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Curious layman

The universe might be a giant loop

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Everything we think we know about the shape of the universe could be wrong. Instead of being flat like a bedsheet, our universe may be curved, like a massive, inflated balloon, according to a new study.

That's the upshot of a new paper published today (Nov. 4) in the journal Nature Astronomy, which looks at data from the cosmic microwave background (CMB), the faint echo of the Big Bang. But not everyone is convinced; the new findings, based on data released in 2018, contradict both years of conventional wisdom and another recent study based on that same CMB data set...

The difference between a closed and open universe is a bit like the difference between a stretched flat sheet and an inflated balloon, Melchiorri told Live Science. In either case, the whole thing is expanding. When the sheet expands, every point moves away from every other point in a straight line. When the balloon is inflated, every point on its surface gets farther away from every other point, but the balloon's curvature makes the geometry of that movement more complicated.

"This means, for example, that if you have two photons and they travel in parallel in a closed universe, they will [eventually] meet," Melchiorri said.

In an open, flat universe, the photons, left undisturbed, would travel along their parallel courses without ever interacting...

more at link....

https://www.space.com/universe-may-be-curved.html

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Keep calm 😉: Wild New Study Suggests The Universe Is a Closed Sphere, Not Flat

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A curved Universe may explain this one anomaly, but there are several big problems - not least of which is that all other analyses of Planck datasets, including the 2018 legacy data, have concluded that our cosmological models are correct. That includes the flat Universe.

<snap>

So, broadly speaking, much of the data seems to be in support of a flat Universe, rather than a closed one - except for that one Alens anomaly. Like a pebble in your shoe, or a burr down your shirt, it just keeps on niggling. And we don't know whether the discrepancy between it and all other measurements is actually meaningful, or a problem on the human end.

 

 

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Is it even possible to know the shape of the universe without stepping outside it?

Edited by Star Walls

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31 minutes ago, Star Walls said:

Is it even possible to know the shape of the universe without stepping outside it?

As the measurements in question were made within the universe, then the answer to would appear to be yes. Which is good, because there is no "outside".

A more detailed article on the research here: https://www.quantamagazine.org/what-shape-is-the-universe-closed-or-flat-20191104/

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10 minutes ago, Strange said:

As the measurements in question were made within the universe, then the answer to would appear to be yes

But those results are inconclusive, are they not? But, I thought I was quoting Max Tegan more or less. And I forgot to ask if all these curves in fact correspond to a cannon ball either going into orbit, flying into space or hitting the ground?

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10 hours ago, Star Walls said:

But those results are inconclusive, are they not?

So far. That is not because we are measuring from "inside" but simply because the possible deviation from flat is very small.

10 hours ago, Star Walls said:

And I forgot to ask if all these curves in fact correspond to a cannon ball either going into orbit, flying into space or hitting the ground?

Not really. It is more like saying whether space is Euclidean (for example, the angles of a triangle add up to 180º) or curved (like the surface of a sphere where the angles of a triangle add to more than 180º). In the latter case, if you travelled far enough, you would end up back where you started (ignoring the fact that the universe is expanding).

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1 hour ago, Strange said:

So far. That is not because we are measuring from "inside" but simply because the possible deviation from flat is very small.

Not really. It is moralise saying whether space is Euclidean (for example, the angles of a triangle add up to 180º) or curved (like the surface of a sphere where the angles of a triangle add to more than 180º). In the latter case, if you travelled far enough, you would end up back where you started (ignoring the fact that the universe is expanding).

What if on a flat plane you traveled so far that, by the idea of the multiverse, you returned not to point A, where you started, but instead reached a point B that was indistinguishable from point A?

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6 hours ago, Star Walls said:

What if on a flat plane you traveled so far that, by the idea of the multiverse, you returned not to point A, where you started, but instead reached a point B that was indistinguishable from point A?

I wonder if you know yourself what you are asking. What has a flat plane to do with 'the idea of the multiverse' (which idea exactly? Many worlds theory? Bubbles in the inflational universe? Infinite universe with repeating patterns?). How can two points be indistinguishable and not be the same? If they are not the same, they are distinguishable per definition. (And how do points differ anyway?).

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19 minutes ago, Eise said:

I wonder if you know yourself what you are asking. What has a flat plane to do with 'the idea of the multiverse' (which idea exactly? Many worlds theory? Bubbles in the inflational universe? Infinite universe with repeating patterns?). How can two points be indistinguishable and not be the same? If they are not the same, they are distinguishable per definition. (And how do points differ anyway?).

There are two types of universe being purposed here, are there not ? One, on a flat plane, Euclidean. And one on a spherical plane. Has it not been suggested that on the first type, at least, there exists such a thing as a type 1 multiverse, where everything would repeat after a certain while?

Edited by Star Walls
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1 hour ago, Star Walls said:

There are two types of universe being purposed here, are there not ? One, on a flat plane, Euclidean. And one on a spherical plane. Has it not been suggested that on the first type, at least, there exists such a thing as a type 1 multiverse, where everything would repeat after a certain while?

As far as I remember, a type 1 'multiverse' is not really a multiverse: it is an infinite universe. An infinite, spherical universe does not make sense to me (but if some cosmologist knows that this would be meaningful I hope (s)he will chime in),  but then we are still left with a flat universe, a parabolic or a hyperbolic universe. But you are right, nothing (at the moment!) points to a parabolic or a hyperbolic universe. And 'repeating' might be a to strong expression. One should always be very careful with 'infinity'. You cannot think about infinity as just a big number. 

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8 hours ago, Star Walls said:

What if on a flat plane you traveled so far that, by the idea of the multiverse, you returned not to point A, where you started, but instead reached a point B that was indistinguishable from point A?

What do you mean by "indistinguishable"?

The point is that in a closed universe you would get back to the same position you started from. So, on Earth, if you travel in a straight line from Paris, you will need up back at Paris. 

 

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29 minutes ago, Eise said:

As far as I remember, a type 1 'multiverse' is not really a multiverse: it is an infinite universe. An infinite, spherical universe does not make sense to me (but if some cosmologist knows that this would be meaningful I hope (s)he will chime in),  but then we are still left with a flat universe, a parabolic or a hyperbolic universe. But you are right, nothing (at the moment!) points to a parabolic or a hyperbolic universe. And 'repeating' might be a to strong expression. One should always be very careful with 'infinity'. You cannot think about infinity as just a big number. 

Okay. I read a thread a while back that you posted in and was impressed by the arguments you made even though opinion in the thread seemed to be mainly against you, and even though much of what was being said was above my head. I think it was on the subject of time and the line: "loop endless: see endless loop" came up. Anyway, my suggestion was that a closed "loop" universe, where you arrived back where you started, might be indistinguishable from one on a flat plane, where you just kept going until things repeated. What do you think?

 

Edited by Star Walls
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1 hour ago, Star Walls said:

Anyway, my suggestion was that a closed "loop" universe, where you arrived back where you started, might be indistinguishable from one on a flat plane, where you just kept going until things repeated. What do you think?

But why would things repeat exactly? I guess that it does not work like that. I think in an infinite, flat universe, you will find small areas (parts of space around a point) that are  the same as the point where you left. But how big must such an area be to be exactly the same as where you left? I think infinitely large, otherwise they'd differ, namely at a finite distance, and so the points are not exactly the same, and therefore distinguishable.

Maybe there is a way out if you look at the observable universe only: that is finite. If you would manage to travel faster than light and the expansion of the universe, you could travel outside our 'bubble' and enter completely distinct, but finite bubbles. Then it could work out. But that is of course not practicable... 

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