What is the time for a photon

Physics of light: And yet they collide!

What happens when two particles of light meet? Nothing at all. For a long time it was said in school books that light does not break through light. The particles that make it up (photons) would fly freely through the area and, in an emergency, past each other. Not true, researchers from Cern are now suggesting. As early as 2015, they had found the first direct evidence of collisions between light particles in experiments at the Geneva particle accelerator. Well, two years later, they officially (Nature Physics: Atlas Collaboration, 2017) published.

Among the four billion lead ion collisions that took place in the accelerator, the researchers recorded 13 events that they believe to be photon collisions. According to the high standards of physicists, a few more events are missing for an absolutely reliable proof. According to Andreas Hoecker, the deputy head of the experiment, these are expected for the next experiments at the end of 2018.

The researchers discovered the interactions between the light particles rather casually - during the experiments with the lead ions, which actually have a different purpose. The researchers use them to study plasma as it was present at the time our universe was formed. In these experiments, lead ions are set on a collision course at almost the speed of light. If they rush past each other, a large electromagnetic field is created that corresponds to a fairly high level of real high-energy photons. The creation and immediate annihilation of virtual pairs - so-called electrons and positrons - creates the interaction of the photons of the two lead ions that snap together.

LHC particle accelerator

Cognition machine

The Large Hadron Collider (LHC) at the Nuclear Research Center Cern should help that final questions of physics to answer: How did the universe begin? What is it made of? What's holding it together? For this purpose, protons are almost raised in a 27 kilometer long ring-shaped tunnel Speed ​​of Light accelerated and brought to a collision. Detectors as high as a house record the traces of those particles collision arise.

The main goal of the LHC was to clarify whether it was Higgs boson gives. The particle, transfigured by some into a "particle of God", was the last component in the for a long time Standard model of modern physics, which has not yet been proven. It explains why things are one at all Dimensions to have. In 2012, physicists finally did first clues found - meanwhile the existence of the Higgs boson has been confirmed. Peter Higgs and François Englert therefore received the Nobel Prize in Physics in 2013. They had theoretically predicted the existence of the particle as early as 1964.

These events are very rare, said Hoecker. He doubts that there will be any practical use for the quantum computer, for example. Nevertheless: "It could be that not only electrons and positrons, but also heavier, as yet unknown particles are produced. To prove that would be revolutionary new physics," he said.

Physicists had suspected it for a long time

A good 150 years ago, the physicist James Clerk Maxwell formulated an equation for understanding electromagnetism, according to which light rays do not influence each other. It has become a standard assumption in physics. That something could not be right about it became clear at the latest since the German physicists Werner Heisenberg and Hans Euler made a prediction in the context of quantum electrodynamics in 1935 that in very rare cases there is a possibility of an interaction between photons. Since the 1970s, such phenomena had been measured indirectly, but never directly.

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However, proving that they do that was considered almost impossible. Therefore, the results that have now been published are already considered to be very important. The first media reported on the success as early as February.