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May
2
comment An explanation of Hawking Radiation
@CuriousOne: I improved my answer accordingly. But the massive cse is indeed easier to explain since one can do a rough balance in terms of rest masses rather than energies.
May
2
revised An explanation of Hawking Radiation
allowed for photons rather than electrons
May
1
comment Vacuum is not really empty
@JohnDuffield: You speak a different language than I. I was not talking about quantum gravity (where there is no vacuum state at all).
May
1
comment An explanation of Hawking Radiation
@CuriousOne: The process $2g\to2\gamma$ that works at arbitrarilyy low energies was already mentioned in my post. I discussed the corresponding electronic process because of the analogy with the e/m field and (in the comments) because John Duffield had referred to it.
May
1
awarded  Nice Answer
Apr
29
awarded  Nice Answer
Apr
27
comment An explanation of Hawking Radiation
@JohnDuffield: electron-positron annihilation in reverse is pair creation from photons, which naturally happens in a strong electromagnetic field. But under usual circumstances the pair flies in nearly opposite directions and will never meet again, which they would have to do to annihilate again. This is why the photon-photon scattering effect is almost vanishly small.
Apr
27
awarded  Revival
Apr
27
comment An explanation of Hawking Radiation
If you discredit the Unruh effect by saying it hasn't been observed so far, you should discredit for the same reason the page you linked to - photon-photon scattering hasn't been observed either (according to the page). In addition, unlike my processes which are at tree level yours is a loop process involving renormalization.
Apr
27
comment An explanation of Hawking Radiation
@JohnDuffield: I am nowhere using magic; I just work without the geometric interpretation since this is inappropriate in QFT, where one doesn't have a pseudo-Riemannian spacetime. Everything I said follows from canonical QFT in the tree approximation, without any resort to either magic or geometry.
Apr
27
revised An explanation of Hawking Radiation
added useful information from the discussion
Apr
27
comment An explanation of Hawking Radiation
@JohnDuffield: The inhomogeneity is described by a massless tensor field called the gravitational field. This translates the geometric language you used (and referred to) into the language of quantum field theory, which must be used in order to describe particle production. In canonical gravity space-time is just a smooth manifold without predefined metric. the metric is instead a quantum field tensor operator that gives rise to creation and annihilation operators in the usual way. If one looks at the S-matrix in the tree approximation one gets the process I talked about.
Apr
27
answered Born-like measuring rule in classical experiments
Apr
26
comment An explanation of Hawking Radiation
@JohnDuffield: How can vacuum be inhomogeneous?? A strong gravitational field is like a strong electromagnetic field, not vacuum but full of energy (as defined by the energy-stress tensor). And just as particle production from strong electromagnetic fields is inevitable through the process $2\gamma\to e+e^+$ so particle production from strong gravitaitonal fields is inevitable, though the same process with photons replaced by gravitons. This follows already form canonical quantum gravity + QED in tree approximation, i.e., without needing to worry about unsolved problems about renormalization.
Apr
26
comment An explanation of Hawking Radiation
Thanks! You are welcome.
Apr
26
comment An explanation of Hawking Radiation
''The vacuum state of a quantum field is the state that has no particles.'' I agree with you but the wikipedia reference you give doesn't! It says: ''According to quantum mechanics, the vacuum state is not truly empty but instead contains [...] particles that pop into and out of existence.'' This is nonsense since the vacuum state is an eigenstate of the particle operator with eigenvalue zero, hence there is no uncertainty about the particle content. You'd look for better references!
Apr
26
comment An explanation of Hawking Radiation
Not Hawking radiation (I just checked), but lots of other effects making shameless use of all the magic properties ascribed to virtual particles by several generations of physicists, without the slightest justification except cartoon analogy and thinly veiled fantasy! See physicsforums.com/posts/5453034
Apr
26
comment An explanation of Hawking Radiation
''Given that Hawking said this in his original paper in 1975 it is something of a shame that the pairs of virtual particles analogy is still being trotted out as an explanation for the process some thirty years later.'' Look at the explanations of particle physics in popular science books such as ''Facts and Mysteries in Elementary Particle Physics''' by Martinus Veltman, and you'll understand that influential physicists themselves are responsible for this.
Apr
26
comment An explanation of Hawking Radiation
''The quantum field state that looks like a vacuum to you will look to me as if it contains a non-zero number of particles.'' Actually an indefinite number of particles.
Apr
26
revised An explanation of Hawking Radiation
added 106 characters in body