Doctor Who’s TARDIS is unique in that it appears larger on the inside than it does from the outside. According to scientists from the University of Helsinki, our universe may exhibit similar properties, a phenomenon they're dubbing Tardis spacetime. It’s a new theory that could solve a longstanding mystery in cosmology.

Scientists aren’t entirely sure why the universe is accelerating. To that end, they’ve posited a number of theories, including the presence of a mysterious dark energy that’s causing space to expand at an accelerating rate.

But according to Mikko Lavinto and colleagues, the universe isn’t actually expanding. It only looks that way from our perspective. Our view of the cosmos, they argue, is the product of an optical illusion created by regions of space that are bigger on the inside than they appear on the outside.

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