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Thread: Why mass variance predicted by str doesn't take place

  1. #1 Why mass variance predicted by str doesn't take place 
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    Please can anyone give me the reason,why streams of masses more than 2kg in this link below,where relativistic efffects takes place,the mass variance predicted by STR does not tend to infinity. http://en.wikipedia.org/wiki/Astroph...etRelativistic jets are extremely powerful jets[2] of plasma which emerge from presumed massive objects at the centers of some active galaxies, notably radio galaxies and quasars. Their lengths can reach several thousand[3] or even hundreds of thousands of light years.[4] The hypothesis is that the twisting of magnetic fields in the accretion disk collimates the outflow along the rotation axis of the central object, so that when conditions are suitable, a jet will emerge from each face of the accretion disk. If the jet is oriented along the line of sight to Earth, relativistic beaming will change its apparent brightness. The mechanics behind both the creation of the jets[5][6] and the composition of the jets[7] are still a matter of much debate in the scientific community; it is hypothesized that the jets are composed of an electrically neutral mixture of electrons, positrons, and protons in some proportion.


    Elliptical Galaxy M87 emitting a relativistic jet, as seen by Hubble Space Telescope's WFPC2 in the visible spectrum.
    Similar jets, though on a much smaller scale, can develop around the accretion disks of neutron stars and stellar black holes. These systems are often called microquasars. An example is SS433, whose well-observed jet has a velocity of 0.23c, although other microquasars appear to have much higher (but less well measured) jet velocities. Even weaker and less-relativistic jets may be associated with many binary systems; the acceleration mechanism for these jets may be similar to the magnetic reconnection processes observed in the Earth's magnetosphere and the solar wind.

    The general hypothesis among astrophysicists is that the formation of relativistic jets is the key to explaining the production of gamma-ray bursts. These jets have Lorentz factors of ~100 (that is, speeds of roughly 0.99995c), making them some of the swiftest celestial objects currently known.

    Rotating black hole as energy source[edit]
    Because of the enormous amount of energy needed to launch a relativistic jet, some jets are thought to be powered by spinning black holes.
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    the mass variance predicted by STR does not tend to infinity
    SR does not predict any "mass variance", contrary to popular opinion. The rest mass of a system is an invariant quantity and never changes; what does change is the total energy of a system if you put it into relative motion - obviously, since it gains momentum. For some ( to me utterly incomprehensible ) reason this measure of total energy used to be called "relativistic mass" in older textbooks, even though it isn't actually a "mass" at all. Precisely because of the confusion this causes the unprepared student, this concept is generally no longer taught in modern relativity textbooks. The basic idea was originally that the faster something moves, the more energy you need to accelerate it even further, and the relationship is an exponential one ( unlike in classical mechanics ); to get to the speed of light you would need an infinite amount of energy, which is of course impossible.
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    Indeed Markus,

    Yes, would it be incorrect to refer to the "relativistic mass" as a "relativistic inertia"? The relativistic inertia (total inertia) being the inertia of the rest mass + the added kinematic inertia.

    Thank You,
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    Last edited by SinceYouAsked; 09-16-2014 at 04:08 AM.
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    Yes, would it be incorrect to refer to the "relativistic mass" as a "relativistic inertia"? The relativistic inertia (total inertia) being the inertia of the rest mass + the added kinematic inertia.
    That's probably not wrong, but I personally prefer to just understand it to be quite simply the total energy content of the system.
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    Quote Originally Posted by Markus Hanke
    For some ( to me utterly incomprehensible ) reason this measure of total energy used to be called "relativistic mass" ...
    There are very good reasons for it. All you need to do is look for it rather than trying to reason out why you wouldn't use it yourself. You see, everybody thinks differently. Therefore just because you simply can't fathom why someone would want to use it, others who think differently also find that its very useful concept. Do you see what I mean? It's purely a matter of taste and I find it very useful to use it but it depends on what context I'm working in. When I'm doing calculations in particle physics I find using it annoying.

    Look in textbooks, journal articles and other books (such as Max Jammer's last book) to learn why. Wolfgang Rindler wrote an article on it for physics today as did. Here's an example: In defense of relativistic mass by T.R. Sandin, Am. J. Phys., 59(11), Nov. (1991) In defense of relativistic mass | Sandin, T. R. | digital library booksc

    I myself wrote an article. David Griffiths proof read if for me and although he disagrees with the use of rel-mass he recommended that I submit if for publication. I'm working on a rewrite at the moment.

    Quote Originally Posted by Markus Hanke
    Precisely because of the confusion this causes the unprepared student, this concept is generally no longer taught in modern relativity textbooks.
    That is quite incorrect Markus. In fact a large proportion of modern relativity texts use it. To see the results of a quantitative study done on this see On the Use of Relativistic Mass in Various Published Works by Gary Oas. It's online at [physics/0504111] On the Use of Relativistic Mass in Various Published Works

    I was talking to Alan Guth about this last year. He teaches this concept in his course on the Early Universe. Alan found that since o many of his students thought that since "light has no mass" that they had a difficult time understanding that radiation can generate a gravitational field. Even in texts whose authors say they don't use it still refer to the mass density of radiation.

    I've lost count of how many people think that because light has no "mass" that they can't generate a gravitational field. I also found that a large number of people think that since "mass does not depend on speed" that the gravitational field of a body is not a function of its speed, contrary to fact (i.e. what we find by calculations starting with the postulates of relativity).
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    Quote Originally Posted by Markus Hanke View Post
    SR does not predict any "mass variance", contrary to popular opinion.
    That's a misleading statement. In order to say that you first need to define how "mass" is defined. When you've done that it follows whether mass is invariant or not. But you can't logically say that "SR does not predict.." when its a matter of definition first.
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    Quote Originally Posted by Physicist View Post
    There are very good reasons for it.
    No, Peter, there aren't any reasons, it is just people like you who graduated 40 years ago who cling to the notion of "relativistic mass".




    I myself wrote an article.
    Yes, it is well known that you wrote an article on this subject. It was never published.


    David Griffiths proof read if for me and although he disagrees with the use of rel-mass he recommended that I submit if for publication. I'm working on a rewrite at the moment.
    The point is that "relativistic mass" is a useless concept, so, it is doubtful that your paper will ever get accepted. Even if you find some journal to accept it, it will not contribute an iota to the advancement of physics.




    I've lost count of how many people think that because light has no "mass" that they can't generate a gravitational field.
    Not any physicist knowing his physics thinks that, you are beating a strawman.
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    Quote Originally Posted by Physicist View Post


    That is quite incorrect Markus. In fact a large proportion of modern relativity texts use it. To see the results of a quantitative study done on this see On the Use of Relativistic Mass in Various Published Works by Gary Oas. It's online at [physics/0504111] On the Use of Relativistic Mass in Various Published Works
    Actually, the author of the paper CONTRADICTS you:

    "This category of these works is the most significant reported here and more effort has been made to classify each
    textbook edition. In all 315 editions of textbooks have been examined with the general result that a majority
    utilize RM (223 versus 92). However, as reported in [Intro1] , the modern trend has been one of moving away
    from this concept.
    This is hypothesized to result from scrutiny of the literature on physics education research in
    writing introductory textbooks. Generally, one does not refer to this body of research when writing an advanced
    text or popularization of physics. It is interesting to note that this trend creates a widening gap between the two
    viewpoints, leading to significant inconsistencies in what is put forth. [b]I have found that students arriving into my course on relativity have deep preconceptions of relativistic mass and often point to widely read popularizations19
    penned by some of the most prominent physicists today. To have them unlearn this concept requires significant convincing (and time) and presents a sizable obstacle to an understanding of the modern geometrical formulation of relativity. Thus, those who introduce this concept as a fact of nature are doing a disservice to those that want to go on to become practicing relativists"
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    Quote Originally Posted by Physicist
    I've lost count of how many people think that because light has no "mass" that they can't generate a gravitational field.
    That may be true, but I have also lost count of how many people think you can turn a star into a black hole just by putting yourself into relative motion to it - "because its mass increases"

    Do you see what I mean? It's purely a matter of taste and I find it very useful to use it but it depends on what context I'm working in. When I'm doing calculations in particle physics I find using it annoying.
    Yes Physicist, I see what you mean and agree with you - it's a concept that works fine if used and understood correctly; it isn't wrong, and can safe time and space in writing out formulas. Personally though I had the experience that, when I first starting learning about relativity, this concept really really confused me because if you fail to understand it correctly you can easily construct all manner of apparent paradoxes from it - had I realised at that point that "relativistic mass" is really just a measure of total energy, it would have saved me a lot of headaches. For that reason I have a deep dislike towards it.

    But look, this is not a subject I am super-passionate about, so there isn't a need for a lengthy discussion; I know of course that it works fine once employed correctly. I just wouldn't use it myself, and based on my own learning experience I generally tend towards trying to steer other learners away from it.

    That's a misleading statement.
    You are right, it is. I should have said "rest mass variance".
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    Alan found that since o many of his students thought that since "light has no mass" that they had a difficult time understanding that radiation can generate a gravitational field.
    Granted. However, if I was to teach a class ( which will never happen ha ha ) my approach here would not be to play around with definitions of mass, but rather go away from it altogether and make them understand that the source of gravity is not just mass, but energy-momentum - the reason why radiation generates a gravitational field then becomes intuitively clear, even if you don't know any tensor calculus. I think when teaching GR and cosmology it is crucially important to aid a student in freeing him/herself from the confines of Newtonian thinking, which - albeit being useful locally - just doesn't translate very well into the strong field and high energy domains.

    But every teacher is different, and I wouldn't dare criticising someone like Alan Guth, whom I have the greatest respect for - it's just that I personally would take a different approach
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    Quote Originally Posted by Markus Hanke
    Personally though I had the experience that, when I first starting learning about relativity, this concept really really confused me ...
    That's the only part of relativity that confused you? Cool. From that frame of mind I take it that nothing in GR confused you?

    Quote Originally Posted by Markus Hanke
    ...because if you fail to understand it correctly you can easily construct all manner of apparent paradoxes from it - had I realised at that point that "relativistic mass" is really just a measure of total energy, it would have saved me a lot of headaches. For that reason I have a deep dislike towards it.
    Let's first distinguish the difference between "same thing" and "measure of." Think of the energy of a photon. The frequency of a photon is a measure of its energy. However that doesn't mean that that the frequency of the photon is the same thing as it's energy.

    Moving on; the relativistic mass of a body is proportional to total energy only if the body is isolated, i.e. not subject to any external forces. How often are bodies not subject to external forces in real life when we need to think about mass? After all we need mass to determine how a body (like a rocket ship) will accelerate, correct? Once you exert forces on it the total mass is not proportional to total energy anymore. Einstein proved this soon after his 1905 paper. He showed that when you have a body at rest in frame A and exert equal and opposite forces to the body parallel to the x-axis then in a frame moving parallel to the x-axis the relation E = mc2 no longer holds.

    When the object's mass is changing then it gets even more complicated. All too often when people talk about this subject they're thinking about particles and not macroscopic objects. You can't treat them the same way in general. It's too complicated to go into and I don't think you'd be very interested.

    It's better to think of all this as Einstein suggested in his 1916 GR paper - mass is nothing more or lass than energy which finds its complete description in a second rank tensor, the stress-energy-momentum tensor. (I don't like the way he phrased it exactly but its the best phrasing I've seen).

    Quote Originally Posted by Markus Hanke
    But look, this is not a subject I am super-passionate about, ..
    I don't like discussing it in open forum myself since its not a useful thing to do. I only do it when I see people being mislead as to what is actually out in the real world and actually being used and taught. That's all. In fact I just got a brandy new special relativity textbook in the mail Special Relativity and How it Works by Moses Fayngold (2008). Quite a recent publication as far as these texts go and it uses rel-mass.

    Although the subject bores the hell out of me now, when I was trying to determine which was the best way to go I chose to spend a great deal of time learning all about the history of the subject because when so many respected physicists agree on something then not only are they not confused about the concept (as so many people have erroneously claimed in the past) but they have very good reasons for doing it. Especially Richard Tolman who is quite thorough on the subject. He does a complete study of mass from the point of view of the stress-energy-momentum tensor in special relativity. Following him came authors who illuminated the fact that inertia is a function of pressure. E.g

    The inertia of stress by Rodrigo Medina, Am. J. Phys., 74(11), Nov. (2006)
    The inertia of stress
    We present a simple example in which the importance of the inertial effects of stress is evident. The system is an insulating solid narrow disc whose faces are uniformly charged with charges of equal magnitude and opposite signs. The motion of the system in two different directions is considered. It is shown how the contributions to energy and momentum of the stress that develops inside the solid to balance the electrostatic forces have to be added to the electromagnetic contributions to obtain the results predicted by the relativistic equivalence of mass and energy.
    A simple relativistic paradox about electrostatic energy by Wolfgang Rindler and Jack Denur, Am. J. Phys., 56(9), Sep. (1988)
    A simple relativistic paradox about electrostatic energy
    A charged parallel‐plate vacuum capacitor moves uniformly through an inertial frame. Its field energy alone does not transform according to the familiar law ‘‘energy=γ× rest energy.’’ However, when the stresses in the supports are taken into account, the entire system does satisfy this relation.
    So you see, there's a great deal to learn than just telling someone mass is invariant and that's all there is to the concept. There's nothing more to talk about the subject because that's all there is to it. Well, most people don't really come out and say it like that but most people that I've seen posting in forums such as this don't care much about people explaining everything there is to mass in the theory of relativity.
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    The truth maybe puzzling.It may take some work to grapple with.It may be counterintuitive.It may contradict deeply held prejudices.It may not be consonant with what we want desperately to be true.But our preferences do not determine what is true. - Carl Sagan.
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    Quote Originally Posted by 07CAUCHY View Post
    The truth maybe puzzling.It may take some work to grapple with.It may be counterintuitive.It may contradict deeply held prejudices.It may not be consonant with what we want desperately to be true.But our preferences do not determine what is true. - Carl Sagan.
    While that's all fine and dandy, has your question been answered to your satisfaction?
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    Markus is current with the revised thinking.
    Since energy cannot be transferred faster than light speed, there is an increasing delay for an accelerating object.
    What in reality is time dilation was initially interpreted as inertial resistance. A particle with a unit of mass cannot gain more units since that is one of the attributes that determines its identity.
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    Quote Originally Posted by phyti View Post
    Markus is current with the revised thinking.
    What are you talking about? What is this "revised thinking" that you're talking about and why do you imply that he's the only one "current" in it?
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    Physicist:

    I didn't say he is the only one. The revised thinking is the total energy expressed as a composition of rest mass and kinetic energy, with relativistic mass/energy as the total. Wiki has a detailed explanation for starters.
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    Quote Originally Posted by phyti
    Physicist:

    I didn't say he is the only one.
    Nor did I suggest that you did. I said implied since you selected him out of all the people who post in this thread to say that about only him.

    Quote Originally Posted by phyti
    The revised thinking is the total energy expressed as a composition of rest mass and kinetic energy, with relativistic mass/energy as the total. Wiki has a detailed explanation for starters.
    I don't understand the purpose of your post. I'm an expert on the concept of relativistic mass so there's nothing that anybody can tell me that I don't know about it. It's a virtual certainty that I know more about it than most physicists do since it was a subject of intense study of mine for a very long time, and still is. I even wrote a paper about which some physicists, such as David Griffiths, recommend that I publish it.

    Regarding your comment, it's still not clear what you're saying. The total energy E of a particle or an isolated object when not subjected to any external forces is

    E = K + E0

    Anybody who knows relativity knows this since it's a basic fact of relativity. So why make a big deal of it?
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    Physicist:
    Anybody who knows relativity knows this since it's a basic fact of relativity. So why make a big deal of it?
    I just took them in order!
    MY mistake to not address the response to 007CAUCHY, using #2 from Markus.
    Most regulars here are aware of the use of 'energy' instead of 'mass' for particle physics experiments, as an example.
    It is not a big deal for me, but maybe it is for you.
    If you care to lecture, direct it to the op.
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    Quote Originally Posted by phyti View Post
    Physicist:

    I just took them in order!
    Ah. I understand now.
    Last edited by Physicist; 09-26-2014 at 03:59 AM.
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    Why black holes doesn't exist
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  21. #21  
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    Quote Originally Posted by 07CAUCHY View Post
    Why black holes doesn't exist
    Where did you get that from? Black holes do exist. Observational evidence to their existence exists.

    See Untitled Document
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