Adam G. Riess and Michael S. Turner via Scientific American: The Expanding Universe: From Slowdown to Speed Up.
From the time of Isaac Newton to the late 1990s, the defining feature of gravity was its attractive nature. Gravity keeps us grounded. It slows the ascent of baseballs and holds the moon in orbit around the earth. Gravity prevents our solar system from flying apart and binds together enormous clusters of galaxies. Although Einstein’s general theory of relativity allows for gravity to push as well as pull, most physicists regarded this as a purely theoretical possibility, irrelevant to the universe today. Until recently, astronomers fully expected to see gravity slowing down the expansion of the cosmos.
In 1998, however, researchers discovered the repulsive side of gravity. By carefully observing distant supernovae—stellar explosions that for a brief time shine as brightly as 10 billion suns— astronomers found that they were fainter than expected. The most plausible explanation for the discrepancy is that the light from the supernovae, which exploded billions of years ago, traveled a greater distance than theorists had predicted. And this explanation, in turn, led to the conclusion that the expansion of the universe is actually speeding up, not slowing down. This was such a radical finding that some cosmologists suggested that the falloff in supernova brightness was the result of other effects, such as intergalactic dust dimming the light. In the past few years, though, astronomers have solidified the case for cosmic acceleration by studying ever more remote supernovae.
But has the cosmic expansion been speeding up throughout the lifetime of the universe, or is it a relatively recent development— that is, occurring within the past five billion years or so? The answer has profound implications. If scientists find that the expansion of the universe has always been accelerating, they will have to completely revise their understanding of cosmic evolution. But if, as cosmologists expect, the acceleration turns out to be a recent phenomenon, researchers may be able to determine its cause—and perhaps answer the larger question of the destiny of the universe—by learning when and how the expansion began picking up speed.
Expanding Universe
ReplyDeleteAccording to popular theory in Cosmology, the univers had an inflationary period (first 400,000 years maybe) followed by a period when the expansion rate was slowing down due to dark matter (up to 6 billion years ABB) followed by the an inflection point where the current period is dominated by dark energy and the rate of expansion is accelerating (up to now). This data was obtained by mapping out the Cosmic Background Radiation with the W-Map satellite.
Although, then when you look at this Chart Showing the Composition of the Cosmos, that's enough to shake up my confidence in the Big Bang Cosmology a little bit. There must be something that accounts for the observed phenomina that can be tested in a laboratory setting, and I'm not talking about Perpetual Motion. Where is my inflationary "faster than light" jetpack, and where is my Dark Energy powered flying saucer!?
Perhaps there is some validity to some (but not all) of the claims in the Electric Universe. Or perhaps it really truly can be explained away as Dark Matter, Dark Energy, Strange Matter, and Twister Field-Superstring Theory. Oh well, probably should wait for the outcome of the Large Hadron Collider experiment to find out what things things are missing then.
The Stability of Penta-Neutronium (1988)
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