Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: PmbPhy on 16/11/2014 14:24:38
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Question: Who here believes that relativistic mass is merely another name for energy, and why?
According to lightarrow at https://www.physicsforums.com/threads/relativistic-mass.642188/page-2 he falls in to that category but I don't know why.
I'd also like to ask folks here what E = mc2 means. Do you also believe that anybody knows why E = mc2, i.e. what is the mechanism(s) for this to be true? Do you believe that anybody knows the answer to this question?
Thank you.
Edit: I took an example out so as not to divert attention to it.
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Can I vote for myself or it was already taken for granted? [:)]
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lightarrow
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Can I vote for myself or it was already taken for granted? [:)]
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lightarrow
Sure. :)
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e=mc^2 is just energy. Relativistic mass is energy with momentum. It is also affected by gravity as you showed above. e=mc^2 cannot be used to determine the mass of a photon as it has zero rest mass.
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Wonder if not the key point to people arguing with you Pete is this "While relativistic mass is useful in the context of special relativity, it is rest mass that appears most often in the modern language of relativity, which centres on "invariant quantities" to build a geometrical description of relativity. " What is relativistic mass? (http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html)
"Einstein preferred to think of his theory in terms of the coordinates of space and time: x, y, z and t. The essential ideas of the theory were conveyed by the algebraic properties of these quantities, treated as variables in equations. Its basic equations are the Lorentz transformation, which, in Einstein's hands, is a rule for changing the variables used to describe the physical system at hand.
The laws of physics are written as symbolic formulae that include these coordinate variables. The principle of relativity of relativity then became for Einstein an assertion about the algebraic properties of these formulae; that is, the formulae stay the same whenever we carry out the symbolic manipulation of change of variables of the Lorentz transformation. The emphasis in Einstein's algebraic approach is on variables, not spacetime coordinates, and formulae written using those variable, not geometrical figures in spacetime.
For many purposes, it makes no difference which approach one uses, geometric or algebraic. Sometimes one is more useful or simpler than the other. Very often, both approaches lead us to make exactly the same calculations. We just talk a little differently about them. However there can be a big difference if we disagree over which approach is more fundamental. We now tend to think of the geometric conception as the more fundamental one and that Einstein's algebraic formulae are merely convenient instruments for getting to the geometrical properties. There is some evidence that Einstein saw things the other way round. He understood the geometric conception, but took the algebraic formulation to be more fundamental. A simple example illustrates how this difference can matter a lot." How Did Einstein Think? (http://www.pitt.edu/~jdnorton/Goodies/Einstein_think) /
Einstein did not use geometry to describe it, not as I've understood it at least. It's a later and very useful approach for making relativity come alive in a intuitive way. But the point there is that he did not use it geometrically at all, he used Algebra. And there's a definite difference there. Considering the site you linked, the attitude shown by those commenting on you wasn't too impressive to me. (htt_p://sci.tech-archive.net/ that is)
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As for you asking what E = mc2 means :)
You pick the difficult ones, don't you?
what does it mean? (http://www.scientificamerican.com/article/significance-e-mc-2-means/)
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Btw: I'm less and less sure Einsteins approach is the 'worse one'. A geometrical approach goes out from an assumption of a unifying geometrical universe, a 'common container' of us all. Treating it algebraically makes no such assumptions, even though they may linger when you ask the one creating the algebra. Einsteins intuition is still famous, and worth listening too.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
Well I think you should know. Thanks for another informative post.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
Photons alone can never generate a couple e+ e-: simultaneous conservation of system momentum and energy would be violated. You have to collide the light beam with another massive particle (an atom's nucleus for ex.) in order to do that.
E = mc2, if E is the system total energy and m is the system's mass (that is, invariant mass) is valid only in a frame of reference in which the system's momentum p is zero.
The correct equation in SR is:
E2 = (cp)2 + (mc2)2.
For the OP: I know almost nothing about GR so I can't say if relativistic mass can have a meaning there; according to Pervect in the Physics forum thread you linked (post 18), other concepts of mass are used:
"Relativistic and invariant mass are just the tip of the iceberg, and wind up having little to do with gravity in the end.
Concepts such as Komar mass, ADM mass, Bondi mass, and quasi-local mass wind up as being more directly related to gravity than either relativistic or invariant mass."
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lightarrow
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e=mc^2 is just energy.
To be very clear, it's not energy per se. It's what I call inertial energy, since it's depending only on inertial mass. If the object is a particle and it's not in something like an electric field then there's no potential energy (such as electric potential energy). However if the field is an electric field then the total energy of the particle must include the electric potential energy.
Relativistic mass is energy with momentum.
I don't understand why you say that it's energy with momentum. Can you please elaborate as to why?
e=mc^2 cannot be used to determine the mass of a photon as it has zero rest mass.
Actually, you're wrong. From Relativity: Special, General and Cosmological by Wolfgang Rindler, Oxford Univ., Press, (2001), page 120
According to Einstein, a photon with frequency n has energy hf /c2, and thus (as he only came to realize several years later) a finite mass and a finite momentum hf/c.
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Maybe you would like this one Lightarrow?
Quasi-Local Mass in General Relativity. (http://intlpress.com/site/pub/files/_fulltext/journals/sdg/2010/0015/0001/SDG-2010-0015-0001-a012.pdf)
Found it while trying to see what those 'quasi-local masses' you mentioned referred too. It's amazingly readable, considering its subject, and mathematics :)
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Maybe I should have found this one first? The Hawking mass for ellipsoidal 2-surfaces in Minkowski and Schwarzschild spacetimes. (http://liu.diva-portal.org/smash/get/diva2:114136/FULLTEXT01.pdf)
"In general relativity, the nature of mass is non-local. However, an appropriate definition of mass at a quasi-local level could give a more detailed characterization of the gravitational field around massive bodies. Several attempts have been made to find such a definition. One of the candidates is the Hawking mass."
And "In the light of modern quantum field theoretical investigations it has become clear that all physical observables should be associated with extended but finite spacetime domains. Thus observables are always associated with open subsets of spacetime whose closure is compact, i.e. they are quasi-local. Quantities associated with spacetime points or with the whole spacetime are not observable in this sense."
Still struggling with this concept, but it fits nicely with Pete's definitions of what 'mass' is, as I gathered from his writing before. "Imagine a system of two massive bodies at rest relative to each other. If they are far apart, then there will be a gravitational potential energy contribution that makes the total energy of the system greater than if they are close to each other. There is a difference in total energy, despite that integrating the energy densities yields the same result in both scenarios. That energy difference is the energy attributed to the gravitational field. Since the gravitational field has energy, and therefore mass, it is a source of gravity, hence it is coupled to itself. Mathematically, this is possible because the field equation is non-linear."
So, what it discuss is gravity, as potential energy, as mass, between two points of proper mass (as planets). Trying to isolate 'patches' of the vacuum between, giving a 'patch' a 'quasi-local mass' mathematically (gravity->energy->mass), that should fit all expressions and descriptions of a SpaceTime? Remembering that there is no static representation of that gravity in/at any given point, as it change with distance, motion and time, observer dependently too? What about Lorentz contractions? Also that it will be transformed away locally in any geodesic (free falling). Seems a most difficult thing to define, if I now got it right?. As well as for a black hole, of any type. Or is it just black holes that's interesting here?
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Photons alone can never generate a couple e+ e-: simultaneous conservation of system momentum and energy would be violated. You have to collide the light beam with another massive particle (an atom's nucleus for ex.) in order to do that.
Which is why the "evidence" I cited was the annihilation photons, not the initial interaction with air or tissue. I might get my hands dirty doing physics instead of talking about it, but dumb I ain't.
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Photons alone can never generate a couple e+ e-: simultaneous conservation of system momentum and energy would be violated. You have to collide the light beam with another massive particle (an atom's nucleus for ex.) in order to do that.
Which is why the "evidence" I cited was the annihilation photons, not the initial interaction with air or tissue. I might get my hands dirty doing physics instead of talking about it, but dumb I ain't.
Ok, but I haven't understood how you interpret the equation
E = mc2.
What is that m for you? Invariant or relativistic mass? When the equation is valid, for you? Always; only in SR; only in SR *and* if the system's momentum is zero; else?
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lightarrow
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Maybe you would like this one Lightarrow?
Quasi-Local Mass in General Relativity. (http://intlpress.com/site/pub/files/_fulltext/journals/sdg/2010/0015/0001/SDG-2010-0015-0001-a012.pdf)
Found it while trying to see what those 'quasi-local masses' you mentioned referred too. It's amazingly readable, considering its subject, and mathematics :)
My compliments to you, I have understood nothing of it! [:)]
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Question: Who here believes that relativistic mass is merely another name for energy, and why?
I'm no expert but here is how I understand the answer to this question.
Relativistic mass is the increase in mass that an object acquires from the energy of acceleration. The energy of acceleration is thus applied to the invariant mass of the original object. Invariant mass remains the same whether in motion or not. So yes, relativistic mass is just energy transferred thru acceleration to the original invariant mass.
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Photons alone can never generate a couple e+ e-: simultaneous conservation of system momentum and energy would be violated. You have to collide the light beam with another massive particle (an atom's nucleus for ex.) in order to do that.
That isn't right actually, there's such a thing as gamma-gamma physics. Two photons can interact to create an electron and a positron. It's the reverse of electron-positron annihilation.
For the OP: I know almost nothing about GR so I can't say if relativistic mass can have a meaning there; according to Pervect in the Physics forum thread you linked (post 18), other concepts of mass are used:
"Relativistic and invariant mass are just the tip of the iceberg, and wind up having little to do with gravity in the end. Concepts such as Komar mass, ADM mass, Bondi mass, and quasi-local mass wind up as being more directly related to gravity than either relativistic or invariant mass."
It's all rather ambiguous. For example invariant mass varies when a body falls down, hence the mass deficit. But conservation of energy applies. If you're up in space and you drop a 1kg brick onto the Earth, then provided the kinetic energy is retained rather than radiated away into space, the mass of the Earth increases by 1kg. And at all points the rest-mass of the falling brick plus its kinetic energy or relativistic mass, which is said to be a measure of energy, add up to a mass-equivalence of 1kg.
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Photons alone can never generate a couple e+ e-: simultaneous conservation of system momentum and energy would be violated. You have to collide the light beam with another massive particle (an atom's nucleus for ex.) in order to do that.
This can happen with any nucleus. The nucleus merely acts as a catalyst. It isn't used up by the interaction meaning that it's there before and after and is unchanged by the process just like any catalyst.
For the OP: I know almost nothing about GR so I can't say if relativistic mass can have a meaning there; according to Pervect in the Physics forum thread you linked (post 18), other concepts of mass are used:..
Sorry. I have no interest in what he thinks. Only those who post here. He doesn't have a good grasp of the subject. That nonsense about ADM and Komar mass demonstrates that fact.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
Dear Alan,
What does that have to do with relativistic mass?
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Question: Who here believes that relativistic mass is merely another name for energy, and why?
I'm no expert but here is how I understand the answer to this question.
Relativistic mass is the increase in mass that an object acquires from the energy of acceleration. The energy of acceleration is thus applied to the invariant mass of the original object. Invariant mass remains the same whether in motion or not. So yes, relativistic mass is just energy transferred thru acceleration to the original invariant mass.
No. Mass and energy are NOT the same thing. Mendel Sachs wrote a paper on E = mc2 and clarified this point very clearly. He explained that mass is related to inertial and energy is (loosely) related to the ability to do work. They are therefore not the same thing and they're not even closely to being related in that way. In general E doesn't even always equal mc2 anyway. In cases of a closed system, such as when a rod is subjected to stress, then they aren't related in that way.
Also, there are different ways that relativistic mass can increase. You merely mentioned one of them. First of all the relativistic mass of a photon is not zero so it can't be accelerated. It merely has that mass when it's created, same as all elementary particles in particle accelerators. Another way to see an increase in relativistic mass is to change from one frame of reference to another one in which the speed is greater.
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
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Which is why the "evidence" I cited was the annihilation photons, not the initial interaction with air or tissue. I might get my hands dirty doing physics instead of talking about it, but dumb I ain't.
That's an excellent point, Alan. Well stated. Just because we leave something out or don't express something as others might, it doesn't mean it's wrong. This being a perfect example. In fact when you wrote
...and when my photon beams in air or tissue exceed 1.022 MeV we get pair production..
When you wrote this you made it precisely clear that something else was needed and that made it clear that the photons were not alone. In that case lightarrow was wrong in attempting to "correct" you. We all know that air and tissue contain nuclei. :)
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heh "My compliments to you, I have understood nothing of it!" As mysterious to me too Lightarrow. But I've seen this type of reasoning, as well as Komar mass, in physics forum before, and I want to know why and how they reason in it. This idea with quasi local mass seems to cover it all. The point there is that the idea of using a defined patch to then give it a mass to me collides with Einsteins concept of gravity, in where you transform it away locally. If we call it mass then that mass disappear locally, same with 'energy' which I think describe it (as in doing experiments inside a 'black box') even better.
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Or expressed another way, to argue that there is a mass locally, although not experimentally provable, is to define one observer dependency as primary, the other secondary, to a universe. Alternatively I will relate it to a concept of a universal container, in where it all have to even out. The last one sounds as if it can explain it, but it depends on how you define that 'container' to me. Locally defined, or, as some idea of a premade universe in where it all should 'even out'. As I use only the local definition, a 'premade' universe doesn't exist, it's observer defined.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
Dear Alan,
What does that have to do with relativistic mass?
relativistic mass = γm = m√(1-v2/c2)
so we start with a positronium pair with rest mass 2me and end up with two photons of zero mass, thus γ = 0 and v = c.
OK, it's cheating to multiply by zero, but when we accelerate massive particles to relativistic speeds, the incremental energy required to do so turns out to be proportional to γm, not m. You can do this experiment most easily (!) in a cyclotron but relativistic effects are just measurable with megavolt electrons, which you can generate with a simple Van de Graaff. Which, come to think of it, is also cheating as I suspect few of our other correspondents have one in the backyard, so we'll have to look for an astronomical example, or you can take my word for it.
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Nothing to do with belief. I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
Whether you believe it or not, it happens every damn time, which is how we diagnose tumors on the one hand, and calibrate small accelerators on the other.
Dear Alan,
What does that have to do with relativistic mass?
relativistic mass = γm = m√(1-v2/c2)
so we start with a positronium pair with rest mass 2me and end up with two photons of zero mass, thus γ = 0 and v = c.
OK, it's cheating to multiply by zero, but when we accelerate massive particles to relativistic speeds, the incremental energy required to do so turns out to be proportional to γm, not m. You can do this experiment most easily (!) in a cyclotron but relativistic effects are just measurable with megavolt electrons, which you can generate with a simple Van de Graaff. Which, come to think of it, is also cheating as I suspect few of our other correspondents have one in the backyard, so we'll have to look for an astronomical example, or you can take my word for it.
That equation is not correct for photons. You say "cheating" where I'd say "writing incorrect equations".
The one which is always true in SR is the one I've already written:
E2 = (mc2)2 + (cp)2 (1)
where "m" is the (invariant, aka proper, aka rest) system's mass. I prefer "invariant" because, for particles moving at c, the terms "proper" and "rest" are meaningless.
Now let's apply it to a system of a couple e+ e- which disintegrates into a couple of γ photons in the couple's centre of mass frame of reference:
a. Before disintegration.
System's mass m is 511 keV/c2 + 511 keV/c2 = 1022 keV/c2.
System's momentum p is zero because we are in the couple's centre of mass. Using equation (1) we have:
→ E = 1022 keV
b. After disintegration in a couple of γ photons.
The system's energy E is conserved and so E is the same as before, 1022 keV (when I say "system's energy" I'm obviously referring to the total energy of the system of the two photons taken together).
Let's see the system's mass m.
From (1):
m = (1/c2)sqrt[E2 - (cp)2]
Because of symmetry, the two photons have the same energy and opposite direction of propagation, so their total momentum p sum up to zero. So:
m = (1/c2)sqrt[E2 - 0] = 1022 keV/c2.
So, invariant mass is conserved, in this case.
I didn't have any need of relativistic mass.
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, because the concept of "mass" is not as straightforward as we usually think.
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lightarrow
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...and when my photon beams in air or tissue exceed 1.022 MeV we get pair production..
When you wrote this you made it precisely clear that something else was needed and that made it clear that the photons were not alone. In that case lightarrow was wrong in attempting to "correct" you. We all know that air and tissue contain nuclei. :)
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 you specify that it has done it. Indeed, how could they make radiographies to you, if the absorption coefficient of tissues/bones for X-rays photons were 100%?
And gamma photons are even more penetrating...
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lightarrow
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I'm an experimental physicst, and when my photon beams in air or tissue exceed 1.022 MeV we get pair production, signalled by the appearance of two 511 keV photons, exactly as predicted by E = mc2 and the known mass of the electron (another experimental value).
I imagine you have already made that computation even in the frame of reference of a fast moving nucleus on which the photon collides, as high energy particle physicists do every day. Did you use E = mc2 in that case?
In case, please ask to a particle or nuclear physicist, which is the equation he uses...
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lightarrow
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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.
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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.
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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
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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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lightarrow
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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
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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.
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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.
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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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Lightarrow, you're one of the brightest lights here,
because of the nickname? [:)]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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lightarrow
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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.
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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.
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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.
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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' ”. [:(]
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I was speaking to a friend of mine, Dr. Wolfgang Rindler, who's an authority in in the field of relativity and asked him
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
Most relativists use relativistic mass, whereas particle physicists use rest mass, and they are the main consumers of SR! Best, W
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"On the Abuse and Use of Relativistic Mass".
Gary Oas.
http://arxiv.org/abs/physics/0504110
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lightarrow
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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.
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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.
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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 (http://en.wikipedia.org/wiki/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 (http://en.wikipedia.org/wiki/Breit%E2%80%93Wheeler_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."
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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.
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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.
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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.
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I am an experimental physicist. I don't have a personality.
Add a "therefore", stir, and serve in any order you choose.
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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
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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
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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.
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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.
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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.
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lightarrow
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...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.
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Ah well.
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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.
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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.
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...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.
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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.
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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.
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I am currently reading Lee Smolin's Three Roads to Quantum Gravity. When I have finished that I will get back to you.
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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.