Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What happens in a black hole?

  1. Nov 12, 2009 #1
    First let me say that I am a premed student who's just interested in physics so please forgive me for asking stupid questions, but I sure do have a lot of questions that I feel could best be answered by human beings rather than by looking them up and just getting more confused.

    So as I understand it, all the matter that crosses the event horizon gets compressed at the singularity after a finite amount of time, but what does that mean? Does every particle that enters the black hole occupy the same 0-dimensional point at the center? Does this mean that there are a huge number of particles at the center of each black hole that all occupy the exact same three-dimensional point?

    I read the other day about the concept of a Bose-Einstein condensate the forms when the temperature of a material is dropped to about a microkelvin above absolute zero, where the particles' wave functions begin to interfere because they are so close to each other. If each of these particles at the singularity of a black hole occupy the same 0-dimensional point, does that mean their wavefunctions are all interfering? Does a particle that reaches a singularity have a temperature/internal energy associated with it, or does it reach absolute zero? Do particles at a singularity have mass/rest energy? Also, if the singularity itself has a mass associated with it, and this mass is growing with each new victim that gets sucked into the event horizon, does that mean that the gravitational force the singularity exerts on outside objects increases infinitely over time (according to GMm/r^2)?

    Also, I heard that the speed of massless gauge bosons are all c (the speed of light), and that this would include the yet-to-be-observed graviton. If a graviton and a photon are both massless particles that both travel at the speed of light, why is it that light gets sucked into a black hole? Don't the photons and gravitons have the same velocity? Also, if a photon is massless, and assuming GMm/r^2 still applies at the quantum level, what property of a photon is the graviton acting upon that would cause the photon (or any electromagnetic wave, really) to be "sucked into a black hole"?

    If anyone could answer even one of the above questions (not necessarily all of them), I would really appreciate it, because they are bugging the hell out of me and this I suspect this is probably the last chance I'll get before medical school to think about things like this.
    Last edited: Nov 12, 2009
  2. jcsd
  3. Nov 12, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    The 'classical' view is that you can't ask any questions about what happens inside the event horizon - it's a bit of a cop-out though!
  4. Nov 12, 2009 #3
    No question is too stupid for Physics Forums... except ones about *banned topics*

    They don't let us bait or feed the trolls.

    As I understand it the singularity erases the identity of everything it swallows. Thus there is just one particle at the centre. Think of it as the Big Bang origin in reverse.

    In theory a black hole can keep growing so long as there's energy and mass flowing into it from surrounding space. Whether it can grow to infinity depends on the cosmology of the Universe which we don't have any solid answers for. The possible never-ending acceleration scenario due to a cosmological constant might influence things in important ways - I think Fred Adams and Greg Laughlin have written a paper or two on the consequences.

    Gravitons are a fashionable hybrid of quantum and general relativity theory but we don't know if they're real or not. Photons follow geodesics - the shortest paths in curved space - and beyond the event horizon ALL geodesics end at the singularity, at least in Schwarzschild geometry. Photons have no rest mass but they have mass-energy and so are affected by gravity like everything else, except they never 'slow down' they merely lose energy in a gravitational field (red-shift.) A photon emitted from the event horizon is infinitely red-shifted and thus doesn't escape.

    Oddly enough plenty of medical Doctors have learnt GR as a hobby. Some just have a knack for mathematics that they keep alive by doing physics. Might take a long time because you don't have a lot of spare time for a long time...
  5. Nov 15, 2009 #4
    Thanks for your response! I think I understand where the mistake in my thinking was, I guess I was trying to applying quantum mechanical principles to a situation which is traditionally governed by general relativity, which is apparently an incorrect thing to do. Thanks!!
  6. Nov 16, 2009 #5
    Hi All, like qm, I also am not a physicist (so please be kind) but have more than just a passing interest and conveniently enough, my question also realtes to black holes and is this:
    A lot of time, money and effort has been spent searching for the missing mass and energy of the universe and it seems the generally accepted theory is now that it is contained in 'dark matter/energy', now, it would seem to me that the most obvious place to find all this missing mass and energy would be in black holes. Given that it's now thought there is a super massive black hole at the centre of every galaxy and that a black hole of such size could have almost infinite mass would this not be the 1st place to look? Just a though...
  7. Nov 17, 2009 #6

    Black Holes did seem like a good choice but microlensing surveys haven't seen enough objects for them to be dark matter black-holes. A small black hole can't be seen directly, but when it passes between us and other stars it focuses their light, producing a microlensing event - a distinct brightening of the star.

    Black holes that are too small are currently believed to decay away into nothing due to Hawking radiation, but not enough x-rays and gamma-rays are seen for lots of small black holes to be out there decaying. Black holes in between star-mass and about 100 billion tons can be ruled out by microlensing, while small holes aren't decaying enough if they exist. Could the problem be that we don't understand how black-holes decay?

    Maybe. It's possible that small black-holes only decay so much, then stop, due to a field created by the decay process itself - a process called vacuum back-reaction. A Russian scientist has determined that black-holes convert about 10% of their mass into energy, then about 50% becomes the vacuum back-reaction field. This is an unusual result, but based on standard physics, and may well be confirmed. In which case "dark matter" might well be micro black-holes... and could the vacuum back-reaction be the "dark energy"?

    Maybe. We need more data, more people verifying the theory and observational tests of the consequences of such micro-BHs everywhere.
  8. Nov 17, 2009 #7

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Could you give a reference for this?
  9. Nov 17, 2009 #8
    http://arxiv.org/abs/0911.2368" [Broken]
    Last edited by a moderator: May 4, 2017
  10. Nov 17, 2009 #9
    Completely wrong. Big Bang did not come from the black hole.
  11. Nov 17, 2009 #10
    It's a physical analogy not an isomorphism.
  12. Nov 17, 2009 #11
    The concept of a black hole converting it's consumed mass into a singularity would suggest that they cannot grow unless they merge with other black holes. If the gravity of an increasing singularity over the life of the hole would be immense if it were to reach outside of the event horizon. The merging mass on the event horizon maybe the source of the gravitation field rather than the singularity. The 0-dimensional point of all the mass is a strange notion. No big bangs from black holes please. Particle vibration or wave functions on condensing before reaching this 0-dimension, would surely increase temperature as the friction and gravity increased, bringing them closer and closer until they interfere with each other (fusion). So if there is a transfer from vibrating matter to static at or near absolute zero, it is going to be very dramatic with an amazing change in temperature. It would be like trying to stop an ice cream cone from melting inside a fission reactor.
    Some black holes emit vast plumes or jets of radiation from their poles, this expulsion of energy is converted mass, so they are losing mass in this manner. The photon capture is explained by conventional physics (mass-energy) but stated as having no rest mass? Mass or no mass, i am not convinced that this has been explored to a complete conclusion. Just because it seems to fit and it makes the math work, does not mean the reasoning is correct.
    The retention of photons and the release of radiation with both being waves of no mass, i feel requires a closer look and re-think.
    It has been posted by graal that 10% of a black holes mass is converted into energy. All the black holes in the history of this universe and all the holes we have present today that emit these jets or lose energy in heat equates to a hell of a lot of lost mass to energy. It is no wonder we are coming up shy of expected mass in the universe. All the exploding suns over the eons also convert a proportion to energy, not to mention all living suns through the eons. Is it even possible to try an calculate that percentage lost to energy, as it seems on every new revelation the universe gets older and older. The dark matter as suggested for this mass discrepancy is a fanciful notion for the solution. It may exist but i suspect it will quite different from what is expected. How much mass was lost to energy in the initial big bang? If there was any mass at all at that point but that's another argument.

    It does not matter who you are or what you do, we all learn things one step at a time, just some quicker than others, but even the thickest person on the planet can have a brain wave or a unique perspective. Genious has no educational or social boundaries.
  13. Nov 24, 2009 #12
    Hi qmstudent, first let me say that no question about physics is a stupid question on physics fourms (after all thats why its there right?) About the black hole: in theory this is how a black hole works: matter goes into the acrettion disk (the field of gravity produced by the black hole just outside the event horizon) then it gets sucked trough the event horizon and into the singularty of the black hole, nobody knows for sure what happens next but here is a theory, matter is then compressed into smaller and smaller particles untill it is destroyed . (I know the laws of physics say that matter cannot be destroyed, but we dont know for sure do we?) There are other theories that say a conecting structure is formed, and the matter is transported into another point in spacetime (white hole theory). But that is the one that I think is most provable.
  14. Nov 24, 2009 #13


    User Avatar
    Science Advisor
    Gold Member

    Just an aside, black hole jets are not fed by mass from the black hole. The jets are fed by material from the accretion zone outside the event horizon.
  15. Nov 25, 2009 #14
    Mass/energy is conserved by a black hole singularity. What is 'destroyed' by a semi-classical black-hole is quantum information about the particles that fall in.

    BUT this is only for the strange hybrid of quantum mechanics and general relativity that is a semi-classical black-hole which has Hawking radiation. Real "black holes" might preserve the information somehow. The point is we don't know currently if it is preserved or how it might be. But then we don't know if a singularity forms behind an event horizon either. Some other process might cause a collapsing mass to look much like a "black hole" from the outside, but be something completely unlike the general relativistic (classical) black-hole on the inside. Gravastars are one possibility and I am aware of several other options. A general relativistic singularity might not exist at all.
  16. Nov 29, 2009 #15
    Can we really say that a black hole is a singularity? Is there any theory that says that a black hole can't have a circumference/volume?
  17. Nov 29, 2009 #16

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

  18. Nov 29, 2009 #17
    I would agree with George the black hole is the whole volume inside the event horizon (the radius that has an escape velocity of >c). It is three dimensional. I think it is correct to say all point within this volume are singular. That is we currently have no physics theory to say anything about this place and what happens. There is no need for all the mass to fall to the exact center there may be a pressure that provides enough force to hold up the matter (as in a normal star). This gets very close to talking about the big bang at a time when the extend of the universe was small enough that the escape velocity was >c.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook