Einstein’s Theory Still SafeThose faster-than-light neutrinos that everyone was talking about last month have actually slowed down; it looks like modern physics will withstand after all. Ironically, the theory that these neutrinos would have disproved may be the only explanation as to what happened to them.
In September, physicists sent a bunch of neutrinos from Switzerland to Italy and analyzed how long it took for the particles to make the trip. Over a series of 15,000 experiments, the neutrinos came back to the lab around 60 nanoseconds earlier than expected, which means 60 nanoseconds faster than the speed of light. According to Einstein’s theory of relativity, nothing should be able to travel faster than the speed of light.
The mere fact that the experiment’s results were so consistent suggested that one of two things had to be true: either the neutrinos really were going faster than the speed of light and Einstein’s theory would have to be revised or that there was something wrong with the experiment, which was more likely than a single experiment destroying the framework of modern physics. The results now seem to indicate that there was indeed something wrong with the experiment itself, and oddly, the flaw may actually reinforce Einstein’s theory.
Neutrinos move very fast (at or very near the speed of light), and the distance traveled in this experiment was only about 450 miles. This means that in order to determine how long it takes a neutrino to make the trip, you have to know the distance between the two points, the time that the neutrino leaves the lab, and what time it arrives at its destination.
What Went WrongIn the original experiment, the CERN scientists used GPS to analyze both the distance measurement and the time measurement. They got the distance measurement down to about 20 centimeters, and since GPS satellites can broadcast accurate times via radio, they used these devices to measure the times. While the team took a lot of variables into account, including the amount of time that it takes for a clock signal to go from the satellite to the ground, it looks like they forgot Mr. Einstein’s observation: relativity.
The Theory of RelativityBasically, relativity explains that distance and time can change depending on the way you look at them. Since the GPS satellites are so high in space, the difference between the time ‘reference frames’ of the Earth and the satellites are significant enough so that strange things will begin to happen in experiments like this.
As the neutrinos leave the first lab and move towards the lab in Italy, from the satellites’ perspectives, the neutrinos are moving towards the lab and the lab is moving towards the neutrinos as the Earth rotates. From a ground perspective, none of this happening; the experiment is going as anticipated. Once the neutrinos arrive, the satellite team takes a time measurement and determines that the neutrinos’ arrival clocks in at the expected time, while scientists on the ground determine that the neutrinos went faster than expected. The varying time differences are due to the fact that the ground team’s ‘reference frame’ was shorter than the satellite’s ‘reference frame’, and the ground team didn’t account for the differences in relativity.
Researchers at the University of Groningen in the Netherlands took relativity into account and ran through all the numbers, determining that relativity does account for the speed boost that the CERN team thought they saw. While the new analysis hasn’t been reviewed yet, it looks like Einstein’s theory and modern physics are safe after all.