Slashdot Mirror
More on the Fine Structure Constant
Bonker writes "Neat news from the Beeb. It turns out that data collected from observation of quasars indicates that the fine structure constant of the universe, aka 'Alpha', may have changed since the universe began. It may have been very slightly smaller than it is right now. The article hints that other constants we're familiar with, such as high, holy 'c', may also vary over time. Of course values can't have changed dramatically, because that would mean that low-weight atoms such as carbon would be unstable, and without carbon, there wouldn't be anyone around to measure the fine structure constant anyway." We ran a story about this last year. It looks like the team has continued to check their work for errors and hasn't found any yet.
c is the speed of light in a vacuum . That's what's been assumed to be a constant.
The speed of light in other materials varies quite a bit. That's what causes refraction to occur. Things like diamonds have a low speed of light (high refraction).
It's not possible to go faster than the speed of light in a vacuum. However, it is possible to go faster than light in some medium.
This actually happens fairly often in nuclear physics. Radiation given off by, say, radioactive waste in a nuclear power plant's storage pool can go faster than the speed of light in water. When it does this, you get the eerie blue glow everyone imagines with radioactivity (which usually isn't really there).
This effect is called Cherenkov radiation, unless I've forgotten how to spell.
It is not possible for any medium to speed up light, so far as in known.
The simplest way to understand why light slows down in a medium is to think of it this way:
Light is zooming along at its full vacuum speed, right? But, there are all these atoms there! Zillions of them! So, light runs into an atom. Luckily for light, the way this works is that it temporarily "charges" the atom, which then almost immediately (but not quite) "discharges" a photon going in pretty much the same direction with the same frequency. Depending on how many atoms there are, and how the atoms behave, this can have varying effects on the light.
This isn't really particularly accurate, but it's easy to understand and more or less vaguely similar to how it works.
Of course, IANAP.
No. c is the speed of light in a vacuum. The slowed light down by passing it through a certain material.
Actually, this is also, technically, incorrect. The speed of light is a constant. Always. Light always moves at light speed. Now, the time it takes for light to pass through various mediums is different, but this is not because the light is being slowed down. It's because the light is hitting the atoms in the medium and is kicking the electrons in the atom to a higher energy state. When the electron falls down from its higher energy state, it in turn release a particle of light. You could go so far as to say that it's the same particle of light. With denser mediums, light takes longer to get through. In the sun, for example, the plasma surrounding the fusion core is so dense, the light from that fusion takes many millions of years to reach the surface. During those millions of years, the light is always moving at light speed. It just keeps running into stuff.
---- El diablo esta en mis pantalones! Mire, mire!
Well C just "happens" to be speed of light in a vacumm but it doesn't bind to light really. 'C' really is just the maximum possible speed period. This can only be acheived in a vacumm with light but there is no such thing as true vacumm. In fact light goes about 75% of C in regular water. So indeed you can go fater than light but not 'C'. So realyl 'light' should not be associated with 'C' for any other reason that it "theoretically" could go the maxim speed. So really "theoretically" many things could go 'C' but many of ours law quickly break down should we break 'C' such as but not limited to entropy (im sorry but oyu cant get more than 100% return of energy). So this is why 'C' is not 'L' for light or something.
unzip; strip; touch; finger; mount; fsck; more; yes; unmount; sleep
alpha is the coupling constant for the electromagnetic force.
In other words, it determines the "strengh" of the electromagnetic force. It is important because
a) it has no units (it's just a number, approximately 1/137)
b) it is easy to measure to a great degree of accuracy
c) it can be measured using a variety of different experiments
d) many fundamental phyiscal constants (such as c - the speed of light in a vacuum, e - the charge of an electron, and h - the Planck constant.
So a change in alpha would mean a change in one of the fundamental constants of physics.
For more information, you can read NIST's wonderful description.
"You have the option of insanity. I do not. And that makes me crazy!" - Brian to Angela, My So-Called Life
They're also gearing up to try some obs w/ the iodine cell in at Keck to really firm up the wavelength solutions.
VLT data would be best though, I agree.
-------- The thought plickens....
(1) The quadrant of the Earth.
(2) The length of a particular metal bar.
(3) The wavelength of a particular atomic spectral line.
(4) The speed of light and the frequency of an atomic clock.
Each change improved the reproducibility of the best length measurements, given the technology at the time the change was made.
The observations that suggest alpha varies are based on comparing wavelengths of light from different atomic oscillations, potential distance standards similar to (3) above. They appear to vary relative to each other. If you want to attribute this to varying c, which one is the reference yardstick?
For our present technology the most reproducible clocks and yardsticks are atomic oscillations. If these lack relative constancy and you choose the frequency of one as your time standard and the wavelength of another as your length standard, you will apparently observe a changing value of c. However, the direction and magnitude of the change will depend on which pair you choose. If we had really independent distance and time standards (and it was clear which was which) it would make sense to consider c an experimental quantity. Since we don't we have just chosen one standard (a particular oscillation of cesium), and c is a defined constant.
Similarly, the electromagnetic quantities "epsilon nought" and "mu nought" were once experimental quantities, but are now by definition exactly {10^7/(4 Pi c^2)} and {4 10^-7 Pi} respectively. This means that the coulomb is no longer defined electrochemically: it is a derived unit, not a fundamental one in the SI system.
As philosophically nice as that would be, this just isn't true. The spacing of atoms and molecules in bulk matter is mediated by electromagnetic forces, but is determined by the solution to the local Schrodinger equation in a periodic potential, and it is not at all straightforward to evaluate this spacing given only fundamental constants and the composition of the material. In particular, the spacing in question definitely does not vary linearly with c.
To take an example from a previous comment, suppose you wanted to express c in terms of the radius of a U-238 nucleus and a Lymann-alpha photon period. Using only first-order effects, the energy of the Ly-alpha photon varies as 1/c. Since h is experimentally determined, we'll suppose it doesn't change (you'd notice immediately if it did), in which case the Ly-alpha period is linear in c.
For the nuclear radius the matter is more complex. For the droplet model it becomes a matter of QCD to determine the effective nucleon radius. If we use the less realistic but easier point-particle non-local-potential model, it depends primarily on the mass of the pion: the volume depends (to rough first order) on c^2, so the radius goes as c^(2/3).
Finally, the measured value of c goes as length over time, so this measurement varies as c^(2/3-1) = c^(-1/3). So you really can't claim that every possible measurement of the value of c is invariant under changes in c, because this one clearly isn't.
Quantum mechanics: the dreams that stuff is made of.