Question regarding the speed of light?

Question

Relativity Question
This has been bugging me off and on since high school, and not even my science professors in college were able to help me out. It suddenly occurred to me that for the first time in my life I have access to every science geek with an internet connection IN THE WORLD, so maybe I can get an answer.

It is accepted as an axiom that nothing can travel faster than light.

Imagine a lighthouse. This particular lighthouse sweeps its beam in a full circle once every second. We build a circular wall all the way around the lighthouse at a distance of one mile, so the beam from the light house sweeps around the inside of the wall like a search light once every second. A circle with a diameter of 1 mile has a circumference of 3.14159 miles, so the spotlight cast by the lighthouse is moving at 3.14159 miles per second, or 11309.724 miles per hour. The speed of light is 186262 miles per second. If the wall we had built were 59290 miles in diameter, its circumference would be 186264.8711 miles, the spotlight from the lighthouse would still be making a full sweep in one second, but in doing so it would be moving at 186264.8711 miles per second. In other words, it would be moving across the inner surface of the wall 2.8711 miles per second FASTER than the speed of light.

There has GOT to be something wrong with this scenario.

Answer 1

The light is still travelling at 186262 mps. The distance that it is travelling is the radius of your wall. The shadow cast by the light fixture is the only thing causing the light to seem to travel in a circle. So the fixture is the only thing moving, at whatever rate you set it.

Answer 2

Questions about speed of light always have to take into consideration the observer. With regards to this question you act as though the light would travel from the lighthouse to the wall 60,000 miles away instantaniously which it would not. It would be like spraying a hose while turning, certain light particles would be hitting before other light particles. The light would not appear to be moving faster than the speed of light. Another way to look at it is if I had a flashlight that could shine into space one light year and I swoshed it by how quickly would it move across the sky. The answer is it would take a year for the light on the left side of the arc to travel and it would take a year plus more time for the arc in the middle to travel and again a year for the arc on the right side. So the observer would observe two beams from the left and right moving in twoard the center. The observer in your observation would notice a pulsing from where he was standing rather than a moving around. You also have to take into account the time it would take for the light to bounce off the wall and and reach your observation point.

Answer 3

the light in the beam is not moving AROUND the wall, it is moving radially, OUTWARDS from the light bulb to the wall. In the FIRST Circle, the light beam is only traveling 1/2 a mile! However, the BULB is turning at 1 revolution per second.



Same holds true with your SECOND Wall. The BEAM is only traveling a distance of 29645 MILES -- the RADIUS of the circle! AND -- the BULB is still turning only one revolution per second!



Now. suppose that you built a THIRD wall that is 372564 miles in diameter (186,282 miles radius), or 1170443 mile in circumference. In THIS case, the light beam actually travels 186282 miles (and would take 1 second to do so). And the bulb is rotating at one revolution per second. Now, you would see the beam ONLY when it is pointed at you, so you would see a "flash" once per second.



The trick here is that the flash you SEE is actually DELAYED by one second, with respect to the lighthouse bulb. The flash you SEE actually happened one second ago!





The problem with YOUR scenario is that you are measuring the time AROUND the circle, when you should be measuring the RADIUS of the circle -- the actual path the light is taking.

Answer 4

My understanding is that the speed of light is constant from the point of view of the observer: If that is true then you, traveling just under the speed of light would see the beam take off just as if you were standing still. An Observer off to the side however, would see the beam of light move ahead of your incredible speed at 10 ft/sec. faster than you yourself are traveling. I think I have a headache now, I'm going to contemplate the hole theory of electrical flow. Or maybe if the North Pole is actually the South magnetic pole because the N on the compass points to it. Or is the Compass labeled backwards to begin with?

Answer 5

The beam's position on the wall might be moving at faster than the speed of light, but the light shining on the wall is still only going at the speed of light.



Think of it this way: replace the lighthouse with a machine gun. The gun is in the center of this enormous wall, spinning and firing bullets (each traveling at 1000 ft/sec). No matter how fast you spin the gun, the bullets themselves are still traveling at 1000 ft/sec.



The positions on the wall where each subsequent bullet hits does become greater the faster the gun is spun, and if you spin the gun fast enough, the speed something would have to travel along the wall to get hit by each bullet might be exceed the speed of light, but nothing is doing that.



So back to the lighthouse: each photon from the lighthouse is traveling in a straight line (straight enough) from the lighthouse to the wall. From one position on the wall to the next, different photons are doing the illuminating.



In both the cases of the lighthouse and the machine gun, neither matter nor light is moving faster than the speed of light.

Answer 6

Great question -- I remember we talked about this when I was taking physics in college.



The fact is, when it's said that "nothing" can travel faster than light, what is really meant is that no energy, matter or information can travel faster than light. This is prohibited because it would violate laws of causality and conservation of energy, because of the ways that space, time, matter and energy are tied together by the constant "c" (speed of light).



But the moving spot of light on the wall does not carry any energy or information from one point on the wall to another; so it's "allowed" to exceed lightspeed.



In another experiment, you could line up a bunch of people in a line (say) 186,282 miles long, furnish them all with exactly synchronized timepieces, and instruct each of them to raise and then lower their arm at a particular instant, in such a way that the "wave" of arm movements traveled from one end of the line to the other in under 1 second. The "wave" would be traveling faster than lightspeed; but that's OK, because no material, energy or information is moving from one end to the other.

Answer 7

Yes, the spotlight appears to move faster than speed of light, but that does not violate the postulate that nothing can travel faster than speed of light because it is apparent motion and not real motion.



In other words, it's an illusion and not real. It's like saying I see a mirage somewhere where nothing like what I see can exist.

Answer 8

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