[jeffreyH]

Excuse me, Sir, but how can I know if he knows it or not?

Because in post #5 he wrote I'm an experimental physicist,.. and as such he'd know it.

Ah, ok. So if I say that I'm a theoretical physicist you stop talking about relativistic mass?
 []

--
lightarrow.

Alas, theoretical physics provides plenty of insights but no actual knowledge.

That is so true. I have been looking for observational data to help to either confirm or dismiss some of my hypotheses and can't find any. Too much appears to be taken on trust. Simply because of the reputations of those proposing the theories.

[JohnDuffield]

If pair production occured in vacuo the cosmos would be full of 511 keV gamma rays. I'm sure that most of the people who follow this forum know it isn't.

That's a non-sequitur. See two-photon physics on Wikipedia: "Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. If the energy at the center of mass of the system of the two photons is large enough, matter can be created." Now you might say that the Breit-Wheeler process has not been convincingly demonstrated, but it's only the reverse of electron-positron annihilation to gamma photons.

"Breit–Wheeler process or Breit–Wheeler pair production is the simplest mechanism by which pure light can be potentially transformed into matter.[1] The process can take the form of γγ′ → e+e−, that is the emission of positron–electron pairs off a probe photon propagating through a polarized short-pulsed electromagnetic field (for example, laser).[2]

The process was described by Gregory Breit and John A. Wheeler in 1934 in Physical Review.[3] Although the process is one of the manifestations of the mass–energy equivalence, as of 2014, it has never been observed in practice because of the difficulty in preparing colliding gamma ray beams. However, in 1997, researchers at the Stanford Linear Accelerator Centre were able to conduct the so-called multi-photon Breit–Wheeler process using electrons to first create high-energy photons, which then underwent multiple collisions to produce electrons and positrons, all within same chamber.[4] In 2014 a model of a photon–photon collider was proposed, where Monte Carlo simulations suggest that it is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot."

[alancalverd]

it has never been observed in practice

My point precisely. No shortage of high energy photons in the cosmos, so there should be plenty of 511 keV photons whizzing around as a result of the annihilation of positronium formed from the gamma-gamma reactions. Indeed one would expect the spectrum to be dominated by the blighters as the ultimate decay product.

Not that it detracts from the original statement anyway: photon energy creates mass which selfannihilates to produce characteristic photons: whether the presence of a nucleus is necessary, is irrelevant to the fundamental  equations.

[jeffreyH]

Well either gamma ray production is being inhibited by some process or energy is being removed from those that are produced or some other process is converting them into something else.

[PmbPhy (OP)]

That is so true. I have been looking for observational data to help to either confirm or dismiss some of my hypotheses and can't find any. Too much appears to be taken on trust. Simply because of the reputations of those proposing the theories.

It's neither trust nor reputation. It's the knowledge that the theory has been thoroughly tested and knowing the theory well enough to know what can be accepted to be true based on what has already been tested. It's not based on anybody's reputation because the physicists doing the work rely on their understanding of the theory and how to use it. Personalities never come into play when it comes to what the theory predicts. In facts personalities/reputations rarely, if ever in fact, come into play in physics.

[alancalverd]

I am an experimental physicist. I don't have a personality.

Add a "therefore", stir, and serve in any order you choose.

[lightarrow]

photon energy creates mass

Sorry, this is incorrect. See, e.g., my Reply #21.
There, at the end, I also wrote:
<<It was just *an example* of the fact that people usually (I'm not referring to you) have the incorrect idea that "energy is transformed in mass" or the other way round>>.
Now I can refer to you too...

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lightarrow

[PmbPhy (OP)]

It was just *an example* of the fact that people usually (I'm not referring to you) have the incorrect idea that "energy is transformed in mass" or the other way round>>.
Now I can refer to you too...

Good point. It's so unfortunate that so many people make that mistake, regardless of how many articles are in the physics literature correcting that erroneous idea such as

Does nature convert mass into energy? by Ralph Baierlein, Am. J. Phys., 75(4), Apr. (2007)
http://home.comcast.net/~peter.m.brown/ref/baierlein.pdf

[yor_on]

A interesting link Pete, always pleased to read them. And no Lightarrow, you and me both know you would be a bright light, even without your 'Nom de guerre' . Any which way, I enjoy reading you all, forces my brain into something more than just vegetating. But let's not get stuck in the swamp of defining what is the most correct nomenclature please. I consider Alan a very smart guy too, although working in a slightly different field.

[PmbPhy (OP)]

A interesting link Pete, always pleased to read them. And no Lightarrow, you and me both know you would be a bright light, even without your 'Nom de guerre'

What does 'Nom de guerre' mean in this context?

But let's not get stuck in the swamp of defining what is the most correct nomenclature please.

If that's what you got out of all of this then you've missed the entire meaning of everything. It's not about worrying about terms. It has to do with whether a term has a physical meaning in all cases. You mean to tell me that you missed that from everything that I've said? Wow! You sure missed a lot. E.g. in post #37 I examined to Ethos_

There is also a lot more to do with invariant mass than you've mentioned and that most people are aware of. See "An Incorrect Application of Invariant Mass " in the webpage:
http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

The problem with posting such references is that nobody reads them and thus they never learn what the problems really are. They think that they know everything about the subject matter so they think they will learn nothing by reading any reference I post and therefore they remain ignorant of the problems.

[lightarrow]

Alas, theoretical physics provides plenty of insights but no actual knowledge.

I (think to) understand what you mean, Alan, and I partially agree.
But remember that without any sort of theoretical framework, you can't even give any interpretation to experimental results...
So, actual knowledge is made of both experimental and theoretical physics, I believe.

--
lightarrow

[JohnDuffield]

...See "An Incorrect Application of Invariant Mass " in the webpage: http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

The problem with posting such references is that nobody reads them and thus they never learn what the problems really are. They think that they know everything about the subject matter so they think they will learn nothing by reading any reference I post and therefore they remain ignorant of the problems.

People do read them. I've read this article, and I can say this: the mass of a particle is not invariant. It varies with gravitational potential. The kinetic energy of a falling particle comes from the mass-energy of that particle. Once the kinetic energy is dissipated you're left with a mass deficit. The mass is less than it was. It is not the same as it was and there is some magical mysterious negative energy thrown into the mix. There is now less positive energy, and less mass.

[yor_on]

Ah well.

[PmbPhy (OP)]

I am an experimental physicist. I don't have a personality.

Add a "therefore", stir, and serve in any order you choose.

You said that you're a medical physicist, did you not? If so then you're not an since they're defined differently. A medical physicist does applied physics whereas an experimental physicist does experiments to test theories, i.e. they do experiments.

http://en.wikipedia.org/wiki/Medical_physics

Medical Physics is generally speaking the application of physics concepts, theories and methods to medicine or healthcare.

http://en.wikipedia.org/wiki/Experimental_physics

Experimental physics is the category of disciplines and sub-disciplines in the field of physics that are concerned with the observation of physical phenomena and experiments.

In my very humble opinion it was deceptive to say that you're an experimental physicist. I suggest that from now on you state the full truth, that you're a medical physicist, even if you do experiments! Einstein himself did a few experiments in his day. However that didn't make him an experimental physicist in addition to a theoretical physicist. I myself worked in a lab for a while calibrating the CCDs for the Chandra X-Ray observatory but just because I worked in a lab that didn't make me an experimental physicist. I didn't do experiments in that lab. The only experiments I've done were for my chemistry and physics courses.

[jeffreyH]

It was just *an example* of the fact that people usually (I'm not referring to you) have the incorrect idea that "energy is transformed in mass" or the other way round>>.
Now I can refer to you too...

Good point. It's so unfortunate that so many people make that mistake, regardless of how many articles are in the physics literature correcting that erroneous idea such as

Does nature convert mass into energy? by Ralph Baierlein, Am. J. Phys., 75(4), Apr. (2007)
http://home.comcast.net/~peter.m.brown/ref/baierlein.pdf

Thanks for that Pete. I will be saving a copy for future reference.

[jeffreyH]

...See "An Incorrect Application of Invariant Mass " in the webpage: http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

The problem with posting such references is that nobody reads them and thus they never learn what the problems really are. They think that they know everything about the subject matter so they think they will learn nothing by reading any reference I post and therefore they remain ignorant of the problems.

People do read them. I've read this article, and I can say this: the mass of a particle is not invariant. It varies with gravitational potential. The kinetic energy of a falling particle comes from the mass-energy of that particle. Once the kinetic energy is dissipated you're left with a mass deficit. The mass is less than it was. It is not the same as it was and there is some magical mysterious negative energy thrown into the mix. There is now less positive energy, and less mass.

Hang on a minute John. If that is your viewpoint then I think a mathematical proof is in order. I'm sorry but opinion just doesn't cut it. I've been down this path mathematically and my conclusion is that mass itself IS invariant.

[PmbPhy (OP)]

I've been down this path mathematically and my conclusion is that mass itself IS invariant.

Hold on Jeff. If that is your viewpoint then I think a mathematical proof is in order for you too. Can you prove that mass is invariant other than choosing a definition in which it's invariant by definition. That's how everyone who presents such an argument does so. They either define the term mass as the value of mass as measured in the rest frame of the object/particle or they attempt to define it as the value of the particles 4-momentum (letting c = 1 for simplicity). Which do you do?

Let's once and for all resolve the problems with such a definition. Jeff: Please study the following page
http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

very deeply so that you don't miss a trick. After you study that please study the section called "Definition of Mass" in my article at http://arxiv.org/abs/0709.0687

After you've studied those then you'll have an excellent understanding of these issues. Also let it be know that there is a difference between mass and energy in relativity. In GR the relativistic mass of a particle is defined as the time component of the particle's 4-momentum while the energy of the particle is defined as the time component of the particle's momentum 1-form. These two expressions do not equal each other. They're not even proportional. This is a fact that is all too often missed by most students studying relativity. It's one of the most important reasons why you can't say that relativistic mass and energy are the same thing.

[jeffreyH]

I've been down this path mathematically and my conclusion is that mass itself IS invariant.

Hold on Jeff. If that is your viewpoint then I think a mathematical proof is in order for you too. Can you prove that mass is invariant other than choosing a definition in which it's invariant by definition. That's how everyone who presents such an argument does so. They either define the term mass as the value of mass as measured in the rest frame of the object/particle or they attempt to define it as the value of the particles 4-momentum (letting c = 1 for simplicity). Which do you do?

Let's once and for all resolve the problems with such a definition. Jeff: Please study the following page
http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htm

very deeply so that you don't miss a trick. After you study that please study the section called "Definition of Mass" in my article at http://arxiv.org/abs/0709.0687

After you've studied those then you'll have an excellent understanding of these issues. Also let it be know that there is a difference between mass and energy in relativity. In GR the relativistic mass of a particle is defined as the time component of the particle's 4-momentum while the energy of the particle is defined as the time component of the particle's momentum 1-form. These two expressions do not equal each other. They're not even proportional. This is a fact that is all too often missed by most students studying relativity. It's one of the most important reasons why you can't say that relativistic mass and energy are the same thing.

It's the time component and the dilation effect that appears to produce more mass. It depends upon the interactions of the gravitational field with the elctromagnetic field. That is not easy to derive.

[jeffreyH]

I am currently reading Lee Smolin's Three Roads to Quantum Gravity. When I have finished that I will get back to you.

[PmbPhy (OP)]

I am currently reading Lee Smolin's Three Roads to Quantum Gravity. When I have finished that I will get back to you.

Okay. Let me know how that book is.