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Name: Jack
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Question:
I have recently been reading "A Brief History of Time" in which Hawking talks about how a particle can have a negative energy when it gets close to a black hole. I am interested as to how this can happen.



Replies:
Jack,

I do not understand this either. We are in good company. Dr. Richard Feynman, in his Lectures on Physics, says (and I paraphrase) that one cannot understand Quantum effects in the way that one can understand normal physical entities. One has to learn the physics and math and then be careful to verify any conclusions one draws by experiment. To my knowledge, no-one has been able to perform a laboratory verification of this particular negative energy.

Here is an interestingly written essay from which I have extracted one paragraph. You may find the remainder of the essay at http://physicsweb.org/articles/world/19/9/4/1

"Near the event horizon of a black hole, virtual particle-antiparticle pairs are being created all the time. Every now and then, half of one of those pairs falls into the hole and cannot get out to recombine with its partner. If the partner outside the hole has sufficiently high energy, it can escape the gravitational pull of the hole and thus create the illusion that the hole is radiating. Entanglement then demands that the partner that does not escape the black hole has negative energy. Because of Einstein's relation between mass and energy, E = mc2, the negative-energy partner effectively has a negative mass, so when it falls into the hole it causes the mass of the hole to decrease."

Best wishes on your studies. Stay curious! But; be careful what you believe; particularly where Quantum is concerned.

George Martin



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