«

[Evad]

hey people, I am currently trying to learn about his subject a little, and from the interesting and intelligent discussions I've read here, I'm sure there is a wealth of knowledge about these theories here. What I need is for someone to explain to me the significance of this theory, as I don't have a strong foundation in the subject.

[Playbahnosh]

Relativity?
Cooooooool! :cool:
I guess you know everything about it by now. It is, that everything is releated to each other in a way. Like speed. We can only measure speed if we relate it to something, like the road. Example, beware :
A car is travelling from A to B with a speed of 50 Km/h. Related to the ground. Another car is travelling with it too, with a speed of 60 Km/h. If we look it like this, the speed of both cars are related. The first one is 10 Km/h faster than the other. So if we realte the speed to the ground: car1: 50 Km/h, car2 60 Km/h. BUT if we relate the speed to each other and make the 0 when they are moving with equal speed, car1: -10 Km/h, car2 10 Km/h. And the 0 is when the two cars are not moving related to each other, regardless of their real speed related to the ground.
Phew, that was, um...exhausting...
Try to decode it! k:

[Evad]

that makes sence. :Brain:

[Playbahnosh]

FINALLY! :Brain:
Someone fillally understands what I said!

The Theory of Relativity is more complex than this lil exaple though. It has numerous formulas and thing like that I don't know a thing about, but I know what is relativity k:

The other one is like Earth is moving. It is rotating with and Incredible speed, just imagine the dimensions. We, on the ground, doesn't sense a thing about it, bu we are moving righ now, when in fron fo the computer, we are travelling with more than 10000 Km/h round the axis. And more 1000K Kmh around the Sun. That is relative too. I'll come up with a more understandable exaple later, but I'm hell tired right now (it is 3 AM here GMT+1)

[Data]

the basic assumption on which the whole theory of relativity is based is
that the speed of light is always the same no matter how fast you travel yourself. (as you can not determine your own speed if there isn't any refence point).

Some people argue that this basic assumption follows from a different assumption:
the laws of physics are the same no matter your own speed and derive the speed of light from the electromagnetic theory (maxwell equations)

The result of this statement is that there is need for a transformation from system that are "at" rest to systems which "move". (this is offcourse ambigous as for the moving system they are at rest and the other system moves.)

It goes quite deep to explain the mathematics and how to derive lengthcontraction and time increase but these are the results of moving.

To get to the example of the cars that move towards each other.....
50 km/h to left is one car
60 km/h to the right one car
if you would measure the speed of one car compared to the other the result would be
110 km/h
this is wrong according to the theory of relativity.
it's less then 110. I will not explain how and why but it's a result not many people know

[Quintopotere]

Another important point it's that two events (A & B ) are simultaneous only if a ray of light passing in A cuold reach B... and from here start all the paradoxes...

My english it's too poor to put here an extended explanation, but i can suggest you a great book about relativity: The ABC of relativity, by Bertrand Russel, who was a great friend of Einstein!

The only thing i want to say is that many people think that Einstein said that all it's relative, but that's not true: all it's relative about the observation point!
But it's all absolute using a calculating sistem based on tensores (which are cubic matrix used to change the reference sistem... too hard to explain for me )

Anyway relativity seems to function even if isn't right...

[Evad]

@all
thanks, and feel free to keep giving examples and your thoughts, the more the merrier. I have Einstein's actual theory translated, and am trying to work through it, but even though he dummies it down, I find it hard to understand the way he explains things. That abc of relitivity looks good. The thing that is troubling me right now is this. The speed of light in a vaccum is 300,00 km/s. And it has been proven that the light sorce doesn't change this.
Now it says in this book, that if you put a train and a beam of light next to each other, and
measure their speeds relitive to each other then this will mean that the speed of light is slower then 300,00 km/s. speed of light - trains velocity=>300,00 km/s, and this is a problem for some reason?. Why? And how? The light is still moving at 300,000 km/s reletive to a stationary body reference right? Does the law of propagation of light mean that that a light beam should always be going 300,00 km/s faster then everything or what? Hope I'm making sence.

[Quintopotere]

Originally posted by Evad@Jun 20 2005, 03:40 PM
Now it says in this book, that if you put a train and a beam of light next to each other, and
measure their speeds relitive to each other then this will mean that the speed of light is slower then 300,00 km/s. speed of light - trains velocity=>300,00 km/s, and this is a problem for some reason?. Why? And how? The light is still moving at 300,000 km/s reletive to a stationary body reference right? Does the law of propagation of light mean that that a light beam should always be going 300,00 km/s faster then everything or what? Hope I'm making sence.

But does a stationary observer is really stationary? For example i'm stationary on my chair but i'm on the rotating surface of the Earth: so i'm faster than a train, but light beams overtake me at lightspeed, and not at lightspeed-(rotation velocity of the Earth) !!!

A light beam isn't 300000km/s faster than everything, but it should be 300000km/s for every observer

[BeefontheBone]

Not just "should be" - it is that speed for every observer (in a vacuum anyway). It seems i'm not the person to ask about General Relativity - I got 36 on my exam recently Special Relativity I'm much better at, but to properly explain it requires some fairly advanced maths.

@Data: the "some people" you mentioned include Einstein - the principle of special relativity is that the laws of physics are the same in any inertial frame (ie for any observer moving with constant velocity) from which one derives the fact that light travels at c in a vacuum for every observer.

[Playbahnosh]

I have a little paradoxonal joke regarding this:
"If a car is moving with lightspeed, what happens if we turn on the headlights?"

In my opinion, the anwer is simple:
Assume we are in vacuum. The car travels at lightspeed relative to the light source (Sun or whatever), so the car and the light, as a ray projected from the source, travels at equal speed. The law says that nothing can travel faster than light. Now, if we turn on the headlight, that creates another light source, wich will emit light rays. Now as I see, two things can happen.

First, if we see the whole thing relative to the orig light source, and the light travells with 300,00 km/s in vacuum no more no less, the light emitted from the secondary source(the headlights) should remain the speed of the other (original) light ray, due to the lightspeed law (300,00 km/s). If this is true, the secondary light rays shall remain stationary in the source(the headlight), wich is a bit unbeliavable to me

The second theory is that we turn on the headlights, the secondary light rays shall travel with the same speed too(300,00 km/s) wich will add up. So 300,00 km/s + 300,00 km/s = 600,00 km/s is the speed wich the secondary ligh(emitted from the headlights) will travel relative to the original source. This breaks the lightspeed law.

So what now?