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Doomsday Fears at RHIC
Skeptical Inquirer, May, 2000 by Thomas D. Gutierrez
This year, the Relativistic Heavy Ion Collider (RHIC) is poised to begin a program of cutting-edge nuclear science. Recently, alarmist journalism unnecessarily raised public fears about implausible doomsday scenarios associated with the machine.
The Relativistic Heavy Ion Collider (RHIC; pronounced "rick") is a 2.4-mile circumference collider at Brookhaven National Laboratory (BNL) on Long Island. The machine is scheduled to go online in May 2000 and is designed to, among other things, collide two gold nuclei, each with 197 nucleons (protons and neutrons), head-on at 99.995 percent the speed of light. This will allow physicists to study the quark-gluon plasma, along with a wide variety of nuclear properties. Such words can certainly spark the imagination, but what exactly are these scientists doing?
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At just over [10.sup.-15] meters, fifty thousand times smaller than a typical atom, a gold nucleus is made of a soup of hundreds of nucleons which together act very much like a glob of liquid. Each nucleon is an individually wrapped "bag" containing three objects known as quarks. In the bag, the quarks are bathed in a seething sea of energy fluctuations. The primary denizens of this sea, gluons, are responsible for mediating the strong nuclear force--the force holding the bag of quarks together.
Oddly, no free quark or gluon has ever been directly observed. Indeed, based on quantum chromodynamics (QCD), the theory governing the forces between quarks and gluons, we may never expect to see such objects. On everyday human scales, gluons and quarks interact so strongly and in such a peculiar way that they are forever hidden from direct observation through a process called confinement. However, vast and reliable indirect evidence for quarks and gluons has accumulated since the 1960s (Halzen 1984; Carrigan 1990; Close 1993; Icke 1995).
When RHIC slams together two nuclei at such fantastic speeds, one goal is to raise the temperature of the colliding nuclei to about a trillion degrees Celsius. At this temperature, nuclear matter undergoes a phase transition analogous to liquid water becoming a gas. The individual bags of nucleons within the nucleus boil away, unleashing the quarks and gluons trapped inside, creating a new state of nuclear matter known as a quark-gluon plasma (QGP). [1] The QGP acts as a single "giant" bag of confined quarks and gluons just a little bigger than the whole nucleus. Within [10.sup.-24] seconds the QGP will expand in a fireball, cool, then precipitate into a fantastic flurry of subatomic particles racing off to highly sophisticated detectors.
The Collider will give scientists insight into, among other things, the early moments of the universe. A millionth of a second or so after the Big Bang, our own universe began cooling nor unlike the QGP fireball. However, at the beginning of time, the whole universe was steeped in a QGP. At RHIC, experimenralists are struggling to get a glimpse of just two nuclei undergoing a phase transition. In other words, the amount of matter and energy involved at the RHIC experiment is tiny by universal standards. The RHIC Web site notes that the total energy of the two colliding gold nuclei is only equal to about the energy of a mosquito hitting a screen door! Understanding the "smallness" of this experiment is important in addressing doomsday claims. Although the experiment is quite grand on a human scale, it is a far cry from "playing God."
The Doomsday Claims
In 1999, some segments of the media and the public fixated on several speculative doomsday scenarios at RHIC. How such claims began can be traced to a few articles in the popular press. However, there may have been latent confusion in the public regarding the science at RHIC that allowed the doomsday claims to easily rake hold. One common doomsday scenario claimed that the violently colliding nuclei would create a mini-black hole which would swallow Earth and everything on it. Another scenario involved the creation of strange matter which, through a chain reaction, may go on to precipitate all "regular matter" into "strange matter", also destroying the world. These concerns have been directly and rationally addressed officially by the lab itself and unofficially by the lab individual experts.
The mini-black hole scenario can be dismissed with simple physics arguments. There isn't enough matter or energy at RHIC to create a black hole. A back-of-the-envelope calculation demonstrates that RHIC lacks about thirty-six orders of magnitude in mass and energy to create a nucleus-sized black hole! With this heavy constraint, it is just about as likely that a black hole will randomly appear next to your head as you read this article. If a black hole were to be created with RHIC energies (using very generous assumptions), it would have to be around [10.sup.-38] meters in radius. Gravity expert Steven Carlip of the University of California at Davis has estimated that such a small black hole would harmlessly evaporate in about [10.sup.-90] seconds in a puff of Hawking radiation (Carlip 1999). Creating black holes at RHIC is not a realistic possibility.
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