We can build a real wormhole, but if the universe has extra dimensions

We can build a real wormhole, but if the universe has extra dimensions

It might be possible to build a real one, but only if our universe has extra dimensions, a group of physicists have discovered.

To make a wormhole, you need to stick together different parts of the universe, connecting them with a bridge or tunnel, which is usually called a “throat”. This throat can be as big or as long as you want, but it should generally be shorter than the normal distance to your destination. In Einstein’s general theory of relativity, creating a wormhole is pretty easy: You just create a black hole and connect it to a white hole (which is the exact opposite of a black hole), and boom, there it is: a tunnel through spacetime.

Unfortunately, the biggest problem with wormholes is that they are fantastically unstable. Once they form, their enormous gravitational force (they are literally made up of black holes, after all) rips them apart faster than the speed of light, making them pretty useless as shortcuts in the universe.

The only known way to stabilize a wormhole is to use some form of exotic matter. Exotic matter could take the form of negative mass matter that doesn’t seem to exist in the universe, or another scenario that violates the so-called energy conditions of general relativity. Energy conditions simply state that everyone should experience positive energy, on average, just about everywhere they go. However, in order to stabilize the wormhole, the traveler must experience an area of ​​negative energy.

There are some physical scenarios that lead to the violation of certain energy conditions at certain times. However, physicists do not know of a single case where all energy conditions would be violated on average over long periods of time – and this is exactly what is needed to create a wormhole.

Gravity is extremely weak; it is billions and billions of times weaker than any other force of nature. This fact worries many physicists, because when something is so strikingly different from the rest of the universe, there is usually some interesting physical explanation behind it.

But we have no physical explanation for why gravity is so weak. One of the ideas of theoretical physicists is that there is more to the universe than meets the eye. Inspired by the string theory concept of many extra spatial dimensions wrapped around themselves and compressed to submicroscopic scales, some theories suggest that there are actually extra spatial dimensions beyond the usual three.

In these theories, our three dimensions are simply a “brane,” a relatively thin membrane that exists within a higher-dimensional “volume.” These extra dimensions are not necessarily huge; if they were huge, we would see particles or planets appear and disappear from the extra dimension. But the extra dimensions could be larger than the meager dimensions of string theory—perhaps as small as a millimeter.

In this case, all the forces and particles of nature will be confined to a three-dimensional brane, and gravity will have the privilege of traveling through the volume. So gravity can be as strong as all the other forces, but it’s so heavily diluted with all the extra dimensions that it seems weak to our 3D experience.

Through a wormhole

Because these brane-based ideas are attempts to understand gravity, they open up new possibilities for studying the nature of wormholes. Our knowledge of wormholes is governed by general relativity, but it could be that the presence of extra dimensions changes how general relativity works, making wormholes possible, an Indian research team suggests in a new paper published in the arXiv preprint database.

In the paper, physicists explored the possibility of creating a wormhole in the “branching world” model first proposed by physicists Lisa Randall and Raman Sundrum in 1999.

The authors of the new work have found that they can actually build a stable, traversable wormhole in this brane-based gravity model. Moreover, for this they did not need any exotic matter.

While the team found that this situation still violates the energy conditions of general relativity, they argue that this violation is a feature, not a bug. Instead of some strange and exotic (and probably impossible) ingredient being required to create a wormhole, the nature of gravity in the extra spatial dimensions naturally led to a violation of the energy conditions. Once these conditions were violated, wormholes became a natural consequence, they said.

Researchers have even gone so far as to suggest that if we are ever able to directly observe or create a wormhole, this could indicate that the universe has more spatial dimensions than the usual three.

Like all theoretical work on the topic of wormholes, this is not the last word. Nobody knows if the Randall-Sundrum theory or any other theory based on branes and extra dimensions is correct. And no one has a quantum theory of gravity – a theory of strong gravity on small scales – that would almost certainly change the calculations, perhaps to the point of ruling out the possibility of wormholes again.

But this result is interesting nonetheless, as it joins a series of attempts to explore the limits of our understanding of gravity by pushing general relativity to its absolute limits. Wormholes may or may not exist, but trying to understand them will definitely increase our knowledge of the universe.

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