Making the Jump to Lightspeed

posted by Pat Galea on February 7, 2012

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My article on The Interstellar Communications Problem has been published in the Project Icarus series on DiscoveryNews.

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.


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3 Responses to Making the Jump to Lightspeed

  1. Fran says:

    Just pondering,

    If 2 spacecraft traveling at near light speed,approximately 1 light year apart were to communicate with each other would the leading spacecraft stay ahead of the latters signals or would the rear craft run into its own signal?
    I would believe the signal would leave the rear craft at 186000 miles per second faster than the craft is moving,regardless.
    Another mindbender to me is this, 2crafts traveling at the speed of light in opposite directions are traveling away from each other faster than light speed..
    Just pondering these thoughts knowing I’m probably way off base
    Thank for listening

    Fran leavens

  2. Pat Galea says:

    Hi Fran.

    This is where Einstein’s Special Theory of Relativity comes in!

    When you add up normal velocities that we are familiar with, the calculation is quite simple. But when things are travelling very fast (at speeds approaching light) relative to each other, the calculation gets more complicated.

    Basically, every non-accelerating observer measures the speed of light to be exactly the same, no matter where the light came from. So if I shine a flashlight and measure the speed of photons coming out of it, I get the value of c, 186000 mps. If you are travelling toward me at half the speed of light (93000 mps), you might think that you’d measure the speed of these photons as 1.5 c, or 279000 mps. But you don’t! In fact you measure the speed of the photons as 186000 mps, just as I did.

    That might seem weird – and it is! But from this starting point, we get the interesting effects of Special Relativity such as time dilation (clocks don’t tick at the same rates for everyone when they’re moving relative to each other) and length contraction (different observers measure things to be different lengths if they’re moving relative to each other).

  3. Given the current state of development in science and technology it might seem unfeasible to achieve FTL “speeds”, but remember: The same was said about many other things that now we take for granted. Nothing is impossible.

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