WHAT EXPERTS SAY
Madhusree Mukerjee's article on the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
["A Little Big Bang", March] alarmed several readers, such as Michael Cogill of Coquitlam, B.C. "I am concerned that physicists are boldly going where it may be unsafe to go", writes Cogill, who worries that creating stuff that has not to anyone's knowledge existed since the early universe -- namely a quar-gluon plasma -- could result in a catastrophe. "What if they somehow alter the underlying nature of things such that it cannot be restored?" he asks. Another reader wondered whether the RHIC experiments could result in miniature black holes (below).
BLACK HOLES AT BROOKHAVEN?
Thank you for the article by Madhusree Mukerjee entitled "A Little Big Bang" [March]. In the 1970s Stephen W. Hawking postulated that in the early moments of the big bang, miniature black holes would have been present. Although they no longer exist in our region of the universe, such mini black holes could be created by smashing a proton into an antiproton with enough energy. If one were created near a large congregation of mass and if it started absorbing that mass before exploding, the black hole would reach a relatively stable half-life and thus continue to grow. If this happened on the earth, the mini black hole would be drawn by gravity toward the center of the planet, absorbing matter along the way and devouring the entire planet within minutes.
My calculations indicate that the Brookhaven collider does not obtain sufficient energies to produce a mini black hole; however, my calculations might be wrong. The only way to determine the energy density at which a mini black hole would be created as an intermediary step to the type of explosion depicted in your article is to build a collider and do the experiment. Is the Brookhaven collider for certain below the threshold?
WALTER L. WAGNER
via email
Frank Wilczek of the Institute for AdvancedStudy in Princeton, N.J., replies:
Whenever we explore new physical (or chemical, or biological) phenomena, questions like Cogill's arise regarding whether we might unwittingly trigger some catastrophe. For example, in the early days of the Manhattan Project, Fermi and others carefully considered whether a nuclear explosion might ignite the atmosphere. Scientists must take such possibilities very seriously -- even if the risks seem remote -- because an error might have devastating consequences. In the case of the Brookhaven RHIC, dangerous surprises seem extremely unlikely. First, nuclear collisions with larger energies take place regularly as cosmic rays rain down on our atmosphere -- so if a disaster were possible, it would have already occurred. Second, related regimes have been explored in detail, and so we have substantial evidence that our theoretical framework for understanding what will happen is reliable. Although we cannot calculate the consequences in complete detail, we can distinguish credible from incredible scenarios.
The idea that mini black holes will be formed, as Wagner suggests, definitely falls in the latter category. The energy densities and volumes that will be produced at RHIC are nowhere near large enough to produce strong gravitational fields. On the other hand, there is a speculative but quite respectable possibility that subatomic chunks of a new stable form of matter called strangelets might be produced (this would be an extraordinary discovery). One might be concerned about an "ice-9"-type transition, wherein a strangelet grows by incorporating and transforming the ordinary matter in its surroundings. But strangelets, if they exist at all, are not aggressive and they will start out very small. So here again a doomsday scenario is not plausible."
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It is to be noted that in 1975 Dr. Wagner discovered the tracks of a novel particle on a balloon-borne cosmic ray detector. "Evidence for Detection of a Moving Magnetic Monopole", Price et al., Physical Review Letters, August 25, 1975, Volume 35, Number 8. A magnetic monopole was first theorized in 1931 by Paul A.M. Dirac, Proceedings of the Royal Society (London), Series A 133, 60 (1931), and again in Physics Review 74, 817 (1948). While some pundits claimed that the tracks represented a doubly-fragmenting normal nucleus, the data was so far removed from that possibility that it would have been only a one-in-one-billion chance, compared to a novel particle of unknown type. The data fit perfectly with a Dirac monopole.
It is to be further noted that since the above-quoted Scientific American article, the idea that colliders might create miniature black holes has gained wide credence in the scientific community, with many theorists postulating such, but also concluding that they would likely quickly evaporate via Hawking Radiation [Dr. Wagner's initial surmise as well]. Google on the term "Black Hole Factory" for a plethora of articles.