In 1994, the physicist Miguel Alcubierre proposed a radical technology that enables faster than light travel: the warp, a hypothetical way of concealing the ultimate velocity constraint of the universe by bending the fabric of reality.
It was an interesting idea – even NASA investigated it in Eagleworks laboratory – but Alcubierre’s proposal contained problems that seemed insurmountable. Now, a recent paper by American physicists Alexey Bobrick and Gianni Martire, has solved many of these problems and caused much uproar.
But while Bobrick and Martire have managed to significantly demystify warp technology, their work actually suggests that traveling faster than what will be out of the light for creatures like us, at least for now.
However, there is a silver lining: warp technology can have radical applications outside of space travel.
Across the universe?
The story of warp drift begins with Einstein’s award: general relativity. The equations of general relativity capture the way in which space-time – the fabric of reality – bends in response to the presence of matter and energy, which in turn explains how matter and energy move.
General relativity places two constraints on interstellar travel. First, nothing can be accelerated over the speed of light (about 300 000 km per second). Even if we travel at this dizzying speed, it will take another four years to reach Proxima Centauri, the closest star to our sun.
Second, the clock on a spaceship moving near the speed of light will slow down relative to a clock on earth (this is known as time dilation). Assuming a constant state of acceleration, it is possible to move the stars. One can reach a star that is 150 light-years within your lifetime. The catch, however, is that with the return more than 300 years will have passed on earth.
A new hope
This is where Alcubierre comes in. He argued that the mathematics of general relativity makes ‘chain bubbles’ possible – regions where matter and energy are arranged in such a way that it bends the space-time in front of the bubble and backwards in a way that a ‘flat’ area inside the bubble travels faster than light could move.
Read more: Do not stop me now! Superluminal journey in Einstein’s universe
To get an idea of what ‘flat’ means in this context, note that space-time is a kind of a rubber mat. The mat bends in the presence of matter and energy (think of putting a bowling ball on the mat). Gravity is nothing but the tendency for objects to roll in the dives created by stars and planets. A flat area is like a part of the carpet with nothing on it.
Such a ride would also avoid the uncomfortable consequences of time dilation. One can possibly make a round trip in the deep space and still be greeted by the nearest of your home.
A spatial strangeness
How does Alcubierre’s device work? Here the discussion is often based on analogies, because mathematics is so complex.
Imagine a rug with a cup on it. You are on the mat and you want to get to the cup. You can move over the mat or pull the mat towards you. The warp is like putting on space time to bring you closer to your destination.
But analogies have their limits: a warp drive doesn’t really drag your destination to you. It contracts space time to shorten your path. There is just less mat between you and the cup when you turn on the drive.
Alcubierre’s proposal, although mathematically rigorous, is difficult to understand on an intuitive level. Bobrick and Martire’s work will change that all.
Starship bloopers
Bobrick and Martire show that any warp must be an envelope of material in a constant state of motion, which includes a flat area of space-time. The energy of the shell changes the properties of the space-time region in it.
It may not sound like a great discovery, but so far it has been physically unclear what warp may be. Their work tells us that a warp, somewhat surprisingly, is like a car. A motor is also a scale of energy (in the form of matter) that encloses a flat area of space-time. The difference is that you do not age faster when you get in a car. However, this is the kind of thing a warp drive can do.
Using their simple description, Bobrick and Martire demonstrate a method of using Einstein’s general equations of relativity to find space-times that can provide for matter and energy that can act as warp bubbles. This gives us a mathematical key to finding and classifying warp technologies.
Their work succeeds in addressing one of the core problems for warp stations. To balance the equations, Alcubierre’s device works on ‘negative energy’, but we have not yet discovered any viable sources of negative energy in the real world.
Applied Physics
Worse, the negative energy needs of Alcubierre’s device are huge. According to some estimates, the whole energy is needed in the known universe (although later work makes the number a little lower).
Bobrick and Martire show that a warp drive can be made from positive energy (ie ‘normal’ energy) or from a mixture of negative and positive energy. That said, the energy needs will still be huge.
If Bobrick and Martire are right, a warp is just like any other object in motion. After all, it would be subject to the universal speed limit applied by general relativity, and it would need some sort of conventional propulsion system to accelerate it.
The news is getting worse. Many types of chain drive can only change the space time in a certain way: by slowing down the passenger’s clock in exactly the way that a ride in deep space makes a problem.
Bobrick and Martire do show that some warp drives can move faster than light, but only if they are created that are already moving at that speed – which is no help to an ordinary person hoping for a bit of interstellar tourism.
The final game
Remember that a curve driver can change the area of the flat space period it encloses. It can especially speed up or slow down a clock inside the queue.
Think about what it would mean to have such an object available. Do you want to put someone with a terminal illness on the ice? Put them in a warp drive and slow down their watch. From their perspective, a few years will pass, while a hundred years on earth will pass – enough time to find a cure.
Read more: The art and beauty of general relativity
Do you want to grow your crops overnight? Put it in a warp drive and speed up the clock. A few days will pass for you, and a few weeks will pass for your seedlings.
There are even more exotic possibilities: by turning space time within a drive, you can produce a battery that can hold a lot of energy.
Faster travel than light remains a distant dream. But warp technology would be revolutionary on its own.