The End of Time

Imagine strolling up to a very unusual department store. There are no windows, so you can’t see inside. But the external walls of the store list everything it contains: Every party dress, handbag, kitten-heel shoe, and silk scarf is inventoried; the exact size and color and shape is recorded; all the information about every thread of every stitch is emblazoned there on the brick wall.

Now imagine that the shop isn’t really a shop. It’s a black hole, and it contains our entire universe. Not just the stars and galaxies that we can see with telescopes, but many other regions of space, where the laws of physics operate differently. Our familiar universe, with its hundreds of billions of galaxies, is rather provincial, the cosmic equivalent of the Ladies’ Shoe department.

That’s a rough analogy for a new view of the universe being proposed by FQXi grant winner David Anthony Lowe, a physicist at Brown University, that will allow him to explore the "big questions" of cosmology: How big is the universe? Will it expand forever? Has it always existed? Will it always exist?

Lowe’s work builds on the holographic principle, the idea that all the information in our universe can be mathematically represented on a cosmic horizon like the surface of a black hole. Just like the two-dimensional hologram on your credit card, which appears to spring into a third dimension when you hold it just so, this cosmic hologram encodes information for one more dimension than it exists in itself. Lowe interprets the holographic principle as more than just a handy mathematical tool: "It means we’re inside a black hole," he says. "It is a physical reality."

Living in a Black Hole

Though Lowe’s view that we are literally living in a black hole seems bizarre, it’s perhaps not as crazy as it may sound at first. After all, "initially, we thought black holes were just a mathematical curiosity," says FQXi member Richard Easther, a physicist at Yale University. He points out that even Einstein, whose theory of general relativity provided the first glimpse of the possibility of black holes, believed that they would not emerge in nature. "Now, we see that they are something profound," adds Easther.

Lowe is working with a particular description of the holographic principle that shows that a certain kind of universe with gravity can be described, after dropping a dimension, by quantum field theory. (See "The Black Hole and the Babel Fish" for more about the holographic principle.) Instead of trying to wrestle with an infinitely large universe, as many others have done, Lowe is now applying the holographic principle to a finite cosmos—viewing it as a black hole—which contains multiple "bubbles," each with its own physical laws and constants.

The idea that our world is just one bubble among many—one department in the cosmic Macys—isn’t new. Tufts University cosmologist Alexander Vilenkin, who has studied another species of bubble universes with an FQXi grant, points out that fifteen years ago, most of the physics community was opposed to the idea that different physical laws and constants might prevail beyond our cosmic horizon. But "today, it is becoming almost mainstream," he says.

Lowe’s universe may be finite in space, but in time, it has no end and no beginning, so the total number of bubbles that could live inside it is infinite. If a super-observer could live forever into the past and future, she could see these bubbles materialize, live, evolve, and die, over and over, like the fizz in a glass of Coke that never goes flat. The big bang would be a process that would recur, repeating itself endlessly.

There is a problem with living in a universe that is both finite and expanding, though: Because the finite speed of light can’t catch up with the rate at which space is expanding, we constantly lose access to distant objects that move outside our horizon. "If you go to the infinite future and look back, you’ll lose access to almost everything," Lowe explains.

Not that you would be around to see such an event. By then, cosmic expansion will have overcome the gravitational and electrostatic forces that bind our everyday world together, and the subatomic particles that used to be you will be scattered across the universe, terminally out of touch with each other. This marks the "end of time," which begins when every particle becomes fatally isolated—effectively locked in its own private universe, with no external events occuring to mark the passing of time.

Time no longer exists.

This end of time also marks the end of physics. Because the expanding bubble that we call home is embedded in a finite universe, there is a limit on the number of different configurations it might have, says Lowe. Like a Rubik’s Cube, it can only be arranged and rearranged so many ways before it begins to repeat. In 50 billion years or so—just a few multiples of the current age of the universe—the number of options open to our bubble may dwindle so far that "things would break down into some kind of quantum pixels," Lowe says.

Cosmic Crosstalk

No one will be around to see the end of time, so Lowe needs another way to test out his hypothesis. Or, as he puts it: "I’d like to find another leg for it to stand on!" He hopes that current astrophysical experiments could provide support, but first Lowe has to figure out what that "leg" might look like—which he will do with the help of an FQXi grant of almost $103,000—so that astronomers and physicists will know it when they see it. It might be hidden in data from satellites like Planck, a European Space Agency observatory that launched in the spring of 2009. Planck picks up faint microwave signals that are a sort of afterimage of the very early universe.

There may be other even stranger signs that Lowe is on the right track. The rendering of the holographic principle that mapped out the duality between gravity and quantum field theory has another strange side effect: It predicts that some things in the universe might be able to "talk" to each other across wide distances, even when light wouldn’t have time to traverse the space between them. This kind of "intrinsic nonlocality" violates general relativity, so looking out into the universe, we should see some signals that the cosmos is breaking Einstein’s rules. Exactly how those rules are being broken, and what the telltale signs might be, is what Lowe is now trying to define.

Evidence like this could help Lowe’s idea rise above other competing models of the universe. "Lots of people have tried to solve this problem. The literature is littered with promising approaches," notes Easther. But most ultimately didn’t work out.

Lowe is cautiously optimistic: "This perspective does seem to sweep away a lot of the problems that cosmology suffers from," says Lowe. But will it provide the final answer? Perhaps. In the meantime, theorists will keep on shopping.