[Paleopsych] NS: New twist in wrangle over changing physical constant

[Premise Checker]

New twist in wrangle over changing physical constant
http://www.newscientist.com/article.ns?id=dn7285&print=true
      * 15:33 19 April 2005
      * Maggie McKee

    A new study of distant galaxies is adding a fresh perspective to the
    debate over whether a fundamental physical constant has actually
    changed over time. The work suggests the number has not varied in the
    last 7 billion years, but more observations are still needed to settle
    the issue.

    The controversy centres on the fine-structure constant, also called
    alpha, which governs how electrons and light interact. Alpha is an
    amalgam of other constants, including the speed of light. So any
    change in alpha implies a change in the speed of light - and indeed in
    the entire standard model of physics - with string theories touting
    extra spatial dimensions stepping in to fill the breach.

    So it caused a sensation in 2001 when a team led by John Webb, an
    astrophysicist at the University of New South Wales in Australia,
    announced the constant had changed by about one part in 100,000 over
    12 billion years. Webb's team studied about 140 clouds of gas and dust
    that absorb light from distant, bright quasars. Subtle changes in the
    relative position of absorption lines from elements in the clouds'
    spectra suggested alpha had changed over time.

    But another team using higher-quality quasar absorption data, though
    fewer observations, failed to find any change in 2004. And different
    researchers studying a [12]natural nuclear reactor in Oklo, Gabon in
    Africa have also come to opposing conclusions about alpha's constancy.

Slippery customer

    John Bahcall, an astrophysicist at the Institute for Advanced Study in
    Princeton, New Jersey, US, helped pioneer quasar absorption studies in
    the 1960s, but he says this method can be slippery to interpret.

    "The absorption line data is subject to misidentification of the lines
    and to the introduction of theoretical assumptions which may not be
    correct," he told New Scientist. He adds that the spectral lines may
    be faint and can overlap, making it difficult to tell the lines'
    source, and that astronomers must assume that all of the clouds share
    the same basic composition. Similarly, he says, interpreting the Oklo
    data involves making assumptions about other physical constants that
    might be subject to change.

    Now, astronomers have used another method Bahcall developed to probe
    alpha. Rather than using absorption lines from clouds in space, a team
    led by Jeffrey Newman of Lawrence Berkeley National Laboratory in
    California, US, has focused directly on a pair of emission lines from
    ionised oxygen in the galaxies themselves.

    "With emission lines, you can choose systems that have a very strong,
    characteristic appearance and are isolated to be sure you have the
    right objects," says Bahcall. And because the average wavelength of
    the light emitted by the oxygen ions is a direct measurement of alpha,
    he says, "the fine-structure constant pops out without any
    interpretation".

Clean and simple

    However, the new study cannot yet claim the precision of Webb's
    result. Newman's group used observations of 300 galaxies, lying
    between 4 billion and 7 billion light years away, to find that alpha
    has changed by no more than one part in 30,000 - the resolution limit
    of the data - in 7 billion years.

    But Newman says the method is superior to the absorption line
    alternative, telling New Scientist: "It's simpler, it's cleaner, and
    to date people haven't gotten contradictory results from it."

    Bahcall says the team has done an "absolutely superb job" and adds
    that more observations - including more distant galaxies - will
    improve the precision of the measurement still further.

    Newman presented the results, from a survey of distant galaxies called
    DEEP2, at a meeting of the American Physical Society in Tampa,
    Florida, on Monday.

Related Articles

      * [13]13 things that do not make sense
      * [14]http://www.newscientist.com/article.ns?id=mg18524911.600
      * 19 March 2005
      * [15]Speed of light may have changed recently
      * [16]http://www.newscientist.com/article.ns?id=dn6092
      * 30 June 2004
      * [17]Disputed 'building block' of physics is constant
      * [18]http://www.newscientist.com/article.ns?id=dn4844
      * 02 April 2004

Weblinks

      * [19]DEEP2 survey, UC Berkeley
      * [20]http://deep.berkeley.edu/
      * [21]John Bahcall, Institute for Advanced Study
      * [22]http://www.sns.ias.edu/~jnb/
      * [23]American Physical Society meeting
      * [24]http://www.aps.org/meet/APR05/

References

   13. http://www.newscientist.com/article.ns?id=mg18524911.600
   14. http://www.newscientist.com/article.ns?id=mg18524911.600
   15. http://www.newscientist.com/article.ns?id=dn6092
   16. http://www.newscientist.com/article.ns?id=dn6092
   17. http://www.newscientist.com/article.ns?id=dn4844
   18. http://www.newscientist.com/article.ns?id=dn4844
   19. http://deep.berkeley.edu/
   20. http://deep.berkeley.edu/
   21. http://www.sns.ias.edu/~jnb/
   22. http://www.sns.ias.edu/~jnb/
   23. http://www.aps.org/meet/APR05/
   24. http://www.aps.org/meet/APR05/

E-mail me if you have problems getting the referenced articles.