If you rotate a beam of light, is there a point at which the 'tip speed' will excede the speed of light itself

Answer 1

Yes.

Namely if frequency of rotation is f, then speed of light
is achieved at distance R = c / 2πf.

Answer 2

Remember that the beam is not a rigid structure: it propagates from the source at c (speed of light). If you consider a circle with a radius large enough, a series of observers stationed around the circle would see the "phenomenon" of the light beam running around the circle at more than c.

This does not mean that the light is moving that fast: each photon from the source moves at c, from the center to the edge of the circle. An observer above would perceive the "beam" as an arc, much as the distribution of spray from a rotary water sprinkler.

Imagine a laser beam attached to the pivot of the hour hand of a clock in space, such that the beam sweeps out a full circle every 12 hours. Now, consider a *huge* clock face, three light-hours in radius (about 2 billion miles).

Turn on the flashlight at noon. The 12:00 photons will head toward the "12", 2b miles away. They continue in a straight line, not affected by the motion of the hour hand. At 1:00, those photons are still traveling "straight up", while the newly-generated photons are headed toward the "1". By the time 3:00 rolls around, the first photons are finally hitting the "12", the ones headed toward "1"a are two-thirds of the way there, the ones headed for the "2" are almost 670M miles from the center, and the ones destined for "3" are just leaving the center.

Overall, the "beam" forms a large spiral with the equation r = c*theta. The "wave" of photons hitting the clock face will exceed the speed of light when the clock face gets large enough, but each photon still travels at c.

Answer 3

Nope. You will get what I call the "swinging hose effect." If you swing a running hose nozzle back and forth, you see that the tip of the water flow most often lags behind the nozzle direction.

That results because it takes time for the water to get from the nozzle to the point on the tip of the stream of water some distance away. Meanwhile, while that water from the nozzle is getting to the tip of the stream, the nozzle has moved on in its direction. Thus, the stream tip lags the position of the nozzle.

Same thing for light. Although those photons scurry along pretty fast, they are limited in how fast they can go. Thus, it takes time for light to flow from the nozzle (e.g., a laser projector) to the tip of the light beam, say, four light years away. Clearly, that tip of light will lag four years behind wherever the laser light projector might be currently.

For example, if you were shine a planet around Alpha Centauri, about four light years away, and then suddenly move your very powerful laser projector ninety degrees to one side, the Alpha Centaurians would not see that motion until four years after you moved the projector..."the swinging hose effect."

Answer 4

My guess is no. The reason is, in space, you can see these jets of both matter and light. All of them, including the arms of galaxies, bend against the rotation like a stream from a lawn sprinkler. As the beam goes out, every photon continues out at the direction it was sent originally. As each new photon leaves the emitter, It goes at the speed of light its new direction. The net effect is the beam would look like a water sprinkler also. Expanding out from the center at the speed of light, but having zero velocity from the sideways motion of the emitter.

Answer 5

Yeap but it breaks no physical laws because technically the tip speed is a mental construct. Nothing is actually moving faster than the speed of light.