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Let there be light

  1. Oct 14, 2003 #1
    Ongoing long term theory developement discussion

    Observations of light

    1. It's only seen when it is within a very narrow spectrum

    2. It can not be seen except in reflection and at it's source.

    3. It generates heat.

    4. It doesn't appear to have mass.

    5. Every thing suggests that it is 2 dimensional.

    6. An awful lot of contraversy surrounds it's understanding

    7. There seems to be alot of tail chasing going on.


    If light has no mass but is a particle then it would have to be 2 dimensional I would think. Actually when you look at reflected light it certainly seems to be 2 dimensional. Like it's not something you can peel away is it. It definitely appears to have no thinkness.

    Another point to make is that if light was 3 dimensional particles then you would actually see it looked at from the side. Which of course we can't unless it is reflecting of something.

    The laser pistol seen in the movies where a beam of light fires from a gun would be the effect of light if it was 3 dimensional.

    Can any one offer a counter arguement that can be observed without getting all techo. Anything that is real and not theory that can prove light to be three dimensional?

    If not then why are we chasing our tails on this one?

    an apple is an apple is an apple is an apple when do we stop and say hey this is an apple

    have fun
     
    Last edited by a moderator: Oct 14, 2003
  2. jcsd
  3. Oct 15, 2003 #2
    Light, as a particle, is supposed to be zero dimensional.
     
  4. Oct 15, 2003 #3

    pmb

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    Light does have mass. It just doesn't have rest mass.

    Pete
     
  5. Oct 15, 2003 #4
    Re: Re: let there be light

    Photon doesn't have mass, it just does have a non-zero linear part of four-momentum, therefore it call a massless linear particle.
     
    Last edited: Oct 15, 2003
  6. Oct 15, 2003 #5
    Because photon has both linear part of four-momentum, and helicity, therefore it needs the four-dimensional space. You can't describe a photon in space having smaller dimensionality. You can't conserve both momentum, and helicity, and spin, without four-dimensional space.
     
  7. Oct 16, 2003 #6
    By zero dimensional, I mean that it has no effective size when veiwed as a particle.
     
  8. Oct 16, 2003 #7
    so we have a "particle" that is thought of as being zero dimensional, two dimensional and 4 dimensional the 4th being time I assume. hhhmmmmmmm......It just shows you that the light is in the eye of the beholder....ha...oops excuse me....
     
  9. Oct 16, 2003 #8
  10. Oct 16, 2003 #9

    pmb

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    Re: Re: Re: let there be light

    That's rest mass. Not mass.

    Some people call the "mass" in relativity "relativistic" mass. What light does not have is "rest mass."

    This is nothing new by the way. Even Einstein said light has mass. It's mass is E/c^2.

    The same thing can be found in the Feynman lectures since Feynman said it too. Rinlder does as well in his new relativity text as does Mould and D'Inverno etc.

    'mass' is defined as the quantity m such that the quantity mv is a conserved quantity. This, along with the postulates of relativity, gives enough information to show that, for a tardyon (particle with non-zero mass) has a mass m given by

    m = m(v) = m_o/sqrt[1-(v/c)^2]

    where m_o = m(0) is the rest mass.

    But according to the definition of mass above - anything which has a non-zero momentum has a non-zero mass. In fact if you look in the well-known text "Special Relativity," A.P. French, MIT intro series and turn to page 16 and look at the footnote you'll see this
    This text is still used at MIT by the way. See
    http://web.mit.edu/8.20/820Info_2003.pdf
    And lists French and Rindler's text. Each of which define mass in exactly this way. Einstein argued that light had mass back in 1906.

    I know of one new physics book by a very famous author on this subject, i.e. Max Jammer, who even labels the time component of 4-mommentum as m where

    m = m_o/sqrt[1-(v/c)^2]

    See
    "Concepts of Mass in Contemporary Physics and Philosophy," Mass Jammer, Princeton University Press, (2000), pages 49-50


    Pete
     
  11. Oct 16, 2003 #10
    Re: Re: Re: Re: let there be light

    That's mass, you can call it the rest energy, but not rest mass.

    You've made mistake. In general, E0=mc2, but total energy of particle E is equal to mc2 if and only if the particle's momentum p is equal to zero, because E=p2c2+E02=p2c2+m2c4
    Let c=1, then
    E=p2+E02=p2+m2.

    The serious scientific literature is deprived of such definition of a mass, because the mass is an invariant concerning Lorentz and Poincare transformation groups. Invariant signifies not varying, without dependence from a velocity or something else (of course, if the particle is free). A mass is a mass and it is an invariant. Be exacter.
    1. Landu L., The theoretical physics. Field theory, vol 2;
    2. Einstein A., Ann. d. Phys., 1905.Bd 17.S.891;
    3. Ìi1ler A. I., Albert Einstein's Special Theory of Relativity: Emergence (1905) and Early Interpretation (1905-1911). -Addison-Wesley, 1981;
    4. Einstein A.//Ann. d. Phys., 1905. Bd 18. S. 639;
    5. Einstein A.//Ibidem. 1906. Bd 20. S. 371;
    6. Einstein A.//Ibidem. 1907. Bd 23. S. 371;
    7. Åinstein A.//Ibidem. 1911. Bd 35. S. 898;
    8. Jammer M. Concepts of Mass in Classical and Modern Physics.- Cambridge: Harvard Univ. Press. 1961;
    9. Feynman R.//Phys. Rev. 1949. V. 76. Ð. 749, 769;
    10. Feynman R., Leighton R., Sands Ì. The Feynman Lectures on Physics.- Addison-Wesley, 1963, 1964. - V. 1. Chs/15, 16; V. 2. Ch. 28;
    11. Fåónmàn R. P.//The reason for antiparticles//Elementary Particles and the Laws of Physics; The 1986. Dirac Memorial Lectures.- Cambridge; New York; New Rochel-le; Melbourne: Sydney: Cambridge Univ. Press, 1987 - P. 1;
    12. Adler C.//Am. J. Phys. 1987. V. 55. P. 739.
    Especially Adler C., because he has proved that my point is right. He also has criticized the majority of the educational literature because of presence of this erroneous definition.
     
  12. Oct 16, 2003 #11
    Then what is a photon's wave length?
     
  13. Oct 16, 2003 #12
    as an amatuer i find all this particle, non particle, mass , non mass very interesting.

    Could it be we could agree on one thing?

    That what is trying to be described is just a very small centre of attraction that has no mass, isn't a particle but definitely has intensity.

    This would accomodate all approaches and make a lot more sense.

    It also doesn't require dimensional definition either.
     
  14. Oct 16, 2003 #13
    Intensity is a scalar dimension.
     
  15. Oct 17, 2003 #14

    pmb

    User Avatar

    Re: Re: Re: Re: Re: let there be light

    As I said above - it depends on how the term "mass" is defined. And there is no definition that is used uniformly throught the physics literture. In special relativity there

    mass = relativistic mass
    mass = proper mass aka rest mass

    Sorry dude but I've made no mistake.


    That holds true if and only if m = proper mass. If m = relativistic mass then E = mc^2 where m = m_0/sqrt[1-(v/c)^2] = re;ativistic mass


    That too is incorrect. The following are very much serious scientific literature as are the texts used at MIT to teach relativity

    "The Feynman Lectures on Physics," Vol I - III, Feynman, Leighton, and Sands, Addison Wesley, (1963)(1989)
    As Feynman says (lectures V-1, page 7-11 "Gravity and Relativity")
    "Relativity: Special, General and Cosmological," Rindler, Oxford Univ., Press, (2001). From pagte 113
    Then there are two other new texts which I know of off hand which define mass in this way. They are

    "Basic Relativity," Mould, Springer Verlag, (1994)

    "Introducing Einstein’s Relativity," D’Inverno, Oxford Univ. Press, (1992)

    Then there is the American Journal of Physics. See

    "An elementary derivation of E = mc^2," Fritz Rohrlich, Am. J. Phys.58, 348 (1990)

    Are you familiar with Gravitation by Misner, Thorne and Wheeler? If so then see Section 5.7 "Symmetry of Stress-Energy Tensor"
    This mass cannot be rest mass must be relativistic mass.

    Are you familar with Alan Guth? I have a copy of his lecture notes for his course "The Early Universe"
    All of the above are very serious.


    Let me tackle a few of these.
    1. Landau = Landau simply defines mass differently. I see no problem with anyone choosing a definition that they like

    2. Einstein A., Ann. d. Phys., 1905.Bd 17.S.891;

    Not sure of the referance numbers. But if you're refering to Einstein's 1905 article then that was his first paper. Not his last. He does speak of transverse and longitudinal mass which are velocity dependant. These are two different quantities. Max Planck came up with a better definition the next year and said that m = m_o/sqrt[1-(v/c)^2] is better since you can now write force as

    f = dp/dt

    where p = mv


    3. Not familar with it. But I suspect that its just a different definition - like Landau

    4. Einstein A.//Ann. d. Phys., 1905. Bd 18. S. 639;

    Einstein's first derivation. Not his last

    5. Einstein A.//Ibidem. 1906. Bd 20. S. 371;

    If this is the paper that I think it is, i.e. the conservation of the center of mass, then I ahve to ask you if you've actually read this paper. In this paper Einstein was investigating the mass of light. It consists of two parts. The first part Einstein concludes light mass carries mass with it. In the second part he defines the mass density of light as rho = u/c^2 where u is the energy density of radiation. He also implies in the math that the mass of a particle = energy of particle/c^2

    6. Einstein A.//Ibidem. 1907. Bd 23. S. 371;

    I have to reread that since I don't recall that the subject arose in that paper

    7. Åinstein A.//Ibidem. 1911. Bd 35. S. 898;

    Again I have to ask you if you've read this? He does say that light has mass in that paper. He calls it radiation though.

    8. Jammer M. Concepts of Mass in Classical and Modern Physics.- Cambridge: Harvard Univ. Press. 1961;

    What about this book are you refering to? He does explain relativistic mass. However he has a new book out.

    "Concepts of Mass in Contemporary Physics and Philosophy," Mass Jammer, Princeton University Press, (2000)

    On pages 49-50 Jammer argues that the time component of the 4-momentum is mass m. I.e. he starts out with P^u = (cq, um, 0, 0) and shows that q = m = relativistic mass

    9. Feynman R.//Phys. Rev. 1949. V. 76. Ð. 749, 769;

    Sorry but I haven't read it. I've read his lectures and a few others in which he does state that mass = m_o/sqrt[1-(v/c)^2] and that light has mass. And he said that many years after this article was written.

    10. Feynman R., Leighton R., Sands Ì. The Feynman Lectures on Physics.- Addison-Wesley, 1963, 1964. - V. 1. Chs/15, 16; V. 2. Ch. 28;

    I don't understand your reason for citing this. They agree with my definition of mass. Not yours.


    11. Fåónmàn R. P.//The reason for antiparticles//Elementary Particles and the Laws of Physics; The 1986. Dirac Memorial Lectures.- Cambridge; New York; New Rochel-le; Melbourne: Sydney: Cambridge Univ. Press, 1987 - P. 1;

    Never heard of it. Sorry.

    12. Adler C.//Am. J. Phys. 1987. V. 55. P. 739.

    This article is loaded with errors. In fact all of his arguements are very flawed. I'll point them out one by one if you'd like.

    Rindler is much better at relativity than Adler. See Rinlder's comments on this topic in Physics Today. I placed it on my web page with Rindler's permission

    http://www.geocities.com/physics_world/rindler_article.htm


    But if you're interested in the other point of view then see


    "In defense of relativistic mass," T.R. Sandin, Vol. 59(11), No. 1991

    For a more complete listing of articles on this debate then see
    http://www.geocities.com/physics_world/mass_articles.htm


    Pete
     
  16. Oct 17, 2003 #15

    pmb

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    Mass (and hence energy) is the source of gravity. Not rest mass. Since light has energy then it has mass and thus creates a gravitational field. For an example of such a field see

    http://www.geocities.com/physics_world/grav_light.htm

    Pete
     
  17. Oct 17, 2003 #16
    Once again, mass is an invariant concerning Lorentz and Poincare transformation groups. You can't defining mass by gravitation, because measure of attraction within dependence to both an energy and direction of moving. E.g. two photons with the same energy, but the perpendicular momentums will be differ twice by attractive force by the massive body.
    However, your point - almost religion. Believe and enjoy.
     
  18. Oct 17, 2003 #17
    an example of massless intensity could be described using three magnets

    Place them in a circle so that they are poled so at to be attractive....leave a gap of say 6 inches between all of them

    So we have a circumferance of magnets and their attractions.

    Each magnet is also attracted to each other across the diagnal or diameter.

    In an appropriate center there is an intensity and if one swings a magnet across this arangement the magnet will eventually settle at this point. I call this a culminant centre of attraction where the total attractions are averaged and a point in the magnetic middle is achieved.

    So the relevance is that this centre of attraction is a mass less intensity. a resultant centre of attraction.

    Say apply the logic to 6 stars in any arrangement it would show an averaged centre of attraction i would think..

    Theory of gravity in developement.
     
    Last edited by a moderator: Oct 17, 2003
  19. Oct 17, 2003 #18

    pmb

    User Avatar

    Rest mass yes. Relativistic mass no.

    That is why mass is completely defined by a tensor and not a scalar.

    This has nothing to do with "religion." I'm not being dogmatic about it whatsoever. I just took the time to explore every single aspect that I could about this subject and I came to the conlusion I have, not because I'm being dogmatic, and not because I learned it a long time ago and "don't know the new way." But I do so becuase I've come to understand that it is the best choice since it stands up as the one that can have the most most rigourous definition.

    By the way - I see you didn't answer my questions. Is there a reason for that?

    Pete
     
  20. Oct 18, 2003 #19

    pmb

    User Avatar

    Not sure what you mean by "You can't defining mass by gravitation." The soruce of gravity is mass i.e. mass-energy. The source is not rest mass.

    But if you're refering to the mathematical quantity then the mass-tensor aka stress-energy-momentum tensor is the quantity which acts as the source.

    Consider the EM analogy. The source of the EM field in Maxwell's equations is the 4-current. Yet one can truly say that charge is the physical entity which acts as the source. In this context - In gravity the physical entity which acts relativistic mass.

    Relativistic mass is to gravitation as charge is to electromagnetism.

    Pete
     
  21. Oct 18, 2003 #20
    Light as a basis of all.

    In this list is absent the most important book. It is…. the Bible, where creation of the world is described how it was actually. All other scientific books in the sum costs nothing in comparison with one phrase from this book. This phrase says that all

    OUR WORLD IS CREATED OF LIGHT!!!

    I CAN PROVE IT!

    1. The Bible, a first book of Moses, Life, chapter1.
     
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