# A feasible experiment that can decide!

1. Dec 24, 2005

### martillo

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. Dec 24, 2005

### pervect

Staff Emeritus
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.

3. Dec 24, 2005

### Staff: Mentor

I'm a little confused - electron guns already accelerate electrons to a high fraction of C. So what's the problem here?

4. Dec 24, 2005

### inha

Considering that accelerators and synchrotrons actually work I'm wondering about the existence of any problems too.

5. Dec 24, 2005

### JesseM

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?

6. Dec 24, 2005

### krab

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.

7. Dec 24, 2005

### rachmaninoff

Err, you're off in one small detail - it's 2006 now. :rofl:

8. Dec 24, 2005

### Staff: Mentor

Where do you live...?

9. Dec 24, 2005

### rachmaninoff

Oh yeah, it is 2005. My mistake. :uhh:

10. Dec 24, 2005

### Staff: Mentor

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
11. Dec 24, 2005

### Hans de Vries

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

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

12. Dec 25, 2005

### ZapperZ

Staff Emeritus
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
13. Dec 26, 2005

### martillo

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.

Last edited by a moderator: Apr 21, 2017
14. Dec 26, 2005

### Staff: Mentor

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

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.)

Last edited by a moderator: Apr 21, 2017
15. Dec 26, 2005

### ZapperZ

Staff Emeritus
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.

Last edited by a moderator: Apr 21, 2017
16. Dec 26, 2005

### martillo

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" [Broken] 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" [Broken] 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 by a moderator: May 2, 2017
17. Dec 26, 2005

### ZapperZ

Staff Emeritus
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.

Last edited by a moderator: May 2, 2017
18. Dec 26, 2005

### martillo

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.

19. Dec 26, 2005

### ZapperZ

Staff Emeritus
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.

20. Dec 26, 2005

### martillo

Zapperz,
Theres 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.

21. Dec 26, 2005

### ZapperZ

Staff Emeritus
Er.. NO THEY DON'T!

If I don't do a relativistic correction to the mass, I would be measuring a horribly wrong energy in the spectrometer.

You are forgetting that giving a "name" is irrelevant - it is the correct mathematical expression that is more important. I strongly suggest you talk to people who design particle accelerators and tell them that you don't buy into this "relativistic mass" and see their reaction. I'm sure they'll show you all the design that would have gone terribly wrong had they not take those into account. So many experiments have been done at the relativistic regime, it is almost funny to ignore all those body of evidence. So why are you?

Zz.

22. Dec 27, 2005

### martillo

I should have been more explicit.
In the equation above k is the relativistic factor as named by Einstein:
k = 1/sqr(1-v2/c2)
I have no problem with the factor there. I'm not denying the validity of all those experiments.
I think there are problems with Davisson-Germer/Thomson experiments at higher velocities where the classic aproximations are not aplicable.

I think the modified version is very feasible. May some kind of lenses must be added to distinguish the smaller separation of the scattering "peaks" and may some other technical aspects must be developed but is feasible.

23. Dec 27, 2005

### Staff: Mentor

What nonsense! Anyone doing these experiments knows perfectly well that you must use the relativistic formulas in computing the de Broglie wavelength.

While relativistic corrections didn't matter to Davisson and Germer, who used energies in the 50 - 300 eV range, they certainly mattered to Thomson who used energies 1000 times greater. And that was in 1927!

Electron diffraction at relativistic speeds has been done countless times since then. (See http://en.wikipedia.org/wiki/Electron_diffraction)

Only for those who ignore relativity!

24. Dec 27, 2005

### ZapperZ

Staff Emeritus
I am still trying to figure out just exactly what your "beef" is with the Davisson-Germer experiment. Are you saying that if we INCLUDE the relativistic effects, there will STILL be results that cannot be accounted for from this experiment? If this is true, would you care to tell me explicitly what the anomolous result is that is beyond the relativistic correction?

And if this is true, do you think such a thing has no ramifications to ALL the high-energy physics results that you have already explicitly indicated that you agreed to?

This is getting to be rather confusing, and I wish you would just say what you obviously have in mind, rather than just pussyfooting around the issue.

Zz.

25. Dec 27, 2005

### martillo

Doc Al,

I visited the link you gave and I found this:

I'm sorry but theres an error because the TEM and the SEM are electron microscopes and use electron lenses made by electric and/or magnetic fields to amplify images! They do not explore electrons diffraction!

Then I still sustain that today there is no available valid data at the internet about electrons diffraction experiments at relativistic speeds and I suggest to do them but with the mentioned modification in the method of determining the velocity.

Zapperz,
I believe the experiment will determine in a very important way the dependency of mass with velocity. Just that.