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snowplusb... snowplusb...
 
M$1.15 September 14, 2009 07:55 PM

A man is driving a car at the speed of light, he turns on the headlights, what happens?

He is driving forward, not in reverse
Interesting Question?  Yes (3)   No (0)   

Interesting: stanar M$0.05, hillo M$0.05, jasoncalacanis M$0.05

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philipy philipy
 
 September 14, 2009 09:46 PM
According to our present understanding of physics, objects that have mass cannot be accelerated up to the actual speed of light.

Therefore, if a car were to be travelling at the speed of light, it is for sure that the theory of relativity is wrong in some respect, and since that is the only scientific basis we have for answering your question, all bets are off!

Now the car could be accelerated up close to the speed of light, without quite getting there. In that case, using the headlights works as normal.

However if you plan to drive at close to the speed of light, I advise you to do it in deep space. Doing it on a road would have unfortunate consequences because of friction, if nothing else. Also it would be illegal. :)

http://www.physlink.com/Education/AskExperts/ae161.cfm
http://www.physlink.com/education/askexperts/ae476.cfm
Asker's Rating:
• Very good answer! Prompt response in comments section! Great speculation at my impossible question, lol. Keep up the good work! and congrats on the answer of the day nomination!

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snowplusbr... snowplusbr...
 
September 14, 2009 09:51 PM
hehe, I should have just put this in offbeat questions. Everyone answering is very knowledgeable about the laws of physics, but I wonder as to what you believe happens if such a case occured. The laws of physics would break down yes, but what do you imagine the fate of the light projected from the headlights would be to the driver? would he see them since he is travelling at the exact speed that it would be emitted from the bulbs? or would the light not even leave the headlight sockets?

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philipy philipy
 
September 14, 2009 10:49 PM
If you started approaching the speed of light, your car and your headlights would appear normal to you, but the universe would look very weird.

Because of something called Lorentz contraction, everything would appear squished along the direction you're travelling. Not only that, because of something called time dilation, it would also appear to be slowed.

The squishing and slowing down would approach infinity as you approached the speed of light. If you somehow could actually get to the speed of light, we can only imagine that the universe would appear entirely flattened into nothingness but your car and headlights would seem normal.

That's about as good a guess as I can make. :D

http://www.fourmilab.ch/cship/lorentz.html
http://www.fourmilab.ch/cship/timedial.html

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stanar stanar
 
September 15, 2009 01:39 PM
nice!

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bunnyphuph... bunnyphuph...
 
September 15, 2009 06:57 PM
@philipy - I'm not stalking you, I just think you have another great Answer of the Day!
http://farm3.static.flickr.com/2633/3917686970_7e4341ef33.jpg

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snowplusbr... snowplusbr...
 
September 15, 2009 07:02 PM
Be sure to include his answer and added comment, @bunnyphuphu . He was very prompt at responding both times :-)

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philipy philipy
 
September 15, 2009 08:16 PM
Thanks for the nomination again @bunnyphuphu!

I don't mind being nominated lots of times. :D

Thank goodness I found a nice page about Lorentz contraction! I didn't fancy trying to explain the theory of relativity in a Mahalo answer. :)

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shinju shinju
 
September 16, 2009 02:52 PM
670,616,629 mph: It's not just a good idea, it's the law!

Well done, Philipy!

Respectfully,
Shin

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lesliec lesliec
 
September 16, 2009 03:25 PM
Congratulations! Your answer won first place!

http://www.flickr.com/photos/33749589@N07/3917677890/

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philipy philipy
 
September 16, 2009 03:47 PM
Woo hoo! Awards, two days running. Really pleased. :)

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nickunders... nickunders...
 
September 14, 2009 08:25 PM
Answer: The headlights work as normal.

Theory of Relativity, therefore the speed of light is constant for any inertial observer. Suppose someone watching the car, who is stationary, he will see the light of the headlights traveling at the speed of light.

And even for the driver the headlights will work just fine, as normal, traveling at the speed of light. Everything in this universe is relative, you cannot trick the system, the light will not travel 2x the speed of light and neither will they not travel at all.

Besides the point is that no human being with no known or imaginable technology would be able to survive the trip at the speed of light anyway.
Source(s):
http://www.straightdope.com/columns/read/709/if-you-turn-on-your-headlights...


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snowplusbr... snowplusbr...
 
September 14, 2009 09:50 PM
OK, the light might not travel at 2X the speed of light, but how can it display in front of him if he is travelling at the speed of light with the source of the light. Would it really beam out in front of him? or never leave the headlight bulb? hehe

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nickunders... nickunders...
 
September 15, 2009 06:39 AM
As I said the light would shine out normal infront of him, just as @philipy says ... better than I, I must admit

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satish440 satish440
 
September 14, 2009 09:17 PM
according to law... if u run at speed of light... u can easily jump out of earth bcoz u dont have gravity at that speed.

coming to ur que... if he turns on his light of car... firstly car wont travel at that speed... secondly car cannot have friction and will travel on road... thirdly man wont b alive at that speed... and finally even though with miracles it happens.. then car will obviously travel with light... where the car headlight falls... if in dark he cannot see the road... in day time... he doest need the headlight......

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zwaldo zwaldo
 
September 15, 2009 02:47 AM
Nothing would happen.
the guy wouldn't be able to reach up to hit the lights, because he wouldn't be able to go faster than the speed that he's already going , which is light speed.
Source(s):
me


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nickunders... nickunders...
 
September 15, 2009 06:38 AM
Ofcourse not, if you are driving 100 mph on the highway do you need to move your hand at 100 mph to turn the lights on??? no!

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kty2777 kty2777
 
September 15, 2009 06:45 AM
If he had my bomb of an old car his windscreen wipers would turn on and the radio would stop working :P

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stanar stanar
 
September 15, 2009 01:48 PM
It's a good off beat question and is good for a thought experiment! Though it is one of the impossibilities based on the laws we know today.

I would say, from the driver's frame of reference, since he and the light from the headlights are the moving at c (speed of light), he would see the photons suspended in space (it travels at its own speed)!

or would he see the waves?

or would he not see any light coming out at all?

Off beat question got an off beat answer!
I am confused! my thought process was broken as I was travelling at C as the laws of physics were broken down.

I am not Einstein!

I gotta go now, will come back add more!


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stanar stanar
 
September 15, 2009 03:55 PM
ok, I am back. for some reasons, I was considering the headlights as a coherent light source and the light in the same direction of the vehicle.

Since it is a regular headlight, light in all forward directions along with a beam of light (from the headlight lens and the reflector), we have much more to think about.

and also other scenarios, what about faster than the speed of light?

Another angle to look at this "at c" scenario.

Since only massless can travel at c, the car and driver have to be massless too, so there is no human entity there to experience or see what happens at "c" (celeritas - Latin for speed). But for the people at rest it is business as usual.

I am sure a lot of physicists including Einstein and people like us would have thought about this! I wonder if there is anything Einstein has left for us to read in this line of thought!

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stanar stanar
 
September 15, 2009 05:19 PM
update!

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stanar stanar
 
September 15, 2009 05:28 PM
One more thought...

Since you didnt mention about "c" which is a constant (240k MPH in vacuum), there is another way to look at your question and consider slowed down refracted light.

As we all know that light slows down in denser medium, can we repeatedly slow down light so that its speed is humanly achievable? I know it regains its speed once it emerges into a lighter medium, but can we do this using denser but non opaque medium?

hmm, after I typed this, I found this when I googled for slower light, it seems physicists can slow down light to a mere 38mph!!!

"Light, which normally travels the 240,000 miles from the Moon to Earth in less than two seconds, has been slowed to the speed of a minivan in rush-hour traffic -- 38 miles an hour.

An entirely new state of matter, first observed four years ago, has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super- atom with characteristics similar to a laser."

http://www.news.harvard.edu/gazette/1999/02.18/light.html

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snowplusbr... snowplusbr...
 
September 15, 2009 07:20 PM
Awesome answers and great research into alternate answers!

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stanar stanar
 
September 15, 2009 07:42 PM
@snowplusbrd - thanks for the tip!

But, since this was a hypothetical question - what happens at the speed of light, I had to put myself into an extraordinary thought process to come up with these views! smile!

We all know what the reality is.

Otherwise I would have just answered as what @philipy said.

I thought the question is specifically about the light from the headlights and not about how the universe would behave or about the laws of physics. If we were to apply the Laws of physics, the question would be meaningless.

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hillo hillo
 
September 15, 2009 04:13 PM
...His girl friend, sitting next to him, asks him to "SLOW DOWN!!"

BTW: nice question, great responses above...

Source(s):
Image: http://farm4.static.flickr.com/3300/3334229465_2354df51fb.jpg


Tags: light, speed, physics

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