[MayoFlyFarmer]

well when you look at it THAT way, maybe its and EXCELLENT question.

If I met you in a scissor-fight, I'd cut off both your wings; on principle alone!!

[neilep]

Think about the poor copper trying to stop the guy/gal for speeding...by law he will have to travel faster than light to stop the car !!..(I know I know ,it's all silly ! )

'Men are the same as women...just inside out !'

[NakedScientist (OP)]

Here's the answer to the last QOTW "WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DO WE HAVE TO HAVE MONDAYS ?"

It all comes down to the ancient Greeks, Romans and Babylonians.

Early observers of the sky saw several prominent features - the Sun, the Moon, and the stars. But closer inspection of the stars showed that whilst most moved across the sky in a uniform way, some moved at different speeds and even turned back on themselves. These errant stars were named 'wanderers' which in ancient Greek is planetes, from which we get our modern word "planet". At that time early observers only found 5 'planetes' (Mars, Jupiter, Saturn, Mercury and Venus) - the discovery of the rest would have to wait for the telescope to come along.

Observations on these 'planets' showed that they take a different amount of time to complete a cycle and return to their starting position. The planets were assigned a seniority according to how long they took to complete their own cycle :

Saturn 29 years
Jupiter 12 years
Mars 687 days
Sun 365 days
Venus 225 days
Mercury 88 days
Moon 28 days

The Babylonians decided to divide a day into 24 hours (in place of the 12 used by Egyptians) and decided to name each hour of the day after each of the 'planets' in order of seniority, and startign again when you run out of planets. e.g. :

1 am - Saturn
2 am - Jupiter
3 am - Mars
4 am - Sun
5 am - Venus
6 am - Mercury
7 am - Moon ...and start again with...
8 am - Saturn
9 am - Jupiter and so on...
...10 pm Saturn
...11 pm Jupiter
...12 pm Mars

Obviously 7 doesn't divide equally into 24 so the next day starts with a new 'dominant planet' (the one at the top of the list). It was the custom to name the day after the dominant planet on that day.

Looking on the list you can see that after Mars comes "Sun" and hence the next day starts with Sun and works through the list. The day after that starts with "Moon", then "Mars", then "Mercury", then "Jupiter", then Venus and finally back to Saturn.

If you then write out these dominant planets in order you see a familiar pattern emerge :

Planet       English   French

Saturn day   Saturday  Samedi
Sun Day      Sunday    Dimanche
Moon Day     Monday    Lundi
Mars Day     Tuesday   Mardi
Mercury Day  Wednesday Mercredi
Jupiter Day  Thursday  Jeudi
Venus Day    Friday    Vendredi

This 7 day week was adopted by the Romans who spread it across their empire. The Pagan English preferred to keep Sunday for the Sun God, and also named the previous 4 days of the week after Anglo-Saxon gods - Tiw (Tuesday), Woden (Wednesday), Thor (Thursday) and Frig (Friday). The Christians wanted a different holy day to the Jews - so they took Sunday (Dimanche) which is a contraction of Dies Dominici (Day of our Lord) in Latin). Because Sunday is the Christian day of rest, we have to have Monday mornings on which to return to work...ouch.

[NakedScientist (OP)]

Here is this week's QOTW :

"IF A CAR IS DRIVING AT THE SPEED OF LIGHT AND IT TURNS ON ITS HEADLIGHTS, WILL THE WAY AHEAD BE ILLUMINATED ?"

That should keep you busy !

TNS

[tweener]

Yes.

----
John - The Eternal Pessimist.

[BlooGoo]

if the car were travelling NEAR the speed of light, and turned on its lights, the way would be lit (i think) because the photons that are emitted from the lights would a) be propelled forward (with some dopplar shifting in there) and b) would be travelling at the speed of light (just that little bit faster than the car itself).

if the car were travelling AT the speed of light ... hmmm ... i would imagine that as the lights were turned on, they would illuminate in front of the car, but as your eyes focused on the light (assuming that you're in the car too) it would look like you're going faster than the light, and would give you the warp speed look that's associated with going really really fast.

just a guess.

[tweener]

Here's the long version of my previously short answer:

Any photon emitted by your car would travel away from the car at the speed of light, relative to the car.  The photons would also be travelling at the speed of light relative to the signpost at the side of the road.  The photons reflected off the signpost back to your car would arrive at your eye travelling at the speed of light.  There would be considerable doppler shifting here, so that a mere eye would not be able to detect the photons, but with appropriate instrumentation technology, the "way ahead" would be lit.

----
John - The Eternal Pessimist.

[Rabbit]

Nice Easter question this one! Ask some of the clever boys on the autobahns in Germany, they will have real experience to share with us. No, I do not know any of these people. Come to that, travelling at this speed and messing around with the lights sounds pretty dangerous...

[gsmollin]

The speed-of-light-car question has a "no" answer, because a car can't travel at the speed of light. We don't ever see the lights come on because time dilation stops the car. All the energy in the universe is required to accelerate the car to the speed of light, and the car gets crushed to infinite density by Lorentz contraction. The light cannot escape the car because it turns into a black hole. This is not a good question.

[MayoFlyFarmer]

well when you look at it THAT way, maybe its and EXCELLENT question.

If I met you in a scissor-fight, I'd cut off both your wings; on principle alone!!

[neilep]

Think about the poor copper trying to stop the guy/gal for speeding...by law he will have to travel faster than light to stop the car !!..(I know I know ,it's all silly ! )

'Men are the same as women...just inside out !'

[nilmot]

I think it has nothing to do with whether the car will be crushed or not. My contribution is (might not be right) that the road in front will not be illuminated because as you are travelling at the speed of light (suppose you can) the light will not have time to hit the road in front and reflect back to your eyes so you can see it. You are travelling as fast as light

Tom

[neilep]

Isn't the speed of light relative to a persons perspective ?(like Tweener has said)...so, from the cars point of view the way ahead will be lit, but from a spectators point of view sitting on a bench as the car goes whizzing by the lights will appear off....(please feel free to castigate and taunt me as my inadequate understanding is made plainly obvious) makes my head-Ache !!!

'Men are the same as women...just inside out !'

[gsmollin]

Special relativity does not tell us what will happen when a car travels at the speed of light, because special relativity prohibits the car from ever attaining the speed of light. Now, one can examine the equations of special relativity, in the limit, as v goes to c, and we can make some extrapolations as to what will be happening as the car gets infinitesimally close to the speed of light.
The light from the headlights still travels at c, as measured by all observers.
The light from the car appears blue-shifted by observers at the stop sign.
The reflected light from the stop sign appears blue-shifted by the car's occupants (assuming the light doesn't just penetrate the stop sign, because it would be of nearly infinite energy), because they see the stop sign approaching them at nearly c.
The usual Lorentz contractions and time dilations occur.

The question posed above asked what happens with a car traveling AT the speed of light. Well, the equations of special relativity return a bunch of singularity points when c is plugged into v, so we don't get any answers.

[neilep]

Well...seeing as you put it like that !!!.....err..no sweat !!! *gulp*

'Men are the same as women...just inside out !'

[Buster]

Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.

[tweener]

quote:Originally posted by Buster

Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.

It was covered recently.  Here is the link:

http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=850&SearchTerms=gravity,earth

----
John - The Eternal Pessimist.

[Dan B]

The way ahead would be lit, RELATIVE to the car [] A better question would be "how come we can see the beam of energy that comes from a star trek phaser?"

[Dan B]

quote:Originally posted by Buster

Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.

The question wasn't exactly answered by the link above. You would fall towards the centre, pass it, be drawn back, then "oscillate" about it []

[neilep]

quote:Originally posted by Dan B

The way ahead would be lit, RELATIVE to the car [] A better question would be "how come we can see the beam of energy that comes from a star trek phaser?"

You cant see it !!..its there specifically for special effect.

'Men are the same as women...just inside out !'