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    A New Hypothesis About A Theory: The 80-Year Quest To Turn Light Into Matter
    By News Staff | May 18th 2014 03:56 PM | 9 comments | Print | E-mail | Track Comments

    Physicists say they have discovered how to create matter from light - a feat thought impossible when the idea was first theorized 80 years ago. There is just one problem. In order to test the newest hypothesis, a new& machine would have to be built.

    In just one day over several cups of coffee in a tiny office at Imperial College London, three physicists believe they worked out a relatively simple way to physically prove a theory first devised by scientists Breit and Wheeler in 1934. Yes, they solved a puzzle that has eluded the rest of the world in an afternoon. Well, on paper.

    Breit and Wheeler suggested that it should be possible to turn light into matter by smashing together only two particles of light (photons), to create an electron and a positron – the simplest method of turning light into matter ever predicted. The calculation was found to be mathematically sound but Breit and Wheeler said that they never expected anybody to physically demonstrate their prediction. It has never been observed in the laboratory and past experiments to test it have required the addition of massive high-energy particles. 




    This shows theories describing light and matter interactions. Credit: Oliver Pike, Imperial College London

    The new proposed 'photon-photon collider' would convert light directly into matter using technology that is already available, would be a new type of high-energy physics experiment. This experiment would recreate a process that was important in the first 100 seconds of the universe and that is also seen in gamma ray bursts, which are the biggest explosions in the universe and one of physics' greatest unsolved mysteries.

    They had been discussing fusion energy when they determined that what they were working on could be applied to the Breit-Wheeler theory. 


    Obviously, demonstrating the Breit-Wheeler theory would provide the final jigsaw piece of a physics puzzle which describes the simplest ways in which light and matter interact - but it hasn't been realistic. The six other pieces in that 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 (see image). 

    Professor Steve Rose from the Department of Physics at Imperial College London said, "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."

    The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light.

    The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars.

    They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can.

    Lead researcher Oliver Pike who is currently completing his PhD in plasma physics, said: "Although the theory is conceptually simple, it has been very difficult to verify experimentally. 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!"



    Published in Nature Photonics.
    Source: Imperial College London


    Comments

    testing anonymous functionality.

    MikeCrow
    Oh cool!
    I have an idea for a space propulsion system that would require this ability. I decided that it probably wouldn't work as the forces would most likely cancel, but....


    My idea is that you would use such a process to create electrons/positrons at the front of your craft, accelerate then to the rear of the ship where some of that force would accelerate the craft forward, then at the rear of the craft you let them annihilate, collecting the energy to be routed back to the front, to continue the process. Energy moves forward, mass moves to the rear.
    The forces would be small, but you wouldn't need reaction mass that you'd run out of over long periods of time.

    We can call it the Micro Drive :)
    Never is a long time.
    test

    This would trivially not work because you would just pump the moment around

    Exactly here:

    " collecting the energy to be routed back to the front"

    .... soorrryyy

    MikeCrow
    As I mentioned, I did come to the same conclusion.
    But let me ask, at the back, if you let the positron and electron collide in the middle of a sphere that would collect the gamma's, wouldn't the gamma's radiate in all directions? Ones hitting the rear of the sphere would remove inertia, but ones hitting the front would add to the inertia, and the ones hitting the side would do neither. That would still leave some forward force, right?

    Anyways, maybe some clever human can come up with a configuration that has even a fraction of directional force.
    Never is a long time.
    If your positrons and electrons were accelerated back (with what energy ?) to give the ship forward momentum, then the gammas from annihilation wouldn't radiate symmetrically : the doppler effect of the velocities of particles relative to ship would blue-shift (more momentum) the gammas on the back of the collecting sphere and red-shift the front facing ones (less momentum) in such a way as to exactly cancel any net momentum benefit. You can bet without bothering calculations because there is nothing in special relativity and particle physics that locally (and therefore globally) breaks momentum conservation, I think. Short of playing with GR (and exotic extensions like negative mass) any more convoluted attempts would be futile and would only serve as wasting more energy in the inescapable inefficiencies of the process. If your ship has so much energy to waste, better of just beaming it backward as photons.

    That energy would have to be stored as sacrificial mass anyway : even if you could "push" on empty space, the gained kinetic energy would have to come from somewhere. Well, maybe for slow speeds well below c that could be interesting to be able to "push on space", mass-wise, for instance a sacrificed gram of antimatter + matter could accelerate a 100 tons ship at about 42km/s (manned "short" trips to Jupiter and beyond possible) without having first to accelerate much more than 100 tons of propellant with your ship to be expelled later...

    The LA Times Article on this,
    http://www.latimes.com/science/sciencenow/la-sci-sn-creating-matter-from...
    also has a link to the Nature Photonics paper. Unfortunately it is behind a paywall. And it is not on Arxiv. (Or I didn't find it)
    So Pike et al. propose to make real photons by bremsstrahlung in a gold foil, which then hit photons in a cavity.
    So do they need a NIF-scale laser to generate enough photon density in the cavity? Or is something smaller possible?
    The SLAC experiment they quote is at
    http://www.slac.stanford.edu/exp/e144/e144.html and has preprints of their publications linked.

    John Duffield
    See the Imperial reportage http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummar... and note that they say "using the technology we have today in the UK". As far as I can tell this is massively important. It will demonstrate a direct photon-photon interaction which isn't actually modelled in QED. See http://en.wikipedia.org/wiki/Two-photon_physics and note this: "From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple". That's a tautology. Pair production does not occur because pair production occurred. There's all sorts of ramifications. Like the electron field is merely the photon field with a "spinor" frame-dragged chiral configuration.
    Zoran S. D.

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