I am at the rear wall of my spaceship travelling at the speed of light. I switch on my flashlight. Will the light reach the front wall? (continued)
Dave Rowsell
Swansea, UK
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This is pretty much the same question that Albert Einstein posed over a century ago when he asked himself what it would be like to travel alongside a light wave. In this case, he imagined travelling in a superfast tram at the speed of light, c.
With that in mind, I felt that some of the previous answers fell short, as they considered the scenario of travelling at a tiny fraction less than c and hence avoided the real issue: what would it be like to travel at the speed of light, not just close to it.
The difference is very important. As we move towards c, we approach the mathematical limits of the equations of special relativity. This is where maths takes us to both zero and infinity 鈥� never happy places in physics.
At c, conclusions emerge that run counter to our common sense. Space shrinks right down to zero. There is no space. Neither is there any time. This tells us that, from the viewpoint of light, there is no space-time, and therefore no such thing as 鈥渢ravelling鈥�. For light, everything is instantaneous, and there is no such thing as 鈥渉ere to there鈥� or 鈥渢hen and now鈥�. It would be impossible for Einstein to run alongside light, like we could drive alongside one particular carriage of a train. His thought experiment was a misconception.
However, from our point of view, as conscious beings living in the environment of space-time, light takes time to get from A to B. So how do we square these two seemingly opposite views?
Our view of the universe clearly needs to be thought out anew. In a way, it is a shame we are asking the same question that Einstein did and, worse, that we are still settling for incomplete answers.
We still don鈥檛 really question what we mean by reality, yet there could be so much to gain by doing so. Surely it is time to accept imagination as a key part of our scientific endeavour, and start applying it seriously and on a broad scale. Changing how we approach relativity and its limits might offer new clues to reconciling relativity and quantum mechanics. And who knows, it might also shed some light on the 鈥渉ard problem鈥� of consciousness?
To answer this question 鈥� or ask a new one 鈥� email lastword@newscientist.com.
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