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Pikkugnome
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- TL;DR Summary
- A common scissor blade problem stemming from special theory of relativity.
This is a common exercise stemming from special theory of relativity courses all over the world it seems. Show that the intersection of scissor blades can move faster than the light. If we imagine that we put a pen in between the scissors, touching the blades, and it is sliding without much friction, then the intersection point of the blades is at a certain distance from the pen. If the blades are pushed together, the pen slides forwards. However due to geometry of the situation, the point of intersection lags further behind from the pen. Therefore it is moving slower than the pen, thus less than the speed of light, since the pen can't move faster than the light.