You can look at it that way. When you stretch a piece of rubber, its surface area increases. Where does the surface area come from?
Let me parse this question a little. Feel as free as you have been so far to comment continously!
The 'universe' as defined by Webster's Ninth, says it is a "whole body of things observed or postulated" which would cover all galaxies and those things not seen but inferred. This, then, is how the universe is defined. And that makes sense, since only by measurement of things observed can we say anything is moving, and therefore say the universe is expanding.
But by our definition, the unverse consists of things we can see or infer, and therefore refers to contents. It does not define the container, only the contents of that container. Relative to us, those contents are moving away. And I say the contents are moving within space, which may or may not also be expanding.
So my question, based on this, is, does space have limits that the unverse will sometime bump up against? Or am I just blowing smoke? :dubious:Dictionaries are useful only if you understand exactly what their functions are. They give the standard meaning of the way terms are used in mainstream writing.
That’s very limited. Scientific terms are especially badly limited. The definition of universe that you quote is not the scientific definition that is being talked about here. The universe here is space-time and that is everything. It cannot bump up against anything. There is nothing outside of it. Space is not its contents: it is the whole.
Kids get taught in school that dictionaries are the answer and contain all knowledge. That’s not close to true. Dictionaries really don’t do more than give you a first approximation at how to understand a word when you read it in a sentence. All the shades of meaning and technical exactitude have to be added from context, experience, and additional sources.
I’m ranting about this because I’ve seen this dictionary problem presented here all too often. Dictionaries aren’t the last word on any subject. They’re just the first word. And here you’ve been steered wrong by them.
Even if you can’t do the math (and I can’t), you can understand that the word ‘expanding’ does not have the meaning we use in a 3 dimensional world. We could use the analogy of the universe being a sphere where everything is shrinking inside of it. From the our own perspective, we seem to be the same size, but everything appears to be getting further away, and the universe appears to be getting bigger, but its not actually expanding. Any such analogy will be limited, because the universe is not a 3 dimensional sphere, but you can use it to see that the universe doesn’t have to be expanding into anything.
Okay now physicists, I’ve seen very informal theories regarding the concept of shrinking vs. expanding, and gravity being a repulsive instead of attractive force, etc… Is there any validity to, or use for, any of these concepts. For the purpose of describing reality, not analogies.
I have never yet encountered any scientific phenomenon which could be better explained by matter shrinking than by the Universe expanding, and the expansion hypothesis can explain the observations much more simply.
I don’t want to be a dick and say “Cite”; but could you direct me to some relevant information? I’ve never heard of dark matter being a property of expansion.
General relativity is usually seen as a relational theory. I.e. spacetime describes the relationship between matter, objects, etc, and no ontological value is assigned to spacetime itself.
Shrinking vs expanding seems more like a matter of semantics, when an object shrinks or expands we have other objects to compare it to, we don’t have pther universe to compare the universe to.
Like I said earlier what we actually mean by expansion is that in a certain ‘preferred’ (preferred due to the large sclae symmetries of the universe) spacetime coordinate system the distance between objects is tending to get larger. We could say it’s because these objects are shrinking or we could say it’s because space is expanding, as long as in both cases we’re not diverging from the model that predicts this effect.
Dark energy is deeply related to expansion, it’s postulate to explain the accelerated expansion rate observed in the current universe.
Dark matter, which is a totally distinct concept, relates to expansion as due to it’s abundance it has a signifcant effect on expansion.
The simplest model of dark energy is that it can be represented by a cosmological constant, meaning that its density remains constant in time, regardless of expansion (or contraction) of the Universe. To be fair, there are also models of dark energy, called quintessence or phantom energy, that do vary their density, and such models can’t be ruled out, but all observations show that the dark energy must be very close to a cosmological constant model (that is, if the density does change, it does so very slowly relative to what you’d expect from expansion), so the models with varying density are disfavored due to Occam’s Razor.
The rubber being stretched, which is totally not the same thing. The amount of rubber in existance hasn’t changed. Unless the idea is that dark energy in a given area is decreasing as that area expands.
Dark energy is really starting to sound like the new aether.
-Joe
Okay, who else looked at the date of the OP when they saw the word Zombie?
I understand space is not the contents, and it has within it those objects known as the “observable universe” which also implies there are things we can’t see. But there are things we can measure and determine that they are moving away from us, and from what I’ve read, this is why we can say the universe is expanding. As far as space-time itself is concerned, we can’t measure that, so we have no idea how big it is; it may well be infinite.
So if space-time is infinite, which we don’t know since it isn’t measurable, from our viewpoint the idea that the universe is expanding has to come from somewhere. All texts I’ve seen treat the balloon thing as an example of the expansion of the universe, and the dots on it as the galaxies and other objects in that universe.
I just used the dictionary as a benchmark. If you want to include the space-time continuum in that definition, then I don’t see how you can say anything is expanding, since we can’t measure space-time.
Or are we going to do the Time Warp again??? 
Radishes
It’s not a particularly good analogy; it’s just the best I could come up with.
And you’re not alone in thinking that dark energy might be the new æther… I mean, even the name “quintessence” is just a recycled word for “æther”. Fact is, there’s enough we don’t know or understand about the dark energy that we wouldn’t be surprised by pretty much anything we might learn about it, and it may well be that there’s some other way of interpreting the phenomenon that works much better.
Of course we can measure space-time. I have a device on my wrist that does that, and another one in my desk drawer that measures it in a different way.
It’s space that’s expanding, which from a spacetime perspective is due to the particualr way we’ve choosen to paramterize spacetime.