# Particle accelerator relative mass and redshift

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Hi all

Relativity tell us that we cannot accelerate something up to c. The closer we get to c the more energy is needed to get the same acceleration. An explaination I often readed is that a part of the energy is converted to relativist mass and having more mass to accelerate need more energy.

An experimental proof often cited is the case of particle in accelerator. I don't know if there are other experimental proof...

The basic principle used in particle accelerator is to used an electric field to "push" the particle. How the electric field push on the particle is by mean of virtual photon exchange.

My question is do we need the relative mass increase to explain that we need more energy to get the same acceleration? I have an other explaination:

The closer the particle speed get to c the more redshifted the virtual photon getting to the particle and redshift mean less energy delivered to the particle. In short, it is an eneergy transfer problem and has nothing to do with increase in relative mass.

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I'm not sure I understand. Do you mean that for a field to act on the particle to accelerate it virtual photons have to reach the particle; catching up with the particle means they are red shifted an they have leass energy?

If I have understood that bit then please help me ot here because my physics isn't that good.

Imagine I have an electron between two metal plates. I put a voltage beween those plates and the electron accelerates towards the positive one.

Do the virtual photons that carrry the energy move from the positive plate (in which case they would be blue shifted or the negative one (red shifted) and how do they know which plate to come from- after all, until they get there they don't know if I started with a positron?

Do they come from both plates and, if so, do the effects cancel out?

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You understand me correctly. I am not that good also in physic that is why I asked, but you make a good question about how the virtual photons are exchanged. I don't really understand how the electric force is mediated with the virtual photons. I know the analogy using two persons on ice, pitching eachother a ball... That easy to imagine for the repulsive force but it is an other story triing to have an analogy for the attractive force.

Before you brought that point, I took a look at the equations for the relativistic doppler shift and for the relative mass increase, and I remarked that both use the same gamma factor...

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