Does a photon have mass equivalent to its energy?

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Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #50 on: 13/05/2012 15:54:43 »
Those who insist on calling m what was once called "relativistic mass" don't explain that this term is just another name for "total energy" (divided by c2).
Since this concept has already a name, that is "Energy", why using a new one?

The reason in physics it is used the term "mass" intending "invariant mass" (or "proper mass") is in its very name: it is INVARIANT.
In relativity is extremely useful to use quantities which are INVARIANT; every one who has solved meaningful problems on the subject, understands it. Another example of invariant quantity is "interval" or "proper time" (interval divided by c2).

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Offline Phractality

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Re: Does a photon have mass equivalent to its energy?
« Reply #51 on: 13/05/2012 19:44:51 »
 We expect religious fundamentalists to fight over a word. Scientists should be a bit more tolerant and understanding.

Confusion over the term "mass" and it's various symbols and abbreviations results from a lack of consensus and authority. Until all leading international governing bodies pass a resolution, binding on their members, to adhere strictly to an accepted nomenclature, the controversy will continue. Authors will be free to use their own favorite nomenclature. We can only hope that each author will make it clear what he means by "mass" and the letter "m", or whatever letter he uses.

I've gotten into the bad habit of using the terms "mass" and "m" without distinguishing which kind of mass I'm talking about. I've been doing it since my first intro to physics as a college freshman, before I learned about relativity. It's a hard habit to break, but I shall make an effort to do so.
I won't attack those who disagree with me, but I will argue in favor of my preference. I prefer to define "inertial mass", mi, as a measure of how much momentum changes per unit change in velocity in a given reference frame; mi = dp/dv. By that definition, the mass of a particle depends on the reference frame. The opposite camp in this controversy defines mass as the momentum change for the first small increment of velocity change beginning at rest. By that definition, the mass of a particle is the same in all inertial reference frames.

[EDIT 2012-05-16: I see a problem with my definition of mi. It works for particles with a rest mass, but not for photons. A photon's momentum changes as it passes thru a gravity well, but in GR a photon's velocity is constant. In Minkowski space-time, the path of light is the definition of a straight line, so a photon can't change direction. In GR, dp/dv for a photon would be infinite.
What's needed is a definition of inerial mass that works for photons as well as for particles with rest mass. I'll give this some more thought and get back to you.]
 
Since "m" has been used in the literature to represent both kinds of mass, perhaps the best solution is to abandon "m" altogether (except where relativity is clearly not an issue) and use only symbols that, historically, have been used only to mean one kind of mass or the other. I like the term "m0" for rest, invariant or proper mass, and I like the term "mi" for relativistic inertial mass. PMB likes to use "μ" instead of "m0" and "m" instead of "mi". I guess Lightarrow prefers "m" instead of "m0" and "γm" instead of "mi". I will be happy with any nomenclature that is unambiguous until such time as the international governing bodies make a unanimous ruling on the matter. [Edited to change "mr" to "mi".]
 
I define "gravitational mass", "mg", in terms of a slightly modified Newton's universal law of gravitation; f = dp/dt = G(mg1mg2 / r2). I believe that mg ≠ mi at relativistic speeds because time dilation makes planets orbit slower, not faster. Time dilation of planetary orbits is consistent with mg = m0 and mi = γm0. I haven't yet figured out whether mg = m0, or mg = mi when one body is stationary in the reference frame and the other is moving at relativistic speed.
 
I see no reason to distinguish between active and passive gravitational mass, as PMB does. While PMB is not saying they differ, simply giving them different names hints that they could differ. If they're not equal, momentum is not conserved, and conservation of momentum is one of a physicist's favorite security blankets. Please; leggo my security blanket! Waaaah! 
« Last Edit: 16/05/2012 19:19:45 by Phractality »
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Offline imatfaal

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Re: Does a photon have mass equivalent to its energy?
« Reply #52 on: 14/05/2012 10:07:48 »
We expect religious fundamentalists to fight over a word. Scientists should be a bit more tolerant and understanding.

Nicely said.  Let's have no more wrangling over terminology please Ladies and Gentlemen
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Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #53 on: 14/05/2012 14:24:04 »
We expect religious fundamentalists to fight over a word. Scientists should be a bit more tolerant and understanding.

Confusion over the term "mass" and it's various symbols and abbreviations results from a lack of consensus and authority. Until all leading international governing bodies pass a resolution, binding on their members, to adhere strictly to an accepted nomenclature, the controversy will continue. Authors will be free to use their own favorite nomenclature. We can only hope that each author will make it clear what he means by "mass" and the letter "m", or whatever letter he uses.

I've gotten into the bad habit of using the terms "mass" and "m" without distinguishing which kind of mass I'm talking about. I've been doing it since my first intro to physics as a college freshman, before I learned about relativity. It's a hard habit to break, but I shall make an effort to do so.
I won't attack those who disagree with me, but I will argue in favor of my preference. I prefer to define "inertial mass", mi, as a measure of how much momentum changes per unit change in velocity in a given reference frame; mi = dp/dv. By that definition, the mass of a particle depends on the reference frame. The opposite camp in this controversy defines mass as the momentum change for the first small increment of velocity change beginning at rest. By that definition, the mass of a particle is the same in all inertial reference frames.
 
Since "m" has been used in the literature to represent both kinds of mass, perhaps the best solution is to abandon "m" altogether (except where relativity is clearly not an issue) and use only symbols that, historically, have been used only to mean one kind of mass or the other. I like the term "m0" for rest, invariant or proper mass, and I like the term "mi" for relativistic inertial mass. PMB likes to use "μ" instead of "m0" and "m" instead of "mi". I guess Lightarrow prefers "m" instead of "m0" and "γm" instead of "mi". I will be happy with any nomenclature that is unambiguous until such time as the international governing bodies make a unanimous ruling on the matter. [Edited to change "mr" to "mi".]
Ok. Anyway, in favour of my...school of thought  [:)] I just want to ask you a simple question: at school or university or at work, you have to solve a written problem where you find the symbol "me" and the text explain is the "electron mass" (see any book of physics for it).
Which value do you give it? Where do you look up for that value or how do you compute it?


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Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #54 on: 14/05/2012 14:32:27 »

Since "m" has been used in the literature to represent both kinds of mass, perhaps the best solution is to abandon "m" altogether (except where relativity is clearly not an issue) and use only symbols that, historically, have been used only to mean one kind of mass or the other. I like the term "m0" for rest, invariant or proper mass, and I like the term "mi" for relativistic inertial mass.
Maybe, the fact  people used the term "relativistic mass" and a symbol "m" for it, is because a lot of physicists still believe there is a difference between that mass and energy.

Some still make confusion about mass and energy and talks about "converting mass into energy", for example when they talk about the energy freed in a nuclear reaction.

I also talked in that terms, in the past, but it's incorrect. I have to thank a professor of physics for having (with difficulty) understood it. Actually, it's quite easy to understand; the difficult part is to accept it...

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Edit:
Let's make a simple example: a nucleus of rest  mass m = 10-25 kg  undergoes nuclear fission and two equal fragments are shoot away in opposite directions.

Let's say the total kinetic energy of the fragments is 1/1000 the energy of the initial nucleus: 0.0001*m*c2 = 0.001*10-25*(3*108)2 Joule

Question: compute the *Rest* mass of the system before and after the nuclear reaction.

Rest mass of the system before reaction: 10-25 kg
Rest mass of the system after reaction: 10-25 kg

There are no mistakes.

Now I ask again: why using a different concept of mass different from rest mass?

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« Last Edit: 14/05/2012 14:51:32 by lightarrow »

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Offline JP

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Re: Does a photon have mass equivalent to its energy?
« Reply #55 on: 14/05/2012 17:54:46 »
Not to mention that invariant mass is an extremely elegant quantity in the geometric formulation of special relativity.  The motion of an object with respect to an observer can be characterized by a 4-vector in space and time, which has length equal to invariant mass, and whose direction specifies the motion of the object in the observer's reference frame.  Changes of reference frame are accounted for by rotating this vector rather than using cumbersome formulas. 

Ok, so invariant mass is elegant and useful and agrees with the non-relativistic definition of mass in the appropriate limit.

What about relativistic mass makes it elegant or useful?  Does it have properties that energy alone does not?  I'm legitimately curious--I have used invariant mass in computations and know enough about its use in modern physics that I can see its virtue.  I can't say the same for relativistic mass, but I'd be interested in hearing where it still finds use.

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Offline Phractality

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Re: Does a photon have mass equivalent to its energy?
« Reply #56 on: 14/05/2012 19:24:17 »
 

 Maybe, the fact people used the term "relativistic mass" and a symbol "m" for it, is because a lot of physicists still believe there is a difference between that mass and energy.
 
 Some still make confusion about mass and energy and talks about "converting mass into energy", for example when they talk about the energy freed in a nuclear reaction.
 
 I also talked in that terms, in the past, but it's incorrect. I have to thank a professor of physics for having (with difficulty) understood it. Actually, it's quite easy to understand; the difficult part is to accept it...
I totally agree that rest mass (or proper mass) is captive energy. Any energy that is bound within a system, by any attractive force, is captive energy; it contributes to the rest mass of the system. Any energy has both gravitational and inertial mass, whether it is bound within a system or not. Both kinetic energy and photons have mass.


Edit:
 Let's make a simple example: a nucleus of rest mass m = 10-25
kg undergoes nuclear fission and two equal fragments are shoot away in opposite directions.
 
 Let's say the total kinetic energy of the fragments is 1/1000 the energy of the initial nucleus: 0.0001*m*c2 = 0.001*10-25*(3*108)2 Joule
 
 Question: compute the *Rest* mass of the system before and after the nuclear reaction.
 
 Rest mass of the system before reaction: 10-25 kg
 Rest mass of the system after reaction: 10-25 kg
 
 There are no mistakes.
 
 Now I ask again: why using a different concept of mass different from rest mass?
 
 --
 lightarrow
 
Assuming that the split was spontaneous and not triggered by any external particle, the sum of rest masses of the two halves after the split must equal the original rest mass MINUS the kinetic energy of the fragments. Kinetic energy is the difference between relativistic mass and rest mass.
 
The key word in your argument is "system". If the two halves are bound by opposite electric charges, they are a system. Then, you are correct about the rest mass of that system. The rest mass of the system is the sum of rest masses of the two halves PLUS their kinetic energy. The kinetic energy of the halves is 10-28 kg; the kinetic energy of the system is zero. Kinetic energy of the two halves is captive within the system; captive energy is mass. [edited from 10-27]
 
If their kinetic energy is too great to be bound by electrostatic attraction, then I would consider the halves to be two independent systems. The sum of rest masses of the two systems would be 9.999 * 10-26 kg. [edited from 10-24]
« Last Edit: 14/05/2012 22:59:21 by Phractality »
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #57 on: 14/05/2012 20:45:12 »
Sweet idea and I agree.

"A photon can accelerate by the way. It does so by scattering off, say, an electron  as in Compton Scattering. The magnitude of the photon's velocity remains constant. It's the change in direction that changes, which means that velocity changes, i.e. the photon accelerates."

By definition everything outside of a geodesic should be accelerating as I understands it. And there both Newton and Einstein agree. So :)

Does our earth accelerate more ways than one?
Well, sort of.
That's the equivalence principle when comparing a acceleration relative a 'mass' or 'proper/invariant mass'
Then we also have the fact that it is rotating, which should introduce another acceleration for all.

And it's pretty weird that the ('dynamic' as in using a 'motion' measured in time, as our earth spinning) geometry can be defined as creating a mass.

Where does the mass come from in a spin? And for a 'rotational mode' it don't matter if the spinning object is in a constant uniform spin, does it? It still should be seen to generating a 'mass' if I use the equivalence principle.

That is if I'm thinking right here :)
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #58 on: 14/05/2012 20:50:46 »
The argument against it might be that you seem to be defining it from a 'wave picture' here Pete? As in a 'perfect reflection' of a wave as I think of it. If you instead use a 'particle' as a 'photon' it should interact with the material/atoms/electrons and annihilate as its interaction present us with a new 'photon'?
=

But no matter that, it doesn't change the way a uniformly spinning object 'accelerates' and so should gain a 'mass', as I think of it. Which should be a very strong argument for 'gravity' being a 'geometry', in some weirdly mysterious way. The Higgs field/bosons, what does that have to say about uniform spins?
« Last Edit: 14/05/2012 20:59:12 by yor_on »
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Re: Does a photon have mass equivalent to its energy?
« Reply #59 on: 14/05/2012 21:09:57 »
I totally agree that rest mass (or proper mass) is captive energy.
 
You don't need the new term "captive energy", since you can call it "binding energy".
Quote

Any energy that is bound within a system, by any attractive force, is captive energy; it contributes to the rest mass of the system.
But this definition is very sneaky: as soon as you change the definition of which is the system, you have to change the phrase "it contributes to the rest mass of the system" to "it doesn't contributes to the rest mass of the system"  [:)] You see that it's impossible to separate the two concepts of mass and of energy, in some cases; also to avoid confusion, I prefer to talk about invariant mass, total energy, kinetic energy, without talking of which energy "contributes" to mass or of "mass converted into energy".
Quote

Any energy has both gravitational and inertial mass, whether it is bound within a system or not. Both kinetic energy and photons have mass.
But now you are again talking about relativistic mass...
Quote

Edit:
 Let's make a simple example: a nucleus of rest mass m = 10-25 kg undergoes nuclear fission and two equal fragments are shoot away in opposite directions.
 
 Let's say the total kinetic energy of the fragments is 1/1000 the energy of the initial nucleus: 0.0001*m*c2 = 0.001*10-25*(3*108)2 Joule
 
 Question: compute the *Rest* mass of the system before and after the nuclear reaction.
 
 Rest mass of the system before reaction: 10-25 kg
 Rest mass of the system after reaction: 10-25 kg
 
 There are no mistakes.
 
 Now I ask again: why using a different concept of mass different from rest mass?
 
 --
 lightarrow
 
Assuming that the split was spontaneous and not triggered by any external particle, the sum of rest masses of the two halves after the split must equal the original rest mass MINUS the kinetic energy of the fragments. Kinetic energy is the difference between relativistic mass and rest mass.
The key word in your argument is "system". If the two halves are bound by opposite electric charges, they are a system. Then, you are correct about the rest mass of that system. The rest mass of the system is the sum of rest masses of the two halves PLUS their kinetic energy. The kinetic energy of the halves is 10-27 kg
10-28 kg, but just to be picky... [;)]
Quote
; the kinetic energy of the system is zero. Kinetic energy of the two halves is captive within the system; captive energy is mass.
 
If their kinetic energy is too great to be bound by electrostatic attraction, then I would consider the halves to be two independent systems. The sum of rest masses of the two systems would be 9.999 * 10-24 kg. [/font]
Ok.

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Re: Does a photon have mass equivalent to its energy?
« Reply #60 on: 14/05/2012 21:20:21 »
"A photon can accelerate by the way. It does so by scattering off, say, an electron  as in Compton Scattering. The magnitude of the photon's velocity remains constant. It's the change in direction that changes, which means that velocity changes, i.e. the photon accelerates."
I answer just this because the rest is too complicated for me and I don't want to get a headache  [:)]

I am not so sure we can talk of a single photon changing direction; I prefer to see it in terms of an incoming photon from a direction which interacts with the atom (or molecule) and then another photon being emitted by the atom in another direction.

Just because the idea of accelerating a photon gives me "cold sweat"
  [:)].

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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #61 on: 14/05/2012 21:29:37 »
And what about those rotating black holes 'frame dragging'?
That should create a mass too, shouldn't it?

And they seem to be spinning close to 'c', some of them? Which either should be incredibly energy consuming, assuming that a spinning geometry as defined from us on earth observing, can't be a uniform motion and so somewhere must create 'energy' constantly, or else bleed that spin of?

All of it assuming a spin to be equivalent to mass, as it is a acceleration. That one has bothered me before and it keeps bugging me :) Because all 'uniformly constant' spins should lose energy if this is correct, shouldn't they?

Ouch, been away for some time here.

Also, if it is true then we have a definition of something maybe possible to prove from only one frame of reference. As a rotating mass in a otherwise 'empty universe', as long as 'they' had a knowledge of relativity, but that may only become a academic question in that case, as they would define the 'energy' relative whatever  'mass' they found anyway. But then it should differ depending on diameter, shouldn't it?
The closer you get to the center mining the more 'energy' in a interaction, if I'm thinking right?

Maybe it would work for a sf :)

Yeah, the equivalence principle is weird, but it seems to be correct as far as I know..

Although. http://news.softpedia.com/news/The-First-Test-That-Proves-General-Theory-of-Relativity-Wrong-20259.shtml   argues somewhat otherwise, possibly
 :)

But I suspect they got that one slightly wrong myself, although I would dearly like to see it tested, once and for all.
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #62 on: 14/05/2012 21:42:16 »
It's an 'acceleration' to me lightarrow :) if we assume a wave picture for it, although I'm also questioning all 'motion' there is I'm afraid? And if you do so there it becomes no big deal calling it a 'acceleration' as 'motion' itself is misunderstood, well, possibly so?

I think it is anyway, eh, possibly :) When I think of it I believe we 'see things' from a instinctive definition, making sense to us, using a linear description inside a arrow, and that is the best working hypothesis we have. But it doesn't tell the whole truth, just the truth when looked at from one direction.

But I'm pretty weird :)
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Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #63 on: 15/05/2012 08:04:41 »
And what about those rotating black holes 'frame dragging'?
That should create a mass too, shouldn't it?
In GR the concept of mass becomes infinitely more smooth and vague:
http://en.wikipedia.org/wiki/Mass_in_general_relativity

(they say "more complex" but it's euphemistic  [:)])

As long as we stay in SR, I can talk about something; in GR, mass or energy is still...science fiction for me.
« Last Edit: 15/05/2012 08:06:45 by lightarrow »

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Offline Phractality

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Re: Does a photon have mass equivalent to its energy?
« Reply #64 on: 15/05/2012 18:36:22 »
And what about those rotating black holes 'frame dragging'?
That should create a mass too, shouldn't it?
In GR the concept of mass becomes infinitely more smooth and vague:
http://en.wikipedia.org/wiki/Mass_in_general_relativity

(they say "more complex" but it's euphemistic  :) )

As long as we stay in SR, I can talk about something; in GR, mass or energy is still...science fiction for me.
If you want to get technical about it, mass doesn't belong in special relativity, at all. Mass has no meaning apart from gravity and acceleration, and the absence of gravity and acceleration is what makes SR "special". Einstein was bending the rules when he gave us a formula for relativistic mass.

When you talk about chemical processes (at the molecular level) and oscillating springs, you're talking about accelerations. At the atomic level, time can be reckoned in terms of electrons accelerating around a nucleus. The only sort of clock that doesn't involve acceleration is the theoretical light clock, in which light reflects back and forth between ends of a vacuum tube.

When we discuss mass in the context of SR, we also must bend the rules to include minimal gravity and acceleration within a bound system which has relativistic motion in the observer's reference frame. That's how I am able to talk about time dilation of a planetary system. The bodies accelerate toward one another, due to their mutual gravitational attraction. As long as motion within the planetary system is not a significant fraction of the speed of light, the formulas of SR can be applied to the planetary system which has relativistic speed in the observer's reference frame.

If the barycenter of a planetary system is moving at gamma = 10 in Frame A, time dilation slows the orbital period to 1/10th of what it is to an observer in Frame B, moving with the barycenter. So in Frame A, the acceleration is 10th normal. If both the gravitational mass and the inertial mass were 10 times normal, the attractive force would be 100 times greater, and the acceleration and orbital period would be 10 times faster, not 10 times slower.
(The problem is simple if the orbital plane is perpendicular to the line of relative motion of the barycenter in Frame A. For other orientations of the orbital plane, you have to take length contraction into account.)
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Re: Does a photon have mass equivalent to its energy?
« Reply #65 on: 15/05/2012 20:00:07 »
If you want to get technical about it, mass doesn't belong in special relativity, at all. Mass has no meaning apart from gravity and acceleration, and the absence of gravity and acceleration is what makes SR "special".
Then you shouldn't even talk about energy and not even momentum, in SR. What you are left with? No mechanics at all, just kinematics. So long Galileo, so long Newton... [:)]
As long as the spacetime curvature introduced by the mass-energy is negligible (and notice that this is not just a rough way of proceding, all physics is based on this concept) you can use SR and treate even infinite accelerating bodies.
Anyway, if you find a simple concept which generalizes and unites all the various concepts of mass in GR, I will be very honoured to know it (and I say seriously).

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Quote
Einstein was bending the rules when he gave us a formula for relativistic mass.

When you talk about chemical processes (at the molecular level) and oscillating springs, you're talking about accelerations. At the atomic level, time can be reckoned in terms of electrons accelerating around a nucleus. The only sort of clock that doesn't involve acceleration is the theoretical light clock, in which light reflects back and forth between ends of a vacuum tube.

When we discuss mass in the context of SR, we also must bend the rules to include minimal gravity and acceleration within a bound system which has relativistic motion in the observer's reference frame. That's how I am able to talk about time dilation of a planetary system. The bodies accelerate toward one another, due to their mutual gravitational attraction. As long as motion within the planetary system is not a significant fraction of the speed of light, the formulas of SR can be applied to the planetary system which has relativistic speed in the observer's reference frame.

If the barycenter of a planetary system is moving at gamma = 10 in Frame A, time dilation slows the orbital period to 1/10th of what it is to an observer in Frame B, moving with the barycenter. So in Frame A, the acceleration is 10th normal. If both the gravitational mass and the inertial mass were 10 times normal, the attractive force would be 100 times greater, and the acceleration and orbital period would be 10 times faster, not 10 times slower.
(The problem is simple if the orbital plane is perpendicular to the line of relative motion of the barycenter in Frame A. For other orientations of the orbital plane, you have to take length contraction into account.)

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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #66 on: 16/05/2012 00:27:05 »
"the idea of accelerating a photon gives me "cold sweat""
Yep, somehow the universe seems to steered by equivalences, symmetries and?

That we find 'rules and regulations' is a very strong indication of there being real 'constants' to me. The question is what those constants are. I find 'c' to be the one relativity is built on, and 'c' is defined through SR.

It discuss a two way (mirror) experiment of reflected light in a vacuum, ignoring 'gravity' bending 'space', instead assuming a 'flat space'. And it seems to be correct? 'c' I mean, we've found all sorts of evidence for it, from frame dragging to ... Because what GR does is to add gravity 'distorting/bending/reshaping the 'space' that light 'propagates' in.

And that reshaping is equivalent both to a acceleration, and a 'weight'. But the spinning disk?? How does it create a mass? And why?
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Re: Does a photon have mass equivalent to its energy?
« Reply #67 on: 16/05/2012 11:58:10 »
"the idea of accelerating a photon gives me "cold sweat""
Yep, somehow the universe seems to steered by equivalences, symmetries and?

That we find 'rules and regulations' is a very strong indication of there being real 'constants' to me. The question is what those constants are. I find 'c' to be the one relativity is built on, and 'c' is defined through SR.

It discuss a two way (mirror) experiment of reflected light in a vacuum, ignoring 'gravity' bending 'space', instead assuming a 'flat space'. And it seems to be correct? 'c' I mean, we've found all sorts of evidence for it, from frame dragging to ... Because what GR does is to add gravity 'distorting/bending/reshaping the 'space' that light 'propagates' in.

And that reshaping is equivalent both to a acceleration, and a 'weight'. But the spinning disk?? How does it create a mass? And why?

Sincerely I have understood...nothing of what you wrote (but it's probably me...) but maybe you ask how spacetime would be distorted in presence of a particular accelerating field, that is a centrifugal field? If it were 2-dimensional, you can imagine a sort of dome-shaped surface. But we are entering...esotericism here.

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Re: Does a photon have mass equivalent to its energy?
« Reply #68 on: 16/05/2012 13:11:59 »
Yor_on, if I understand you correctly, I believe you have to think not about energy or mass or momentum creating gravity/bending space-time.  You have to think about the stress-energy tensor as a source of gravity.  The stress energy tensor not only contains information about how much mass/energy/momentum an object has, but how that mass/energy/momentum flows over space and time, so the motion of objects causes gravitational effects that are different from if the objects were stationary.

The field of gravitomagnetism (http://en.wikipedia.org/wiki/Gravitomagnetism) deals with this, and likens gravity to electromagnetism: stationary masses emit a gravitational field, but moving masses generate a different gravitational field (much in the same way that stationary charges emit an electric field, but moving charges emit a magnetic field).

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Re: Does a photon have mass equivalent to its energy?
« Reply #69 on: 17/05/2012 10:14:52 »
There is a subtle difference to my thinking between uniform and accelerated 'motion'. And a spin can be perfectly uniform and still become a 'acceleration' as I see it. And then it must create a added mass, but from where would that very real mass come? The stress energy tensor?

How?

If that is correct I dearly wonder how you would explain define that from a Higgs boson, as we still see a uniform motion? In China they used to say that demons can't take angles, maybe that is it? Which ever way you look at it the geometry must have a importance for what is a acceleration. Using an idea of a 'field' you might formulate it differently though? And all respect for those gravitomagnetic analogues JP but to me gravity is a geometry, not 'forces'. And that makes it a real headache, because then we have 'fields' although not 'forces' acting.
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Re: Does a photon have mass equivalent to its energy?
« Reply #70 on: 17/05/2012 10:22:02 »
Maybe you could use the arrow for defining it? After all, it do have a 'direction' for us, and as far as I know there is no evidence for it being able to be 'played backwards', although we do find a temporal symmetry to it? Because without 'forces', what do we have?
==

Here is two interesting guys discussing 'gravity'.

http://www.einstein-online.info/spotlights/scalar-tensor
http://www.mathpages.com/home/kmath613/kmath613.htm
« Last Edit: 17/05/2012 10:30:32 by yor_on »
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Re: Does a photon have mass equivalent to its energy?
« Reply #71 on: 17/05/2012 13:07:41 »
There is some more points one seems to be able to make. Consider something 'weighlessly' orbiting our earth, their weigh and so gravity itself transformed away in their 'free fall'. Weight can't be mass even though it is 'coupled' to mass. So is the mass for those astronauts increased by them spinning around us? It can't be, they should be following a geodesic there, which can be expressed as the 'straight paths' of SpaceTime.

But it is still a spin to us observing them.
So what would consist a spin in SpaceTime?

Something that breaks a geodesic.
==

So how do you break a geodesic?

You need invariant mass for it. Bosons do not break geodesics. And you can't assume that something spinning in space as observed by you is breaking that geodesic. You need something like that plate spinning, confined in its mass.
« Last Edit: 17/05/2012 13:24:33 by yor_on »
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Re: Does a photon have mass equivalent to its energy?
« Reply #72 on: 23/05/2012 12:02:29 »
Quote from:  “Phractality”
PMB likes to use "μ" instead of "m0" and "m" instead of "mi".
I prefer to use what is best at the time I use it. Last night I was working on the basic derivations of SR such as E = pc for a photon and in general E^2 – (pc)^2 = (mc^2)^2jsyr.

Note: "μ" is sometimes used as proper mass density so I try to try

Notice that here I used m to mean proper mass. Otherwise its hard on my eyes for some reason.  ;D

only chose to use the letter "μ" in my paper. It was for two reasons

(1) There are many different concepts floating around in that apper I wanted to make sure it was a clear as could be.

(2) Greek letters are often used when people name proper quantities such as proper distance and proper time.
« Last Edit: 24/05/2012 12:24:46 by Pmb »

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Re: Does a photon have mass equivalent to its energy?
« Reply #73 on: 24/05/2012 15:28:27 »
Pete, perhaps you could clear up a question I've had.  I've done some work in quantum mechanics and a little in (special) relativistic quantum mechanics.  In that case, invariant mass is the mass of choice because it's generally easier in the math to deal with quantum particles in terms of their energy-momentum four vector by describing it in terms of rapidity (essentially an angle in space-time specifying its velocity in the lab frame) and its length (the invariant mass).

Could you comment on where relativistic mass sees use in physics?  Where do calculations get simplified by its use? 

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Re: Does a photon have mass equivalent to its energy?
« Reply #74 on: 24/05/2012 17:35:10 »
Pete, perhaps you could clear up a question I've had.
I'll do my best!

I've done some work in quantum mechanics and a little in (special) relativistic quantum mechanics.
The only relativistic quantum mechanics I've had touch with is towards the end of Liboff's Quantum Mechanics. So I don't feel qualified to comment there. Relativist mass obviously has no place in non-relativistic quantum mechanics. But I say that one should go with what they find easier to use. I know experts who teach rel-mass but who don't use in a great deal in their scientific publications. They tell me that they find it useful to think of, say, light having mass. I recommend not assuming that what one uses is practice is not what they use on the path to getting there. Texts on the Philosophy of Science point this kind of thing out. I'll scan that portion of my undergrad text in to a PDF file and make it available for you to read if you're interested.

Could you comment on where relativistic mass sees use in physics?  Where do calculations get simplified by its use? 
Moslty its not about calculations. Did you read my paper on the concept of mass in relativity? In the abstract I wrote
Quote
Although I argue for the usage of relativistic mass I do not argue that proper mass is not an important tool in relativistic dynamics.
So I'm not really disagreeing with you for the most part. The article explains much more than I can lay out here. For a compete answer please see and read http://arxiv.org/abs/0709.0687

I'll do my best in this post.

A lot of my paper discusses bulk systems with extended bodies instead of systems which are only systems of particles.

JP - Have you ever used special relativity in any other cases other than systems of particles? Consider this
Quote
Measuring the active gravitational mass of a moving object, D.W. Olson and R.C. Guarino, Am. J. Phys. 53(7), July 1985

If a heavy object with rest mass M moves past you with a velocity comparable to the speed of light, you will be attracted gravitationally towards its path as though it had an increased mass. If the relativistic in active gravitational mass is measured by the transverse (and longitudinal) velocities which such a moving mass induces in test particles initially at rest near its path, then we find, with this definition, that
 M_rel = \gamma(1 + \beta)M. Therefore, in the ultrarelativistic limit, the active gravitational mass of a moving body, measured in this way, is not \gammaM  but is 2\gammaM

As far as reasons people use rel-mass goes, I've aleady explained what I know in the paper I wrote and is located here and mentioned in this thread. It's online at http://arxiv.org/abs/0709.0687

I wrote a paper on this because it deserves a full treatment in all generality. Most people who ask the question you just did seem to have only systems of particles in mind and then only closed systems.

Special relativity is much richer than just using it in particle physics. Particle physicists seem therefore to never consider anything besides systems of particles.

The world is composed with continuos systems of matter. Such systems are described by the stress-energy-momentum tensor.

Take a look at Physical Principles of Cosmology by Peebles. It shows the density of active and passive gravitational mass as well as inertial mass densities. They are not the same! I.e. the density of active gravitational mass is different than the density of passive gravitational mass (this addresses a question someone was wondering about above). Inertial mass density is the same as the density of passive gravitational mass. Schutz rigorously derives the inertial mass density and shows that it's a function proper mass density and pressure.

Schutz's book touches on this in his text Gravity from the Ground Up so if you have that text look uo those terms.

In general, SR can be applied to anything in an inertial frame of reference in flat spacetime. It covers systems which are fully described by the stress-energy-momentum tensor. In Gravitation by Misner, Thorne and Wheeler, the authors use relativistic mass (which they simply call "mass") in their proof that the stress-energy-momentum tensor is symmetric. Schutz does the same thing in his GR text.

I considered a simple system which consists of a rod which was cooling down by radiating energy in the form of emitting photons/EM radiation. The question was to find the momentum of the rod using the relation  P = \gamma*m*v. If one tried to use that relation from a frame moving with respect to the rod then they'd get an error. I was finally able to get this page online yesterday. Please see

http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

Please scroll down to where it says An Incorrect Application of Invariant Mass

Here's another web page I wrote on this subject to demonstrate how physicists - Well known physicists I mnight add - use the concept.
http://home.comcast.net/~peter.m.brown/ref/relativistic_mass/relativistic_mass.htm

Here is a list of articles I've read (at least most of them - I just can't recall which ones and iof I did read them all) on the concept of mass.
http://home.comcast.net/~peter.m.brown/ref/mass_articles/mass_articles.htm

Also take a look at the web pages at
http://home.comcast.net/~peter.m.brown/sr/sr.htm

Many of them use rel-mass to derive many SR relationships. They can all be derived using proper mass. However I myself found it easier using relativitic mass. All of our brains work differently and, to me anyway, its irrational to assume that all people think alike and therefore some people will find it easier and some will find it harder. I'm one of the people who finds it easier.

Here is something Guth told meto my face - He finds it easier somtimes to think of light as having mass.

Thinking about physics is much much more than deriving equations. Have you ever heard of Wheeler's First Moral Principle? It states
Quote
Never make a calculation until you know the answer. Make an estimate before every calculation, try a simple physical argument (symmetry! invariance! conservation!) before every derivation, guess the answer to every paradox and puzzle. Courage: No one else needs to know what the guess is. Therefore make it quickly, by instinct. A wrong guess brings refreshment of suprise. In either case life as a spacetime expert, however long, is more fun!

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Re: Does a photon have mass equivalent to its energy?
« Reply #75 on: 25/05/2012 15:12:32 »
Thanks for the information, Pete.  It'll probably take me a while to wade through the links. 

You're right that I haven't done much work with general relativity/cosmology, which is where it sounds like relativistic mass finds use.  I'm much more familiar with quantum mechanics, where invariant mass is useful, and quantum optics, where invariant mass of single photons is zero. 

My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 

My other general impression is that arguing over what should be called "mass" actually obscures a more important point: that when you transition from Newtonian physics to general relativity, there is no single quantity that has all the properties of Newtonian mass, so of course you can argue over the proper generalization of mass! 

The reason I take this track is that there's an analog that I do know well: in transitioning from classical to quantum mechanics, you can generalize the idea of classical trajectories to incorporate the wave nature of particles.  There are multiple ways of defining the quantum version of classical trajectories, and you usually pick one of those definitions based on whether its going to be useful in some computation (or useful in understanding a problem).  It would be silly to argue over which definition is "correct," since they all are correct models--the ones that have survived and been used are those which are useful.

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Re: Does a photon have mass equivalent to its energy?
« Reply #76 on: 25/05/2012 20:52:22 »
My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
Note: I use [math]E = \gammamc^2 [/math] = as inertial energy so as to distinguish it from W =  Energy = inertial energy + potentiual energy.

Answer to your question: No. Not in all generality. Then again what's in a name? The main thrust of my work has been to investigate all possible areas of application so as to find ways where people might make mistakes and seek out a way to describe it so that people won't make this mistakes - i.e. to raise awareness. I'm convince that inertial energy can be dispensed with and replaced by relativistic mass. So my question would then be - Why have two names for things when one can be replaced by the other. E.g.  inertial energy can be replaced wtih inertial mass in any concievable instance. So toss energy out. See my point? The proper mass people use that argument and neglect the other side to that argument.

This is like Hertz's views on force. He wrote a mechanics text and nowhere can the word "force" be found in it.

Keep in mind that inertial Energy and inertial mass are different conceptually. Why kill a concept? E.g just because I can write E = hf/c^2 it doesn't mean that we should replace E with hf/c^2 whenever we found it.

I just got home from a long luncheon. That caused a of pain and I'm just now trying to relax. How about I get back to the rest of this later tonight when I've had a chance to recover?

Please keep in mind that worrying about trivial things like definitions is very silly to me. Once each side provides their views then let it go is what I say. Unfortunately there was a lot for me to learn, things that nobody ever speaks about but which is very important. This lack of desire to learn is shameful. I'm saddened by people's lack of desire to learn about the relativistic mechanics of continuous systems in special relativity. This is where some very important stuff is learned.

What is your viewpoint of lifetime of particle vs proper life time of particle? Who really needs to define the lifetime of a particle when it's proportional to the proper lifetime of the particle. I can replace tthe later by the former can't I? :)
« Last Edit: 25/05/2012 21:45:41 by Pmb »

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Re: Does a photon have mass equivalent to its energy?
« Reply #77 on: 29/05/2012 01:17:44 »
It's amazing! No matter where you go on the internet there's always someone trying to force their views down your throat. It never ends!

Simple solution - stay off the internet, but what does that have to do with this thread?
There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.

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Re: Does a photon have mass equivalent to its energy?
« Reply #78 on: 30/05/2012 17:51:54 »
Thanks for the information, Pete.  It'll probably take me a while to wade through the links. 
You're most welcome! :)

You're right that I haven't done much work with general relativity/cosmology, which is where it sounds like relativistic mass finds use.
It's also used in basic relativity.  E.g. if somone wishes to ge a better understanding of the consequences of relativity in all its generality they need to understand the relativity of continuos media. There's a question aboiut it in Gravitation by Misner, Thorne and Wheeler. One good reason to study these things is to understand what others are saying in peer reviewed articles and to get the correct answer when your studying a text and are working on the problems.

I decided that I should post the answer to the question about the mass densiy of a magnetic field. It's at
http://home.comcast.net/~peter.m.brown/sr/mass_mag_field.htm

Quote
I'm much more familiar with quantum mechanics, where invariant mass is useful, and quantum optics, where invariant mass of single photons is zero.
I love QM. In a few months I might just refresh me QM. Grad school was a long time ago and even though I try to stay refreshed often it's just not enough unless you use of often. In the fall I'm sitting in on an EM course to refresh my EM. After that I'm hoping that there will be a QM course I can sit in. I need the exercise! :)

As I always say, use what is most useful at the time. People here got the impression that I never use proper mass in my work and leave the inertial mass out of it. Sometimes it's just easier. That seems to be the case for me, and of course others, when working on basic equations of particle physics balance equations. But when it came to working out the physics of cyclotron I found that inertial mass was easier for me. E.g.
http://home.comcast.net/~peter.m.brown/sr/cyclotron.htm

My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
No. It's not true. First off they are not the same thing. They're equivalent, not identical. And even then only in a limited use of the relationship. That use is the limitation to particle physics or any physics which is not a closed system. E.g. a drop of water in an electric field like, for example, an electrical storm. The electric field polarizes the drop of water. This leaves the drop in a state in which there is stress in the drop. This stress contributes to the inertia of the drop. In this case the relation E = mc2 is wrong. I thought I stated this when I quoted Mould's text Basic Relativity. Doesn't matter. I've been planing on creating a web page to describe such scenarios. I keep putting it off. Too lazy I guess.  I can send you an article in the inertia of stress if you'd like. It's very interesting.

My other general impression is that arguing over what should be called "mass" actually obscures a more important point: that when you transition from Newtonian physics to general relativity, there is no single quantity that has all the properties of Newtonian mass, so of course you can argue over the proper generalization of mass! 
My  philosophy is to use what works bestin all conceivable cases. Then use what is easier i the particular problem that you're working on. Myself? I have those damn subscripts all over the place. When using inertial mass the labeling can be a pain in the butt. Instead of m01 for the proper mass of particle one I can more easily use m01. It's much cleaner to look at. When things like this are employed all over then the entire derivation looks cleaner all over.

What really irritates me is when people constantly repeat themselves every single time I use inertial mass. That's quiet rude and that behaviour should be prohibited.

Here are a few derivtions that help explain my points. The main list his here
http://home.comcast.net/~peter.m.brown/

The page which lists all problems worked for SR is here
http://home.comcast.net/~peter.m.brown/sr/sr.htm

Here is the page on invariant mass. It demonstrates the uses and abuses of the concept. http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

The term invariant mass is nomally used to apply to a system of non-interacting particles. The invariant mass is obtained using the 4-momentum 4-vector of the system. This 4-vector is calculated by summing up the 4-vectors of the particles. There is a hitch though. Normally when summing 4-vectors you have to evaluate them at the same point in spacetime. And also one has to make sure that the particles are no longer interacting. then the 4-vectors can be summed even though the 4-vectors are at different points in spacetime. Then you find the proper mass of this vector as you would a single particle. n the link these things are analyzed in detail.
« Last Edit: 30/05/2012 17:55:31 by Pmb »

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Re: Does a photon have mass equivalent to its energy?
« Reply #79 on: 30/05/2012 17:57:17 »
It's amazing! No matter where you go on the internet there's always someone trying to force their views down your throat. It never ends!
I'm dibled and can't get around much. I can only take so miuch TV. If I don't use my mind then I'll forget alot about the physics I know. I won't be challenged. The alternate is worse, hence my staying where the nuts are.

Simple solution - stay off the internet, but what does that have to do with this thread?

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Re: Does a photon have mass equivalent to its energy?
« Reply #80 on: 02/06/2012 16:32:53 »
Thinking of the original question. "If E =mc^2, and the photon transfers energy, how can it have no mass even if the mass is minuscule?"

One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure. Then invariant proper mass and the photon share that ability. They both influence other particles, as well as get influenced by them.

The problem here being one of experience. We all differ between bosons and what we call matter, but as Pete pointed out, Einstein didn't. He called both EM and invariant proper mass 'matter'. And EM is defined through photons.
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Re: Does a photon have mass equivalent to its energy?
« Reply #81 on: 02/06/2012 17:09:44 »
. . . One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure  . . .

My current opinion is that the best way to teach a lot of modern physics is to teach that classical ideas like "mass" or "particle" are useful approximations to more complex quantities like the stress-energy tensor or quantum wave/particles. 

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Re: Does a photon have mass equivalent to its energy?
« Reply #82 on: 02/06/2012 17:51:09 »
Thinking of the original question. "If E =mc^2, and the photon transfers energy, how can it have no mass even if the mass is minuscule?"

One way of thinking of it may be to leave the concept of mass and instead consider tension and pressure. Then invariant proper mass and the photon share that ability. They both influence other particles, as well as get influenced by them.

The problem here being one of experience. We all differ between bosons and what we call matter, but as Pete pointed out, Einstein didn't. He called both EM and invariant proper mass 'matter'. And EM is defined through photons.
photons are a quantum entity, not a classical one. SR and GR are classical physics, not quantum ones. And EM field is a classical field, not a quatum one. In classical mechanics one doesn't deal with photons.

I use photons in classic theory by never mixing quantum with classical. In SR/GR I use the luxon which is a particle whose energy is related to its momentm by E = pc and m = 0 (where m = proper mass). To see how to use it in an example please consider Einstein's box. See http://home.comcast.net/~peter.m.brown/sr/einsteins_box.htm

See Eq. (8). Does this help?

Antipa presented the idea of considering instead an atom that emits a photon and applies the center-of-mass theorem to the atom-photon system. This is dicussed in my page listed in the above link.

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Re: Does a photon have mass equivalent to its energy?
« Reply #83 on: 02/06/2012 19:52:58 »
My general take on the subject was along the line of what Lightarrow said: that relativistic mass is just renaming energy, and we can use energy to do all the computations required without introducing a new name for it.  Is this true? 
No. It's not true. First off they are not the same thing. They're equivalent, not identical. And even then only in a limited use of the relationship. That use is the limitation to particle physics or any physics which is not a closed system. E.g. a drop of water in an electric field like, for example, an electrical storm. The electric field polarizes the drop of water. This leaves the drop in a state in which there is stress in the drop. This stress contributes to the inertia of the drop. In this case the relation E = mc2 is wrong.
That relation can't be wrong, if you consider the right system and compute the correct energy. For example, If an external field interacts with the drop, you can't pretend to apply the equation to the drop only.

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Re: Does a photon have mass equivalent to its energy?
« Reply #84 on: 02/06/2012 22:46:24 »
That relation can't be wrong, if you consider the right system ....
That's what it means when it is said that E = mc2only works under certain circumstances.

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Re: Does a photon have mass equivalent to its energy?
« Reply #85 on: 03/06/2012 20:16:36 »
That relation can't be wrong, if you consider the right system ....
That's what it means when it is said that E = mc2only works under certain circumstances.
So your ojection that relativistic mass and energy are not the same, means that we have to specify which is the system and which is the energy?
It's a poor argument...

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Re: Does a photon have mass equivalent to its energy?
« Reply #86 on: 03/06/2012 22:04:32 »
So your ojection that relativistic mass and energy are not the same, means that we have to specify which is the system and which is the energy?
It's a poor argument...
That makes no sense. I already showed you a counter example which proved you wrong. Why are you making no attempt to show that the physics is wrong? You seem to think that this is something I created by my loansome. I didn't invent this by any stretch of the imagination. You can find this in the physics literature. Pick up Mould's text Basic Relativity and it will teach you the relavent physics. Or see Rindler's text. Or Moller's text. Or look through the literatuire such as the American Journal of Physics which is a  teaching journal. I can help you find your way around if you really want to.

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Re: Does a photon have mass equivalent to its energy?
« Reply #87 on: 04/06/2012 03:04:38 »
I finally found that paper on this topic I was referring to. There is an earlier paper than this by the same author but I'll have to start searching for that tomorrow.

The article is On the Inertial Mass Concept in Special Relativity by Mendel Sachs, Foundations of Physics Lectures, Vol. 1, No. 2, 1988
------------------
In this regard I have re-examined in an earlier paper the meaning of Einstein's energy-mass relation in special relativity

E = m0c2   (proper frame)


E = m0c2/[1 - (v/c)2 ]1/2   (moving frame)

demonstrating that, in the frame of the free particle with inertial mass m0, this equation does not signify that "energy is equivalent to mass", as it is usually asserted.
      What was pointed out earlier in this regard is that the concept of “energy” per se and the concept of “inertial mass” per se are, firstly, the same as they are in classical physics, and secondly, that they are logically different concepts: “energy is defined as the capacity of matter to do work  and “inertial mass” is defined as a quantification of the inertial property of matter, i.e. a measure of its resistance to a change of state of constant speed (or rest) with respect to any observer..
      Since these are entirely different concepts, energy cannot be said to be “equivalent to mass”.

------------------

which is exactly what I've been saying for years of course.

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Re: Does a photon have mass equivalent to its energy?
« Reply #88 on: 11/06/2012 13:51:33 »
I don't really know if Einstein used 'photons' as a description? I've seen people saying that he rather though of it as 'light quanta'? And the 'light quanta' definition naturally comes from black body radiation and the photo electric effect.. http://www.aip.org/history/einstein/essay-photoelectric.htm

Where the difference between that idea and the idea of a 'photon' goes may be discuss-able though? I like the idea of 'fields' myself in where what we call 'photons' are the fluctuations/emissions(?) measured by us. But I don't support waves either although the duality definitely exists. All as I then doesn't necessarily need to consider 'photons propagating'. And that's also the reason why I like the concept of indeterminacy better.

It's a very tricky subject.
« Last Edit: 11/06/2012 13:54:19 by yor_on »
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Offline lightarrow

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Re: Does a photon have mass equivalent to its energy?
« Reply #89 on: 12/06/2012 12:21:10 »
I finally found that paper on this topic I was referring to. There is an earlier paper than this by the same author but I'll have to start searching for that tomorrow.

The article is On the Inertial Mass Concept in Special Relativity by Mendel Sachs, Foundations of Physics Lectures, Vol. 1, No. 2, 1988
------------------
In this regard I have re-examined in an earlier paper the meaning of Einstein's energy-mass relation in special relativity

E = m0c2   (proper frame)


E = m0c2/[1 - (v/c)2 ]1/2   (moving frame)

demonstrating that, in the frame of the free particle with inertial mass m0, this equation does not signify that "energy is equivalent to mass", as it is usually asserted.
      What was pointed out earlier in this regard is that the concept of “energy” per se and the concept of “inertial mass” per se are, firstly, the same as they are in classical physics, and secondly, that they are logically different concepts: “energy is defined as the capacity of matter to do work  and “inertial mass” is defined as a quantification of the inertial property of matter, i.e. a measure of its resistance to a change of state of constant speed (or rest) with respect to any observer..
      Since these are entirely different concepts, energy cannot be said to be “equivalent to mass”.

------------------

which is exactly what I've been saying for years of course.

I have coloured in blue the last sentence.
*Which* energy is he talking about there? Energy in the proper frame is a thing, energy in the other frame is another.
So, as you see, not even "Energy 1" is the same concept as "Energy 2"...
We were discussing if your relativistic mass is the same concept of total energy or not. It is.

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Offline Pmb

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Re: Does a photon have mass equivalent to its energy?
« Reply #90 on: 15/06/2012 14:47:45 »
We were discussing if your relativistic mass is the same concept of total energy or not.
That wasn't the subject of the thread but a spin off topic. But yes, we discussed this. See the responses that I provided JP earlier in this thread
It is.
Is that supposed to be an argument? That is a useless statement.

I'm curious. Why do you think that you can simply claim the opposite and expect people to accept that as a factf? I'm sure that you know that it's not a valid argument tactic. People never believe that kind of thing.

That's a poor arguement tactic since its the universality of E = mc2 that is being challenged? Besides, I already provided proof that E = mc2 is not universally correct. If I recall correctly, you seemed to think that modifying the scenario at hand to a configuration where E = mc2 was true was a valid method of a counter proof. It is not. That was a logical fallacy known as a straw man argument.

See - http://en.wikipedia.org/wiki/Straw_man
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A straw man is a type of argument and is an informal fallacy based on misrepresentation of an opponent's position. To "attack a straw man" is to create the illusion of having refuted a proposition by replacing it with a superficially similar yet unequivalent proposition (the "straw man"), and refuting it, without ever having actually refuted the original position.

Also, why did you refuse to answer my very direct question? I.e. see post #86
Quote
I already showed you a counter example which proved you wrong. Why are you making no attempt to show that the physics is wrong?

And if you really want to know which energy he' talking about then I'll send you the articles and you can read them. Taking snippets out of an article more than once is a good way to misunderstand the article.

It all you are able to do is to repeat yourself then we have nothing further to discuss. My counter example is proof enough that you're wrong. Anbybody can read an Mould's text and confirm this.
« Last Edit: 15/06/2012 15:05:01 by Pmb »

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Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #91 on: 25/06/2012 03:39:22 »
Mass from a photon should only be present as a result of the photon's bent path, the tighter the bend the greater the mass however minute it may be, but then a photon's path is never straight, it will forever bend through gravitational fields and also interact with the weak and strong forces from former to latter with increasing proportionality. There is a specific reason why matter can never travel faster than light, ergo, E does = MC squared, ***(NOT CUBED)***, as the electric plane and magnetic plane of a photon are opposed at 90 deg and do not form a sphere, and the field strength from a photon decreases proportionally as a square from the distance to the source. It's all just a piece of Pi.   
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Offline LetoII

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Re: Does a photon have mass equivalent to its energy?
« Reply #92 on: 28/06/2012 11:13:01 »
i think the answer should be "potentially it does"

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Offline Phractality

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Re: Does a photon have mass equivalent to its energy?
« Reply #93 on: 02/07/2012 05:54:24 »
I was going to put this response in the thread How "fast" does force "travel", but perhaps it belongs here, instead.

A supernova converts a significant fraction of a dying star's mass to energy (light and neutrinos) in a matter of hours, and that energy radiates at the speed of light.

If that energy has no gravitational mass, the gravity felt here from that star should drop after a speed-of-gravity delay. If the force of gravity propagates instantaneously, the gravity should drop when the supernova happens, not when we see it. If the speed of gravity is the speed of light, the gravity should drop here when we see the supernova.

On the other hand, if the energy does have gravitational mass, which forms a uniform spherical shell of light and neutrinos, and gravity propagates instantaneously, then Newton's shell theorem is applicable. (The shell theorem tacitly assumes that gravity is instantaneous at all distances.) According to the shell theorem, gravity outside a uniform spherical shell of matter (due to the presence of that matter) is inversely proportional to the distance from the center of the sphere, and gravity inside the sphere (due to the presence of that matter) is zero. As the spherical shell of energy leaves the supernova it would continue to exert the same gravity on us as it did before the matter was converted to energy. As soon as the supernova becomes visible, we enter the spherical shell and the gravity from that spherical shell of matter drops to zero in the time it takes for the light and neutrinos of the supernova to fade from our view.

So, when matter is converted to energy, the drop in gravity should occur after a speed-of-light delay. The only way it can occur instantaneously is if A: gravity propagates instantaneously, and B: energy has no gravitational mass.

Of course, all this is moot, since the drop in gravity would be too minute to be detected by our instruments. Perhaps it could be detected as a change in the trajectories of the supernova's neighbor stars during the time after the supernova occurs and before it becomes visible at the locations of those neighbor stars.

If the supernova's energy does not radiate uniformly in a spherical shell, then the shell theorem is not applicable.
« Last Edit: 02/07/2012 05:56:23 by Phractality »
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Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #94 on: 05/07/2012 07:09:21 »
Let's assume for a moment that mass is a condition exhibited by a photons bent path as it completes it's saturation of maximum amplitude toward increasing electromagnetic field strength in space. Light does have the potential to show mass equal to it's energy. An electron will show the same amount of energy as a photon that has a wavelength equal to the circumference of the electron. This implies that all of matter is made of electromagnetism, as photons locked in their own fields to become points measured as particles.  Forget all the pseudo science out there that includes thoughts of extra dimensions, worm holes, everything's from nothings and the like. There is a specific reason why matter cannot travel faster than light. Mass is a property of light. Light does not travel faster than light.
« Last Edit: 05/07/2012 07:18:19 by Robro »
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #95 on: 05/07/2012 13:30:24 »
I think of it as a field, consisting of all mass there is. In that (dynamic) field all updates on 'gravity' should propagate at 'c'. That means that if you have a star going supernova, radiating away a lot of energy, you won't notice a difference until the information has reached us, and it should be gradual as the radiation pass us by. As I think of it that is :)

The field is instantaneous if one mean that it is 'everywhere', but the information exchange about its equilibrium should obey 'c'.
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #96 on: 05/07/2012 13:55:01 »
 Maybe I should change this a little to get my idea through :)

Think of a static field. That is 'gravity', without a arrow. The arrow and mass/energy/motion translate this static field into a dynamic field that always must find its equilibrium, in each instant of 'the arrow of time', but to us ever so weakly changing if we now could measure it.

But ignoring 'the arrow' the field is static, and always in a equilibrium. And that may sound weird as we should be able to assume that if something 'change' then there must be moments of unbalance, but we're speaking of a whole 'SpaceTime' now and I doubt it ever can be found to be unbalanced, changing under the arrow yes, but always in a equilibrium. And that sounds weird, doesn't it :)
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Offline Robro

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Re: Does a photon have mass equivalent to its energy?
« Reply #97 on: 06/07/2012 01:03:58 »
I am wondering; By what 'means' does the presence of mass curve space/time? And, how exactly is space linked to time?
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Offline yor_on

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Re: Does a photon have mass equivalent to its energy?
« Reply #98 on: 07/07/2012 00:16:15 »
The metric of space is 'gravity' according to Einstein. What that means, my view, is that there can be no 'space' without gravity existent. Gravity change 'time rates' if compared between frames of reference, as proven on Earth by NIST at as short distances as decimeters. Special relativity doesn't discuss this but General relativity does, all as I see it :)

As for how mass distorts space?

That one is a tough one to answer. It follows as a logical conclusion from general relativity and light as a constant and it has recently been tested by gravity probe B if i remember right, and there found to distort the space around Earth. Then you also have the other experiments proving it, in fact it was one of the first real proofs of relativity as i remember. But how? I don't really know. It also depends on what 'space' is.

What is a vacuum/space made of ? :)

Nothing? Or something?
Why do we expect 'bosons' as the Higgs particle to exist, although in themselves unmeasurable to us?
Maybe because it possibly could describe the 'why and how'  of that distortion existence? Although I'm not sure at all of how that would be explained just by us expecting the 'Higgs syrup'? And to that you can add how the Higgs particle then should be related to measuring 'time rates' between frames of reference, as that too is proven to exist. And as mass is coupled to gravity?

Myself I do think we have a lot of 'unmeasurabels' around :) although I'm not sure on the Higgs theory as a 'particle'. I prefer 'fields' myself. As for photons and EM, they don't bend to a EM-field. Depending on hypothesis you might explain that but experimentally they never have, as far as I know.
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