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When researchers reanalysed the gold-standard data set of the early universe, they concluded that the cosmos must be "closed," or curled up like a ball. Most others remain unconvinced.
A provocative paper published today in the journal Nature Astronomy argues that the universe may curve around and close in on itself like a sphere, rather than lying flat like a sheet of paper as the standard theory of cosmology predicts. The authors reanalysed a major cosmological data set and concluded that the data favours a closed universe with 99% certainty — even as other evidence suggests the universe is flat.
The data in question — the Planck space telescope's observations of ancient light called the cosmic microwave background (CMB) — "clearly points towards a closed model," said Alessandro Melchiorri of Sapienza University of Rome. He co-authored the new paper with Eleonora di Valentino of the University of Manchester and Joseph Silk, principally of the University of Oxford. In their view, the discordance between the CMB data, which suggests the universe is closed, and other data pointing to flatness represents a "cosmological crisis" that calls for "drastic rethinking."
In your opinion, which shape is more likely ?
(Score: 0) by Anonymous Coward on Tuesday November 05 2019, @08:50PM (2 children)
Oh sure I guess I was just thinking what would it be like if we could measure something like an on average positive or negative curvature. If there was an on average positive or negative positive curvature I think that to mean we would be on the inside or the outside but not both. Oh, and yes I understand that the idea was that we are in the surface if a shphere not just someplace inside the clolume of it.
(Score: 2) by DannyB on Tuesday November 05 2019, @09:31PM (1 child)
If we measure a curvature, in what way is it "positive" or "negative".
Mariner 9 was a spacecraft to Mars long ago. Communication is along a straight line between Earth and Mariner 9. Due to planetary motion, that straight line eventually gets nearer to the surface of the sun. As it does, the "ping time" between Earth and Mars (eg Mariner 9) gets longer. The gravitational field of the sun warps the space. Eg, it is curved in another dimension. We can't see it in our 3D space. But we can tell that there is more "space" there because of the longer ping time. Is that space a "hill" or a "valley" in the 4th dimensional space? Can it possibly matter? Or does the question even make sense.
On flatland, suppose there were a hill in the surface. Suppose Flatlanders mark two points A and B on opposite sides of that hill. Now the flatlanders cannot see or perceive this hill in any way. But if the hill is sufficiently high, they can observe that movement from A straight to B (going over the hill) takes longer than going on a curved path (avoiding the hill) and arriving at B. In other words going "out of your way" from A to B is actually shorter than a straight line from A to B. By careful measurements, flatlanders could map out a circle around this "hill" or expanded space.
Similarly if we observed such a phenomena, we could map out a sphere around which any travel through that region is actually a longer path than going around the sphere. And if the "hill" or "valley" were infinitely tall/deep, then it is really just a black hole. If you try to make a straight line through that spherical region, there is so much space that you never make it across. If you stretched that tall hill around and merged it into another tall hill from some other part of the universe, you have a wormhole. And since this is space-time not just space, you could join the other end to another point in time as well as space. There are more than just 4 dimensions. One of the "spacial" dimensions is time.
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(Score: 2) by Immerman on Wednesday November 06 2019, @02:24AM
The inside and outside of a sphere both have positive curvature, negative curvature is not so straightforward.
A plane has zero curvature - simultaneously shoot two projectiles (in frictiononless vacuum, etc) parallel to each other across the surface, a short distance apart, and their paths will forever stay the same distance apart
A sphere has positive curvature - do the same thing, and the paths of the projectiles will eventually cross
A hyperbolic "saddle" has negative curvature - do the same thing, and the paths of the projectiles will diverge
Hyperbolic space is profoundly weird. As a visualization aid of 2D hyperbolic space, some projections of hyperbolic space onto a flat plane as drawn by Escher, using one of the more common mathematician's visualization transforms: http://www.josleys.com/show_gallery.php?galid=325 [josleys.com]
The figures are all the same size, but there's an infinite distance between the center of the circle and the rim. If you were to follow parallel lines extending from each side of the black X, you will see that the farther you travel, the more figures there are that can fit between the lines - the more space there is between those lines. And that's true no matter where in the drawing you start - all points in space are still equivalent, the center point is just where you happen to be looking from.
I've heard that hyperbolic space can actually be useful for describing some aspects of Relativity, but I don't really know anything more about that.