For some reason my mind has been dwelling on a scenario. I think I may have been reading a little too much sci-fi lately perhaps. Physics has never been a strong point for me, so I am curious what people think to the following.

Say you had some system for recording video that didnt use frames, in the sense that it recorded a "live stream" which could be paused and incremented at an infinitely small stepping. (Please dont get hung up on the impossibility of this). This device is required in the scenario due to the uber speed of light, and the short distances required for the experiment.

Say you had it set to record a mile long stretch. Someone is stood halfway down the stretch. Say they could theoretically travel at, or just under the speed of light (for those who say its impossible to travel at the speed of light).

Now, this person moves at this speed to the far end of the stretch, and then to the near end.

What would this camera record in those split second period of travel?

Theres two things. Initially I was wondering whether it would be possible to stage it so that at a very very very short point in time the image would have recorded the person stood at 2 or more of the points. Secondly is the issue of if the person is travelling away from the camera near the speed of light, the speed of the light reflected off of him/her would be altered and so surely theyd look a bit funky?

Even though for a while I was thinking question 1 would be possible for ages, having now typed it out I dont think it would be. I was thinking of the speed of sound and how watching footballs get kicked you hear the kick after you see it, and so if you could make a similar noise at different points but timed so that the pause between noises is shorter than the speed of sound, theyd hit the ears at the same time (if set right). But its possible to go faster than sound, not light?

they used warp drive (moving faster than the speed of light) in star trek TNG to make the ship appear in one place while actually being in another for a tactical advantage... sounds like a similar idea

(no im not a trekkie)

Doppler effect of light springs to mind for the secondly, no idea what that would be like though

http://en.wikipedia.org/wiki/Laser_Doppler_Vibrometer

So probably yes, but itd have to be a crazy acceleration, like going from 0 to 1 million * c in under a femtosecond etc.

Yeah. The second question comes to mind from a few books Ive read RE star travel, and how the characters when speeding up noticed the stars changing colour and grouping up into the view screen etc befrore disappearing.

What would happen if you had a light source that was travelling faster than the speed of light, and you were stood behind it? I presume you wouldnt see it as the light emitted in your direction would actually still be going away from you.

In this case, what would happen if you faced the opposite direction to the light sources travel, and looked at the light which was emitted away from you but is travelling "backwards"?

Quote from: Binary Shadowthey used warp drive (moving faster than the speed of light) in star trek TNG to make the ship appear in one place while actually being in another for a tactical advantage... sounds like a similar idea

(no im not a trekkie)
 

Thats called the Picard Manoeuvre.  (I am a bit of a trekkie) Technically, warp drive isnt faster than light, rather it uses massive amounts of energy to bend space time, shrinking it ahead of the ship and expanding it behind, while keeping the ship itself in a field of normal space.

As for the light travelling away/toward you, the speed of light is constant for all observers, regardless of motion, in accordance with the theory of special relativity. The normal thought experiment is to imagine a car travelling at the speed of light. If you switch the headlights on, does the light "pool" in the headlamps? No, it moves away from the car at the speed of light, even though the car is already going at that speed. For an external observer the light is still moving at the speed of light.

It makes my brain hurt too. The Wikipedia introduction to relativity page isnt much help either, but this explanation page is a little easier to read.

but...but...but, thats light emitted in front.

What about BEHIND the car? If the car is travelling at the speed of light, and has a light on the back, the light emitted behind it will be travelling away from the car at the speed of light. But to an observer outside of the car, the light would not be emitted? Similarly someone in front of the car would be seeing the light at 2x the speed of light surely? Before being smooshed to nothingness by the car of course...

No, the people behind the car will see the light emitted at the speed of light. Regardless of the relative frame of reference light is *always* measured at a constant speed. The people in front of the car would see the light coming toward them at the speed of light while the people in the car would also see it leave them at the speed of light.

Its impossible to apply the ideas of normal speeds to the speed of light, the universe doesnt work that way.

I have an MSci in Physics, and you hurt my brain!

Ill think about it and maybe post a proper answer later on, but Goblin is right. Special Relativity states that the speed of light is a constant in all frames of reference. No matter how fast anything travels, all observers measure the speed of light to be 3x10^8 ms.

This has been tested experimentally, I think the Michelson-Morley experiment was the first, although they were actually aiming to prove the existance of an "ether" which was postulated as the medium through which light waves propagate. They failed (since no such ether exists), and instead proved that the SoL is constant. They also developed a fantastically useful instrument called the Michelson-Morley Interferometer. Not wishing to sound too geeky, this is probably my favourite experiment of all time.

That is just boggling.

I mean, say I am running at 10mph, and throw a ball at 10mph (relative to me)...that ball would hit its target at 20mph.

At what point does the speed of light "slow down" in relative terms for the 2 reference points? (I know it doesnt slow down, but hopefully you get my meaning...if it leaves the car travelling at SoL at the SoL relative to the car, technically thats 2x the SoL relative to a bystander, but is actually still only the SoL?)

Yeah, this is why I hate physics, yet find it so cool...

Youre making the assumption that time proceeds at the same rate for both observers. At the speed of light time dilates.

I forgot about that. So basically the people in the car, travelling so fast, are really technically frozen in time in relation to the observer...

Quote from: zpyderI forgot about that. So basically the people in the car, travelling so fast, are really technically frozen in time in relation to the observer...

yup, an observer standing still will see the cars dashboard clock start to run slow as the car accelerates towards the speed of light.

I remember my reaction to relativity more clearly than I remember the subject itself, and Im pretty sure it was something like

Quote from: Younger Mongoose"ahhhhhhhhh my brain is melting.........but actually once you get your head around the concept of time as a variable it all makes sense"

I did find that it made more sense after 4 or 5 beers though.

Relativity can indeed appear to cause some extreme effects, the car will also appear shorter than it really is.

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If he moves at any sub-light speed then nothing much happens for the camera except he moves very quickly and probably dies horribly.

The Picard manouver requires a faster than light speed, and movement towards the enemy ship, in which case it appears, for a very short time, to be in 2 places at once.

Exactly at the speed of light the man will vanish when moving directly towards the camera and reappear at the closer position, hes travelling at the same speed as light reflected off him. Going away he should look a lot darker as the light cant catch up from behind him, so its down to light coming in from the sides.

and you wonder why this forum hardly ever picks up new members?

wheres the naked pics of paris hilton ffs?

Matt

Quote from: bytejunkieand you wonder why this forum hardly ever picks up new members?

wheres the naked pics of paris hilton ffs?

Matt