Thursday 25 October, 2007

Faster than light?

The other day i was explaining the relativity theory to a friend. At the speed of light, any object would have infinite mass so would need infinite energy to make it go faster."This means that there is a maximum speed at which anything can travel, and only massless things like light can travel at that speed," I explained.My friend is very bright, and after a little thought he came up with three situations that semmed to contradict Einstein. Is any of them valid?


1. The poles outside barber shops have helical stripes painted round them. If the pole is rotated, its stripes are seen to travel along it. If the rotation is fast enough the stripes should travel faster than light.
2. If you shine a flashlight on a wall, you will see a spot of light. You can make this spot move along the wall by rotating the flashlight. The speed of the spot depends on the distance from the wall and the speed of rotation of the flashlight. If you shine a laser on a target some miles away, the spot of light formed could be made to move faster than the speed of light by rotating the laser.
3. Very small particles, like neutrons, can penetrate matter very easily. Imagine such a particle, travelling at nearly the speed of light, entering a block of glass. The particle is so small that it will not be impeded by the glass, but light is slowed down to about two-thirds of its speed in air. Therefore, the particle would be travelling faster in glass than the light.


My conclusion:
My friend correctly identified three situations in which something travels faster that light. However, none of them contradicts Einstein, whose work could be more correctly summarized as: " The maximum speed at which INFORMATION can travel is represented by the speed of light in a vacuum. "In the first two examples, nothing physical moves faster than light.

The barber's pole stripes only appear to move along the pole.

The spot of light at one end of the sweep is different from the one at the other end as it is made up of different photons. Neither system could be used to carry INFORMATION.
The third example has been observed experimentally. Such particles break the "light barrier" and produce minute photonic flashes equivalent to sonic booms.

2 comments:

Anonymous said...

Interesting! optical illusions can move faster then light?

Michael

gauravragtah said...

Yup, theoretically.

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