[Jonnytombstone (OP)]

Does a photon have truly zero mass? or is it just so tiny we cannot weight it? Just curious how it could collide without a mass

[Janus]

To the best of our knowledge, photons have zero rest mass.    But this does not mean that they cannot have momentum.  While in Newtonian physics, momentum is only a property of "mass", such is not the case under Relativity.

[Kryptid]

I'm pretty sure that any method we know of to measure mass would indicate that photons do have mass. They are pulled by the gravitational field of the Sun, so Newton's third law dictates that they must also be pulling on the Sun as well. You can't weigh a photon on a scale normally, but I'm pretty sure that what we know of physics indicates that a hollow sphere made of perfectly-reflective material would become heavier when placed on a scale if you had a lot of high energy photons bouncing around inside of it.

The difference between a photon and a particle like an electron is that there is no minimum mass that a photon can have. It can have an arbitrarily low mass that is related to its energy. Electrons, on the other hand, have a finite mass (0.511 MeV) even when they are practically motionless.

[yor_on]

I'm surprised Kryptid,  but it's different, and knowing you it will make me think.
Make your case

[Bored chemist]

Make your case

What?!

[yor_on]

for "I'm pretty sure that any method we know of to measure mass would indicate that photons do have mass." Bored chemist

[evan_au]

I'm pretty sure that any method we know of to measure mass would indicate that photons do have mass. They are pulled by the gravitational field of the Sun...

When physicists talk about the mass of some particle, they mean the mass measured when it is stationary relative to you.
Given this "rest mass", you can calculate the effective mass when it is traveling at any other velocity, relative to you.

Photons are pulled by the gravitational field of the Sun when they are traveling at the speed of light.
Relativity tells us that the effective mass of an object traveling at the speed of light is infinitely more than the mass when the same object is stationary (relative to you).
(Something finite)/Infinity = 0

Of course, light can never be stationary relative to you...

[PmbPhy]

While in Newtonian physics, momentum is only a property of "mass", such is not the case under Relativity.

Not necessarily. It depends on how mass is defined. There are two ways its defined in physics today, one of which defines mass as the m =p/v. The qualifier which distinguishes this is "relativistic mass"  whereas the other use is as you used it, i.e. rest mass. A significant fraction of any text a reader my buy on relativity or astronomy etc will use it. In fact its used in the text on the early universe that Alan Guth is working on. I placed a page which uses it on my website at
http://www.newenglandphysics.org/other/guth.jpg

Guth also did a video on this subject which anyone can see at
http://www.newenglandphysics.org/common_misconceptions/Alan_Guth_01.mp4

[Kryptid]

I'm surprised Kryptid,  but it's different, and knowing you it will make me think.
Make your case

I'm pretty sure that any method we know of to measure mass would indicate that photons do have mass. They are pulled by the gravitational field of the Sun...

When physicists talk about the mass of some particle, they mean the mass measured when it is stationary relative to you.
Given this "rest mass", you can calculate the effective mass when it is traveling at any other velocity, relative to you.

Photons are pulled by the gravitational field of the Sun when they are traveling at the speed of light.
Relativity tells us that the effective mass of an object traveling at the speed of light is infinitely more than the mass when the same object is stationary (relative to you).
(Something finite)/Infinity = 0

Of course, light can never be stationary relative to you...

I am, of course, speaking of relativistic mass since photons cannot be stationary relative to an observer. As such, I'm speaking of any method of measuring mass that would actually work for a photon.

[yor_on]

ok Kryptid.

Particles as a proton are presumed to consist of a boundary in where we find other 'smaller particles'  as gluons and quarks 'speeding around', which 'speeding' then creates a higher 'energy' if I got it right ;) that then due to the boundary defining it, also add up to its rest mass. The reason why they then are presumed to not break through this 'proton boundary' is then referred to as the strong nuclear force. If I now presume some of those 'particles' being at 'c' it then gives us two definitions of how to contain something at 'c', particles (of rest mass) and, event horizons.
=

Now, is that right?

When thinking of a event horizon it's the geodesics that is presumed to 'lead' the propagating photon. It's not a 'force' but a path. Then again, depending on definitions gravity also could be seen as 'negative energy' in which case?

The reason why a (rest)massless particle can be at 'c' is that it has no rest mass. The reason why something of rest mass can't be at 'c' is that it has one. But inside that 'proton boundary' we define gluons (or 'gluon fields') that presumably are mass less, and so 'traveling/propagating' at 'c'. And then we have ( https://en.wikipedia.org/wiki/Valence_quark ) quarks. " Quarks have an astonishingly wide range of masses. The lightest is the up quark, which is 470 times lighter than a proton. The heaviest, the t quark, is 180 times heavier than a proton -- or almost as heavy as an entire atom of lead... According to their results, the up quark weighs approximately 2 mega electron volts (MeV), which is a unit of energy, the down quark weighs approximately 4.8 MeV, and the strange quark weighs in at about 92 MeV. "  https://phys.org/news/2010-05-masses-common-quarks-revealed.html

This one is worth reading too.
https://physics.stackexchange.com/questions/261400/what-is-meant-by-rest-in-rest-mass#

[jeffreyH]

It may be more productive to think in terms of inertia. The energy of the photon can affect the inertia of other particles while only affecting it own energy. That is if we only consider collisions in a vacuum and in the absence of significant gravitational fields.

[yor_on]

Yes, inertia is a defining factor in the definition of 'relative mass' but what surprises me specifically is the fact that a particle can be seen as confining something of a massless nature. That makes me wonder how it does it, also if we then need to separate one massless particle from another. F. ex a photon relative a gluon, as the gluon is confined inside a particle (proton) whereas a photon isn't
=

How would one do that?
Define what differs one massless particle from another?
A combination of 'negative and positive' energy differing them? spin?
Or/and possibly, where they are situated at the measurement?

[yor_on]

There is a way around it of course :)
Stop talking about propagating, and start questioning motion.
But where would that leave relativistic mass?

What that would do the idea of particles never being without 'motion' should then be about the probabilities of them being before defined/measured, well possibly :)

[yor_on]

Let me put it as simple as I can and you point out where I go wrong.

We talk about invariant 'rest mass'. People tend to say nowadays that 'invariant' is the better expression. I don't agree with that. to me it's still the 'rest mass' that you measure. Why that is is because there is no golden standard that I know of when it comes to measuring your 'speed'. All uniform motions are the same from a 'black box scenario'. What that means is that you can't define anything as being 'still', except in the capacity of you being 'at rest' with what you measure.

So, how do we define a relativistic mass? You could argue that it's only in accelerations you can measure something, but that can't be correct as we can find different uniform motions, relative our own f.ex. Also we have ample evidence of it existing in our daily lives. So the relativistic mass must 'exist' even in a uniform motion.

But if the correct definition of measuring somethings 'intrinsic energy' only can be done while being 'at rest' with it, and if we then consider that there is no way of defining a speed to our combined 'system', then how can we define its relativistic mass?

As I think of it at the moment you have two choices

Either Einstein is correct, all uniform motions are equivalent (black box), and the 'speed' becomes superfluous for defining somethings energy. It's enough being 'at rest' with it, and so it also can be called 'invariant'.

Or there is something more to it. The speed you have build a added energy, even though we can't define what that speed is, and even though we can't measure a difference in a black box scenario.
=

Actually, the second definition would imply that there is a golden standard hidden, and with that rewrite relativity
And the first one imply something very thought provoking, but I leave that to you to find out :)

You can also consider a third in where the 'added energy' only is at the very moment of collision, but you would then have to define how and where it was before it?

Nowhere?

(See why I wonder about 'motions and propagation's' :)

[Jonnytombstone (OP)]

So a photon with a 300Ghz f and 124 eV the mass would be around 2.21092x10^38kg?

I got that by using the formula eV/c^2

[PmbPhy]

Does a photon have truly zero mass? or is it just so tiny we cannot weight it? Just curious how it could collide without a mass

Its not possible to tell. The limit on the photons proper mass as given in Classical Electrodynamics - 3rd Ed. by J.D. is les than 10^-51 kg.

Not too long ago everyone was nearly certain that the mass of the neutrino was zero. That turned out to be wrong.
 -

[evan_au]

a photon with a 300Ghz f and 124 eV

This does not sound right.
Green light has a frequency around 560 THz (or 2,000 times higher than the longwave IR photons you are considering).

A green-light photon has an energy of around 1.7eV, which is enough to trigger some chemical reactions (eg vision and photosynthesis).

This comes from the formula E=hf
Where:
- E is the energy in electron-Volts
- h is the Plank constant (4.135667662×10⁻¹⁵ eV.s)
- f is the frequency in Hz

124eV represents X-Rays, and has enough energy to rip inner electrons out of big atoms.

See: https://en.wikipedia.org/wiki/Planck%E2%80%93Einstein_relation

I got that by using the formula eV/c^2

To look at the energy of a photon, you should use this more complete equation:
E² = (pc²) + (m₀c²)²
where:
- p is the momentum of the photon
- c is the speed of light
- m₀ is the proper mass of the photon

Since the proper mass of the photon is immeasurably different from zero (if not exactly zero), most of the energy of the photon comes from its momentum, which is definitely not zero and is easily measured.
See: https://en.wikipedia.org/wiki/Energy%E2%80%93momentum_relation

[yor_on]

A funny thing about 'photons' is the idea that they are the force carriers of Electromagnetism. And I think one might connect this to the question of 'massless particles' found to being confined by 'gravity', or inside a 'atom'. The reason why they don't speed away at 'c' when commuting at/in a EM field seem to be that they are 'virtual' , That one I read as a result of time though?
=

It's a question of amplitude in QM if I got it right,  indeterminate values (as in 'action and reaction' although not really:) in a 'field' that doesn't 'interact' as much as it negates (quench) whatever fails some rules of possibility/probability. But very little of that is about time, at least not from the point of it being a 'arrow of time', or possibly nothing at all. The outcomes we see though is a direct description of our arrow of time.

If you can imagine such a 'field' made out of 'probabilities', then the idea of virtual photons seems to be wrong, at least not carrying a full picture of what's 'happening'. It's much more of a 'gestalt' falling out into outcomes than of 'propagating force carriers' to me. The really interesting thing about this 'gestalt' though, is that it gets its further determination through whatever outcomes that defines it under our arrow. We make it dance, and the way we do it is through probability and 'free will'. And yeah :) It makes us dance in a way through its rules, but don't forget HUP and 'free will'. That's what creates one future, of many possible.

Although one might to be able to argue both as a result of time? But then one also would need to introduce a new concept of time, one in where 'time' 'under' some threshold (scale?) loses its arrow. Which in a way knits nicely to the idea of decoherence

Also, this is a much more satisfying concept to me than the idea of 'many worlds'. If there is a 'gestalt' then it is all there, and it stays the same, although outcomes do become varied, through rules, probability and 'free will'. And yes, it demands a arrow of time to exist (for us at least).

The main difference is that this stay inside 'what you see is what you get' without introducing new 'universes' generated through unfulfilled probabilities. And it defines a 'magnitude of energy' without the need of explaining how those new 'universes' get theirs, and of course, their off springs too. Because what holds for us should then hold for them, ad inifinitum.

Logically the problem I see goes like this. In a many worlds scenario you can't define a magnitude of energy to whatever 'gestalt' generating new ones. It  has to be infinite, as the the new ones will generate their own versions, generating their own, ad infinitum.

If we now presume there to be a limited set of rules and conventions defining a single outcome, then this will put into question this infinity of universes creating, that is if presuming that what holds for us (rules etc) also holds for those new 'universes'. There can only be so many possibilities, presuming a defined set of rules, which then leads one to the conclusion that the (meta) universe /gestalt then infinitely must repeat itself as it meets the limit of possibilities defining a outcome in each specific case/moment. The whole concept becomes ludicrous when thinking of it this way as what it should mean is that there also must be a infinity of 'universes' being the exact same as ours in every aspect, as in 'you' being there doing the same things, using the exact same shoes, thinking the same thoughts etc etc.

Although, once more, this demands 'time' to be something in itself.
No illusion.