Black Holes

Now that the politicos are huddling again, this time to come up with a plan that is both workable and politically acceptable, we can consider other topics, like the End of the World.

As you probably know, the Large Hadron Collider at CERN, once its helium leak is repaired, is expected to create particles never observed before.  The main goal is to find the Higgs boson, which somehow gives other particles their mass.  Don’t ask me how it does that.

Another expected event is the creation of black holes.  The black holes people commonly think about are massive, sucking whole stars into itself, and generally acting like a bully to anything that comes too near.  However, it is possible if subnuclear particles are crushed together strongly enough, to create a submicroscopic black hole.  However, its half-life would be so short that it would “evaporate” via Hawking Radiation, before it captures its first particle. (The smaller the particle, the more it radiates.)  Now it’s also true that because of quantum uncertainty, anything can happen, including the creation of a black hole large enough to capture particles before it evaporates.  The probability of that happening is so low that the mean time for such an event to occur is substantially longer than the age of the universe, which is about 13.7 billion years.  Not to worry.

However, it is interesting to consider how such an event would progress.  Let’s say that such a particle was created in the LHC, just barely massive enough to survive.  Would we know it immediately?  I think not.  It takes weeks and longer to analyze the data from collisions, and they would not be looking for that particular event.  Also, it would just be collecting particles at rate just slightly faster than it was radiating, so at first it might not grow quickly, just a few nuclear fragments at a time.

However the particle would be influenced by gravity, and would fall out of the LCH towards the center of the earth picking up particles as it goes, but we might not know it, except there would be a vacuum leak (not a helium leak, by the way) of some size.  When would we notice it?  That’s the question I am wondering about.  Eventually it would reach the center of the earth, and it could just sit there sucking particles at an exponential rate as it grew.  But exponential doesn’t mean fast, especially at first, and we might not know it for a while.  Pick your own definition of a while.

The mass of the earth wouldn’t change, but maybe gravitational sensors would eventually notice something was different, that gravity was behaving differently.  At some point would the earth become a hollow shell and then collapse suddenly?  How long would the process take?  Seconds, minutes, years?  Remember, it would of necessity start slowly, a few electrons or other particles at a time.  Maybe it has already started and we just don’t know it yet.


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7 Responses to Black Holes

  1. Spyros says:

    Well, we seem to be getting back to the original discussion. All i did was to call attention that these calculations (10 grams etc) are questionable. I am in no position to speculate. All that you cite in your original post make up an interesting topic though. However i wish that this discussion could be made in a more scientifically established manner (i am not referring to your approach, it’s just a wish i make as a physicist).

    PS. 10 micrograms is a macroscopic quantity, surely out of the quantum world.

  2. jfistere says:

    Since you are not interested in speculating, that effectively ends the discussion, wouldn’t you say?

    However, you do ask how we know it will grow by absorbing particles. A black hole just large enough to be stable weighs about 10 micrograms, according to one source. That is well out of the quantum fluctuation world, I would say. As a matter of fact, by definition, it must be so.

    So, what else could happen to a particle that strays too close to the BH, whatever its mass?

  3. Spyros says:

    You wrote: “As the BH grows, it will happen at a faster and faster rate.”. And i ask, how do we know that it will grow by absorbing particles? I know that it seems logical to suppose this, however i must call your attention to the fact that the quantum world is far beyond our classical logic.

    So this is the reason for which i don’t want to speculate on such things. I know that many physicists do (even prominent ones), but i don’t think that speculation is part of the physics vocabulary. Physicists either know (or at least have some solid clues) or don’t know. In this case i (and most of the physicists) don’t know what will happen.

    PS I said most, because there may be some brilliant mind that could have discovered quantum gravity without us knowing about it, but i think that’s highly unlikely.
    PPS If you ask mr Hawking he will probably begin to write equations explaining what will happen if a black hole is created, etc etc. I like to be more conservative on my approach, as cosmology and general relativity is not the field of my expertise.

  4. jfistere says:

    My message was to solicit your speculation on what would happen if the smallest possible stable black hole existed on the surface of the earth, or at its center. I’m not asking for proof.

    I agree that “sucked” was a poor choice of words. However, randomly moving particles will, at some rate, approach close enough to be absorbed by the BH. As the BH grows, it will happen at a faster and faster rate. I wonder how long it would be before we noticed it.

  5. Spyros says:


    you asked how i think that such a BH would behave. Well, if i had a scientific answer to this question, i would certainly be the strongest candidate for the next Nobel prize in physics. I will say again that the calculations you cite are made using classical General Relativity which apparently does not apply to quantum objects such as mini BH.

    As for the last of your questions. It is correct. You are constantly falling towards the center of the earth. I didn’ quite get the point of your question, however i will give some clues.

    Black holes are not vacuum cleaners. They don’t suck up matter. For an object to get sucked up, it must have a trajectory that crosses the event horizon of the BH. For instance, if the sun was replaced by a BH, the planets would continue to revolve around it without falling into the black hole.

  6. jfistere says:

    Thanks for your interesting comments.

    Commenting on your points:

    1) 2) and 3) I wasn’t really commenting on how or whether dangerous black holes could be created in hte LHC or anywhere else, or how they would disappear. I was simply hypothesizing the creation of one.

    4) A black hole that could last long enough to attract matter would weigh about 10 micrograms, about the same as a speck of dust. Huge in Planck terms. ( So classical mechanics may apply to at least some degree. My main question is how do YOU think such an object, if created on earth, would behave?

    5) Although a particle may have only a small gravitational field of its own, if it has any mass, it would be affected by the earth’s gravitational field and therefore fall towards the center of the earth, right?

    What do you think would happen?

  7. Spyros says:

    These microscopic black holes are quantum objects. So they require quantum gravity to be described. Since we don’t know how to do quantum gravity we cannot tell how they will behave. Some comments.

    1) Hawking radiation has not been observed yet in nature, so it may not exist.
    2) These BH have other decay channels as well. For instance they might be decomposed into the particles from which they were formed.
    3) You are wrong about quantum uncertainty and the creation of big BH. This is scientifically wrong. There is no possible way that LHC can create big black holes.
    4) Your description of the behaviour of the hypothetical BH that may be formed in LHC is completely classical, hence not correct.
    5) By the way the gravitational field of such a BH would be macroscopically negligible. Maybe even microscopically.

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