Making the Jump to Lightspeed
posted by Pat Galea on February 7, 2012
A question that often arises when we discuss interstellar communications is why we are restricting ourselves to the limitation of the speed of light. Surely an interstellar craft would have much to gain from the ability to send signals Faster Than Light (FTL)?
The answer is that it is perfectly true that FTL comms would provide many benefits. Getting the data back from the destination as fast as possible is always going to be a bonus, but also the ability to provide faster reactions from Earth could alter the fundamental architecture of the craft. Given the speed of light restriction, signals will take many years to travel from the craft to Earth, and another several years to get any response back to the craft. This means that the craft must display a significant degree of autonomy, being able to take decisions about self-repair and targeting observations at the destination. However, if we were able to get the data quickly and provide a rapid response, we might be able to get away with a craft that’s a bit less intelligent. We could do all the intellectual “heavy lifting” back on Earth, just as we do with our space probes at the moment.
The trouble with FTL is that we simply do not know how to do it. Actually, it’s worse than that. We simply do not know whether it is even possible in principle. It’s not like the situation in the early-to-mid twentieth century with respect to the sound barrier. We at least knew then that it was possible for objects to travel faster than the speed of sound, even if the engineering challenge of building a vehicle to do so reliably and controllably was tough. We have no physical examples of FTL in reality.
Now, there’s an intriguing possibility that quantum mechanics may provide a technique for getting around this speed limit. Quantum entanglement appears to involve some form of “update” passing from one particle to another when certain measurements are performed on entangled particles, and this update appears to travel faster than light. So far, though, it has not been established that this mechanism can be used to transmit actual information from one place to another faster than light. The distinction is a tricky one to understand, and I won’t attempt an explanation here.
Einstein’s Special Theory of Relativity suggests that if you can send a signal FTL, then you can send a signal backward in time. There’s a lot more to the argument than that, of course, but the point is that the theory suggests that FTL allows the violation of causality. That’s one of the reasons why many scientists are sceptical about the possibility of FTL.
It’s quite possible, of course, that Einstein’s theory is wrong under certain conditions that we haven’t explored yet. And perhaps further experiments in quantum entanglement will reveal definite proof that FTL information transmission is possible. That would certainly be a very important scientific result.
For Project Icarus, we need to base our design in plausible, credible science and engineering. Until we have a good understanding that FTL is possible, we’ll stick to things that we know can work, such as laser light and radio transmission.
In the meantime, outside the scope of Project Icarus, we support research into the more ‘exotic’ fields. Even if the result is negative (and personally, I suspect that the universe does not allow FTL), the result will be a valuable contribution to science. Whichever way it turns out, it’ll be fascinating.