I seem to have read somewhere that some things could move faster than the speed of light. It was said that the imaginary point where the two blades meet in a pair of scissors can travel at speeds faster than light, given a sufficiently long pair of scissors, even if the individual particles that constitute the mass of the scissors don't approach that speed.

When you close a pair of scissors, the aforementioned imaginary point travels the length of the scissors in a certain amount of time (the exact amount of time you take to close the scissors). The moment when the point reaches the pointy end of the scissors could be defined as the moment the scissors are completely closed; the moment the two blades align at their pointy end.

Now imagine we have a pair of scissors that are roughly 744,000 miles long and slightly open. They don't have to be uber-large, just uber-long. We'll say the fulcrum is at the exact center of their length, at 372,000 miles from either end. Now, Alice and Bob synchronize their watches and Alice stands at the rounded end of the scissors, with Bob making a short journey and manning the pointy end. Let's have Alice close the scissors, starting at precisely noon. What's more, lets have her do it naturally, taking only a quarter of a second to fully close them. Let's have Bob observe the pointy end and take down the time when they are fully closed. After the experiment, Alice and Bob will meet somewhere and compare their observed times.

So you might say that Alice started closing the scissors at 12:00:00.00 and Bob saw his end of the scissors close at 12:00:00.25, meaning that the imaginary point traveled the full 372,000 miles from the fulcrum to the pointy end in only a quarter of a second. The speed of light in a vacuum is roughly 186,000 miles/sec, so you might say that the point traveled at eight (8) times the speed of light. If you did say those things... you obviously weren't there when Alice and Bob compared their times.

See, the kicker is this: Information cannot travel faster than light. Period. If Bob is standing on the pointy end of this pair of scissors, he won't actually witness the closing at the same moment as Alice. Why is this? We must ask ourselves how the pointy end of the scissors knows when the other end has been closed? The atoms in the scissor material bump into one another conveying the energy along its length via a compression wave, much like the balls in Newton's Cradle. This compression wave of particles can only travel at the speed of SOUND in the given medium, likely steel if that's what our scissors are constructed of. The speed of sound in steel, depending on the exact alloy, is roughly 12,300 miles per HOUR. So when Alice closes the scissors, it's going to be 06:15:00.00 THE NEXT DAY before Bob knows it, and consequently, 30 hours and 15 minutes between the time that the little imaginary point left Alice and made it to Bob. The speed of the compression wave in a solid is a function of the elasticity of the solid. With rubber scissors, it will take even longer for Bob to get closure.

The concept gets even weirder when you make the scissors longer. For a pair of steel scissors that are seven light years long, it will be 381,554 years from the time force is applied until the pointy end actually closes. That little point, whether the individual particles of the scissors moved uber-fast or not, cannot move faster than light. Hooray physics!

*Update: Many thanks to Santo for correcting my originally incorrect assumptions and pointing me in the right direction concerning compression waves.*