A question on the speed of light - does relative velocity matter?

Question

When you are in a car going at 70 miles per hour, and you throw a stone forwards out of the window, it briefly benefits from the relative velocity of the car, and therefore travels much further than the speed it would normally travel at after being thrown. Scientists say that if you were going the speed of light in a car, then turned the lights on, you would not see them, as you would be travelling as fast as the light, and therefore it would not have time to travel forward so you could see it.

Why does the same principal as the stone benefiting from the velocity of the car not apply? Surely the light would still be visible, as it would be travelling away from the car at (speed of light) + (speed of light)?

Answer 1

Scientists don't say that. No matter how close to the speed of light you move, light will always appear to travel at the same speed.

The speed of light is usually designated as the variable "c" and has a numerical value of just under 3*10^8 meters/second. Even in your fast car, when you turn on the headlights, you will see light moving away from you at that speed.

A person standing on the roadside will also see the light from your headlights moving at speed c down the highway.

The reason is subtle. The fact that you are moving in your fast car means that you observe the passage of time at a different rate than the person standing on the roadside.

You can understand this by considering a simple clock inside your fast-moving car, and an identical clock with the person standing alongside the road, say, a hitchhiker.

Imagine this clock is just a simple pendulum that swings back and forth. For you inside the car, a single swing of the pendulum measures a unit of time. To you, the end of the pendulum moves through an arc of some distance that you could measure.

However, to the person standing along the roadside, your pendulum does not swing through the simple arc you see. To the hitchhiker, your pendulum's movement is a compound movement of both the motion of your car, and the swinging motion. So even though you both have identical pendulums, the hitchhiker sees your pendulum cover a larger distance in each unit of time you measure.

Since the distance your pendulum moves in a single oscillation is larger, units of time must be longer for you, so says the hitchhiker.

Now the reverse also applies. To you, your pendulum in the car swings in just a simple arc. According to you, the pendulum outside your car, along the road, moves not just in an arc, but also over the distance your car carries you down the road. It looks like the pendulum outside your car is moving away from you while it swings.

You see the hitchhiker's pendulum cover a larger distance in a single swing than your pendulum. So you reason units of time for the hitchhiker must be longer.

The net result is, when you measure the speed of light with your clock, and the roadside observer measures the speed of light with their clock, you get the same answer for the speed, c.

Now this time-difference effect is not just something to do with the fact your clock is a pendulum.

Consider this: *Every* physical process taking place in your car, from the swinging of a pendulum, to the flow of electrical current in your wristwatch, to the molecules moving in chemical reactions in your body's cells, is seen by the person on the roadside to be occuring over these longer distances than you see.

And again, you can reverse the viewpoint: To you in the car, every physical process outside the car appears to be moving over longer distances.

So when you and the hitchhiker are comparing times, no matter what mechanism you use to mark time, you will encounter the same effect, and end up measuring the same speed, c, for light.

Answer 2

No. The speed of light in a vacuum is an absolute. Remember that speed is a function of space (distance) and time. Einstein discovered that both time and space are relative, but that lightspeed cannot change. If two photons (or two anythings) travel in opposite directions at the speed of light, they will disappear over each other's event horizon. That means that from the perspective of each one, the other has disappeared from the observable universe.

Answer 3

It is all Einsteins fault.

He said that time is not the constant but the speed of light is the constant.

So just taking you first example, when you turn your lights on and you are travelling at 70mph the light that is emitted is not travelling away from you at speed of light + 70 mph. It travels away at the speed of light - this is the constant and is the faest it can go.

In order to maintain this time has to slow down. So time changes with the speed that you are travelling. Ultimately time would slow to a stop as you approach the speed of light.

The argument goes - if you were travelling at almost the speed of light and wanted to burn that extra bit of fuel to push you through the light barrier you would not be able to because time has stopped and therefore you can not burn the fuel.

Make sense?

If not please study Einstein at College for at least 6 years.

Answer 4

It is commonly thought that the speed of light is the fastest anything can travel, so if you tried to throw a stone your hand would travel backwards but not forwards, because you are travelling at v-max.
But if another object was travelling towards you at the speed of light, your relative position would give the impression of it travelling at twice the speed of light, which is impossible, or is it!

Answer 5

A car can not travel as fast as light.

A car moving along the road at seventy miles per hour contracts in length (very slightly) and its clocks and engines slow down (very slightly). In fact, it does this than any observer inside the car with accurate instruments would measure the speed of the light emitted from the headlights as traveling at the speed of light.

Answer 6

According to the theory of relativity, the speed of light, referred to as "c", is always constant in any frame of reference regardless of what may or may not be moving. This is accomplished by way of a fourth dimension, time. We are used to thinking of time as progressing at a constant rate, but the rate of change of time slows down as one approaches the speed of light. This fact accounts for many other interesting and strange phenomena as one approaches the speed of light, such as lengths getting shorter, and mass increasing.

Answer 7

Hi >
You hit the nail on the head by mentioning relativity.
It is all relative.
Take for example teo folks playing ping-pong on a train.
The ball is going back and forth at, say, 40mph.
The train flashes through a station, doing 90mph.
How fast is the ball going?
Same thing with electromagnetic radiation, which includes "light"
Great fun.
Bob

Answer 8

because light has a maximum velocity - there's nothing to say the headlight beam doesn't get pushed faster, it's obviously never been demonstrated, but it can only go so fast, and there is nothing to limit the stone's velocity

theoretically, if you consider a photon a particle, current physical law says it must happen IMHO

Answer 9

The stone and the light. That is a question for the ages. I agree with you completely. No one has ever had the correct proof to that theram. Good Luck ! :)

Answer 10

have you test it it out? try it and your own experience is the truth