Worlds Visible and Invisible

March 27, 1994

Seeing may be believing, but now it appears that nature consists of more than meets the eye. Last week, astrophysicists at the Space Telescope Science Institute in Baltimore and the National Optical Astronomy Observatories in Tucson, Ariz., reported a startling discovery that could profoundly alter our perception of the universe -- and indeed our most deeply-rooted conceptions of reality itself.

Using their instruments to peer deep into space, they found that the local group of galaxies that includes our Milky Way is speeding in the direction of the constellation Virgo, apparently drawn by the gravitational pull of an enormous but invisible concentration of matter there.

At present, scientists can only guess on the source of this attraction. For years, astronomers studying the motions of distant galaxies have speculated that the universe may contain as much as 10 times more matter than can be observed through even the most powerful telescopes. This invisible matter has been variously dubbed "missing mass" or "dark matter" to distinguish it from luminous objects like stars and galaxies.

It once was thought that "black holes" -- collapsed stars whose gravitational tug is so strong not even light can escape -- might account for the "missing" mass. Other candidates included dwarf stars, interstellar gases, Jupiter-sized planets or even swarms of massive neutrinos, elusive subatomic products of certain nuclear reactions.

Now, however, it appears that even more exotic mechanisms may have to be invoked to explain the observations. One theory, for example, suggests that the universe is traversed by giant "cosmic strings" -- incredibly massive one-dimensional "seams"

in the fabric of space-time that permeate the cosmos like veins through a rock and around which luminous matter tends to congregate.

Another idea holds the cosmos may actually have 10 or 26 dimensions instead of the usual three dimensions of space and one of time we experience. In this view, most matter is hidden in the "extra" dimensions, which are "compacted," or curled up, in ordinary space on a scale infinitely smaller than the tiniest subatomic particle.

Perhaps the most intriguing notion is that the invisible attracters are not in "our" universe. Instead, they mark "tears" in the space-time continuum through which gravity from other universes "leaks" into ours. In this theory, there are an infinite number of universes that exist "parallel" to our own and whose presence is detected only by the gravitational force they exert.

The implications of these ideas are mind-boggling. They suggest the reality of a vast but invisible physical realm whose existence, until now, was barely suspected. We may be on the brink of a revolution in thinking comparable to that which followed the groundbreaking discoveries of Copernicus, Newton and Einstein. Stay tuned.

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