The Collider Debate
There is a well-developed debate on the collider issue. Most confidently-asserted safety factors have exceptions. Respectable albeit speculative theories enable trouble. The speculative aspect means that the probability of trouble may be low, but expected value (probability times value if the probability is actualized, the standard metric of decision theory) is high because the cost of trouble-in this case destruction of earth-is 6.7 billion lives, to say nothing of future lives.
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Posts here mention Hawking radiation as a safety factor. Most physicists are confident that Hawking radiation will work, but it has never been seen, and physics papers have been published that question the fundamental theory behind Hawking radiation. [William G. Unruh and Ralf Schützhold, "On the Universality of the Hawking Effect," Physics Review D 71(2005) 024028.], [Adam D. Helfer, "Do black holes radiate?" Reports on Progress in Physics. Vol. 66 No. 6 (2003) pp. 943-1008.]
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An analogy between collider-created black holes and cosmic-ray-created black holes is supposed to demonstrate safety. The argument is as follows: Cosmic rays have been hitting earth with energy in the collider range for billions of years. If collider-created black holes are dangerous, then cosmic-ray created black holes should be dangerous too. The fact that we are still here demonstrates that they are not. However, the analogy is not precise. Because of the asymmetry in momentum between the cosmic ray and the earth particle it hits, cosmic-ray-created black holes will always be moving at high velocity in the rest frame of earth. If they accrete slowly, and if they are uncharged, as some theories predict, they will zip right through earth like a neutrino. A very small number of neutrinos stop in earth. However, if a fast black hole hits something, it will only accrete, slow a bit, and continue. It would have to accrete many particles to slow below escape velocity. The binomial probability that any will accrete enough to slow below escape velocity, even in trillions of trials over four billion years, is still vanishingly small. On the other hand, the Large Hadron Collider is designed with beams of equal energy, energy that cancels out when particles collide. Someone mentioned the point that the energy will rarely cancel out precisely. Quarks, the colliding particle of consequence for black hole creation, have large random energy. Greg Landsberg calculated that only about 0.00001 of collider-created black holes would be moving at less than escape velocity from earth. However, since he predicts that the LHC will produce a black hole per second, that still results in 315 per year moving at less than escape velocity. Some of these will orbit within earth, and have forever to accrete. The speed of accretion depends on the accretion model; with some models accretion takes forever, other models allow fast accretion. Giddings and Mangano, collider supporters, in a paper cited by other posters here, recognize that the collider/cosmic ray analogy is not definitive when considering conditions on earth. They had to extend it to consider conditions on neutron stars and white dwarf stars, which (they claim) should be able to trap even cosmic-ray created black holes, making the lifetimes of neutron stars and white dwarfs shorter (if BHs are dangerous) than apparently observed. However, several scientists have put forth somewhat speculative theories to dispute this.
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This website is named for James Randi, a magician who supported the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP) by showing how some fraudsters worked their tricks. My father, who was both an engineer and a magician, knew Randi. This is relevant since Skeptical Inquirer, the magazine of CSICOP, published an article “Doomsday Fears at RHIC” [by Thomas Gutierrez in the May 2000 issue] (RHIC, the Relativistic Heavy Ion Collider, started at Brookhaven in 2000.) Richard Posner says Gutierrez “implies incorrectly that only irresponsible journalists raised fears . . .” [Posner, Catastrophe, p 274.] The safety factor at the time was the impossibility of black hole production at colliders. Gutierrez claimed that a black hole was as likely to form randomly as at RHIC. Gutierrez was not the only one to make this claim. A Brookhaven paper claimed that black hole production required energy beyond reach of any collider. [W. Busza, R.L. Jaffe, J. Sandweiss, and F. Wilczek; "Review of Speculative ‘Disaster Scenarios' Brookhaven, 2000] The interesting thing about these claims is that shortly afterward string theorists began to predict black hole production at colliders. (If their somewhat speculative theories are true.) Hawking radiation and the collider/cosmic ray analogy as applied to earth were other confidently-asserted safety factors that also proved inadequate, as discussed above. This raises the question of whether science in this area is mature enough to produce adequate safety factors. Toby Ord of the Future of Humanity Institute at Oxford says that the low probabilities of collider trouble asserted by some scientists are inaccurate because the probability that the scientific theory on which those probabilities are based is wrong is higher than the low probabilities asserted. [Toby Ord, Rafaela Hillerbrand and Anders Sandberg, Probing the Improbable: Methodological Challenges for Risks with Low Probabilities and High Stakes] (For the probability that a scientific theory is wrong, they consider things like the frequency of retractions in scientific journals.)
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Since the probability of trouble seems low, it seems unlikely that the collider will destroy us. However, it seems hubristic and immoral to risk the lives of billions when that risk is only “unlikely.” Individuals regularly take risks of 1 in 1,000. Subjecting earth to that risk has an expected value of 6.7 million lives lost, a number in the Hitler range. Of course the actual result is either zero or 6.7 BILLION lives lost; the mathematics of subjective value say that this risk is “worth” 6.7 million lives. This is only an example. I am not claiming this level of risk for colliders. Estimate your own subjective probability considering the existing safety factors. Given the poor record for collider safety factors, any reasonable estimate results in a large number here.
