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Peter Macinnis, 7/0/2002,

The shrill babble of Fairfax journos doesn't move me much -- where were they when the real story broke, 12 months ago?  And what makes them confuse the e  in e=mc² with e, the charge on the electron, as the SMH story appears to be doing?

One reporter WAS there, and he got the story from UNSW physicists.   Comments at the end.

*********

Is the fine structure constant changing? (August 2001)

An international team of astrophysicists from the University of New South Wales and others from Britain and the USA have raised the possibility that the fine structure constant (alpha) might have changed slightly as the universe got older. This is the conclusion they have reached from spectroscopic studies of gas clouds that lie between us and distant quasars.

The value of (alpha) is equal to e²/hc, where e is the value of the charge on an electron (or a proton), h (more correctly, 'h-cross', the letter h with a line through it) is one way of stating Planck's constant*, and c is the speed of light.   For this constant to be changing, one of the values would also need to change, and most of the comparatively few media accounts tended to follow the lead of the New York Times, which suggested that it was the speed of light which was changing, but physicists say this is the least likely of the three 'constant' values to change.

But first, a quick look at the technical details: the researchers examined ancient light being re-emitted from ancient (and more distant) gas clouds, and compared what they saw with light being re-emitted from nearby and more recent gas clouds. They then corrected their data to allow for the redshifts caused by the movement of the gas clouds, and examined the spacing of doublets of absorption lines in the spectra of a variety of different atoms in the dust clouds. These gave a steady result: a consistent shift in alpha with increasing redshift, especially where z>1.

The news broke almost two weeks before the official date of the print publication in Physical Review Letters, but raised remarkably little interest, in part, perhaps, because a number of physicists suggested that there might be other explanations (which they left carefully unspecified). The authors identify 13 potential systematic errors that could have produced the result, and indicate that most of the possible false causes may be ruled out. The only two that cannot be ruled out should have produced smaller values of alpha, not the larger values that are being detected.

For example, one possible systematic error, caused by a wrong alignment of the spectrograph slit would, if it had occurred, have reduced the observed effect, not increased it, and they comment that:

"We summarise and stress the following important points regarding potential systematic effects: (i) a thorough investigation reveals no systematic effect which can produce the results we report. (ii) Furthermore, applying either of the 2 significant corrections would enhance the significance of our results."

Putting it another way, the value of alpha is very close to 1/137, and the measured change is about 1 part in 100,000, while there remains a chance of around 1 part in 10,000 that the observed effect is a statistical fluke. That means the probability that the effect is real is 99.99%, fairly good odds.

So whatever they have captured here, it would appear to be significant, and that probably means that one or more of the values that physicists regard as constant does in fact change over time. So how do people go about looking into the past, to assess what the value of the fine structure constant should be?

Quasars shine with the sort of intensity you expect from a whole galaxy, but they appear to be 'tiny' - about small enough to fit inside the orbit of Mercury, and that makes them an extremely small and bright point-source of light, when they are seen from any distance. The other key feature of a quasar is that they have a continuous spectrum, emitting at all wavelengths.

When you shine a continuous spectrum through a cloud of gas, some wavelengths are absorbed, and as Robert Bunsen and Gustav Kirchhoff knew almost a century and a half ago, the wavelengths that are absorbed are exactly the same wavelengths that would be emitted if the same atoms were 'excited', given extra energy. The effect is slightly varied if the gas is whizzing away from us, due to the effects of redshift.

Now the lines are also divided up, with small variations either side, and the extent of this shifting is proportional to the fine structure constant. (Note that this is a deliberately non-mathematical account of a complex issue.) The redshift of radiation depends on how old it is, so we can determine the age of each quasar, and we can also look at the extent of the shift away from the central line. So if the extent of the shifting differs with age, this would be a good reason to argue that the fine structure constant was changing. It may not be a sufficient reason, but it is certainly a good reason.

The sample looked at the quasars covering a period from 23% of the age of the universe up to 87% of the age of the universe, using measurements made on the Keck telescope's HIRES spectrograph at Mauna Kea on Hawaii, with observations being made on frequencies associated with iron, zinc, magnesium, chromium and other metals in the clouds, and the results for all the measurements showed a consistent trend.

The fine structure constant is the fundamental constant of electromagnetism, and may be thought of as a measure of the inherent strength of the electromagnetic force. In the past, others have explored the possibility of what are known as secular changes in fundamental constants, but the previous cases have all been explained away by other means - which is perhaps part of the reason why physicists have not been carrying on too much about the result so far.

So what does it mean if the value of alpha has been shifting slowly with time? The fine structure constant explains how electromagnetic forces hold atoms together. There are certain stable orbitals around atoms, and there is a very precisely known amount of energy that an electron needs to absorb when it jumps from one orbital to one with higher energy, and the same amount of energy is emitted when the electron drops back down again. Now it seems that, in the past, this amount of energy may have been slightly different.

This means that physicists would need to go back and revise the 'standard model', if, as the evidence seems to suggest the value of alpha has increased by even a tiny amount. The people who will gain most from this are those who hold that string theory is valid, because this theory holds that there are many more dimensions than time and the three dimensions of space that we can see, and if these are real, they could account for the value of alpha increasing.

It is lucky for us that the increase, if it is real, is small, because if the value of alpha had increased too much, carbon atoms could not be stable, and life forms like us could not exist.

*Note: h-cross or h-bar is actually Planck's constant divided by twice the value of pi. The value of the fine structure constant alpha is normally given in units which need not concern us here, because if h-cross is changing, then so is h-bar.

Key names: John K. Webb, Michael Murphy, V. V. Flambaum and V. A. Dzuba of the University of NSW, John Barrow (Cambridge), Chris Churchill (Penn State), J. X. Prochaska (Carnegie Observatories) and A. M. Wolfe (UCSD). It is worth noting here that Michael Murphy is just six months into his PhD studies, and already has his first publication in the world's leading specialist journal.

Our source for this is Peter Reece, also at the same stage in his PhD studies, and second author in a paper which appeared in Nature for August 23, a story described in  “The glowing photovoltaic cell”, this month. Peter and Michael have known each other since they were 12, when they were at the same school, St. Columba's High School at Springwood, in the Blue Mountains to the west of Sydney. Is there something in the mountain air, or is it special teaching? All we can ascertain from the school is that both students were always keen on their mathematics and science, and there was an enthusiastic staff.

**********

Basically, the Davies, Davis Lineweaver paper argues that if e is changing, then the second law of thermodynamics would be violated (but on a cosmic scale, not a nano scale).  For some reason not stated, they seem to reject the possibility that Planck's constant may be varying.

It looks kosher (and I am in no position to argue with people of that calibre in any case), but it is no paradigm shift as hailed by "The Age".  If there was one, that happened last year.  This is a reasoned opinion that shows the consequences of previous assumptions.  More later . . .
 

Well, Paul Davies was named as the contact, but he is in the UK, so I
rang Charles Lineweaver, and got John Webb who did the original
research, and Charley later.

They ruled out Planck's constant because current models do not allow
for it to change, then they ruled out changes in e, because that makes
a mess of 2LT, and that left c, which does, after all, change in
different media.  Maybe the dielectric constant of the vacuum changes
 

I am beginning to run into time trouble, and don't like to hassle them for that at this stage, but the answer is no -- they have had the results for several years, and still don't know what to make of them.  I may have a chance next week to ask.

I am getting mightily tired of air-heads demonstrating their scientific acumen by babbling to the camera that e equals mc squared, and this led to the bomb.  Most of them couldn't tell mc squared from M C Hammer.

When was a nuclear bomb first mentioned?  1913.

When was an atomic/nuclear powered rocket first mentioned?  1906.

Peter

Jim Edwards added
 

>They ruled out Planck's constant because current models do not allow
>for it to change, then they ruled out changes in e, because that makes
>a mess of 2LT, and that left c, which does, after all, change in
>different media.  Maybe the dielectric constant of the vacuum changes
>. . .

Stars also have an electromagnetic field, what effect does this have on  light?

Jim

Chris Lawson replied
 

Jim, the observations did NOT measure the speed of light directly. They
looked at the light from a distant quasar and examined its absorption
spectrum. Which means that the findings are already based on the effect of
the light travelling through gas clouds. What they discovered was that the
light was abosrbed in such a way that it appears that the physical
behaviour of gasses has changed since way back when. This particular
property is determined by what is known as the fine structure constant,
which is actually dependent on Planck's constant, the quantized electrical
charge, and the speed of light. For various reasons, the Australians have
argued that the only one of these constants that is likely to have changed
is the speed of light.

The following makes for some interesting reading.  Perhaps a little worrying.

http://theage.com.au/articles/2002/08/07/1028157961167.html

What bothers me a little is that unless we work out the whys of this things could pass a critical point anytime and the universe could just "stop working" - at least in a manner which supports intelligent life.

At least it bugs off inflation.

Interestingly it gives some clue as the the future of the universe.  If light continues to slow, then the amount of energy stored by mass (as mass) decreases.  Will "solid objects" eventually become ghosts?

Trouble is, shouldn't light be getting faster, not slower?  If light speed limits and mass are constrained/artifacts of the quantum foam, then light slowing suggests that the quantum foam is getting busier. If the energy in e=mc² is to remain constant, then mass must increase.  If e lessens with c, then where does the energy go?

Arrgghhh!
- --
Zero Sum
 

Here's my take on it.

 From http://members.ozemail.com.au/~claw/frankenblogger.htm

Is the speed of light slowing down?
8 AUG 2002 | source Nature
Australian astronomers Paul Davies, Tamara Davis, and Charles Lineweaver
have examined light from a distant quasar and interpreted as showing that
the way light is absorbed by electrons in interstellar gas has changed
since the time of the early Universe. The absorption of light is determined
by a physical constant known as the fine structure constant. Since the fine
structure constant is derived from other more fundamental constants, any
such change must be due to variations in in the value of electrical charge
of electrons, Planck's constant, or the speed of light. The authors have
rejected the possibility of changes in electrical charge or Planck's
constant as these could lead to violations of the Second Law of
Thermodynamics - but as we have seen, the Second Law is not a fundamental
physical law, it is a statistical outcome, and if the rules of the game
have changed then the Second Law may go with them.

The authors' work is based on observations from a single quasar and has yet
to be analysed by other astronomers, so it remains highly speculative. This
blogger's skeptical alarm bells are ringing, partly because of the
staggering implications of the interpretation, partly because it has yet to
be verified, and partly because it has eerie echoes of Young-Earth
Creationist attempts to dismiss radioisotope dating by claiming that the
speed of light has been slowing. The Creationist interpretation was pure
fantasy - in fact it had to be retracted by the journal that published it
when it was shown that the evidence had been presented in a highly
selective manner (that is, the authors reported historical estimates of the
speed of light that suited their hypothesis, ignored estimates that did not
agree, and did not report the error bars for the studies they included).
The study in Nature does not share any of this Creationist dishonesty, and
it certainly doesn't support the hypothesis that the Universe is only a few
thousand years old, but without doubt it will be trotted out by clueless
Creationists as further evidence for their delusions.
 

regards,
Chris Lawson

> -And IF we work out the whys of this we might be able to fix it? :-)
> Changing the speed of light throughout the universe sounds a tad
> difficult..

Zero responded

It would be nice to know the order of magnitude of the lifetime of the universe.  It would be nice to know that it will still be there and support life in a few thousand years.

If the velocity of light is tied to the density of the quantum vaccum and the energy in the vaccum foam is finite, well, it looks like we want to know that to me because the expansion of the universe is occuring in at least three dimensions so the change in the speed of light will accelerate (based on the third power).
 

> The short answer to the question is that the speed of light is
> determined by the electromagnetic properties of the medium in which
it's
> propagating.  In the absence of a medium, it's determined by the
> electromagnetic properties of the vacuum.

Hi Sue,

And I'd like to know - how long is a photon?

In other words, from the its length and speed we should be able to calculate how much time it takes for an individual photon to travel past a point.

And, as I asked on this list many years ago, why does light speed up again when it emerges from a diamond where it was travelling at less than half its speed in vacuum?

Cheers

Geoff
 
 
 

Peter answered

Which is why all the BS about "Einstein wrong" is such crapulous garbage.  Aside from the fact that the tabloidoids thought the variable e (charge on the electron) in the fine structure constant was the well-known variable e (energy) in e=mc^2, all it takes is a slight variation in the dielectric constant of the vacuum, and all is explained. (That, BTW, is what I had from one of the authors, filtered through my weak grasp of the details.)

Everybody knows that LOTS of things were different close to the Big Bang -- but in the period under study by Webb, Barrow, Murphy et al., everything should have been settled down.

I say again: the speed of light often changes, the speed of light in a vacuum is constant -- now it appears that maybe the vacuum is not constant.  That is interesting.

At 10:03 12/08/02 +1000, Sue Wright wrote:
>I know I'm a simple soul ... but what do people mean when they say light
>travels at such and such a speed and that the speed is a constant?
>
> From what point is light measured?

The speed of light generally refers to the speed of light in a vacuum. In other media, such as air or water, light slows down. However, it must be pointed out that this is not because the photons that make up light go any slower, it is because the light is bouncing around inside the material.
Transparent materials have the amazing property that light can bounce around inside, like a carefully-designed pinball machine, and come out the other side relatively unaffected. (Please excuse the mangled analogy, but it's important to realise that the slowing of light in glass/water/air has nothing to do with relativity and everything to do with quantum mechanics, and so it is not relevant to the question about light speed being a constant.)

According to Special Relativity, light moves at a constant speed for all inertial frames of reference. This means that if two people are travelling in spaceships that are inertial (ie not rotating or accelerating), then all the photons they observe will travel at c -- even if the two spaceships are moving at high velocity relative to each other. This is counter-intuitive, but it works.

To answer another question: how long is a photon? Well, that question doesn't really make sense in relativity. In relativity, photons are treated like point sources; that is, they have no width, length, etc. To answer the question, one has to look at quantum theory. In quantum theory, a photon's length is its wavelength. This means that, in principle, a photon with a long wavelength takes longer to pass a given point than one with a shorter wavelength. Since there is no theoretical upper or lower limit on the wavelength of light, then the question about how long it takes to pass a point can only be answered for a given photon, and not for all photons in general. But even then it gets tricky. Quantum theory doesn't like absolute spatial points (it is the opposite of relativity in this regard), so when you talk about a photon passing a point, it can only be a theoretical point. Any "real" point will be made up of atoms or other quantum particles, and quantum particles cannot be pinned down with certainty.

Unfortunately, questions like "how long is a photon?" are usually asked by people who have the Newtonian physics in their head. It's not that it's a silly question, because it illustrates the difference between the Newtonian world-view and the quantum world-view, but it is a question that is not as easy to answer as "how long is a train?", which can be measured by knowing its speed and timing it as it goes past a fixed observation point. In quantum theory, we know the speed of the photon very well (it is always c), but what is not easy is getting the fixed observation point.
 

regards,
Chris Lawson
 
 

Sue said

Ah ha - I think I'm much clearer.
Part of my confusion was/is around the notion of 'the constant'. That is,
how different people (in reading matter) explained light seemed to suggest
that it was constant under certain conditions, as P. suggests - the vacuum.
Therefore to me, the vacuum or  something like the fixed observation point,
as C. puts it, is the constant.

I shall now let go of the notion of light travelling from one given point
to another - as it makes more sense to me to think of it as bouncing off
the walls (so to speak).
 

A. David Martin replied

Hi Sue, Geoff and any others interested,

I'll have a go at this one :-)

In answer to Sue's original email, the speed of light (which, in vacuum, is given the symbol c) can quite easily be measured with some modest equipment. By turning a light source e.g. solid state laser or LED, on and off very quickly (e.g. 10 ns can easily be achieved) and measuring the time taken for the light pulse to travel a known distance (e.g. 100 m is obtainable by bouncing it back and forth between two parallel mirrors), c can be measured to within a few percent of the defined value.

There are much more accurate ways of measuring c; in fact it's value can be measured to such great precision that
it's actually *defined* to be 2.99792458 x 10^8  m/s (in case you needed to know this sometime :-)

What's really interesting about c is that it's value remains the same, regardless of the speed of the source or observer. E.g if someone in a spaceship fired a flash of light towards you, you would still measure the speed to
be c, regardless of the speed or direction of the spaceship. This rather peculiar fact is the basis for the theory of relativity and is why c is said to be "constant".

Nobody knows where c actually comes from (or, indeed, any of the other physical constants such as G or h). It's
widely assumed that c is a property of the vacuum. I can't think of any reason why c should not have changed over time, but any such change would have to be extremely small between now and a few billion years ago otherwise the distant universe would look very different from the way it does.

Geoff asked about light in matter which is, in general, quite a complicated business (see, for example, Feynman's little masterpiece "QED, the strange theory of light and matter" ). However, photons always travel at speed c.
When they interact with atoms or molecules they are absorbed and then re-emitted after a very short time delay.
It's this delay which effectively slows light down.

Geoff also asked "how long is a photon?". This is an even trickier question. To give a direct answer would be to
assume that photons are like little bullets, but quantum particles are not like that at all. In the "two slit
experiment" one photon appears to somehow go through both slits to give the resulting interference pattern. There is also the problem of the Heisenberg principle, which limits the precision with which the position can be
measured to something in the order of a wavelength. I don't think this question is meaningful unless put into the
context of a better model for quantum particles than we have now; you could be asking, for example "how long is a wave?"

Hope some of this is of use.

Regards,

David.

Peter Macinnis added:

> Recent evidence is that for the past 6 billion years of so, the speed of
> light in a vacuum, has been a constant (within the error of the best
> experimental evidence we have to date), and that IF the data concerning
> variations in the fine structure constant are confirmed and IF Paul Davies
> theoretical treatment is correct, THEN between 6 and 10 billion years ago
> the speed of light was different from today's by 7 parts per million.

Having talked with several of the players in and around that paper, what we have is a fine structure constant that appears to have changed. Three things go into that: Plank's constant, e, the charge on the electron (NOT the e in e = mc-squared, as the Sydney Morning Herald and ABC had it) and the speed of light.

For a variety of reasons (it's more interesting in the predictions it leads to, it doesn't violate the Second Law of Thermodynamics), they decided the speed of light was the best candidate to target.

Note please, how this differs from saying "the speed of light is changing", or "Einstein lied".

Note also that even though we know Einstein is mire reliable than Newton, when we go to the moon, we use Newtonian physics and don't say "left hand down a bit to allow for Einstein" -- we don't need it.