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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Chemistry4me on 09/08/2009 08:54:47

Title: Will you see the headlights of a car travelling at light speed?
Post by: Chemistry4me on 09/08/2009 08:54:47
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?
Title: Will you see the headlights of a car travelling at light speed?
Post by: WiredScientist on 09/08/2009 10:01:25
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: lightarrow on 09/08/2009 10:24:51
Quote from: Chemistry4me on 09/08/2009 08:54:47
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?
Title: Will you see the headlights of a car travelling at light speed?
Post by: Chemistry4me on 09/08/2009 10:25:52
I'm not sure about the first one but let's just say receding from the observer.
In front of.
Title: Will you see the headlights of a car travelling at light speed?
Post by: neilep on 09/08/2009 11:22:30
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: neilep on 09/08/2009 11:24:25
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 !!
Title: Will you see the headlights of a car travelling at light speed?
Post by: Don_1 on 09/08/2009 11:57:27
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: Madidus_Scientia on 09/08/2009 16:20:31
You can't go the speed of light, so the light would always be faster than you, so yes you will see the headlights.
Title: Will you see the headlights of a car travelling at light speed?
Post by: lightarrow on 09/08/2009 19:57:29
Quote from: Chemistry4me on 09/08/2009 10:25:52
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: Chemistry4me on 10/08/2009 03:31:13
What is the opposite case? What do you mean lightarrow?
Title: Will you see the headlights of a car travelling at light speed?
Post by: wanhafizi on 10/08/2009 07:57:12
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?
Title: Will you see the headlights of a car travelling at light speed?
Post by: lightarrow on 10/08/2009 14:42:49
Quote from: Chemistry4me on 10/08/2009 03:31:13
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: lightarrow on 10/08/2009 15:02:59
Quote from: wanhafizi on 10/08/2009 07:57:12
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: Stefanb on 11/08/2009 03:41:20
Quote from: wanhafizi on 10/08/2009 07:57:12
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.
Title: Will you see the headlights of a car travelling at light speed?
Post by: Chemistry4me on 11/08/2009 05:58:42
Quote from: lightarrow on 10/08/2009 14:42:49
Quote from: Chemistry4me on 10/08/2009 03:31:13
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 [:)]