May 19, 2014
Turning Light Into Matter: Scientists Say 80-Year-Old Theory Is Provable
Lawrence LeBlond for redOrbit.com - Your Universe Online
First theorized in 1934 by a pair of scientists – Gregory Breit and John Wheeler – turning light into matter was deemed a fantastical and equally impossible feat. By smashing two photons together at a high rate of speed, the scientists hypothesized that it could create an electron and a positron.An occurrence of such magnitude was deemed extremely rare and difficult to reproduce. So rare that it has never been observed in any laboratory setting since it was first theorized 80 years ago.
At the time, Breit and Wheeler said they never expected anybody would actually physically be able to demonstrate their theory – despite it being a theoretically sound prediction – due to the requirement of massive high-energy particles to test it.
But new work, published in the journal Nature Photonics, shows for the first time how Breit and Wheeler’s theory could be proven in practice.
On a single day, while enjoying several cups of coffee in a tiny office, three physicists working at Imperial College London worked out the relatively simple way to physically prove the Breit-Wheeler theory.
They explain that a ‘photon-photon collider,’ which would convert light directly into matter using technology already available, would be a new type of high-energy physics experiment. The experiment would recreate a process that existed within the first 100 seconds of the Universe’s creation and has also been observed in gamma ray bursts, which are the biggest explosions in the known universe and one of the greatest unsolved mysteries of physics.
The team was investigating an unrelated problem in fusion energy when they realized what they were working on could be easily applied to the 80-year-old light-matter theory. The breakthrough was achieved as the two researchers collaborated with a fellow theoretical physicist from the Max Planck Institute for Nuclear Physics, who was visiting ICL.
Demonstrating this decades-old theory would provide a final piece of the physics puzzle which describes the simplest ways in which light and matter interact. Six other pieces of the puzzle, including Dirac’s 1930 theory on the annihilation of electrons and positrons and Einstein’s 1905 theory on the photoelectric effect, are all associated with Nobel Prize-winning research.
“Despite all physicists accepting the theory to be true, when Breit and Wheeler first proposed the theory, they said that they never expected it be shown in the laboratory. Today, nearly 80 years later, we prove them wrong. What was so surprising to us was the discovery of how we can create matter directly from light using the technology that we have today in the UK. As we are theorists we are now talking to others who can use our ideas to undertake this landmark experiment,” Prof Steve Rose from the Department of Physics at ICL, said in a statement.
The experiment would involve two key steps.
In the first step, scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire them into a slab of gold to create a beam of photons a billion times more energetic than visible light.
In step two, the experiment involves a tiny gold can called a hohlraum (German for ‘empty room’). Scientists would fire a high-energy laser into the inner surface of the can to create a thermal radiation field and generate light similar to the light emitted by stars.
Then, the photon beam from the first step would be directed into the can, causing the photons from the two sources to collide and form electrons and positrons. The scientists can then detect the formation of the electrons and positrons as they exit the gold can.
“Although the theory is conceptually simple, it has been very difficult to verify experimentally,” said lead researcher Oliver Pike, who is currently completing his PhD in plasma physics. “We were able to develop the idea for the collider very quickly, but the experimental design we propose can be carried out with relative ease and with existing technology. Within a few hours of looking for applications of hohlraums outside their traditional role in fusion energy research, we were astonished to find they provided the perfect conditions for creating a photon collider. The race to carry out and complete the experiment is on!”
The research, was carried out in collaboration with MPI-Kernphysik and was funded by the Engineering and Physical Sciences Research Council (EPSRC), the John Adams Institute for Accelerator Science, and the Atomic Weapons Establishment (AWE).
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