Via the arxiv Blog, a review article has been posted by the Haensch group with the title“Testing the Stability of the Fine Structure Constant in the Laboratory.” The fine structure constant, usually referred to by the symbol α is a ratio of fundamental constants– the electron charge squared divded by Planck’s Contant times the speed of light (e2/hc)– and usually assumed to be constant. Some beyond-the-Standard-Model theories of physics, though, include effects that could cause this ratio to change over time.

For this reason, people have been looking to see if the fine structure constant is really constant for quite some time. These measurements involve things like the natural nuclear reactor at Oklo and observations of spectral lines in distant galaxies, and their interpretation is highly controversial (despite what some people write).

The new paper is a very nice review of the state of laboratory measurements of the stability of the fine-structure constant. If the constant were changing, this would change the frequencies of light emitted by different atoms, so you can test whether the constant is really constant by (for example) measuring the frequencies of light absorbed by two different elements, waiting a while, and then measuring the same two frequencies a second time. If the frequencies are the same, then α is a constant; if they’re different, then α might be changing.

The possible change is really small– current experiments limit it to less than 0.00000000000000001 per year– but new laser-based experimental techniques make it possible to measure frequencies at the level needed. That number is actually drawn from a laser-based measurement comparing transition frequencies in mercury and aluminum ions. The same techniques might also prove useful as a reference in measuring the frequencies of lines seen in distant galaxies, and thus help settle the question of what those measurements really mean.

The linked article is intended for a conference proceeding, and contains a very nice explanation of the various techniques used to make these ultra-precise measurements. There are also references aplenty if you want more detail about the state of play of the fine-structure-constant business.

Comments

  1. #1 Markk
    April 17, 2009

    So if I’m counting the zeros correctly this means it has changed by less than 1 millionth part in the age of the universe? 10**-17 per year, so 10**-7 per 10 billion years. I think. Using ** instead of ^ so it doesn’t disappear.

  2. #2 Uncle Al
    April 17, 2009

    Set up a Yukawa potential, make the log-log graph, and demand all those alpha-lambda square decades of “undecided” leave the question wholly unanswered. Forever. The answer to theory is more theory, not observation. Look how badly proton decay worked out in Super-Kamiokande.

  3. #3 Brad
    April 17, 2009

    My memory of the high redshift alpha measurements is that they were some discontinuous and plagued with systematics (they maybe biased by early reported results). The last talk on this I heard said that no significant signal was found but, as Chad points out, new metrology techniques will allow observers to really push these measurements.

    The somewhat discontinuous measurement means that lab based techniques do not directly test the result. But of course, the systematics mean that the results may have another explanation.

  4. #4 Ivar Nielsen
    December 29, 2010

    THE INCONSTANCY OF CONSTANTS
    1. Of course the laws of natural cosmic movements and forces and behavior counts everywhere in cosmos. It is just that modern physicians and cosmologists fail to grasp that “everything out and in there” are dynamic and not static.
    2. Varying effects depends only on varying electrical cosmic charges that moves molecular gas and matter, and therefore there are no such things as “fine-structure constants” or other static constants.
    3. The physical and cosmological “laws of constants” is just a result of the modern scientific method, reducing everything fluent in cosmos to specific “scientific” branches of “constant-still-images” of a cosmos that constantly (sic!) changes.

  5. #5 Ivar Nielsen
    December 29, 2010

    THE INCONSTANCY OF CONSTANTS
    1. Of course the laws of natural cosmic movements and forces and behavior counts everywhere in cosmos. It is just that modern physicians and cosmologists fail to grasp that “everything out and in there” are dynamic and not static.
    2. Varying effects depends only on varying electrical cosmic charges that moves molecular gas and matter, and therefore there are no such things as “fine-structure constants” or other static constants.
    3. The physical and cosmological “laws of constants” is just a result of the modern scientific method, reducing everything fluent in cosmos to specific “scientific” branches of “constant-still-images” of a cosmos that constantly (sic!) changes.

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