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tommac
2008-Apr-10, 08:00 PM
I am a bit confused about distances.

My novice understanding of relativity has me to believe that distance and time are relative to a frame of reference. Gravity can effect this frame as well as relative speed. Would it be wrong to say that distance is really a perception of space?

My main question will be about gravities effect on distance but I will start with an overview of velocity on distance.

Lets say I am in a fast train travelling at half the speed of light. I shine a light towards an object one light year away. a half a year later. I see the light is half way there.

An observer standing on the track watches this and sees that a train moving quickly shined a light. After a half a year the light appears to be half way there.

The trick is that the two space-times of reference are not the same. In fact I believe ( please correct me if I am wrong ) when the train observes that it has shined the light 1/2 a year ago, from the observers point of view the train is really only 1/3rd of the way there or 1/3 of a light year. The distance on the train has compressed, and the time has slowed down compared to the observer on the track.

Is this correct?

Now this is the question I really have. Near a gravity well, distance compresses and time slows. As I look out into the universe, am I looking out into a compressed space universe with slowed down time compared to if I was in the vacuum of space?

This was the initial question I wanted to ask:

If there were 2 objects, one in the vacuum of space and the other was a very massive object say a star or a black hole or really anything very massive. Does the percieved distance from object 1 to object 2 differ from the percieved distance from object 2 to object 1? By percieved I mean relative to or are they equal?

01101001
2008-Apr-10, 08:20 PM
Lets say I am in a fast train travelling at half the speed of light.

As usual: relative to what?

tommac
2008-Apr-10, 08:29 PM
As usual: relative to what?

relative to the observer standing at the station.

captain swoop
2008-Apr-10, 08:34 PM
So this isn't on Network South East then?

lol sorry , joke about the British rail network lol.

Jeff Root
2008-Apr-10, 08:38 PM
Perhaps the first thing that should be pointed out here is the difference
between the special theory of relativity (SR) and the general theory of
relativity (GR). The special theory is quite simple in its mathematical
expression. It uses an extension of the Lorentz equations to transform
between different coordinate systems (different reference frames).
It completely ignores gravity. So if you have a situation that requires
understanding the role of gravity, SR can't give a good answer.

General relativity uses mathematics that is beyond my comprehension
to describe the shape of space, which is equivalent to describing gravity.
It has been tested in many, many ways, and has always stood up to the
tests, so we have high confidence that it is "correct" in some sense.
There are aspects of GR that have not been tested, though, because
the math is too difficult to make predictions or because the tests are
beyond current abilities. And mathematical extrapolations of GR to
extremely high energies appear to conflict with extrapolations of
quantum mechanics to those same energies, so it seems that one or
the other must be "wrong" in some way.

So your questions concerning only SR can be answered readily; your
questions involving gravity, maybe or maybe not.

-- Jeff, in Minneapolis

tommac
2008-Apr-10, 08:42 PM
So your questions concerning only SR can be answered readily; your
questions involving gravity, maybe or maybe not.

-- Jeff, in Minneapolis

OK lets only concern SR.

tommac
2008-Apr-11, 01:42 PM
Back to my orinignal question ...

If I am in a deep gravity well, Does that mean that I measure the universe with my relative measuring capabilities? time and distance?

So if someone is a vacuum with no gravity effecting it, does the distance they perceive me being from them different than the distance that I perceive them being at? I think yes but I am not sure. What I question, is that do I perceive only the space around me as being compresses or do I perceive everything as being compressed?

If I go out into a vacuum does the sun get smaller?

tommac
2008-Apr-14, 05:43 PM
Can we get back to my initial question:

If there were 2 objects, one in the vacuum of space and the other was a very massive object say a star or a black hole or really anything very massive. Does the percieved distance from object 1 to object 2 differ from the percieved distance from object 2 to object 1? By percieved I mean relative to or are they equal?

ToSeek
2008-Apr-15, 01:59 AM
Motor Daddy's ATM posts and responses thereto have been moved to this thread. (http://www.bautforum.com/against-mainstream/72702-gravity-c-distance.html) Any further posts to this thread that don't adhere to the scientific consensus will be dealt with severely.

ToSeek
BAUT Forum Moderator

worzel
2008-Apr-15, 10:01 AM
tommac, I'm pretty sure that in SR the distance between two objects is the same from either object's point of view if they are not moving relative to each other.

If they are moving relatively then the fact that their clocks can't remain synchronized means that the question needs to be put a little more concisely for it to be answerable. I think that if theywere synchronized at some time when they were at the same place in space then they will both measure the same distance to the other after having the same amount of time elapsed on their own clocks.

In GR I'm not so sure (and that's what your question is really asking, due to some gravitationally significant object). I suspect that if they're both using the same coordinate convention then the same will hold.

Hopefully one of the gurus will be along soon to confirm or correct my suspicions :)