Concepts of physics unclear

[ronthepon]

I had a good deal of problems with the physics I've been figuring out lately, and would really love anyone's help in having me clear them up.

 

For a start, let me ask the question I've always been bursting to ask:

 

Is the photon considered a particle with mass in any theory?

[Mercedes Benzene]

Is the photon considered a particle with mass in any theory?

 

I would say no, but then again I'm just saying that... I'm not backing that up with anything.

 

Here's one link that may help:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

 

 

This deals mostly with the relativity theory.

[ronthepon]

That's pretty vague over there. So is the answer more like: "nobody knows"?

[Mercedes Benzene]

Probably.

I'll do more research.

[UncleAl]

Is the photon considered a particle with mass in any theory?

Photons travel at lightspeed. The vacuum is not a dichroic or birefringent medium for photons even over millions of lightyears pathlength. Phenomena with photons as their virtual vector bosons have infinite range. A photon must have zero rest mass.

[ronthepon]

Photons must be massless when they are in a state of rest. However, is it possible for them to be in this condition?

 

dichroic or birefringent medium

I do not know what these terms refer to.

[UncleAl]

A massless particle's point of view is not an inertial coordinate system. It must travel at lightspeed for all inertial observers in all inertial frames of reference. Lorentz invariance is the reason Relativity works.

 

All frequencies of light from deep radio to hard x-ray travel through vacuum at exactly lightspeed. If the vacuum were dichroic or birefringent (if it were a dispersive medium vs. frequency or optical alignment) then lightspeed and path would be contingent upon frequency. There would be spectral spatial separation (chromatic aberration) around a point source viewed from a distance. Hubble views of galaxies do not chromatically smear. Supernovae in distant galaxies are point sources throughout the spectrum.

[Jay-qu]

I would say no, nowhere are photons considered to have mass, but I had heard of them having a momentum

[ronthepon]

I see. So photons have no mass associated with a rest condition.

 

Which brings me to asking the little deal Jay-Qu has said.

 

Photons must have momentum, I have heard of the term 'radiation pressure', and have seen an article in discovery where they experimentally prove that laser has indeed the power to impart momentum to objects of finite mass.

 

So can we say they have mass while they are in motion?

[InfiniteNow]

So can we say they have mass while they are in motion?

I would think you have to, but it seems odd if they truly have mass = 0.

 

If momentum = mass x velocity, then regardless of velocity, once you multiply it by zero you get a zero product.

 

Yet, the effects of mass (like gravity) are indistinguishable from uniform acceleration... so you could argue that the velocity itself provides some sort of mass. oyyy... ;)

 

 

This is a dilly of a strange question ron, but you know the answer is probably exceedingly simple. :)

[ronthepon]

Even I guessed that the velocity could contirbute to the mass of the photon.

 

But do we say that the energy that was once associated with the photon contributes to it's mass?

 

hf = mc^2 ...?

 

I have already been told that it has no rest mass. Obviously, withuot velocith it also lacks energy... because that's all there is to it, I think... energy due to travelling fluctuation of 'feild'.

 

However, I have come across references that quantum mechanics completely disbelieves in the concept of feild, and only in particles. Have I got that correct?

[Janus]

I see. So photons have no mass associated with a rest condition.

 

Which brings me to asking the little deal Jay-Qu has said.

 

Photons must have momentum, I have heard of the term 'radiation pressure', and have seen an article in discovery where they experimentally prove that laser has indeed the power to impart momentum to objects of finite mass.

 

So can we say they have mass while they are in motion?

 

Actually, No. What we run into here is a problem with definitions.

 

Today, in physics, the term "mass" in most circles refers to rest or "proper" mass only. Even the term "relativistic mass" has fallen into disuse.

 

You still can have relativistic momentum, but there need not be any mass associated with it.

 

Thus light is considered massless under all conditions.

[Shekhar]

photons rest mass doenot make sense but it can exert pressure ! If anything doesnot has mass then what's the meaning of its existence and physical properties ?

[Shekhar]

Even the term "relativistic mass" has fallen into disuse.

 

yes because the variance in mass on attaining speed as per relativity has no meanong as all speeds are relative.

[ronthepon]

We can have relativistic momentum, without associated mass, and photons are an example.

 

What is the equation for this momentum?

[Michaelangelica]

How come the eye of a frog can register a hit from one photon?

[CraigD]

Is the photon considered a particle with mass in any theory?

A few variant particle physics theories propose a rest mass for the photon (and many other massless particles). All that I’ve read propose that this rest mass is very low – in many cases, too low to be experimentally tested.

 

As many people have pointed out, the main consensus among particle physicists is that the rest mass of a photon is exactly zero. “Rest mass of a photon” is a somewhat troubling term, as, according to these theories, photons don’t truly ever travel at less than the speed of light, let alone stand still.

We can have relativistic momentum, without associated mass, and photons are an example.

 

What is the equation for this momentum?

 

The quantum mechanical equation for a photon’s energy:

Energy = Frequency * Plank’s constant

 

The classical equation for kinetic energy:

Energy = .5 * Mass * Velocity^2

 

Put them together, using the velocity of light © for Velocity, and you get:

Frequency * Plank’s constant = .5 * Mass * c^2

 

Rearranged:

Mass = 2* Frequency * Plank’s constant / c^2

 

So, for example, a photon of nice, hypography-blue (about 6*10^14 hz) can be thought of as having a mass of:

2 * 6*10^14 * 6.6*10^-34 / (3*10^8)^2 = about 9*10^-36 kg

 

As always when mixing quantum and classical equations, one must be careful not to jump to strange conclusions about what such things as “the mass of photon” actually means, but such calculations are still useful for such things as designing solar sails.