Is Relativistic Mass Still Relevant in Modern Physics Discussions?

[learningphysics]

You may have wanted to give the entire quote:

"(6) E0_bar - E0 = m_bar - m:
The rest-energy changes, therefore, in an inelastic collision (additively) like the
mass. As the former, from the nature of the concept, is determined only to within
an additive constant, one can stipulate that E0 should vanish together with m.
Then we have simply
E0 = m;"

What is your point?

I would love to see you try to make two baseballs collide to become "one" - what you are referring to only happens on the quantum level, not the macroscopic level. All the kinetic energy will be given off as energy in another form in actuality.

So you're saying Einstein was wrong? He used simple conservation of energy, and conservation of momentum... and he makes no mention of this "other form" of energy you're talking about? What exactly are you talking about here?

And who talked about two baseballs becoming one? The paper is about an inelastic collision. I mentioned a simple inelastic collision between two baseballs... nothing about two baseballs becoming one.

Einstein's derivation is general... it makes no mention of being at the quantum level... it applies to any two material bodies.

You might want to verify it as it is in direct contradiction to the quote by Albert I gave.

Which quote is that?

 

[pmb_phy]

Aer - I've explained that I will not participate in this discussion since anything you could possible ask has been addressed in the material I've linked to. If you have chosen to ignore my response to all of your questions (my response is in the material since I've pretty much knew what you were going to ask - and you did) then I will be ignoring your questions as well. It appears to me that even with my answers you are misquoting me, i.e.

Then we have people like pmb_phy claiming a contained gas's weight is a measure of the rest mass of the particles PLUS the kinetic energy they possess. UMMM - NO! That's wrong, the weight is only a measure of the rest mass of the particles and nothing more.

You've got this quite wrong. There is a mass corresponding to the kinetic energy. Problem with the "mass = rest mass" definition is that people make mistakes like the one you've made here. Proof is not only given in my paper but these types of things have been done in the American Journal of Physics and I've posted those articles on my website and posted the link here as I recall. If you don't have the drive to look for the answer to your question in the paper given to you then here - m = p/v where p is the magniture of the momentum of the particle and v is the speed of the particle. I'm sure you'll object to this and as such your objections are in all probability addressed in the material I gave you.

Pete

 

[jtbell]

If two identical macroscopic baseballs collided in a symmetric inelastic collision losing some of their kinetic energy to heat, then each baseball would increase its rest energy, and therefore change its "rest mass". The increased "rest mass" is due to heat (which is the kinetic energy of the constituent particles that form the baseball)

I would love to see you try to make two baseballs collide to become "one" - what you are referring to only happens on the quantum level, not the macroscopic level. All the kinetic energy will be given off as energy in another form in actuality.

Actually, both of you are right, but you're looking at different stages in the compete sequence of events. To make the analysis simpler, instead of baseballs, consider two lumps of putty with equal (invariant) masses. They are both at room temperature. They move towards each other, with equal speeds in opposite directions. They collide and smush together. The result is a single stationary lump of putty.

The gross kinetic energy of the two original lumps is converted to thermal energy, i.e. random kinetic energy of the individual atoms in the putty (many people loosely and incorrectly call this "heat"). Therefore, immediately after the collision, the single lump is slightly warmer than room temperature. The (invariant) mass of this single lump is also slightly larger than the sum of the (invariant) masses of the two original lumps.

As time passes, the warm lump of putty cools to room temperature and loses its "extra" thermal energy to its surroundings via some combination of radiation, convection in the surrounding air (if it's not in a vacuum) and conduction (if it happens to be resting on a tabletop or something). As the putty cools and loses energy, its (invariant) mass also decreases.

 

[Aer]

What is your point?

The conclusion was that mass is proportional to rest energy.

Which quote is that?

"It is not good to introduce the concept of the mass of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the 'rest mass' m. Instead of introducing M it is better to mention the expression for the momentum and energy of a body in motion."

 

[pmb_phy]

You really shouldn't insult someone who took the time to respond to your post despite the fact that he was tired of the topic.

Thanks. Please note that I'm not ignoring all this because I'm lazy. I've had horrible back pain when I sit for more than a few minutes. It took a long time to figure out what it was. Turns out that I have a stone in my gall-bladder. It will be comming out when I have surgery in the near future. But for now I'm spending very little time on the internet. Especially on this topic and especially since this person is insulting me and ignoring the answers given to him by me that he asked for.

Why should he bother? He's not trying to make any argument here... You asked for his input and he gave it to you. Then you turn around and insult him for it.

Thanks. Its true that I'm not arguing here - a question was asked of me and I answered it. The insults are unwelcome. This seems odd for a moderated forum. What's happened since I've been absent?

Here is a point I rarely make - If I was a particle physicist then in all likelyhood I'd use the term "mass" to mean proper mass and I'd use no subscript. People in a field understand the meaning of a term. The meaning changes between fields. Their definion would fail if they can't treat their objects as having no extent into space. But then again they ignore that stuff. I've never seen a particle physicist try to anayze systems like a dipole in a field. Einstein did and then published it. People always ignore this since they only look at the 1905 paper and never at his later work where he gets more general. The topic of his paper in 1907 was posted and addressed in my website and has been ignored as I see.

Pete

 

[Aer]

Let's start with a simple question. Does a photon have energy?

It is very simple really. Either a photon has energy or it does not. Either all energy in a system contributes to it's mass or it does not. Awaiting answers.

 

[learningphysics]

The conclusion was that mass is proportional to rest energy.

All this while I've only been taking about mass as rest mass... I get the feeling you're not reading my posts.

In an inelastic collision the rest energy of constituent bodies change! And as a result of a change in the rest energy, the rest mass changes. This is a basic consequence of special relativity, as Einstein shows in the paper I showed you! Do you agree with this or not?

If you think Einstein's derivation does not apply to macroscopic bodies, please explain why.

 

[Aer]

All this while I've only been taking about mass as rest mass... I get the feeling you're not reading my posts.

In an inelastic collision the rest energy of constituent bodies change! And as a result of a change in the rest energy, the rest mass changes. This is a basic consequence of special relativity, as Einstein shows in the paper I showed you! Do you agree with this or not?

If you think Einstein's derivation does not apply to macroscopic bodies, please explain why.

A system can have multiple energies. As you've said, it can have kinetic energy and thermal energy to name a few. One of the energies a system has is mass. That is, mass is a form of energy. So when we add all the energies together of this puddy, we get total energy = mass energy + kinetic energy + thermal energy. In this case, the kinetic energy has been converted to thermal energy - notice that the mass energy is still there. Now answer my question: Does a photon have energy?

 

[JesseM]

That is not my claim when dealing with masses at the quantum level!

Really? Then what did you mean when you said "All this says is that the proton and neutron lose rest mass when they are bound together. This rest mass is referred to as the potential energy since all mass is essentially a form of energy." Were you not saying here that the deuteron's rest mass is still the sum of the rest masses of the proton and neutron, but that the proton and neutron's rest masses had actually decreased and that this was the explanation for why the deuteron's mass is less than the sum of the rest masses of a free proton and a free neutron?

Just to be clear - this example is on the quantum level, in which energy and mass -do- lose distinction.

So now you are agreeing that potential energy must be included when finding the inertial mass of a compound object on the quantum level, and that potential energy is not just a change in the rest masses of the parts?

How does it make sense to distinguish between the quantum level and the macro-level here? Are you claiming that the inertial mass of a compound object whose parts are not interacting (so there's no potential energy between these parts, like with molecules in a gas) is not just the sum of each part's inertial mass individually?

Also, regardless of whether you think the experimental evidence justifies the claim that the inertial mass of a compound object is proportional to its total energy, do you still deny that this is what the theory of relativity predicts?

You must show that this kinetic energy -adds- to the mass at the macroscopic level and not just state it to be so. THIS, and only this is the only point I am contending. Whether you believe physics is the same at the microscopic level and the macroscopic level is your prerogative. However - I know there is a difference as there is a thing called quantum physics! So unless you are willing to talk about your macroscopic level example, then you'll have to excuse me if I do not respond to your BS!

Are you saying that the mainstream theory of quantum physics predicts that inertial mass is not proportional to total energy? If so, it's you who's talking BS. If you're just saying "quantum physics shows that weird stuff happens when you go from the micro level to the macro level, so maybe one new weird thing could be that inertial mass is no longer proportional to total energy on the macro level, even though the current theory says it would be" then sure, anything's possible I guess. But once again you've shifted the goalposts, since you were clearly arguing originally that learningphysics' understanding of the theory was wrong.

 

[Aer]

Really? Then what did you mean when you said "All this says is that the proton and neutron lose rest mass when they are bound together. This rest mass is referred to as the potential energy since all mass is essentially a form of energy."

You are obviously dense. You started talking about quantum physics while I still had in my mind that we were dealing with the macroscopic world, did you not read where I said right after that:

If I said anything similar to that, it was because you were confusing the issue of whether we are talking about the quantum level or macroscopic level.

 

[Aer]

How does it make sense to distinguish between the quantum level and the macro-level here?

Woah! Quantum physics doesn't behave like we see in the macro world. If we can't agree on even this, then there is no point in using the quantum level example!

 

[Aer]

Also, regardless of whether you think the experimental evidence justifies the claim that the inertial mass of a compound object is proportional to its total energy, do you still deny that this is what the theory of relativity predicts?

It is apparent now that there are differing views on what the theory of relatiivty predicts, even pmb_phy states that in his papers! How can I deny that -no one- thinks relativity predicts something specific when there is no agreement on what it does predict. Their personal belief is beyond my control.

 

[Aer]

quantum physics predicts that inertial mass is not proportional to total energy?

Quantum physics only deals with things in their rest frame - that is why Relativity and Quantum physics are not combined in any way. In the rest frame, at the quantum level - all energy is essentially mass energy as far as my knowledge of quantum physics goes because the distinction between mass and energy is lost at this level.

 

[JesseM]

The conclusion was that mass is proportional to rest energy.

Which quote is that?

"It is not good to introduce the concept of the mass of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the 'rest mass' m. Instead of introducing M it is better to mention the expression for the momentum and energy of a body in motion."

Yes, but as I've told you a million times, for a compound object the "rest mass" is defined as the total energy divided by c^2 in the compound object's rest frame, which of course includes the kinetic energy of individual components of the compound object in this frame. If this wasn't true, he wouldn't have said that an iron gains mass as it heats up. So this quote is not inconsistent with that one, provided you understand the definition of rest mass for a compound object.

 

[Aer]

Yes, but as I've told you a million times, for a compound object the "rest mass" is defined as the total energy divided by c^2 in the compound object's rest frame, which of course includes the kinetic energy of individual components of the compound object in this frame. If this wasn't true, he wouldn't have said that an iron gains mass as it heats up. So this quote is not inconsistent with that one, provided you understand the definition of rest mass for a compound object.

More like - provided you misunderstand the definition of rest mass for a compound object. I do not agree with the defintion you provide! All energy contributes to an objects mass? Perhaps a photon is not an object, but then - what really is an object? Does a photon have energy? Does it have mass?

 

[JesseM]

Really? Then what did you mean when you said "All this says is that the proton and neutron lose rest mass when they are bound together. This rest mass is referred to as the potential energy since all mass is essentially a form of energy."

You are obviously dense.

Don't be a jerk, Aer.

You started talking about quantum physics while I still had in my mind that we were dealing with the macroscopic world,

Uh, I was responding to your statement "That is not my claim when dealing with masses at the quantum level!" Sounds like you were talking about what is true of the quantum level there, not of the macroscopic world. And I was definitely talking about quantum physics rather than the macro-world--I was asking whether, in the domain of quantum physics, you agree that the inertial mass of a compound object is not just the sum of the rest masses of the parts. In the quote I provided above, it seemed you were still maintaining that at the quantum level the inertial mass of the compound object is the sum of the rest masses of its parts, but that the rest masses of the parts had actually changed. So once again, dealing only with the realm of quantum physics, do you or do you not think that the inertial mass of a compound object is equal to the sum of the rest masses of its parts? If you do, do you think that mainstream physics theories would agree with you on this?

Woah! Quantum physics doesn't behave like we see in the macro world. If we can't agree on even this, then there is no point in using the quantum level example!

You can't just use the fact that some things behave differently on the quantum level to handwave an "anything goes" approach to what happens on the macro-level--quantum physics makes definite predictions about the micro-macro transition, and in some cases it predicts that things do look the same on both levels. For example, it predicts the charge of a macroscopic compound object is just the sum of the charges of all the individual charged particles that make it up. Similarly, quantum physics does not in any way contradict the idea that the inertia of a compound macroscopic object is dependent on its total energy. If you just want to say that the theory could be wrong, fine, but if you're denying that the theory itself says this you're just being ignorant.

Quantum physics only deals with things in their rest frame - that is why Relativity and Quantum physics are not combined in any way.

Yes they are, special relativity and quantum physics were combined long ago by people like Dirac, all quantum field theories incorporate special relativity. It's only general relativity where they haven't been combined, but the question about the inertial mass of a compound object doesn't require general relativity.

 

[JesseM]

More like - provided you misunderstand the definition of rest mass for a compound object. I do not agree with the defintion you provide!

But it's the one Einstein was using, otherwise there's no way to make sense of his claim that an iron gains mass when it heats up.

All energy contributes to an objects mass? Perhaps a photon is not an object, but then - what really is an object? Does a photon have energy? Does it have mass?

Where are you going with this? Of course the energy of a photon contributes to the total energy and thus the inertial mass--if you have a box filled with radiation it will have more inertia than an empty box, that's what's predicted by the theory anyway.

 

[JesseM]

It is apparent now that there are differing views on what the theory of relatiivty predicts, even pmb_phy states that in his papers!

Which paper are you referring to, and what specific quotes are you talking about? I think you've likely just misunderstood something here.

 

[Aer]

Uh, I was responding to your statement "That is not my claim when dealing with masses at the quantum level!" Sounds like you were talking about what is true of the quantum level there, not of the macroscopic world. And I was definitely talking about quantum physics rather than the macro-world--I was asking whether, in the domain of quantum physics, you agree that the inertial mass of a compound object is not just the sum of the rest masses of the parts.

NO! In quantum physics, there is no distinction between mass and energy. As I said - I was talking with my foot in my mouth before as I failed to point out that your example was in the quantum world and not the macro world.

 

[Aer]

quantum physics makes definite predictions about the micro-macro transition

Does it make definite predictions about mass and energy? If so, why is it important to state in quantum physics that at the quantum level, there is no distinction between mass and energy. If this was true at the macro level, why is there this firm statement?

 

[Aer]

Where are you going with this? Of course the energy of a photon contributes to the total energy and thus the inertial mass--if you have a box filled with radiation it will have more inertia than an empty box, that's what's predicted by the theory anyway.

So you are claiming a photon has inertia and thus mass?

 

[Aer]

Which paper are you referring to, and what specific quotes are you talking about? I think you've likely just misunderstood something here.

From pmb_phy's paper:

There is currently an unfortunate trend to ban the concept of
relativistic mass from physics. Why such a trend is occurring is difficult to
say for sure but is probably related to the various usages in certain
branches of relativity. Generally speaking, the concept of proper mass
finds more usage with the particle physics community while the concept
of relativistic mass finds more usage within general relativity and
cosmology.

And:

This is surely due, in part, to a debate regarding the
concept of mass in relativity that has lasted for several decades. 2-12 This debate
concerns the use of relativistic mass versus proper mass as being “the” mass in
relativity.

 

[JesseM]

NO! In quantum physics, there is no distinction between mass and energy.

That certainly isn't true, quantum physicists talk about the rest masses of particles all the time, and they don't talk about the rest mass of binding energy (which again, is just a type of potential energy) or of kinetic energy. It is true that in quantum field theory it is easy for kinetic/potential energy to be converted into mass or vice versa in reactions that create or destroy particles, but if we're talking about chemical reactions or the binding of a proton and a neutron into a deuteron, there is no creation or destruction of particles involved.

 

[Aer]

That certainly isn't true

So now you claim that the mass of a system is not the total energy divided by c^2? Make up your mind!

 

[JesseM]

From pmb_phy's paper:

There is currently an unfortunate trend to ban the concept of
relativistic mass from physics. Why such a trend is occurring is difficult to
say for sure but is probably related to the various usages in certain
branches of relativity. Generally speaking, the concept of proper mass
finds more usage with the particle physics community while the concept
of relativistic mass finds more usage within general relativity and
cosmology.

And:

This is surely due, in part, to a debate regarding the
concept of mass in relativity that has lasted for several decades. 2-12 This debate
concerns the use of relativistic mass versus proper mass as being “the” mass in
relativity.

As I thought, this is just your misunderstanding. The debate over whether to use the concept of relativistic mass is purely an aesthetic one, it's not like people who use relativistic mass will make any different physical predictions than people who don't, any statement involving relativistic mass can be translated into an equivalent one involving only concepts like rest mass, momentum and energy. Since everyone agrees on what relativity actually predicts physically, everyone agrees on the prediction about the resistance to acceleration of a compound object (ie the object's inertia)--no physicist would dispute the fact that relativity predicts the inertia of a compound object is proportional to its total energy.

 

[JesseM]

So now you claim that the mass of a system is not the total energy divided by c^2? Make up your mind!

No, I dispute the claim that "there is no distinction between mass and energy"--by "mass" I meant rest mass, as I made clear in my post. If you mean there is no distinction between the inertial mass of a compound object and its total rest energy, then I agree with that, but I'd say that all mainstream theories predict this is just as true of the macro-world as the micro-world.

 

[learningphysics]

A system can have multiple energies. As you've said, it can have kinetic energy and thermal energy to name a few. One of the energies a system has is mass. That is, mass is a form of energy. So when we add all the energies together of this puddy, we get total energy = mass energy + kinetic energy + thermal energy. In this case, the kinetic energy has been converted to thermal energy - notice that the mass energy is still there. Now answer my question: Does a photon have energy?

In the paper I referred you to... Einstein is defining rest energy of the body as total energy of the body in the center of mass frame. There are only two energies... the translation kinetic energy and the rest energy (this includes thermal energy...nuclear binding energy and anything that is not translation kinetic energy)

His paper shows that a change in rest energy is proportional to a change in rest mass.

Yes a photon has energy.

 

[learningphysics]

Thanks. Please note that I'm not ignoring all this because I'm lazy. I've had horrible back pain when I sit for more than a few minutes. It took a long time to figure out what it was. Turns out that I have a stone in my gall-bladder. It will be comming out when I have surgery in the near future.

I'm really sorry to hear about this Pete. Hope everything turns out well. Take care of yourself. Best wishes!

 

[Aer]

As I thought, this is just your misunderstanding. The debate over whether to use the concept of relativistic mass is purely an aesthetic one, it's not like people who use relativistic mass will make any different physical predictions than people who don't,

Just like I thought, you'd come up with another BS answer.

You can't even keep your arguments consistent! Pick a theory and stick with it. Either all energy contributes to an objects mass or it does not (and I am referring to the macroscropic world here). If you claim that quantum physics is the same regarding mass and energy as is on the macroscopic world, then the mass of an object in quanutm physics would be the total energy / c^2. I don't dispute the latter, it is the former that I dispute. That is - on the macroscopic level, other forms of energy exist other than mass energy.

 

[JesseM]

So you are claiming a photon has inertia and thus mass?

Physicists generally define "inertial mass" in terms of resistance to acceleration in the object's own rest frame, and you can't do this for a photon, although you can do it for a compound system which contains a photon. If you want to define the inertial mass of an object in a frame other than its rest frame, this is the same thing as using relativistic mass, and as you've pointed out many times, most physicists prefer to avoid using this concept.