Im not sure if there is any viable way to answer this question. I have heard some people mention that the flow of time itself may be changing but how is that testable?
Short answer: It doesn't. Motion affects relative time... but this does not apply to motion due to the expansion.
The distinction is between matter moving with space, as apposed to moving through space. Time is simply our perception of relative movement through space.
I would say the geometry of the universe affects time. Think about it like this - If the universe consisted of one Schwarzschild black hole, time for a very distant observer would pass at a different rate to an observer falling directly toward the black hole. Something that makes it very easy to see the difference in the observers perception of time is the presence of a horizon. Now we know that the universe on large scales is not described by the Schwarzschild solution but is more like the de Sitter solution. The de Sitter universe also contains a horizon so it's natural to suppose that time for different observers is different. It's quite late and I'm afraid I'm too lazy to look it up so if someone wants to correct me I won't argue. The reason I mention the Schwarzschild example is that most first courses in general relativity are the Schwarzschild solution in quite a bit of depth. Also, this is my first post - hello! Please Register or Log in to view the hidden image!
I have read the responses so far, and to be fair, i think the interpretations lack. For instance, space is also time, so there can be no seperate entity; we know this, because space is one continuum with time, as spacetime. The calculations that deal with space are mostly time-independant, especially on our scale of understanding, so if space expands, it expands as spacetime. The reason why is if we say space expands, and extrapolates time, then space is acting as a reference for time. This is not the correct view of time, because speaking from the widely accepted relative theory, time is space, as much as space is time, so time is not effected by space, its actually spacetime in one whole that seems to change, not that space expands, and therefore time is subsequent to change, because theoretically, they are simply the same. So i would say spacetime expands, not that the expansion of space gives rise to time.
Reiku, you've been told many times that relativity does treat time and space differently. Yes, it's all woven together into a single coherent description so that an effect on one causes an effect on the other but saying "space is time" and "time is space" and that they are the same is wrong. Can you stop in time? Nope. But you can in space.
But fundamentally, or essentially, relativity does not. This is my point. It was Minkowski's realization that spacetime ''played exactly the same roles,'' (as qouted him saying), unite spacetime as a single thing. This is why the current explanations at large here, are essentially missing out the importance of physics. You simply can't deny the fact, that space is the same thing as time, just two different sides to a single coin.
*sigh* If time and space were completely interchangable, the symmetry of space-time would be SO(4), not SO(1,3). The metric of relativity wouldn't have signature -+++, it would be ++++. There wouldn't be limits on Lorentz boosts, just like there's no limit on rotations. You'd be able to stop and reverse your motion in time, just as you can in space. Shall I stop there? Or do you need more counter examples? After all, it only takes one to prove you wrong (wasn't it Einstein who said that? Please Register or Log in to view the hidden image!). And I like how you quote Minkowski when you don't know his actual work. Nice. Melding space and time into 'space-time' and giving the entity a highly geometric interpretation doesn't mean the individual components are the same any more than combing SR and QM into a coherent theory we call QFT doesn't mean SR and QM synonymous. Comprende? Or shall I type slower.
If they are the same thing, why do they have all those different properties? If they are the same thing, if I can swap my motion in time and space, like I can swap my motion in terms of different, orthogonal, directions in space. But I can't. If they are the same, they are interchangeable, because I should be able to rotate my notions of time and space so t->x and x->t and fundamentally nothing changes. But I cannot. Hence my comments on SO(4) and SO(1,3). You once posted threads with length 'essays' on SO(3,1) on PhysOrg but Euler and I ripped you apart. This is yet more evidence you don't have a clue about such things. You just complained over in Astrophysics that people like me don't give you enough credit. Credit is earned and you're proving you don't deserve it yet again.
You know that qoute i gave? It was actually something part of a bigger paragraph, one which you called, ''meddling it nice;'' ''Gentlemen, the idea's of space and time which i wish to develop before you grew from the soil of experimental physics. Therein lies their strength. Their tendency is radical. From now on, space by itself and time by itself must sink into the shadows, while only a union of the two preserves independance... ... the provision of equations in which the special laws of relativity take on a new form in which the time coordinate plays exactly the same role as the spatial coordinates.'' You can't interpret this any other way.
The time coordinate and the space coordinate appear together in 4-vectors. Doesn't mean their physics are the time. Infact, the difference between them is fundamental to relativity. You talk about 'complex time' a lot but you don't understand it's implications. In special relativity the metric has signature (-+++). That clearly treats time and space differently. If you do a Wick rotation you end up with a metric signature (++++). That would give time and space the same. There is only one rank 2 isotropic tensor, up to multiplicative factors. It's the Kronecker delta, which is equivalent to a metric with signature 'all pluses'. The eta tensor is not isotropic in both space and time in the strictest sense. As usual, all you can do is mindlessly repeat a single line from one person over 100 years ago. Why? Because you don't actually know the details of relativity. If you understood the concepts you've wasted a great many hours writing essays on, you'd understand why you're wrong.
Whatever. I know what it is that i read from Minkowski's words, and the meaning behind why we unite space and time as a single entity. It's clear you don't.
Two extra dimensions found. -Time loop paradox. http://physics.usc.edu/~bars/ Changing our picture of time from a line to a plane (one to two dimensions) means that the path between the past and future could loop back on itself, allowing you to travel back and forwards in time and allowing the famous grandfather paradox, where you could go back and kill your grandfather before your mother was born, thereby preventing your own birth. You better put this in the cesspool...
