Cienciaes.com: The tiny Universe, that strange world. We spoke with Mr. Alberto Casas.

2010-02-02 23:32:48

Our ancestors used stones to break stones. With skill, they collided with each other and managed to extract sharp-edged pieces that they used as tools. Now, in the largest and most complex machine in the world, the same system is used. Tiny particles are made to collide with each other and the pieces are looked at in search of signals that allow us to understand the Universe.

The LHC (Large Hadron Collider) is used to collide protons. Inside an underground tunnel 27 kilometers in circumference, two beams with 300 billion protons circulate at speeds close to that of light and in opposite directions. In certain places of the ring there are gigantic and sophisticated detectors that capture the explosion of particles that occur in each collision.

However, two protons, when colliding, do not produce “pieces of protons” but hundreds of different particles, some of them much more massive than a proton. How is it possible? The laws that govern this world are a martyrdom for our reason, accustomed to observing the behavior of great things, susceptible to being captured by the senses. Newton does not rule there, that is the world of Special Relativity and Quantum Mechanics.

In our environment of big things, a car accelerates and remains a car, faster, but a car. This is because the speed that we are able to give it is ridiculously small compared to that acquired by the protons inside the LHC. There each proton is accelerated to speeds 99.999999% that of light. And, at those speeds, the protons change. The closer they are to the limit, the harder it is to accelerate them. It’s as if they were getting bigger and heavier.

Let’s imagine that we have a marble in our hand and that, by some means, we have the possibility of speeding it up as much as we want. At first it can be accelerated easily, like the car, but when its speed reaches values ​​comparable to those of light, the marble begins to put up more resistance. It behaves as if it had the mass of a larger object, one more acceleration and it behaves as if it were a billiard ball, if we continue to accelerate it the mass continues to increase and, at a given moment, when the speed approaches that of the light, it behaves as if it were heavy like a mountain. If at that speed we make it collide with another marble that is moving in the opposite direction, pieces of the mountain will fly out of the tremendous collision… of the mountain!

Among the remains of the LHC proton collision, scientists search for particles that no one has seen but whose existence is predicted by existing theories. The difficult thing is to find them because not only two protons collide in the detector, 600 million protons collide every second. In each collision hundreds of particles are created, including protons, antiprotons, electrons, positrons and many more. Analyzing them is a challenge that only the powerful computers at the LHC can do. Despite everything, looking for a new particle in that gibberish will be much more difficult than finding a needle in a haystack.

Don Alberto Casas explains to us today, in Talking with Scientists, the ins and outs of particle physics. Our conversation with him will allow us to enter that complex world. Don Alberto is the author of a magnificent popular book in which he reflects, in more depth, the contents expressed in the interview. The title is The LHC and the frontier of physics edited by Catarata and the CSIC.