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A feasible experiment that can decide!

  1. Dec 24, 2005 #1
    The Davisson-Germer experiment is the classical experiment that verifies the formula of De Broglie: λ = h/mv
    It is proposed here that a feasible modification in the original Davisson-Germer experiment could finally decide If Relativity Theory is right or wrong.
    Detailed descriptions of the Davisson-Germer experiment can easily be found in the web

    The original experiment uses the constant (“rest”) mass of the electrons and the classical formula for the Kinetic Energy in the applied formula. The classic magnitudes give exact results.
    The electrons are accelerated by only 50 volts to reach velocities about 1% of the constant c. It must be considered that even at those velocities some mass variation should be detected but also it is easy to accelerate them more and precisely verify any dependency between the mass and the velocity of the electrons.

    I can reasonably speculate why this experiment haven't been performed for higher velocities by both Relativity defenders or fighters to verify the if the mass of the electrons varies with velocity as sustained by Relativity or not? This is very strange!

    Try to state that only the "rest mass" must be considering in the De Broglie formula is not aceptable. The original development of the formula determines that the "relativistic mass" must be used.
    I suggest to add a Velocity Selector in the Davisson-Germer apparatus just after the acceleration stage to measure the velocities directly.

    A Velocity Selector is a stage were the electrons pass through both an Electric Field that produces a force to deflect them in one direction and a Magnetic Field that produces a force to deflect the electrons in the opposite direction. At the end of the stage there's a hole where only the electrons of a precise velocities can pass through. The Magnetic Force is velocity dependent and so the Electric Force can be adjusted to compensate the effect of the Electric Force. It's another method to mesure the velocity.

    There's nothing to loose and a lot to win performing the new version of the experiment. At least more precise results will be determined.
    It's a very interesting idea to be consider by someones who have the resources to make a new apparatus and perform the suggested experiment.

    I can't.
     
    Last edited by a moderator: Dec 25, 2005
  2. jcsd
  3. Dec 24, 2005 #2

    pervect

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    You may have missed it, but relativity theory has been tested before, and succeeded.

    The proposed experiment is hardly any sort of "final test". Theories are never "finally proven", though they can be falsified.

    Personally I think there is little doubt that relativity would pass this test, as it has passed others, but of course the reason to do experiments are for those rare occasions when new and unexpected results occur.

    The proposal sounds simple enough that it's possible it has already been done.
     
  4. Dec 24, 2005 #3

    russ_watters

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    I'm a little confused - electron guns already accelerate electrons to a high fraction of C. So what's the problem here?
     
  5. Dec 24, 2005 #4
    Considering that accelerators and synchrotrons actually work I'm wondering about the existence of any problems too.
     
  6. Dec 24, 2005 #5

    JesseM

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    This equation was originally found in the context of nonrelativistic quantum mechanics--does anyone know if it still is supposed to apply in relativistic QM, ie quantum field theory?
     
  7. Dec 24, 2005 #6

    krab

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    So where have you been? This is 2005, not 1905. Electrons have been accelerated to not only 50 volts, but to 50,000,000,000 volts. Relativity has been verified in every detail.
     
  8. Dec 24, 2005 #7
    Err, you're off in one small detail - it's 2006 now. :rofl:
     
  9. Dec 24, 2005 #8

    russ_watters

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    Where do you live...?
     
  10. Dec 24, 2005 #9
    Oh yeah, it is 2005. My mistake. :uhh:
     
  11. Dec 24, 2005 #10

    Doc Al

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    This is quite funny, actually. As others have stated, diffraction of high-energy electrons is routine nowadays. But do you realize that while Davison-Germer used 50 eV electrons, during that same year (1927) Thomson verified electron diffraction for energies 1000 times greater. (And of course he used the relativistic momentum to calculate the wavelength!) They shared the 1937 Nobel prize for this. Where have you been?
     
    Last edited: Dec 24, 2005
  12. Dec 24, 2005 #11

    Hans de Vries

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    Special Relativity is essential at all speeds for the de Broglie
    wave behavior, even at mm's per second. The non-simultaneity can
    be demonstrated dramatically with electrons moving at this speed.

    It is SR which guarantees that the direction of the de Broglie wave front
    is always in the direction of the motion of the particle. Now with an
    electron moving at 1 mm/s to the right you only have to move your
    eye balls to have it going 3 mm/s to the left or 2 mm/s upwards relative
    to your pupils.

    Yet. you will see that while moving your eyeballs the de Broglie wave
    front will adjust itself (rotate) to be always in the direction of the
    motion of the electron.


    See here for the background and the images (par.6, figure 2):

    http://www.chip-architect.com/physics/deBroglie.pdf



    Regards, Hans
     
  13. Dec 25, 2005 #12

    ZapperZ

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    I will add even more that SLAC has even accelerated POLARIZED electrons under the NLC scheme. I should know since I refereed several of their work in using doped GaAs as a source of polarized electrons. So we know how to deal with electrons that have spins alligned, how to filter them out, and how to accelerate them to practically c. In fact, for the proposed International Linear Collider, the design calls for polarized electrons. We certainly won't be proposing a $10 billion project using something that we don't know.

    Zz.
     
    Last edited: Dec 26, 2005
  14. Dec 26, 2005 #13
    I know electrons have been accelerated at very high velocities in several experiments but I'm focusing in experiments analog to the Davisson-Germer one which intends to verify the De Broglie's λ = h/mv equation.
    At least at the internet there's no available description of such kind of experiment done at higher velocities than those of the original Davisson-Germer experiment.


    I made a search and have found that in the Thomson experiments the energies of the electrons are much smaller than the Davisson-Germer experiment!
    Please take a look at the following url I have found: http://library.thinkquest.org/19662/low/eng/electron-wave-exp.html
    There is presented that the energies of the electrons in the Davisson-Germer experiment are of 54MeV while in the Thomson experiment are about 10exp4 eV which is = 0.01MeV.
     
  15. Dec 26, 2005 #14

    Doc Al

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    I suspect that the quoted energy of 54 MeV for Davisson-Germer is a misprint. :rolleyes:

    Figure it out for yourself: Calculate the de Broglie wavelengths for electrons with energies of 54 eV and 54 MeV and see how they compare to the quoted wavelengths. (Measured wavelength = 0.165 nm; de Broglie's predicted wavelength = 0.167 nm.)

    (For electrons with energy in the 50 MeV range, you must use the relativistic momentum to calculate the de Broglie wavelength.)
     
  16. Dec 26, 2005 #15

    ZapperZ

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    I don't get this whole thing and what you're trying to "verify" here.

    Are you trying to verify the wave nature of electrons per the deBroglie relationship? If you are, why are you only looking at this particular experiment? The Bragg scattering of electrons off crystal lattice planes are not sufficient? What about LEED experiments? Those are not good enough either?

    Zz.
     
  17. Dec 26, 2005 #16
    Doc Al,
    You are right, the energy used in the original Davisson-Germer experiment is 54eV.

    Zapperz,
    I have found at: http://www.chem.qmul.ac.uk/surfaces/scc/scat6_2.htm that the energies of the electrons in Leed's experiments are about the same of the Davisson-Germer (20-200 eV) and the constant "rest mass" of the electrons is used.

    To all,
    I have difficulties to find accurate information on Thomson's scattering experiment but I can see at: http://online.cctt.org/physicslab/content/PhyAPB/lessonnotes/dualnature/Davisson_Germer.asp that Thomson a cathode tube similar to that of Davisson-Germer and the separations of the pictured rings tell me that at least for this figures the energy of the electrons are in the same range.

    I will look more for Thomson scattering experiments.
     
    Last edited: Dec 26, 2005
  18. Dec 26, 2005 #17

    ZapperZ

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    Yeah, so? I still don't get what you are trying to accomplish here, which was the question I asked in my last post. The LEED experiments and the Bragg diffraction experiments are not enough to show such effects?

    Zz.
     
  19. Dec 26, 2005 #18
    The point is that the De Broglie equation have been verified in all those electrons diffraction experiments but always considering the classic physics aproximations using the "rest" mass for the electrons and the classic formula KE = 1/2 mv2 for their kinetic energy!
    This means that the formula hasn't been verified for the relativistic effects.
    The experiment at higher velocities can show the exact dependency between mass and velocity. This is of interest for both relativity defenders and opposers and then I ask why it is not mentioned and it seems of haven't been done?
    As I say in the head post I sustain that at higher velocities "strange" results can be obtained and I have reasons to believe that the method to deduce the velocity fails. I propose to add a velocity selector to determine the velocity of the electrons.
    You can question my reasons but if I'm right in that the done experiments give "strange" results at higher velocities the modification I propose can bring excellent results.
     
  20. Dec 26, 2005 #19

    ZapperZ

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    Then I suggest you scour ALL of the high energy physics experiments and point out to me where in all those experiments give any indication of your "strange" results.

    I accelerate electrons practically to c. I see nothing strange at all in dealing with the EXPECTED relativistic effects, especially when I cause it to bend in magnetic fields to measure their energies. Ditto to all the synchrotron centers around the world. If there's something strange going on at such speeds, we haven't seen it. So why don't you make a quantitative prediction on what exactly I should see when I pass these electrons through a slit and then bend their path in a magnetic field.

    Zz.
     
  21. Dec 26, 2005 #20
    Zapperz,
    There`s nothing wrong with the "strong magnet", "ciclotron", "etc" experiments. They are very accurate.
    They show accurately that the equation q.v.B = k.m0.a is valid (m0 = "rest mass").

    I will be honest. The problem is that for me they don't prove that the mass vary with velocity since exist the possibility that the factor k could belong to the other side of the equation. This way it could be that the Magnetic field be afected by the factor and not the mass. But I was adviced by an administrator that new theories cannot be treated here and I will follow the guide.
    I have found that the mentioned new experiment could be done to prove/disprove the variation of mass with velocity and it would be of interest for everybody to have new experimental data.

    I have seen in many forums people discussing about this subject including people that totally agree with relativity but have problems with the notion of "relativistic mass" as introduced by the proper Einstein.

    I believe that this experiment can finally decide on the subject about mass variation.
     
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