# A thought Experiment on velocity greater than C

by I_am_learning
Tags: experiment, greater, velocity
 P: 664 Supoose at the center of A huge cylinder of radious say 1km we place a high speed motor of say angular speed w > 3E5 . And in the motor we attach a laser directed towards the walls of the cylinder. When we rotate the motor with the laser lighted, won't the laser point move along the cylinder walls at speed greater than the speed of light? (I have attaced a drawing) Attached Thumbnails
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 Quote by thecritic Supoose at the center of A huge cylinder of radious say 1km we place a high speed motor of say angular speed w > 3E5 . And in the motor we attach a laser directed towards the walls of the cylinder. When we rotate the motor with the laser lighted, won't the laser point move along the cylinder walls at speed greater than the speed of light?
Yes. "Points" are free to move at any speed. Of course each photon travels at c, and no photons (or masses) are moving "along the cylinder wall".
 P: 664 THEN this means "something" can travel faster than light as opposed to the famaous quote "NOTHING CAN TRAVEL FASTER THAN LIGHT"
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## A thought Experiment on velocity greater than C

 Quote by thecritic THEN this means "something" can travel faster than light as opposed to the famaous quote "NOTHING CAN TRAVEL FASTER THAN LIGHT"
Correct, that famaous quote is wrong. It is an oversimplification.
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 Quote by thecritic THEN this means "something" can travel faster than light as opposed to the famaous quote "NOTHING CAN TRAVEL FASTER THAN LIGHT"
That famous quote is simply not true in SR or GR. It's just a faulty paraphrase.

The speed limit of c is for particles relative to inertial reference frames only. In your example, no particle exceeds the speed of light.
 P: 9 Sorry I didn't understand the experiment quite clearly. But acc. to my knowledge optimum speed is the speed of light.
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 Quote by rozan977 Sorry I didn't understand the experiment quite clearly. But acc. to my knowledge optimum speed is the speed of light.
In common language "optimum" means "best"! In any case everyone here is agreeing that no physical object (as opposed to a spot of light on a wall) can move faster than light.

If I aim a very, very bright laser at the moon, and then move it through a small angle, the spot of light it makes on the moon will appear to move across the face of the moon faster than the speed of light. That's the basic concept of the initial post. But neither the laser nor the photons making up the light has moved faster than the speed of light.
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 Quote by thecritic THEN this means "something" can travel faster than light as opposed to the famaous quote "NOTHING CAN TRAVEL FASTER THAN LIGHT"
What is the "something" that is traveling faster than c? The points at which the photons strike the cylinder? That's not really a "something".
 P: 664 Wait a minute. If we consider the spot of light as some sort of information, Doesn't this also implies that information has traveled faster than light ?
 Mentor P: 15,552 No, the information in the spot has traveled from the laser to the wall at the speed of light. No information traveled from one point on the wall to another.
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 Quote by thecritic Supoose at the center of A huge cylinder of radious say 1km we place a high speed motor of say angular speed w > 3E5 . And in the motor we attach a laser directed towards the walls of the cylinder. When we rotate the motor with the laser lighted, won't the laser point move along the cylinder walls at speed greater than the speed of light? (I have attaced a drawing)
These types of reasoning are largely referred to a gorgian arguments. It's like saying "If you are a father, then you must be the father of everything, because you cannot not be a father." It's semantic.
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 Quote by thecritic Wait a minute. If we consider the spot of light as some sort of information, Doesn't this also implies that information has traveled faster than light ?
Think of it this way. One have person standing where the spot of light starts and one that is standing where it moves to. There is no way for the person at the first position to affect the spot in any way that would allow him to use it to send a signal to the second person.
 P: 664 Yeah, I have now understood this. Thanks Janus.
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 Think of it this way. One have person standing where the spot of light starts and one that is standing where it moves to. There is no way for the person at the first position to affect the spot in any way that would allow him to use it to send a signal to the second person.
What about if there weren't two people, but 1guy moving the laser and on the other side some sort of a digital sensor-platform for example, that would recognise the movement of the laser from one point to the other as one bit of information?
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 Quote by RogiNicba What about if there weren't two people, but 1guy moving the laser and on the other side some sort of a digital sensor-platform for example, that would recognise the movement of the laser from one point to the other as one bit of information?