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thought experiment

Blogs > nimysa
Post a Reply
nimysa
Profile Blog Joined March 2008
United States383 Posts
September 02 2009 01:12 GMT
#1
Recently I was asked a qeustion that has been boggling my mind for a while now, and alas my thought processes behind answering this question is not too qualified nor too logical toward answering the question; it has been bugging me and driving me crazy, so I thought I should post it here. My knowledge of physics is quite small, but here is the question:
"if a car is travelling at the speed of light, and while travelling, turns it's head lights on, what happens?"

Symmetry
Profile Blog Joined June 2009
Canada294 Posts
September 02 2009 01:18 GMT
#2
Light travels at the same speed from all frames of reference.
micronesia
Profile Blog Joined July 2006
United States24782 Posts
Last Edited: 2009-09-02 01:20:12
September 02 2009 01:19 GMT
#3
It would shoot ahead of you at 3e8 m/s from your perspective.

Your time would dilate in order to make up for the apparent discrepancy an outside observer would see.

edit: I took the question to mean your car was moving at ALMOST the speed of light so it would make sense.
ModeratorThere are animal crackers for people and there are people crackers for animals.
Severedevil
Profile Blog Joined April 2009
United States4839 Posts
Last Edited: 2009-09-02 01:22:06
September 02 2009 01:19 GMT
#4
I'm pretty sure light doesn't care how fast its emitter is moving, and a car can't travel at the speed of light since it's a massive object.

Anyways, I think the light appears to be moving at the speed of light from the perspective of a viewer in the car (as Micronesia said) as well as from a stationary perspective, but time is different from the perspective of the car as from the perspective of a stationary viewer. (Hence the slower aging for people going near the speed of light.)
My strategy is to fork people.
Murlox
Profile Blog Joined March 2008
France1699 Posts
Last Edited: 2009-09-02 01:22:08
September 02 2009 01:20 GMT
#5
SC2 beta key for the driver.

edit : and yeah, car is a massive object.
Resistance ain't futile
Rev0lution
Profile Blog Joined August 2007
United States1805 Posts
Last Edited: 2009-09-02 01:25:48
September 02 2009 01:21 GMT
#6
I really don't understand the question.

What happens is so broad a question that you can really answer it in many ways.

1) The car remains the same at constant speed.
2) In the point of view of a bystander who could see the car moving at the speed of light would not see the light emiting from the car if standing on its side. Since the car and the light are traveling at the same speed the shining of the light would be diminished so low that you could not notice it.
3) Standing in front of the car you would see a ray of light passing you by.


etc.

Another reason the light can't project itself outside of the car is because it would mean that the light of the car is traveling faster than the car itself. Since nothing can travel faster than the speed of light. You'd probably not see light coming from the car if you were looking at it pass you by.

you -> looking at this direction car -^ lights going that way.
My dealer is my best friend, and we don't even chill.
sigma_x
Profile Joined March 2008
Australia285 Posts
September 02 2009 01:30 GMT
#7
Good work! that is the very thought experiment that got Einstein into developing special/general relativity.
vAltyR
Profile Blog Joined July 2008
United States581 Posts
September 02 2009 01:31 GMT
#8
Relativity is awesome. We usually think of time and distance as constant, whereas speed is changing depending on both time and distance. In actuality, it's the other way around. Speed remains constant, and time and distance is what changes to keep it constant.
내 호버크라프트는 장어로 가득 차 있어요
Sky
Profile Blog Joined July 2004
Jordan812 Posts
Last Edited: 2009-09-02 03:35:07
September 02 2009 01:56 GMT
#9
Well nimysa, if you had fun trying to figure that problem out, you should check...

Public Science Papers

Many research papers have other ideas that weren't touched upon included in the "limitations" or "conclusions" section. The drawback being that there are a lot of terms that have complex meanings.

At least you have that quality of dwelling on something unknown to you.

+ Show Spoiler +
Always favored Feynman over Einstein... Feynman was a PLAYA!!!
...jumping into cold water whenever I get the chance.
Pawsom
Profile Blog Joined February 2009
United States928 Posts
September 02 2009 01:59 GMT
#10
On September 02 2009 10:20 Murlox wrote:
SC2 beta key for the driver.


Haha
theonemephisto
Profile Blog Joined May 2008
United States409 Posts
September 02 2009 02:01 GMT
#11
That's why the car CAN'T travel at the speed of light.

From the perspective of the DRIVER, the light would zoom ahead of you at the speed of light.

From the perspective of the BYSTANDER, the light would still be moving at the speed of light, just as fast as the car is. Which is impossible. Which is why it's theoretically impossible to go the speed of light.

Now if the car was moving at ALMOST the speed of light, time would dilate for the car, making the speed of the headlight seem the same from both perspectives.
KwarK
Profile Blog Joined July 2006
United States44195 Posts
September 02 2009 02:01 GMT
#12
On September 02 2009 10:31 vAltyR wrote:
Relativity is awesome. We usually think of time and distance as constant, whereas speed is changing depending on both time and distance. In actuality, it's the other way around. Speed remains constant, and time and distance is what changes to keep it constant.

I very much dislike this. It makes my brain hurt to think about just how far I'm moving when you take the expansion of the universe and the whirling of galaxies into account.
ModeratorThe angels have the phone box
ghostWriter
Profile Blog Joined January 2009
United States3302 Posts
September 02 2009 02:20 GMT
#13
On September 02 2009 11:01 Kwark wrote:
Show nested quote +
On September 02 2009 10:31 vAltyR wrote:
Relativity is awesome. We usually think of time and distance as constant, whereas speed is changing depending on both time and distance. In actuality, it's the other way around. Speed remains constant, and time and distance is what changes to keep it constant.

I very much dislike this. It makes my brain hurt to think about just how far I'm moving when you take the expansion of the universe and the whirling of galaxies into account.


Have you ever seen the pictures where they compare the sizes of the earth to jupiter/the sun then the solar system to the largest stars ever discovered?

This is seriously mindblowing.
Sullifam
citi.zen
Profile Joined April 2009
2509 Posts
September 02 2009 03:14 GMT
#14
Technically the answer is indeterminate, since the relative velocity formula contains a 0/0.

+ Show Spoiler +
v = (w - u)/(1 - wu/c2), where u = c
Aut viam inveniam, aut faciam.
Dasher
Profile Blog Joined February 2009
United States71 Posts
September 02 2009 03:31 GMT
#15
On September 02 2009 10:18 Symmetry wrote:
Light travels at the same speed from all frames of reference.

Not true!
http://en.wikipedia.org/wiki/Slow_light
"My favorite race is zerglings"
micronesia
Profile Blog Joined July 2006
United States24782 Posts
September 02 2009 03:37 GMT
#16
On September 02 2009 12:14 citi.zen wrote:
Technically the answer is indeterminate, since the relative velocity formula contains a 0/0.

+ Show Spoiler +
v = (w - u)/(1 - wu/c2), where u = c

First of all that's no surprise since a massive object can't travel at the speed of light anyway (hence my claim that we should assume the car is moving very close to the speed of light). Second of all I don't believe you can use that formula for photons.
ModeratorThere are animal crackers for people and there are people crackers for animals.
CharlieMurphy
Profile Blog Joined March 2006
United States22895 Posts
Last Edited: 2009-09-02 05:41:25
September 02 2009 05:40 GMT
#17
the most basic answer would be the lights go on but don't seem to shine anywhere.

A better way to think of it is if you take a ray of light and assume that it can shoot off another ray of light. But since they both move the same speed it would just be a brighter ray, not a longer ray.
..and then I would, ya know, check em'. (Aka SpoR)
micronesia
Profile Blog Joined July 2006
United States24782 Posts
September 02 2009 05:57 GMT
#18
On September 02 2009 14:40 CharlieMurphy wrote:
the most basic answer would be the lights go on but don't seem to shine anywhere.

A better way to think of it is if you take a ray of light and assume that it can shoot off another ray of light. But since they both move the same speed it would just be a brighter ray, not a longer ray.

This is the second time tonight I am speechless.
ModeratorThere are animal crackers for people and there are people crackers for animals.
Nitrogen
Profile Blog Joined February 2008
United States5345 Posts
September 02 2009 06:01 GMT
#19
On September 02 2009 14:57 micronesia wrote:
Show nested quote +
On September 02 2009 14:40 CharlieMurphy wrote:
the most basic answer would be the lights go on but don't seem to shine anywhere.

A better way to think of it is if you take a ray of light and assume that it can shoot off another ray of light. But since they both move the same speed it would just be a brighter ray, not a longer ray.

This is the second time tonight I am speechless.


LOL.
UNFUCK YOURSELF
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