Okay, then. So objects themselves are not growing. Only the distance between them is growing.
Then why is this phrased as “space is expanding”? It seems to me that space itself is not expanding. It’s merely that everything is moving farther apart. And that is totally logical, within the big bang theory: There was a big bang, which spread everything out in every direction, and it is all still moving outward. Big deal!
As I see it, the only thing that is expanding is the humongous boundary, probably shaped like a sphere or close to it, on the inside of which is all the stuff of the universe, and on the outside of it is all the infinite empty space where the stuff of the universe hasn’t reached yet.
(The above presumes a universe which goes to infinity in all directions. If you want to go with the idea that the universe is closed somehow, so that if I continued far enough I’d end up where I started, then I guess one could say that space itself is doing the expanding. Hmmm – maybe the “space is expanding” folks do indeed support the “closed universe” idea?)
Keeve, one of the reasons we know space itself is expanding is because the observable size of the universe is far larger than would be possible if it were just the objects themselves traveling. As you know, nothing can reach the speed of light, and even assuming that galaxies and whatnot could somehow be flying in every direction near the speed of light, the known age of the universe would not allow for the observable size that we see. Space itself must be expanding, and at a rate that far exceeds the speed of light.
I was under the impression that that is precisely what is going on. If there are local forces counteracting the drifting apart of objects due to this expansion (as some people in the thread seem to be saying - I am not entirely convinced about this myself) surely that means that the objects in question are moving through space towards each other just enough to counteract the movement apart due to the expansion, but the space itself is still, very slightly, expanding.
This is a common misconception about the Big Bang. It wasn’t an explosion at a point that flung everything out into the void. Instead the entire universe started out very hot and dense. Over time the universe has expanded and become less hot and less dense, but nothing is actually moving.
There is not a sphere of stuff expanding into the void. The universe is filled with stuff in all directions. It’s just getting less dense.
Nope… it just seemed like a good example of why two objects might stick together when two identical objects weren’t. I wasn’t just thinking of gravity, either, since any attractive force would work. (Attraction -> couples, hence the idea).
If expasnion existed at small scales, it would be pretty much undetectable anyway. For example it would cause the poles of the Earth to move apart at about 1 mm per year even without taking in to consideration the attractive force that Earth exerts on them.
But the realtionship between the large scale struture of the universe (from which Hubble expansion emerges) and the small scale structure of the universe is complex and it’s wrong to assume that the universe is necessarily expanding on a small scale, even as a negligibly small effect counteracted by other effects.
Nope, you’re missing an important point. The expansion rate is accelerating. If it were simply the force from a big explosion, it would be decelerating, and eventually gravity would pull it all back together again. There’s some additional force - which we don’t understand and we give the placeholder name “dark energy” which is accelerating the expansion.
As I see it, the only thing that is expanding is the humongous boundary, probably shaped like a sphere or close to it, on the inside of which is all the stuff of the universe, and on the outside of it is all the infinite empty space where the stuff of the universe hasn’t reached yet.
The “space is expanding” folks isn’t some sect or rebel contingent of scientists - it’s all scientists. The scientific community agrees on this.
If you bake a cake with raisins in it, the raisins spread apart as the cake rises. However, the raisins aren’t moving THROUGH the cake.
It’s the same way with galaxies. They’re not moving through space. (Or rather, if they are moving, their velocity is relatively small.) They’re being spread apart by the expansion of space itself.
Yeah, I knew that. But I thought there was a split on whether or not one can continue in a straight line without coming back to where he started.
Let’s look at this fourth-dimensionally. If our 3D universe is infinite from a 4D point of view (the way we 3Ders accept that a 2D surface can be infinite) then I just can’t figure where the expansion is going. BUT if our 3D universe is a finite shape of some sort from the perspective of a 4Der (and that’s what I meant by “closed universe”) then I can sort of understand how it is expanding in the 4D world, and how even the 3D surface can become larger even when measured by its own yardsticks.
I was going to ask if “space is expanding” therefore proves “it’s a closed universe”. But instead, I went to Wikipedia, and found that “closed universe” redirected me to an interesting article titled Shape of the Universe, which I’m gonna go read now. Good night all!
Try blowing at your monitor again. The force of the air going out of your mouth can’t overcome the friction between your chair and the floor, so you don’t go backwards. But that doesn’t mean you’re moving toward your monitor.
No. We see galaxies that appear to be moving away from us at greater than the speed of light (have a redshift greater than 1- the record for a galaxy now is about 8.6). You can’t have two objects moving in space relative to one another at greater than the speed of light. Space is not a physical object, though, so it can do that. Galaxies can’t.
No, wrong. This is a common misconception, that the Big Bang happened within a space that was already there, and that there’s some space where the stuff of the universe hasn’t reached yet. Space itself was created in the Big Bang. The Big Bang happened at every point in the universe at once. It happened right where you are sitting, and right where I am sitting. Those two points started out as the same point in space. There is no space outside the universe that you could get to if you could travel fast enough.
Where I’m sitting and where you’re sitting are not getting farther apart with time (well, unless they are due to plate tectonics, but that has nothing to do with the expansion of the universe, so let’s pretend you’re somewhere on the North American plate and not moving relative to Pittsburgh due to plate tectonics). If you buy a plane ticket to Pittsburgh (or drive here, if you’re close enough) and leave in a month, you’ll travel the same distance as you would if you left today. The same would happen if you sent a message to me at the speed of light. It isn’t going to take longer for it to get here if you send it next month than it will if you send it now. Those two points started out in the same place, and now are not the same place, so they were moving apart at some time in the history of the universe, but they’re not now.
I think you’re wrong. Space is expanding, and it is expanding everywhere, including here on Earth. For two points separated by 1000 km, the speed of expansion would be approximately:
72 * 1000/(3×10^19) = 2.110^-15 km/s. So if you wait a year, the distance between those two points will increase by 610^-9 km, that is, 6 microns.
I’d like to learn more about this, as it sounds like one of the possibilities that I had suggested. Some questions:[ul]
[li]Can you tell us where you got that formula and/or other explanations of it?[/li][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][li]If Space Expansion does cause even solid objects to expand, wouldn’t that also include our measuring devices? How would we be aware of this expansion?[/li][/ul]
It’s an expansion of space, so those 6 microns over 1000 km are counteracted by gravity and molecular forces. No plate tectonics required to keep NAm together, and without gravity and molecular forces there’d be no Earth, so that’s not a useful speculation.
Hmm. So imagine I have a lone hydrogen atom in intergalatic space, quietly sitting there for billions of years. Say long enough that space expands enough that the space occupied by the atom doubles in width. Is the energy from the expansion of space at some point translated into the electron finding itself in a higher energy orbital? Or something similar? Might the atom emit a photon or two over the gazillions of years due to this?
What about two rocks gravitationally bound orbiting one another? Does the expansion of universe push energy into the pair?
In either case it would seem that the “overcoming” of the expansion of space by the much stronger forces would result in work being done. And being done in a manner that directs energy into the local system.
The part that keeps hanging me up is that solid objects don’t really exist. Even an atom or molecule isn’t really solid, but is made up of components which are held in place by gravity and molecular forces. And those same forces connect the Milky Way and Andromeda galaxies. The forces are incredibly miniscule over such distances, but they do still exist.
That’s why I’m having trouble distinguishing between distances which do expand and distances which don’t expand.
All distances do expand; the difference is that the astonishingly strong forces between the components of an atom are so strong that the components don’t get carried away with the expansion; they’re held tightly in place, and the space expands “under them” kinda like the rubber sheet analogy above.
Eventually the acceleration of the expansion will result in such high speeds that even those forces won’t be enough to hold the components in place; this is a theory popularly referred to as the “big rip”.
Think of it as a basic equation:
Expansion = X mph
Nuclear forces = Y mph
Where Y is larger than X, the objects do not recede from each other - they’re moving towards each other faster than the universe is pulling them away from each other (the reason they don’t get pulled into a single blob by those strong attraction forces is that other very strong, very short range repulsive electromagnetic forces prevent them doing so, but that’s a separate thing).
When X eventually becomes larger than Y (billions of years in the future), then they will, according to the big rip theory. The universe will consist of nothing but elementary particles and black holes floating around in a lonely empty universe, light years away from each other.