If a car travels at the speed of light and turns headlights on what happens?

callmeBadger · 10 Mar 2006 at 12:49

Pudney@work said:
Can't be bothrered with a proper response, but the duality of light states that in some cases light behaves as a wave, and in other cases it behaves as particles. Or am I thinking of sommit else, it's been years since I last did physics....

Oh, and off topic, where has my quick post gone, my laziness enjoyed having that thing!

Wave-Particle Duality more wierd stuff from Phyics, seems the more you look at something in Phyics the questions are asked.

Light has a mass which can be measured, and can be affected by gravity, thats why black holes are black.

Light is a EM wave, it can pass through stuff, like glass and water.

Light just can't make its mind up!

Freefaller · 10 Mar 2006 at 13:11

callmeBadger said:
Light just can't make its mind up!

I didn't realise light was female....

yer_averagejoe · 10 Mar 2006 at 13:23

hmmm I never read the whole thread, so I dunno whats been posted But I'll say this:

Einsteins theory of relativity proved that space and time were infact entwined, newtonian physics suggested that space and time were cmpletely different things, therefore if you chased after a cars headlights at 500 million miles per hour, the light would be speeding away from you at 170 million miles per hour (light =670 million miles per hour). Yet einstein suggested that the speed of light doesnt travel relative to any object or newtons "aether" yet it travels relative to spacetime if you like, becuase he believed that space and time are both entwined. So therefore, If you travel in the same direction of a beam of light at whatever speed, the light will always move away from you at the speed of light. So the light then seems to be travelling faster than the speed of light. However if travelling at a fixed speed, through a fixed distance, time will compensate by slowing down. Einstein's theory said that your combined motion through space and time are always equal to the speed of light.

This was proved using atomic clocks. Two atomic clocks were synchronised and one left stationary while the other flew around the world (and in doing so, travelling through space) once the journey was complete and the clocks compared, there was found to be a few hundred billionths of a second difference between the two clocks. Pretty much securing einsteins theory.

IN CONCLUSION: Live Fast, Die Old!

Joe

Visage · 10 Mar 2006 at 13:24

callmeBadger said:
Light has a mass which can be measured

Nope, light has momentum.

yer_averagejoe · 10 Mar 2006 at 13:30

Light does not have mass, I'm sorry

Vonhelmet · 10 Mar 2006 at 13:47

Oracle said:
Taken from Wiki Pedia! The Worlds most OFFICIAL website for Encylopedia type things!

Hold on, i'm just going to create a page on how Flying Pigs are real but are not infact pink! Because you see, they can travel at the speed of light....therefore they appear Blue!

The internet is NOT vetted! Why do people rely on its information so much?? Yes, if two or more sources reveal similar theories / information then fine! until then, stop redirecting people to junk websites!

/end rant!

Wikipedia was compared to the Encyclopedia Brittanica and found to have a comparable amount of errors i.e. it is of equal quality.

The trick being, any inaccurate information is pretty quickly edited so that it is accurate.

But sure, if you want to have a whine, then feel free.

Amleto · 10 Mar 2006 at 13:50

yer_averagejoe said:
hmmm I never read the whole thread, so I dunno whats been posted But I'll say this:

Einsteins theory of relativity proved that space and time were infact entwined, newtonian physics suggested that space and time were cmpletely different things, therefore if you chased after a cars headlights at 500 million miles per hour, the light would be speeding away from you at 170 million miles per hour (light =670 million miles per hour).

If you are on the headlights, the light will be travelling away from you at exactly the speed of light, not SoL-<your speed>.

Yet einstein suggested that the speed of light doesnt travel relative to any object or newtons "aether" yet it travels relative to spacetime if you like, becuase he believed that space and time are both entwined.

Nope. The SoL is constant to all observers. The SoL doesn't 'travel' anywhere, but it may be measured from anywhere, and is always relative to whatever is measuring it, therefore it IS relative to any object.

So therefore, If you travel in the same direction of a beam of light at whatever speed, the light will always move away from you at the speed of light. So the light then seems to be travelling faster than the speed of light.

:/

However if travelling at a fixed speed, through a fixed distance, time will compensate by slowing down. Einstein's theory said that your combined motion through space and time are always equal to the speed of light.

What are you on about? :confused:

Time will compensate??? Do you mean that if you are travelling relative to some observer, then their time will seem to pass quicker when compared to your time?

combined motion - some sort of translation ie has units length
=
SoL - units Lenght/Time

Sorry, but you are talking rubbish.

This was proved using atomic clocks. Two atomic clocks were synchronised and one left stationary while the other flew around the world (and in doing so, travelling through space) once the journey was complete and the clocks compared, there was found to be a few hundred billionths of a second difference between the two clocks. Pretty much securing einsteins theory.

IN CONCLUSION: Live Fast, Die Old!

If 'This' = Time dilation, then yes, it pretty much proved Einsteins Special Relativity.

Zefan · 10 Mar 2006 at 13:53

I hate these questions, they're so tiringly easy to work out. If you're going faster than the speed of light people will only see you once you've passed them. If you're travelling at the speed of light and you turn your lights on, the car will apear to be travelling at the speed of light with its lights on. It will just appear to be there at a later instance than it was actually there.

callmeBadger · 10 Mar 2006 at 14:34

Visage said:
Nope, light has momentum.

.

Good point, but as momentum can be calculated by velocity x mass, can't the its mass be derived?

hang on, typing this had one of those thoughts that make you type slowly, objects with mass have a fixed body, dimensions and what not. As light travels in wave as well as particle, how do you define the the dimensions of a wave which is continuous?

hmmm, seems Light is more like a woman the more you think. Can't make its mind up, wants the best of both worlds, and no matter how hard you think, it won't let you know how much it weighs.

yer_averagejoe · 10 Mar 2006 at 14:36

Amleto said:
What are you on about? Time will compensate??? Do you mean that if you are travelling relative to some observer, then their time will seem to pass quicker when compared to your time?

combined motion - some sort of translation ie has units length
=
SoL - units Lenght/Time

Sorry, but you are talking rubbish.

This is the point I was trying to get accross:

Brian Greene said:
Special relativity declares a law for all motion: The combined speed of any objects motion through space and its motion through time is always precisely equal to the speed of light. At first, you may recoil from this statement since we are all used to the idea that nothing but light can travel at light speed but that familiar idea refers soley to motion through space. We are now talking about something elated, yet richer: an object's combined motion through space and time. The keyfact, Einstien discovered, is that these two kinds of motion are always complimentary. When an object speeds away, what really happens is that some of its lightspeed motion is diverted from motion through time into motion through space, keeping their combined total unchanged. Such diversion unassailably means that the objects motion through time slows down.

Amleto · 10 Mar 2006 at 14:36

Zefan said:
I hate these questions, they're so tiringly easy to work out. If you're going faster than the speed of light people will only see you once you've passed them. If you're travelling at the speed of light and you turn your lights on, the car will apear to be travelling at the speed of light with its lights on. It will just appear to be there at a later instance than it was actually there.

If a bystander is watching a car travelling at c, the bystander will not know when the car's lights turn on, since the light (from the headlights) cannot go any faster (and therefore never appears to leave the headlight) relative to that bystander.

On the other hand, the driver will know exactly when the lights operate, as he will see the light extend from the front of the car.

I think this is an instance of a paradox, and is one way to show that travel (in this sense) @ SoL is not possible according to SR.

Amleto · 10 Mar 2006 at 14:39

yer_averagejoe said:
This is the point I was trying to get accross:

That makes more sense

Visage · 10 Mar 2006 at 14:41

callmeBadger said:
.

Good point, but as momentum can be calculated by velocity x mass, can't the its mass be derived?

No, because, in relativistic situations, momentum does NOT equal m * v.

Amleto · 10 Mar 2006 at 15:04

Visage said:
No, because, in relativistic situations, momentum does NOT equal m * v.

Relativistically, momentum is m(u)*u though (for massive bodies).

Visage · 10 Mar 2006 at 15:14

Amleto said:
Relativistically, momentum is m(u)*u though (for massive bodies).

True - the fact that i used m, rather than m(u) indicated that i was talking about rest mass.

Soul Rider · 10 Mar 2006 at 16:02

Apopcalyptic said:
Physics isn't really my thing, but because of the laws of perpetual motion, would the light not be projected at twice the speed of light?

The light will be projected from the car at the speed of light. If you were stationary standing next to the car the car would appear to be travelling at the speed of light and the light would appear to be travelling at twice the speed of light.

But as the car is already going the speed of light, the light is only going away from it's source at the speed of light.

That clears it up for me!! :eek:

NONONONONO thats wrong!! Damn i forget everything!!!

Nevermind, i will leave my foolish mistake up here for everyone to see and to shwo them the importance of proof reading.

Amleto · 10 Mar 2006 at 16:06

Soul Rider said:
The light will be projected from the car at the speed of light. If you were stationary standing next to the car the car would appear to be travelling at the speed of light and the light would appear to be travelling at twice the speed of light.

But as the car is already going the speed of light, the light is only going away from it's source at the speed of light.

That clears it up for me!!

I think I explained why that won't happen a few posts back

Visage · 10 Mar 2006 at 16:19

OK. lets clear this up.

For ANY observer, light will always travel at c. No ifs, no buts, no maybes.

Always.

Apparent paradoxes like 'What ahppens if you turn the lights on while travelling at c' are a result of applying galilean transformations to objects in relative motion - simply put, saying 'If object A travels away from me at 10 mph in a given direction, and object b travels away from object a at 20mph in the same direction, then object b is travelling away from me at 30mph'.

That doesnt work when the magnitude of velocities involved approach c. The basic reason for this is that velocity of an object in a given frame is defined as the rate of change of distance with respect to time of that object, in that frame.

The simple derivations of SR between inertial frames shows that, in frames moving with respect to an observer, time is observed to flow at a different rate than the frame in which the observer is situated.

It is the notion that conversion between frames is galilean that creates the apparent paradox. Once you use lorentzian transforms the figures resolve themselves and all is well.

(The apparent contradiction between high speed - lorentzian and low speed - galilean is reconciled by the fact that the lorentzian transform reduce to their gallilean counterparts for small values of v).

Vonhelmet · 10 Mar 2006 at 16:31

Visage said:
OK. lets clear this up.

For ANY observer, light will always travel at c. No ifs, no buts, no maybes.

Always.

Apparent paradoxes like 'What ahppens if you turn the lights on while travelling at c' are a result of applying galilean transformations to objects in relative motion - simply put, saying 'If object A travels away from me at 10 mph in a given direction, and object b travels away from object a at 20mph in the same direction, then object b is travelling away from me at 30mph'.

That doesnt work when the magnitude of velocities involved approach c. The basic reason for this is that velocity of an object in a given frame is defined as the rate of change of distance with respect to time of that object, in that frame.

The simple derivations of SR between inertial frames shows that, in frames moving with respect to an observer, time is observed to flow at a different rate than the frame in which the observer is situated.

It is the notion that conversion between frames is galilean that creates the apparent paradox. Once you use lorentzian transforms the figures resolve themselves and all is well.

(The apparent contradiction between high speed - lorentzian and low speed - galilean is reconciled by the fact that the lorentzian transform reduce to their gallilean counterparts for small values of v).

Yeah, I dug 1st year physics degree SR too

Visage · 10 Mar 2006 at 16:35

vonhelmet said:
Yeah, I dug 1st year physics degree SR too

All from memory. FACT.

Mind you, it was 12 years ago, and now my BRANE HURTS.