Understanding the Mass of Light: Wave or Quanta?

[Monique]

Originally posted by decibel
SO at the end of all this...light does NOT have mass ( real kind of mass)...?

To end all of this? Isn't a person allowed to understand? Isn't this a discussion forum? Oh well..

 

[chroot]

Originally posted by Monique
To end all of this? Isn't a person allowed to understand? Isn't this a discussion forum? Oh well..

Monique -- what do you not understand? We'll certainly try to help.

- Warren

 

[Monique]

thanks Warren, I think I have to read up and refresh my mind before I can make a sensible discussion :)

 

[Arcon]

Originally posted by Monique
To end all of this? Isn't a person allowed to understand? Isn't this a discussion forum? Oh well..

I've never understood the desire to end a polite conversation when people still wanted to discuss it. But such is life!

This is one of those topics which has been debated in the physics literature for many decades and has been rather heated even in that literature.

However there is always PM. But I'll do whatever I can to clarify anything.

 

[Michael F. Dmitriyev]

Originally posted by HallsofIvy
No, light does NOT have mass. Haven't we had this question a number of times?

We’ll check up it now.
E=mc^2 (1)
Is it right?
E=h \nu\ (2)
Is it right?
When
mc^2=h \nu\
or
m=k\nu\ (3)

here k= h/c^2
m – the rest mass.
So?

 

[chroot]

No, Michael, that's not right. The equation you want is

E = \sqrt{m^2c^4 + p^2c^2}

In the case of light, m is zero, so this reduces to

E = pc

- Warren

 

[Michael F. Dmitriyev]

Originally posted by chroot
No, Michael, that's not right. The equation you want is

E = \sqrt{m^2c^4 + p^2c^2}

In the case of light, m is zero, so this reduces to

E = pc

- Warren

Whence you have taken m=0? Prove your statement please.

 

[chroot]

Read more.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

- Warren

 

[Arcon]

Originally posted by Michael F. Dmitriyev
We’ll check up it now.
E=mc^2 (1)
Is it right?
E=h \nu\ (2)
Is it right?
When
mc^2=h \nu\
or
m=k\nu\ (3)

here k= h/c^2
m – the rest mass.
So?

Things sure would be easier if terms were explicitly defined when they're used in a thread whose subject is about the meaning of a term. Since the topic of this thread is the mass of light and since there are different answers depending on what mass you're referring to it would be nice if we these terms were defined.

If the equation

E = mc^{2}

is supposed to hold for all values of energy/velocity then m is relativistic mass. If, on the other hand, you wrote instead

E_{0} = mc^{2}

then m would be proper mass (aka "rest mass"). Since you wrote it as it applies to a photon then the "m" is relativisitc mass and not rest mass. This is implied in your equation (2)

E=h \nu\

For this reason you can write

mc^2=h \nu\

But m is not rest mass.

Warren - You used the same symbol, m, to mean rest mass when the context Michael was using it implied it implied it was relativisitc mass.

Note: These arguements/expressions only apply to inertial frames of referance. I.e. the expression

E = \sqrt{m^2c^4 + p^2c^2}

(where "m" is proper mass) is invalid when the frame of reference is not an inertial one.

 

[chroot]

Arcon,

I don't ever use relativistic mass. I should perhaps have stated that I meant that m is rest mass, but I thought it was obvious.

- Warren

 

[Arcon]

Originally posted by chroot
Arcon,

I don't ever use relativistic mass. I should perhaps have stated that I meant that m is rest mass, but I thought it was obvious.

- Warren

It's obvious to me but it was not obvious to Michael.

 

[Michael F. Dmitriyev]

Originally posted by chroot
Read more.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

- Warren

I am informed on that explanation where you gave the reference...

Moderator edit: crackpotism deleted. Michael, please post your personal theories only in the Theory Development forum.

 

[Arcon]

Originally posted by Michael F. Dmitriyev
I am informed on that explanation where you gave the reference...

Moderator edit: crackpotism deleted. Michael, please post your personal theories only in the Theory Development forum.

Moderator - Please don't snip like that. I was comming back to this post to try to understand what Michael was talking about. Now I can't see how or where he was getting confused (which I think is the case).




By the way Michael - I can't recall if I mentioned this already - Since 1906 Einstein always assigned mass to light. The was a conclusion that he reached in his paper The Principle of Conservation of the Center of Gravity and the Inertia of Energy, Albert Einstein, Annalen der Physik, 20 (1906): 626-633.

The first part of the paper he gave this arguement
http://www.geocities.com/physics_world/sr/einsteins_box.htm

In the second part of that paper he used that argument to assign mass to radiation (i.e. light). He then derived an expression for the center of gravity. However this was a theme he maintained throughout the rest of his life.

In the 1906 paper Einstein wrote

If we assign the electromagnetic field too a mass density (rho_e)..

In his 1916 review paper on GR Einstein wrote

The special theory of relativity has led to the conclusion that inert mass is nothing more or less than energy, which finds its complete mathematical expression in a symmetrical tensor of second rank, the energy-tensor.
...
We make the distinction hereafter between “gravitational field” and “matter” in this way, that we denote everything but the gravitational field as “matter.” Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field as well.

That of course means Einstein was saying that light has mass (and therefore he was referring to what we call today 'relativistic mass")
In an section of one of his books Einstein was explaining the bending of light in a gravitational field. He wrote, referring to a man in an elevator

(1938) But there is, fortunately, a grave fault in the reasoning of the inside observer, which saves our previous conclusion. He said: "A beam of light is weightless and, therefore, it will not be affected byu the gravitational field." This cannot be right! A beam of light has energy and energy has mass. But every inertial mass is attracted by the gravitational field as inertial and gravitational mass are equivalent.

For more examples of relativistic mass see
http://www.geocities.com/physics_world/relativistic_mass.htm

There was a paper published a few months ago on this subject, i.e.

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71(9), 878, Sept. (2003).

 

[chroot]

Originally posted by Arcon
Moderator - Please don't snip like that.

This is my forum. I am upholding its rules. We have an entire forum for Michael to post his personal theories. This is not it.

- Warren

 

[Arcon]

Originally posted by chroot
This is my forum. I am upholding its rules. We have an entire forum for Michael to post his personal theories. This is not it.

- Warren

How do you know it was his personal theory and not his misunderstanding which needed to be corrected?

 

[chroot]

Originally posted by Arcon
How do you know it was his personal theory and not his misunderstanding which needed to be corrected?

I know the difference. If you'd like to discuss this more, please use the PM feature.

- Warren

 

[GRQC]

Originally posted by Arcon

By the way Michael - I can't recall if I mentioned this already - Since 1906 Einstein always assigned mass to light.

Light does not have mass, nor is mass a quantity which is relativistic. It is on par with proper time, which is a relativistic invariant. Simply put:

Proper time $\tau = \sqrt{t^2-x^2}$

Mass: $m = \sqrt{E^2 - p^2}$

Both are the magnitude of a four vector in spacetime, which is invariant under Lorentz rotations. For photons, both quantities are null vectors, and thus are 0.

The was a conclusion that he reached in his paper The Principle of Conservation of the Center of Gravity and the Inertia of Energy, Albert Einstein, Annalen der Physik, 20 (1906): 626-633.

I'm not convinced he said this, but even if he did: have you never said something, and later realized you mis-spoke your reasoning?

That of course means Einstein was saying that light has mass (and therefore he was referring to what we call today 'relativistic mass")

He wasn't saying that -- you are putting words in his mouth.

There was a paper published a few months ago on this subject, i.e.

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71(9), 878, Sept. (2003). [/B]

Am. J. Phys. is not where you go for cutting edge research in GR. It's a teaching journal. Go to arxiv.org instead and find some papers.

 

[eagleone]

Let’s simplify it. And take it my way :).
Does the light have it’s own gravitational field, or is it a source of gravity ?
No - as much as I know, but you’re here to correct me.
And that’s the “type” of mass people (nonphysics) are thinking about when they say “common” mass in this thread Acron - they think on non relativistic one (I believe that there’s better term in English than this one).

I’m more interested in this, on page one russ was talking about curved space (by gravity), and that being the reason why light seems to bee attracted by gravity (by just fallowing the curved space), then Acron sad “no”- light will bee attracted any way, and “attraction” isn’t direct consequence of curved space . So what is it, could we discus this more detail.

Could someone briefly (Warren seems to be good at it) line most important conclusions and consequences deriving from GR, I think that it would help answering some questions from this thread.

Greetings

p.s. what particle has characteristic like photon (non rest mass, but attracted by gravity/bydefault :)/)

 

[pmb_phy]

Originally posted by eagleone
Let’s simplify it. And take it my way :).
Does the light have it’s own gravitational field, or is it a source of gravity ?

Yes. Since light has energy and energy has mass then light will generate a gravitational field. An example was given in

On The Gravitational Field Produced by Light, Tolman, Ehrenfest and Podolsky, Physical Review, Vol(37), March 1, 1931, pg 602-615

See --
http://www.geocities.com/physics_world/grav_light.htm

 

[GRQC]

Originally posted by eagleone

And that’s the “type” of mass people (nonphysics) are thinking about when they say “common” mass in this thread Acron - they think on non relativistic one (I believe that there’s better term in English than this one).

But you can't just go around re-defining accepted terminology to support a "new" claim.

I’m more interested in this, on page one russ was talking about curved space (by gravity), and that being the reason why light seems to bee attracted by gravity (by just fallowing the curved space), then Acron sad “no”- light will bee attracted any way, and “attraction” isn’t direct consequence of curved space . So what is it, could we discus this more detail.

Acron is incorrect if he said that. Light follows geodesics in spacetime (straight lines!). When spacetime is curved, light still follows straight paths on the curved manifold, which end up deflecting the path of the rays.

I don't understand how light can be "attracted" without curvature. To suggest that this is happening is tossing GR out the window. If he really did say that, then his argument is very inconsistent (and hence shows a clear lack of understanding of the subject).

p.s. what particle has characteristic like photon (non rest mass, but attracted by gravity/bydefault :)/) [/B]

Do you mean gravitons? If so, there is no well-established quantum field theory which involves gravitons, so we really can't say for sure if gravity attracts itself (graviton-graviton vertices in the Feynman diagrams). Supersymmetric and supergravity theories involve them, but any quantum gravitational theory is not well founded (and certainly not as well-understood as quantum electrodynamics).

 

[Haelfix]

I think he's talking about a SDM neutrino (different quantum numbers), but yes it too feels gravity, even though naively they are taken to be massless.

The point to take away from this thread, is that in the context of general relativity, is that PRESSURE affects the quantity we experimentally measure as 'mass'. It is a part of the stress energy content (a tensor, with 3 diagonal entries, and off diagonal entries that measure this quantity)

This is the source term that bends or 'creates' the geometry in which we live in. Or you could think of the geometry as being set that forces the source term to be what it is.

 

[Michael F. Dmitriyev]

Originally posted by Michael F. Dmitriyev
I am informed on that explanation where you gave the reference...

Moderator edit: crackpotism deleted. Michael, please post your personal theories only in the Theory Development forum.

It is not crackpotism. I have proved the correctness of my claims on TD Forum in a thread “Particle/wave duality on a scale of light frequencies”.
I want to notice it does not reject a duality, but on the contrary asserts it in the wider frameworks. In these frameworks I have proved also a general origin of all fundamental forces .

 

[GRQC]

Originally posted by Michael F. Dmitriyev
It is not crackpotism. I have proved the correctness of my claims on TD Forum in a thread “Particle/wave duality on a scale of light frequencies”.
I want to notice it does not reject a duality, but on the contrary asserts it in the wider frameworks. In these frameworks I have proved also a general origin of all fundamental forces .

If it's not crackpotism, then your claims should be proven correct by submitting them to a peer-reviewed journal, not an internet message board.

 

[Michael F. Dmitriyev]

Originally posted by GRQC
If it's not crackpotism, then your claims should be proven correct by submitting them to a peer-reviewed journal, not an internet message board.

Hence TD forum it is type of a specific garbage box where all that does not correspond to establishment physics is sent. Then my achievements on that forum are a vainly lost time. Can you give, please, the references or even the names of these journals...
I suspect, that I’ll have problems with publication.