haron1
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Why do two protons collides close to the speed of light in the LHC when two high energy photons can collide at the speed of light?
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teachercol
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Not sure what the question is.
Protons cant reach the speed of light because they have rest mass.
Photons always travel at the speed of light.
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Manitude
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Mass dilation of massive particles means you need ever increasing accounts of energy to accelerate protons towards the speed of light (in a vacuum). Ultimately you can never accelerate protons to c unless you can find 'infinite' energy. Photons are massless so don't have to obey the same rule.

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haron1
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(Original post by Manitude)
Mass dilation of massive particles means you need ever increasing accounts of energy to accelerate protons towards the speed of light (in a vacuum). Ultimately you can never accelerate protons to c unless you can find 'infinite' energy. Photons are massless so don't have to obey the same rule.

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so why in the Large Hadron Collider don't they collide photons
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teachercol
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Because photons don't have charge so you cant accelerate them .

The energy of the protons used is way more than the most energetic photons around. Gammas from radioactive sources typically have up to 10MeV; the protons used have more than a Tev. ie a hundred thousand times more
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Manitude
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(Original post by haron1)
so why in the Large Hadron Collider don't they collide photons
There's a number of reasons.

Photons aren't charged particles so they can't be manipulated by electric or magnetic fields. To get the same energy levels as the LHC achieves with protons you'd need extremely small wavelengths of light which would be very dangerous (I'm not even sure it would be possible given current technology to generate gamma rays of that energy anyway). Photons don't tend to interact much with other photons, and when they do the resulting products are not especially interesting to particle physicists. You can create fermion and anti-fermion particles but I think you'd be hard pushed to create anything more massive than an electron which severely limits the value of this process to science. An electron has a mass less than a couple of electron volts whereas the Higgs boson has a mass of more than 100 billion electron volts. To create a particle of that mass you need a highly energetic environment and pair production from accelerated photons (if it were possible to get them to collide like protons) wouldn't be a practical way to achieve that.

I'm not a particle physicist (did a few courses in it at university but that's it) but you'd also have to consider conserved quantities like strangeness, baryon number, charge, colour charge and lepton numbers. Photons don't have these properties so they're not helpful for investigating them.

Does that help?
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aamirac
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I want to go CERN and see the LHC....
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teachercol
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Been there and done that
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Joinedup
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(Original post by teachercol)
Been there and done that
Got the T shirt?
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