I think Fraser and Pamela are stationary with respect to their local space ('bubble' of space as I imagine it)--just like the Milky Way is. At least as far as expansion is concerned--we're not considering spin or tidal forces or any of that good stuff.

If we think of our rope as just atoms, not molecules and all that complicated chemical stuff, I think it stretches at the level of the electro-magnetic bond between atoms--which is why I think we can compare it to the concept of the Big Rip--at some time in the distant future the atoms fly apart when they can't stretch no more. I think this is kinda comparable to the red-shifted light astronomers observe--when you think about it, photons are the force carrier of electro-magnetism, and light is photons too... my thinking is that the electromagnetism, like light, just gently stretches to accomodate the increase in distance. Red-shifted light, at least, we already observe.

I think all this would look nice and soft and gentle to an observer if we could see the whole length of the rope at once (which we can't because of relativity). I think if we consider how long the rope is, compared to how much it stretches - it's a tiny percentage. I reckon the entire observable universe expands about one ten thousandth of one percent over a whole year. So in other words - our rope ain't expanding much. We could stretch a rope ourselves that much right here on Earth, and you and me are only very small regions of quarks, gluons, electrons and photons.

The universe is expanding everywhere, all at once, except where gravity (mainly gravity because it is a force that acts at a distance, but also the other forces I suppose) is holding it back. I'm dividing up space into bubbles to help me imagine what might be happening where Fraser is, and where Pamela is. We could imagine dividing space into bubbles up and down the entire length of our rope, and suppose that they are all expanding simultaneously.

Not even on the atomic level perhaps? It's space (spacetime) that is said to be expanding, so in other words the 'background' on which all particles and forces exist - I'm thinking more of red-shifted light now, which is a real observable phenomenon.

Remember - I don't think nature really has to worry about actual megaparsec ropes 'cos they don't exist.

Space is the background - but it also interacts with particles and forces, for example via electromagnetic fields. And, I'm thinking particles are also wave-like, and waves happily expand every day, just like at the beach. And we know that space happily bends and curves and stretches... General Relativity tells us so and we (well not me!) have tested it. Heaps. I suspect somewhere in all of that stuff, is the mechanism whereby space expands, whether its vacuum energy, virtual particles, dark energy or some screw-up with gravity. But we don't know.

On the scale of atoms, Frasers, trucks and galaxies - the 'normal' forces do laugh at expansion, 'cos after all, we aren't expanding, at least not in any meaningful way anyone has observed. On the largest scales, distant galaxies are all receding from each other, apparently due to the expansion of space between them. Astronomers see it through their telescopes. I think we have to go with that.

I don't believe the planck length is changing at all. The reason I don't believe it, is that I've never seen or heard of any evidence that it is. But I have often wondered, like you. I've concluded, even if it were changing, we wouldn't know, because any measure stick we could devise, would be changing exactly the same, and so would we.

The Big Rip hypothesises first galaxies, then solar systems, then planets, then atoms, then all matter... is torn apart by the accelerating expansion of the universe. Then time stops. Apparently. But it's all hypothetical. Like our rope. Try this link perhaps?

http://www.space.com/scienceastronom...ip_030306.html

The *pop* is just how I have imagined the expansion, 'cos I've never seen it myself. It could be smooth and classical. If it were quantized (we don't know) it could really be a *pop* from a certain point of veiw. To paraphrase Obi-Wan.

I don't know how we would line up our stones, any more than I know how we would make a megaparsec rope.

There are plenty of stones in space, but all the stones we can see are in our galaxy and wouldn't count. If a comet or meteor, or even a planet, somehow got chucked into an intergalactic void where there was no gravity (there would probably be some?) - I don't imagine that anything particular would happen to it any time soon.

We're much better off sticking with light.

I'd be more inclined to look at the Sloan Digital Sky Survey, then look at it again later (much later if possible) and observe what has happened to the great voids, and bubbles, and filaments and sheets of galaxies and galaxy clusters that make up the structure of the universe.

There's our rope.

http://www.sdss.org/background/science.html

http://www.windows.ucar.edu/tour/lin....html&edu=high

Steve

I need a lie down.

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If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein