Exploring the Mysteries of Time and Spacetime

[Max364]

I should have added: Andromeda Paradox explained here: https://en.wikipedia.org/wiki/Rietdijk–Putnam_argument

 

[nitsuj]

By emerging , i mean each person/object experiences its own rate of time passage...

Instead of "emerging", which would likely tend to be interpreted as referring to the concept of emergence. You described Proper Time...so just call it that.

 

[Ibix]

By emerging , i mean each person/object experiences its own rate of time passage (hence, can not agree on simultaneity of events etc),

Everyone experiences one second per second. But different frames do not define time the same way, which is what I think you are getting at.

Everyone at rest in the same inertial frame agrees on simultaneity. Frames in relative motion do not agree on simultaneity, though, no.

my time is unique to me even though it is almost exactly the same as yours, as we occupy almost the same space (relatively)

The space we occupy has nothing to do with it. What matters is our relative velocities, or our history of relative velocities, depending on how exactly you mean "time" in this context.

v+t=1, yes for wordlines or even worldtubes (solid 4d object)

I already told you this was wrong. If you believe otherwise please cite a source.

Two people passing each other can not agree on what is defined by exact moment "now" - extended to Andromeda galaxy this gives difference of days not just nanoseconds like on Earth etc.

They can agree. What you might call the "natural" definition of simultaneity is different for the two, this is true. But neither is obliged to adopt that convention. That it is merely a convention is obe of the points of the Andromeda paradox.

 

[PeterDonis]

Andromeda Paradox explained here: https://en.wikipedia.org/wiki/Rietdijk–Putnam_argument

We have an insights article on this (of which I am the author ):

https://www.physicsforums.com/insights/block-universe-refuting-common-argument/

 

[Max364]

Thank you for that Peter and your further explanation of the Block Universe in that article.
Would it be true to say that every point in space exists in a different time? (due to spacetime nature - ie, its own time for every point) - this is because in objects/mass causing warping of space must then also cause warping of time? ...however small...
or do two points separated by space exist in the same time frame? (in the same inertial frame etc)

 

[Ibix]

The block universe models spacetime as a solid block. Splitting it into space and time is equivalent to (imagining) slicing the block into infinitely thin sheets. Each sheet is all of space at one instant.

The point about no global simultaneity is that there is more than one way to slice the block - you can tip it over slightly and make slices at an angle to the first set of slices. That's a different definition of now, and whether or not two events lie in the same slice (are simultaneous) depends which set of slices you choose. The choice of which way to slice is your choice of inertial frame.

But "every point exists in its own time" makes no sense. It's like saying every point in a block exists at its own height. No. A whole plane shares the same height, and similarly the whole of space now (however you chose to define now) shares the same time.

What is true is that, if you trace the paths of two objects through spacetime, they may meet, move apart and meet again. And the paths may have different lengths. Path length through spacetime turns out to be the elapsed time, which is how the twin paradox works.

 

[StandardsGuy]

As @Nugatory says, that picture is very poor. For a start, it implies that the grid is a 2-dimensional model of spacetime, then draws a 3-dimensional Earth sitting outside spacetime.

The picture is very pretty, but it's not even internally consistent, let alone much like the reality.

I don't particularly like the rubber sheet. It is a 3-dimensional model of 4-dimensional spacetime. Perhaps the Earth should be shown below to indicate that the gravity of the Earth is pulling the sheet downward (the third dimension). Anybody using it should point out the inconsistencies and limitations. However it does give a visual understanding to a difficult concept. Let's don't throw out the baby with the bathwater.

 

[Boing3000]

I don't particularly like the rubber sheet. It is a 3-dimensional model of 4-dimensional spacetime.

That's a quite common stance from physicists. From my layman's perspective this 4-dimensional model of a 2-dimensional slice of space-time is a perfectly fine analogy to introduce some key concepts of GR. I don't think I have even heard some of these internet "guy" pretend that the sheet will emulate a inverse square root law and true elliptical "orbits" (do they ?, I mean ignoring friction ?)

Nonetheless it introduce quite naturally what "curvature" is, and how seen from above some invisible local effect are interfering with object movement and their presence.
This made visible sheet "steepness" quite naturally introduce to the audience the urge to understand how to evaluate that change in "curvature" and learn about derivative. How many will then try to follow the rabbit and extend the computation over a 4D manifold using tensor geometry is not the point.

The point is that thanks to that analogy I can explain my grand-ma that gravity is not a force, that all these marble are in free fall and not accelerating, and I can even explain that a black hole is just that same marble but reduce to the smallest dust and projected to infinity, actually puncturing a (black) hole, into this sheet, but then without actually changing anything beyond where the marble "was", and thus also explaining that black hole don't suck anything.

 

[PeterDonis]

Would it be true to say that every point in space exists in a different time?

I'm not sure what this means, but I think the answer is "no".

this is because in objects/mass causing warping of space must then also cause warping of time?

Since the separation of spacetime into "space" and "time" is not invariant--it depends on your choice of coordinates--there is no such thing as "warping of space" by itself or "warping of time" by itself; there is only warping of spacetime.

do two points separated by space exist in the same time frame?

What does "exist in the same time frame" mean?