Did the early universe have just one spatial¹（空间的） dimension? That's the mind-boggling concept at the heart of a theory that University at Buffalo² physicist³ Dejan Stojkovic and colleagues proposed in 2010.

They suggested that the early universe -- which exploded from a single point and was very, very small at first -- was one-dimensional (like a straight line) before expanding to include two dimensions (like a plane) and then three (like the world in which we live today).

The theory, if valid⁴, would address important problems in particle physics.

Now, in a new paper in Physical Review Letters, Stojkovic and Loyola Marymount University physicist Jonas Mureika describe a test that could prove or disprove the "vanishing dimensions" hypothesis.

Because it takes time for light and other waves to travel to Earth, telescopes peering（凝视） out into space can, essentially⁵, look back into time as they probe the universe's outer reaches.

Gravitational waves can't exist in one- or two-dimensional space. So Stojkovic and Mureika have reasoned that the Laser Interferometer Space Antenna⁶ (LISA), a planned international gravitational（重力的） observatory⁷, should not detect any gravitational waves emanating⁸ from the lower-dimensional epochs（新纪元，新时代） of the early universe.

Stojkovic, an assistant professor of physics, says the theory of evolving dimensions represents a radical⁹ shift from the way we think about the cosmos¹⁰ -- about how our universe came to be.

The core idea is that the dimensionality of space depends on the size of the space we're observing, with smaller spaces associated with fewer dimensions. That means that a fourth dimension will open up -- if it hasn't already -- as the universe continues to expand.

The theory also suggests that space has fewer dimensions at very high energies of the kind associated with the early, post-big bang universe.