# Why photons are massless

1. Nov 11, 2014

### jerromyjon

From what I understand Einstein was the person who decided length contraction would indeed occur in the vector of velocity, more so as you approach c.

If it were possible to accelerate a particle to c, would the length would become 0?

If the length were to become zero, would the notion of mass become 0 as well?

Also, if the passage of time does tend to reach 0 at c and z becomes 0 would it not make sense that x and y would scale proportionally as well?

I'm not positive of the proper terminology but looking at the spin foam models it would be like the tetrahedral 4 dimensional "imagined" shape where you are in the point in the center and the time points behind your direction of travel and the face triangle would be perpendicular to your velocity vector and the x,y,z would depict your "view" of space.

Is any of this supported by accepted theories?

2. Nov 11, 2014

### mathman

Since it is impossible to accelerate a particle to c, requiring infinite energy, the other questions are not too meaningful.

Time dilation and length shortening are not intrinsic to the particle being accelerated. They are observations made in the rest frame.

3. Nov 11, 2014

### jerromyjon

I'm basically asking hypothetically since the data that we do have leads to the prediction that it would take an infinite amount of energy to achieve a velocity of c. Is there a linear relationship between dilation and contraction and do they both reach infinity at c?

From my understanding, an observer approaching c would not be able to detect anything changing within their local frame of reference, a second would remain a second and a meter would remain a meter, but would the universe around them appear larger and faster?

4. Nov 11, 2014

### Staff: Mentor

Not really. (Bringing in spin foams in particular is not helpful; spin foams are an advanced quantum gravity concept, and you're trying to understand basic SR.)

No, it would appear smaller (at least along the direction of relative motion) and slower. (If by "appear" you mean "what the observer would actually observe through a telescope", there are other more complicated effects as well, such as relativistic Doppler and aberration of light.)