Testing Einstein’s relativity with the most Energetic Photons in the Universe

Hello, I’m going to get you some pics (and maybe a movie) of inside the telescope when it STOPS RAINING.

Anyway, I said that I would start to tell you about my latest research.  I recently put a new paper on the arXiv called “The CTA Sensitivity to Lorentz-Violating Effects on the Gamma-Ray Horizon” catchy title, yeah?

CTA stands for Cherenkov Telescope Array which is a special kind of telescope which is being designed and having test parts built at the moment which looks for very high energy photons called gamma rays (in increasing photon energy from low to high you have radio waves (urm.. radio), microwaves (cooking), infra red (night vision), red, yellow, green, blue, ultra violet (sunburn), x-rays (dentist), gamma rays (incredible hulk) then you run out of words and have to say “very high energy gamma rays” (VHE gamma rays).  We should probably call them stupo-rays or something.).  There may be higher energy gamma rays that are detected in cosmic ray detectors but you can’t really easily tell if they are photons or something else like protons.  So lets just stick to the story that CTA will detect the highest energy photons in the Universe.

CTA will look like this which I think you will agree doesn’t look much like a normal telescope for optical (red, green, blue etc) photons.  It may be built in Namibia where there is already a really good VHE gamma ray telescope called HESS or it may be built somewhere else and since I’m just an associate member of the collaboration and not a full member I get to avoid politics like that completely. HESS is really good, a great success but CTA will hopefully be even better and detect more and higher energy gamma rays.

Anyway, what is my paper about?  Most photons fly through the Universe and only stop or get scattered if they hit a charged particle like an electron or a proton.  These VHE gamma rays are so energetic they can actually hit other low energy photons, for example the photons that are emitted by stars, so hard that they can annihilate each other into matter and anti-matter, an electron and an anti-electron (positron) to be precise.  So they don’t get very far.  So you shouldn’t see very high energy photons arriving from very distant sources in the Universe.

Thing is, all of this relies upon Einstein’s theory of special relativity being correct at very high energies.  Some theories of quantum gravity may lead to his theory breaking down at high energies so that these VHE gamma rays don’t travel quite at the speed of light any more.  If this is the case then this matter/anti-matter collision business might not work so well, which means that they will be able to get through space after all!  So the signal we are looking for is some distant active galaxy which is pumping out loads of gamma rays.  We detect the lower energy gamma rays, then we see that at higher energies they start to go missing because they don’t arrive to the Milky Way, they hit another photon on the way and turn into electron-positron pairs.  However at REALLY high energies, if Einstein’s theory breaks down, we might start to see them turning up again.  So we would expect to be able to detect lower energy gamma rays (around a TeV), no detection of medium energy gamma rays (around 10 TeV) because they don’t make it through without creating matter and anti-matter but then if Lorentz symmetry is broken (Einstein’s special theory of relativity goes wrong at high energies) we could start to see the very high energy gamma rays turn up after all (around 100 TeV).

So we have estimated how well we will be able to test Einstein’s theory at high energies and it’s not bad, very competitive with some of the best other constraints which exist.  So that’s the kind of thing I do for my day job.  Hopefully the next post will be about the telescope…

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One thought on “Testing Einstein’s relativity with the most Energetic Photons in the Universe

  1. Pingback: Testing Einstein’s relativity with the most Energetic Photons in the Universe - CTA-UK

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