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Topic: Speed of light (Read 915 times) |
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JCJC454
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Speed of light
« on: Oct 16th, 2005, 9:45am » |
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Im going to start this topic off with what most people hate to see at the beginning of a post.
I wasn't sure where this post should go....but(  ) I decided to put it here because it only requires alittle bit of research (for me at least) and a bit of thought maybe.
Its not really a riddle either I guess but I spend a lot of time here and there are a lot of clever people here which are always looking for a puzzle.
Anyway here is the question which for some reason I thought up while watching the snooker this afternoon.
If an object or person was moving faster than the speed of light, would it be possible to take a picture of it?
Also, would it be able to be caught on a video camera?
I thoguht of this while i was watching the snooker because i thought if Rocket Ronnie took a shot and moved faster than the speed of light to nudge the ball in the pocket and then move back to his original position would anybody notice?
Obviously that scenario is not humanely possible but you get the gist.
P.S. If you dont know what snooker is its bascially a game of pool on a larger table and different rules.
P.P.S. First post 
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24 beers in a case. 24 hours in the day....coincidence?? I think not.
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BNC
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Re: Speed of light
« Reply #1 on: Oct 16th, 2005, 11:24am » |
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Hi JCJC454,
1. Welcome!
2. To avoid being cought on tape, you don't have to move that fast -- you only need to move to your destination and back faster than the frame-to-frame time span (say 20 ms). Do, to move around the billiard table (say 10m), in less than 20ms (say 1ms), you need to move at 10m/1ms = 10km/s = 104m/s << c .
3. Acording to the theory of relativity, it is impossible for anything moving slower than c to move faster. AFAIK, it is also impossible for anything moving at > c to decelarate to < c. So, if you move at > c, you will probably not be cought on film, as you don't exist in this universe of ours (well, I think...)
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Oyibo
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on Oct 16th, 2005, 9:45am, JCJC454 wrote:
If an object or person was moving faster than the speed of light, would it be possible to take a picture of it? |
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You tell me first: if 2 = 1, what would be the ratio between the circumference and the diameter of a circe?
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JCJC454
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Re: Speed of light
« Reply #3 on: Oct 16th, 2005, 1:59pm » |
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Well we know (or at least everybody has agreed) that nothing can move faster than c, but I was thinking lets just assume for the moment that something can.
(I know I am just going to confuse myself and possible others with what I am about to say, as I have a limited knowledge of physics)
Let's say we point a camera a blank wall. There is an object, lets say a fork (I was discussing this over the dinner table earlier) that was travelling at 2c and at some point would cross between the camera and the wall.
Assuming we know the exact speed direction and everthing else that is relevent would it be possible to take a picture of the fork.
At the moment of the picture the image might appear but the fork would actually have passed the camera I assume.
Like when something is travelling faster than the speed of sound you see it before you hear it.
(I am sufficiently confused now so I'll stop but I hope you see what I am trying to get at)
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towr
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Re: Speed of light
« Reply #4 on: Oct 16th, 2005, 2:02pm » |
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I don't think people should confuse logic and physics too much.
If an object moves faster than light, there is no logical reason why you couldn't catch it on tape. As long as it emits or reflects photons.
In that respect it doesn't matter whether it's physically impossible that it happens.
Compare it to a vehicle with a siren moving faster than sound. You'll still hear it. It'll just have passed before you hear it.
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| « Last Edit: Oct 16th, 2005, 2:45pm by towr » |
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JCJC454
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Re: Speed of light
« Reply #5 on: Oct 16th, 2005, 2:22pm » |
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I suppose that is right. I Didn't think about this one long enough and it was hurting my poor head. Also my family was hurting my head by giving me stupid answers like Ronnie wouldn't have lost if he could do that. Or asking if this is in anyway related to the 100 prisoners and a lightbulb problem.
So I gave up to ask you guys and learnt that I will never get a serious answer from my family or if it requires a little bit of thought they will give up so fast.
Thanks BNC and Towr for helping me here.
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24 beers in a case. 24 hours in the day....coincidence?? I think not.
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honkyboy
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Re: Speed of light
« Reply #6 on: Oct 16th, 2005, 5:52pm » |
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In order to take a picture of this fork you would have to break a few more laws of physics than just the speed of light. For one thing we should consider the Doppler effect.
Light from an object moving away from you at >c would be red shifted to have a frequency of zero and be undetectable.
Light from an object moving toward you a >c would be blue shifted to have an infinite frequency and do unimaginably bad things to your camera.
In your dinner table example, you, your camera, and the room you were in would be vaporized by light from the fork directly after the fork enters the room. Luckily our little univers doesn't allow this sort of thing to happen.
Anyway if an object was moving at 2c it would not be possible to know its exact speed and direction.
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JCJC454
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Re: Speed of light
« Reply #7 on: Oct 16th, 2005, 6:24pm » |
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Yea I didnt do much research on the matter.
I think i was just trying to make the problem too simple and broke too many rules.
I would ask why nothing can move faster than the speed of light, and how that can be proved but im sure i could find out for myself if I truely wanted.
Also its 2:20AM here and I dont want to think about it anymore.
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24 beers in a case. 24 hours in the day....coincidence?? I think not.
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BNC
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Re: Speed of light
« Reply #8 on: Oct 16th, 2005, 10:54pm » |
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on Oct 16th, 2005, 2:02pm, towr wrote:
If an object moves faster than light, there is no logical reason why you couldn't catch it on tape. As long as it emits or reflects photons.
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That's interesting. Again, we assume that objects in this universe cannot accelarate to speed faster than c, but nothing prevents a (let's call it) "parallel universe" where things move faster than light. There, nothing may decelarate to lower than light speed. My point is that in "this universe" we have photons at c. So, I assume that at that assumed "parallel universe" photons may exist as well, being the slowest elements there. These may allow that other universe to be detected here. Of course ,no such detection was made...
on Oct 16th, 2005, 5:52pm, honkyboy wrote:In order to take a picture of this fork you would have to break a few more laws of physics than just the speed of light. For one thing we should consider the Doppler effect.
Light from an object moving away from you at >c would be red shifted to have a frequency of zero and be undetectable.
Light from an object moving toward you a >c would be blue shifted to have an infinite frequency and do unimaginably bad things to your camera.
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Wouldn't that reasoning hold for object at = c? Yet photons do travel at that speed without doing harm. And, yes, I know photons aren't objects, but that's part of the same basic rule preventing accelaration past c.
BTW, if these > c objects would exist, what would their size be?
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| « Last Edit: Oct 16th, 2005, 10:55pm by BNC » |
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towr
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Re: Speed of light
« Reply #9 on: Oct 16th, 2005, 11:05pm » |
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on Oct 16th, 2005, 10:54pm, BNC wrote:| BTW, if these > c objects would exist, what would their size be? |
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Mass or impulse would be imaginary under our (syspected) physical laws..
As for the doppler effect, it seems in both cases the frequency turns out imaginary. In other words instead of ~ei a you get ~eb.
However, I would hazard to guess the formula breaks down in this case. Because the same could be said for sound, and you 'simply' break the sound barrier instead.
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| « Last Edit: Oct 16th, 2005, 11:21pm by towr » |
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Oyibo
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on Oct 16th, 2005, 11:05pm, towr wrote:
However, I would hazard to guess the formula breaks down in this case. Because the same could be said for sound, and you 'simply' break the sound barrier instead.
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This is a classical error.
Sound travels through a medium. Exactly 100 years back some bright guy proved that the same does not hold for light. There simply is no such thing as an absolute 'light ether'.
Speaking about speeds > c is meaningless if you don't specify alternative (and consistent!) laws of physics.
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towr
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Re: Speed of light
« Reply #11 on: Oct 17th, 2005, 4:58am » |
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I'll admit it's an imperfect analogy. But as you say, 'faster than light' doesn't make sense in our physics. So none of the formulas really take it into account.
[sqrt] (c+v)/(c-v)
or
[sqrt] |(c+v)/(c-v)|
No difference as long as v < c. But rather than turning imaginary, I'd sooner expect the waveform to flip direction.
(Another imperfect analogy,
if you draw a sine on a pievce of paper, moving your hand at constant speed v to the rightt, look at the result when at the same time you move the paper to the right at speeds 0, 0.5v, v, 1.5 v and 2 v)
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Grimbal
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Re: Speed of light
« Reply #12 on: Oct 17th, 2005, 6:15am » |
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A path that goes from A to B faster than the speed of light, if you change referential, can become a path that goes from B to A faster than light or a path that goes instantly from A to B, which means the object is simultaneously everywhere on the path. If the path is not straight, or the speed not constant, the same path can appear as appearing somewhere between A and B and split to join A and B. So there really can be no material object going faster than light. That would be like travelling back in time.
But you still can imagine that the object in question is a projected image. Imagine you project an image on a large screen and you rotate the projector. If the projector is far enough, the image can move faster than the speed of light. I see no reason why you couldn't see the image pass or take a picture of it, provided your shutter time is short enough. Of course there wouldn't be any doppler effect because the light isn't really emitted from a fast moving object.
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Icarus
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Re: Speed of light
« Reply #13 on: Oct 17th, 2005, 3:47pm » |
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on Oct 16th, 2005, 9:45am, JCJC454 wrote:If an object or person was moving faster than the speed of light, would it be possible to take a picture of it?
Also, would it be able to be caught on a video camera? |
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Yes. Light emitted by objects moving faster than light is called "Cherenkov radiation", and is used in detecting some cosmic radiation (in particular, solar neutrinos). It is indeed similar to the shock wave (sonic boom) produced when objects move faster than sound.
How can particles be moving faster than light? Simple - in a material medium, the speed of light is < c, which is the speed of light in a vacuum.
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rmsgrey
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Re: Speed of light
« Reply #14 on: Oct 18th, 2005, 3:38pm » |
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My understanding is that relativity allows objects to travel faster than c in our universe - just that nothing can accelerate through light speed. Unless something's changed in the last 7 years, "tachyons" are still in the category of "theoretically possible but believed not to actually exist" - within the last decade, some physicists were seriously contemplating the possibility of neutrinoes being tachyons as a way of explaining the shortage of solar neutrinoes. Measurements suggesting they have a positive rest mass, so are stuck at subluminal speeds like the rest of us were still unconfirmed when I stopped actively following the debate.
With an object moving FTL perpendicular to your camera's line of sight, the light from it wouldn't be Doppler-shifted. I think there are some other weird effects that should happen, but you should be able to get a photo - provided your camera ahs a fast enough shutter speed!
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