Decline of speed of light?
Paul R. Chernoff
there was decent experimental evidence that the
speed of light had decreased by a few hundred
kilometers per second over a number of decades.
Has there been follow-up to this, one way or the
other? (I would suppose that really solid evidence
of temporal change of speed of light would be
famous...I'd just like to know of further work,
or, for that matter, exactly what was the original
work which I recall only vaguely.)
Uncle Al
Pull a CRC, look at the physical constants that contain c. We can
look back (including spectroscopy) more than 12 billion years.
Lightspeed is invariant.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Alfred Einstead
Uncle Al <Uncl...@hate.spam.net> wrote:
> "Paul R. Chernoff" wrote:
> > Some years ago I read an article reporting that
> > there was decent experimental evidence that the
> > speed of light had decreased by a few hundred
> > kilometers per second over a number of decades.
> look back (including spectroscopy) more than 12 billion years.
> Lightspeed is invariant.
The evidence was actually concerning a change in the fine structure
constant alpha, not light speed. It was widely (mis)reported at the
time in the popular media as evidence for "a change in light speed".
The jury's still out on the question of whether and how alpha is
changing over time.
eb...@lfa221051.richmond.edu
Alfred Einstead <whop...@csd.uwm.edu> wrote:
>
>Uncle Al <Uncl...@hate.spam.net> wrote:
>> "Paul R. Chernoff" wrote:
>> > Some years ago I read an article reporting that
>> > there was decent experimental evidence that the
>> > speed of light had decreased by a few hundred
>> > kilometers per second over a number of decades.
>> Pull a CRC, look at the physical constants that contain c. We can
>> look back (including spectroscopy) more than 12 billion years.
>> Lightspeed is invariant.
>
>The evidence was actually concerning a change in the fine structure
>constant alpha, not light speed. It was widely (mis)reported at the
>time in the popular media as evidence for "a change in light speed".
Even if you interpret the experimental results suggesting a changing
alpha in terms of a changing light speed, you still wouldn't describe
this as "evidence that the speed of light had decreased by a few
hundred km/s over a number of decades," unless "a few hundred km/s"
means "a few km/s" and "a number of decades" means 10^9 decades.
(I know, I know: 10^9 is a number! But it's not what people mean when
they say "a number of" something. And in any case, 0.01 is not "a
few.")
Just to be clear: I'm not disagreeing with anything Alfred Einstead
said, just amplifying a bit on it.
It's possible, I suppose, that what the original poster heard about
was the thoroughly debunked claim by some young-earth creationists
that large changes in the speed of light occurred over human time
scales. This was proposed as a way to get around the problem
young-earthers face of how we can see light from objects that are
further away than the 6000 light-years you should be able to see in
their theories. It's so wrong that even the creationist community has
rejected it. I think the talk.origins FAQ has details.
>The jury's still out on the question of whether and how alpha is
>changing over time.
Indeed.
-Ted
--
[E-mail me at na...@domain.edu, as opposed to na...@machine.domain.edu.]
John Q. Lurker
http://focus.aps.org/story/v8/st9
If not, its an interesting article anyhow.
JQL
John Q. Lurker
J. J. Lodder
It is a well know creationist ploy to have both the observations,
and a 'really' only 6000 year old universe.
The universe merely looks so old
because of the decreasing speed of light, see?
Googling on creation and decreasing speed of light, or young earth,
will give you far more than you will ever want to know.
No reason to take any of it seriously,
Jan
car...@no-physics-spam.ucdavis.edu
> there was decent experimental evidence that the
> speed of light had decreased by a few hundred
> kilometers per second over a number of decades.
> Has there been follow-up to this, one way or the
> other?
As others have said, the claim in question was that
the fine structure constant alpha was slowly changing.
One possible (and controversial) interpretation
of this -- see below -- is that the speed of light
is changing.
The original claim came from a series of observations
of quasar spectra by an Australian group: see Webb
et al., Phys. Rev. Lett. 87 (2001) 091301, and Murphy
et al., Mon. Not. R. Astron. Soc. 345 (2003) 609. The
idea is that various spectral lines depend on the fine
structure constant in different ways, so by comparing
relative line positions in distant quasars to those
observed now, one can see whether alpha was the same
in the early Universe. The Australian group used the
``many multiplet method,'' comparing large numbers
of lines of different elements. This is in principle
highly accurate, but is also quite susceptible to
systematic errors.
A recent set of observations by a different group, using
the same method but a smaller and (it is claimed) more
carefully selected set of sources, found no evidence
of changes in alpha, at a claimed significance that is
higher than that of the Australian group: see Srianand
et al., Phys. Rev. Lett. 92 (2004) 121302. This paper
has a nice discussion of possible systematic errors.
Another paper by Ashenfelter et al., Phys. Rev. Lett. 92
(2004) 041102, argues in particular that the observations
of a changing alpha might be explained by evolution in
the ratio of various isotopes of Magnesium.
The upshot, I think, is that while the question is not
settled, the case for varying alpha looks rather weak.
There is a second issue of whether a variation, if it
exists, can be interpreted as a variation in c. A paper
by Davies et al., Nature 418 (2002) 602, claimed that
considerations of black hole thermodynamics suggested
that the variation should be interpreted as a variation
of c, but their black hole analysis was not quite right
-- see Carlip and Vaidya, Nature 421 (2003) 498. More
generally, there is a strong argument that it doesn't
make sense to talk about the variation of a dimensionful
constant like c; only dimensionless quantities are really
measurable. (See Duff, hep-th/0208093, for a strong
form of this argument, and Uzan and Ellis, gr-qc/0305099,
for a more nuanced version.)
Steve Carlip
backdoorstudent
> Has there been follow-up to this, one way or the
> other?