Jacques

In Newton eye space and time are absolute. In Einstein eye space and time are relative. In our every day experience newtownian physics match observation and relativity with is complexity look like a luxury that we don't need to try to understand. We observe the universe from the external eyes of Science! The equation are simple enougth that with little effort you can understand. Relativity deal with the extreme . We don't observe these effects in our everyday life and culturally we are not incline to see the world throught these glasses. A little tought: Does Relative presuppose that there is an Absolute. Thanks

Do you mean that Lorentz transform apply only to constant velocity ? Suppose Bill going away at constant speed we will see his clock going slower. We can use Lorentz transform to calculate how much slower we will read. (It is a guess ) Suppose Bill coming back at constant velocity after is turning back. We will see his clock runing faster than our clock (mesurement effect). But the Lorentz transform will not give the correct answer.

I know that people here thinks Tom Flander is a crackpot, but I read some articles of what he call "gravity aberation" The delay in the gravitation propagation would cause orbit degradation...(http://www.metaresearch.org/cosmology/speed_of_gravity.asp). That make sense to me. Maybe I missed the flaw in his reasonning??? What do you think of that ?

If it was a measurement difference then when Bill come back, Bob will see Bill's clock going faster. Lorentz transform doesn't distinguish between motion away from the observer and motion toward the observer: the v term is squared v^2 . I am still puzeled....

Am I right about how orbits are calculated using Newton equations? The positions calculated are positions in the absolute NOW of YT ???

That's a question I been asking myself for a long time too. I don't have an answer

Absolute time... I think that's the way gravity equations works. You compute the position of the sun in the sky where he is now . If you want to observe it with your telescope, you will point to where it was 8 minute ago. There is also an other way to think about now: Now is the sensation caused by the set of perception that hit my senses. Everybody have is own Now.

The difference of clock rate of the GPS and the surface clock is consequence of the difference of the gravity field. Yes the difference is caused by an inverse square field so there is a relation with distance. But the depth of the gravity well or more exactly the difference of depth, is the difference of the acceleration. The difference between Bob and Bill is 0 so the gravity field depth is zero. Do you think that make sense ?

Thanks Martin for your reply I see here it is almost a chat by looking at the post time. So you are telling that the paradox is solved because you have a prefered reference frame ? What if the spaceship accelerate at exactly 1 G ? Bob and Bill will feel the same acceleration, so what is the prefered frame. Do you have some internet references or other post, about the solution to this paradox? Thanks

In relativity everything is relative. The brother on earth Bob sees is twin Bill aging more slowly because Bill is going near the speed of light. For Bill in the spaceship sees Bob on earth going away from him at near the speed of light so he see him aging more slowly. That's the big paradox of relativity and I don't know it is resolved by the physicists.

Then what is the space curvature used to explain gravity?