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Is quantum mechanics applicable to blackholes?

  1. Feb 28, 2007 #1
    I have a very little knowledge in physics and I am new to this forum. I have read that quantum physics is a branch of physics that deals with microscopic objects i.e. objects of extremely small size (less than 1 nanometer). I have learnt that blackholes are extremely small objects with close to point size and infinite density formed by uncontrolled gravitational contraction of a star. Thus by definition, blackholes being extremely small objects (point like singularity) formed by uncontrolled gravity should be microscopic and therefore should obey quantum uncertainity just like any other microscopic object would do. Is it a correct conclusion or is there any misconception somewhere in my understanding? Is quantum mechanics applicable to blackholes? This doubt occured to me a few days back. Please clarify me as early as possible. Advanced thanks for your kind response.
    Last edited: Feb 28, 2007
  2. jcsd
  3. Feb 28, 2007 #2
    The size of a black hole is usually defined as the diameter or radius of the event horizon. You can picture the event horizon as an imaginary sphere around the black hole where anything inside of it can never escape, anything on the borderline can escape only if it is travelling at the speed of light, and anything beyond it can escape at lower velocities. The event horizon can be several kilometers across, depending on the mass of the black hole. There is a disk of particles circling the black hole beyond the event horizon, called an accretion disk, that extends even farther out.

    The very center of the black hole, the singularity, is thought to have no size and infinite gravity, and this is difficult to use in equations. Quantum mechanics cannot deal with singularites.

    However, there is a lot of stuff going on around black holes that is govered by quantum laws. There are virtual particles, pairs of particles and antiparticles, that are created all the time according to quantum mechanics because they quickly annihilate after they're created. If one of these pairs is created on the border of a black hole's event horizon, one particle could fall into the black hole while the other stays outside. Radiation of this sort has actually been detected from black holes. It was predicted by Stephen Hawking.
  4. Mar 1, 2007 #3
    Quantum gravity wrote:
    "Radiation of this sort has actually been detected from black holes. "
    But this sentence is wrong.
  5. Mar 1, 2007 #4
    I have a limited understanding of black holes.

    But there is a theory that the centre of any galaxy contains a super massive black hole, these holes are formed from immense clumps of mater that got sucked into the centre of the Galaxy during the formation of our galaxy and before the first formations of stars, they have been used to explain how a Galaxy can form and how their motion is caused.

    These I can assure you are very very large objects, if the theory is correct the accretion disc itself is probably in the order of light years across. The Black hole proper, is probably also substantial. However this is entirely theoretical and there is no direct evidence of black holes, only inferred information. Every now and again the Black hole gobbles up some more of the galaxy and a bright spot can be seen at the centre of the galaxy? how can we tell it is the centre? Because all the stars around it are moving and it isn't.

    AAMOI when Andromeda collides with us in a several billion years, the two super massive black holes will collide forming an even bigger black hole and a much larger galaxy, unfortunately it's likely we'll either get tossed into the void by the collision or tossed into the black hole, assuming of course it is a black hole?

    There's a nice little mpeg of the collision here.

    Last edited: Mar 1, 2007
  6. Mar 1, 2007 #5
    I had a thought on this sort of thing a while back...

    Consider a proto-black hole which is accumulating matter and approaching the threshold of mass concentration required to be a true black hole. It follows that at some point the object will be approached by the last little chunk of mass required to push it 'over the edge'. Suppose that mass is an electron. We know that as objects approach the event horizon, time dilation effects become infinitely strong and time effectively stops on the event horizon.

    The electron is a quantum object, however, so its position is uncertain. It can therefore be on either side of the event horizon. The black hole's state, whether it is a proto-black hole or a true black hole, depends on whether or not this electron is inside the event horizon.

    Does this make the black hole a quantum object?
  7. Mar 1, 2007 #6
    there has been a lot about bouncing singularities of late- however it seems to me that the Superposition Principle would explicitly state everything beyond the event horizon is in superpostion - but I haven't really seen anything that addresses this because you need a theory of Quantum Gravity first
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