure to prevent gravitational collapse. This only produces large black holes, and their coalescence in regions of high stellar density produces the super-massive black holes located at the centers of most galaxies ... and these super massive black holes are the only ones for which we have evidence.

Finally, if one could create mini black holes, nature should have done so long ago (Big Bang), and the extreme cosmic rays should be creating them today: they have much more energy than in any possible accelerator collision that can be managed today. And these extreme cosmic rays hit the earth on a regular basis ... but so far, no micro black holes the natural way, so it seems likely that they are not possible to create this way.

6. Jun 8, 2014

### pervect

Staff Emeritus
The "charge radius" of a proton is about .88 * 10^-15 meters. A classical black hole this size (I am assuming that the charge radius is the right number to use in a semi-classical analysis) would have a mass of 10^12 kg, or 9*10^28 joules.

I'm not sure this is a valid use of "charge radius", but it's the best number I have for the "size" of a proton.

A proton accelerated to 1 TeV (like fermilab) would have an energy equivalent of 1.8*10^-14 kg.

The idea of getting enough energy in a small enough space to form a black hole isn't wrong, but if you look at the numbers above you can see why it's impractical with known particle accelerators.

I gather there are some quantum gravity theories that predict that it's a lot easier to make black holes that classical GR, but I don't know the details.

7. Jun 8, 2014

### Staff: Mentor

Makes me think of The Krone Experiment

8. Jun 8, 2014

### stevendaryl

Staff Emeritus
On the other hand, two fast moving particles, moving at the same speed in opposite directions toward one another can be considered a composite object whose "rest" mass is equal to the sum of the relativistic masses.

9. Jun 8, 2014

### stevendaryl

Staff Emeritus
Instead of protons, if we consider an electron then it is (as far as we can tell) a point-particle. So classically (that is, non-quantum) it seems that it should be modeled as a black hole with a characteristic charge $Q$, angular momentum $L$ and mass $M$. But if you include the effects of charge and angular momentum on a black hole, you get a Kerr-Newman black hole (as described here: http://en.wikipedia.org/wiki/Kerr–Newman_black_hole). On that Wikipedia page, it is stated that there is no event horizon in the case where the charge and/or the angular are too great, compared to the mass. An electron has too large a charge and angular momentum to be a black hole.

10. Jun 8, 2014

### WannabeNewton

It doesn't work that way in GR. The notion of a point-particle is notoriously difficult to define in GR if you start trying to use its energy-momentum as a source in the EFEs in order to examine non-regularity properties of point-particle solutions and time scales for such solutions to evolve into black holes (if at all). One of the main issues is the EFEs are non-linear whereas the energy-momentum tensor of a point-particle is a distribution and squares of distributions are not defined. Others (such as Wald) have instead considered narrow world-tubes in the limit as the world-tube width goes to zero. There are some papers you can read regarding such prescriptions. The point is one cannot naively apply the definition of a point particle to that of a black hole.

11. Jun 8, 2014

### stevendaryl

Staff Emeritus
As I mention at the end of my post, the electron couldn't be a black hole in any case because its charge and angular momentum are too great. The conclusion from the approach you're talking about holds for any point-particle, regardless of its charge or spin?

12. Jun 8, 2014

### WannabeNewton

What I'm saying is that a point-particle cannot actually be defined in GR in terms of a distribution if one wishes to use the point-particle as a source term in the EFEs. In such a case it does not even make sense to consider whether or not this point-particle could be a black hole. But there are ways to get around this issue and one can in fact describe in detail the gravitational field of a "point-particle" and examine to what extent it could be considered as that of a black hole's.

You can find the details here http://relativity.livingreviews.org/open?pubNo=lrr-2004-6&amp;page=articlesu29.html [Broken]

Last edited by a moderator: May 6, 2017
13. Jun 8, 2014

### putongren

I forgot to tell you guys the reason why I wanted to create a black hole. The reason is to conduct tests on the black hole, to potentially unify QM and GR.

Would that work? For the sake of argument, you have a black hole in front of you, and you get to study it and conduct tests on it. Could you make scientific discoveries on it?

14. Jun 8, 2014

### pervect

Staff Emeritus
A full discussion probably needs quantum gravity, so "Beyond the Standard Model" might be able to tell you more about that. Offhand I'd think that such a small hole would evaporate almost as quickly as it formed, the interesting thing would be to see how many of the usually conserved things were not conserved .

15. Jun 9, 2014

### Activee

I'm a novice but wouldn't it be dangerous to create a black hole here on earth ? It frightens me a bit that they tried to do it.

16. Jun 9, 2014

### Staff: Mentor

Nobody tried.

17. Jun 9, 2014

### stevendaryl

Staff Emeritus
I'm not an expert on GR (especially quantum gravity), but I don't think a tiny black hole would be dangerous. The popular idea of a black hole is something with enormous gravity, but the gravity is only significant when you get close to the black hole. If you had a black hole the size of a proton, the gravity would be about the same as the gravity of a proton---completely negligible.

Of course, there are two problems with tiny black holes: (1) They can grow by having new mass fall into them. (2) They can shrink and explode (by Hawking radiation). The latter process can produce a burst of X-rays, but if you're talking about a black hole the size of an elementary particle, it's not going to produce a lot of X-rays. I don't think it would be that dangerous.

If we forget about Hawking radiation, and just think about a tiny classical black hole, I wonder how quickly it would grow.

18. Jun 9, 2014

### Staff: Mentor

I'm coming up with the same order of magnitude that pervect did in #14 of this thread. It's dangerous.

19. Jun 9, 2014

### stevendaryl

Staff Emeritus
Order of magnitude of what? #14 just says that such a tiny black hole would instantly evaporate. But when it evaporates, it just gives off the same energy that went into making it. So the danger is the same as the danger of the high-energy beams that created it.

20. Jun 9, 2014

### ZapperZ

Staff Emeritus
You should never read only bits and pieces of something, because you will get only part of the idea.

The very same physics that describes the creation of such black holes also predicts that such black holes can't be sustained for very long and would disintegrate. So if you buy one, you have to buy the other as well. You can't pick and choose.

Zz.