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  #1  
Old 03-19-2004, 07:20 PM
Campione Campione is offline
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If you are traveling at the speed of light in a dark tunnel...

and you're wearing one of those helmets with a flash light on it, and you flicked it on, what happens?

Sorry for the dumbass question. I heard someone ask this before and I can't remember who.
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  #2  
Old 03-19-2004, 07:26 PM
MC Master of Ceremonies MC Master of Ceremonies is offline
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You can't travel at the speed of light, even theoretically, so the question does not have an answer.
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Old 03-19-2004, 07:27 PM
Joe Random Joe Random is offline
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Quote:
Originally Posted by Campione
If you are traveling at the speed of light in a dark tunnel...

and you're wearing one of those helmets with a flash light on it, and you flicked it on, what happens?
Unfortunately, that's an invalid question (much like "If you went north from the north pole, where would you be?") You can't travel the speed of light, so the question can't be answered.

Now, if you were traveling close to the speed of light (relative to some frame of reference), then the light from the flashlight would appear to travel at the speed of light both to you and to whatever you're traveling relative to.
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Old 03-19-2004, 07:37 PM
DarrenS DarrenS is offline
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If you turn on your headlights while driving at the speed of light, what happens?
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  #5  
Old 03-19-2004, 07:40 PM
x-ray vision x-ray vision is offline
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Here is a good explanation.
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  #6  
Old 03-19-2004, 07:42 PM
trudi fermelli trudi fermelli is offline
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If you travel at the speed of light you are light, so you couldnt be wearing a helmet. In fact you couldnt be in a dark tunnel either.
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  #7  
Old 03-19-2004, 07:50 PM
MC Master of Ceremonies MC Master of Ceremonies is offline
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Quote:
Originally Posted by trudi fermelli
If you travel at the speed of light you are light, so you couldnt be wearing a helmet. In fact you couldnt be in a dark tunnel either.
well not necessarily other massless particles travel at c. It's impossible to have refrence frame (in special relativity) for any particle that travels at c with respect to a valid (and therfore all valid) reference frame(s).
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Old 03-19-2004, 08:04 PM
trudi fermelli trudi fermelli is offline
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Quote:
Originally Posted by MC Master of Ceremonies
well not necessarily other massless particles travel at c. It's impossible to have refrence frame (in special relativity) for any particle that travels at c with respect to a valid (and therfore all valid) reference frame(s).
ummmm...yeah, what he said
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  #9  
Old 03-19-2004, 08:09 PM
trudi fermelli trudi fermelli is offline
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If you are in a dark tunnel after travelling at c

Go to the light! Go to the light!

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  #10  
Old 03-19-2004, 08:50 PM
Exapno Mapcase Exapno Mapcase is online now
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Just to put the icing on this cake, you can't even ask as a thought experiment what would happen if a massless particle were to try this.

Particles that move at the speed of light do not experience time: time stops for them. It's meaningless to try to speak of doing an action at the speed of light. In its own frame of reference, a massless particle is created moving at the speed of light and with no interval interacts with another particle ending its existence.

Darn that Einstein.
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  #11  
Old 03-19-2004, 09:14 PM
Bret Bret is offline
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...but on a different note...Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object?
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Old 03-20-2004, 02:01 AM
LtningBug LtningBug is offline
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Quote:
Originally Posted by Bret
...but on a different note...Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object?
This depends on what you mean by taking a picture of a laser beam. It would be entirely possible to fire a laser at a target, and from the side take a picture such that the light being reflected from the laser beam off of particles in the beam's path would make it appear that the laser beam has been caught in midstride, so to speak. This would require either a very short shutter speed or a very long laser beam path (with the camera appropriately far away).

Of course, the above assumes the laser beam is actually hitting many objects (dust, smoke, whatever), and so perhaps is not an answer to your question. I suppose a better answer might be that in order to take a picture of a light beam, the light beam has to hit the camera.
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  #13  
Old 03-20-2004, 07:30 AM
Cardinal Cardinal is offline
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That would be one HECK of a shutter. Using Google, I find out that (runs to check) light (in a vacuum) could go around the entire earth in .1339 seconds.

So, either speed that shutter up a bit, or get Tim Taylor to step up the power on the laser and step waaaaaaaaaayyyy back.
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  #14  
Old 03-20-2004, 08:03 AM
Arturius Arturius is offline
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Quote:
Originally Posted by Exapno Mapcase
Darn that Einstein.
Yeah, he made science no fun
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  #15  
Old 03-20-2004, 04:46 PM
Mangetout Mangetout is offline
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Quote:
Originally Posted by Bret
...but on a different note...Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object?
If the beam is sufficiently bright and is travelling trough a medium that scatters light, and you're viewing from sufficiently far away, then you might even be able to see the progres of the wavefront visually.

This has been done with powerful telescopes (not with lasers though) - light from a supernova event (or other sufficiently bright pulse) can be seen to progress through nearby (in astronomical terms) nebulae.
This is particularly useful in calculating the distance of the object - knowing that it took a whole year for light to move from distant point A to distant point B, the calculation of distance from the subtended angle is a primary school task.
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