High beams

[alcanfor]

I was reading a book the other day and one of the characters was talking about his physics class. He was trying to explain to his friend that physics was cool. but she just wasn't buying it. To get her to realize that it's actually interesting he gave an example of some of the questions.

 

His example was "Say you're traveling at the speed of light in your car, and you turn on the high beams, what happens?" What was said in response to this in the book is unimportant, but it got me thinking. What would happen.

 

If you have any idea at all let me know...and please...and explanation would be nice. ;-)

[Cap'n Refsmmat]

Answered before:

http://www.scienceforums.net/forums/showthread.php?t=4451

[5614]

Yeah, that thread can get a bit confusing if you don't know the answer!

 

Basically you in your car cannot travel at the speed of light. It is impossible.

 

But say you were travelling at 99.9% speed of light (which is theoretically possible) then you would see the light from the headlights travelling away from you at the speed of light.

 

It would look exactly the same (to you) as if you turned on your headlight when the car was stationary.

[Sisyphus]

You can't travel at the speed of light, so the question doesn't make sense. However, if you were travelling at 99% the speed of light, the beam would look to me as if it were travelling at C, i.e. 0.01C faster than you, ahead of you. However, to you it would appear to be travelling at C faster than you.

[alcanfor]

1st off i guess i should have looked around for this in previous posts, so i apologize for that. 2nd I obviously realize that a car cant travel at the speed of light. It was more of a "what if" question. 3rd..physics is crazy. I would never have thought that it would look the same. 4th thanks.

[insane_alien]

welcome to the wacky world of relativity. if ou think this stuff is confusing, try and visualize a 4 dimensional cube then a 5 dimensional cube or take a peek at quantum mechanics.

[alcanfor]

Oh its not just relativity thats confusing..its life in general.

[Sisyphus]

2nd I obviously realize that a car cant travel at the speed of light. It was more of a "what if" question.

 

It's more than that, though. It's not like "if you had X-ray vision, would you spy on your neighbors?" Yes, X-ray vision is impossible, but the question still makes sense. Travelling at the speed of light doesn't even make sense as a concept, because of the way relativity works. Light (in a vacuum, anyway) always appears to be moving the same speed relative to you, no matter how fast you yourself are moving. The only way this can happen is for time itself to move more slowly for you the faster you're moving. If you're going at 99% C, then time only moves 1/100 as fast for you. At 99.9%, it's 1/1000, etc. But of course you don't notice any of this, and time always moves forward, making 100% C impossible, since that would imply time stopping entirely. Also, force acting on you acts relative to you, so it takes the same amount of force to go from 0% C to 10% C as it does to go from 99% C to 99.1% C, which to you seems like the same thing. Thus you can keep accelerating forever, and you'll get closer and closer to C in smaller and smaller amounts but never reach it.

[5614]

Relativity only says there are 4 dimensions.

 

There are other theories which suggest more dimension, the most popular would probably be string theory.

 

Having said that, visualising a 4D cube is pretty damn hard!

 

And Sisyphus: snap, and I beat you by 2mins!

[5614]

X-ray vision is impossible

Well, if you had an x-ray source and an x-ray detector you could have x-ray vision. They use it in hospitals to check your bones are all right.

 

If you used it to spy on someone you could probably only see their bones, but it's still a type of vision. Obviously you need special equipment, can't do it with your eyes, but still. Maybe I'm just nit-picking!

[alcanfor]

I have to be honest, some of you people are very very....i dont know....well informed on pretty much anything i could ever have a question about.. relating to science that is. So uh...cheers!

[[Tycho?]]

I have to be honest, some of you people are very very....i dont know....well informed on pretty much anything i could ever have a question about.. relating to science that is. So uh...cheers!

 

Well this is a science forum! And a good one, a number of people in the physics section are actually physicists; its what they do for a living. Certainly adds some legitimacy to the posts that you dont get in most other places on the net.