Hi again,

I'm definetly a layman when it comes to all of this. (I.e., I haven't gone far beyond just watching Sagan's Cosmos series and reading some of Brian Greene's Elegant Universe.)

Previously, I posted:

"The easiest model for my silly brain to understand is curved, finite, unbounded, and expanding into 5D space."

Or, as William posted, expanding into a 4D spatial dimension.

Anyway, while reading something, my layman brain came up with an idea. I thought it may have been a unique idea, until I discovered that it was asked a century ago. LOL

I wouldn't even know how to begin doing the math on this, but it just seemed to "make sense".

Here is the idea: The universe is curved, finite, unbounded, expanding into a dimension we can't experience, etc, but also spinning.

Would it make sense if the entire universe was spinning? I.e., could a spinning universe account for so-called "dark matter"? "Dark matter" simply being the centrifugal force?

The "makes sense" part comes when I look at galaxies. Galaxies look almost identical to hurricanes. The spinning of the Earth causes hurricanes' unique design, so couldn't the spinning of the entire universe cause the similiar design of galaxies?

Just drawing straws here, I know...

Most likely the best way to get your mind around this is to think about Dimensions. Lets take away one spatial dimension and think that we are in a two dimensional space (plus time). Assume that our universe is shaped like the surface of a sphere and we cannot see the third dimension --In other words we are now living right on the surface--no meaning to the inside of the sphere and no height above this surface. So we are just like a very flat bug crawling along on a basketball.

The surface of a sphere is curved back upon itself . It is said to be finite but there is no boundary in the two dimensions. If the sphere were sufficiently big the bug would think that his universe was flat. He would also see that Euclid's Geometry would hold over regions that were relatively small when compared to the size of the bug's total universe.

If the two dimensional universe were expanding then it would be expanding into the third dimension of which the bug has no knowledge. The measurable size of the two dimensional surface would, of course, be increasing

So if we extrapolate this thinking to three dimensions then we would be in a finite, unbounded universe that would appear to be flat. It would be increasing in size. I don't know what it means (or if it is true) that it is expanding into the fourth spatial dimension.

Mathematically, adding another dimension and then differentiating Einstein's equations of general relativity in three dimensions yields Maxwell's equations. It was really Maxwell who showed that the speed of light is not dependent on the speed of the observer. Does this mean that there really is a fourth spatial dimension (or 10 or 25) that we can't see? I would think, "yes" but Math doesn't always yield reality all of the time--just most of the time.

Regards,

DADDIO

If you are really interested, I've read two great books on the subject:

"The View from the Center of the Universe" - by Joel R. Primack and Nancy Ellen Abrams.

and "Cosmic Jackpot" by Paul Davies.

I think this books complememnt each other and they are very well written.

The sphere analogy....

I guess the definition of "infinite" would be in question in that scenario, at least from a layman perspective if you can "go on forever and never find and end" i guess that's "virtually(subjectively?) infinite" if its not , lets say "objectively infinite".

I assume there has got to be standard definitions for these concepts somewhere. The stuff i read is all 'general reader" stuff (Brain Greene , Carl Sagan etc) and they tend to use analogies , rather than the actual terms i guess.

There is a solution to Einstein's general relativity equations in which the Universe returns, after a long time, to its initial state, that is its evolution is cyclic. It was found by the great logician Kurt Goedel but of course there is no way to verify or falsify it. It seems to me that the sphere analogy is patterned along this idea, for whatever it may be worth.
Tullio

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The sphere analogy....

I guess the definition of "infinite" would be in question in that scenario, at least from a layman perspective if you can "go on forever and never find and end" i guess that's "virtually(subjectively?) infinite" if its not , lets say "objectively infinite".

I assume there has got to be standard definitions for these concepts somewhere. The stuff i read is all 'general reader" stuff (Brain Greene , Carl Sagan etc) and they tend to use analogies , rather than the actual terms i guess.

I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"?

The easiest model for my silly brain to understand is curved, finite, unbounded, and expanding into 5D space.

I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"? Nothing? So if you somehow fly in a spaceship to the edge of the current universe.. what happens? You hit a wall of "nothing" not even empty space?

If you travel on the surface of a sphere you can go on forever without finding any boundary. And the radius of the sphere might be expanding.
Tullio

Philosophy was never my strong point, but if I may enquire?
Do you refer to the interior or exterior surface of a sphere?
Are you within, or without (outside) the sphere whose surface you travel?

Andrew

I would be outside, but the surface I am thinking of is three dimensional, while the sphere is four dimensional (three spatial dimension and one temporal dimension). So the sphere is like an expanding bubble. There is a very interesting article in the NYTimes on modern cosmological theories that look even more far-fetched than this, so I am in good company.
Tullio

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I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"? Nothing? So if you somehow fly in a spaceship to the edge of the current universe.. what happens? You hit a wall of "nothing" not even empty space?

If you travel on the surface of a sphere you can go on forever without finding any boundary. And the radius of the sphere might be expanding.
Tullio

Philosophy was never my strong point, but if I may enquire?
Do you refer to the interior or exterior surface of a sphere?
Are you within, or without (outside) the sphere whose surface you travel?

Andrew

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AndrewM

If you travel on the surface of a sphere, you are always accelerating to remain on that surface. Whether due to gravitational attraction toward the interior masses, dark matter or whatever, it is still needed. Using internal mass to provide that thrust will not work for long.

duke

The path might be a geodetic line in a spacetime continuum, according to Einstein's general relativity.

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<<<<<<<<<<
I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"? Nothing? So if you somehow fly in a spaceship to the edge of the current universe.. what happens? You hit a wall of "nothing" not even empty space?

______

If you travel on the surface of a sphere you can go on forever without finding any boundary. And the radius of the sphere might be expanding.
Tullio
>>>>>>>

If you travel on the surface of a sphere, you are always accelerating to remain on that surface. Whether due to gravitational attraction toward the interior masses, dark matter or whatever, it is still needed. Using internal mass to provide that thrust will not work for long.

duke

I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"? Nothing? So if you somehow fly in a spaceship to the edge of the current universe.. what happens? You hit a wall of "nothing" not even empty space?

If you travel on the surface of a sphere you can go on forever without finding any boundary. And the radius of the sphere might be expanding.
Tullio

---

I guess this is almost a philosophical question.

Spacetime is expanding yes? So if we took a snapshot of the universe as it is now its "not infinite" but its continually expanding right? So its um... "potentially infinite?"

If its not currently infinite, what is at the "edges"? Nothing? So if you somehow fly in a spaceship to the edge of the current universe.. what happens? You hit a wall of "nothing" not even empty space?