By Tom Siegfried / The Dallas Morning News
Beyond the Unverse
In a sense, the universe is like Jonathan Swift's flea.
On a big flea prey smaller fleas, Swift wrote, "and these have smaller still to bite 'em; and so proceed ad infinitum."
Humans understand the universe in a similar way. Except instead of always a smaller flea, there is always a bigger space.
Everything is made of atoms - mostly empty space, with tiny particles buzzing about a dense core. From atoms are built planetary systems - a grander empty space with little objects flying around a big one, a star. Stars themselves are mere particles in huge clouds of galaxies, and galaxies in turn are mere particles within the immense empty space of the universe - supposedly, all there is.
Yet on the eve of a new millennium, science's view of everything is on the edge of transformation. The universe itself, many experts now believe, is just one particle in a new kind of space, previously unknown and unimagined.
It's not a space that people can see, any more than an ant crawling on a book's cover can read the chapters inside. If it exists, this mother of all spaces is in fact a new dimension, a realm beyond visualization in which many whole universes might reside.
In other words, maybe Rod Serling was on to something. But this new view of space has nothing to do with TV science fiction. Rather it may signal the most dramatic revision in humanity's conception of the cosmos since Copernicus.
Half a millennium ago, Copernicus pictured the universe as what we now call the solar system - the sun in the center, the stars on the outer edge. As the centuries passed, astronomers realized that the stars were like the sun, all part of a huge cloud called the Milky Way galaxy. Only in the 20th century did astronomers discover that the galaxy was not the whole universe, and that billions of additional galaxies lurked in a space much vaster than Copernicus could have dreamed.
And now, just as the millennium marks its final year, explorers of the realms beyond sight and sound have begun to suspect that the entire known universe sits within a grander, virtually unfathomable space.
"There's really a change in our thinking about what the possibilities
are for the way that the universe could be put together," says
physicist Joe Lykken of the Fermi National Accelerator Laboratory
in Batavia, Ill.
In the old days, like a decade ago, scientists scoffed at questions about what's outside the universe. The universe is all there is, they insisted. You aren't allowed to ask what's outside. That question made as much sense as asking what's north of the north pole, or who won the World Series in 1994. There's nothing north of the pole, the players went on strike in 1994, and there's no space "outside" of space itself.
Physicists had, however, contemplated dimensions beyond the three of familiar experience. All objects have three dimensions - length, width and height. And any object's position in space can be identified with just three numbers - latitude, longitude and altitude, for example. You can describe any movement using a mix of just three directions - forward-backward, left-right, up-down. In other words, space possesses three dimensions. The world would seem to make no sense with more or fewer (not counting time, commonly referred to as the "fourth dimension").
But nature might have hidden away, at subatomic size, some extra dimensions too small to be noticed, physicists noted as early as the 1920s. By the 1980s, it seemed that those tiny dimensions might supply the missing ingredient in the math describing matter's basic particles and forces. The extra dimensions could not be directly detected, though - they were supposed to be as much smaller than an atom as a flea is smaller than a galaxy.
Physicists now wonder, however, whether the extra dimensions must really be so tiny. At first glance it seems they must; a big extra dimension would alter the law of gravity. But precise tests of gravity's strength extend down only to distances greater than a flea's width. An extra dimension could, in fact, be perhaps as large as a millimeter across, and nobody would have noticed.
Except for one problem - fleas don't disappear into unseen
dimensions. If other dimensions do exist, nobody is allowed
to go there. The familiar universe of three dimensions, in
other words, would be a very big prison. Physicists have a
name for such a prison. They call it braneworld.
Here is the idea of the next millennium - the universe is a brane. It's a term derived from membrane, a two-dimensional surface like the outer surface of a soap bubble. Since the known universe has three dimensions, it's called a three-brane.
In the picture that some scientists are now developing, all ordinary forms of matter and energy are confined to the surface of the three-brane universe. Matter, light, radio waves, magnetism, all operate only on the three-brane's surface - that is, in the universe's three familiar dimensions of space. Nobody can see outside this universe because light can't go there.
But the whole three-brane universe can fit into an extra dimension, even one a mere millimeter wide. Because in the extra dimension, the universe is very skinny.
Think of the ant on a page of a book. The page has, to all appearances, two dimensions - width and height. Both width and height extend for several inches. Yet rip the page out of the book, and it could fit nicely in a file space a mere millimeter wide, because the paper has an extra dimension, thickness, too thin to be noticed by the ant.
In a similar way, the whole universe can have an extra dimension, too thin to be noticed by its human inhabitants.
Countless other ultrathin three-brane universes could also fit into a millimeter-wide dimension, tucked in a stack like pages in a file folder.
And that would make the universe really interesting.
Take the pages out of the file folder and place them flat. How does the ant wandering over the top page know whether there are parallel-world ants living on the page below? The ant can't see through the paper, just as humans can't see outside their own three-brane universe. But people could detect the effects of gravity in a parallel brane. Gravity is not imprisoned in braneworld.
Since gravity distorts the shape of space, an ant noticing a bump in the paper could deduce, without seeing through the page, that the next one down was also inhabited. In the same way human telescopes could detect distortions in space caused by massive objects inhabiting a parallel brane - black holes, perhaps, or even ordinary stars. Such objects would be invisible, yet exert a gravitational influence on objects that could be seen.
This is precisely the sort of thing astronomers have been noticing for decades. Some source of gravity affects how galaxies spin and how fast they fly away from one another. Closer to home, the light from distant stars appears to be distorted by gravity from invisible intervening objects. Scientists have assumed such effects are caused by "dark matter," unseen because it doesn't shine like ordinary stars. But it may well be that the matter is unseen because it lies beyond human view, in a parallel universe a mere millimeter away.
All this is fantastic enough. But somehow a new dimension a silly millimeter wide does not seem so dramatic in the cosmic scheme of things. It turns out, though, that the millimeter-wide dimension may have just been one small step toward a giant leap in mankind's understanding of the true extent of the cosmos.
On the cosmological menu at millennium's end are proposals more dramatically different from current thought than the Copernican sun-centered universe was from the Ptolemaic system, with the Earth in the middle of everything. All of a sudden it appears possible that the whole universe that humans know, supposedly everything that exists, is not even itself in the middle of the true everything.
This latest twist comes from studies suggesting that extra hidden dimensions are not merely a millimeter wide, but maybe infinitely large. The whole known universe could, in other words, turn out to be just a bubble of foam in an endless ocean, a tiny island in a vast cosmic sea. The true totality of creation would extend beyond human sensation and imagination.
Lisa Randall, of Princeton University and MIT, with her colleague Raman Sundrum of Boston University, has recently published papers describing mathematically a possibly infinite fifth dimension beyond the four known dimensions of space and time.
"We have found that we can . . . exist with an infinite fifth dimension, without violating known tests of gravity," Drs. Randall and Sundrum wrote in the Dec. 6 issue of Physical Review Letters.
While an infinite hidden dimension might sound like infinitely wild speculation, it could in fact help solve some of science's deepest mysteries. In particular, Dr. Randall and Fermilab's Dr. Lykken have shown that this scenario might explain why the force of gravity is so weak.
It's well-known that electromagnetism is much stronger than gravity. A strong magnet can yank a heavy piece of metal into the air, easily defying gravity's pull. Nothing in physical theory explains the huge difference in strength between such fundamental forces.
In the Randall-Sundrum picture, though, gravity does not have the same strength everywhere. Gravitons, the particles that transmit gravity, would condense most densely around some brane. Suppose, Dr. Lykken explained at a recent cosmology conference, that humanity's brane resides a tiny distance away from this prime gravity brane. If so, gravity could be weakened by just enough to match its observed strength. By displacing our universe from the center of space, the way Copernicus displaced the Earth, a basic problem in physical theory goes away.
"Gravity is weak because the graviton likes to be somewhere else in the extra dimension," Dr. Lykken said in an interview. "If we could move a little bit over in the extra dimension, gravity would look much stronger."
Another speculative new view of the cosmos displaces humanity
not only slightly from the center, but more like all the way
to one side. In this view the parallel branes are not really
separate universes, but merely just long arms of one brane-universe
folded back and forth so as to lie next to one another. This
manyfold universe could fit nicely even within a dimension
only a millimeter wide.
Look to your right while driving down a mountain highway, and you might see another road running parallel a little way below. But it's really the same road that you're on; after a while you'll come to a switchback and head back the opposite direction along the parallel road. Maybe this is the way the universe is arranged, suggests Savas Dimopoulos of Stanford University. A brane could stretch a long way in one dimension and then in a region of extreme curvature of space turn around and head back, parallel to itself.
"It's like a new continent except it's in some ways much more than that - it's a new space, new dimensions," Dr. Dimopoulos said in an interview. "It expands our vision of space, and it makes us in some ways even less significant than we thought before."
Although these parallel branes, or folds, might be less than a millimeter away, they would remain invisible because light could not cross the gap (just as you wouldn't drive your Jeep across the gap between parallel stretches of mountain road). But gravity can cross that gap. So the gravitational effects of invisible dark matter could really be just the gravity of ordinary objects in a nearby fold.
"It's all the same stuff, except we can't see it," Dr. Dimopoulos said. The objects might eventually be visible, he said - if you had time to wait for light to arrive from the long way, around the bends of a folded universe.
At scientific conferences and in a paper appearing recently on the Internet, Dr. Dimopoulos and colleagues have proposed that humans inhabit just the warmest of these folds. The other folds need to be colder, otherwise the cosmic chemistry of the early universe would have produced the wrong mix of chemical elements. The different folds would cool one at a time following the hot big bang explosion at the universe's beginning. The last to cool - at one far side of the group of folds - would be the likely one for people to live in today.
Other folds must contain less matter than the fold that people live in. It would take perhaps 100 to 200 extra folds to provide enough matter to account for the dark matter that astronomers have detected, Dr. Dimopoulos said.
But the new space also offers exciting possibilities, Dr. Dimopoulos said. He speculated that future computers could store information in extra dimensions. And atom-smashing technology might be able to create high-energy particles to communicate with other branes - maybe not to talk to aliens, but to learn what physics is like on other branes and in the intervening space, known as the bulk.
"We can perhaps harness the bulk, we can communicate with other branes. It becomes completely wide open," Dr. Dimopoulos said. "We may not have seen anything yet."
Other physicists are skeptical of the folded universe picture, but nevertheless find it intriguing.
"I'm very happy with them exploring these possibilities," said
Fermilab's Dr. Lykken. "If he's right, and it's a folded universe,
that's again a completely new picture of the universe than
anything else anybody has ever thought of before."
Of course, the manyfold idea may also turn out to be completely wrong. Like all the new dimension ideas, it mixes lots of speculation with small dashes of data.
"We know almost nothing about what the universe might be like in extra dimensions," said Dr. Lykken. "We don't know how many extra dimensions there are, how big they are, what kinds of stuff lives there."
However, he noted, there are ways to find out. Measurements of the strength of gravity at short distances and experiments in atom smashers could probe the extra dimensions.
"You can go out and do an experiment in our lifetimes that will test whether these things are really there," Dr. Lykken said. "So it's not just fantasy, it's experimental science."
In any case, the point isn't that these ideas are right, but that they illustrate how profoundly little scientists really know about the ultimate shape of reality.
"We're going to find in the next century that there are all kinds of just amazingly weird things, and that we have not yet begun to make all of the discoveries that we're going to make, in physics and in all other fields," said Dr. Lykken. "Physicists have been lulled into a sense of self-satisfied security that we know almost everything. And undoubtedly that's wrong. We don't know almost everything. In fact, we may know almost nothing."