Physical constant is constant even in strong gravitational fields

September 19, 2014 by Ans Hekkenberg, Fundamental Research on Matter (FOM)
Picture of the laser system with which the hydrogen molecules were investigated on earth. Credit: LaserLaB VU University Amsterdam/Wim Ubachs

An international team of physicists has shown that the mass ratio between protons and electrons is the same in weak and in very strong gravitational fields. Their study, which was partly funded by the FOM Foundation, is published online on 18 September 2014 in Physical Review Letters.

The idea that the laws of physics and its do not depend on local circumstances is called the . This principle is a cornerstone to Einstein's theory of . To put the principle to the test, FOM physicists working at the LaserLaB at VU University Amsterdam determined whether one fundamental constant, the mass ratio between and electrons , depends on the strength of the gravitational field that the particles are in.

Laboratories on earth and in space

The researchers compared the proton-electron mass ratio near the surface of a to the mass ratio in a laboratory on Earth. White dwarfs stars, which are in a late stage of their , have collapsed to less than 1% of their original size. The gravitational field at the surface of these stars is therefore much larger than that on earth, by a factor of 10,000. The physicists concluded that even these strong gravitational conditions, the proton-electron mass ratio is the same within a margin of 0.005%. In both cases, the proton mass is 1836.152672 times as big as the electron mass.

Absorption spectra

To reach their conclusion, the Dutch physicists collaborated with astronomers of the University of Leicester, the University of Cambridge and the Swinburne University of Technology in Melbourne. The team analysed absorption spectra of hydrogen molecules in white dwarf photospheres (the outer shell of a star from which light is radiated). The spectra were then compared to spectra obtained with a laser at LaserLaB in Amsterdam.

Absorption spectra reveal which radiation frequencies are absorbed by a particle. A small deviation of the proton-electron mass ration would affect the structure of the molecule, and therefore the absorption spectrum as well. However, the comparison revealed that the spectra were very similar, which proves that the value of the proton-electron is indeed independent of the strength of the gravitation field.

Rock-solid

FOM PhD student Julija Bagdonaite: "Previously, we confirmed the constancy of this fundamental constant on a cosmological time scale with the Very Large Telescope in Chile. Now we searched for a dependence on strong gravitational fields using the Hubble Space Telescope. Gradually we find that the fundamental constants seem to be rock-solid and eternal."

Explore further: Variables of nature

More information: Limits on a Gravitational field Dependence of the Proton-to-Electron Mass Ratio from H2 in White Dwarf Stars, Physical Review Letters, 18 September 2014. Paper on ArXiv: arxiv.org/abs/1409.1000

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13 comments

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julianpenrod
1 / 5 (5) Sep 19, 2014
Among other things, "relativity" asserts that physical laws are consistent from one inertial frame to another! Not between inertial and non inertial frames or between two non inertial frames! The "equivalence principle" said that the metrics for gravitational fields are the same as for accelerated frames so that "gravitational mass" and "mechanical mass" are the same. They aren't even testing what the article claims they are testing. Leaving aside the fact that they evidently ignore that various other constants could change along with the proton to electron mass ratio, keeping the emitted light the same. Note that they only characterize the observed spectra and the comparison spectra as "very similar". Also, note that absorption spectra occur due to relatively cool, extended gas envelopes of stars, preferentially absorbing continuous radiation from the star, and such an envelope can be less affected by any strong gravitational fields from the star.
Da Schneib
5 / 5 (6) Sep 19, 2014
Ummm, yes, I'd say "identical to 0.005%" is "very similar."

Did you have some point other than bashing the second most successful theory in the history of physics (relativity)? (For bystanders, the most successfully predictive theory in the history of physics is Feynman, Tomonaga, and Schwinger's renormalization of Quantum Electrodynamics, which had, the last time I checked, been verified to over seventeen decimal places, one of the most accurate measurements ever.)

How about you show your work on how "other physical constants" can "keep the light the same?" I bet you can't.

This experiment is a very good check of relativity, and yet another one that confirms its predictions. Using this data, astrophysicists will be able to further constrain their conjectures and hypotheses about what happens around black holes.
Goika
Sep 20, 2014
This comment has been removed by a moderator.
Da Schneib
5 / 5 (3) Sep 20, 2014
Hey @swordsman, what's "energy density, within these particles" mean?

Hey, Zeph, did you forget about the gravity of the white dwarf?
phprof
5 / 5 (1) Sep 21, 2014
Careful. QED is so successful because it is built on the shoulders of giants. In this case that would be E&M theory. However, I would agree. The verification of this ratio to this level is very striking. The possibility of other values changing in the right ratios so that this particular ratio is still the same is even more astonishing.

Ummm, yes, I'd say "identical to 0.005%" is "very similar."

Did you have some point other than bashing the second most successful theory in the history of physics (relativity)? (For bystanders, the most successfully predictive theory in the history of physics is Feynman, Tomonaga, and Schwinger's renormalization of Quantum Electrodynamics, which had, the last time I checked, been verified to over seventeen decimal places, one of the most accurate measurements ever.)
Goika
Sep 21, 2014
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Goika
Sep 21, 2014
This comment has been removed by a moderator.
Goika
Sep 21, 2014
This comment has been removed by a moderator.
Goika
Sep 21, 2014
This comment has been removed by a moderator.
Goika
Sep 21, 2014
This comment has been removed by a moderator.
Da Schneib
5 / 5 (1) Sep 21, 2014
did you forget about the gravity of the white dwarf?
I'm thinkin' about it all the time. How your question is supposed to be relevant to the violation of equivalence principle?
Because they're measuring the ratio of the mass of the proton to the electron, which, if the equivalence principle does not hold, should vary under strong gravity.

And it doesn't. The equivalence principle holds.
Goika
Sep 21, 2014
This comment has been removed by a moderator.
Da Schneib
5 / 5 (1) Oct 04, 2014
Ummm, why should the strength of the Coulomb forces change? What exact other force besides the electric force do you propose as an additional "Coulomb Force?" And why should it have anything to do with the spectrum if it does, and if it does that how come we can't detect it in the lab, with extremely sensitive equipment? And how come the Coulomb force doesn't change other places where we can detect it?

Your claim raises more questions than it answers.

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