Did early version have just one dimension?

• Position: The Universe

Did the early universe have just one spatial dimension? That is the mind-boggling concept at the heart of a theory that physicist Dejan Stojkovic and colleagues proposed in 2010, suggesting that the early universe-which exploded from a single point and was quite 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 valid, would address important problems in particle physics.

In a piece printed in Physical Review Letters, Stojkovic and fellow 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 out into space essentially can look back into time as they probe the universe's outer reaches.

Gravitational waves cannot exist in one- or two-dimensional space. So, Stojkovic and Mureika have reasoned that the Laser Interferometer Space Antenna (LISA), a planned international gravitational observatory, should not detect any gravitational waves emanating from the lower-dimensional epochs of the early universe. Stojkovic says the theory of evolving dimensions represents a radical shift from the way we think about the cosmos--about how our universe came to be.

The core idea is that the dimensionality of space depends on the size of the space we are observing, with smaller spaces associated with fewer dimensions. That means that a fourth dimension will open up--if it has not 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.

If Stojkovic and his colleagues are correct, they will be helping to address fundamental difficulties with the standard model of particle physics, including the following:

The incompatibility between quantum mechanics and general relativity. Quantum mechanics and general relativity are mathematical frameworks that describe the physics of the universe: quantum mechanics at very small scales, while relativity is better for that purpose at large ones. Currently, the two theories are considered incompatible but, if the universe, at its smallest levels, had fewer dimensions, mathematical discrepancies between the frameworks would disappear.

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