Speed of Light Car

[Beaker]

Just one more brainteaser for this week. (I will try and find some more for next week :)) I can't resist putting this one up.

You are in a car out in space that is traveling at the speed of light. You then decide to turn on the head lights. What do you observe?

Skatie

[Dave]

Nothing. No light will be shed from the headlights -well, it will but it wont travel faster than the car and so it wont reflect back. The speed of light is not relative.

Dave.

[D87 SMW]

Come on, that was easy! :eek: :rolleyes: :(

[Mat_C]

The car can't be travelling at the speed of light ;)

[e692wtt]

Errm, everything, headlights on or not...

Theoretically...

[Ricky]

I may not be hot on physics, but I assume you will observe the warning light for the headlights on the dashboard come on? If not, you must be doing the speed of light in a peugeot with dodgy electrics, and therefore are a very silly person indeed! :laugh: :laugh: :laugh:

[Wonko_The_Sane]

You are in a car out in space that is traveling at the speed of light. You then decide to turn on the head lights. What do you observe?

That Lucas, Prince of darkness has decreed that ONCE AGAIN, your car will show as much light as a black hole..:laugh:

Either that, or as you look down to flick the switch, you hit a small planet and crack your plastic bumpers...:rolleyes:

[J199 HHG]

[QUOTE]Originally posted by Wonko_The_Sane
You are in a car out in space that is traveling at the speed of light. You then decide to turn on the head lights. What do you observe?

You will see light coming from your headlights.

The problem lies in the frame of reference. If you travel at the speed of light, you appear not to travel forwards in time to a bystander, i.e. if you have a watch which broadcasts seconds and you have it in the car, a bystander with a receiver will think the watch has stopped.

I think!

[Dave]

What you say is true - BUT, NOTHING can travel faster than the speed of light, regardless of frame of reference. It is not relative. However, you may begin to notice that either answer seems to be correct - it is not possible to answer this question, how ever you try to achieve an answer you will stumble over paradoxes. But, seeing no light is my personal preference.

Dave

[Mat_C]

No matter what inertial frame of reference you are in, the speed of light (c) is always constant.

Despite the car being at the speed of light, the light from the headlights will still be moving away at c.

This all gets terribly complicated as now we're dealing with time dilation as well - and the fact the car CAN'T be travelling at the speed of light!

[Alan the Vanner]

Doctor who:
"Aha! I have finally got the chameleon device to work on the TARDIS and it has taken the form of an MG Maestro Turbo!":laugh:

Actually, if you could make light-speed would you get flashed by a speed camera, or am I just confusing matters?:confused: :rolleyes:

[Beaker]

No you wouldn't get flashed by a speed camera.

When you go past the speed camera, you will set it off. But by the time the camera mechanically reacts to take the picture, you will not be in view.

I think the last series of topgear covered this, seeing if they could drive a car fast enough so the car would not be in view when the camera clicked. Not sure what the final outcome was, but I seem to remember it was around 200mph.

Skatie

[e692wtt]

I thought that the 'critical speed' was around 130mph for a speed camera - above this speed the camera will only get one shot of your car and so the evidence is inadmissible (need 2 photos to prove the car is moving?)... allegedly. What speed the car needs to do to not be seen at all I don't know, but 200mph sounds reasonable? Someone with the critical measurements (road distance over which the camera can photograph your car, the delay between registering the car's speed and taking the first photo) could tell us.

[Alan the Vanner]

Originally posted by Skatiechik
No you wouldn't get flashed by a speed camera.

When you go past the speed camera, you will set it off. But by the time the camera mechanically reacts to take the picture, you will not be in view.

I think the last series of topgear covered this, seeing if they could drive a car fast enough so the car would not be in view when the camera clicked. Not sure what the final outcome was, but I seem to remember it was around 200mph.

Skatie
Hmm. That makes you wonder how that woman in Wales got clocked at "480mph".:laugh:

[SimonR]

I seem to remember that in the Top Gear test if the camera still went off then it took the two photos in time and therefore it could have caught you. I'm pretty sure that it was at either 156 or 176 mph when the shutter was no longer triggered.

I take that to mean that the police in this country are encouraging us to drive at speeds exceeding 176 mph on motorways....

Speaking of speed cameras, I was considering the possibilities of this little jape:

Get two identical-looking cars and give them the same registration number at the front, preferably the same car/registration number of someone you don't particularly like but who will share it with you when things get interesting...

Now find the location of two specs cameras (which measure average speed) on the same length of road, the M6 would be perfect, and you and a friend position yourselves by careful driving so that you pass these cameras 5 minutes apart.

If you got the distance correct you could read an average speed of, say, 2,000 mph and don't forget that the software that controls these cameras automatically issues tickets to offenders.

Your mate would get a fine and points on their license because they did 2,000 mph on the M6.

It would, needless to say, be a little bit illegal in almost every way, but it would considerable shorten the journey time betweeen Coventry and York ;)

[SimonR]

Originally posted by Alan the Vanner
Hmm. That makes you wonder how that woman in Wales got clocked at "480mph".:laugh:

Especially since she was on a bike...