Expert: James Gort - 9/6/2011

Question
It is said that nothing,even information,can exceed the speed of light in this universe.However if you join two regions of space mechanically,say with a rigid rod/tube of any length,at either end of which is a short'T' piece at right angles to the rod and these are set precisely in line,then if the rod is turned about its horizontal axis such that the 'T' pieces impinge on,say,a 0 or 1(duplicated at both ends) then this message is instantly transferred to the other end of the rod.This is not a trick question,I've had this idea going round in my head for ages.What am I missing please?.ob

Answer
Hi John,

What you're missing is that no rod is truly "rigid". For instance, steel has a carbon and iron lattice structure, which appears rigid due to strong intermolecular bonds. However, it takes time to transfer information between adjacent molecules. So no matter how slowly we rotate the rod about its horizontal axis, the rod is actually twisting slightly. When we stop, the intermolecular forces will bring the rod back to its original shape (a materials engineer can actually give the time frame for this to happen). So we're not actually fooling Mother Nature - although "in theory" it should work. But the devil is in the details!

BTW, the above is strictly a "classical" explanation. If you want to rotate the rod extremely quickly (a percentage of the speed of light), then Relativity kicks in, and we end up distorting space-time in the vicinity of the rod. Which again inhibits "instantaneous" information transfer!

Cheers,

Prof. James Gort