# Can eletrons travel faster than light?

G

#### Guest

##### Guest
Okay I'm not entirely sure of myself here but is it possible to accelerate an electron past the speed of light.

I refer to the equation eV=1/2mv^2 where 'e' is the charge of the electron, V is the potential difference between two points, 'm' is the mass of the electron and 'v' is the speed of the electron.

Right the speed of light is taken as 3X10^8 so lets work with obtaining a speed of 4X10^8. Using 9.1X10^-31 as the mass of the electron when we substitute these values into the formula of kinectic energy 1/2mv^2 we get the value of 7.28X10^-14 which according to the above equation is equal to eV.

Now when we divide this value by 'e'(1.6X10^-19) we get 455000V as the potential difference. So to satisfy my curiousity what happens when you apply this potential difference to a cathode ray tube?

Well, an electron can not exceed the speed of light in a vacuum i.e. c. However, it is possible for an electron to exceed the local speed of light in a medium. We know that the speed of light in a medium is reduced from that in the vacuum by c/n, where n is the index of refraction of the medium. This sort of phenonmenon of exceeding the local speed of light produces Cerenkov radiation which is a sort of an electromagnetic version of a sonic boom. The problem that you have encountered in your calculation is that you have taken the mass of the electron to be constant. However, mass is not constant when you are talking about relativistic velocities, i.e. speeds close to light. You must substitute the following for mass, m = m0/(1-(v/c)^2)^0.5, where m0 is the rest mass of the object in this case the electron. So you find that it takes an infinite amount of energy to accelerate an object with mass to the speed of light. Sorry.

I read where an experiment was done in california where a photon was accelerated and it beat the speed of light because the photon changed its shape at the end of its acceleration resulting in what appeared to be the fact that it reached its destination faster than the speed of light....It changed into a teardrop forward and got to its point microseconds faster than it should have. It was written up in a recent Discover Mag article....there was a lot of scientific reluctance to believe this results and the experiment was going to be repeated/

Electrons can't travel faster than light fopr the simple reason that as a lepton (which an electron is) it's much much bigger than a photon and therefore has more friction. I'd say that the best way to travel at faster the speed of light is to accellerate a photon. This would mean it goes back in time.

But you forget the &amp;#268;erenkov radiation effect...

is electromagnetic radiation emitted when a charged particle (such as a proton) passes through an insulator at a speed greater than the speed of light in that medium. The characteristic "blue glow" of nuclear reactors is due to &amp;#268;erenkov radiation. It is named after Russian scientist Pavel Alekseyevich &amp;#268;erenkov, the 1958 Nobel Prize winner who was the first to characterise it rigorously.

more at:

It's been a while since I saw this post...like 9 years. /ttiforum/images/graemlins/smile.gif

Anyway, James made a simple error in his post - one of omission.

He has the correct equation for Newtonian physics. But in the case of objects having velocities closely approaching the speed of light his knietic energy (1/2 mv^2) has to have the following notation:

m = m(o)/sqrt(1-v^2/c^2)

As v/c ---&gt; 1, m ---&gt; infinity.

As mass tends to infinity the inertia of the electron also tends to infinity. Inertia is the property of mass that resists acceleration. As the electron approaches the speed f light the force required to overcome the inertia that is approaching infinity in order to further change the velocity, also approaches infinity.

And that's why the electron can't be accelerated to the speed of light.

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