Could Earth cross a wormhole?

The universe is huge. Is space the final fronteer? No one knows that, yet! Travelling at light speed to the nearest star would take more than four years.

A shortcut would be only a wormhole, a tunnel through the fabric of space. This seems to be the best choice for most of the fictional space travellers, including the characters in the upcoming film Interstellar, directed by Christopher Nolan.

The travel would be incredibly difficult, say scientists.

A wormhole is more like a tube. The mouth of a wormhole acts like a cosmic window, which give the pleasure to have all the stars in between to be admired. That’s the theory anyway.

The theory of general relativity, Einstein's revolutionary notion describes gravity as the warping of space and time, which forms the fabric of the universe called spacetime.

Einstein and Nathan Rosen published a paper in 1935 describing these wormholes.

There's a force that allows exotic matter to prevent a wormhole from collapsing.

In the vacuum of space, some small regions of spacetime can be filled with negative energy, surrounded by regions of positive energy. "Think about them like waves of an ocean," explains physicist Larry Ford of Tufts University, Boston.

If you collect a lot of negative energy, it can only exist within a tiny space.

The problem is that for a wormhole to last, we would need more negative energy than the rules allow! The amount of energy needed would be as much as the Sun produces over 100 million years to make a wormhole about the size of a grapefruit.

"People are quite confident that quantum inequalities prevent macroscopic traversable wormholes", says John Friedman, a physicist at the University of Wisconsin, Milwaukee. "But it's certainly not airtight".

Tiny wormholes could also arise from quantum foam. Since these wormholes would be too minuscule for anything to squeeze through, we would have to inject some negative energy to blow them up.

"Based on what we know now, it's hard to see how you would make a traversable wormhole", Ford says. Yet physicists will keep trying to figure this out!