Massless particles

>but something without mass cannot interact with something that does have mass right?

What gave you that idea?

>>7637143
>but something without mass cannot interact with something that does have mass right?

Why would you assume that? That seems rather silly.

>>7637143
It says it has 0 mass. It then lists the inertial mass.

>>7637164
chill senpai not everybody is albert einstein, some of us had to learn this stuff in physics class.

>>7637143
photons can interact despite being massless because they have momentum, which is inversely proportional to their wavelength, rather than proportional to their mass. similarly, particles with mass also have a wavelength inversely proportional to their momentum. it's cool shit.

The confusion here is that the word 'mass' refers to a number of different quantities:
-The inertial mass (the resistance to acceleration)
-The gravitational mass (determines the force on a body in a gravitational field), -The rest mass
-Even energy is described as mass in relativity.

Newton united showed that gravitational and inertial mass were the same. Einstein then united energy and mass, so these three masses are treated as the same quantity: inertial mass.

However, rest mass remains divorced from the three masses united by Newton and Einstein.

Thus a photon has inertial mass, and therefore momentum, but no rest mass, so is 'massless' in quantum mechanics.

Quantum gravity fundamentally seeks to unite rest mass and inertial mass.

>>7637170
Zero rest mass.

>>7637170
>inertial mass of a photon
>how hard it is to accelerate it
ok

>>7637143
>>7637170
the 1 x 10^-18 eV/c^2 is not an inertial mass. it is the limit to which we have measured and confirmed that photons are massless. If a photon does have mass, it must be less than this amount.

Theory strongly indicates that photons are strictly massless.

>>7637200
OP here, how could a photon has mass though? As far as I understand Even if it's mass were infinitesimally small, it couldn't go the speed of light without infinite force pushing it

>>7637143

The number in question is an experimental upper bound, as listed in the Particle Data Group "bible".

>>7637205
If it had any mass, it would not travel at c. c could still exist, however, as a universal constant.

If a photon moved at less than c, it would have a variety of effects on physics, and we would be able to detect it. These experiments (all of which have been negative as to date) are the basis for the lower limit that is posted.

>>7637205

Nobody actually thinks that photons have mass, it's just that from an experimental point of view it's impossible to measure whether or not something has no mass. You can only go as far as the precision of your measurement apparatus.