Speed of light

[bystander]

Why should nature abhor a vacuum?

'Nature abhors a vacuum' is a well known idiom used to express the idea that empty or unfilled spaces are unnatural as they go against the laws of nature and physics. True vacuums are not known to exist anywhere in the observable universe.

[aristarchusinexile]

existing theory was that this forum can generate enough purely scientific discussion, which it failed to do.

Perhaps the forum's authorities' definition of 'Science' needs to scientifically re-examined. (I do not say that with an accusatory inflection, merely with a degree of intensity.)

[aristarchusinexile]

Why should nature abhor a vacuum?

'Nature abhors a vacuum' is a well known idiom used to express the idea that empty or unfilled spaces are unnatural as they go against the laws of nature and physics. True vacuums are not known to exist anywhere in the observable universe.

Ah - "not known to exist" is a good way of putting it. We often fail to recognize what is staring us directly in the face. This is a common human condition so striking that many of fail to find the salt shaker on the dinner table even when the shaker is touching our plate.

[astrolabe]

Hello aristarchusinexile,

Aw gee ari, weez buds- didn't know you's just funnin'!

[aristarchusinexile]

Hello aristarchusinexile,

Aw gee ari, weez buds- didn't know you's just funnin'!

Lest there be any miscontrusion, Astro, I wast not offendedeth in the leasteth .. yeah, I wast kiddingeth aroundestlike.

This forum's poster of Shakesperience seemeth to be contagiouseth .. or is it the King Jameseth contagest? Forsooth, in either uPpEr or lOwEr caseth.

[astrolabe]

Verily, verily.

[Qev]

Entropy and Uncertainty are the enemies of a true vacuum. If it were just entropy, a true vacuum would be possible, but hideously unlikely. Heisenberg completely rules out such a beast, though; truly empty space would be a violation of the Uncertainty Principle, and modern quantum mechanics, while incomplete, is on pretty solid ground.

[aristarchusinexile]

Entropy and Uncertainty are the enemies of a true vacuum. If it were just entropy, a true vacuum would be possible, but hideously unlikely. Heisenberg completely rules out such a beast, though; truly empty space would be a violation of the Uncertainty Principle, and modern quantum mechanics, while incomplete, is on pretty solid ground.

I absolutely can't understand why true vacuums are thought of in such hideous ways when they're such benevolent creatures.

[Zarathustra]

If we assume the known Universe is surrounded not by a vacuum, but by matter, does this not explain the acceleration of the expansion of the universe without needing to resort to the positing of a mysterious dark energy? In fact, the force that would seem to be in opposition to gravity would simply be gravity itself. Imagine the known Universe as contained within a bubble as one in swiss cheese, being pulled by gravity to its sides.

[Chris Peterson]

If we assume the known Universe is surrounded not by a vacuum, but by matter, does this not explain the acceleration of the expansion of the universe without needing to resort to the positing of a mysterious dark energy? In fact, the force that would seem to be in opposition to gravity would simply be gravity itself. Imagine the known Universe as contained within a bubble as one in swiss cheese, being pulled by gravity to its sides.

Unfortunately, this notion would place the Earth in the 3D center of the Universe, a proposition that is unsupportable by any current theory. It is generally believed that the Universe is much bigger than the observable universe, and that there is no preferential position (in 3D) within it.

[Zarathustra]

Why would this place the earth at the center of the universe? The galaxies are all moving away from eachother, not just away from us. What does this have to do with our relative position in all this?

[Chris Peterson]

Why would this place the earth at the center of the universe? The galaxies are all moving away from eachother, not just away from us. What does this have to do with our relative position in all this?

How can it not mean the Earth would be in the center? Since we see everything moving away from us at a speed (and acceleration) that depends on distance, and is isotropic, your shell of attractive matter would have to be centered on us. Otherwise, our observation wouldn't be isotropic.

[Zarathustra]

How does the theory of dark energy explain these observations without placing us at the center?

[Chris Peterson]

How does the theory of dark energy explain these observations without placing us at the center?

Because dark energy isn't an attractive force. It is (theoretically) a property of space itself, and is repulsive. So over cosmological distances, there is a slight counter "force" to gravity, thus increasing the rate of expansion. That effect will look the same no matter where you are in the Universe (the entire universe or just the observable universe).

BTW, I think you need to consider causal distance with your suggestion. A massive sphere doesn't exert any gravitational force on its contents, so to get the behavior you describe, you would need to carefully size it so that some material was too far away from distant walls to have been affected yet (given the finite age of the Universe). Even then, I'm not sure you would see what we actually observe- I'd have to give that some more thought.

[Zarathustra]

Yes, I see what you mean.

[iknownothing]

This is probably a stupid question, or the wrong place to ask it...please be gentle with me.

I have been having a big argument with a friend about what is beyond the universe. I say nothing at all. He says the universe must be expanding into something and that that something is black. I think black is 'something', and so can't be beyond the universe. Help!

[orin stepanek]

What is nothing? Void? Space? Vacuum? I think even nothing is something.

Orin

[iknownothing]

Blimey! I can see this is going to be even more complicated than I thought! By 'nothing' I mean the total absence of anything at all. Void, space and vacuum, I agree, are all 'something'.

[aristarchusinexile]

Private message has been sent the enquirer relating to what biblical scripture says is beyond the universe.

[Orca]

Quantifying anything outside the universe is kind of like remembering events that occurred before you were born. Since there is no possible system of measurement for comparison, any hypothesis on extra-universal events are untestable and therefore meaningless.

Kinda anti-climactic, but well, there it is.

[aristarchusinexile]

Why would this place the earth at the center of the universe? The galaxies are all moving away from eachother, not just away from us. What does this have to do with our relative position in all this?

How can it not mean the Earth would be in the center? Since we see everything moving away from us at a speed (and acceleration) that depends on distance, and is isotropic, your shell of attractive matter would have to be centered on us. Otherwise, our observation wouldn't be isotropic.

But we haven't seen to the limits of the universe yet. Perhaps, if we do, we will find the universe shaped like an oval with us located in one end of the oval. As you have said, there is already indication that the universe is asymmetric. Further .. Dark Energy is at this stage pure speculation, as is Dark Matter, as are my anti-gravity bubbles.

[aristarchusinexile]

Quantifying anything outside the universe is kind of like remembering events that occurred before you were born. Since there is no possible system of measurement for comparison, any hypothesis on extra-universal events are untestable and therefore meaningless.

Kinda anti-climactic, but well, there it is.

Two to Five years maximum we will have found, with the instruments being built today, what lies beyond the universe.

[makc]

if, by definition, universe is everything we know about, then there is nothing we know about beyond it. could be something we dont know about, but as soon we'll know it is included and no longer beyond.

[Chris Peterson]

But we haven't seen to the limits of the universe yet. Perhaps, if we do, we will find the universe shaped like an oval with us located in one end of the oval.

Well, the observational evidence is strongly in favor of a flat universe (that is, flat in four dimensions), so "oval" doesn't really seem to work (assuming the shape is extended to its 4D equivalent; certainly there is no reason to think that in 3D the Universe has any shape at all).

As you have said, there is already indication that the universe is asymmetric.

Not the Universe, but the observable universe. The two are probably very different. The Universe as a whole can be highly uniform, and we could still see variability on the much smaller scale of observable universes. Lots of observation and analysis remains in this area.

Further .. Dark Energy is at this stage pure speculation, as is Dark Matter, as are my anti-gravity bubbles.

I agree that your anti-gravity bubbles are pure speculation, even fantasy, as there is no theory describing them, their behavior, or how they fit in with observation. "Speculation" is the wrong word for both DE and DM, however. These are solid concepts backed by observation and testable theory. They are far from speculative (as most people would interpret that word), even if there remains much research to understand them (or the effects attributed to them).

[makc]

Perhaps, if we do, we will find the universe shaped like an oval with us located in one end of the oval.

Nah, I think it is dodecahedron.