# The Naked Scientists Forum

### Author Topic: A poll on relativistic mass  (Read 18220 times)

#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #25 on: 20/11/2014 15:33:30 »
Quote from: lightarrow
Ok, but the fact a photon is travelling in air or in a biological tissue does not ensure that it collides with a nucleus, unless,
Why did you think he posted that part about air and tissue? It's because he wanted to make it clear that there'd be nuclei in the way for a chance for a collision to take place. I knew that. The question in my mind is why you didn't.

#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #26 on: 20/11/2014 16:03:33 »
Quote from: alancalverd
relativistic mass = γm = m√(1-v2/c2)
That's an equality for relativistic mass and proper mass for a tardyon. The definition for relativistic mass is m= p/v which holds for photons.

If you were to look in SR texts which use relativistic mass then you'd see them use this definition of the relativistic mass to find the rel-mass of a photon. E.g. see

http://home.comcast.net/~peter.m.brown/ref/relativistic_mass.htm

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #27 on: 20/11/2014 18:06:19 »
I lioke my patients to be stationary. Sometimes we anaesthetise them, and from time to time they are even dead. The dead ones don't produce good functional data but there's no doubt about their mass  - the padre sees to that.
And all this means what? That you can use E = m*c2 ? Of course you can use an equation which is valid only in a special case, if you use it only in that special case. For example I can say that Earth gravity doesn't depend on height if height variations are small and the distance from the Earth centre is large; or I can say that pendulum oscillations are isochronous if the oscillation angles are <<1, or I can say that a body's total energy doesn't vary with its speed, if its kinetic energy is much smaller than its mass multiplied by c2. If you want to restrict physics to such special cases, why talking about relativistic effects at all and so, for example, talking about E = m*c2 ?

Edited the format. 07/12/2014

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« Last Edit: 07/12/2014 12:14:05 by lightarrow »

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #28 on: 20/11/2014 18:10:28 »
Quote from: lightarrow
Ok, but the fact a photon is travelling in air or in a biological tissue does not ensure that it collides with a nucleus, unless,
Why did you think he posted that part about air and tissue? It's because he wanted to make it clear that there'd be nuclei in the way for a chance for a collision to take place. I knew that. The question in my mind is why you didn't.
I know, you know and he knows. Do everyone who read it understand that it's necessary a nucleus and that an electron is not enough, for example?

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lightarrow

#### yor_on

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##### Re: A poll on relativistic mass
« Reply #29 on: 20/11/2014 21:56:53 »
Lightarrow, you're one of the brightest lights here, not always comfortable though.
Whoever told me that science is comfortable?

So do your thing, I will do mine, and in the end we might get a good laugh of it.

#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #30 on: 22/11/2014 05:52:19 »
Quote from: lightarrow
Ok, but the fact a photon is travelling in air or in a biological tissue does not ensure that it collides with a nucleus, unless,
Why did you think he posted that part about air and tissue? It's because he wanted to make it clear that there'd be nuclei in the way for a chance for a collision to take place. I knew that. The question in my mind is why you didn't.
I know, you know and he knows. Do everyone who read it understand that it's necessary a nucleus and that an electron is not enough, for example?

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lightarrow
If that's the case, i.e. you were worried about the forum not realizing that then you could have simply pointed  that out to the forum instead of Alan. Saying that to Alan makes it appear as if our friend Alan doesn't know what he's talking about and at least I know better than that.

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #31 on: 22/11/2014 11:31:01 »
If that's the case, i.e. you were worried about the forum not realizing that then you could have simply pointed  that out to the forum instead of Alan. Saying that to Alan makes it appear as if our friend Alan doesn't know what he's talking about and at least I know better than that.
Excuse me, Sir, but how can I know if he knows it or not? I do not have gifts of divination
How many times we correct people and we are corrected from others (me more than you, certainly) simply because of what we/others have written? Or should we always have to write "in order to inform people reading this post, I have to correct this phrase/equation/concept/reasoning even if I know (or presume to know) that the poster knows very well the subject"?

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#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #32 on: 22/11/2014 11:32:49 »
Lightarrow, you're one of the brightest lights here,
because of the nickname?
Quote
not always comfortable though.
Whoever told me that science is comfortable?
So do your thing, I will do mine, and in the end we might get a good laugh of it.
Ok.

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#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #33 on: 22/11/2014 13:45:12 »
Quote from: lightarrow
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.

#### alancalverd

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##### Re: A poll on relativistic mass
« Reply #34 on: 22/11/2014 18:31:24 »
Trust me. I'm an experimental physicist.

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.

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #35 on: 22/11/2014 18:36:44 »
Quote from: lightarrow
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?

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#### Bill S

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##### Re: A poll on relativistic mass
« Reply #36 on: 22/11/2014 20:40:05 »
Pete, when you have contributed so generously to my “poll”, it feels a bit mean not to have reciprocated by joining yours.  However, I’m sure you will understand that I don’t want to get too far out of my depth.

Before I read this thread I thought relativistic mass was effectively equivalent to inertia.

Now I’ve read the thread, I thing “I don’t know nuffin' ”.

#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #37 on: 22/11/2014 23:10:30 »
I was speaking to a friend of mine, Dr. Wolfgang Rindler, who's an authority in in the field of relativity and asked him
Quote
When I start writing my paper I need to get a good feeling of how many people either use relativistic mass or who find it useful etc. I can't figure out what gives all these physicists who claim that it's not used anymore the idea that such is the case. So how do I go about finding out what percentage of relativists use it? Any ideas? Thanks.
He gave me permission to quote his response as follows
Quote
Most relativists use relativistic mass, whereas particle physicists use rest mass, and they are the main consumers of SR!  Best,  W
« Last Edit: 23/11/2014 05:14:40 by PmbPhy »

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #38 on: 23/11/2014 16:40:00 »
"On the Abuse and Use of Relativistic Mass".
Gary Oas.

http://arxiv.org/abs/physics/0504110

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#### alancalverd

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##### Re: A poll on relativistic mass
« Reply #39 on: 23/11/2014 17:39:21 »
Quote from: lightarrow
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?

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lightarrow.

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

#### jeffreyH

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##### Re: A poll on relativistic mass
« Reply #40 on: 23/11/2014 21:06:19 »
Quote from: lightarrow
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?

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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

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##### Re: A poll on relativistic mass
« Reply #41 on: 23/11/2014 22:25:38 »
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

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##### Re: A poll on relativistic mass
« Reply #42 on: 24/11/2014 00:55:38 »
Quote
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

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##### Re: A poll on relativistic mass
« Reply #43 on: 24/11/2014 01:39:35 »
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

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##### Re: A poll on relativistic mass
« Reply #44 on: 24/11/2014 16:48:41 »
Quote from: jeffreyH
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.
« Last Edit: 24/11/2014 17:08:55 by PmbPhy »

#### alancalverd

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##### Re: A poll on relativistic mass
« Reply #45 on: 24/11/2014 17:39:17 »
I am an experimental physicist. I don't have a personality.

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

#### lightarrow

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##### Re: A poll on relativistic mass
« Reply #46 on: 24/11/2014 18:29:19 »
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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« Last Edit: 24/11/2014 18:32:18 by lightarrow »

#### PmbPhy

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##### Re: A poll on relativistic mass
« Reply #47 on: 25/11/2014 17:49:58 »
Quote from: lightarrow
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

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##### Re: A poll on relativistic mass
« Reply #48 on: 06/12/2014 03:02:23 »
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

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##### Re: A poll on relativistic mass
« Reply #49 on: 06/12/2014 04:01:18 »
Quote from: 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' :)
What does 'Nom de guerre' mean in this context?

Quote from: yor_on
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_
Quote
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.

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##### Re: A poll on relativistic mass
« Reply #49 on: 06/12/2014 04:01:18 »