10 Questions Science Can't Answer (Yet) - by Michael Hanlon

Author:Michael Hanlon [Hanlon, Michael]
Language: eng
Format: epub
Tags: Science
Published: 2011-01-20T06:00:00+00:00

what is the dark side?

97

If dark matter is terra incognita, then dark energy amounts to the dragons that live there. It accounts for the remaining three quarters of the missing mass-energy account of the Universe.

It sounds like something out of science fiction, vintage Asimov perhaps, yet it seems to be quite real.

Dark energy is a strange force field which permeates all of space, creating a repulsive force that seems to be causing the Universe to expand. It was first mooted by Einstein. He considered it an unfortunate bodge and his ‘greatest mistake’.

Today, physicists agree that something very like Einstein’s bodge, a repulsive force which stops the galaxies falling into each other due to their mutual gravitational attraction, is needed to explain the Universe that we can see.

It may have been Einstein who first hinted at the existence of a mysterious, all-pervasive energy field, but it wasn’t until 1998

that astronomers realized that the expansion of the Universe –actually the expansion of the Universe’s fabric, space–time, in which the superclusters of galaxies are embedded – was slower in the past than it is today and is hence accelerating.

The discovery was made by observing distant supernovae, which can be used as markers of the speed of expansion of far-flung bits of the Universe, just as hydrologists throw brightly coloured balls into rivers to measure the velocity of the water in various streams of the channel. One explanation is that gravity works in different ways at different scales. But it is now accepted that some form of energy is pushing the galaxies apart.

In a Scientific American 2 article in February 2007, the astronomer Christopher Conselice described the essence of dark energy nicely:

The very pervasiveness of dark energy is what made it so hard to recognize. Dark energy, unlike matter, does not clump in some places more than others; by its very nature it is spread smoothly everywhere.

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