In a particle accelerator, the first fractions of a second after the Big Bang were reconstructed

Scientists were able to recreate in a particle accelerator the first millionths of a second after the Big Bang, and collect circumstantial evidence that during a series of experiments they conducted, new matter was created, which only existed close to the Big Bang

In a particle accelerator, scientists managed to recreate the first millionths of a second after the Big Bang, and to gather circumstantial evidence that during a series of experiments they conducted, new matter was created, which only existed close to the Big Bang - the massive explosion in which scientists believe the universe was created about 12 billion years ago.

The discovery may help to better understand the process of organizing the chaos that reigned near the big bang into the material that exists in the universe today. The series of experiments, conducted at the CERN particle accelerator in Geneva, began in 1994 and involves scientists from 25 countries, including a group of physicists from the Weizmann Institute.

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The new material is considered to be the source of all matter in the universe, and the experiments in Geneva may help explain how the particles, their mass, and ultimately the entire universe were formed from this material, says Prof. Yitzhak Tsaroya, who heads the group of physicists from Israel.

The new material - or "quark-gluon plasma", as it is called scientifically - is a compressed gas, consisting of particles called quarks and gluons that float freely in it. In the normal state, the quarks are tightly connected to each other by the gluons. Together they make up larger particles, protons and neutrons, which are found in the atomic nuclei of all matter in the universe.

The quarks and gluons, today considered the building blocks of matter, floated freely in the plasma only in the first fractions of a second after the Big Bang. At that time there were no atoms or atomic nuclei in the universe, and in fact, the protons and neutrons had not yet been born either. Later, when the universe cooled a little and its density decreased, the quarks and gluons organized themselves in different combinations that created more complex particles, such as protons and neutrons. Since then, the quarks - and the gluons connecting them - have been trapped in them.

In the past, physicists have already discovered that, strangely enough, the strong force acting between quarks and gluons weakens when the quarks are close to each other and strengthens precisely when they move further apart. No matter how much they try to separate, they will remain connected, as if they were connected by a kind of spring or rubber band.

The scientists in Geneva tried to recreate the conditions that prevailed in the first fractions of a second of the Big Bang. For this purpose, they accelerated lead nuclei in the particle accelerator. The nuclei flew at a speed close to the speed of light and collided with each other, creating a heat approximately 100 thousand times higher than the temperature in the center of the sun and their density was 10 times greater than that of a normal atomic nucleus.

The new quark-gluon plasma existed for a very short time, so scientists could not get direct evidence of its existence. It cooled down in the blink of an eye, turning into thousands of particles in a normal state. Then, in a series of different experiments, the scientists collected data from seven particle detectors and examined the remnants of millions of collisions of lead nuclei to find out whether the plasma was indeed formed.

The results of the experiments matched the predictions. Thus, for example, in an experiment headed by Prof. Tsaroya, a large excess of electron and positron pairs was discovered (the positron is the antimatter of the electron) - far beyond what would have been created in a collision with normal matter.

One of the main points in the announcement of the discovery concerns an exciting prediction known as the "theory of quantum chromodynamics", which predicted the transition of matter from a normal state to the state of the quark-gluon plasma under extreme conditions of density and temperature.

Some claim that political considerations were involved in publishing the results of the experiments from the European accelerator on Thursday, and that they rushed to publish an interim summary of all the years of work, even though they do not constitute conclusive evidence of the existence of the quark-gluon plasma. This is to advance the publication of the results from a new American accelerator, whose experiments will begin soon, and which are expected to receive much better evidence for the existence of plasma.

Prof. Tsurya is now staying at the Brookhaven National Laboratory, New York, where the experiment is expected to begin in the spring in the new particle accelerator, where the nuclei of gold atoms will collide with each other, with an energy 10 times greater than that at CERN. In Brookhaven, the conditions will be much better, because the energy It is higher, the life time is longer and the density and temperature will also be higher", says Prof. Tsroya. Therefore, "we hope to see things much stronger and clearer than what we saw at CERN."
{by Tamara Traubman. appeared in Haaretz newspaper, 15/2/2000)
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