Weekend Post - Was Einstein right all along?

In September there was a big fuss, reported all over the world, about an experiment conducted in Italy that suggested that Albert Einstein, his Special Theory of Relativity and his notion that nothing can travel faster than light might be wrong.

Almost every newspaper in the world asked “Was Einstein wrong?” The Italian scientists claimed that they had managed to force a beam of neutrinos to travel faster than the speed of light. Admittedly only very slightly faster than light, but even a little bit would have been enough. Their beam of neutrinos had travelled all the way from the CERN laboratory in Geneva, a trip of 730km, across the border into Italy and they arrived 60 billionths of a second earlier than light would have covered the same distance. Clearly something is wrong. Either one of the cornerstones of our understanding of the universe is wrong or there’s been a mistake by the scientists. My money was on the latter.

Obviously the results are interesting. Was Einstein right or wrong? It’s a big question. But I think it’s just as interesting for the public to see how science works. The researchers in Italy went public with their results and said to the entire world (in an Italian accent) “Hey, look at this, can this be right or have we made a mistake?”

The physics community around the world went into overdrive. They thought about repeating the experiment, tried to think of new rules of physics and, most critically, tried to help the Italians discover any mistakes.

It didn’t take long for things to happen. As we speak they’re trying to repeat the experiment in a slightly different way to rule out any systematic errors in their measurements. Just as importantly experts at the University of Groningen in the Netherlands might have come up with an explanation.

This is where it gets complicated. Einstein’s Special Theory of Relativity is simultaneously simple and complex. At it’s simplest he just suggested two things: firstly that it doesn’t matter where you are or what you’re doing, the law of physics remain the same. That’s the easy one. The second is more complicated. It says that wherever you are and whatever you’re doing, the speed of light is always the same. That isn’t as simple as it sounds. Imagine you are the passenger in a car travelling at 50km/h and you lean out of the window and throw a ball ahead of the car at 10 km/h. The speed of the ball will be 60km/h.

But instead imagine now that you lean out of the car window and shine a beam of light from a torch ahead of you. Light travels at roughly a billion km/h. So the light will now be going at a billion plus 50 km/h? No. It still travels at a billion km/h. The speed of light in a specific medium doesn’t change. Not ever. If you travel in a spaceship at half the speed of light and shine that torch forwards the light will still just travel at a billion km/h.

The effect of this is profound. I don’t have the skill or space to explain the steps (I’ll put links on the web site) but it follows from this that as you go faster and faster some pretty strange things happen. The faster you go the greater your mass and the more energy is needed to accelerate further so that actually to get to light speed you would need infinite energy. Most importantly, the closer you get to the speed of light, the slower time itself progresses as seen by an outside observer.

That last element is the critical one for the Italian experimenters. The critics at Groningen noticed that the Italians had used GPS satellites to measure the time the neutrinos were travelling. But GPS satellites are themselves moving, nowhere near light speed but fast enough that their ability to measure time as accurately as the Italians needed was affected. The Groningen scientists did the maths and worked out that this would affect the calculations by, yes, you’ve guessed it, 60 billionths of a second.

The new experiments aren't done yet but we now have a very plausible possible explanation for the effect the Italians saw. Will they be proved right? Only time will tell.

Sources

The original news story can be seen here courtesy of the BBC. The original notice in Nature is here.

For an overview of Special Relativity see How Stuff Works or the Wikipedia page here.

For news on the repeat of the experiment see the BBC story here. For a summary of the Groningen suggestions about GPS satellites and their time dilation see here.