Sun-Earth-Moon Gravity

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?

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 Measuring to either sets of marks no longer represents where the lightning strikes occurred. They are simply marks that were made in the past and no longer represent where the lightning strikes occurred because the marks have moved.

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?

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.

That's what they do.

That's not what they do. They measure to marks left by the lightning strikes. This is not where the light from the lightning strike was emitted.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 and this would not coincide with either mark.

I'm on a miles long moving sidewalk when the tire blows out right on top of the moving sidewalk. An hour later, the police ask me what happened and I point to a spot 5 feet in front of me on the moving sidewalk and say the tire blew out right there. The police, using my reference-frame, measure from that point to where the car stopped and can't believe how far the car traveled on a flat tire and what good condition the tire is in. Only problem is, the car didn't travel that far. Using my reference-frame does not represent the correct point where the tire really did blow. It represents a point in the past where the tire blew.

The whole problem is there is on one true frame of reference and everything is in motion in that frame.There is no train reference frame or embankment reference frame.Measuring to a mark left by a lightning strike does not represent where the lightning strike occurred. It's just a mark made by the lightning strike and represents a point where the lightning strike occurred in the past. You cannot measure to it now.

Measuring to marks left by a lightning strike, that no longer represent where the lightning strike occurred, to prove there are multiple frames of reference is weak at best, and to me, it is simply wrong.Thanks for your time.

When we discussed cosmological distances we agreed that the distance to the galaxy cluster millions of light years away should be measured to where the light is emitted, not to where the galaxy cluster is now.When we measure the distance to the lightning strikes, we need to do the same; measure to where the light from the lightning strikes was emitted, not to where the lightning strike marks are now.The marks on the train and the marks on the embankment do not represent where the light from the lightning strikes emitted from, just as where the galaxy cluster is now does not represent where the light from the galaxy cluster emitted from.This might just make things worse, but here is an attempt at an example:Our train reaches from here to the galaxy cluster millions of light years away. The observer, train and galaxy cluster are in the same reference-frame. When the lightning strikes the train it leaves a mark on the train at a point in the train that is in the galaxy cluster. The observer is millions of light years from where the lightning strike leaves a mark on the train. After millions of years, the light finally reaches our observer and she decides to measure the distance to where the lightning strike originated. Should she measure to where the light was emitted, or should she measure to where the mark is on the train (i.e. to where the galaxy is now)?Edited by mpc755, : Trying a better example

In the ground's frame of reference, the light was emitted at the strike marks.

No, the light was not emitted at the strike marks. The strike marks were made in the past and no longer represent where the light emitted from.If there is one thing any observer knows as fact, is that his reference frame is in motion and the marks in his reference frame have moved since the light from the lightning strikes made the marks.

so, after some time, the strike marks are no longer at the point in space where the light was emitted.

Exactly!

All we can know about the galaxy and train is from the light (or other signals) that reach us from there. So this is going to determine to where we measure the distance. We cannot measure the distance to where the train is now, because we don't know where the train or the galaxy is now. Millions, even more, have passed since the events that we are observing now. The train and galaxy could be anywhere now. In fact, for all we know, the train and the galaxy don't even exist any more. We know nothing about the train or the galaxy now.

Exactly! That is why measuring to the marks left by the lightning strikes makes no sense, because they might not even exist anymore and even if they do, do not represent where the light emitted from.

I am not trolling.You just made my point exactly in your previous email.

Sure, but the point in space where they used to exist certainly exists.

This is exactly my point!!! Ugh!!! The point in space where the mark was made by the lightning strike still certainly exists, but the mark itself has moved from that point in the millions of years it has taken the light to reach our observer.

The mark isn't moving at all in the reference frame of the mark itself, but it no longer exists where the light emitted from.After millions of years, the point in space where the light emitted from and the point in space where the mark is are two separate points in space. After millions of years, we don't even know if the train and the mark even exist anymore, but we still know where the light emitted from.Any observer, in any reference frame, would measure the distance the light traveled to reach her to where it emitted from, not to where the mark is now.Edited by mpc755, : No reason given.

...where the lightning struck...was emitted...

Yes, past tense. But after millions of years, when the light from the lightning strike reaches her, the flash of light she sees is no where near where the mark is now. The mark does not represent the distance the light traveled to reach her.

Removed rant.Edited by mpc755, : No reason given.Edited by mpc755, : Removed rant.

What if the two lightning strikes occur at points in space and do not leave marks on the train?What if instead, the Observer on the train whips a long wooden rod through the lightning strike the instant he sees the light from it which causes the lightning strike to burn right through the rod.Wouldn't the length of the rod be a good indication of how far the light traveled to reach him?If he had multiple rods, he could keep whipping them through the lightning strike. He would then be able to tell how he is moving relative to the lightning strikes and calculate back to determine the exact distance the light from the lightning strikes traveled to reach him. He would then conclude that the lightning strikes occurred simultaneously.