Answers to some of the biggest questions in physics are hanging by a thread in a laboratory at the University of Washington in Seattle. The thread is made of tungsten and measures a bit over 30 inches long and less than one-thousandth of an inch thick. It is part of a tabletop instrument called a torsion pendulum, which can measure gravity’s strength across small distances with unprecedented accuracy.
Although the behavior of gravity acting on large bodies and over long distances is well understood, what gravity does between small objects at very small distances is uncharted territory. No one even knows if Newton’s laws (which state that the pull of gravity varies in proportion to the square of the distance between two objects) still hold at that level. Raman Sundrum, a theoretical physicist at Johns Hopkins University, is betting that they do not. If he is right, the Seattle experiment may explain strange goings-on halfway across the universe.
Seven years ago, cosmologists discovered something astonishing: The expansion of the universe is accelerating, perhaps driven by a repulsive force known as dark energy. The force seems to be a basic property of empty space. In some ways that makes sense because, according to quantum mechanics, empty space is not empty.
Rather, the vacuum is filled with fields and particles that constantly pop in and out of existence. The problem is that when physicists estimate how much energy is contained within those fields and particles, they come up with a number—called the cosmological constant—that is insanely large, 10120 times greater than what we observe. A cosmological constant of that magnitude would rapidly tear the universe apart. It is an embarrassing error, often described as the biggest mathematical mistake in the history of physics.
