Most people think of space as nothingness, the blank void between planets, stars, and galaxies. Kip Thorne, the Feynman Professor of Theoretical Physics at Caltech, has spent his life demonstrating otherwise. Space, from his perspective, is the oft-rumpled fabric of the universe. It bends, stretches, and squeezes as objects move through it and can even fold in on itself when faced with the extreme entities known as black holes. He calls this view the “warped side of the universe.”
Strictly speaking, Thorne does not focus on space at all. He thinks instead of space-time, the blending of three spatial dimensions and the dimension of time described by Einstein’s general relativity. Gravity distorts both aspects of space-time, and any dynamic event—the gentle spinning of a planet or the violent colliding of two black holes—sends out ripples of gravitational waves. Measuring the direction and force of these waves could teach us much about their origin, possibly even allowing us to study the explosive beginning of the universe itself. To that end, Thorne has spearheaded the construction of LIGO [Laser Interferometer Gravitational Wave Observatory], a $365 million gravitational-wave detector located at two sites: Louisiana and Washington State. LIGO’s instruments are designed to detect passing gravitational waves by measuring minuscule expansions and contractions of space-time—warps as little as one-thousandth the diameter of a proton.
Despite the seriousness of his ideas, Thorne is also famous for placing playful bets with his longtime friend Stephen Hawking on questions about the nature of their favorite subject, black holes. Thorne spoke with DISCOVER about his lifetime pursuit of science, which sometimes borders on sci-fi, and offers a preview of an upcoming collaboration with director Steven Spielberg that will bring aspects of his warped world to the big screen.
What does a black hole actually look like?
A big misconception is that a black hole is made of matter that has just been compacted to a very small size. That’s not true. A black hole is made from warped space and time. It may have been created by an imploding star [where the gravity becomes so concentrated that nothing, not even light, can escape]. But the star’s matter is destroyed at the hole’s center, where space-time is infinitely warped. There’s nothing left anywhere but warped space-time. A black hole really is an object with very rich structure, just like Earth has a rich structure of mountains, valleys, oceans, and so forth. Its warped space whirls around the central singularity like air in a tornado. It has time slowing as you approach the hole’s edge, the so-called horizon, and then inside the horizon, time flows toward and into the singularity [the central spot of infinite density and zero volume], dragging everything that’s inside the horizon forward in time to its destruction. Looking at a black hole from the outside, it will bend light rays that pass near it, and in this way it will distort images of the sky. You will see a dark spot where nothing can come through because the light rays are going down the hole. And around it you will see a bright ring of highly distorted images of the star field or whatever is behind it.
How sure are you about this model of a black hole? Could the picture be wrong?
It is a firm prediction from Einstein’s general relativity laws. Gravitational waves will bring us exquisitely accurate maps of black holes—maps of their space-time. Those maps will make it crystal clear whether or not what we’re dealing with are black holes as described by general relativity. It’s extremely unlikely that they are anything else, but that’s the exciting thing—we’ve been wrong before. We’ve had enormous surprises before.
Einstein thought of black holes as theoretical curiosities. Since no one has directly observed one, how do we know that black holes truly exist?
We see very strong evidence right at the center of our own galaxy. Astronomers have seen massive stars fall toward some central object and whip around it, like a comet around the sun, and fly back out. They have weighed that central object by measuring how strongly it whips stars around it. It turns out to have the same gravitational pull as approximately 3 million suns, and it is very dark—astronomers see only weak radio waves there. It almost certainly is a black hole. And when quasars [extremely bright, compact objects at the centers of some galaxies] were discovered in the early 1960s, it was obvious that the source of power had to be gravitational because even nuclear power, which powers the stars, is too inefficient. The idea that quasars are powered by the accretion of matter onto black holes was proposed within months after the discovery of quasars. This was a huge change of people’s views of the universe, and it came very quickly. There followed a period of rapid research, and by the mid-1970s we came to understand that black holes are dynamic objects with a rich set of properties. They spin, and they can vibrate.
What are the latest discoveries about black holes?
The most exciting things to me are the first supercomputer simulations of two black holes that spiral together and then collide, triggering wild vibrations of their warped space and time. There’s a fascinating recent simulation by a group led by Manuela Campanelli and Carlos Lousto, who are now at the Rochester Institute of Technology, in which the two holes are spinning with their axes pointed in opposite directions in the plane of their orbit. As they come together, the whirling space around each hole grabs hold of the other hole and throws it upward, just before they collide. The merged hole flies upward from where the collision occurred, vibrating wildly, and fires a burst of gravitational waves in the opposite direction in order to conserve total momentum. It’s similar to how a smoke ring propels itself forward through air.