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

if our apmosphere had a high level of sodium vapour(where the speed of light is 27mph),

what would that mean for travel, what would happen to vehicles traveling faster than the speed of light????

what would it mean for physics, would einstein still have come up with his answers or would his brains be dribbling out of his ears??

If our atmosphere had a high level of sodium vapour, then it wouldn't have any oxygen in, given that sodium and oxygen rather enjoy each other's company. I suspect sodium vapour and nitrogen would have a similar problem, so the remainder of the atmosphere would have to consist of inert gases. The very fact that they're inert means that no life of any chemistry would be able to evolve.

Therefore we'd all be non-existent and it wouldn't be too much of a problem.

Chemistry trumps physics any time.

B

i knew that would be one of the first answers

so

in the far off future we come across a planet with a high sodium vapour atmosphere and we land on it, the 'nauts get out thr 'rover' and trundle off

what happens when they go faster than 27 mph???

do they vanish?? look all stretched?? get red/blue shifted?? experience time dilation??

Sodium light only travels at 27mph ?! That can't be remotely right can it? So when the sodium street lights in the towns across the firth of Forth switch off in the morning, it will take an observer 10 miles away around 9 minutes to notice?!!! And if I am traveling at 30mph away from said town, the lights will never switch off

no!!!!!!!

the speed of light can be as low as 27mph in a sodium vapour, it depends on the medium it is traveling through, thats why they measure the speed of light in a vacuum, because thats as fast as it gets

The speed of light in a vacuum is constant and very fast. But it is much less than in certain media. When something travels faster than the speed of light in that medium, there is a "optic boom" like the sonic boom when aeroplanes go above the speed of sound. This causes flashes of light, and these are known as Cherenkov radiation.

All the relativity stuff with time dilation would still take place relative to the speed of light in a vacuum, so it wouldn't be noticeable on the motorways.

Mu, physics cannot be trumped because sooner or later *everything* is physics.

Nope. Mathematics. Physics isa practical application of Mathematics, not the other way round.

http://xkcd.com/435/

(And I post this despite being a biologist...)

I'm not sure I agree with that. Maths is a useful tool that can be used to model real-life things but I don't think physics is a subdivision of maths per se.

Science is the study of how things work really. Maths is more abstract than that I think although of course they weren't developed independently.

'tis true thought that chemistry is essentially the physics of the outer (valence) electrons.

Physics is a mathematical study of the real world. Mathematics is a study of an imaginary mathematical world which may or may not correspond with the real world.

To get back to the question, is the asker happy that it has been answered?

i get there would be flashes of light, but what would happen to the vehicle from the observers pov and from the drivers pov?

Nothing. The relativity stuff only kicks in when you get close to the speed of light in vacuum, which is 300 million metres per second.

Mathematics is the language of physics, not its foundation. Too much spurious maths is used to 'explain' incorrect or downright mental hyptheses for it to be anything other than a language. Sure, the A2 pages of minute equations for a 'groundbreaking' theory (I forget specifically which one, but it did happen) might be interesting or even beautiful to some but really it's the scientific equivalent of Lord of the Rings.

""Nothing. The relativity stuff only kicks in when you get close to the speed of light in vacuum,""

i meant the visual stuff

if he is moving away from you at 30mph and the light is coming from him at 27mph what do you see??

same as he is coming toward you at 30 mph and the light is coming at 27 mph??

I think you would not see him coming towards you.

If he was moving away, I suppose you'd see him massively red-shifted.

Wouldn´t the amount of redshift/blueshift depend on the frequency compared to the speed of the object moving? Then even if light is being absorbed and re-transmitted between sodium atoms, it would still have a "normal" frequency in between I´d imagine. So the "stretching" the light would undergo would still be very little, and not enough to be noticed.

I don't think the light is being absorbed and re-emitted by the sodium atoms.

>>if our apmosphere had a high level of sodium vapour(where the speed of light is 27mph)<<

The fastest human footspeed on record is 27.79 mph seen during a 100 metres sprint (average speed between the 60th and the 80th meter) by Usain Bolt.