## Do photons have non zero rest mass?

According to electromagnetic theory, the rest mass of photon in free space is zero and also photon has non-zero rest mass, as well as wavelength-dependent. The very recent experiment revealed its non-zero value as 10 – 54 kg ( 5.610 × 10 – 25 MeV c – 2 ) .

## What is the meaning of non zero mass?

From Wikipedia, the free encyclopedia. In particle physics, a massless particle is an elementary particle whose invariant mass is zero. The two known massless particles are both gauge bosons: the photon (carrier of electromagnetism) and the gluon (carrier of the strong force).

**How can a photon have no mass?**

Since photons (particles of light) have no mass, they must obey E = pc and therefore get all of their energy from their momentum. If a particle has no mass (m = 0) and is at rest (p = 0), then the total energy is zero (E = 0). But an object with zero energy and zero mass is nothing at all.

### Do photons gain mass?

Also, photons never gain mass, they are always massless particles. They have energy due to their momentum, but no mass.

### How does gravity affect light if it has no mass?

It might be surprising to you to hear that gravity can affect light even though light has no mass. If gravity obeyed Newton’s law of universal gravitation, then gravity would indeed have no effect on light. However, when gravity is very strong, the bending of light’s path becomes significant.

**Why photon rest mass is zero?**

The rest mass is the mass of a particle (in our case the photon) as measured by an observer who sees the particle still and with zero speed. Thus comes the term REST mass. But according to special relativity, light ALWAYS travels with the light speed c, and is NEVER at rest. And so it has zero REST mass.

## Which particle has no mass?

electron

The subatomic particle with almost no mass is the electron. The approximate mass of the electron is 1/1840th of an atomic mass unit.

## What is the smallest nonzero mass?

The smallest, non-zero mass of a particle that has actually been measured, would be the electron mass, 511 keV. There is no limit to how small a mass can be.

**Why is light affected by gravity if it has no mass?**

It might be surprising to you to hear that gravity can affect light even though light has no mass. According to general relativity, gravity is actually caused by a curving of space and time. Since light travels in a straight line through straight spacetime, the curving of spacetime causes light to follow a curved path.

### What is the effective mass of photon?

A Photon has zero mass but since it can do work it is done in terms of kinetic energy. As it possesses kinetic energy, using Planck’s constant, speed of light and wavelength we can obtain a relation for calculating the effective mass. Hence, this is the effective mass of a photon of wavelength λ.

### Why can’t light escape a black hole if it has no mass?

Even though photons have no mass, they are still affected by gravity. That’s how we can see black holes – by the way they distort the light going near them. The reason nothing can escape a black hole is because within the event horizon, space is curved to the point where all directions are actually pointing inside.

**Can gravity exist without mass?**

The only way to get gravity is with mass. The more mass, the more gravity you get. Without mass, you can’t have gravity. The force of gravity that we feel is actually just an acceleration towards the center of the Earth at 9.8 meters per second squared, or 1G.

## Is the rest mass of a photon zero?

It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces.

## Why are photons required to be massless?

Well, in the case of photons, it is simply not possible to add or include any kind of mass term for a photon without violating this gauge symmetry principle in the theory of QED. Thus, photons are required to be massless for quantum electrodynamics to work.

**How is the mass of a photon related to its energy?**

If we set the rest mass equal to zero (regardless of whether or not that’s a reasonable thing to do), then E = pc. In classical electromagnetic theory, light turns out to have energy Eand momentum p, and these happen to be related by E = pc. Quantum mechanics introduces the idea that light can be viewed as a collection of “particles”: photons.

### What is the upper limit on photon mass?

The original concentric spheres experiment performed by Cavendish in 1773 gave an upper limit on q of |q| 0.02, and this result was improved to |q| 5 ×10−5 in 1873 by Maxwell. The corresponding limits on the photon rest mass are 1 ×10−40 g and 5 ×10−42 g, respectively, as was mentioned above.