Praxus

If the Earth was a closed system, there would be no energy or matter leaving it or hitting it. This obviously is not the case. The Earth is indeed an open system, a system open to the rest of the Universe.

Anon

The Earth is merely a very, very, very, very, very, very small part of a CLOSED system, end of story. The Earth is merely a subsystem of a much larger mechanism.

Praxus

Whats your point? It doesn't change the fact that the Earth is not a closed system, it is affected by things outside of the Earth.

Praxus

The Universe is not expanding, only the Galaxies within the Universe are spreading apart from one another.

astralis

so...what was the action of the big bang?

and here you go.

http://www.space.com/scienceastronom...on_020320.html

Parihaka

Bit of a mind bender the old acceleration thing.... Maybe the 'travel in a straight line far enough and you'll end up where you started' crowd were right. Perhaps we're accelerating towards our start point whilst still travelling in a straight line.

Praxus

That is refering to the distances between the Galaxies. The distances between atoms or molecules are not increasing.

dalem

You are wrong. Every galaxy is not moving away from every other galaxy within a bounded and fixed enclosure called "the universe". Instead, every galaxy has its own intrinsic velocity vector and the space through which they move, called "the universe", is also expanding.

The best way I've ever read it explained is roughly as follows:

1. Take a spherical balloon.

2. Inflate it just enough so that it has a spherical shape.

3. Take a black magic marker and randomly dot the surface of the balloon with spots.

4. Begin inflating the balloon.

5. Think of the dots as galaxies, the surface of the balloon as a 2-dimensional model of the 3-dimensional space of the universe, and the radial distance "r" between the center of the balloon and the surface as time.

6. Note that as the balloon inflates, the surface of the balloon expands and the absolute distance between the dots increases. To tune this model further, assume that each black dot is instead a very slow-moving ant that crawls on the surface of the balloon.

7. As long as the rate of expansion is greater than a certain value, the surface of the balloon, our universe, expands so fast that even two ants crawling towards one another on the surface will always become farther apart.

8. Also note that the universe has no "beginning" or "end" in terms of physical distance - the surface is continuous, i.e. "infinite".

So the universe itself is indeed expanding, and everything is indeed moving away from everything else.

-dale

Praxus

If the Universe is unbounded, it can not expand, as it would have nowhere to expand. So no, I am not wrong. Specific things within the Universe are moving away from each other, but the Universe in it's totality is not expanding.

Atoms/Molecules are not moving apart from each other, in the sense of an expanding Universe, and I would challange you to prove otherwise.

dalem

Again, you are wrong. Please go through the model I posted above and note that, although it suffers a bit for being a 3-dimensional model of a 4-dimensional (3 space dimensions and a time dimension) system, in broad scope it matches many of the key cosmological conditions.

The universe is expanding and there is a mountain of evidence to back that observation up.

If you are saying that matter itself is not expanding, as in the protons in an Oxygen molecule moving away from each other, and the subatomic particles within the protons moving away from each other, then yes, you are correct. But the space in which the particles move is getting larger.

Addendum:

The idea that you are proposing, that the universe is not expanding but that objects within it are merely moving with their own intrinsic velocities, is invalidated by the fact that all galaxies are observed to be all moving away from our vantage point of the Earth. All of them, every single one, everywhere, in every direction we look.

-dale

Parihaka

Thats a nice description of it, thanks

dalem

After re-reading my post myself, I should correct the model above slightly. The rate and nature of the expansion is such that local galaxies can remain clustered and with real velocity vectors that close the distance between each other. The dots/ants should rather be thought of as galactic clusters. I think that is a little less muddy.

-dale

Anon

My point is that the earth is not a system, it's a subsystem of a closed system.

Hell, we don't even really know if the universe is a closed system either. We can't see that far.

Anon

Not really true. The milky way is on a collision course with Andromeda.

Oh, and Praxus, it is a universally accepted tenet that the universe IS expanding(at approx the speed of light).

Praxus

The only thing that is happening is that certain existents (Galaxies) are spreading apart. That is not the same thing as saying that the Universe - the sum of all that exists - is expanding. Something with no boundries (e.g. the Universe), by definition, can not expand.

I think this is what people mean when they say the Universe is expanding. My only point, is that it is a misuse of the concept of the Universe.

If the Universe - the sum of all that exists - were expanding, it would have to expand into something that doesn't exist for it to expand into.