Thread: "Shape" of the Universe

Hopefully this doesn't sound too stupid from a science noob like me but here it goes...

I've come across one interesting idea that, if I interpreted it correctly, states that our 3-dimensional existence is merely the "surface" of a higher dimensional object, as in a 3-dimensional manifold existing in hyperspace.

This would explain why many members here keep arguing that space does not expand from any particular center point, but expands uniformally, as in the analogy of blowing up a balloon.

Is this the same thing as the model of a "closed" universe? And in general, what is the most accepted model regarding the size/shape of our universe?

The same thing can apply whether the universe is open or closed. May I suggest you have a look at the website below, it is a very simple introduction to these concepts.

Bob Gardner's "Shape of Space" Talk, Introduction

I want to know more about plasma u theory and wonder I could interject that same question to learn more of the origins of plasma u theory? Thanks!

Originally Posted by ampwitch

I want to know more about plasma u theory and wonder I could interject that same question to learn more of the origins of plasma u theory? Thanks!

Hi ampwitch. If you'd like to learn about "plasma u theory", I suggest starting your own thread, as not to veer off the purpose of this thread.

Originally Posted by SpeedFreek

The same thing can apply whether the universe is open or closed. May I suggest you have a look at the website below, it is a very simple introduction to these concepts.

Bob Gardner's "Shape of Space" Talk, Introduction

Thanks! Looks like a perfect introduction.

Thank You, I will. Please accept my apology.

Originally Posted by ampwitch

Thank You, I will. Please accept my apology.

Fine. But there's no need. Have a good day.

Who knew there a models of the universe where the universe is finite but still has no boundary?!

I've seen the idea when I looked into topology but never really associated it with the geometry of the universe. If the universe is like this, doesn't that mean there are infinite images of us due to light coming back around constantly?

Originally Posted by halorealm

Who knew there a models of the universe where the universe is finite but still has no boundary?!

There is no finite and bounded model, as far as I am aware, due to err.... boundary conditions!

Originally Posted by halorealm

I've seen the idea when I looked into topology but never really associated it with the geometry of the universe. If the universe is like this, doesn't that mean there are infinite images of us due to light coming back around constantly?

It would mean something like that, but only if the universe were small enough or expanding slowly enough for the light to be able to "circumnavigate" it.

At the end of that introduction (which is quite old now), the author mentions the possibility of there being evidence for the topology in the cosmic microwave background. Well, since then, we have looked for this!

Have a look at the paper below, the introduction is quite interesting, and so are the conclusions (although I suppose that depends how you look at it):
[astro-ph/0604616] Extending the WMAP Bound on the Size of the Universe

Originally Posted by SpeedFreek

Originally Posted by halorealm

Who knew there a models of the universe where the universe is finite but still has no boundary?!

There is no finite and bounded model, as far as I am aware, due to err.... boundary conditions!

Think of the surface of a ball. It has no boundary in itself but it still has finite surface area. Raise that up a dimension. Does that count? That's what I remember reading from some related Wiki article, but it could be different.

It would mean something like that, but only if the universe were small enough or expanding slowly enough for the light to be able to "circumnavigate" it.

At the end of that introduction (which is quite old now), the author mentions the possibility of there being evidence for the topology in the cosmic microwave background. Well, since then, we have looked for this!


Have a look at the paper below, the introduction is quite interesting, and so are the conclusions (although I suppose that depends how you look at it):
[astro-ph/0604616] Extending the WMAP Bound on the Size of the Universe

Yes. I read into that last part. Then I remembered reading an article not too long ago titled something like "Circles in the sky might shed light into the nature of the universe". I guess I just grazed right over the content Thanks for the link!

Originally Posted by halorealm

Originally Posted by SpeedFreek

Originally Posted by halorealm

Who knew there a models of the universe where the universe is finite but still has no boundary?!

There is no finite and bounded model, as far as I am aware, due to err.... boundary conditions!

Think of the surface of a ball. It has no boundary in itself but it still has finite surface area. Raise that up a dimension. Does that count? That's what I remember reading from some related Wiki article, but it could be different.

Yes, that is finite and unbounded (no boundary).

Originally Posted by Kerling

Just a small correction on your train of thought. You do not live in a 3 dimensional world, but in a 4 dimenional one. You have time, your life is far from static. Hell the very act of observation and communication doesn't exist in static universes. The reason why space expands uniformely as it does can also only be explained from a 4 dimensional model, as it woudl require time to do so.

I understand that. Even though time is critical to our existence, this question mainly focuses on the spatial aspect of the universe. I'm not ignoring time; the arrow keeps going. But the spatiality of the whole thing is a more trivial matter.

Fact remains that in many derivations, take for instance the Higgs particle, an infinite size of the world is assumed. But that isn't very relevant as the very notion of spacelike interaction only impose that the universe is as large as it can be spacelike. Meaning that it doesn't have to be of infinite size to have a practically infinite reality. After all, our universe has an age.

I'm not sure what you're trying to say from this. What does the Higgs have to do with the geometry of the universe? What do you mean when comparing "infinite size" and "practically infinite reality"? As for the age of the universe, it may or may not be relevant. Isn't the reference always exclusive to the Big Bang theory?

True shape of the Universe:

And I wish people would stop typing "Universe" starting with a small case "U".

*Waits to be banned for irrelevant post*

Technically universe is not capitalized (check a dictionary). And while I do it myself out of respect, it would be improper to complain about people who don't.

Originally Posted by halorealm

Originally Posted by Kerling

Just a small correction on your train of thought. You do not live in a 3 dimensional world, but in a 4 dimenional one. You have time, your life is far from static. Hell the very act of observation and communication doesn't exist in static universes. The reason why space expands uniformely as it does can also only be explained from a 4 dimensional model, as it woudl require time to do so.

I understand that. Even though time is critical to our existence, this question mainly focuses on the spatial aspect of the universe. I'm not ignoring time; the arrow keeps going. But the spatiality of the whole thing is a more trivial matter.

Fact remains that in many derivations, take for instance the Higgs particle, an infinite size of the world is assumed. But that isn't very relevant as the very notion of spacelike interaction only impose that the universe is as large as it can be spacelike. Meaning that it doesn't have to be of infinite size to have a practically infinite reality. After all, our universe has an age.

I'm not sure what you're trying to say from this. What does the Higgs have to do with the geometry of the universe? What do you mean when comparing "infinite size" and "practically infinite reality"? As for the age of the universe, it may or may not be relevant. Isn't the reference always exclusive to the Big Bang theory?

Okay, in short: The universe doesn't expand at the speed of light. But information traverses with the speed of light. This means that the ends of the universe have been communicating, albeit slowly in comparison to our age. In other words, what we can know about the universe is whatever space-like connections allow. In the beginning there might have been another universe (Roger Penrose has a beautiful idea for this with aoens). Fact is though that whatever information we have about this previous universe most be a non commuting observable. As far as I know only gravity waves have this property. So yes, maybe there was something before. But I do not know of propper ways to retrieve this information. And at what speed they move, at best by now there is probably only ripples of ripples of ripples left. This makes proving such a concept practically impossible. And as (in my opinion) reality is what is observable, so as long as I don't see good proof of prior universes I don't believe it! (and yes, it doesn't mix very well with my own theory about it)

Originally Posted by Kerling

Okay, in short: The universe doesn't expand at the speed of light. But information traverses with the speed of light. This means that the ends of the universe have been communicating, albeit slowly in comparison to our age.

This isn't right, unless I am misunderstanding you. The universe does expand at the speed of light, in fact it expands faster than light. The particle horizon (the comoving horizon where the CMB we detect today was originally released from) was receding at 58 c at the time of recombination (when the CMB was released) and is today 46.5 billion light-years away and is still receding at more than 3 c.

[astro-ph/0310808] Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe

We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.

Originally Posted by Kerling

In other words, what we can know about the universe is whatever space-like connections allow.

Right. But our cosmological event horizon, which puts a limit on those connections, always lies beyond our Hubble horizon where objects apparently recede at the speed of light.

Good point.