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/sci/ - Science & Math

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2617284 No.2617284 [Reply] [Original]

So I have watched "A Universe from Nothing".
Please help to understand. As far as I know these are facts:
1) There is no centre to the universe in space, everywhere is equally the centre
2) The overall curvature of space is open and flat (as opposed to closed like a sphere or open like a saddle)

These two facts seem to contradict. Unless, the universe is infinite in size and matter. If it isn't, then there must be a centre of mass to the universe. If it were spherical, then it can expand without a centre, and it can be finite. But Krauss said they proved it was flat. So there must be infinite matter?

>> No.2617304

Assuming the universe has no special point or directions:

Curved like a sphere => finite
Flat => infinite
Saddle-shaped => infinite

It's flat as far as we can measure, but that doesn't rule out it being sphere-shaped or saddle-shaped with a very large radius of curvature.

>> No.2617314

>>2617304
I see. But if it is flat overall, there must be either
a) infinite space and matter
OR
b) a centre of mass to the universe

correct?

>> No.2617325

>>2617314
Yes, or
c) there is a special direction (e.g. the universe could wrap around like one of those video games where if you go off the top, you wind up on the bottom)

>> No.2617331

HAHAHAHAHAAH people from the 21'th century are so stupid

They think the universe is flat!

HAHAHAHAHAHAHAHAAH

>> No.2617334

>>2617325
> (e.g. the universe could wrap around like one of those video games where if you go off the top, you wind up on the bottom)
But that's closed, which is the same as curved like a sphere

>> No.2617336

>>2617325
>>2617314

BASICALLY WHAT HE SAID. FIND THE "CENTER" OF THE SURFACE OF A BALL. NOT THE CENTER OF THE BALL ITSELF, BUT THE SURFACE.

THE SURFACE IS FINITE, BUT HAS NO CENTER.

>> No.2617337

>>2617334
It's closed, but not curved. If you draw a triangle in such a geometry, the angles add up to 180 degrees.

>> No.2617340

>>2617284
Where is the center of the real number line? There is no center. No matter which spot you pick, there an "equal" infinity on both sides.

As I was corrected in that other thread, flat does not imply infinite. It might be a non-Euclidean geometry where if you look far enough in one direction, you see your own head. At least, maybe. I'm not clear on this. I need to do more research. Did Lawrence make a special reference to this in that video? I'll have to rewatch it myself.

Now, it's hard to imagine such a thing, but imagine that universe where you look far enough in a direction, you will see the back of your own head. In that sense, the universe is finite, but there is still no "center". Any point along the line of sight has no particular special property compared to any other.

>> No.2617345

>>2617336
I know dickhead, but space shows evidence of being flat hence the possible contradiction.

>>2617337
Yes I see. Personally I doubt that is the case because it seems very unnatural.

>> No.2617354

>>2617345
>Personally I doubt that is the case because it seems very unnatural [read: intuitive].
>implying General Relativity, and especially Quantum Mechanics, is intuitive.
Yeah, about that...

>> No.2617362

>>2617284
Also, here's the link for other people.
http://www.youtube.com/watch?v=7ImvlS8PLIo

>> No.2617368

>>2617354
Those do seem natural to me. But a flat area where when you go out the top you come out the bottom seems too artificial ya know? Could be true though.

>> No.2617384

>>2617368
Except there's no top and there's no bottom.