Sun-Earth-Moon Gravity

Last example: the way light is bent around the sun is explained by Einstein as due to the Sun's mass causing the warping of space time.Isn't it a simpler explanation to describe the bending of light around the Sun as being due to the space that has been displaced by the Sun?You're right, until I can prove something, the theory will remain in the crack-pot realm.

No. Both are just strings of words without any meaning until the terms are rigorously defined enough to make testable predictions.That is what Einstein's Theory of Relativity does -- it provides rigorous mathematic definitions so that we can predict phenomena that should be observed. In fact, the bent starlight was one such prediction. So Relatitivity is no longer a meaningless string of words. It is now a well-tested theory.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

Since we're discussing words, let's take a look at Einstein's Train Thought Experiment, from which he derives much of his Special Theory of Relativity.Let's change Einstein's Train Thought Experiment by adding another observer at midpoint M'. This observer knows he is on a train moving at velocity v. When the lightning strikes occur at A' and B', both observers measure the distances to the marks left by the lightning strikes.The observer who doesn't know he is on a moving train concludes that the lightning strike at B' occurred prior to the lightning strike at A'. The observer who knows he is on a moving train, tells the other observer to look out the window and notice that they are on a train moving at velocity v. The observer who didn't know he was on a moving train now determines that both lightning strikes must have occurred simultaneously.I think you are on shaky ground when you base much of a theory on a observer who isn't smart enough to look out a window and realize he is on a moving train.Edited by mpc755, : Message clean-up. Better Example.Edited by mpc755, : No reason given.

Except that the observer looking out the window may as well conclude that it is the ground that is moving past at a velocity v. The point of relativity is that there is no preferred frame of reference in which to determine absolute velocities. It is indeed not possible to determine whether the two lightning strikes occurred simultaneously or whether one occurred before the other until one decides on a frame of reference in which to make the time/position measurements.It is impossible to determine whether it is the train that is moving, or the world outside that is moving.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

...until one decides on a frame of reference...

So when the lightning strikes occurred depends on what an Observer thinks?

No. It depends on the frame of reference one chooses to determine the times and locations of the lightning strikes.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

It depends on the frame of reference one chooses

One Observer on the train says the ground is moving past the train, so the lightning strike at B' occurred before the lightning strike at A'.A second Observer on the train says the train is moving at velocity v relative to the ground, so the lightning strikes occurred simultaneously.A third Observer says the train is moving so fast towards B' and away from A', that the lightning strike at A' had to occur before the lightning strike at B'.A fourth Observer says the train is moving toward A' and away from B', so the lightning strike at B' had to occur before the lightning strike at A' and had to occur earlier than to the lighting strike at A' relative to the other Observers.They are all correct since they all take different frames of reference.So there are an infinite number of different times that the lightning strikes occurred?So an Observer who decides to take the "train is traveling at almost the speed of light toward B' reference-frame" could decide that the light from A' has taken billions and billions of years to reach him?Einstein states, "unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event." Who tells the Observer the reference-body to which the statement of time refers?

Indeed.- A better way to say this is that there are different choices for a frame of reference, each of which will provide a different timing (and distance) between the lightning strikes.- That is a choice that needs to be made by the observer. Usually the observer chooses her frame of reference -- that is the most natural one to use -- but she may decide to use a different one if it is more convenient for the problem at hand.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

What will the different Observers see at midpoint M'?For example, what if there is a 6' person standing at A'?The Observer who takes the train as the reference-frame will see a 6' person. However, if the train is moving extremely fast relative to the embankment, and a second Observer at midpoint M' takes the embankment as his reference frame, won't the 6' person look like she is way off in the distance when she is lit by the lightning strike?How can something appear visually different to two Observers simply because of the reference-frame they choose?

Unless the train was passing by when the lightning strikes. Then she would be right outside the train window.- I don't like the word "appear" -- it makes it sound like this is some sort of optical illusion when in fact the different observers really do measure time and distance differently.Why do different observers measure time and distance differently? Well, that's the way the universe is. Why should different observers measure time and distance the same? The reason that latter question doesn't get asked is because, being unfamiliar with relativistic speeds, we are just used to it -- it seems normal to us.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

The 6' person is on the train. Not outside the window.Let me try and rephrase...The person at midpoint M' is on the train, but takes the embankment as her frame of reference because she knows she is on a train moving towards B'. There are two people, of identical height, standing at A' and B'. The train is dark. When the light from the lightning strike from B' reaches her, she uses some type of instrument to measure how tall the person is that is lit by the lightning strike. She does the same when the light from the lightning strike at A' reaches her.She knows she is moving towards the light from B', she knows A' and B' are equidistant from her, so she knows the light from B' did not travel as far as the light that reaches her from the A'. Since the light has traveled different distances to reach her, the people must register as being different heights.For the other Observer who takes the train as her reference-frame, the people must register as having the same height.

Why should different observers measure time and distance the same?

Because otherwise, they are measuring to marks that were made in the past. Why are some observers allowed to measure to marks on the train while other observers measure to marks on the embankment simply because that is the reference frame they choose? Measuring to either sets of marks no longer represents where the lightning strikes occurred. They are simply marks that were made in the past and no longer represent where the lightning strikes occurred because the marks have moved.

Huh? This doesn't make sense. What does the distance light travels have to do with a person's height?- I can't make any sense out of this paragraph either.Don't worry about things like "past" and "present". We assume that we can tell where an event occurred and when it occurred. How we measure these things aren't important, just that we do.We have something that occurred. Say lightning strikes a point on the ground, since that is the example you choose. A person standing on the train platform sees the lightning strike. She can presumably tell where it struck the ground and when. Maybe you're worried that it took some time for the light signals to travel from that point so that she could see it -- don't worry about that -- the observer is smart enough to take the speed of light into account so that she can figure out precisely when the lightning struck.Now say that two bolts of lightning strike the ground at different places, A and B to use your labeling. Suppose that the person on the platform (after taking into account the time it takes to reach her form each of these points, of course) determines that each of these lightning strikes occurred at exactly the same time in her frame of reference.Now there is someone sitting on a very high speed train, and this train happens to be travelling along a path that is parallel to the line between A and B. In fact, suppose that this train is travelling in the direction that goes from A toward B. This person also sees the two lightning strikes, and can tell where they occurred, and can also take into account the speed of light to tell exactly when they occurred. When he does so, he discovers that (in his frame of reference), B occurred before A did.Who's right? They are both right. We have no way of determining locations except by marking a special point as "location=0" and using a ruler to measure the distances from that special point to other points. We have no way of determining times of events except to designate some time as "time=0" and using a watch to determine how long afterwards other events occur.However, different observers in different frames of references will measure lengths and times very differently from one another. The observer on the train platform may have a measure stick that is exactly (to her) one meter long. However, the observer on the train will notice, if the measure stick is lying parallel to the path of the train) to be shorter than one meter. The observer on the platform will have a watch -- she will notice that it takes one minute for the second hand to go all the way around. However, the observer on the train will notice that it takes more than a minute for this second hand to go all the way around.Of course, this is all relative. The person on the train may also have a measuring stick that is exactly (to him) one meter long. However, if it's lying on the floor parallel to the direction the train is traveling, the the observer on the platform will notice that it is shorter than a meter. Likewise, the observer on the platform will notice the second hand on the person on the train's watch takes more than a minute to go all the way around.This isn't merely an optical illusion, but a fundamental fact of the universe that time/space coordinates "rotate" and mix together when we jump from one frame of reference to another.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

When we use a telescope and view an object billions of light years in the past, do we estimate the distance to what we are seeing as to where we see the light originating from, or to where the object is now?

Hmm. Now we're talking about cosmological distances where General Relativity becomes important. I'm not sure whether my answers here are going to make any sense, so don't take them too seriously.As far as I know, if an object is billions of light years away, then we are estimating the distance between the point at which the light was emitted (billions of years ago) and our position here, now. After all, we don't really have any idea where that object is now anyway, since we won't see the present time object for another billion years or so.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

Just as we estimate the cosmological distance the light has traveled as to where the light was emitted (billions of years ago), the observers who take the embankment or the train as their reference-frame should determine the distance the light from the lightning strike has traveled by measuring to where the light was emitted (moments ago).Measuring to where the marks are on the embankment or on the train do not represent where the light was emitted. They simply represent where the marks are now.If the observer who takes the embankment as her reference-frame and the observer who takes the train as her reference-frame are able to measure to where the light from the lightning strike was emitted, they will wind up at the same point.Edited by mpc755, : No reason given.Edited by mpc755, : No reason given.