h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

What happens if I am traveling at the speed of light in a car and I switch the headlights on?

Would I see any light? Would I be able to see the light on the dash board?
What if I look in my rear view mirror?

This question has been with us at the dinner table for some years and has stimulated great debate, with much call my bluff posturing.

normally ending with a burst of the galaxy song!

Spoilsport answer: It's impossible to travel at the speed of light.

Well, photons do it for breakfast

But not in cars.

How do we know they're not using very, very, small Bugatti Veyrons?

Notwithstanding the infinite amount of energy you would need to achieve light speed and the infinite mass you would attain when reaching that speed and the fact that to an observer your time will have stopped then I suggest the following:

- When you switch your lights on the light emitted would be blue-shifted into the hard gamma ray end of the EM spectrum (extremely short wavelength). It would not travel any faster than light speed.
- You would see that your lights were on by virtue of light reflected off the road, but again blue shifted into the gamma ray portion.
- You would see your dashboard lights as normal because they are part of your frame of reference and therefore affected in the same way and in the same proportion as you.
- You would see nothing in your rear view mirror as all light would be red shifted into the far radio (ultra-long wavelength).
- Finally, anything you could perceive would effectively be experiencing time infinitely faster than you as time is relative.


I may be wrong though as I am no expert in relativity physics. I also dread to think of the carbon footprint of the car you are in

t.

"How do we know they're not using very, very, small Bugatti Veyrons?" Jack

t.

I imagined the car to be traveling in space, so no road, so no reflection.
Talking of radio waves would I be able to hear the the music coming from the back speakers?

I would think the back speaker sends sound waves for you to hear, which are ridiculously slow (they rather travel in a Citroen 2CV).

Maybe.

Ah... the car is traveling at the speed of light so the speakers are traveling at the speed of light so the sound system should work OK.

Any suggestions for the type of music one would listen to while travelling at 12 million miles a minute?

>>> Talking of radio waves would I be able to hear the the music coming from the back speakers?

Yes, but you wouldn't like it, because of the doppler effect causing the music to sound like some annoying boy band from a bygone era.

Glad to be of no help.


HN

But with only a small distance between the source and the listener would it be OK to listen to Robbie Williams? or is that a no no from the start!

"Any suggestions for the type of music one would listen to while travelling at 12 million miles a minute?"

Clutch > 'Spacegrass' would be amongst my choices. And I think the this particular example of bluesy stoner rock fits with the subjects that have come up.

Listen here:
http://www.youtube.com/watch?v=NTuo1sSxCM4

No Clutch ~ driving an automatic. Given the speed we are traveling at we need something light, ethereal.JF

Spaceman - Babylon Zoo.
Major Tom - David Bowie
Rubicon - Tangerine Dream (1970s pre-Trance Trance if you get my drift!)
Silver Machine - Hawkwind

t.

It was contemplating this that led Einstein to the conclusion that you can't travel at the speed of light. That is the correct answer.

if your car would travel near the speed of light, as seen by a stationary observer, its dimensions (length, in the direction of travel) would be changed dramatically. It would probably look like a very thin car shaped but quite flat object, travelling at a fair speed.
From where you sit, in your car, things would look perfectly normal, lights would shine ahead, dashboard would dash, batteries would bat. If you'd care to note the stationary observer however you'd see that it whooshes by like a deadline, its dimensions would have changed .. as it moves close to the speed of light compared to your car.
Oh, and you had better steer clear of the trees along the road..

Now for the next discussion: if there's a speed camera somewhere ..
what speed would it register, and what would be on the speeding ticket?

I think it was Mala who pointed out some time ago that the redshift caused by moving objects was the reason that lights on a car driving towards you are clear whitish, sometime even blue, and lights on a car driving from you are mostly red. This is confirmed by experiments

Ok so I no longer have blue shift at the frony of the vehicle and red shift behind
Lights would shine ahead.

I like the slim speed thing. I am still not sure, for me if i am sitting in a vehicle traveling at the speed of light there is no vision in front of me (black) and it is pure white looking in the rear view mirror.

I have assumed there is nothing coming towards me or any zebra crossings

I had forgotten tangerine dream



thank you for reminding me will put it on my play list

Ta

Perhaps

But as albert once said

''Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted"

Is there really a correct answer?

JF