September 2001 Sky from Keeble Observatory

The constancy of the speed of light in a vacuum (usually represented as c = 300,000 km/s, or 186,282 mi/s) is one of the foundation ideas of modern physics. Einstein's Special Theory of Relativity includes this notion along with the constancy of all physical law. Irrespective of any state of motion of the source or observer, it represents an inescapable maximum speed limit for our universe. Isaac Asimov once remarked, that if someone didn't like the fact that you couldn't go faster than c, they should find another universe where the rule wasn't enforced. Science fiction has invented all sorts of fanciful mechanisms to get around this universal maximum, including "warp drive," "worm holes," and "hyperspace."

Now an international research team has found subtle evidence that c may have changed over the 13 billion years since the Big Bang. If their analysis of spectra from distant quasars is confirmed by subsequent work, their work suggests that another unproven theoretical framework known as string theory may be more than just an interesting mathematical exercise. Using one of the 10-meter Keck telescopes in Hawaii, they examined the absorption of quasar light by intervening clouds of gas. In particular, they looked at trace metals like zinc and aluminum, and looked at details in those spectra which depend on another constant, known as the fine structure constant. What they found, by statistical analysis, was that this constant (usually designated by the Greek letter "alpha") is apparently larger now than it was 12 billion years ago. The inference is statistical, only about one part in 100,000, and some theorists suggest that the result may not hold up under further analysis.

What does this have to do with possibly changing the speed of light? The fine structure constant is not itself considered fundamental. It is a combination of several other constants, which appears so often in calculations of atomic spectra that it has been given its own symbol, largely for convenience. One of the constants in the calculation is c, and if we can assume that the other constants (including Planck's constant and the charge on the electron) are really constant, then the change in the fine structure constant could mean that the speed of light has changed by one part in 100,000. The chain of inference is not really as tenuous as it seems - much of science is done by reasoning from theory to plan observation, then using the observations to test and refine the theory. Evolution of fundamental constants as the universe ages is one of the predictions of string theory - so, if this result is confirmed, string theorists will have at least one bit of potential observational support for their work. We'll say more about string theory next month.

Lunar phases for September: Full on the 2nd, 5:43 pm EDT; Last Quarter on the 10th, at 2:59 pm; New on the 17th, at 6:27 am; First Quarter on the 24th, at 5:31 am. Autumnal Equinox occurs at 7:04 pm on the 22nd, as the Sun crosses the equator moving south.

Early evening planet watchers will have to be content with Mars. Mars is fairly low to the south, less than 30 degrees off the horizon. Mercury is very low to the WSW, and will be difficult to find with any haze or ground clutter. Saturn rises about 4 hours after sunset, Jupiter follows a couple of hours later. They make good early morning viewing targets. Saturn is especially nice because the rings are tipped about 26 degrees from the line of sight, making a spectacular 3-D effect with a small telescope. Venus is the brightest object in the predawn. Look with binoculars on the 2nd to see the planet only a degree or so below the Beehive Cluster.

An overhead view at mid-month, approximately 8:30 pm, finds bright Vega at zenith. Deneb to the east, and Altair to the south-southeast mark out the early autumn sky. Our solar system is moving roughly in the direction towards the center of this triangle. The Milky Way arches overhead from northeast to southwest. To the south, where we find Mars, is the direction towards the center of the Galaxy. The eastern sky is largely empty of bright stars, but the northeast sees the rise of the Andromeda Galaxy. The western sky shows a few more stars, with bright Arcturus visible almost due west. The middle of the month is a good time to take out your binoculars and look for some fainter "deep-sky" objects. Without competition from the Moon, you can find the Ring Nebula in Lyra, not too far from Vega. Sweeping your field of view from Vega to Arcturus, a little before you get half way you will encounter M13, a relatively bright globular cluster in Hercules. To the northwest, not far from the end of the "handle" of the Big Dipper, you may see M51, also known as the Whirlpool Galaxy. Sweeping your view along the plane of the Milky Way will reward you with many bright and colorful clusters within our own home Galaxy.