a flat universe?

[infoseeker]

hey..im currently working on a big research papaer talking bout the shape of the universe..i jus started and im alreayd confused..it seems that ther are three posibilities for the shape and that the universe is flat.what does this mean? flat would mean having a single flat plane..but how is that possible when space time actually curves..i mean isnt the universe have depth to it? how can it simply be flat..please help!

[syntax252]

If everything started out with a big explosion, why would it be anything other than spherical?

[Johnny5]

If everything started out with a big explosion, why would it be anything other than spherical?

 

If, by the word 'universe' we mean everything with inertial mass, and everything without inertial mass, then the universe cannot have a shape.

 

Saying everything without inertial mass, is a fancy way of referring to the vacuum. 'Space' cannot be spherical, it cannot be cylindrical, it cannot be a cube.

 

Regards

[5614]

If everything started out with a big explosion, why would it be anything other than spherical?

If some parts were accelerated by the bang quicker than other parts the universe would be a pretty (to us) random shape... also during expansion different body's gravity will have effect expansion, so it could be a very weird shape.

[[Tycho?]]

The curvature of space is because of gravity. Consider: the earth has a lot of mass, and so curves space. Try to visualize how it is curved. .... .... Right, its curved in 4 dimensions, which humans can't visualize. A way to think about this however is to think of space as say a soft matress. Think of the earth as a bowling ball on the matress. It causes the matress to curve down, so that if something like a marble was near it, the marble would roll down the slope towards the bowling ball. In a similar way a sattellite falls towards the earth through curved space.

 

The shape of the universe itself is the same thing on a much larger scale. It wouldn't be completely flat, there would be bumps in it caused by matter. The actual curvature of the whole universe depends on a number which is not really known... hubbles constant perhaps, I'm not really sure. I think its believed that the universe is pretty close to flat.

[infoseeker]

ok....can you please go back to answering the intial question in the thread??? pleaseeeeeeee

[Johnny5]

ok....can you please go back to answering the intial question in the thread??? pleaseeeeeeee

 

The term 'flat' has to do with whether or not the universe will expand forever, or not.

 

Flat universe

[Syd]

Not so long ago i also read about flat universe. Not totally flat, it supposted to look like a pancake. It's caused by arrangemet of mass all over the Universe, which curves space

[syntax252]

If the universe can be taken as flat, would a pancake be a reasonable way to discribe it?

 

Or perhaps like a disc?

 

If so, does ot have a thickness?

 

How thick?

[KholdStunner]

i agree with syntax. If the big bang theory is true, then wouldnt the explosion be sypherical? how could it explode into a flat area?

 

how flat are we talkin about?

[Bettina]

Ok....I'm still learning, but this is what I've learned so far. I know this is going off topic, but it still is related to the original question.

 

Picture a Christmas tree ball that is round, thin and hollow. On the outside of the ball, take a small brush and paint galaxies, stars, planets, everything you see in the night sky, etc.

 

Now looking at that ball, that is our universe. Nothing exists in the space outside of the surface of the ball, and nothing exists inside the ball. Nothing means just that. Nothing. No time, no matter, no space. You cannot go from one end of the ball to the other by passing thru the middle because there is nothing there.

 

I was also told that the universe went from a pinpoint that appeared out of nothing, and inflated to the size it is today in a few nanoseconds. Much faster than the speed of light since light came after the initial inflation.

 

The flat universe implies a sheet of paper instead of a ball, but all the rules still apply.

 

I think this is correct

 

Bettina

[KholdStunner]

how could the big bang form a flat universe?

 

-so your saying that every galaxy in the universe is on the 'edge' of the universe? If so, why is there no matter in the middle of the 'christmas ball'?

 

if the universe is expanding, that means there would have to be matter in the middle of the 'christmas ball' or else that means that when it expands it also decreases because the center contains nothing... please explain how this is possible

 

if this post is to confusing, tell me, and ill rephrase it.

[syntax252]

I cannot imagine a flat universe, nor can I imagine one like a Christmas ornament, (although that would be easier than flat)

 

I have always wondered why it all has to be one big bang?

 

Look, we think we know that there are such things as black holes. And we think we know that there are many of them. Why couldn't it be the case that once a black hole becomes dense enough--once it has attracted enough matter into it--that it just explodes and creates a galaxy?

 

Does it have to be the whole damned universe at once?

 

Why not a black hole exploding somewhere in the universe every billion years or so? Let's call it the "popcorn theory" of galaxy creation.

[J.C.MacSwell]

I cannot imagine a flat universe' date=' nor can I imagine one like a Christmas ornament, (although that would be easier than flat)

 

I have always wondered why it all has to be [b']one[/b] big bang?

 

Look, we think we know that there are such things as black holes. And we think we know that there are many of them. Why couldn't it be the case that once a black hole becomes dense enough--once it has attracted enough matter into it--that it just explodes and creates a galaxy?

 

Does it have to be the whole damned universe at once?

 

Why not a black hole exploding somewhere in the universe every billion years or so? Let's call it the "popcorn theory" of galaxy creation.

 

I like it already!

 

I would like to see a few more competing theories but you have to adapt them when you have a contradiction or you can add/remove assumptions until they collapse under their own "weight".

 

I read a book by British astronomer Martin Reese "Just 6 numbers" where he says he was originally against the Big Bang Theory, then converted by the evidence to being 90% certain 10 or 15 years ago, and now is 99% certain.

 

seems rather high considering all the basic things we don't know.

 

What are your odds?

 

I'm a Steady State Theorist at heart but I'll go with 50% for some form of the Big Bang, 25% for some form of the Steady State Theory and 25% for "something else".

 

Be interesting to see if people who are really knowledgable about these things would be committed in the 90+ percent range.

 

Edit: I think a universe based on the 3Dsurface of a 4D hypersphere that slowed in expansion forever but never stopped and reversed would be considered "FLAT" (mathematically) no pancake necessary.

[Jacques]

Flat in the cosmologist language doesn't mean flat like a pancake.

Flat means that two parallel lines will never meet and remain at the same distance from each other. A positive curvature mean that two parrallel line will meet and a negative curvature mean parallel will never meet and the distance between them will increase.

The curvature of the universe, like was said is defined by the quantity of matter in the universe.

[J.C.MacSwell]

Flat in the cosmologist language doesn't mean flat like a pancake.

Flat means that two parallel lines will never meet and remain at the same distance from each other. A positive curvature mean that two parrallel line will meet and a negative curvature mean parallel will never meet and the distance between them will increase.

The curvature of the universe' date=' like was said is defined by the quantity of matter in the universe.[/quote']

 

I'm not sure but isn't your definition for flat space (Euclidian), which is different from both a "flat" universe (slowly slowing to infinite) or "flat" space-time (an SR rest frame or GR "no tidal forces" frame)?

[Jacques]

I'm not sure but isn't your definition for flat space (Euclidian), which is different from both a "flat" universe (slowly slowing to infinite) or "flat" space-time (an SR rest frame or GR "no tidal forces" frame)?

I don't know you seem to know a lot more than I about this subject, but my intervention was a reaction to thing like a pancake. Saying the universe is flat doesn't mean that the universe is two dimentional

[J.C.MacSwell]

I don't know you seem to know a lot more than I about this subject, but my intervention was a reaction to thing like a pancake. Saying the universe is flat doesn't mean that the universe is two dimentional

 

I think that's right (the second part, not so sure about my armchair cosmology ).

[Bettina]

how could the big bang form a flat universe?

 

-so your saying that every galaxy in the universe is on the 'edge' of the universe? If so' date=' why is there no matter in the middle of the 'christmas ball'?

 

if the universe is expanding, that means there would have to be matter in the middle of the 'christmas ball' or else that means that when it expands it also decreases because the center contains nothing... please explain how this is possible

 

if this post is to confusing, tell me, and ill rephrase it.[/quote']

 

Like I said, I'm still learning, but there is so much conflicting input, I go with one theory until its proven wrong.

 

The christmas ball could just as well be a large soap bubble that you blew thru a hoop when you were little. The ball is round, but if you look at the surface you can see "designs" and swirls on the outside. Nothing on the inside. This is what our universe is. I wish I could explain myself better.

 

I believe in the big bang...just one, where all matter radiated out on a single plane curving around itself. Wasn't it said that if you travel long enough thru space, you will end up back where you started? I think that was it. I'm typing now without looking anything up.

 

Again, Im still learning, and I don't believe in the flat universe as if it was a pancake...I also dont believe in string theory or branes either.

 

Bettina

[J.C.MacSwell]

.

 

The christmas ball could just as well be a large soap bubble that you blew thru a hoop when you were little. The ball is round' date=' but if you look at the surface you can see "designs" and swirls on the outside. Nothing on the inside. This is what our universe is. I wish I could explain myself better.

 

Bettina[/quote']

 

I think these are good analogies. Your "surface" (2D) is our space (3D).

[[Tycho?]]

Ok....I'm still learning' date=' but this is what I've learned so far. I know this is going off topic, but it still is related to the original question.

 

Picture a Christmas tree ball that is round, thin and hollow. On the outside of the ball, take a small brush and paint galaxies, stars, planets, everything you see in the night sky, etc.

 

Now looking at that ball, that is our universe. Nothing exists in the space outside of the surface of the ball, and nothing exists inside the ball. Nothing means just that. Nothing. No time, no matter, no space. You cannot go from one end of the ball to the other by passing thru the middle because there is nothing there.

 

I was also told that the universe went from a pinpoint that appeared out of nothing, and inflated to the size it is today in a few nanoseconds. Much faster than the speed of light since light came after the initial inflation.

 

The flat universe implies a sheet of paper instead of a ball, but all the rules still apply.

 

I think this is correct

 

Bettina[/quote']

 

Well, the universe did not inflate to its current size in a few nano seconds. In a brief time after the big bang, it did inflate extremely quickly, however this soon slowed down to the speed of inflation we have today. The universe has had at least 13 billions years to expand, and has been expanding continuously for all of that time.

 

I'm not sure how valid your analogy is about the christmas ornament, at least as it pertains to the shape of the universe. That would be a good analogy for explaining how it is the universe expands, all points getting further away from eachother, none getting closer to eachother. For the curvature of the universe I think you'd have to look at it differently, althought im not sure about this.

 

http://en.wikipedia.org/wiki/Universe#Shape_of_the_Universe

 

It mentions a sphere like yours in that paragraph, so perhaps your analogy is correct for this point.

 

You other people need to read my original post in this topic, there is a lot of confusion on what this is. Remember- calling the universe flat, or like the surface of a sphere, or whatever are results of thinking of the universe in 4 dimensions, which we cannot properly visualize. These should not be taken too literally.

[J.C.MacSwell]

']Well' date=' the universe did not inflate to its current size in a few nano seconds. In a brief time after the big bang, it did inflate extremely quickly, however this soon slowed down to the speed of inflation we have today. The universe has had at least 13 billions years to expand, and has been expanding continuously for all of that time.

 

I'm not sure how valid your analogy is about the christmas ornament, at least as it pertains to the shape of the universe. That would be a good analogy for explaining how it is the universe expands, all points getting further away from eachother, none getting closer to eachother. For the curvature of the universe I think you'd have to look at it differently, althought im not sure about this.

 

http://en.wikipedia.org/wiki/Universe#Shape_of_the_Universe

 

It mentions a sphere like yours in that paragraph, so perhaps your analogy is correct for this point.

 

You other people need to read my original post in this topic, there is a lot of confusion on what this is. Remember- calling the universe flat, or like the surface of a sphere, or whatever are results of thinking of the universe in 4 dimensions, which we cannot properly visualize. These should not be taken too literally.[/quote']

 

All of these analogies have their limits and can be useful if we are careful about where they break down. The bowling ball on the matress works well but "requires" a gravitational force (the very thing that we are trying to model) to make it work. A "closer" analogy would have the matress shrink in the area of the bowling ball instead of stretch but the mental image is not as familiar.

[Bettina]

']Well' date=' the universe did not inflate to its current size in a few nano seconds. In a brief time after the big bang, it did inflate extremely quickly, however this soon slowed down to the speed of inflation we have today. The universe has had at least 13 billions years to expand, and has been expanding continuously for all of that time.

 

I'm not sure how valid your analogy is about the christmas ornament, at least as it pertains to the shape of the universe. That would be a good analogy for explaining how it is the universe expands, all points getting further away from eachother, none getting closer to eachother. For the curvature of the universe I think you'd have to look at it differently, althought im not sure about this.

 

http://en.wikipedia.org/wiki/Universe#Shape_of_the_Universe

 

It mentions a sphere like yours in that paragraph, so perhaps your analogy is correct for this point.

 

You other people need to read my original post in this topic, there is a lot of confusion on what this is. Remember- calling the universe flat, or like the surface of a sphere, or whatever are results of thinking of the universe in 4 dimensions, which we cannot properly visualize. These should not be taken too literally.[/quote']

 

When I say nanoseconds, I pretty much meant that 90% of its size was created almost instantly. The soap bubble I mentioned, has to be viewed as a spherical shape without a center. The universe is expanding into nothing, but its only the sphere's edges that are moving outward. There is nothing inside of the sphere.

 

Forget the Christmas ornament....I like the soap bubble better.

 

Imagine the soap bubble the size of a basketball floating still in the air. Now imagine that it was nighttime, and the soapy solution forming this bubble was a faint glowing neon blue. A faint neon sphere.

 

If you could walk up to this bubble without breaking it, walk around it and look closely, you would see many swirls and designs on the outside of this sphere which would represent our galaxies. Yet nothing but blackness would be inside and outside of the bubble. This black represents the nothing that our universe came from.

 

If you walked up to it and looked even closer, you would see that between these many swirls and designs around the circumference there would be plain areas with no swirls. Since these areas of the bubble are thinner than the parts making up the swirls, it is much lighter and fainter. To me this would represent the dark matter that we cannot see. This dark matter is also expanding.

 

If you could add an air source and begin adding air to the inside of the bubble, it would grow larger, but the center nothing would get larger too. The event horizon or outside edge of this bubble would move outwards and the swirls would move farther away from each other.

 

To get from one side of the bubble to the other, you would have to travel its circumference. You cannot go thru the center. Just place a magical car on the surface of the bubble and drive around the outside. Like you do on earth.

 

The pancake universe doesn't cut if for me. I just don't see a big bang creating something flat like that. And, I do believe the big bang had a center at one time with the bubble radiating outward at a pretty uniform rate.

 

I really look at all the links that you guys give me....thanks for that.

Again, I'm still learning, but its hard to find which is the best model to stick with.

 

Bettina

[infoseeker]

yes i know flat means flat sheet of paper and yes i know flat means parallel lines cant meet and sum of triangles are 180 degrees..but which "plane" is it that is exactly flat, when you have such a deep universe?? like if you say the earth is flat, you're referring to the surface on which we live..but for the universe, where is that????????

[Nevermore]

If space can warp, who says it has a fixed shape?