# Does a magnetic field have mass?

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On 9/7/2019 at 10:09 PM, swansont said:

If you want to know what the KE is, you are by definition considering it in isolation. It depends on mass and speed. You had already said the items were identical, so the mass is the same.

I meant identical in composition. I just find it odd that internal KE of the atoms increases the mass of the object but translational KE of the entire object doesn’t.

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6 minutes ago, MPMin said:

I meant identical in composition. I just find it odd that internal KE of the atoms increases the mass of the object but translational KE of the entire object doesn’t.

Because one involves relative motion of the whole object (ie the centre of mass)  but the other doesn’t.

You can treat the extra energy as increasing the relativistic mass, but not the rest mass (because it isn’t at rest): http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

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52 minutes ago, MPMin said:

I meant identical in composition.

Which means the same mass, as I said.

52 minutes ago, MPMin said:

I just find it odd that internal KE of the atoms increases the mass of the object but translational KE of the entire object doesn’t.

That’s not a physics argument. In fact, it’s more of a statement about not being familiar with the relevant physics.

E = mc^2 was derived under the condition of an object at rest, so translation has to be accounted for separately.

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5 hours ago, swansont said:

That’s not a physics argument. In fact, it’s more of a statement about not being familiar with the relevant physics.

E = mc^2 was derived under the condition of an object at rest, so translation has to be accounted for separately.

I disagree with your point of view. I don’t see Vibrational KE and transitional KE being any different. Anything that vibrates is still transitioning around a centre point just because it’s average centre doesn’t change doesn’t mean it’s not transiting a small distance back and forth. If you were to look at an atom vibrating for time frame of one vibration you could say it transitioned in that moment. If an entire object were to transition a short distance then return to its point of origin so it’s centre of mass didn’t change you could say it vibrates did it’s mass increase in that moment?

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9 hours ago, MPMin said:

I disagree with your point of view.

If you disagree post some physics that backs it up. Where is the paper that derives something that contradicts me? But if that's just your private view, well, it's not up to you. The way Einstein derived E=mc^2 is an historical fact.

This is physics — you don't get to have a personalized version of it.

9 hours ago, MPMin said:

I don’t see Vibrational KE and transitional KE being any different.

Well, then, you are free to come up with a self-consistent version where you include vibrational KE as a separate item in the treatment of energy. Meaning you will have to re-work the marriage between mechanics and thermodynamics, among other things. Good luck.

Meanwhile, when we discuss mainstream physics, translational KE is accounted for separately.

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11 hours ago, swansont said:

If you disagree post some physics that backs it up

I did, I thought my explanation  of vibrational KE vs translational KE was quite clear. Im not disagreeing with E=mc^2, in fact I’m agreeing with it, I don’t see why translational KE doesn’t add to the mass of an object when vibrational KE does. I described how vibrational KE can be seen as translational KE to illustrate my point. If you’re going to say that translational KE is frame of reference dependant then that’s just another way of saying there is no way of choosing how to quantify it because we can’t decide where to look at it from but that doesn’t mean there isn’t an actual quantity to the translational KE which would add to the mass of the object.

11 hours ago, swansont said:

This is physics — you don't get to have a personalized version of it.

I do get to have a different point of view though, not everyone interprets information the same way. If everyone completely agreed on every aspect of science there’d be nothing to discuss.

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5 minutes ago, MPMin said:

If you’re going to say that translational KE is frame of reference dependant then that’s just another way of saying there is no way of choosing how to quantify it because we can’t decide where to look at it from but that doesn’t mean there isn’t an actual quantity to the translational KE which would add to the mass of the object.

There is no "absolute" (universal) way to quantify it. It is observer dependent. You can, however, choose to represent the energy as relativistic mass. It is not usually a useful thing to do, though because most physics where mass is involved requires the rest mass.  https://en.wikipedia.org/wiki/Mass_in_special_relativity#The_relativistic_mass_concept

On the other hand, the thermal energy is not observer dependent and so it contributes to the rest mass of the object. An therefore is relevant to anything where the mass of the object is required.

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1 hour ago, Strange said:

You can, however, choose to represent the energy as relativistic mass. It is not usually a useful thing to do, though because most physics where mass is involved requires the rest

So does a magnetic field or an emp have relativistic mass?

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1 hour ago, MPMin said:

I did, I thought my explanation  of vibrational KE vs translational KE was quite clear.

With that you are providing a description of physics. Not actually doing physics. You don’t justify your position with anything.

1 hour ago, MPMin said:

Im not disagreeing with E=mc^2, in fact I’m agreeing with it, I don’t see why translational KE doesn’t add to the mass of an object when vibrational KE does.

Not seeing why is different from making a claim that something is the case.

It’s because of how it is derived, which Einstein did in 1905, and having the physics be consistent with how things had already been defined.

As I mentioned earlier, if you make a change, it will affect a lot more than one equation.

1 hour ago, MPMin said:

I described how vibrational KE can be seen as translational KE to illustrate my point. If you’re going to say that translational KE is frame of reference dependant then that’s just another way of saying there is no way of choosing how to quantify it because we can’t decide where to look at it from but that doesn’t mean there isn’t an actual quantity to the translational KE which would add to the mass of the object.

If the CoM isn’t changing, there is no translation.

1 hour ago, MPMin said:

I do get to have a different point of view though, not everyone interprets information the same way. If everyone completely agreed on every aspect of science there’d be nothing to discuss.

Much like in relativity, there are some things everyone must agree on. And disagreement requires more than a handwave - you need math. You can’t just present a new equation without deriving it.

5 minutes ago, MPMin said:

So does a magnetic field or an emp have relativistic mass?

Relativistic mass is just a proxy for the total energy. E/c^2

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The paper I'm referring to is Einstein's 1905 work "Does The Inertia Of A Body Depend Upon Its Energy-Content?"

In it he derives what happens if two photons are simultaneously emitted or absorbed in/from opposite directions (of course, he doesn't say "photons" because that terminology did not yet exist) and he concludes "The mass of a body is a measure of its energy-content"

Since internal motion is part of the energy content of a body, it's included with the mass. KE is not, as it is quite explicitly dependent on the frame of reference. IOW, you can pick a frame where the body is at rest and thus KE = 0. You cannot pick a frame where a body has no vibrational KE (even in classical physics; in QM the notion disappears entirely since the ground state a an harmonic oscillator has nonzero energy) It's part of the energy content of a body, and thus contributes to the mass.

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On 9/10/2019 at 8:14 PM, swansont said:

The paper I'm referring to is Einstein's 1905 work "Does The Inertia Of A Body Depend Upon Its Energy-Content?"

Einstein, apparently, wasn’t right about everything especially as you mention two photons, I seem to recall some evidence has been discovered which contradicts what Einstein said about two simultaneous photons being co dependant on each other so I think it’s fair to question even what Einstein has said in the past.

I can see why KE is not classically considered to contribute to mass but I don’t agree with it. To exclude an energy because a frame of reference can’t be determined is in its self user dependant. This is exactly the same problem I had in the other thread here talking about the actual KE of an object. Just because we don’t have a universal frame of reference at this time doesn’t mean there shouldn’t be one to determine the true KE of an object.

Imagine you could change your perspective to being on one of the the atoms (as if your standing on it) within an object with vibrating atoms, from that perspective you can only see the atoms in your immediate vicinity and you can’t see all the other atoms. This would seem as though the atoms you can see are all moving around randomly and there’d be no way to choose a frame of reference. In that situation you could perceive that the atom you are standing can not have its KE determined. Just because you can’t see all the other atoms of that object doesn’t mean they are isolated from everything else. It seems unintuitive to ignore some types of energy while counting the more easily quantifiable types of energy as mass contributors.

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18 minutes ago, MPMin said:

Einstein, apparently, wasn’t right about everything especially as you mention two photons, I seem to recall some evidence has been discovered which contradicts what Einstein said about two simultaneous photons being co dependant on each other so I think it’s fair to question even what Einstein has said in the past.

In the absence of any citation to this vague claim, not to mention that Einstein made no claim about "co-dependence" (he was only interested in the momentum being the same, and your nebulous reference says nothing about them not having the same momentum. As I said, this was before the notion of photons, or QM, existed) this "rebuttal" is based on...nothing. There's no physics here, that's for sure.

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I can see why KE is not classically considered to contribute to mass but I don’t agree with it.

Well, tough.

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To exclude an energy because a frame of reference can’t be determined is in its self user dependant. This is exactly the same problem I had in the other thread here talking about the actual KE of an object. Just because we don’t have a universal frame of reference at this time doesn’t mean there shouldn’t be one to determine the true KE of an object.

There is no such thing as a preferred frame, and speeds are relative. This is a fact of life in the world of relativity.

If you can't cope with it, see above.

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Imagine you could change your perspective to being on one of the the atoms (as if your standing on it) within an object with vibrating atoms, from that perspective you can only see the atoms in your immediate vicinity and you can’t see all the other atoms. This would seem as though the atoms you can see are all moving around randomly and there’d be no way to choose a frame of reference. In that situation you could perceive that the atom you are standing can not have its KE determined.

One of the myriad problems with this is that an atom in this circumstance would not be in an inertial frame (there is acceleration), so all bets are off anyway. Another is that we are not viewing this from an atom's perspective — it has to be a perspective of any inertial frame, which would exclude the perspective of any atom in the object.

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Just because you can’t see all the other atoms of that object doesn’t mean they are isolated from everything else.

The problem is quite the opposite – it's because they aren't isolated that you run into trouble.

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It seems unintuitive to ignore some types of energy while counting the more easily quantifiable types of energy as mass contributors.

Nothing is being ignored — conservation of energy requires you account for all of it.

But your argument is like saying that temperature should be incorporated into gravitational potential energy in classical physics. It makes no sense to anyone who has a clue as to what's going on.

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8 hours ago, swansont said:

In the absence of any citation to this vague claim, not to mention that Einstein made no claim about "co-dependence"

Quoted from:

The results, published in May 2018 in the journal Nature, are robust: "The observed correlations strongly contradict local realism," the authors write. Sorry, Einstein. You'll always have relativity.

sorry not codependence but entanglement which is basically the same concept...

8 hours ago, swansont said:

One of the myriad problems with this is that an atom in this circumstance would not be in an inertial frame (there is acceleration), so all bets are off anyway. Another is that we are not viewing this from an atom's perspective — it has to be a perspective of any inertial frame, which would exclude the perspective of any atom in the object.

No matter how you word it, this is still a user dependent point of view. Wether a reference frame is preferential or not doesn’t change the fact that a frame of reference can still be chosen at will.

8 hours ago, swansont said:

Nothing is being ignored — conservation of energy requires you account for all of it.

How is the KE being accounted for when it’s not included as part of the mass of the object and the frame of reference can be user defined?

8 hours ago, swansont said:

But your argument is like saying that temperature should be incorporated into gravitational potential energy in classical physics. It makes no sense to anyone who has a clue as to what's going on.

How am I saying this or even like saying this?

And what’s going is only ever a clue in any case!

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Entanglement is an entirely different topic that has nothing to do with the discussion in this thread

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15 minutes ago, Mordred said:

Entanglement is an entirely different topic that has nothing to do with the discussion in this thread

The context of this was to demonstrate that Einstein’s logic isn’t absolute.

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No one ever claimed he  was infallible however relativity is incredibly well tested in every conceivable manner. It is literally one of the most rigorously tested theories.

Secondly pop media articles are far more hype than actual science. Einstein didn't like the probabilistic nature behind entanglement  doesn't mean he didn't understand what was involved.

Edited by Mordred

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6 hours ago, MPMin said:

Quoted from:

The results, published in May 2018 in the journal Nature, are robust: "The observed correlations strongly contradict local realism," the authors write. Sorry, Einstein. You'll always have relativity.

sorry not codependence but entanglement which is basically the same concept...

That has been known for a long time. I'm not sure how it is relevant to this thread.

6 hours ago, MPMin said:

How is the KE being accounted for when it’s not included as part of the mass of the object and the frame of reference can be user defined?

As kinetic energy, in the chosen frame of reference.

6 hours ago, MPMin said:

The context of this was to demonstrate that Einstein’s logic isn’t absolute.

It has nothing to do with "Einstein's logic". That could be totally wrong. It doesn't affect the validity of the theories.

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10 hours ago, MPMin said:

Quoted from:

The results, published in May 2018 in the journal Nature, are robust: "The observed correlations strongly contradict local realism," the authors write. Sorry, Einstein. You'll always have relativity.

This would have to be entanglement of momentum states to matter, and even then, nothing precludes the momenta from having the same magnitude.

10 hours ago, MPMin said:

sorry not codependence but entanglement which is basically the same concept...

Um, no.

And if your point is that “Einstein was wrong about something” that’s irrelevant. You would need to show he (and thousands of other physicists) was wrong in this specific instance.

10 hours ago, MPMin said:

No matter how you word it, this is still a user dependent point of view. Wether a reference frame is preferential or not doesn’t change the fact that a frame of reference can still be chosen at will.

Yes.  But you can’t find a frame that has no thermal energy.

10 hours ago, MPMin said:

How is the KE being accounted for when it’s not included as part of the mass of the object and the frame of reference can be user defined?

You have a kinetic term in the energy equation.

10 hours ago, MPMin said:

How am I saying this or even like saying this?

And what’s going is only ever a clue in any case!

Because you are lumping terms together that don’t belong, when viewed in a larger context.

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If you are all saying that KE doesn’t contribute to an object’s mass then m=E/c^2 should really be m=(all E except KE)/c^2

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47 minutes ago, MPMin said:

If you are all saying that KE doesn’t contribute to an object’s mass then m=E/c^2 should really be m=(all E except KE)/c^2

It is exactly that. The m is the rest mass, so there is no kinetic energy. So "all E except KE" = "all E".

The equation for a moving object is: $E^2 = (mc^2)^2 + (pc)^2$

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I always like putting in the subscript to make the last equation more obvious. However let's do this

$E^2 = \underbrace{(mc^2)^2}_{rest:mass} + \underbrace{(pc)^2}_{kinetic:inertial:mass}$

Edited by Mordred

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1 hour ago, MPMin said:

If you are all saying that KE doesn’t contribute to an object’s mass then m=E/c^2 should really be m=(all E except KE)/c^2

Yes, but the equation isn’t m=E/c^2

The equation, derived for an object at rest, is E=mc^2

If you rearrange it, you have already assumed KE=0

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On 9/14/2019 at 4:43 AM, swansont said:

The equation, derived for an object at rest, is E=mc^2

But when is an object ever really at rest?

Does relativistic mass contribute to gravitational mass?

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58 minutes ago, MPMin said:

But when is an object ever really at rest?

Good question, it is questions like this that caused modern physics to drop the usage of rest mass. The modern term is the invariant mass.

58 minutes ago, MPMin said:

Does relativistic mass contribute to gravitational mass?

Yes though relativistic mass is replaced by variant mass in modern terminology. Both rest mass and relativistic mass originated in SR treatments where one inertial frame was considered at rest.

Under GR all frames are inertial and no frame is truly at rest. Hence the modern terminology.

To determine the invariant mass of a particle requires extensive experimentation in scattering experiments and particle decays. The CM frame and lab frame is extensively used in these experiments.

Here is an extremely basic oversimplified overview

Edited by Mordred

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1 hour ago, MPMin said:

But when is an object ever really at rest?

Relativity is a classical theory. If not accelerating, an object is at rest in its own frame.

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