October 2001 Sky from Keeble Observatory

Last month we promised to discuss "string theory" - one of the current attempts to produce a "theory of everything." The challenge facing physicists is daunting. We have two very successful theoretical foundations on which most of the structures by which we explain the universe can be built. General Relativity (GTR) is essentially a theory of gravity, and describes beautifully the large-scale structure of the universe. Quantum mechanics (QM) is a theory of the very small, and gives us our description of atomic, nuclear, and elementary particle processes. The problem is, the two descriptions cannot be reconciled!

GTR allows us to express gravity as a curvature of the manifold of space and time, and to describe its effect on objects at every point in space-time. QM tells us that, fundamentally, it is impossible to describe what happens at a particular point. Something known as Heisenberg's Uncertainty Principle, which should probably be called the "indeterminacy principle," tells us that if we know the position of a particle precisely then we will not be able to describe its motion, and vice versa. QM permits a description of fundamental particles like the electron, which have mass and charge and spin angular momentum. GTR describes the collapse of massive objects to point-like "singularities" deep within the event horizon of a black hole. GTR cannot describe an electron, and QM cannot describe a black hole, but both kinds of object are found in our universe.

String theorists seek to solve this problem by supposing the existence of elementary loops of "string" which would be the fundamental building blocks of all matter. Different vibrational states of these strings would represent the various fundamental particles we know of. Imagine a circular violin string - each "note" played on the string would be perceived as a unique particle in nature. In order to account for all the properties we need to describe, these strings vibrate in all three familiar spatial dimensions, as well as in some others which are described as being curled up so tightly that we are not able to perceive them at all. Depending on the particular flavor of string theory you are using, the number of these "hidden" dimensions can be anywhere from 6 to 9.

It is probably safe to be skeptical of the ultimate correctness of these theories, yet they have a certain appeal. They naturally merge GTR and QM, and they provide a handle on why the current formulations don't speak the same language. Equally intriguing, string theory seems naturally to build in the elusive exchange particle required for a quantum mechanical description of gravity. To read in more detail about string theory, I recommend Brian Greene's book, "The Elegant Universe."

Lunar phases for October: Full Moon on the 2nd, at 9:49 am; Last Quarter on the 10th, at 12:20 am; New Moon on the 16th, at 3:23 pm; First Quarter at 10:58 pm on the 23rd.

Evening planet watchers will start with Mars, which is fading but still visible to the south at sunset. Saturn will make an appearance on the eastern horizon about 3 ½ hours after sunset at the beginning of the month, only about 2 hours after sunset at the end of the month. Jupiter rises about two hours later. Jupiter, Saturn, Venus, and Mercury are all visible in the pre-dawn sky.

An overhead view at midmonth, approximately two hours after sunset, finds the constellation Cygnus, with its brightest star Deneb almost at zenith. The Milky Way divides the sky from northeast to southwest, with Cygnus aligned with the plane of the Galaxy. Vega is to the west of Deneb, with Altair towards the south-southwest. This bright triangle overhead marks the beginning of autumn and the approach of winter. The lopsided square shape of Hercules lies between Vega and the WNW horizon. Between Vega and the eastern horizon is the wider great square of Pegasus. Just to the north of Pegasus you may notice on a clear night the faint glow of the Andromeda galaxy, nearly 2 million light years distant. It will be about 45 degrees off the horizon, roughly ENE. Below Pegasus is the wide, faint V shape of Pisces. This part of the sky is largely empty of bright stars, because we are looking up and out of the plane of the Galaxy. The center of the Galaxy is to the southwest, in Sagittarius, while the direction in which the Sun is orbiting is towards Cygnus, overhead.