Study of the Cosmos Proceeds, But Will Take New Directions
by Sharon Begley
April 11, 2003
When cosmologists unveiled the findings of the WMAP satellite two months ago, it sounded like the instrument, orbiting 2.4 million miles above Earth, had not only accomplished its tasks -- answering timeless questions like how old the universe is and how galaxies are born -- but had gone considerably further. The Wilkinson Microwave Anisotropy Probe, it seemed, had taken the eternal enigma of genesis and sucked all the mystery out of it.
The findings were exactly as predicted by Big Bang inflation, which holds that the cosmos began when a quantum fluctuation created from nothingness an infinitesimal bit of space-time (since Einstein, space and time have been viewed as a single entity). This nearly infinite-temperature, infinite-density speck then ballooned in size 10 to the 50th power-times in a quadrillionth of a quadrillionth of a second.
When WMAP's measurements fit this model, it seemed that all the interesting cosmological mysteries were solved. It was enough, one researcher told me, to plunge several of his colleagues into depression.
But like Mark Twain's demise, reports of the death of cosmology are greatly exaggerated. Now that the dust has settled after the WMAP announcement, it's clear that some profound questions are still alive and kicking.
"While WMAP is a great advance," says cosmologist Jeremiah Ostriker, a professor at the University of Cambridge, England, "it does not answer all the questions. Cosmology is not over."
WMAP certainly firmed up some long-squishy cosmic parameters. The universe is 13.4 billion years old, give or take 300 million. Space is flat (if you shine a light straight ahead it won't bend around and smack you in the back in a few billion years). Its total mass-energy (the two are equivalent, Einstein showed) is 4% ordinary matter; 23% some unidentified, like-nothing-we've-seen dark matter; and 73% dark energy, a mysterious, repulsive oomph that makes the universe expand ever faster.
Just when a science seems all settled, though, something tends to pop up to shake up the whole field. So it may be with cosmology now.
"WMAP was an experimental triumph," says Cambridge astrophysicist Ofer Lahav. "But if all the observations fit your model, then most likely it's the wrong model, because observations tend to change."
WMAP measurements, in fact, are not "uniquely consistent with the standard inflationary Big Bang picture," notes Cambridge astronomer Sarah Bridle and colleagues in a recent paper in the journal Science. "There remains room for radical alternatives."
Among them: A new proposal that the universe is eternal, that its supposed genesis in a Big Bang was the beginning of just another in an infinitude of cycles of expansion and contraction alternating for time without end. This cyclic theory "fits all our observations, including WMAP's," says cosmologist Paul Steinhardt of Princeton University, New Jersey.
Besides not knowing how the universe began, we're also in the dark about what it's made of. What is the dark matter? Massive black holes? Exotic new particles? We just know what it isn't: the electrons, protons and neutrons that make up stars, aardvarks, peonies and everything else we see.
Nor do we know what the dark energy is. An eerie, dynamic force field dubbed "quintessence," or the never-changing "vacuum energy" posited by Einstein? "How can anyone say cosmology is over when we don't know the identity of more than 95% of the stuff in the universe?" asks Prof. Ostriker.
The true mark of an unfinished science is the surprises it springs. One, surely, will be the explanation for why the dark energy has precisely the value it does. It is just right for supporting complex physical and chemical processes, and therefore life. The amount of dark energy was minuscule in the past, and is on track to be gargantuan in the future. Neither is any good for supporting the physics and chemistry that allow stars to burn, planets to exist and life to live.
Contrary to the belief that there is nothing special about our place in the universe or our moment in cosmic history, "We are living in an anti-Copernican moment," says Prof. Steinhardt. "We really do live in a special time, and are only beginning to understand why."
Another unsolved mystery verges on science fiction. A recent calculation suggests that zipping off to another universe, or to a distant point in this one, via a black hole can't be ruled out. Black holes harbor space-time singularities, regions of infinite density that rip apart any extended object foolish enough to venture near.
That makes black-hole travel fairly unappealing. But Lior Burko of the University of Utah shows that a gentler black hole might exist. It would push and pull a spaceship only a little, acting as a portal to other worlds.
Whether black holes are destructive depends on what kind of matter pours into their hearts, which in turn depends on things like the nature of dark energy. Since that's an open question, the possibility of black-hole portals is small but real, Prof. Burko calculates in Physical Review Letters.
Until astrophysicists figure out whether there's a shortcut to the Andromeda galaxy, I'm going to consider cosmology unfinished business.