Scientists wonder if shape of the universe is like a doughnut | Hacker News Reader

Scientists wonder if shape of the universe is like a doughnut

theguardian.com

48 pointspseudolus28 comments

Related and for those interested: The Shape of Space [1] by Mathematician Jeffrey R. Weeks [2,3].

"""

The Shape of Space...[t]his lighthearted textbook covers the basic geometry and topology of two- and three-dimensional spaces—stretching students’ minds as they learn to visualize new possibilities for the shape of our universe.

Written by a master expositor, leading researcher in the field, and MacArthur Fellow, its informal exposition and engaging exercises appeal to an exceptionally broad audience, from liberal arts students to math undergraduate and graduate students looking for a clear intuitive understanding to supplement more formal texts, and even to laypeople seeking an entertaining self-study book to expand their understanding of space.

"""

1. https://www.routledge.com/The-Shape-of-Space/Weeks/p/book/97...

2. https://en.wikipedia.org/wiki/Jeffrey_Weeks_(mathematician)

3. https://www.geometrygames.org/

Slightly OT, but from the article…

> It sounds like Homer Simpson’s fever dream

A donut-shaped universe was explicitly mentioned in The Simpsons, in an episode with Stephen Hawking

https://youtube.com/watch?v=Mje7frMYzcY

I've been hearing people posit this theory since I was a child in the 1970s, it's not a new theory by any measure.

This is my favorite possibility, that space has a “finite volume but no edges: if you travel farther than the scale of the universe, you end up back where you started.” It’s comforting on an existential level to imagine the amount of stuff around us is finite.

So how would you explain the fact the galaxies are moving away from each other with an ever increasing speed in this kind of shape?

Edit: To answer it myself: https://www.quora.com/What-are-the-implications-of-the-three...

“ The torus moves into itself and comes out at the other end, where the locations of ‘coming out’ could be what is driving what we observe as the expansion of the universe.”

The donut is getting bigger (but is still finite)

It's also possible particles increase causing expansion, this is just theoretical still. But if that's true, then it is finite but perpetually increasing. Potentially infinitely.

Bigger relative to what?

Relative to what it was before. It has an intrinsic size. Think of it in terms of matter density if you find it more comfortable. The density simply goes down over time; distandes between galaxies increase.

Density has the same issue. Density can only be measured against a baseline established outside of the medium being measured.

Just because you can't measure something directly doesn't mean it doesn't exist. There's plenty of things we only know only through indirect measurement.

Intrinsic expansion. Distances between objects in space grow.

That's what metric expansion of the universe is. Distances grow at speeds that are proportional to their distance from the observer.

This would also be the case on a hypersphere, which would also satisfy the cosmological principle. A torus is not isotropic.

Any closed curve does this. And if that's your only information, the simplest encoding for it is a sphere, not a doughnut.

Universe as a doughnut (2003)

https://www.nytimes.com/2003/03/11/science/universe-as-dough...

https://archive.ph/PYEmB

I find the idea of a fixed-size universe to be myopic. I personally align with the Quilted Multiverse Theory (albeit more fractal, than quilt):

• Matter in the universe only has a finite number of ways it can rearrange itself

• If the universe is infinite, patterns will eventually repeat

• If the universe is infinite, there would be an infinite number of parallel universes within space

Thus, if you could travel far enough, you will perceptually return to where you started. And since perception governs presence, does it matter that you're technically somewhere else? You're essentially in the same place.

I also love this theory, because it means every possible form that can exist, at any point in its development, is taking place somewhere, all at the same time.

https://www.worldatlas.com/space/the-quilted-multiverse-theo...

Well, except Boltzman brains kind of suggests none of that is true.

> The Boltzmann brain thought experiment suggests that it might be more likely for a single brain to spontaneously form in space, complete with a memory of having existed in our universe, rather than for the entire universe to come about in the manner cosmologists think it actually did.

I don't think that's true though, I think it's more unlikely for a brain to form spontaneously, than a simple (simple compared to the brain) system of rules that then causes galaxies, planets and life with brains to form through interacting processes

Yeah, things like Conway's game of Life illustrate that simple rules can create complex interactions

For what it's worth that sounds a lot like what Max Tegmark classifies as the "level 1" multiverse.

https://space.mit.edu/home/tegmark/crazy.html

... are there actually only a finite number of ways matter can rearrange itself? Or are configuration spaces "actually" described by real (or complex) numbers (whether for things like distances or angles, or for things like the probability that a prepared quantum state will collapse to a given outcome)? If real (or complex) numbers are "real", then doesn't the fact that configuration states for some perceptually available region are described by R^(huge number) mean that merely traveling around in R^3 space, one _shouldn't_ expect to see repeats?

> patterns will eventually repeat

I know that theory, but isn't this a non sequitur?

let's image an infinite universe with only two possible patterns. isn't it perfectly conceivable that pattern 1 occurs only once and pattern 2 infinitely often?

edit: ok, "patterns will eventually repeat" is obviously true, what I meant is that "ALL patterns will eventually repeat" does not necessarily follow - which is implicit in the parallel universes thought experiment.

Please, I beg you, let's say it's the shape of a bagel. Ideally an everything bagel.

Consider a video game that consists of a single screen and when the player character walks off one side it appears on the other opposite side (same for top and bottom). The playing field in this case is a torus. Now consider the case of two connected tori; at any point the player exits they could find themselves on the other screen. Now consider a “foam” of many tori. Has this game been made? Or anything that explores this idea of walking around connected tori?

Yeah, I think it was called "Pitfall!".

If the universe is shaped like a donut then what’s in the middle?

It’s more like a bagel, with everything.

When the bagel began it had everything all at once in one place.

The best thing about being a theoretical scientist is nobody can refute your claims.

Reply on news.ycombinator.com