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Shape of the Universe Determined To Be Really, Really Flat
StartsWithABang writes: You might imagine all sorts of possibilities for how the Universe could have been shaped: positively curved like a higher-dimensional sphere, negatively curved like a higher-dimensional saddle, folded back on itself like a donut/torus, or spatially flat on the largest scales, like a giant Cartesian grid. Yet only one of these possibilities matches up with our observations, something we can probe simply by using our knowledge of how light travels in both flat and curved space, and measuring the CMB, the source of the most distant light in the Universe. The result? A Universe that's so incredibly flat, it's indistinguishable from perfection. Which means it's probably even flatter than Kansas.
Not sure what OP is on about.
http://michaelsmith.id.au
So, who are the lucky bastards who get the Dolly Parton universe?
Table-ized A.I.
The assumption of GR is that space/time can be described as a smooth manifold - a manifold being intuitively something like a beach ball, donut or similar. Smooth means that when you look at a piece of the manifold at a sufficiently small scale, it looks more and more flat; it really is that simple, what makes it hard is when you introduce the technical tools you need to make precise calculations. So, since we don't actually know the size of the universe, perhaps what we can measure is that we are looking at a much smaller scale than we imagined.
But, some will say, how about the speed of light? The age of the universe is known, so if it started out in the big bang as a single point, it can only be a limited number of lightyears across, right? There are several things to say, that might rock that particular boat a little. Firstly, we don't know that the universe was just a single point in size - in fact, the way QM is interpreted, it seems reasonable to think it wasn't. Secondly, if inflation happened, the universe went through a phase when it expanded a lot faster than the speed of light. And thirdly, of course, the speed of light is only known to be the limit within what we know as vacuum in the space-time we observe now, it only limits how much of the universe we can see now; we have every reason to assume that there is a lot more of it than that.
it seems likely that the universe is infinite.
That's a bit of an overly-strong claim.
* If the universe were smaller than the observable universe, we'd see the recurring patterns in the CMBR (or we'd see the Edge) and we don't, so we know that's not it.
* If the universe were just a bit larger than the observable universe, that would be once heck of a coincidence, so that's probably not it.
* But to distinguish between an infinite universe and one much larger than the observable universe? No way to tell.
Many theories assume the universe to be infinite as that makes the math easier, but all the theories about where the big bang came from are guesswork, and we shouldn't read too much into that.
The real mystery though is how the universe could be very nearly flat (without being exactly flat). Such "fine tuning" is clear evidence we're missing something quite fundamental. But then, dark energy already tells us that.
Socialism: a lie told by totalitarians and believed by fools.
The universe is all of space and time. We have not observed/measured/etc. most of the universe yet to determine its shape. The parts of the universe we have observed are flat. Until we observe more of the universe, we will not know if the universe is flat or not.
Choosing the lesser of two evils is a choice for evil.
The real mystery though is how the universe could be very nearly flat (without being exactly flat). Such "fine tuning" is clear evidence we're missing something quite fundamental. But then, dark energy already tells us that.
I agree. An observably flat universe is a huge coincidence if there is some force that composes half the mass-energy in the universe that is trying to rip the entire thing apart. Either that is an illusion, or some mechanism forces it to be perfectly balanced out by the other half of the mass-energy of the universe which we think exists but haven't been able to observe. Or, we just happen to be living in the one moment in time where dominance is switching from one to the other, but that seems like quite a coincidence as well.
The universe is all of space and time. We have not observed/measured/etc. most of the universe yet to determine its shape. The parts of the universe we have observed are flat. Until we observe more of the universe, we will not know if the universe is flat or not.
Unless they say otherwise, if you hear physicists talking about the "Universe" they're probably talking about the observable universe.
Everything is just speculation from unimaginative scientists who think they know what happened 14 billion years ago at some random spot that they can't even point their finger in the general direction of.
Good grief, no. Where does this idea of science ultra orthodoxy come from? I haven't worked directly with any cosmologists, but every one says "This is what we think happened. "Know" is a completely different thing, and the only people who "know" how the universe was created use a reference book from the middle east, therefore around 4004 b.c.e.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
Which means it's probably even flatter than Kansas.
The band or the state?
It must have been something you assimilated. . . .
A mathematical note: Tori can be flat.
If the universe (and here we are talking about the large spacetime structure, not any of the weird tiny compactified extra string dimension stuff) is globally flat, it can still have the structure of a torus.
The torus when viewed as a 2 dimensional space in 3 dimensions, is not flat-- it has some positively curved parts (think the outer edge of the donut) and some negatively curved portions (think the saddle like regions on the inner ring of the torus.) However, the total curvature (when I sum up all contributing curvatures) on the torus is zero. This is related to a mathematical fact that the total curvature of any surface is given by a topological quantity called the genus. In simpler terms, no matter how I deform the torus, the sum of the curvature will be zero. This is very different from the sphere, whose total curvature is always 2\pi.
So, a flat universe would imply that we cannot live on a 4 sphere, because such objects must always have at least some positive curvature. However, there are examples of tori that have no curvature.
In the 2 dimensional case, it is best to see this from the ``Pac-Man'' perspective. The pacman game is played on a flat surface, and whenever you head off the top of the screen, you arrive at the bottom, and whenever you go off the left side of the screen you wind up on the right hand side. This describes a possible shape for the universe, and this shape is the torus! To see this, imagine that you took the playing field, and glue the top and bottom sides together. That would give you a cylinder. Taking the left and right sides and gluing them together would give you a torus. Now that we believe the pacman game is played on a torus, notice that the original interpretation was a flat surface. So , there is a flat representation of the torus.
To avoid some confusion and people trying to draw flat tori in 3 dimensional space, it can't be done. Every surface viewed in 3 dimensional space will necessarily have some positive curvature around its maximal value. Sorry folks!
In fact, of all the 2 dimensional (compact) surfaces, the only one that has a flat representation is the torus. So, if the universe is compact (and 2 dimensional, which seems unlikely,) there is hope for a Pacman world.