Scientists officially announced Friday (Sept. 23) that subatomic particles called neutrinos may be passing the ultimate speed limit, zooming at a velocity faster than light. But according to Einstein's special theory of relativity, nothing can cross this barrier. So either the measurements are incorrect, or physicists must revise many trusted theories.
Turns out, the results were likely flawed, according to a growing scientific consensus some six months after the discovery was announced. Even so, here are 10 implications of faster-than-light travel.
The speed-of-light rule represents the backbone of Einstein's 1905 special theory of relativity. This law does away with the concept of absolute velocity, and instead says that motion is relative. Except for light, that is. All observers, no matter what their own speed, will measure the speed of light at a constant 299,792,458 meters per second (about 700 million miles an hour). This speed represents the fastest that anything can travel, an absolute upper limit on motion.
The new findings threaten to overturn this trusted law. "According to relativity, it takes an infinite amount of energy to make anything go faster than light," said physicist Robert Plunkett of the Fermilab laboratory in Batavia, Ill. "If these things are [moving faster than light], then these rules would have to be rewritten."
Special relativity states that nothing can go faster than the speed of light. If something were to exceed this limit, it would move backward in time, according to the theory.
The new finding raises all sorts of thorny questions. If the neutrinos really are traveling faster than light, then they should be time travelers. The particles could theoretically arrive somewhere before they departed. Physicists suggest such an ability, if it really existed, could be used to send neutrinos back in time to deliver messages.
Cause and Effect
A fundamental law of physics, indeed of all science, is causality: that cause always precedes effect. This was accepted in classical physics, and the special theory of relativity took pains to preserve the rule, despite the relativity of an object's motion.
But if something can travel faster than light, it can travel backward in time, according to the theory. In this case, an "effect" could travel back to a point before its "cause" had occurred — for instance, a baby swinging before he gets a push. Such a result would be scientific heresy, surely requiring some hasty rewriting of laws to make sure causality is preserved.
"Most of the theoretical structure that's been erected in the 20th century has relied on this concept that things have to go slower than the speed of light," Plunkett said. "As I understand it if you have anything traveling faster than the speed of light you can have things happening before their causes."
Einstein's famous equation E=mc^2 states that energy (E) and mass (m) are equivalent, and can be converted from one to the other by the ratio "c-squared," where c represents the constant speed of light.
The status of the speed of light as the ultimate cosmic speed limit is the reason for its presence in the seminal formula. But if c is not in fact the fastest possible speed in the universe, and things can go faster, this may have to be adjusted in special situations. Perhaps the special speed of neutrinos deserves to win the title of ultimate speed limit instead.
The Standard Model
The Standard Model is the name of the reigning theory of particle physics, which describes all the known subatomic particles that make up our universe. [Countdown: The Coolest Little Particles in Nature]
But if the speed of light rule, and the theory of relativity are rewritten, this model too may need adjusting.
"One of the foundations of the Standard Model is special relativity," said Stephen Parke, head of the theoretical physics department at Fermilab in Batavia, Ill. "If you start tweaking with the foundation you have to start tweaking with the house on top."
String theory is the cutting-edge idea that all fundamental particles are actually tiny vibrating loops of string. This assumption turns out to have broad-ranging implications, including the possibility that our universe has more dimensions than the known three dimensions of space and one of time.
String theory is incredibly difficult to test, and there is no proof that it's correct. But if the neutrino measurements are correct, some physicists say string theory may offer the best bet of explaining them.
Perhaps, some physicists have suggested, the neutrinos are not traveling along the straight line we thought they were, but instead were hopping into one of the extra dimensions predicted by string theory, and taking a shortcut to their destination. If they traveled a shorter distance in the measured time, then their actual speed may not have been faster than light.
Perhaps the new discovery doesn't mean that just anything can travel faster than light, but merely neutrinos. If that's the case, then there's definitely something special that scientists didn't know about these particles.
Neutrinos are already understood to be oddballs. They are neutral, nearly massless particles that hardly ever interact with ordinary matter. They come in several kinds, called flavors, and they strangely seem to be able to change from one flavor to another. So it's possible that their faster-than-light abilities are unique features as well. (Above, a photo of the Gran Sasso Laboratory detector in Italy, the final destination of the neutrinos sent from the Swiss laboratory CERN.)
In the 1960s physicists suggested that particles may exist that can travel faster than light. These particles, dubbed tachyons, have only been theorized, never detected. Because of tachyons' troubling properties, including the possibility that they would violate the rule of causality, many physicists have considered them a fringe notion.
Yet if the new discovery is borne out, scientists may want to take a closer look at the theory of tachyons. [Read: What Would It Be Like to Travel Faster Than Light?]
One of the most contradictory pieces of evidence to the new findings comes from observations of the supernova SN1987A, which lies about 168,000 light years from Earth in the Large Magellanic Cloud. Observations of this dead star from the Kamiokande II experiment in Japan found that light and neutrinos that departed the supernova arrived at Earth within hours of each other. Over such a long distance, this means that light and neutrinos travel within 1 part in 100,000,000 of the optical speed of light.
This observation was a seminal achievement in astronomy, and won physicist Masatoshi Koshiba the Nobel Prize. [Gorgeous Supernova Photos]
Yet the new findings don't agree with this result. They suggest, instead, that neutrinos actually surpass the speed of light by 60 nanoseconds over 730 kilometers, which corresponds to 2 parts in 100,000.
It seems a revision of either the supernova measurement, or the neutrino findings, is in order. (Above is an image of a remnant of supernova 1987A encircled by a glowing gas ring known as the "String of Pearls.")
Evolution of the Early Universe
Many other aspects of astronomy could also stand to be affected if the new discovery holds. Some important ideas about the history of the universe, in fact, are based on neutrino measurements and theories.
"Neutrinos are abundant in the early universe and if they behave differently, this affects calculations of the evolution of the early universe, nucleosynthesis and the seeds of structure formation," astronomer Derek Fox of Pennsylvania State University wrote in an email to LiveScience.
Furthermore, neutrinos are produced in the fusion reactions that power stars, so if these particles behave differently than thought, star models may need to be revised. (Above, an artist's conception of the history of the cosmos.)