What is Spacetime?

[sprintcyclist]

Very good SuperNova.

Hard to get my head around.
So you are saying if I am running at the speed of light and turn my headlight on, from where I am, the light only goes at the speed of light?

Sounds fair.

If I am in a train going 50 km/h and throw a rock ahead at a speed of 20 km/h, from where I am, the rock is going 20 km/h
To someone up the track, the rock is coming at 70 km/h


How an I going ?

[Super Nova]

Good, have to go to client site, will respond later. I will walk through step by step so you can understand the little I know.

[Black Orchid]

I know someone who absolutely LOVES this stuff

[WellWisher]

I love the explanation from a movie about Marilyn Munroe and Einstein in it, i cant remember the name, now to gather my thoughts
imagine a train going past you very fast from left to right
in the train is a flashlight on the floor pointing at the ceiling
directly above is a mirror, if your in the train u see the light go up to the mirror and back down again in a straight line.
if your outside the light would be like a triangle going from the floor on your left up to the ceiling then by the time it gets to the floor again the torch has moved to the right,
so to you , outside the train , the beam of light has travelled further .
Time is basically light , so in the train the light from the torch is less than for the person outside the train, so time is different for the person outside the train.
ALso look at atomic clocks in space ships, they change just that little from going faster than the rest of the world.

I also love the fact that a vehicle can travel at you at say 100km's a hour and yet its headlight's light still only comes at a set speed (speed of Light) . Not speed of light plus 100Km's.

[BigP]

I love the explanation from a movie about Marilyn Munroe and Einstein in it, i cant remember the name, now to gather my thoughts
imagine a train going past you very fast from left to right
in the train is a flashlight on the floor pointing at the ceiling
directly above is a mirror, if your in the train u see the light go up to the mirror and back down again in a straight line.
if your outside the light would be like a triangle going from the floor on your left up to the ceiling then by the time it gets to the floor again the torch has moved to the right,
so to you , outside the train , the beam of light has travelled further .
Time is basically light , so in the train the light from the torch is less than for the person outside the train, so time is different for the person outside the train.
ALso look at atomic clocks in space ships, they change just that little from going faster than the rest of the world.

I also love the fact that a vehicle can travel at you at say 100km's a hour and yet its headlight's light still only comes at a set speed (speed of Light) . Not speed of light plus 100Km's.

Einsteins theory of relativity was built on the backs of earlier pioneers like Galilieo



"""Galileo formulated the principle of relativity in order to show that one cannot determine whether the earth revolves about the sun or the sun revolves about the earth. The principle of relativity states that there is no physical way to differentiate between a body moving at a constant speed and an immobile body."""

[BigP]

He had an epiphany when on a sailing ship, he was in his cabin and his parrot took flight whilst the boat was under passage and it dawned on him that the boat was traveling at a speed relative to the land and his parrot was moving at a speed relative to the boat

[WellWisher]

He had an epiphany when on a sailing ship, he was in his cabin and his parrot took flight whilst the bout was under passage and it dawned on him that the boat was traveling at a speed relative to the land and his parrot was moving at a speed relative to the boat

what was the parrots name ?

[BigP]

He had an epiphany when on a sailing ship, he was in his cabin and his parrot took flight whilst the bout was under passage and it dawned on him that the boat was traveling at a speed relative to the land and his parrot was moving at a speed relative to the boat

what was the parrots name ?

Aussie I think

[Super Nova]

Very good SuperNova.

Hard to get my head around.
So you are saying if I am running at the speed of light and turn my headlight on, from where I am, the light only goes at the speed of light?

Sounds fair.

If I am in a train going 50 km/h and throw a rock ahead at a speed of 20 km/h, from where I am, the rock is going 20 km/h
To someone up the track, the rock is coming at 70 km/h


How an I going ?

Ok Sprint, Let's go and i will try and explain.

So you are saying if I am running at the speed of light and turn my headlight on, from where I am, the light only goes at the speed of light?

First thing is you can never run at the speed of light. Only massless particles travel that fast. Anything with mass takes more and more energy to accelerate it as we get closer to the speed of light. The energy required increases exponentially and you need infinite energy to push a particle with mass to the speed of light.

However, if we imagine we are travelling at the speed of light and you turn your headlights on, the light probably would appear not to move and appear like a standing wave. This is a prohibited scenario so lets pick one that is allowed.

A more realistic example would be you are travelling just under the speed of light. You turn your light on. It would appear to you to shine like normal inside your space craft. To an outside observer the light would be seen to have red shifted, if you were moving away from them, changed frequency, like the Doppler affect with sound. That is the light is emitted from a fast moving spacecraft, heading away from the observer so the wavelength would be elongated, since the light's speed is always a constant. You would see it as normal because.

1. The wavelength is the same for because you are travelling with the torch and because...
2. Your time has slowed time relative to the external stationary observer

The faster you go, the slower time goes for you relative to an outside observer.

If I am in a train going 50 km/h and throw a rock ahead at a speed of 20 km/h, from where I am, the rock is going 20 km/h
To someone up the track, the rock is coming at 70 km/h

This is true and the classical Newtonian view of the universe. This works for objects travelling at slow speeds. A good approximation.

However, doesn't work for light, think that the speed of a rock is fixed. It can never be a different speed.

A better analogy would be the train wihistle. when it blows, you on the train always hear the same pitch. But people ahead of the train hear a higher pitch. this is the doppler effect. because sound travel at a fixed speed.

Same applies to light.

Next Question or is clarification required. We should move to, how space warps. After we have done special relativity.

[sprintcyclist]

Thanks SuperNova.

I have read it a few times.
Will think on it more with other questions.
You are going well.

So, if I am running away from you at the speed of light (maybe due to a good backwind, or a downhill section), it might be hard for you to see me.
The light shining onto me cannot touch me as I am going the speed of light.
There is no reflected light.