Mysterious "Dark Energy" Grips Universe

Not something from "A Wrinkle in Time", this is a real thing. Very interesting!

Wall Street Journal
May 21, 2004
Science Journal
by Sharon Begley

Universe's Big Events May Help Shed Light on the Smallest Ones

Poets and dreamers have long yearned to "see a world in a grain of sand," as William Blake put it, but physicists and cosmologists have an even grander aspiration.

As physicists try to identify and understand the most fundamental building blocks of the material world, and as cosmologists explore how the universe began, each group is finding some of the best clues in the other guys' realm. This meeting of quarks and cosmos, says physicist Shamit Kachru of Stanford University, Palo Alto, Calif., "is probably the most exciting theme in physics and cosmology today."

The quarks-and-cosmos approach has worked before. In 1973 a young physicist, Edward Tryon, floated the audacious idea that behavior observed in the subatomic world might have brought the universe into existence 13 billion years ago. Quantum physics, which describes electrons and quarks and other fundamental particles, had found that even in empty space, particles can pop into existence, albeit fleetingly. What if, Prof. Tryon asked, the universe sprang from just such a quantum fluctuation that, well, got out of hand?

Perhaps, he wrote, our universe is just "one of those things that might happen from time to time." His speculation became the basis for what is now the leading theory (well supported by astronomical observations) of how the universe was born and evolved.

In the latest convergence of large and small, scientists using NASA's orbiting Chandra X-ray telescope confirmed this week that the universe is in the grip of a mysterious "dark energy." Although scientists don't know what dark energy is, they can measure what it does: It acts as a sort of antigravity that makes the universe even friskier than thought. Instead of expanding sedately from shortly after its moment of creation some 13 billion years ago, the universe is accelerating ever faster thanks to dark energy.

As cosmologists rack their brains for where dark energy came from, some are thinking small. Dark energy, they suggest, may leak out from the hidden dimensions posited by the latest pet proposal from subatomic physics, string theory.

String theory envisions the material world as made of infinitesimally small strings, either loops or snippets. Like a violin string that can produce different notes, these strings, too, emit different notes depending on how they are excited. Each note is a different elementary particle, such as a quark or an electron.

Not ones to let their imaginations stop there, string theorists posit that there are unseen dimensions in space. Besides length, width and depth, there are an extra six or seven, curled up so tightly they are undetectable. It's like seeing a garden hose from far away. The hose seems to have only length and width; its depth becomes visible only close up. Space, say string theorists, might similarly harbor unseen dimensions, visible only on the tiniest scale.

That claim, for a scientific theory, is like going around with a "kick me" sign on your back -- it invites derision and abuse. Since it's hard to imagine how such dimensions might be detected, critics dismiss string theory as more untestable metaphysics than provable physics.
But a growing number of physicists think the hidden dimensions may be detectable after all. "The additional dimensions of space-time," says physicist Eric Linder of Lawrence Berkeley National Lab, Berkeley, Calif., "might give rise to dark energy."

Going back to the garden hose, water pouring out of a flat strip of plastic would seem utterly impossible. But if you saw a gusher, you would realize that the hose is three-dimensional, not two. In much the same way, dark energy gushing out of what seems to be three-dimensional space "might be evidence of these additional dimensions," says cosmologist Michael Turner of the National Science Foundation. Studying the dark energy more closely might provide hard evidence of those hidden dimensions.

Last week, during a conference at the Stanford Linear Accelerator Center in Palo Alto, physicist Richard Easther of Yale University, New Haven, Conn., suggested another way to probe the cosmos for evidence of strings and hidden dimensions.

Strings, he believes, might leave tiny ripples in the cosmic microwave background. This radiation, which bathes the entire cosmos, is interpreted as the fading whisper of the "big bang" in which space, time and the universe were created. Strings, says Prof. Easther, might cause the observed hot and cold spots in the radiation to deviate from expectations by 1% or so.

Studies of the universe might also test another odd prediction of string theory. Matter comes in indivisible chunks, such as quarks and electrons. As far as we know, there is no such thing as half a quark or one-third of an electron. String theory says space, too, might be chunky. "You would reach a point where space can't be sliced up any further," says Prof. Easther.

In that case, everything in the current cosmos arose from a space of finite-though-tiny size back when the universe was in its infancy. "Some memory of this would be maintained" in the structures and cosmic radiation we see today, says Prof. Easther. Blake, it seems, was more right than he knew.