Just a few weeks ago I published a post about how several physicists at the Central Astronomical Observatory Pulkovo in Saint Petersburg Russia had published a paper discussing how astronomers might be able to actually discover the existence of wormholes in space. See my post of 10 March 2021. Basically wormholes are shortcuts in higher dimensions that could allow a space traveler to go from one part of the Universe to another faster than a beam of light could in normal, three dimensional space. By using a wormhole you’re not breaking the law against going faster than light, you’re circumventing it!
Well now physicists Alexey Bobrick and Gianni Martire at Applied Physics have published a paper in the journal Classical and Quantum Gravity that proposes what they consider to be a ‘realistic’ approach to building a warp drive engine that would enable a starship to effectively travel faster than light. Now Bobrick and Martire were not starting from scratch, their work is based upon an idea for using Einstein’s gravitational field equations to warp space first developed by physicist Miguel Alcubierre and which has become known as the Alcubierre drive.
It was back in 1994 that Alcubierre first published his metric tensor that described a region of space generated around an object, a starship. What the tensor would do would be to contract space to one side of the starship while expanding it to the other. The starship itself would remain inside a ‘bubble’ of flat space while the bubble would then ride the contraction – expansion wave in much the same way as a surfboard rides an ocean wave, the starship inside would be like the surfer. Inside the bubble of flat space everything would behave as in normal space, nothing would move faster than light, it’s the entire bubble, an entire region of space-time that is moving faster than light.
As you might guess there are some practical problems. The three biggest are number one, in order to generate the warp you need quite a lot of ‘negative energy’. What’s negative energy? Well it’s some type of energy or matter that exhibits a negative gravitational field. The only kind of negative energy we have any idea about at present is the ‘dark energy’ that astronomers believe is causing the expansion of the Universe to increase. In other words, we know next to nothing about negative energy and the idea of using it in a generator is pure speculation at present.
The second problem is that when Alcubierre calculated the amount of negative matter needed to generate a bubble big enough to hold a reasonably sized starship, say 100m or so, he found that it would be greater than the amount of normal matter in the entire known Universe. And if all that wasn’t enough the use of negative energy would allow the formation of closed time-like curves that could be used to travel backward in time, see my post of 17 November 2020.
Needless to say a lot of other physicists have voiced their opinion about the whole concept of the Alcubierre drive, both for and against. The work of Bobrick and Martire is just the latest. In their paper they show how, instead of requiring negative energy an Alcubierre bubble could be generated with a strong gravitational field from normal matter. As you might guess the strength of that field is pretty much that of a black hole. So if you want to get somewhere faster than light can, all you need is a black hole!
Perhaps the biggest problem with the Alcubierre drive along with wormholes and all the other kinds of other weird solutions to Einstein’s equations of General Relativity is that they don’t work with Quantum Mechanics. You see for over a century now we’ve had these two wonderful theories, General Relativity that describes the very large, and Quantum Mechanics that describes the very small and they not only don’t work together they don’t even follow the same mathematical formalism.
The majority of physicists today are of the opinion that when a theory of Quantum Gravity is finally found weird solutions like Alcubierre’s drive or wormholes will simply turn out to be invalid, like faster than light travel is in relativity. Of course it is quite possible that quantum gravity could actually point us in the direction of realistic faster than light travel. So let’s be glad that some of the more daring theorists out there are trying to see how far they can stretch Relativity and Quantum Mechanics.
After all, as the Sci-Fi writer Arthur C. Clarke liked to say. “The only way to find the limits of the possible is to go beyond them to the impossible!”