# Question about A Calorimetric Test of Special Relativity

#### lalbatros

Question about "A Calorimetric Test of Special Relativity"

In the 70's, as small team on th SLAC facitilites took some opportunities (1) to check an replacement theory for special relativity, called "autodynamics" (2).
The paper (1) relating their results might no be totally understandable for readers unfamiliar with particle accelerator technologies.
Also, the goal of checkin "Autodynamics" is probably not familiar to most people.
However the salient feature are no so complicated.
Here are the main parts of this experimental setup:

• An electron accelerator.
• A "momentum slit" that filters particles according to their momentum.
It is based (I think) on the deviation of charged particle in a magnetic field.
The particles are selected according to their momentum because the deviation depends on two parameters:
- the gyroradius R = P/e.B where P is the momentum of the electron, e its charge, B the magnetic field
- the length of the device
• An ampmeter to measure the beam current
• A beam dump calorimeter to measure the power of the beam (kinetic energy)
Such a measurement might not have a very good precision because of the calorimetric part of it.
However, if two theories disagree widely on the outcome, the precision might not be an issue.
This is what happens when comparing SR to autodynamics.

Therefore, I have no the following question:

Can the results in (1) also be used to discrimates Special relativity (SR) from Galilean relativity (GaR).
There are two aspects, I think, to be considered:

• the momentum selected by the "momentum slit" will be interpreted diffently by SR or GaR.
• the energy-momentum relation is different in SR and GaR.
And of course, is SR or GaR confirmed by this experiment?

(insight from accelerator specialists welcome)

(1) http://www.slac.stanford.edu/pubs/slacpubs/2000/slac-pub-2890.html [Broken]
(2) http://en.wikipedia.org/wiki/Autodynamics

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Staff Emeritus
Re: Question about "A Calorimetric Test of Special Relativity"

First, Autodynamics is considered a crackpot theory. It make predictions contrary to observation and indeed, everyday experience. I wouldn't spend much time worrying about it.

Secondly, in SR, kinetic energy is $\sqrt{(pc)^2+m^2c^4}-mc^2$, and in Newtonian mechanics it is $p^2/2m$. For small m,the ratio is therefore 2mc/p, or about 20,000 times as much heat in the Newtonian case.

Of course, it would be silly to do this experiment, as the size of the SLAC power bill already excludes Newtonian physics - it would also be 20,000 times larger.

#### lalbatros

Re: Question about "A Calorimetric Test of Special Relativity"

I found this paper referenced by J Baez as an experimental support for SR (1).
I was indeed surprised by this consideration of Autodynamics which is very strange.
Nevertheless, this measurement has been done, simply because it was easy to do.
The results are a good pedagogical illustration of SR, for the relation between E and p.
Indeed, also, the SLAC has been engineered on SR.
However, it is not totally obvious that the experiment discriminates between SR and GaR.

I was interrested to play a little bit with this topic.
In doing so, I thought that it was also needed to consider the "momentum slit" carefully.
We should be sure about what 20 GeV/c means when trying to discriminate the two theories.
Otherwise we cannot take this paper as a proof of SR.

(I have no doubt that SR is supported by a lot of other evidences)

(1) http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

Staff Emeritus
Re: Question about "A Calorimetric Test of Special Relativity"

However, it is not totally obvious that the experiment discriminates between SR and GaR.
If you have a specific objection to my calculation, post it. There's a factor of 20,000 difference in the two predictions: the difference between a one degree rise in temperature and the whole beam dump flashing into steam. I'm pretty sure that even in 1975 the experimenters could tell the difference.

We should be sure about what 20 GeV/c means when trying to discriminate the two theories.
The authors describe exactly how this is accomplished - they even provide a schematic of the beam transport elements. How can you argue that the momentum-selected beam doesn't have the momentum the experimenters say it has?

#### lalbatros

Re: Question about "A Calorimetric Test of Special Relativity"

I had no objection on this calculation that I did also before starting this thread.
I had found a classical/relativistic ratio = 19570 for a momentum of 20 GeV/c.

Having found such an enormous difference, I simply wished to look also at the momentum slit with both the classical and relativistic points of view. In this way I could really be sure that this paper is indeed one more experimental evidence for SR.

Now, the expression for the gyrodius R=p/eB is the same in the classical and relativistic case.
Therefore, for measuring the momentum, there is no difference between SR and GaR.

However, I do not know exactly how the slit works. For example I don't know if it needs a kind of calibration or if the selected momentum can be deduced only from the magnetic field and the geometry. Even if these details play probably no role in the conclusion, I would like to check.

Staff Emeritus
Re: Question about "A Calorimetric Test of Special Relativity"

Like I said, they describe their beam optics and even include a diagram. But how do you propose that they mismeasure their optics by a factor of 20,000? Do they think they have one of the world's most powerful magnet but really have one that's weaker than the earth's field?

#### lalbatros

Re: Question about "A Calorimetric Test of Special Relativity"

I just want to know more about the momentum slit.
Partly by curiosity, partly because it is 50% of the conclusion of this paper.
When I am done with this one, I will chose another in Baez's list.
That's just my after-hours fun.

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