or is it the cosmic principle of hot dogs that is doing it?
Here’s why I find this difficult to accept: I concede that “the strong forces between the components of an atom are so strong that the components don’t get carried away with the expansion”, but surely there is some price to be paid for this. They don’t “get carried away with the expansion”, but they can’t ignore it either. There must be some amount of energy that they expend on fighting the expansion, and without that loss, the components would be even closer than currently. The difference may be infinitesimal – maybe even smaller than a Planck length – but I don’t see how it can be zero.
There are other forces (electromagnetic charges and the like) keeping them apart, too, preventing them meshing into a single atomglob (my word).
So, yeah, in a sense there is a teeny cost to “resisting” (if that’s the right word) the expansion, but they can’t get closer together than the repulsive forces between them will allow - so they are forced to stay at the same distance. Think of it like they’re being forced up against a wall, although that’s a terribly vague and inaccurate representation of the forces involved.
[quote=“Keeve, post:34, topic:600961”]
I’d like to learn more about this, as it sounds like one of the possibilities that I had suggested. Some questions:[LIST]
[li]Can you tell us where you got that formula and/or other explanations of it?[/li][/QUOTE]
It’s the Hubble formula.
[QUOTE]
[li]Does it apply even to solid objects? In other words, would the North American continent grow by 6 microns based on Space Expansion alone, without any place tectonics stuff?[/li][/QUOTE]
It applies to space expansion. That’s how much the space between the two points expands. It doesn’t account for any other effects for solids (or planets), like heat expansion/contraction, gravity compression, tectonic movements, etc etc.
I like this question. If the measuring device is a solid ruler, you’re right. But if the measuring device is, I don’t know, a timer connected to a light beam bouncing off a mirror, then no.
But it strictly speaking doesn’t apply here, i.e. on Earth, or within the solar system; it’s only exactly valid for a universe that is homogeneous and isotropic, i.e. basically the same in all directions. This is true of the large scale structure of our universe to a good approximation, but it’s obviously not true here: there’s for instance much more mass in the direction we commonly call ‘down’ than there is in the ‘up’ direction – indeed, the fact that we can distinguish between these shows that the space that constitutes our immediate neighbourhood isn’t really uniform. In fact, local conditions are far more well modelled by a static spacetime with a spherically symmetric central mass; in such a spacetime, there is no expansion.
Of course, reality is messy, and neither one nor the other, i.e. neither FLRW (the expanding uniform universe – the letters stand for Friedman, Lemaitre, Robertson and Walker, who came up with that particular solution to Einstein’s equations) nor Schwarzschild (the spherically symmetric central mass solution), but rather more complicated, and I don’t know that there’s a precise answer to what the local rate of expansion is.
These are my own pants has essentially made this point a couple of times in this thread, but it’s a good enough one to repeat once more…
True. I was attempting to figure out whether the expansion would be detectable locally if it followed Hubble law. But I still think that there is expansion, even here on Earth, it’s just not certain exactly how much.
My argument is though that you can construct a solution that is slighlty more realtsic than the highly-symmetric FLRW solution by inserting Einstein-Straus vacuoles in to an FLRW universe. And further that within the Einstein-vacuoles (which represent the space in the nearby vicinty of a star or maybe even some larger or smaller arrnagement of matter) there is no expansion of space at all, not even as a tiny effect. I.e. there’s no solid reason to say that expansion takes place everywhere once you get down to a small enough scale.
Of course the actual arrangement of matter is even more complicated still than an FLRW-like universe filled with Einstein-Straus vacuoles. The best answer IMO is that expansion only really ‘works’ when certain conditions are fulfilled, but these conditions are always fulfilled if you examine a large enough volume of space.
So, to put this as simply as I can, space is expanding, but gravity (and other forces when you get to the subatomic level) is keeping the objects together?
Because I thought gravity could manipulate space–hence the reason a gravitronic drive could move faster than the speed of light by compressing the space in front of it and expanding the space behind it. And I remember that light bends twice as far as you would expect if gravity only was effecting space, and not the light itself.
No, this is too simplistic, as I said expansion only ‘works’ on scales much bigger than the subatomic level/the planetary level/the stellar level.
This is part of the reason, at say the level of size of a planet or a star you can’t ignore that the gravity of the planet or the star is the most important factor in determining the spacetime representing the local area of space. And there’s alos no reason to think you could represent the behaiour of this space time as something along the lines of
G[sub]contribution of local graviational field[/sub] + H[sub]contribution of Hubble expansion[/sub]
or even non-linearly for that matter.