The results of a recent experiment at CERN, the giant particle accelerator near Geneva, seem to attack one of physics’ sacred cows: Albert Einstein’s postulate that nothing can travel faster than the speed of light.
In the experiment, physicists saw that streams of neutrinos — tiny, ghostly particles which seldom interact with other matter — were traveling just above the speed of light. But this is impossible if Einstein’s theory of relativity is correct. So was Einstein wrong?
Einstein’s near-mythic fame rests on his theory of relativity, which says that the speed of light in a vacuum, approximately 186,282 miles per second, is the ultimate speed limit. Nothing in the universe can travel faster.
In the CERN experiment, physicists fired a beam of neutrinos toward a detector in Gran Sasso, Italy, 454 miles away. Using highly sophisticated equipment, the CERN physicists tracked some 15,000 neutrinos over a period of three years. The neutrinos seemed to be reaching the detector 60 nanoseconds (a nanosecond is one-billionth of a second) faster than light. That may be a minute discrepancy, but it should not occur if Einstein’s theory of relativity is correct.
The CERN team has scrutinized its results and hasn’t been able to find any obvious errors. Physicists everywhere are scratching their heads. Could it be that another scientific revolution is at hand? Are we witnessing a paradigm shift?
Most scientists believe it still too early to say. The CERN experiment needs to be independently scrutinized. And what if this effect were limited to neutrinos, which are very exotic particles?
Testing theories through experimentation has always been the basis for scientific progress. The philosopher Karl Popper called this the notion of falsifiability of scientific theories.
Einstein himself was motivated by an experiment that disproved a 19th century scientific belief. Back then, it was widely held that light, like sound, needed a medium in order to travel. Physicists called it the “luminiferous ether.” Since the Earth revolved around the Sun and the Sun revolved around the center of the galaxy, they reasoned that the presence of ether would cause the speed of light to be different in different directions. Albert Michelson and Edward Morley set out to measure this difference. Instead they found that the speed of light was the same in every direction. In 1887, they published a paper, which then influenced Einstein.
Einstein had predicted that the gravity of a massive object such as the Sun would bend light. In 1919, two teams of astronomers led by Sir Arthur Eddington went to the southern hemisphere to observe a total solar eclipse. During a solar eclipse, the Sun’s disc is covered by the Moon, and Eddington and his colleagues were able to observe the bending of light, which resulted in stars near the Sun appearing out of place.
Eddington’s observations corroborated Einstein’s predictions. (When Einstein first published his complete theory, it was considered so difficult to understand that only three people in the world were supposed to have mastered it. On being asked about this, Eddington is supposed to have asked, “Who’s the third?”)
Nonetheless, relativity has been widely applied. Anyone who uses GPS navigation to find an address is benefiting from a practical application of the theory of relativity — the Global Positioning System’s satellites are programmed to account for the effects of relativity.
Einstein’s celebrated formula about the relation between mass (m) and energy (E), E=mc2, where the speed of light in a vacuum is denoted by the letter c, also comes from relativity. Note how a tiny amount of matter can produce a huge amount of energy. The formula helps explain nuclear power, or how the Sun and other stars produce energy.
In fact, modern physics is built on the pillars of relativity and quantum mechanics (the latter explains the physics of the microscopic world). The speed of light shows up everywhere: from estimates of the size and age of the universe to the radius of black holes to the power generated by nuclear reactors. Over the years, experiments have rigorously and repeatedly tested relativity and quantum mechanics and found no discrepancies — until now.
If it turns out that the CERN experiment is correct, then our scientific understanding is flawed. All sorts of strange things could happen if the speed of light can be exceeded. Causality — the relation between cause and effect — would be affected. Anyone traveling faster than the speed of light would be able to see fragments of a broken vase coming together. Faster-than-light travelers could go back in time — say, leave New York for Paris one evening and return the previous day.
With so much at stake, you can bet that those invisible little neutrinos will now be getting a lot of attention.
By Saswato R. Das, a science and technology writer in New York.