Expanding time?

I've been doing a bit of reading into cosmology and it's pretty heavy going (being completly out of my field).I've been reading about the big bang (please don't groan) and it seems to me that every thing is expanding (in terms of space/time): now, does it mean time as we experience time (with a directional arrow) is expanding, too?Is this just some cock-eyed idea I've dreamt up by not grasping the maths and it's really a non-question or is time actually expanding in a measurable way (in the same way the expansion of space is taking place)?

Thread moved here from the Proposed New Topics forum.

I'm begining to think this is a non question (thanks Catholic Scientist!).But if this does have merit as a question please chime in (especially if you know cosmology/physics).

You're welcome.What I've read on the Big Bang is that the evidence suggests that space is expanding, not that spacetime is expanding.But, could the way we experience time progressing, as a series of instinces, actually just be time "expanding" in a similiar way to that which space expands?I dunno. The answer prolly comes down to the maths.Edited by Catholic Scientist, : added "be"

Space-time is not expanding. In General Relativistic models, space-time exists as a static 4-manifold. To an observer, space appears to be expanding, but that is an illusion created by the "motion" of the observor along her world-line -- that is, as time passes.Consider this analogy: Space time is a 2-manifold, that is, the surface of a sphere. Like all of us, she can't help but experience time passing -- this is represented by her motion south along a line of longitude. Looking sideways is her experience of "space". So at a given point in time, she has moved down in latitude, and the latitude represents that time on her watch. A line of constant latitude is the spatial universe that she sees; that is, to her the universe is a circle.Now, a little bit later, she is a little further south; now the circle of constant latitude is a large circle. To the observer, the universe is bigger; space has "expanded". But that is because her universe at any given time is a cross-section of a higher dimensional manifold, and at different times she is seeing different cross-sections.

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Spare a thought for the stay-at-home voter;
His empty eyes gaze at strange beauty shows
And a parade of the gray suited grafters:
A choice of cancer or polio. -- The Rolling Stones

So if the sphere is expanding does the longitude time line 'change' as the relative curve of the sphere decreases? Or is that just a side effect of the analogy and not important?I fully appreciate I may have totally missed the point of your example and may be taking it far too literally.

The point is, the sphere is not expanding...

As Mod says, the sphere is not expanding. It is a fixed size. What is expanding are the circles of latitude, as you move up the lines of longitude from the South Pole, or down from the North Pole depending on your analogy preference. The circles of latitude represent space, and the lines of longitude are time.

As the circles of latitude expand, does the magnitude of the time dimension get relatively smaller comapared to the magnitudes of the spacial dimensions? I mean, since the longitude line stays the same "size" as the latitude lines expand, is time shirinking relative to the expanding spacial dimensions?

Yes, that's right. And when we put it this way, the time lines can actually shrink and expand, like the space dimensions, depending on the overall geometry/topology. We just don't think of it that way as we're tied to travelling along the time lines, and also the geometry of our own universe is quite boring and doesn't behave that way (think of the lines of longitude around the globe)Edited by cavediver, : No reason given.

Yes, that's exactly the reverse of what I was thinking! But it is a 'change' in time relative to space.Again you put my thoughts into better words than I ever could have.

Ah, I see. We could never percieve it anyway. I've been thinking in a too fancifull way again, have'nt I?. A pox on this conventional universe.I really must learn some more maths so I can stop having to use ananlogies.

Just use different analogies.Think of the topology as that of a horn, like a tuba, instead of a sphere. That can help explain further expansion versus a "collapse" at the end.And if you think of the topology as like a telescope, in the sense that it is telescopic (extendable), you can acually have the time deminsion expanding with the spacial dimensions.You just gotta make sure the analogy conforms to what you are trying to perceive, keeping in mind the limitations of the analogy.But for reality, it all depends on what he actual topology of the universe looks like. And I don't think that we have it totally nailed down yet, but cavediver can correct me if I'm wrong. Yeah good luck with that one

Are you saying that if we could have a superstring that could not be stretched connecting the galaxies the galaxies would prove to be not moving though space however it appears your all saying that its only space time that part of nothing that is being stretched by some force thats giving us the illusion that the galaxies have moved when its only space time between them that has stretched.When your talking about the sphere are you talking about the entire universe. If the galaxies are not moving (the sphere not expanding) is the big bang theory dead?Edited by johnfolton, : No reason given.Edited by johnfolton, : No reason given.

Huh?Try using punctuation, proper spelling, and proper grammer...Here, let me help:

quote:

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Are you saying that if we could have a superstring, that could not be stretched, connecting the galaxies, then the galaxies would prove to be not moving though space? However, it appears you're all saying that its only space time, that part of nothing that is being stretched by some force, thats giving us the illusion that the galaxies have moved when its only space time between them that has stretched.

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Is that closer to what youre trying to ask? Still, I'm having trouble understanding the question...The galaxies are not flying through space away from each other, the distance between them is increasing because the spacial dimensions are expanding. The lititude lines, one dimension, represent all three spatial dimensions of the universe. The longitude line represents time.As you move along the longitude line, the latitude lines become larger, and this represents the expanding of the spacial dimensions. The expansion that the sphere "sees" as you move along a longitude line represents the expansion of the universe but the sphere, itself, is not expanding like the balloon does in the balloon analogy.That is the point of the point that the sphere, itself, is not getting any bigger.