Wormholes, like hyperspace, have become one of the mainstays of science fiction. The only problem is that they remain merely an exotic mathematical possibility. But theorists hope there will soon be ways to detect them for real.
The attraction of wormholes is that they may be a way to get around the biggest problem with space travel: space itself.
Space, as Douglas Adams wrote with magnificent understatement, ‘is big’. Really big. Which is a big problem when it comes to the dream of interstellar travel. Even travelling at a significant fraction of the speed of light – so far as we know, the ultimate speed limit – the nearest stars are still years away. Hyperspace is one fictional way of cheating that limit, by leaving ‘normal’ Einsteinian space (more correctly, spacetime, the four dimensions being inextricably linked), and taking shortcuts through a different kind of space.
Wormholes, in science fiction, work a different way: by ‘tunneling’ through ‘folded’ spacetime. Another shortcut, in other words.
Whether natural or constructed, wormholes seem to be the perfect gateway to traverse distances that would otherwise take hundreds or even tens of thousands of years to cross, even at the speed of light. Wormholes seem to be studded all over outer space like space elevators that are just waiting to speed us along to interstellar destinations. Scientists think that if we could break into the higher dimension in which wormholes probably exist, we could make traveling to the stars a reality.
There are, suffice to say, just a few problems. Firstly, wormholes are purely theoretical. Mathematically, though, Einstein’s equations lead to the conclusion that wormholes can exist. If that sounds a bit of a reach, consider that black holes were similarly purely theoretical. In fact, Einstein himself didn’t foresee them: it was physicist Subrahmanyan Chandrasekhar who explored the maths of Einstein’s equations and realised that gravity could cause a suitably large star to collapse on itself to a ‘singularity’, from which not even light could escape.
Sixty years later, astronomers finally detected black holes for real.
So, what about wormholes?
In 1935, Albert Einstein and his colleague Nathan Rosen mathematically demonstrated a concept, later dubbed an Einstein-Rosen bridge, that built upon General Relativity Theory principles and indicated the possibility of a shortcut through spacetime. In 1957, physicist John Archibald Wheeler gave the concept the name “wormhole” for a particular warping of spacetime.
It all comes down to the same spacetime, and how it is ‘curved’ by mass and gravity, which leads to black holes.
Its properties dictate the movements of all interstellar bodies, such as planets, stars, and galaxies, because the mass of these objects causes all of spacetime to curve. In fact, this curvature is what we feel as the force of gravity.
The steeper the curve, the stronger the gravity. A black hole infinitely curves spacetime into, well, a hole. Imagine, though, that spacetime could be curved so that it folds like a sheet of paper. Punch a hole through the fold, and you’ve made a bridge to points on the sheet which are normally far apart. A wormhole, theoretically, is a tunnel between the two holes.
If you travel through this portal, you’d come out on the other side far more quickly than you would if traveling the normal “length” of spacetime.
How do you do that. Again, theoretically…
One theory says if our technology were to combine exotic matter with a black hole, we may create a wormhole. Exotic matter is hypothetical at this point, described only in mathematical terms. It acts in unexpected ways, like having negative mass and working in opposition to gravity. Perhaps the other side of a black hole, which pulls in all matter and even light, spits out all of it on the other side, which astrophysicists sometimes call a white hole.
But there are still problems. This is spacetime, remember? Listen to the Queen song ’39, written by astrophysicist-turned-guitarist Brian May: Write your letters in the sand/For the day I take your hand/In the land that our grandchildren knew. ‘Our grandchildren knew’: May is referring to the inevitable outcome of space travel: time dilation.
Because space and time are inextricably linked, wormhole travel causes not only a shortcut through space, but an usual distortion of time. Time might speed up, slow down, or even loop, putting you at a point before you even started your journey, or giving you the ability to visit the future when you emerge on the other side of the wormhole. The trip might seem to take seconds to you, but an outside observer could wait for years to see you again. The more you fold spacetime in on itself, the faster you’ll reach the other end of the wormhole; warp spacetime enough, and the entire journey would be like stepping through a doorway – practically instantaneously.
This causes big problems. Walk out tonight and look up at, say, the ‘Pointers’ of the Southern Cross. The bright yellow one is Alpha Centauri, just 4.3 light-years away. You’re seeing it as it was 4.3 years ago. So, if you travelled there instantly, you’ve travelled in time. One end of the wormhole is in a different time than the other. Yet, information is restricted to the speed of light. If you move faster than the speed of light, you’re outpacing information itself.
According to [theoretical physicist Kip Thorne], who served as a consultant on the science of Interstellar, quantum mechanics could hypothetically explain a way to time travel via wormhole. So far, it’s a thought experiment that leads to the conclusion that you’d lose information along the way – not very practical.
“You get caught up in the so-called information loss paradox,” he explains. Thorne would like to keep following the logic of physics and see what happens, since we can’t actually experiment with wormholes today. But someday we will, Thorne believes. In the meantime, he says, “simple thought experiments … can sometimes dig pretty deeply into the laws of nature.”
Ah yes, the laws of nature…
The other problem is that wormhole physics turns us to quantum physics. Relativity deals with the physics of the very, very big, quantum physics with the physics of the very, very small. And they do not get along.
Quantum physics principles theorize that microscopic wormholes probably already exist. They don’t appear for long, popping out of the universe like soap bubbles, but they are an inherent property of a theorized virtual particle called quantum foam. To construct a stable wormhole at a size practical for travel, advanced technology might need to catch hold of one of these microscopic wormholes, enlarge it somehow, and then keep it open for travel.
Which would mean somehow reconciling relativity and quantum theory – something that has eluded the most brilliant minds in physics for nearly a century.
So, don’t go getting your hopes up of travelling to the stars too high. Not yet.
