[Chemistry4me (OP)]

Someone asked me this the other day and I couldn't really find an answer. If a car was travelling at the speed of light, then it turned on it's headlights, will an observer ever see it?

[WiredScientist]

You will see it in motion. You cant really see the headlights, but it LOOKS like a blazing motion.

I ever speed up to 200km/h and your surrounding will looks like kinda of slow, like cutting the space-time.

[lightarrow]

Someone asked me this the other day and I couldn't really find an answer. If a car was travelling at the speed of light, then it turned on it's headlights, will an observer ever see it?

You are approaching or receding from the observer?
He is in front of your headlights or lateral?

[Chemistry4me (OP)]

I'm not sure about the first one but let's just say receding from the observer.
In front of.

[neilep]

I think the answer is No !...can't explain why but I have heard this dilemma before and noted the answer .


I am sure a klevur peep will come with the explanation.

[neilep]

Take your pick from some answers here http://www.google.com/search?q=speed%20of%20light%20car%20headlights  I think they contradict what I thought !!

[Don_1]

I would think the answer is yes, whatever direction the source of the light is moving in. Unless, if traveling away from the observer when the light is switched on, the light stands still. Nah! I don't buy that idea myself.

[Madidus_Scientia]

You can't go the speed of light, so the light would always be faster than you, so yes you will see the headlights.

[lightarrow]

I'm not sure about the first one but let's just say receding from the observer.
In front of.

Then both frequency and intensity of light will go to zero, as your speed goes to c, so you stop seeing anything well before you reach speeds very close to c. The opposite in case of approaching.

[Chemistry4me (OP)]

What is the opposite case? What do you mean lightarrow?

[wanhafizi]

If a car is traveling at the speed of light, why can't its light beam travel at TWICE the speed of light?

Is that possible?

[lightarrow]

What is the opposite case? What do you mean lightarrow?

I mean: when the car is approaching the observer, both frequency and intensity of light goes to infinite.

[lightarrow]

If a car is traveling at the speed of light, why can't its light beam travel at TWICE the speed of light?

Is that possible?

No, because the correct equation for velocities composition is not the sum, but:

V = (v₁ + v₂)/(1 + v₁*v₂/c²).

Note that the previous equation is correct for *all* velocities. Example:

v₁ = v₂ = 1000 m/s -->

--> V = 2*10³/(1 + 10⁶/299,792,458²) ≈ 2*10³ -2*10^-8 m/s ≈ 2*10³ = 2000 m/s.

So, for low speeds the (wrong) non-relativistic law: V = v₁ + v₂ is approximately correct and you can use it.

But if you use greater speeds:

v₁ = v₂ = 200,000,000 m/s -->

--> V = (2*2*10⁸)/(1 + 4*10¹⁶/299,792,458²) ≈ 277,000,000 m/s which is not 200,000,000 m/s + 200,000,000 m/s = 400,000,000 m/s.

Try with other values.

[Stefanb]

If a car is traveling at the speed of light, why can't its light beam travel at TWICE the speed of light?

Is that possible?

Nothing can go the speed of light because the speed of light is relative. However, kicking out all the math that says you can't move at the speed of light, if you went that fast then light you emitted would not go twice the speed of light, but it would move at the speed of light compared to YOU. But to the ultimate benchmark- the universe- the light you emitted would be going (drum-roll please) THE SPEED OF LIGHT! Light will always have a velocity of the speed of light except when enacted upon by a medium. Well... not really. Isn't that astounding!  Just not so easy to grasp with only conventional ways of thinking and no pencil to write down mathematical equations.

The reason the theory of RELATIVITY was made was to describe things that are RELATIVE. Another wave that shares the properties of light's relativity is gravity. Just post again if you need clarification.

[Chemistry4me (OP)]

What is the opposite case? What do you mean lightarrow?

I mean: when the car is approaching the observer, both frequency and intensity of light goes to infinite.

Okay, thanks []