What do we mean when we say the universe is expanding?

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The universe refers to all matter in existence.

If all matter in existence is expanding in size, be it earth, a human being, or his house, then the difference is a trivial one. The relative size of everything to one another will remain the same, even if all objects expand in size.

Does it mean the distance between all celestial objects is increasing as they rush apart from each other? Then why are the sun and Alpha Centauri the same distance from one another that they have always been?

http://en.wikipedia.org/wiki/Metric_expansion_of_space

The article states, "The universe is not expanding into anything outside of itself." And that is precisely the source of my confusion.

The analogies in the article don't help either.



The objects comprising the universe become more distant compared to...one another? It's a tautology here.

First, according to Einstein it's space that's expanding, second, by the observations all objects in the universe are diverging at a constant rate from each other, this means that this is false:

pray to your fucking shiva and shut the fuck up, wyrmlord

They become more distance relative to the distance covered by an object travelling at X distance/second. So maybe we're wrong and the universe isn't expanding, but the speed of everything is slowing at the same rate.

Though that seems like a crappier theory anyways, it might also be disproven by other effects I'm not thinking of (effect of gravity? And are the individual particles comprising matter also expanding? Wouldn't that like, destroy physics as we know them?)

Perhaps it is that things quite near each other have relatively strong forces holding them together, while things far apart (like galaxies) do not.

Physics isn't some foundational study with universal rules - where we take some building blocks and work up from there.

There is a lot of disconnect between what we observe at micro levels and what we observe at macro level. So just because something in advanced, cosmic level physics goes against conventional wisdom does not mean basic level physics is invalidated. It's just that there is no rule in physics that applies universally in all cases, or works as some big theory of everything.

Read up on the inverse square law; or - why should galaxies behave the same as solar systems even though exponentially farther away?

This shitty universe going to end in entropy... pity, i'd like the elegance of a deflation.

But who knows. Maybe there are other "universes" out there to collide with, that'd be interesting.

The best analogy I've seen is baloon analogy.

Imagine you blow up a balloon with some small objects stuck to its surface.

Now imagine that the baloon's surface is a 2D universe and that 3D space outside of it doesn't exist. It's simply an edgeless 2D space that loops back into itself and is constantly expanding as if it was a surface of a rubber balloon.

You will notice that distances between objects increase at equal pace. From every place in the universe it seems like everything is running away from you - faster the further you look. At the same time the universe doesn't really have any edge to expand beyond it. There is nothing outside of universe so it doesn't expand into anything outside of it, just like you can expand a closed sphere without there being any space to expand it into along its surface.

Now it is possible to detect because objects bound together by gravity (galaxies, planetary systems, even groups of galaxies, planets and stars themselves) or even stronger forces (our bodies, solids, atomic nuclei) don't expand and won't expand unless you expand space brutally enough to overcome whatever binds them, so they make a handy reference.

Also notice that the space expanding doesn't really have much influence on objects moving within it at small scales.

I've always thought that that analogy is misleading, because (as far as science can tell) we don't live in a closed universe.

jewsciences at work

http://en.wikipedia.org/wiki/Hindu_cosmology
Hinduism has all the answers Wyrmie.

Honestly I would say that you should not put too much thought into abstract problems that we can hardly solve with sufficient surety. Rather spend time learning some good statistical tools and R.

Is there any real evidence to the finite or infinite nature of the universe or is this just more scienmajifics?

Because if the universe is infinite, "expansion" makes no sense.

The expansion of the potato is something we can believe in, as evidenced by this nifty example.

OTOH it doesn't have equally misleading edges.

BTW: Is current consensus that the universe is open in both space and time, or that it's only open temporally (sheet/saddle VS horn)?

I'm not up to date, TBH.

From what I know the current idea is that we live in a flat universe, so "sheet of paper" analogy. But that's only based on the estimate of the amount of dark energy that makes up the universe. Since we don't have the slightest idea what it is, the view may well change p. soon

The idea is that we don't know what lies beyond our horizon, with the assumption that the universe is finite. Unlikely we'll ever know either way

Points A and B are 1 Mpc apart at t = 0s, inside an infinite universe. At t = 1s they are 1 Mpc 72 km apart, as are all other of the infinite number of points in the universe which were 1 Mpc apart at t = 0s. what doesn't fucking make sense about that?

Also, as far as I know, the universe isn't necessarily flat, it could also be a (finite) sphere or a (infinite) saddle, it's just so large that it appears flat to our measuring instruments.

EDIT: Concerning wyrmlords bullshit, as I understand it new space is created everywhere, we just don't notice it because it is insignificant to the forces holding our body, our solar system or even our galaxy together. As the rate of expansion increases however, it would one day rip all of these things apart. If it becomes stronger than the strong nuclear force it would rip atoms apart. And some time down the road even photons couldn't travel through space because it expands too fast. This process, which would lead to a pretty fucked up universe, is called the 'Big Rip'.

I see.

So these are the horrifying implications for the universe.

I had no idea about the Big Rip. But I suppose mankind will be gone long before that.

So, did you just make this thread without having made any literary inquiry into the topic? I hate to be such an ass, but this is an immensely frustrating habit that you seem to have. You start with the false assertion that the universe is 'all matter in existence' when the universe is comprised of much more than matter. You know, space, energy, and time. Then you have all sorts of questions you give us based on this fundamentally flawed premise.

I mean honestly, it's cool that you want to know, that's better than most people. But, for shit's sake, take the time to do some independent research and at least understand the very dick and jane basics before wasting other people's time with questions that lead to nowhere.

It's his way to expand his knowledge base, sadly someone thought to make it a randomized process for better reproducing human behavior.
Until now he reached the intelligence level of a five years old kid asking why, why, why, only to turn his attention to something else when someone try to answer his questions.
Prateek Sanjay, the first AI with ADHD.