Does just being exotic make them winners?
Further to yesterday’s discussion of Sabine Hossenfelder’s views as to whether Stephen Hawking should have won the Nobel Prize, our physics color commentator Rob Sheldon weighs in on the current difficulties with the black hole as a concept:
It is most unfortunate that both scientists themselves and the popular press discuss black holes (bh) as if they are (a) a scientifically defined object; and, (b) an experimentally observed one. Stan Robertson, a retired cosmologist from Oklahoma University, wrote some papers a few years back (b) pointing out the problems and suggesting (c) an alternative.
(a) Black Holes are not scientifically defined.
(i) They have several mathematical discontinuities. The first is the “singularity” at the center which is still not defined, either physically or mathematically. If I had a theory with a mathematically undefined region, it would be banished as “unphysical” but somehow the BH crowd gets a pass. I do not understand why.
(ii) the second discontinuity is the “event horizon.” The speed of light becomes zero on this surface, which makes anything that depends on the speed of light also discontinuous. This is often pooh-poohed as a mathematically excluded point that makes no difference to the physics. “If an astronaut were falling through the event horizon he wouldn’t feel a thing” is a common rejoinder, “because it is only a mathematical, not a physical surface.”
As it turns out, this statement is just plain wrong. Hawking has his radiation emitting from this surface, and Leonard Susskind challenged him that it made hash of information theory and thermodynamics. This led to proposals that said this surface was “a wall of fire.” Hawking fought tooth and nail to keep his radiation, and in the end admitted that the event horizon wasn’t real (but his radiation was). This is documented in Susskind’s 2008 book, The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics. Then Hawking died, and it seemed no one wanted to keep fighting this battle. But it hasn.t gone away.
(b) Black Holes are not Experimentally Observed
There have been many observations of very dense objects — we have extensive data on neutron stars where the mass of our Sun would be compressed down to an object about 13 miles wide. But a BH event horizon is even tinier than that.
(i) the “Event Horizon Telescope” image of the BH that was widely circulated a few years ago does not actually measure the event horizon (the diameter of a black hole). The resolution was about 3X too poor to measure the actual event horizon. So experimentally speaking, a neutron-star at the center of the galaxy could account for the observations just fine. The counter-argument might be that theorists don’t think neutron stars are stable at that size, but from an experimentalist’s point of view, the all-important density is just too unknown to call it a definitive black hole. That is, its mass is measured but not its radius.
(ii) the BH at the center of our galaxy has also not had its radius measured. There were several stars that got close to Sg A*, but none that were anything like 3X the event horizon. So once again, the 2020 Nobel prize was incorrectly awarded for experimental verification.
(iii) the gravity wave experiment, LIGO, sees two BH spiralling around each other and emitting a faster and faster wave that rises in pitch. The LIGO team argued that if these putative BH were fatter and less dense, then they would collide before they finished their death spiral, and we’d see an abrupt end to the sequence. Therefore, they argued, the gravity waves are not only validation of the wave-equation solution to Einstein’s gravity law, but validation of BH themselves.
The fly in this ointment is that the waves are swamped by noise. Not just noise=signal, not even noise = 10x signal, or noise=1000x signal, but noise=10,000x signal. Now I work for the DoD where radar SNR is often very noisy. But they’d laugh you out of the room if you said you could retrieve a signal that was 1/10,000 of the noise.
Unfortunately the LIGO team work for the NSF. And what the LIGO people say is that they just “know” the signal is in there, so they apply a mask to the noise that is modelled on a binary BH, and this helps to get rid of the noise. It’s called a “matched filter.”
It also means that whatever signal they find will look exactly like a merging BH.
Which is why I do not believe that any results from LIGO are real. None. And one day they will admit this. But not, I suppose, until the funding dries up.
Therefore, both theoretically and experimentally, we do not have evidence of BH, but instead have evidence AGAINST Black Holes.
(1) no Hawking radiation (evidence against event horizons)
(2) no solution to singularity
(3) no solution to information problem at the event horizon
(4) no measurements of BH that are compact enough to rule out neutron stars (or whatever they are)
(5) observed magnetic fields in BH (denied by the “no-hair” theorem)
c) Replacement. Stan Robertson has a model where, as a star contracts, the magnetic field internally resists gravity. In that case, most candidates for BH in our universe are magnetically contracting objects (he uses the acronym MECO). Since most BH are also magnetic, this makes perfect sense to me. Stan also argues that these objects have no singularity, have no event horizon (and no information paradox), and are only 15% larger than an equivalent BH, so they fit inside the volume of all BH candidates.
What’s there not to like?
But black holes are so much a part of our culture that we must preserve them somehow!
See also: Sabine Hossenfelder asks, Should Stephen Hawking have won the Nobel? Rob Sheldon weighs in. Rob Sheldon: Hawking did not get the Nobel, however, because he hung his hopes on the radiation emitted by BH [black holes]–the so-called “Hawking radiation”. And it was never observed. Sabine tries to explain why. But one argument that Sabine doesn.t make, is that Hawking radiation may never have been observed because BH are themselves never observed.