Special relitivity problem

[dimand]

This is a problem using the same train and torch concept. I have thought about it for hours and still cannot think of a solution.:doh: :doh: It is highly likely that someone else will see it straight away.

 

A person is standing on a train, which is travelling from east to west at 10m/s.

That person has a torch, which they are shining directly north. The speed of light is a constant of c where c approximately = 300000000m/s

Since the prorogation of light is not affected by the velocity from its creation I am going to assume that the beam of light emitted only has velocity in the north direction. That is it is not travelling west at 10m/s and north at c. this is impossible as it would give the speed of light to be greater than c to any stationary observers looking down on the train (lets say that observer A is in a helicopter, hovering above the ground and watching the train go past below). Should the light gain this velocity to the east observer A would be seeing the impossible, even though the path of light wild appear to be propagating directly north from the train, it would have to have a greater velocity than c, impossible. With this in mind it can be deduced, that after 1 second, the light from the train is 300000km away from its initial point of creation, bout the person on the train is 10 m away from that point. This means that observer A is seeing the light emerge from the side of the train at a slight angle to the east and the value of c is not broken. This then must be the same for the person on the train, as he is in a true frame of reference (not accelerating). Therefore he must see the light emitted at a slight angle to the east (these angles will be very small by the way, to small for the eye to see). This is my real problem. The person on the train is now seeing light, seeming to travel faster than possible (for the same reason as the helicopter person saw it travelling faster earlier. In one second it appears to him to have travelled the 300000km and the 10m east. So I thought, answer to this problem. Time dilation. If the time frame on the train could speed up (or to timeframe on the earth slow down, it doesn’t really mater). Then the person will see the light travel the 300000km and a bit in one and a bit seconds, no problem. But wait. Velocity = distance/time. The value of time on the train has speed up and therefore become smaller eg. 1 second is now 0.99 seconds. By this there must be an increased velocity and by this increased velocity, the angle of the light propagating from the train will increase, causing further time dilation, causing the trains velocity to continue to increase to the speed of light :( :eek_big: (where the angle of propagation of light is 0 degrees). This does not happen. I have seen people seen people shine lights out the sides of trains.

 

So what is happening to stop the person on the train seeing light travel faster than c?:hihi:

 

There are numerous other solutions I have thought about including length contraction, but it remains a mystery to me. Should someone solve the problem I would be very grateful if they could enlighten me.:) :)

 

if i could draw diagrams on this it would help me explain, but i haven't figuerd out how.:shrug:

 

thanx for any help

[Tormod]

The key thing about relativity theory is, basically, to understand that the observed speed of c will *always* be the same for *all* observers, regardless of which frame of motion they are in, and regardless of where the light is moving.

[CraigD]

A person is standing on a train, which is travelling from east to west at 10m/s. …

 

So what is happening to stop the person on the train seeing light travel faster than c?

What’s happening is that time (what is measured by any clock) for the person on the train is increasing slightly more slowly for the person on the train than for the person in the helicopter.

 

What dimand describes is very similar to a famous geometric derivation of the equation for time dilation. This wikipedia article presents the derivation more clearly and graphically nicely than I can quickly here.

 

Note that the stationary observer (in the helicopter) sees the light move in a slightly longer path, slightly west of due north, than the moving observer (on the train). The person on the train sees it appear to move in a slightly shorter path, directly north. So the question is really “what is happening to stop the person in the helicopter from seeing light travel faster than c?”

 

Also note that it’s best to involve a mirror in the thought experiment. It’s not really physically possible for any observer to observe the position of the leading edge of a light beam or pulse – since the most immediate way one can observe anything is via light, one can only observe some reflection of it. This doesn’t significantly change the thought experiment, but making sure your thought experiments involve things that can really be measured can avoid lots of confusion.

[arkain101]

I found to help me with this is to understand there is no place that is not an observation frame.

 

Okay, so what I mean is, you can not see light travel. You can only see light that has traveled and hit you.

 

The helicopter cant see the torches light, not unless it reflects from something and then comes to it. Though it is now coming from a different source than the torche, and this source will fire it at C to the helicopter, and the observer will not see this source of photons that the helicopter is interacting with.

 

The principle I wrote to describe this is;

 

All observations in all forms of science from any chosen reference frame must uphold the fact that every passing event that can be measured and observed is an expression and impression applied to a single or series of singular zero points and no further beyond this zero point can any observation or measurment be taken. The zero point being the point of which a photon gives energy to an atom of the observer.

 

In a sense there is no world beyond the world of your own atoms.

 

Light covers distance at many different velocities. From a mental view, but not in an ovservable view.

 

Let me explain this in an example.

 

If you are looking at a planet that is orbiting a compact star and on even with its orbital plane. The light that comes from the planet to your eye will be measured to have many different velocities. Lets say the planet is orbiting at a speed of 10,000m/s. As the planet comes at you, the velocity of the light will be worked out to actually reduce, in order to match the constant C. As the planet orbits away from you, the velocity of the light will need to increase in order to match the constant of C in your observation. This is because it is coming from a moving source.

 

Note: I am explaining this in how relativity accepts it and not in my opinion.

 

So defining the constant is confusing when you change where you are observing from. You have to remind that You can not observe anything that has not Interacted with your space-time position.

 

The only constant is in how fast you would measure light to be traveling towards you, or more specifically an observer.