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geometry and shape of universe seems to be not flat

sushi

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Most people think of space as a flat sheet: You travel in one direction, and you end up far from your starting point. But a new paper suggests that the universe may in fact be spherical: If you travel far enough in the same direction, you’d end up back where you started.

Based on Einstein’s theory of relativity, space can bend into different shapes, so scientists assume the universe must be either open, flat, or closed. Flat is the easiest shape to understand: it is how we experience space in our everyday lives, as a plane in which a beam of light would extend off into infinity. An open universe would be saddle-shaped, with a beam of light bending across the curvature. And a closed universe would be a sphere, with a beam of light eventually looping back around it to meet its origin.
whatshapeist 1
Geometry of the universe, with images of the cosmic microwave background above and illustrations of the potential shapes of the universe below.NASA/GSFC
In order to tell which shape our universe is, scientists can look at a phenomenon called the cosmic microwave background (CMB). This is the electromagnetic radiation which remains from the Big Bang, also called “relic radiation.” It fills all of space and can be detected with a sufficiently powerful radio telescope.

In the new paper, the scientists measured the fluctuations in the CMB using data from the European Space Agency’s Planck space observatory. We know that these fluctuations are related to the amount of dark matter and dark energy in the universe. And although we still can’t detect dark matter or dark energy, we do know approximately how much of each exists. So when the researchers found more strong gravitational lensing of the CMB than would be expected, they knew they had a clue to the shape of the universe.

The most obvious explanation for these findings is that the universe is closed, not flat as previously thought. This would be a dramatic finding, to such a degree that the researchers called it a “crisis for cosmology.” However, there are complications which mean we cannot be sure if the universe is definitely closed. For example, the universe is constantly expanding, but researchers disagree on how fast this is happening, making it harder to predict the curvature of the universe. There are also other analyses of Planck data which strongly support the idea of a flat universe.
For now, the shape of the universe remains an open question. The research is published in the journal Nature Astronomy.

 

Cognisant

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A circle is round in two dimensions, a sphere is round in three dimensions, if you travel on the surface of a sphere you can return to your original point by moving in a straight line along the surface of the sphere in any direction (two dimensional movement on a three dimensional object) but in space you can move in three dimensions so in order for space to be round you would need another (fourth) spatial dimension.

Unless that fourth spatial dimension is very different to the other three it would affect us in profound ways, for example you won't be able to store a pressurized gas in a three dimensional container no more than you can in an unsealed cup.
 

Marbles

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I'm also perplexed by pop-science articles relying on the concept of higher spatial dimensions. As portrayed in quantum mechanics where higher dimensions are postulated to be tiny knots, they don't contradict my intuition (I simply have no intuition for them), but it seems a higher spatial dimension large enough to curve the universe would have easily observable consequences in 3D reality. I suppose whatever "matter" exists in 4D space must be distinct from 3D matter, just like 2D "matter" cannot be our own matter, since our matter is 3 dimensional. Perhaps that makes it impossible for matter to leak between dimensions, in any way we can easily grasp.

Id naively guess physicists imagine 3D space as a membrane floating through 4D space, and that matter of the membrane has very limited interaction with 4D space.

A lot of these physics metaphors seem designed merely to give people the illusion of understanding. "Oh, I can imagine a ball on a trampoline! Awesome, general relativity is easy."
 

..

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in order for space to be round you would need another (fourth) spatial dimension.

Not necessarily. General Relativity tells us that the curvature of space time is intrinsic to the three spacial dimensions. While it's useful to think of that curvature occurring in a higher-than-three spacial dimension, it doesn't necessarily have to.
 

..

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in order for space to be round you would need another (fourth) spatial dimension.

Not necessarily. General Relativity tells us that the curvature of space time is intrinsic to the three spacial dimensions. While it's useful to think of that curvature occurring in a higher-than-three spacial dimension, it doesn't necessarily have to.
 

..

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It's interesting though. If the universe were indeed closed and if we assume black holes essentially makes a hole in spacetime, it would mean that all black holes connect different parts of the universe at its centre of the curvature (if we assume the universe is homogenous in curvature). All black holes would all intersect, and curve space time directly downward. As the universe is essentially a sphere, the hole in spacetime created by the black hole would be perpendicular to the tangent to the point of the sphere in which it is at. Not sure if I'm making any assumptions again, but if I am, please correct me.
 

Thurlor

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@sushi
Wouldn't curvature be impossible to determine in an infinite universe? At any scale in which we observe the universe, wouldn't space appear 'flat'?

@Cognisant
All paths on the surface of a sphere are three dimensional. If you were to take a two dimensional path you would have to leave the surface of the sphere. To return to your starting point you must follow a curved three dimensional path.
 

Inexorable Username

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Can I ask you all a few stupid questions? I’m sorry. This isn’t my area of expertise, but I am highly interested in learning more.
(If anyone has a book to recommend, please do!)

If our universe is a closed sphere, what is outside of the sphere? Also, I thought, for some strange reason, that we believed the universe was infinite. Did that theory change, and I missed it? Obviously you can travel around a sphere infinitely, but a closed sphere, itself, isn’t an object of infinite space...right?
 

..

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If our universe is a closed sphere, what is outside of the sphere?

What you're talking about is higher than three spacial dimensions. This hasn't been proven yet, but string theory postulates that there's anywhere from 11 to 26 spacial dimensions curled up at the string level. The closed sphere itself isn't an object, it is a two dimensional representation of four dimensions - three spacial (x, y and z) and one time dimension.

Also, a good book I recommend reading is Relativity: The Special and General Theory by Albert Einstein. Who better than to learn it from than the creator himself. https://www.amazon.com.au/Relativit...ocphy=9070597&hvtargid=pla-426339968574&psc=1

Also, I recommend watching the youtube series 'Special Relativity' by Minute Physics. Henri gives a very intuitive understanding of the subject.
 

Marbles

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It's interesting though. If the universe were indeed closed and if we assume black holes essentially makes a hole in spacetime, it would mean that all black holes connect different parts of the universe at its centre of the curvature

Is it given that a hole would result in a tunnel?

@sushi
Wouldn't curvature be impossible to determine in an infinite universe? At any scale in which we observe the universe, wouldn't space appear 'flat'?
Sounds right to me... If so, if this research is correct, does that mean the 4D universal sphere is finite, and that we could determine its size through measurements of local curvature?
@Cognisant
All paths on the surface of a sphere are three dimensional. If you were to take a two dimensional path you would have to leave the surface of the sphere. To return to your starting point you must follow a curved three dimensional path.
If you take a 2D cross section of a sphere, wouldn't any resulting circle be a 2D path around the sphere? Do you mean there is no 1D path?

Also, I recommend watching the youtube series 'Special Relativity' by Minute Physics. Henri gives a very intuitive understanding of the subject.

Thanks for the recommendation, I'll check that out.



Also, would you say you know a lot of physics/cosmology? If yes...
Do you like Honda trucks? Sneaky, sneaky, Digital Trends.
 

Inexorable Username

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If our universe is a closed sphere, what is outside of the sphere?

What you're talking about is higher than three spacial dimensions. This hasn't been proven yet, but string theory postulates that there's anywhere from 11 to 26 spacial dimensions curled up at the string level. The closed sphere itself isn't an object, it is a two dimensional representation of four dimensions - three spacial (x, y and z) and one time dimension.

Also, a good book I recommend reading is Relativity: The Special and General Theory by Albert Einstein. Who better than to learn it from than the creator himself. https://www.amazon.com.au/Relativit...ocphy=9070597&hvtargid=pla-426339968574&psc=1

Also, I recommend watching the youtube series 'Special Relativity' by Minute Physics. Henri gives a very intuitive understanding of the subject.

Oh, thank you for that recommendation! I'll definitely check out the YouTube series during dinner breaks and such. I'll have to see if I can get the audiobook for the book, though. I don't have much free time, and all of it lately has been sucked up by this forum. I usually spend between-work moments cleaning or walking my dogs, so that's when I listen to audiobooks on topics of interest. I had a great book on string theory - lost it though, before I was done...I wish I could remember the name. Oh well!
Thanks again for the tip! I have a massive YouTube playlist of study material - always excited to add to it! (Let me know if you have any more YT suggestions! I'm interested in most subjects.)
 

..

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[/QUOTE]
Also, would you say you know a lot of physics/cosmology? If yes...
Do you like Honda trucks? Sneaky, sneaky, Digital Trends.
[/QUOTE]

It's hard to determine exactly how much is a lot. If you're comparing to the general public, I'd say yes but if you compare me to an astrophysicist, I'd definitely say no. I'd say I've learnt perhaps much less than 1% of the amount of knowledge there exists on astrophysics and cosmology - I think I've only learnt simplifications of complex models. I'm in high school, so I don't know any of the mathematics behind general relativity or quantum mechanics. I've only learn a slice of Newtonian motion so far, but I plan to look into Lagrangian Mechanics, and perhaps, if I have time, Hamiltonian.

Also, I don't understand the Honda truck joke, mind explaining it to me? I'm a little confused.
 

sushi

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to clarify, flat universe is not 2d, it just means its eculidean space properties

the other two ideas are hyperbolic or spherical geometry, or non ecludiean.

one can travel around the surface of the sphere and still think its infinite.
 

Inexorable Username

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@..

Is it rude if I message you with questions about the psychology of your peer group? Generation Z is very difficult to research, as information on high schoolers is difficult to come by (for obvious reasons). Moreover, though, it’s difficult to find a member of Z that is an “intellectual”, or a thinker/observer/learner. Most teens are fairly distracted by social politics I think.

I’m curious to know, for instance, whether you feel your peers define their sense of self-worth through social media, or if you think that is starting to die out.

You don’t have to answer of course, but like I said - you’re an unusual member of your age group and people like you are hard to come by. We could make a thread if you think you’d be willing to answer anyone else’s questions about the younger gen as well? I can’t be the only person who has an interest in generational research.
 

computerhxr

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This is just my own imagination on the shape of the universe...

If the universe is a closed sphere like a bubble, then what is outside of the bubble would likely reduce to zero, warping the furthest reaches of space to a single point. What is infinitely large would then be no different than what is infinitely small. What we measure as expanding is actually the universe collapsing out into a black hole with a mass parallel to the mass of the universe. Paradoxically, the universe would be the balance between the parallel of a single point in diametric opposition, giving it both a flat and spherical appearance simultaneously.
 

..

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Is it rude if I message you with questions about the psychology of your peer group? Generation Z is very difficult to research, as information on high schoolers is difficult to come by (for obvious reasons). Moreover, though, it’s difficult to find a member of Z that is an “intellectual”, or a thinker/observer/learner. Most teens are fairly distracted by social politics I think.

I’m curious to know, for instance, whether you feel your peers define their sense of self-worth through social media, or if you think that is starting to die out.

You don’t have to answer of course, but like I said - you’re an unusual member of your age group and people like you are hard to come by. We could make a thread if you think you’d be willing to answer anyone else’s questions about the younger gen as well? I can’t be the only person who has an interest in generational research.

Yes, of course. I'm always willing to participate in research where possible. :)
 

Inexorable Username

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Is it rude if I message you with questions about the psychology of your peer group? Generation Z is very difficult to research, as information on high schoolers is difficult to come by (for obvious reasons). Moreover, though, it’s difficult to find a member of Z that is an “intellectual”, or a thinker/observer/learner. Most teens are fairly distracted by social politics I think.

I’m curious to know, for instance, whether you feel your peers define their sense of self-worth through social media, or if you think that is starting to die out.

You don’t have to answer of course, but like I said - you’re an unusual member of your age group and people like you are hard to come by. We could make a thread if you think you’d be willing to answer anyone else’s questions about the younger gen as well? I can’t be the only person who has an interest in generational research.

Yes, of course. I'm always willing to participate in research where possible. :)

Awesome!! I’m so excited. I’ll send you a message later with some questions! :D
 

sushi

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scorpiomover

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Can I ask you all a few stupid questions? I’m sorry. This isn’t my area of expertise, but I am highly interested in learning more.
(If anyone has a book to recommend, please do!)

If our universe is a closed sphere, what is outside of the sphere?
Scientists don't know.

A closed sphere is a closed system.

A closed system is a system where all objects inside the system can only interact in such a way that means that even if they change their position, velocity, momentum, or anything else, would remain inside the system. Think of it like a ring road with no exit. The drivers can go round and round, change lanes, even pull over on the hard shoulder. But they can never get off.

These days, scientists include light such as e-m waves as part of that closed system.
therefore, matter and all forms of energy cannot leave the system either. So the amount of energy cannot decrease. As scientists have a rule that energy is conserved within the system, the total amount of energy cannot increase. So nothing can enter the system from outside either.

So it's like a ring road, where the drivers can see the light that comes from the lights in the road. But no light can come from outside. So none of the drivers would see what is outside of the system.

Also, I thought, for some strange reason, that we believed the universe was infinite. Did that theory change, and I missed it?
Yes. No-one was really sure if the universe was infinite or not. Infinite lengths is just how most Westerners were taught in school. If you were taught to read only those things that were written with black ink, would it not also be a surprise to find that there were clever things that were written with blue ink?

Obviously you can travel around a sphere infinitely, but a closed sphere, itself, isn’t an object of infinite space...right?
Depends on the size of the sphere, doesn't it?
 

The Grey Man

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A lot of these physics metaphors seem designed merely to give people the illusion of understanding. "Oh, I can imagine a ball on a trampoline! Awesome, general relativity is easy."

Metaphorical representations of physical ideas are always inadequate. If they were adequate, they would not be metaphors, for there would be no distinction between what represents and what is represented.

What makes the metaphor of Riemannian space as "spherical" inadequate is that the "curvature" of the space is such that the "sphere" has neither an inside nor an outside. As our young scientist pointed out, its curvature is intrinsic to it, not an extrinsic property of the space defined by its relation to a higher dimension. In this sense, an understanding of elliptical space based on the visual metaphor of a sphere is illusory, though such imaginative constructions might be an aid to actual understanding. I find it harder to imagine Lobatchevsky's "hyberbolic" space, even metaphorically.
 

patrick

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so u say the space is enclosed by a non orientable surface?
 

The Grey Man

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A sphere is orientable. A Klein bottle is non-orientable. A Klein bottle is what you get when you join the two edges of a Möbius strip, which is, of course, impossible in our familiar (approximately) Euclidian space, in which the two edges are identical. In other words, a Klein bottle is an unbounded Möbius strip, just as a sphere is an unbounded version of the "untwisted" Möbius strip, which is like a belt. If space was a "hyper-Klein bottle," then a right-handed person who "circumnavigated" the universe (a hyper-Magellan) would come back left handed. The chirality of his molecules would all be reversed, too, so he wouldn't be able to function in our environment (I think Isaac Asimov wrote a short story about this).
 

patrick

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but u said it cannot be a sphere but rather, a "sphere" which its curvature implies that theres no distinction between its outside and inside, meaning theres more than 1 orthogonal vector for any given point of the enclosing surface of the universe (using euclidean norm and standard sum and product of the R3 space).

u gave some example of non orientable surfaces but i just wanted to know if what u said about the universe not having an outside meant it was enclosed by a non orientable surface, and if yes could this surface be a sphere in the sense that the norm of any coordinate point of the surface could be defined as a constant, or not.
 
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