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/sci/ - Science & Math

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1322132 No.1322132 [Reply] [Original]

the fuck, the universe is flat?

>> No.1322135

Best as we can tell.

>> No.1322133

Yes.

>> No.1322148

>>1322132
rly? request sauce plox

>> No.1322158

can someone explain how to visualize this?

>> No.1322167

>>1322158
not really, except for with a closed universe (far left) being wrong. A closed universe is like if you walk far enough left you will go around the entire universe and end up where you started.

>> No.1322179

>>1322158
A plane.

>> No.1322185

spoiler: "flat" in 4D is not the same as flat in 3D

>> No.1322189

>>1322179
yeah no shit

but how is the universe flat if everything has 3 dimensions?

>> No.1322193
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1322193

>>1322185
now i'm double confused

>> No.1322195

Circles in flat geometry:
<div class="math">C = 2\pi r</div>

Circles in spherical geometry:
<div class="math">C = 2\pi a \sin(r/a)</div>

Circles in hyperbolic geometry:
<div class="math">C = 2\pi a \sinh(r/a) = \pi a (e^{r/a} - e^{-r/a})</div>

>> No.1322196

http://www.youtube.com/watch?v=7ImvlS8PLIo

>> No.1322201

>>1322189
it just means space is unbounded. the real conundrum would be if space were bounded. then you would get things like traveling in a straight line long enough you would arrive at the same point in spacetime repeatedly

>> No.1322212

>>1322201
Still potentially possible. Current tests show that the universe behaves like euclidean space. Too bad that the test might still be too local to reveal any curvature.

>> No.1322217

So does it mean our R^3 universe only spans a R^2 plane in a R^4 super universe or whatever it's called?

>> No.1322222

>>1322148

'A Universe From Nothing', by Lawrence M. Krauss

>> No.1322227

>>1322189

Not "flat" as in 2d, flat as in...It's hard to explain. I sort of get some of it, but you might as well read:

http://en.wikipedia.org/wiki/Shape_of_the_universe

>> No.1322243

>>1322196
This explained everything very well when I watched it.

>> No.1322278

One trick to visualizing curved spacetime is to approximate it by a bunch of blocks of spacetime put together. It's the same as how you can approximate a curved two-dimensional surface by a bunch of flat polygons. Now imagine a two-dimensional creature was on such a surface. At an edge where two polygons came together, he wouldn't notice anything. But wherever there was a vertex, he would notice that if he made a circle around the vertex, the angles of the polygons that came together there wouldn't add up to exactly 360 degrees. He wouldn't be able to tell where one polygon ended and another began, but he would notice the angular discrepancy.

If our universe were made of blocks of spacetime sewn together, then every now and there you would find straight lines where multiple blocks came together. If you drew a circle around such a line, the angles wouldn't add up to exactly 360 degrees. Of course, the real world isn't made up of blocks like that, but I find it easier to imagine space that is mostly flat except at a few places than to try to directly visualize curved space. And you can get a better and better approximation by imagining the block sizes to be smaller and the angle discrepancies at the edges to be smaller too.

>> No.1322335

Also related:
http://www.theiff.org/lectures/02.html

>> No.1322349

>>1322222
Sensationalized pop science with plenty of conjecture.

>> No.1322357

>>1322185
What does flat in 4d look like?
Or am I too derp to understand?

>> No.1322360

>>1322357
there are only three spacial dementions

>> No.1322373

>>1322360
Time is just as much a part of geometry as the three spatial dimensions are. The only difference is a few signs here and there.

>> No.1322389

>>1322360
My brain is full of fuck.

>> No.1322395

>>1322196
>>1322196
>>1322196
>>1322196
>>1322196

>> No.1322401

>>1322357
The surface of a balloon.

>> No.1322417

>>1322357
What is flat is the 3-dimensional slices through spacetime at a constant time since the big bang.

Maybe an analogy can help a little. You can divide a flat 3-dimensional space into a series of curved 2-dimensional spheres. Here the slices are curved, but the larger space is not. It's also possible to have the reverse, although it's harder to visualize.

>> No.1322419

This "flat in 4D" is akin to the "inflating balloon" simile for space expansion? i.e. The balloon is 4D?

>> No.1322425

no, the universe exists in four dimensions, but we perceive it in three dimensions

>> No.1322432

by 4d we don't mean time

shut the fuck up you stupid goddamn idealists

>> No.1322435

>>1322419
The fourth dimension is time. If you want to visualize the universe as a balloon in a higher-dimensional space, you would have to add a fifth dimension. And even that won't work if the 3D slices of the universe are exactly flat. (3D space is flat on large scales to as good a precision as we can measure it so far.)

>> No.1322442

>>1322432
Go learn special relativity.

>> No.1322458

>>1322442
>>1322435

we're not fucking talking about those kind of dimensions you fucking idiots

>> No.1322471

I thought space-time was curved ;_;

>> No.1322476

http://en.wikipedia.org/wiki/Fourth_dimension

we're not talking about quantum shit guys, so shut the fuck up

>> No.1322482

>>1322471
It is. But on large scales, three-dimensional slices of spacetime at a equal time from the big bang are flat.

>> No.1322490

Some good reading:
http://www.astro.ucla.edu/~wright/cosmolog.htm

>> No.1322492

>>1322476
>The fourth dimension in this space was sometimes interpreted as time, but this is no longer done in modern physics.
Oh man...I'm stupid ;_;

>> No.1322504

>>1322482
Oh, I see.

>> No.1322510

>>1322492
Which is just saying that the mathematical 4D space described in that article is different from the 4D model that describes spacetime in special and general relativity.

>> No.1322531
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1322531

My head! It hurts!

>_<

>> No.1322536

>>1322510

nnnnno it's fucking not

time is NOT a fucking dimension

you don't know SHIT about science.

http://www.youtube.com/watch?v=XjsgoXvnStY

this video is not a fucking accurate representation of everything

take your pseudoscience and ram it up your own ass

>> No.1322546

>>1322531
If you go on to learn general relativity, the expansion and geometry of the universe is actually one of the easiest problems you can solve. Especially in the case where space is flat.

>> No.1322553

>>1322536
Learn some special relativity.
http://www.astro.ucla.edu/~wright/relatvty.htm

>> No.1322566

>>1322553

time is not the fucking fourth dimension you fucking idiot

>> No.1322584

>>1322553
http://astro.ucla.edu/~kevinhainline/relativity.html

I was just about to post this. I actually want to go to UCLA for grad school.

>> No.1322607
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1322607

Time and space are united in a single manifold, it's called the Einstein-Minkowski spacetime.

But in Quantum physics and string theory, some hypothesize a 4th (and often up to a 12th, some even 26th) spacial dimention, usually curved and tiny, to explain some data, such as the weakness of gravity.

You are just talking about two different things, guys.

>> No.1322618

>>1322607
But that's wrong. Einstein was a Jew. All of the Jews were killed during the hollow cast.

>> No.1322626

>>1322536
holy fuck my brain esploded

>> No.1322627

>>1322607
Actually, that makes 3 concepts. The other concept of a dimension beyond the 3 ordinary spatial ones in this thread is adding an extra dimension and thinking of space/spacetime as a curved surface in that higher-dimensional space, much like in the balloon analogy. That trick is useful for some problems but does not work for all cases.

>> No.1322633

>>1322626
He's wrong about time not being a dimension, but the video he linked to is indeed pseudoscience and should not be expected to make sense.

>> No.1322644

>>1322627

This is merely an intuitive tool to explain it, a lie-to-children if you want. You don't need an additional dimention to define a curved space, and a curved spacetime doesn't imply there is one or several more dimensions it bends into.

So, I see what you're getting at, but this is not a scientific subject - merely a pedagogical one.

>> No.1322648

>Time is NOT a dimension you stupid fucks!
>yes it is go learn science
>it's fucking NOT
>it is
>its not
>it is
>its notpigjapoijdgag

ITT

>> No.1322652

>>1322644
Right, which is why I pointed out that the trick doesn't always work.

>> No.1322655

>>1322648
Wikipedia stomped its hell into my nutsack and told me it's not.

>> No.1322661

I'm trying to wrap my head around this 4th dimention.. the wikipedia article animated tesselation was intriguing... could the 4th dimension be thought of in terms of say where the Galactica goes during jumps?

>> No.1322666

>>1322661
did you watch that youtube video someone posted. its pretty accurate and a good visualization.

>> No.1322669

>>1322655
That article was pretty clear that time was a dimension, just not the kind described in that article.
>The fourth dimension in this space was sometimes interpreted as time, but this is no longer done in modern physics. In the last century spacetime was developed, which unifies space and time but with a different metric so the time dimension is treated differently from the three spatial dimensions. The resulting space is a Minkowski space which has different properties from this space.

If that doesn't make sense, I can rewrite the article so it does.

>> No.1322672

THERE ARE FOUR DIMENSIONS, AND THESE ARE THE ONES WE ARE TALKING ABOUT

THERE IS ANOTHER SET OF DIMENSIONS RELATED TO QUANTUM PHYSICS BUT THEY ARE AT BEST PSEUDOSCIENCE

RELATIVITY IS SOMETHING ELSE ENTIRELY

>> No.1322677

>>1322666
I hope you're talking about "A Universe From Nothing" and not "Visualizing the 10th Dimension."

>> No.1322678

>>1322633

the video i linked to was pseudoscience, and i said that in the post

>> No.1322688

>>1322672
Relativity is exactly what we are talking about. General relativity is the theory of gravitation you have to use to calculate the geometry and expansion rate of the universe given its matter content.

>> No.1322689

>>1322677

yes i know the visualizing a 10th dimension is pseudoscience. but it does give an accurate portrayal of what the 4th dimension looks/acts like

>> No.1322699
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1322699

http://www.youtube.com/watch?v=uDaKzQNlMFw
welp this didn't help

>> No.1322737

>>1322196
Amazing video, explains it very well

>> No.1322745

>>1322201
You mean an orbit? Thats a straight line, from the satellites point of view.