B How much time dilation is there as time passes?

[Nugatory]

o what I was trying to convey is that if I were able to observe some time measurement somewhere else from where I am it would appear different. Know what I mean? IF time were stretched and I were able to able to observe that other clock in that other place it would appear to measure time differently than my clock.

Think about exactly what you're asking for when you speak of observing the other clock: You are making an observation that permits you to say something along the lines of "At the same time that my wristwatch reads X the other clock reads Y". For example, if the remote clock is ten light-minutes away and at 3:10 PM you observe (really powerful telescope?) that it reads 2:30, you will conclude that the remote clock read 2:30 PM at the same time that your clock read 3:00 - the remote clock was 30 minutes behind yours and then it took ten minutes for the light to get to you.

The key phrase here is "at the same time". Observers who are in motion relative to one another will not agree about which spatially separated events happen at the same time; this is the relativity of simultaneity (google for "Einstein train simultaneity"), absolutely essential for understanding relativity.

We can compare how much time passed for two clocks that start together, separate and follow different paths through spacetime, then come back together because they're colocated when we compare them.

But anything you say about whether one clock is running slower than anpother when they're not colocated is going to depend on an "at the same time" assertion. Your clock reads 3:00 at the same time that the remote clock reads 3:00; later, at the same time that your clock reads 3:40, the remote clock reads 3:20; you will be tempted to say that the remote clock is running slow and measuring time differently from yours. But that's not what's going on. Instead, you're using a definition of at the same time that makes it come out that way. In fact, if the two clocks are moving relative to one another, someone at rest relative to the remote clock will find that at the same time the remote clock read 3:20 your clock read 3:10 so yours is the slow one. They're both right.

 

[Snickers]

This seems to be contrary to what some of the other posters in this discussion have been saying. I would like some others responding to help clarify what you suggest. Can you expand on your thoughts with an example? Thanks.

 

[jbriggs444]

This seems to be contrary to what some of the other posters in this discussion have been saying. I would like some others responding to help clarify what you suggest. Can you expand on your thoughts with an example? Thanks.

There is no conflict.

@sweet springs is suggesting using different coordinates so that instead of thinking in terms of an "expanding universe" we can think about a "slowing universe" where cosmological distances are constant but where time is slowing down.

But it is just a game played with coordinates. It changes nothing physical. Every possible experiment gives the same physical answers no matter what coordinate labels you choose to stick on events. The elapsed time measured by an atomic clock going from a place like "the birth of the sun" to "the first man on the moon" is going to be a fixed value, no matter what coordinate values you choose to place on those two events.

 

[phyzguy]

What NASA saw for the two twins was a difference in biological age. caused by the different environments the two twins experienced. It has nothing to do with time dilation, which, as has been pointed out, was less than 1 second for the time spent in orbit

 

[nitsuj]

... started to think my thinking of space time was way off.

For Einstein too! The "visual" I came across is envisioning a long (one light second maybe) "perfectly rigid" pole/bar next to Earth (inertial/freefall). the curvature of the pole/bar compared to the path of a photon closely beside it are different.

 

[Orodruin]

The "visual" I came across is envisioning a long (one light second maybe) "perfectly rigid" pole/bar next to Earth

There is no such thing in relativity. It is also unclear what this would mean in a curved spacetime.

 

[nitsuj]

There is no such thing in relativity. It is also unclear what this would mean in a curved spacetime.

I searched for it and am mistaken, I incorrectly recalled the "conceptual process" Einstein went through with GR and light bending. Thinking it was the comparative I gave that highlights why 2 times euclidean curve for light (I thought it was 1/2).

Sorry for making a false statement

I mean just keeping ya'll on your toes! :D