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Author Topic: Does light have mass?  (Read 77670 times)

Offline that mad man

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Does light have mass?
« Reply #75 on: 29/07/2008 00:35:02 »
A metallic reflector doesn't absorb the energy as the electrons oscillate because it's a good conductor. A poor conductor will absorb some energy as the electrons move so it will not reflect as much energy.

What happens then when you use a piece of transparent glass sheet as the reflector as any reflection with a glass sheet can also produce an almost perfect image, no metallic reflector there unless silica is classed as metallic. A loss would be expected because of the inverse square law and would be measurable.

Sorry, I still have problems understanding the basics and I would like to know where I am getting it wrong. Truly, I need to know!

Getting back to the crooks radiometer, what happens if it was in a total vacuum?

It seems odd to me now that I had one when I was a child.



 

Offline Mr. Scientist

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Does light have mass?
« Reply #76 on: 19/09/2009 15:44:46 »
does it?

If it has a mass in kilograms, it would have an obsurd value of 10^-51.
 

Offline Dimi

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Does light have mass?
« Reply #77 on: 20/09/2009 00:33:19 »
Does all light have heat?

Or is it possible to have cold light?

I don't know much about the subject and I got lost reading most of it ~ but is it possible that instead of viewing it with having a mass, how about it causes a chemical change due to the heat?

Would heat have a mass instead or is it just a chemical change?

Don't grill me :P
 

Offline Pmb

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Does light have mass?
« Reply #78 on: 20/09/2009 07:47:31 »
This is one of those subjects that one can argue endlessly on. The most important thing to remember here is that you first have to decide what the definition of the term mass you are choosing to use. After that is determined then one can then easily prove whether light has mass or not.  It is clearly and demonstratively a matter of the record that there are two definitions of the term mass in usage in the physics literature today. Some authors’ use the term “mass” to refer to “proper mass” while others it to refer to “relativistic mass”. Relativistic mass reflect the sum of the following properties of matter
Inertial mass – This is the property of light which determines its momentum                   
Active gravitational mass – Light can generate a gravitational field.
Passive gravitational mass – Light is affected by gravity.
The following is list of relativity textbooks which employ the definition of of mass which gives it mass

Relativity: Special, General and Cosmological, Rindler, Oxford Univ., Press, (2001), page 120
According to Einstein, a photon with frequency n has energy hn /c2, and thus (as he only came to realize several years later) a finite mass and a finite momentum hn/c.
From Introducing Einstein's Relativity, Ray D'Inverno, Oxford Univ. Press, (1992), page 50
Finally, using the energy-mass relationship E = mc2,, we find that the relativistic mass of a photon is non-zero and given by
m = p/c.

Combining these results with Planck's hypothesis, we obtain the following formulae for the energy E, relativistic mass m, and linear momentum p of the photons:
E = hf             m = hf/c2            p = hf/c
Special Relativity, A. P. French, MIT Press, page 20
Let us now try to put together some of the results we have discussed. For photons we have
E = cp
and

m = E/c2

(the first experimental, the second based on Einstein's box). Combining these, we have
m = p/c

 

Offline Mr. Scientist

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Does light have mass?
« Reply #79 on: 20/09/2009 13:08:53 »
Does all light have heat?

Or is it possible to have cold light?

I don't know much about the subject and I got lost reading most of it ~ but is it possible that instead of viewing it with having a mass, how about it causes a chemical change due to the heat?

Would heat have a mass instead or is it just a chemical change?

Don't grill me :P

Think of it as a unit of heat/energy which can differentiate due to something it inherently has as a wavelength. The higher and the lower the wavelengths give the particle its given intrinsic energy. It is the smallest unit of energy known on the standard.

But suffice to say, the photon should not have a mass due to relativity. I could give you loads of math on the subject, but it depends on how savvy you are on calculations.
 

Offline Dimi

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Does light have mass?
« Reply #80 on: 20/09/2009 14:34:37 »
The math wouldn't mean anything to me :) I can calculate all I want but I have no where to apply it to.

I'll just leave it to those who are capable and I'll keep making crazy ideas up XD
 

Offline lightarrow

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Does light have mass?
« Reply #81 on: 20/09/2009 19:00:37 »
Does all light have heat?
Nothing can *have heat*. Heat is not a property of bodies, but a kind of energy transfer between bodies.
 

Offline Dimi

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« Reply #82 on: 20/09/2009 23:48:26 »
An uneducated guess ~

Then its impossible to have cold light. So the pile up of energy [which causes the heat?] could be the reason for the supposed weight ~ just an idea, but could it be expanding the apparatus?

So a single busrt of energy would do nothing, but with a pile up it would be enough to create a change in the surrounding air itself?

Of course I have no idea what I'm talking about :P
 

Offline Mr. Scientist

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Does light have mass?
« Reply #83 on: 21/09/2009 02:29:17 »
An uneducated guess ~

Then its impossible to have cold light. So the pile up of energy [which causes the heat?] could be the reason for the supposed weight ~ just an idea, but could it be expanding the apparatus?

So a single busrt of energy would do nothing, but with a pile up it would be enough to create a change in the surrounding air itself?

Of course I have no idea what I'm talking about :P

So --- what you seem to be asking is if you gather enough energy to a given region of spacetime (or some part of the vacuum perhaps?) - does this effect the surrounding spacetime (instead of air?), because if this where the case, then is sounds a bit like general relativity where matter [and] displace space and time through causing distortions.

You're right though about weight being changed, only if there is a specific change in density to suit it. The density is inversely related to weight, and thus so is its volume. If you gather enough energy in the universe, you could potentially create loads of fasinating different things, from exotic objects as black holes, to even possibly wormholes.

But the technology required far exceeds what even possibly earth could even supply. We would need to reach energies which satisfy what are called in physics ''Planck Energies'', and at this energy, we can literally make a rip in the fabric of space and time itself. But whilst these energies cannot be harnest, more problems exist. You would need an antigravity substance called ''exotic matter'' to keep some of these objects stable. Even negative regions which seemed to expand the space and time around them into infinity.

But if none of this covered what you meant, then i never had clue :)
 

Offline Pmb

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Does light have mass?
« Reply #84 on: 21/09/2009 09:45:44 »
Quote from: paul.sr
does it?
Let’s discuss whether photons have mass or not. In my opinion the best and most rigorous way to define the term “mass” (which I’ll label M and reserve “m” for proper mass) is to define it as the M in p = Mv where p and v are the photons 3-momentum and 3-velocity respectively. Since neither p or v is zero it follows that the mass of a photons is not zero.

There are many good reasons for defining it this way. Here are two

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

Quote from: ukmicky
But the only other type of mass is relativistic Mass but that isn't really Mass in the correct sense of the word so therefore a photon has 0 Mass
The “correct sense of the word” is determined by how the term is defined. For example; a study of the prominence of the use of relativistic mass in relativity texts was done and the results posted in an article  locater here http://arxiv.org/abs/physics/0504111

Relativistic mass was used in a large fraction of those texts. To assert that the “correct sense of the word” is as you say it is very misleading for the reasons given above.

I myself wrote an article on the subject which is oneline at
http://arxiv.org/abs/0709.0687
 

Offline Dimi

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« Reply #85 on: 21/09/2009 10:26:07 »
So --- what you seem to be asking is if you gather enough energy to a given region of spacetime (or some part of the vacuum perhaps?) - does this effect the surrounding spacetime (instead of air?), because if this where the case, then is sounds a bit like general relativity where matter [and] displace space and time through causing distortions.
I don't think light/heat could affect space... What would you describe space to be? If space is the absence of an element does it mean its considered 'dead'? [But it can't be an absence because if elmeents can pass through it, then it has to be composed of atoms itself right?] I think before looking into the weight of light, maybe space itself needs to be understood.

Actually would space have energy or is it completely dead?

Too much to consider!

I don't think its possible to weigh light on earth because there would be the constant pressure of something!

And if we gave light a mass ~ we would more than likely feel it and its destructive path, I think the fact that its massless gives it the ability to move at the so called speed of light.

But I think that light would just be causing a chemical reaction to all surrounding atoms by giving them a 'light' .. or is light just a perception given by our eyes and no actual reaction occurs to anything?

I wouldn't have a clue regardless, haha. I think I went too far off tangent.
 

Offline Mr. Scientist

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« Reply #86 on: 22/09/2009 00:25:53 »
So --- what you seem to be asking is if you gather enough energy to a given region of spacetime (or some part of the vacuum perhaps?) - does this effect the surrounding spacetime (instead of air?), because if this where the case, then is sounds a bit like general relativity where matter [and] displace space and time through causing distortions.
I don't think light/heat could affect space... What would you describe space to be? If space is the absence of an element does it mean its considered 'dead'? [But it can't be an absence because if elmeents can pass through it, then it has to be composed of atoms itself right?] I think before looking into the weight of light, maybe space itself needs to be understood.

Actually would space have energy or is it completely dead?

Too much to consider!

I don't think its possible to weigh light on earth because there would be the constant pressure of something!

And if we gave light a mass ~ we would more than likely feel it and its destructive path, I think the fact that its massless gives it the ability to move at the so called speed of light.

But I think that light would just be causing a chemical reaction to all surrounding atoms by giving them a 'light' .. or is light just a perception given by our eyes and no actual reaction occurs to anything?

I wouldn't have a clue regardless, haha. I think I went too far off tangent.
Energy can be thought of a heat radiator. Lots of packets of energy contains what is heat; they are the heat being radiated.

But morever, this energy, but not especially the value of heat, causes disortions. A photon, even though massless, still distorts the space and time around it as it moves through spacetime. This ''distortion'' couples to gravity, and that is why photons themselves can be deflected by gravity.
 

Offline Dimi

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« Reply #87 on: 22/09/2009 02:56:52 »
I would of thought that heat is an energy in its own form, since energy would be radiation in essence ~ so when a subject recieves energy, the result would be heat.

Because heat isn't a solid tangable thing (you can't hold it), it passes through the atoms as a wave ~ and a wave would be an energy.

So in space, energy can't possibly affect anything because there is no solidity there at all? I would of thought the space would be a gas ~ and some gas can be heated up.

Other wise, is there no heat at all, and heat is only a reaction caused by our ozone layer?

So does the energy from the sun is just pure energy, the ozone layer transforms this energy and gives it heat or something, then we feel its effects.

I think I should stop soon, I really do not have a clue what I am talking about hahaha
 

Offline Mr. Scientist

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« Reply #88 on: 22/09/2009 14:39:44 »
I would of thought that heat is an energy in its own form, since energy would be radiation in essence ~ so when a subject recieves energy, the result would be heat.

Because heat isn't a solid tangable thing (you can't hold it), it passes through the atoms as a wave ~ and a wave would be an energy.

So in space, energy can't possibly affect anything because there is no solidity there at all? I would of thought the space would be a gas ~ and some gas can be heated up.

Other wise, is there no heat at all, and heat is only a reaction caused by our ozone layer?

So does the energy from the sun is just pure energy, the ozone layer transforms this energy and gives it heat or something, then we feel its effects.

I think I should stop soon, I really do not have a clue what I am talking about hahaha

Heat can be construded as a form of energy. For instance... what do we think about when we talk about ''temperatures'' in spacetime? The temperature itself is formed of a background heat because of photons; the fundemental unit of spacetime.

At zero-point energies you would expect that motion would cease, because all energy should be frozen - in fact, motion does not cease, and a massive amount of energy for any quantum oscillator at a zero-point region - so its impossible to freeze the vacuum completely. So when talking about temperatures, we can certaintly infer to the existence of energy itself.
 

Offline Mr. Scientist

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Does light have mass?
« Reply #89 on: 22/09/2009 14:41:50 »
Heat or energy can be a form of diffused matter so its true that energy has no tangibility like a solid matter.
 

Offline Dimi

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« Reply #90 on: 23/09/2009 13:41:16 »
So there is no possibility of weighing energy then? What I don't understand is how come not all energy can pass through solid mass.

You can pass radio waves through, but not sunlight? The heat will slowly crawl to the other side but it can't pass through. So is there only 1 type of energy, or are there variations?

Then is there ANY energy that could be weighed? Wouldn't that be another contradiction? I thought if something were to be massless, then it wouldn't have difficulties going through solids.
 

Offline lightarrow

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« Reply #91 on: 23/09/2009 19:55:18 »
So there is no possibility of weighing energy then?
Any *fixed* region of space containing an energy E has a mass E/c2.
 

Offline Vern

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Does light have mass?
« Reply #92 on: 23/09/2009 21:01:05 »
Quote from: Dimi
So there is no possibility of weighing energy then? What I don't understand is how come not all energy can pass through solid mass.
I suspect it is because certain wave lengths of energy like to play with particles and structures within the solid mass. Other wave lengths do not find suitable playmates. Them that don't play pass right through. Them that play stay in the mass for awhile.

 

Offline Mr. Scientist

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« Reply #93 on: 23/09/2009 23:12:42 »
So there is no possibility of weighing energy then? What I don't understand is how come not all energy can pass through solid mass.

You can pass radio waves through, but not sunlight? The heat will slowly crawl to the other side but it can't pass through. So is there only 1 type of energy, or are there variations?

Then is there ANY energy that could be weighed? Wouldn't that be another contradiction? I thought if something were to be massless, then it wouldn't have difficulties going through solids.

They are much smaller than most subatomic particles, which gives them an easy way to move through atoms. Another thing involved is absorption, which only occurs with an angular momentum (THE thing we associate as its spin). In this process, energy it gained, and sometimes lost, but sometimes with different energy results. For instance, the appearance of a photon inside an atom can excite the existence of other particles: so it may create new particles and less energy is released... so, conservation remains in this sense.

Energy can be absorbed so easily though. The tangibility of matter is not necesserily due to weight. Lightarrow is partially true as when you are inviting massless radiation, we must invoke gamma into the equation. This reduces its mass to zero, but is intrinsically-related to its energy-momentum which is inexorably non-zero.

Energy seems to have an energy itself, strangely enough.
 

Offline lightarrow

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« Reply #94 on: 24/09/2009 15:23:51 »
Lightarrow is partially true as when you are inviting massless radiation, we must invoke gamma into the equation. This reduces its mass to zero, but is intrinsically-related to its energy-momentum which is inexorably non-zero.
No, maybe you haven't understood very well what I wrote. I was talking about proper = invariant mass, not about 4-momentum.
 

Offline Mr. Scientist

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« Reply #95 on: 24/09/2009 16:19:11 »
Lightarrow is partially true as when you are inviting massless radiation, we must invoke gamma into the equation. This reduces its mass to zero, but is intrinsically-related to its energy-momentum which is inexorably non-zero.
No, maybe you haven't understood very well what I wrote. I was talking about proper = invariant mass, not about 4-momentum.

Making that distinction does make a difference.

Invariant, or rest mass is always associated to something which has inertial mass - photons though, may have a finite inertia. Question is, should we allow the photon to have an inertia, or should that be reserved only for material bodies?
 

Offline lightarrow

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« Reply #96 on: 25/09/2009 07:55:53 »
Lightarrow is partially true as when you are inviting massless radiation, we must invoke gamma into the equation. This reduces its mass to zero, but is intrinsically-related to its energy-momentum which is inexorably non-zero.
No, maybe you haven't understood very well what I wrote. I was talking about proper = invariant mass, not about 4-momentum.

Making that distinction does make a difference.

Invariant, or rest mass is always associated to something which has inertial mass - photons though, may have a finite inertia. Question is, should we allow the photon to have an inertia, or should that be reserved only for material bodies?
This is a different concept. Inertia is possessed even from objects which don't have invariant mass (photons).
 

Offline Mr. Scientist

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« Reply #97 on: 25/09/2009 20:16:22 »
Lightarrow is partially true as when you are inviting massless radiation, we must invoke gamma into the equation. This reduces its mass to zero, but is intrinsically-related to its energy-momentum which is inexorably non-zero.
No, maybe you haven't understood very well what I wrote. I was talking about proper = invariant mass, not about 4-momentum.

Making that distinction does make a difference.

Invariant, or rest mass is always associated to something which has inertial mass - photons though, may have a finite inertia. Question is, should we allow the photon to have an inertia, or should that be reserved only for material bodies?
This is a different concept. Inertia is possessed even from objects which don't have invariant mass (photons).

I know this, but inertia is not very well defined in physics. For instance, i don't actually believe there are any explanation to what causes inertial effects any further than invoking Mach's principle.
 

Offline yor_on

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« Reply #98 on: 28/09/2009 21:24:17 »
Inertia is truly strange as it seems to be existing in any observable system inside SpaceTime. As like you traveling your space-rocket, changing your course will give you inertia if I got it right. Why?
 

Offline Mr. Scientist

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« Reply #99 on: 29/09/2009 00:35:33 »
Moreover, let us assume everyone thought what lightarrow did. With that, relativity becomes a damn-sight harder to understand when inertia is taken into respect. From that line of thinking, relativity states that gravitational matter is the same thing as inertial effects. Then we specifically know that photons do not possess a gravitational mass, so they cannot be the same thing.
 

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