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Blog

Is the fine structure constant affected by gravity?

Artist's illustration of a white-dwarf star.

Artist’s illustration of a white-dwarf star (Image Courtesy: NASA/JPL-Caltech)

By Hamish Johnston

If there is one thing our readers like it’s a good story about fundamental constants – and the fine structure constant (α) is always a favourite.

In case you are not familiar with α, it’s a dimensionless quantity (about 1/137) that measures the strength of the electromagnetic interaction. As such, it quantifies how electrons bind within atoms and molecules and therefore can be measured to great precision using spectroscopic techniques. And because atoms can be found just about anywhere between here and the edge of the universe, it’s possible to ask whether α is the same everywhere.

In a paper published this week in Physical Review Letters, an international team of physicists have measured α in the atmosphere of a white-dwarf star – where the gravitational potential is about 30,000 times greater than here on Earth.

Julian Berengut at colleagues at the University of New South Wales and universities in the UK and US looked at absorption lines from iron and nickel on G191-B2B, which is a white dwarf about 150 light-years from Earth. The spectra – which were taken by the imaging spectrograph on the Hubble Space Telescope – were compared to similar measurements on iron and nickel made in a lab on Earth.

Some theories that look beyond the Standard Model of particle physics and general relativity predict the existence of hitherto undetected scalar fields. Such fields could affect the values of fundamental constants including α. Detecting such discrepancies could lead to a major breakthrough in our understanding of particle physics and cosmology.

Unfortunately, that’s not what happened! Berengut’s team found that to within about one part in 20,000, α is the same in both places. An interesting thing about the result is that it is limited by the precision of the measurements made here on Earth, rather than those made by Hubble. Indeed, the team say they could improve their results by up to a factor of 100 with better lab experiments.

Berengut is a member of a team in New South Wales that is famous for discovering the “Australian dipole” – evidence that 10 billion years ago, α was slightly larger near quasars in the southern sky than it was near quasars in the northern sky.

For more about this remarkable observation see this news story, this blog post and this feature article.

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5 comments

  1. M. Asghar

    The dimensionless fine-structure constant α = e^2/hbar.c is the ratio of the electrostatic energy(ESE) between the two electrons with their screened (due to quantum EM flustuations) charges in everyday situation and the exchange photon energy, leading to α= 1/137. When these electrons are brought closer, the screening effect goes down and the ESE should go up, leading to a higher value of α. For an interaction energy between these two electrons > 80 GeV, brought in by the environment or by an accelerator, this α does go up to 1/128. Hence, as rule, this α should vary in time and in place during the evolution of the universe, if the required interaction energy is available at a certain place and at a certain time. The gravitational energy of 30000 times greater than that of Earth, is still too weak to effect its value.

  2. Dileep Sathe

    On the gravitational force
    The above story makes me to refer to a logical point, described in my Letter in Physics Education, India (July-September 2001) regarding the comparison of electric force and gravitational force from the point of view of logic. According to our present notion, gravitational force is a very weak force, compared to electric force. This notion is questionable in view of the following point.
    As a physics educationist, the present comparison of forces is not acceptable because the contribution of electric force has to be absolutely free from the gravitational contribution. But the expected elimination of gravitational contribution cannot be made because every charged body has mass. Therefore I think that the present comparison of these forces is not acceptable. The above logical point deserves our attention as the story claims the effect on the fine structure constant.

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  4. I am surprised that this work did not get much more publicity than it did. If it there had been a shift in the ‘fine structure constant’ then there would be a lot of articles about that. This work possibly shows that there is a rigidity present in this constant which fits in very well with the Einstein equivalency principle. This kind of means that such constants as this are responsible for the current structures that we observe in the Universe and do not change according to location. What may not be comprehended is that the ‘fine structure constant’ and associated coupling constants only run or change near the tremendous very extreme Planck energies that were present at the near instant beginning of the Universe in the fires of the Big Bang and do not change drastically thereafter in the large structure formation (i.e galaxies etc.).The coupling constants probably have not varied since then and stay relatively rigid even in intense gravitational fields of neutron stars and close proximity to black holes.

  5. I should mention that the screening effect and vacuum polarisation cloud of the electron can be changed due to accelerative conditions which can change the value of the ‘fine structure constant’ from 1/137 to 1/128 for example. This is not the same as a changing value due to time and variation in space as many proclaim. It is only a change in the value due to the shift in vacuum energy conditions in nature’s accelerators such as gamma jets, highly heated x-ray emissions etc. associated with extremely local natural objects.

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