Chemist@
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How certainly is the universe flat? Is is absolutely approved or not?
If yes, what will cause the big crunch?
If yes, what will cause the big crunch?
Chemist@ said:How certainly is the universe flat? Is is absolutely approved or not?
If yes, what will cause the big crunch?
Chemist@ said:T
1. When was the shape of the universe approved with the 0.4% uncertainty?
Yeah, but I wouldn't put any stock in that. Not yet, anyway. That's just not significant enough to say anything.marcus said:As I recall a very recent report, from South Pole Telescope, said that with 95% certainty the curvature was not zero but just a wee bit on the positive side of zero!
Chemist@ said:Okay, thanks. I need answers to 2 and 3. What is the most approved shape, open or closed?
We haven't yet definitively detected any deviation from zero. Could be 10^-3, 10^-4, 10^-10, 10^-100.Chemist@ said:Someone knows the latest info? How much is the cosmological curvature parameter?
Chemist@ said:...
Someone knows the latest info? How much is the cosmological curvature parameter?
A cylinder is geometrically flat (you can bend a piece of paper into a cylinder without tearing).Chemist@ said:if this deviation is high enough, then the universe would be cylinder shaped.
Chalnoth said:...
If there is a slight positive curvature, then it's like our observable universe is a small piece of a very large sphere. ...
Chemist@ said:I am a little confused now.
The biggest probability is that the universe as a whole is a sphere or the coat of a sphere?
Chemist@ said:You mean time by the 4th dimension?
The coat would have a very short dimension. What would happen if someone reaches the end of it?
Chemist@ said:You mean time by the 4th dimension?
The coat would have a very short dimension. What would happen if someone reaches the end of it?
Chemist@ said:I am a little confused now.
The biggest probability is that the universe as a whole is a sphere or the coat of a sphere?
marcus said:As I understand it, what you call the "coat" of a ball is what I would call a sphere.
in our 3d world, the ball is the solid thing and the sphere is the hollow thing. It has zero thickness. It is a pure 2D surface.
A dimension is a direction you could point, or move in.
Or, in the case of a 2D world, it is the direction a 2D animal living in a zero-thickness purely 2D surface could point, or move in.
As I understand it there is no "very short dimension" because you and I cannot point our fingers in any direction which is the 'thickness" of our 3d space. There is no direction that we can move that we would "reach the end of."
Chemist@ said:What is then a 3D sphere?
Well, the problem is that it can't be visualized. But it perhaps helps to think of the definition of a two-dimensional spherical surface, the 2-sphere. The 2-sphere is, in three-dimensional space, a set of points that are all equidistant from some center. One could similarly construct a 3-sphere in four-dimensional space (note: four spatial dimensions here, we're not even considering time just now), where each point within the 3-dimensional volume would be equidistant from the center of the 3-sphere.Chemist@ said:What is then a 3D sphere?
I think you missed, "That stretch across the visible universe." :)marcus said:Now in 2013 we are measuring triangles,
I don't know what you mean. In flat space, no matter their orientation, triangles always have angles that add to 180 degrees. You have to be in curved space for that to change.Chemist@ said:Okay thanks.
These triangles you are talking about aren't in one plane, so their angles don't have to add to 180 degrees.
Chemist@ said:Okay thanks.
These triangles you are talking about aren't in one plane, so their angles don't have to add to 180 degrees. It's sad that the shape can't be imagined, as it is beyond our senses' experiences.
boisebrats said:snip... we, as inferior mankind, through our limited perception of the world, marvel at the impossibility of ideas like "entanglement", the "sole beginning bang of infinite time from nothingness" and even the the philosophical contradiction of the theoretical existence of "totally empty space" ...snip.
I think you're thinking of cosmogony. Cosmogony is about the origins of the universe. Cosmology is about the evolution of the universe. Cosmology is strongly tied to observation today, and is considered a specific branch of astrophysics. Cosmogony is a bit more speculative, due to a lack of hard data on the subject, and thus most of the arguments regarding it have to be done in the absence of data, which makes the philosophical aspect more important.chasw said:My thoughts exactly. Ultimately, cosmology is a philosophical problem with inputs from physics. - CW
Chalnoth said:I think you're thinking of cosmogony. Cosmogony is about the origins of the universe. Cosmology is about the evolution of the universe. Cosmology is strongly tied to observation today, and is considered a specific branch of astrophysics. Cosmogony is a bit more speculative, due to a lack of hard data on the subject, and thus most of the arguments regarding it have to be done in the absence of data, which makes the philosophical aspect more important.
That said, all of science uses and relies upon philosophy for its conclusions.
chasw said:... I was in fact thinking of the origins of the universe and the highly plausible big bang model. For example, the paradox of rapid inflation, at speeds faster than light, boggles the mind. ...
As I recall a very recent report, from South Pole Telescope, said that with 95% certainty the curvature was not zero but just a wee bit on the positive side of zero! So that while the U is not infinite (according to them) it is so nearly flat that the hypersphere circumference could be as large as 880 billion lightyears. That is, the 3D analog of a sphere so that if you could stop expansion right now and sail off at light speed in some direction you could travel in a straight line for 880 billion years before you found yourself back home. But it might not be that near flat, or that large--there is a range of uncertainty about the mean curvature.
Mordred said:Also keep in mind their is no clear consensus if the universe is open or closed. At this point we can only say that it is flat or extremely close to flat.
As mentioned in a month as Marcus mentioned. We will be getting further data.
The sticky thread on the balloon analogy also has tons of useful links. I highly recommend the ones leading to Ned Wrights tutorials. Particularly his FAQ article. Its one of the better articles for those relatively new to cosmology.
Some things to add on the open closed description. If the universe is closed/finite now then its always finite. Same applies to infinite/open.
Not at all. A torus (doughnut shape) is topologically flat, because you can wrap a flat sheet into a torus without tearing or kinking. Visually, living inside a torus-shaped universe would be rather like the classic video game Asteroids.usmhot said:... which indicates what seems completely logical to me - that if the Universe is flat then it must be infinite. In fact, if the Universe is topologically open then it must be infinite (right? ... at least according to my understanding of the cosmological principal).
... which indicates what seems completely logical to me - that if the Universe is flat then it must be infinite.
No. You can't make a sphere out of a flat sheet without tearing. You can make a torus out of a flat sheet without tearing.usmhot said:Isn't a torus topologically equivalent to a sphere?
Unknown, and possibly unknowable. We can only see a small slice of the universe, due to the speed of light limitation. We haven't yet definitively detected any overall spatial curvature in our visible patch, but even if we did, that would only tell us about our visible patch. Imagine, for example, that we detect some amount of positive curvature. That could mean our universe is sort of like the surface of a sphere, or it could mean we're living on a sort of hill on a sheet with lots of hills and valleys.usmhot said:So, what shape was the Big Bang? Wasn't it finite and unbounded and closed?
The cosmological principle is just a simple assumption that is probably wrong when you get to large enough scales.usmhot said:I should have been clearer in my original question ... my problem is with the fact that the Universe must be infinite if it's flat because otherwise it would have to be bounded and would thus break the cosmological principle. So, logically, if it's flat, it must be infinite and it must always be infinite.
As pointed out before the torus is flat, unbounded and finite.usmhot said:my problem is with the fact that the Universe must be infinite if it's flat because otherwise it would have to be bounded and would thus break the cosmological principle. So, logically, if it's flat, it must be infinite and it must always be infinite.
I don't think it is a simple assumption that is probably wrong, it is "the" assumption that sustains the LCDM model(including the flat space, inflation and dark matter and dark energy assumptions) and GR's FRW metrics.Chalnoth said:The cosmological principle is just a simple assumption that is probably wrong when you get to large enough scales.
It only has to hold within the observable universe for this to be the case. Once we start going beyond the observable universe, well, pretty much anything goes. We expect that the cosmological principle must hold significantly beyond the observable universe primarily because if it didn't, we would expect to see some deviation within it as well. But there's no reason to believe it holds out to infinity.TrickyDicky said:I don't think it is a simple assumption that is probably wrong, it is "the" assumption that sustains the LCDM model(including the flat space, inflation and dark matter and dark energy assumptions) and GR's FRW metrics.
Not at all. I would have told you the exact same thing five years ago.TrickyDicky said:are you influenced by the Planck data confirming anomalies at large scales to say that?