Thought Experiment on the speed of light

In summary, the conversation discusses the concept of matter or energy traveling faster than the speed of light, using a laser pointer as an example. It is explained that while the laser pointer may appear to be traveling faster than the speed of light, it is actually individual photons traveling at the speed of light. This is further illustrated by the example of shooting photons at different locations on the moon. The conversation also mentions the speed of light being 300,000,000m/s and discusses the relative movement of the stars at night.
  • #1
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OK, so I am not a physics major, but I think that I understand that matter or energy cannot travel faster than the speed of light. Today I was using a laser pointer, and I noticed that it traveled rather fast, and it traveled faster as it went farther away from me. So if you imagined the laser beam as a lever arm, I could use velocity=rw to determine the velocity of the point on a laser pointer. So say I built a chamber with a radius of 40,000 meters. Then, I stood in the center and shot a beam of light at the wall of my chamber. I rotated the laser pointer in the center at 10 m/s. The dot would move at 40,000(10 m/s)=400,000 m/s. The speed of light is appr. 300,000 m/s. So that would mean that the photons at the end of the laser pointer would be traveling 100,000 m/s faster than the speed of light...isn't there something wrong here. My guess was that the beam of light would bend once it hit 300,000 m/s so that the dot was only traveling at 300,000 m/s. How would you analyze this?
 
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  • #2
As somebody pointed out recently on this forum, you could do the same thing with a machine gun, poking holes in a wall far enough away that the holes would travel at faster than the speed of light, right?
 
  • #3
This is possible because no physical "thing" is traveling faster than the speed of light in that scenario. Each individual photon from the laser always travels at the speed of light.

Imagine you had a laser pointer that shot out photons 1 at a time. If you shot one out towards one location on the moon, and then shot one out half a second later towards a totally different location on the moon, then the first photon would hit one part of the moon and half a second later another photon would hit another part of the moon. Even if the two locations on the moon are far enough such that d/.5s > c (d being the distance between them), nothing weird is happening here, as it's easy to see. Now just make that laser shoot many many photons at once, it's still nothing special.

BTW, the speed of light is more like 300,000,000m/s not 300,000m/s.
 
  • #4
Thanks, sorry about messing up the speed of light, pretty dumb mistake, i guess change meters to kilometers and now it works, OK, so nothing is actually traveling faster than the speed of light, because it is not the same photon hitting the wall in one direction as it is when i turn the laser pointer. Right?
 
  • #5
You got it :)

You can also rotate your head 'faster than light', relative the stars you see as you do it.
At night I mean.
 
  • #6
Haha, in fact, i guess you are always traveling "faster than light" if you assumed that we were still, and the stars just revolved around us every day. Of course that's not true, but it would seem that way.
 

1. What is a thought experiment on the speed of light?

A thought experiment on the speed of light is a hypothetical scenario where one imagines a situation in which the speed of light is being measured or observed in a unique or unconventional way. It is a way for scientists to explore the implications and consequences of the speed of light without actually conducting a physical experiment.

2. How does the thought experiment on the speed of light work?

In a thought experiment on the speed of light, one typically starts with a hypothetical scenario and uses principles of physics and mathematical equations to explore the implications of the speed of light in that scenario. This can involve imagining objects traveling at the speed of light, or observing the effects of light traveling at different speeds in a given situation.

3. What are some famous thought experiments on the speed of light?

One of the most well-known thought experiments on the speed of light is Einstein's famous "train and platform" experiment, where he imagined a train moving at the speed of light and the implications for how time and space would behave. Another famous thought experiment is the "twin paradox", where one twin travels at the speed of light and returns to find that their counterpart has aged significantly more due to time dilation.

4. Why are thought experiments on the speed of light important?

Thought experiments on the speed of light allow scientists to explore the consequences and implications of this fundamental physical constant in a controlled and hypothetical setting. They can help us understand the behavior of light and its interactions with matter, and can also lead to new discoveries and theories about the nature of space and time.

5. Can thought experiments on the speed of light be proven or disproven?

No, thought experiments cannot be proven or disproven in the same way that physical experiments can be. They are purely hypothetical and are used as a tool for exploration and understanding, rather than for testing and verifying theories. However, the insights gained from thought experiments can lead to new hypotheses and experiments that can be tested in the physical world.

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