Neutrinos on hyper-drive

Last week, the world of physics and beyond was shaken by the news (largely distorted by the media) than neutrinos may be able to go faster than the speed of light, thus breaking the speed record in the universe and also the theory of relativity pioneered by A. Einstein.

During the last euro-apéro, it has been suggested that I write a short note to explain what just happened and what it means for us(you) normal human beings.

What’s a neutrino ?

That is a very good question, in fact the neutrino is not the best known particle in physics. Still, there is plenty to tell about it. First, it is one of the building blocks of the Standart model, which describes very well how the world around us works at the tiniest scale (less than one femtometer, the femtometer is to the meter what the millimeter is to 1 trillion kilometers).

The neutrino is not charge (that means not sensitive to magnetic fields) and is very light.

The consequence is that neutrinos do not interact often with matter. Actually, hundreds of billions of them are passing through your body as you are reading these words, but no worries, it is very rare than a neutrino collides with any atom in matter. It is therefore very difficult to study the properties of this particle.

What has been measured ?

In the experiment that made the news last week, the time of flight of neutrinos have been measured between a production facility in CERN (near Geneva) and a special detector in Gran Sasso (Italy), more than 700 km away. As said before, interacting very rarely with matter, the neutrino don’t suffer on their way and there is no need to build any tunnel or guide between the production and the detection.

It has been measured an early arrival of the neutrino, as early as 60 nano seconds (or 60 trillionth of the second), in respect to the time the light would need to go the distance. It is a very tiny difference, on a race track it would be as if the neutrino cross the 100m finish line while the light is 2.5 centimeters behind.

Why does it matters ?

As we told, the difference is very tiny, but it is six time bigger than what the scientist who published this story claim to be their resolution, i.e. the accuracy of their measurement. And all that we know about physics of particle today is very clear on the speed limit of the universe, nothing should go faster than light, for a lot of reason, one of which being that A. Einstein told us so. The relativity theory have been tested and proved to be right time and time again and it is a very robust theory that won’t be overturn unless we have evidence that it is flowed.

So ?

What will scientist do now ? First, they will try to reproduce the experiment to confirm the results or prove it to be just an error in the analysis. Theorist will also work on the problem to try find how such things as faster-than-light-neutrinos can exists.

In the long run, it is very unlikely that the relativity theory will be proved incomplete, more likely, we will learn a lot on the nature of the neutrino (maybe finally measure its mass, or discover wether the neutrino is its own-antiparticle) and its interaction with matter.

Nothing moves faster than the speed of light, so you may as well relax.#


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