Massar, R. Parentani and Ph. Spindel, A Primer for black hole quantum physics , Phys. Unruh, Experimental black hole evaporation , Phys. D 51 : , Corley and T. Jacobson, Black hole lasers , Phys. D 59 , and A. Coutant and R. Parentani, Black hole lasers, a mode analysis , Phys. D 81 Weinfurtner, E. Tedford, M. Penrice, W. Unruh and G. Lawrence, Measurement of stimulated Hawking emission in an analogue system , Phys. Parentani, and Ph. Spindel, Hawking radiation without transPlanckian frequencies , Phys.
D 52 : , Jacobson and R. Parentani, An echo of black holes , Scientific American, 17 , Sponsored by: Eugene M. Izhikevich , Editor-in-Chief of Scholarpedia, the peer-reviewed open-access encyclopedia Sponsored by: Dr. Categories : Space-time and gravitation Quantum Gravity Physics. Namespaces Page Discussion. Views Read View source View history. Contents 1 Black hole formation 2 Black hole horizon properties 3 Redshift and structure of outgoing light rays 4 Quantum mechanics and Hawking radiation 5 The origin of Hawking radiation 6 Observing Hawking radiation 7 Quantum gravity and the role of very short distance effects 8 Footnotes 9 References 10 See Also.
Figure 1: We have represented the spacetime geometry of a spherical black hole. The time coordinate increases vertically, and one of the three spatial dimensions is not shown. Thus, at a given time, i. This geometry is static, and in particular the horizon keeps the same surface area at all times.
One clearly sees that the horizon is a cylinder that separates the trajectories of outgoing light rays in two classes: those represented in blue that escape the hole, from those represented in dotted lines which are trapped inside. None of them cross the horizon. Instead radially infalling light rays, here represented by straight green lines, cross the horizon without hindrance.
As in Figure 1 , the time coordinate increases vertically. At a later time, one clearly sees the trajectory towards the upper right corner followed by the escaping wave packet and that of trapped partner wave propagating inward. One also sees that these trajectories are basically the same as those of outgoing light rays represented in Figure 1. At an early time, before they split, there is a unique initial wave packet. When reconsidered in quantum mechanical terms, this splitting of waves describes the steady conversion of vacuum fluctuations into pairs of particles.
Izhikevich , Editor-in-Chief of Scholarpedia, the peer-reviewed open-access encyclopedia. Sponsored by: Dr. Reviewed by : Prof. Pietro Menotti , Pisa University, Italy. Reviewed by : Dr. The greatest idea of Stephen Hawking's scientific career truly revolutionized how we think about black holes. They're not completely black, after all, and it was indeed Hawking who first understood and predicted the radiation that they should emit: Hawking radiation.
He derived the result in , and it's one of the most profound links ever between the worlds of the quantum and our theory of gravitation, Einstein's General Relativity. And yet, in his landmark book, A Brief History Of Time , Hawking paints a picture of this radiation — of spontaneously created particle-antiparticle pairs where one member falls in and the other escapes — that's egregiously incorrect.
For 32 years, it's misinformed physics students, laypersons, and even professionals alike. Black holes really do decay. Let's make today the day we find out how they actually do it. The features of the event horizon itself, silhouetted against the backdrop of the radio emissions The dotted line represents the edge of the photon sphere, while the event horizon itself is interior even to that.
Outside of the event horizon, a small amount of radiation is constantly emitted: Hawking radiation, which will eventually be responsible for this black hole's decay. What Hawking would have had us imagine is a relatively simple picture. Start with a black hole: a region of space where so much mass has been concentrated into such a small volume that, within it, not even light can escape.
Everything that ventures too close to it will inevitably be drawn into the central singularity, with the border between the escapable and inescapable regions known as the event horizon.
Now, let's add in quantum physics. Space, at a fundamental level, can never be completely empty. Instead, there are entities inherent to the fabric of the Universe itself — quantum fields — that are always omnipresent.
And, just like all quantum entities, there are uncertainties inherent to them: the energy of each field at any location will fluctuate with time. These field fluctuations are very real, and occur even in the absence of any particles. The quantum vacuum is interesting because it demands that empty space itself isn't so empty, but is filled with all the particles, antiparticles and fields in various states that are demanded by the quantum field theory that describes our Universe.
Put this all together, and you find that empty space has a zero-point energy that's actually greater than zero. In the context of quantum field theory, the lowest-energy state of a quantum field corresponds to no particles existing. But excited states, or states that correspond to higher-energies, correspond to either particles or antiparticles. One visualization that's commonly used is to think about empty space as being truly empty, but populated by particle-antiparticle pairs because of conservation laws that briefly pop into existence, only to annihilate away back into the vacuum of nothingness after a short while.
It's here that Hawking's famous picture — his grossly incorrect picture — comes into play. All throughout space, he asserts, these particle-antiparticle pairs are popping in and out of existence.
Inside the black hole, both members stay there, annihilate, and nothing happens. Far outside of the black hole, it's the same deal. Again, the exact formulation is beyond the scope of our treatment of the subject.
Nevertheless, a good qualitative interpretation can be obtained by considering the energy-time form of the Heisenberg uncertainty principle:. If we restrict ourselves to very short time scales, the uncertainty in the energy can be very large. In the intermediate stage of virtual pair production, conservation of energy appears to have been violated. This is where the uncertainty principle comes to the rescue, as the particles are created and annihilated on such short time scales as to agree with the uncertainty relation above.
When we take delta-t to be large, energy is conserved as we could never have observed the particles in the intermediate stage. At first glance, this process of virtual particle creation may seem a little phony.
With that in mind, we can consider the more tangible case of electric field particle creation. If the field is strong enough, the particles tunnel through the quantum barrier and materialize as real particles.
The field necessary to accomplish this feat is achieved when the work done to separated the charges by a Compton wavelength equals the energy necessary to create the particles:. So if a black hole is not accreting mass from outside, it will lose mass by Hawking radiation, and will eventually evaporate. It is not well established what an evaporating mini black hole would actually look like in realistic detail. The Hawking radiation itself would consist of fiercely energetic particles, antiparticles, and gamma rays.
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