Physics & Math / Subatomic Particles

Extremely potent cosmic rays—high-speed atomic fragments that pack as much energy as a bullet—reach Earth from quasars billions of light-years away. That perplexes cosmologists, whose calculations suggest the rays should collide with the bits of microwave radiation that fill the universe and be destroyed long before they arrive. Some researchers consider the conundrum so strange that it can be solved only by trashing Einstein's theory of relativity. But Richard Lieu, an astrophysicist at the University of Alabama in Huntsville, says the theory is fine, once you understand how to combine it with quantum theory.

Lieu invokes the example of clocks and moving trains to explain the flaw in current thinking. According to Einstein, a clock on a moving train appears to be ticking more slowly than normal from the perspective of a stationary observer on the platform. Furthermore, any error in timekeeping measured by the moving clock would be magnified; at 99.5 percent the speed of light, a clock running a second behind would appear 10 seconds slower than it actually is to the unmoving observer. In this interpretation, the cosmic rays are moving so swiftly that quantum jitters—the smallest possible units of time—appear to expand into large chunks of temporal uncertainty that obscure the exact speed or energy of the cosmic rays.

If it is impossible to measure the speed of the cosmic rays, Lieu argues, we cannot predict how they will interact with the microwave radiation. In fact, that fundamental uncertainty could offer an escape so they do not interact at all. "If so, then the cosmic rays can coast through the microwave background," he says. The persistence of the cosmic rays is not an attack on Einstein, therefore, but another tribute to the subtlety of his ideas.