Does light, theoretically, have any mass?

[$trinick]

Photons are particles, yet they have no rest mass. They have inertial mass, which is not the same thing. If you tried to "weigh" a photon that was theoretically sitting as a regular particle at rest in the gravity field of earth, you would find that it does not have any mass whatsoever.

Actually, photons do have rest mass.

[Ad Bot]

[Blockzillahead]

you can turn mass into energy and vice versa. Light is energy

[Fennis]

the speed for any massless object is the speed of light. particles with mass don't move at the speed of light due to their inertia because of their mass. ergo, light is massless.

[Nexus]

If they don't have mass, how are they matter?

Sorry first-year physics is not doing me any good, but I love thinking about these subjects.

If you have heard of E = mc^2, that formula basically states that energy and mass are interchangeable.  Light has finite and well defined momentum based on its wavelength, and therefore energy.

[Swat 3]

And yet energy can be changed into mass and vice versa?

[$trinick]

Nuclear bombs turn mass into energy. I can't really give an example of energy turning into mass, but that's because it takes an absurd amount of energy to make mass.

[Night Fox]

you can turn mass into energy and vice versa. Light is energy

news flash something can have both energy and mass

[Nexus]

And yet energy can be changed into mass and vice versa?

That is the basis of a nuclear reaction yes.

Also to the person wondering about solar sails, Photons are indeed able to transfer momentum, which does not imply that they must have mass to do so.  That is also how solar panels work.  Any transfer of momentum generates impulse.  Impulse being transferred over time is equivalent to force.

[Ipquarx]

Actually, photons do have rest mass.

http://www.wolframalpha.com/input/?i=mass+of+a+photon

/thread

[Treynolds416]

Nope, maybe you should read back then

There is definitely a consensus on an answer on page one, but that doesn't make it the correct answer.

Alright, I read up a bit more and I think I understand it now. Photons do not have mass. It's impossible to quantitatively measure and confirm this though, which is why there's such a large amount of controversy surrounding this question. It makes more sense in our current version of the universe for the photon to have no mass. The fact that photons react to gravity/force can be explained away because when light is sucked into a blackhole, it's not caused by gravity. Gravity is just a measure of the closest distance between objects in the curvature of spacetime. Therefore, photons only need have energy to be able to experience a force from another entity.

Furthermore, by f=ma, force incurred by this will yield a theoretically infinite acceleration because the mass of a photon is 0. This fits nicely into the theory of general relativity; no physical object can reach the speed of light because they do not have 0 mass.

[Flatflyer]

That moment when I realize I learn more from topics like this than I do from school.

[BluetoothBoy]

Alright, I read up a bit more and I think I understand it now. Photons do not have mass. It's impossible to quantitatively measure and confirm this though, which is why there's such a large amount of controversy surrounding this question. It makes more sense in our current version of the universe for the photon to have no mass. The fact that photons react to gravity/force can be explained away because when light is sucked into a blackhole, it's not caused by gravity. Gravity is just a measure of the closest distance between objects in the curvature of spacetime. Therefore, photons only need have energy to be able to experience a force from another entity.

Furthermore, by f=ma, force incurred by this will yield a theoretically infinite acceleration because the mass of a photon is 0. This fits nicely into the theory of general relativity; no physical object can reach the speed of light because they do not have 0 mass.

Thank goodness, finally. I was wondering when someone would bring spacetime into this. It's really quite important for this topic.

That moment when I realize I learn more from topics like this than I do from school.

Well, most classes don't allow students to discuss a specific topic in class. They just teach the subject and give you homework.