Stationary Centre of Universe Defined?

[ynot]

I suppose so, as long as you can similarly think of a chicken as merely an expanded egg.

I would have no problem with that scenario If the chicken was all that existed and it uniformly expanded from the egg then the egg would be the stationary centre of the chicken.

No. "All things" didn't always exist. The singularity and some time after expansion started, the universe was homogenous, and there were no things.

So the universe wasn’t made from the stuff of the singularity (as in the chicken came from the stuff of the egg) but the stuff of the Universe was created from nothing? Is there a magical big daddy in the sky involved as well?

It's a legitimate analogy, but I understand your frustration with it. For those of us that don't have the mathematical ability to understand these things for real, that's about the best visualization we can get.

I usually called “dumbing down”. I think it’s just dumb. I think math works best when it’s applied to reality, not when it’s used to “create” it.

I prefer just to cling to the idea that the Big Bang happened everywhere in our universe.

I have no problem with that if the Universe is finite. Don’t have any evidence that it is however.

The universe doesn't expand into pre-existing space. Expansion is essentially new space coming into being between the galaxies.

So space is constantly being created and this extra space moves thing further apart. Does this make the Universe bigger? In what way is space a thing that an be created? What is space any more than being distance between things?

If you can, try to imagine St. Louis and Kansas City getting farther apart by the coming into being of more mid-Missouri and NOT by St. Louis moving east into Illinois or K.C. moving west into Kansas. Again, it's only an analogy and not without major flaws.

I think I would find it easier to imagine a magical big daddy in the sky and it would make just as much nonsense to me.

 

[sol invictus]

I'm not the most knowledgeable person on this subject, but I don't think this is accurate.

You're correct that the early universe was extremely hot and dense, and also that no ordinary physical object could survive in such conditions. So if Alexi was asking about, say, three rocks, you're right that it doesn't make much sense to talk about their positions prior to some time.

I was answering a different question. One can ask what happens to the points currently at the center of mass of those three rocks if you trace the points back to the singularity (without worrying about what happens to the rocks themselves). That's a perfectly well-defined mathematical question, and I thought it's what Alexi was after.

Can we at least explain the singularity as being all things of the Universe being in pretty much the same place at the same time (together)?

No, that's simply not accurate. It's much better to think of the singularity as something that happens if the density reaches some critical value. In a uniform universe like ours that happens everywhere in the universe at more or less the same instant. It's not the case that everything in the universe is at one point at that instant.

If you insist that this critical density must be infinity, things simply become ill-defined and your question doesn't have a definite answer. But for any finite value of the density (no matter how large), it's not true that everything is on top of everything else.

I cannot accept an analogy of the Universe as a 2D surface of a sphere and I think it‘s ludicrous woo to do so.

That is essentially a perfect analogy to our current best scientific and mathematical understanding of this isssue, so if you can't accept it you're asking questions in the wrong forum.

The Universe is always spatially 3D. Nothing more, nothing less.

You're not understanding the point. It's an analogy. It differs from the universe in one important respect; namely, that the universe is indeed spatially 3D. But it's not a flat 3D space, it is curved, and in particular it may be a 3-sphere, the 3D analog of the surface of a sphere. A 3-sphere is not the interior of the surface of an ordinary sphere (that's called a 3-ball if you want to know). A 3-sphere is what is sometimes called a hypersphere, it's a 3D volume without boundary or center, just as the surface of the earth is a 2D area without boundary or center.

 

[ynot]

You're not understanding the point. It's an analogy.

I fully understand it’s an analogy. I just don’t accept that it’s an analogy that has validity and credibility in an actual sense. That it may have validity and credibility in an abstract mathematical sense doesn‘t mean to me that it does or can in an actual sense.

It differs from the universe in one important respect; namely, that the universe is indeed spatially 3D. But it's not a flat 3D space,.

“Flat 3D” seems a nonsense oxymoron to me.

it is curved, and in particular it may be a 3-sphere, the 3D analog of the surface of a sphere. A 3-sphere is not the interior of the surface of an ordinary sphere (that's called a 3-ball if you want to know). A 3-sphere is what is sometimes called a hypersphere, it's a 3D volume without boundary or center, just as the surface of the earth is a 2D area without boundary or center.

Is there any evidence that it’s actually possible to have a 3D volume without boundary or center? If so how is this 3D volume defined? Is there any directionality to curved space/time? If so what is that direction and why isn’t it possible to travel counter to that direction and flatten or reverse the curve?

 

[sol invictus]

I fully understand it’s an analogy. I just don’t accept that it’s an analogy that has validity and credibility in an actual sense. That it may have validity and credibility in an abstract mathematical sense doesn‘t mean to me that it does or can in an actual sense.

Your totally uninformed opinion is not relevant. Einstein constructed a theory - general relativity - based on the idea that space can be curved. His theory has been confirmed experimentally many times over. So, you have several choices:

1) accept that his theory is probably correct
2) find a different theory that explains all the evidence equally well but doesn't involve curved space
3) bury your head in the sand and stick to your ignorance

“Flat 3D” seems a nonsense oxymoron to me.

And?

Is there any evidence that it’s actually possible to have a 3D volume without boundary or center?

Yes, lots.

If so how is this 3D volume defined?

Through non-Euclidean geometry, most of which was worked out by Gauss and Riemann in the 19th century. It's not exactly new stuff.

Is there any directionality to curved space/time?

There can be, but not in the case we're discussing (anymore than there is on the surface of the earth).

If so what is that direction and why isn’t it possible to travel counter to that direction and flatten or reverse the curve?

Do you mean something like digging a tunnel under the surface of the earth to make a shorter path? If so, that's almost certainly not possible, because it's 3D space itself that's curved.

 

[AntiTelharsic]

“Flat 3D” seems a nonsense oxymoron to me.

"Flat" doesn't mean "thin". If it seems like an oxymoron, then I suspect you're considering "flat" to mean the same thing as "two-dimensional".

Flat here refers to a lack of curvature. Just as you can have a flat 1D space (a straight line) or a curved 1D space (the boundary of a circle), and a flat 2D space (a plane) or a curved 2D space (the surface of a sphere), you can generalize the concept to any number of dimensions (and we generalize "space" to mean a set with certain structure, and include lines and planes as examples).

Not only is curved spacetime (people often forget time in these considerations -- we're really dealing with four dimensions, not three) a meaningful concept, but it's a very useful model of the universe, both explaining and predicting observations.

It's not surprising that you find your common sense violated by theoretical physics. Human common sense didn't grow up dealing with phenomena related to the very small- or large-scale structure of the universe. You shouldn't, therefore, assume that your common sense notions apply. Common sense feelings about the universe cannot survive an education in physics.

There are very good reasons why physicists assume that the universe is a curved 4D spacetime (and Sol would be a far better person than I to explain them), and it's just a fact that understanding them requires a lot more mathematics than can be grasped by most people. In the end, in this as in every other specialized discipline, you are free to defer to the opinions of the experts, those who do understand the subject, or rail futilely against them. We certainly have no shortage of the latter kind of person on these forums.

 

[Towlie]

I cannot accept an analogy of the Universe as a 2D surface of a sphere and I think it‘s ludicrous woo to do so. The Universe is always spatially 3D. Nothing more, nothing less.

Then I guess that makes you the modern equivalent of a flat Earther because the concept has been part of cosmology for as long as any of us has been alive. Rejecting something because it overtaxes your imagination hardly puts you in a position to call "ludicrous woo".

 

[Myriad]

Can we at least explain the singularity as being all things of the Universe being in pretty much the same place at the same time (together)? And that the expanded Universe is essentially the expanded singularity where all things of the Universe are in different places at the same time (apart)? Forgetting space, if all things were once together and they are now all apart as the result of a uniform expansion (regardless what causes it), then the very point that the things expanded from (where they were together) must be the stationary centre of the expansion.

All right, I admit it. The physicists have been having you on. The actual center point from which the universe expanded is about 3.4 billion light-years south-southwest by west and three points up from here, not far from the Bathtub Ring Galaxy in the fringes of the Lesser Pothole Supercluster. Of course, the cluster didn't move into the area until billions of years after the big you-know-what went down, but that hasn't stopped it from becoming a total tourist trap.

Okay, now, seriously... would any answer of that nature be more satisfactory to you, or to anyone, than a 3D hypersphere with no boundary or center?

Respectfully,
Myriad

 

[arthwollipot]

I have no problem with that if the Universe is finite. Don’t have any evidence that it is however.

The fact that the universe is observably expanding, and the inevitable consequence that it had a beginning, is evidence that the universe is finite.

 

[AntiTelharsic]

To address the original question...

Consider a circle (by this I mean just the line you would draw, not the disc it encompasses). Now consider a smaller circle inside it, and a smaller one, and so on. Now, instead of discrete steps, imagine smoothly contracting your original circle to a point. If you imagine playing this in reverse, starting from a point and expanding into a circle, then you have a (poor) analogy of the big bang: the universe here is the one-dimensional circle, and the singularity is the point.

What makes this analogy suck is that when you're thinking about it, you're thinking of the circle expanding outward in a two-dimensional plane: there's the "space" of the circle's edge, and there's space around it, and space inside it.

But we're really only concerned with the circle's edge, and in fact we can refer to such a space as the one-dimensional circle, or a two-dimensional sphere, or a 3- or higher-dimensional hypersphere without reference to any space in which it might be embedded. Mathematically, we can consider just the object itself, and its intrinsic metric properties; the plane isn't required in order to define the circle, and a 3-space isn't required in order to talk about or do geometry within the surface of a sphere.

In short, treating the universe as a curved 4D spacetime which has expanded from a singularity does not imply that it must expand into anything. And just as in the analogy above you can consider every single point on your circle to have been at the point from which it expanded, so we consider every point in spacetime to have been at the point of the big bang.

As in my previous post I'll note that if this conflicts with your intuition, that's because your intuition isn't for this.

 

[Brian-M]

If the Universe uniformly expanded from a very small singularity doesn't that mean that the original position of the singularity defines a centre point of the Universe that is absolutely/Universally stationary?

Stationary relative to what?

ETA:

I mean, the concept of "stationary" only has meaning in relation to a common point of reference. What point of reference in order to determine whether or not the singularity was stationary or in motion? The question loses coherence.

 

[ynot]

Your totally uninformed opinion is not relevant. Einstein constructed a theory - general relativity - based on the idea that space can be curved. His theory has been confirmed experimentally many times over. So, you have several choices:

1) accept that his theory is probably correct
2) find a different theory that explains all the evidence equally well but doesn't involve curved space
3) bury your head in the sand and stick to your ignorance.

Thanks, but I will go with a choice option you didn’t offer . . .

4) I won’t believe or accept claims credibility just because other people believe or accept them. This applies to both scientific and paranormal claims.

Not accepting a claim isn't saying the claim is wrong and can't be right.

 

[ynot]

Stationary relative to what?

ETA:
I mean, the concept of "stationary" only has meaning in relation to a common point of reference. What point of reference in order to determine whether or not the singularity was stationary or in motion? The question loses coherence.

Stationary relative to the Universe (Universally stationary). The point of reference would be the original position of the singularity relative to the current expanded position of the Universe.

 

[JoeTheJuggler]

I think I would find it easier to imagine a magical big daddy in the sky and it would make just as much nonsense to me.

You're wrong.

And since you refuse to listen to the answers we're trying to give you, I suggest you just learn the maths so you can understand why physicists say what they do.

 

[AntiTelharsic]

Thanks, but I will go with a choice option you didn’t offer . . .

4) I won’t believe or accept claims credibility just because other people believe or accept them. This applies to both scientific and paranormal claims.

So if your doctor tells you something, do you go out and become an M.D. before you'll accept his position or that of his entire profession? I suspect not, and wonder why you'd defer to the judgment of medical professionals (or mechanics, or plumbers, or electricians, or professionals of most fields in which you are not, yourself, an expert) but not physicists.

 

[JoeTheJuggler]

AntiTelharsic, thank you for the very lucid posts on this thread.

Every time I read your posts I can only think, "I wish I could have said that."

 

[AntiTelharsic]

LOL.. thanks.. can't tell you how many times I've practically applauded things you've said...

 

[ynot]

I think my “problem” is that I don’t accept the language of theoretical or modern physics. Or at least I don‘t accept that the way it‘s often used. Not accepting doesn’t mean not understanding and isn‘t saying wrong. As far as I’m concerned a triangle is Euclidean and can’t be drawn on the surface of a sphere. If you want to draw three lines on the surface of a sphere I don’t accept that it’s valid to say you can draw a triangle that has three 90 degree angles. This is no more a triangle than three lines drawn around the circumference with no angles.

 

[lionking]

I think my “problem” is that I don’t accept the language of theoretical or modern physics. Or at least I don‘t accept that the way it‘s often used. Not accepting doesn’t mean not understanding and isn‘t saying wrong. As far as I’m concerned a triangle is Euclidean and can’t be drawn on the surface of a sphere. If you want to draw three lines on the surface of a sphere I don’t accept that it’s valid to say you can draw a triangle that has three 90 degree angles. This is no more a triangle than three lines drawn around the circumference with no angles.

For goodness sake, this was resolved by mathematicians centuries ago. Or don't you accept the authority of mathematicians either? Tell me, do you recognise the authority of anyone but yourself?

 

[ynot]

So if your doctor tells you something, do you go out and become an M.D. before you'll accept his position or that of his entire profession? I suspect not, and wonder why you'd defer to the judgment of medical professionals (or mechanics, or plumbers, or electricians, or professionals of most fields in which you are not, yourself, an expert) but not physicists.

I certainly don’t accept everything that my doctor, dentist, lawyer (especially), etc tells me. Do you? Whether I accept what they say or not depends on how credible it sounds to my current understanding of what is credible. And how important to me my accepting what they say is or not. If you tell me you ate an egg for breakfast I would be inclined to believe you as it's common for people to have eggs for breakfast. And if you're lying who cares?. If you tell me you laid an egg that you ate for breakfast I would be inclined not to believe for obvious reasons.

ETA - The Pope is a professional that has put a lifetime of study into his profession (as have more people I suspect than scientists). Does that mean I should believe in a God?

 

[AntiTelharsic]

I think my “problem” is that I don’t accept the language of theoretical or modern physics.

That language is mathematics. General relativity, quantum mechanics, these and other scientific theories are all essentially "mathematical models", by which I mean they are mathematical constructs which, when interpreted in the light of observation, appear to give very good results in terms of being able to account for and predict observed properties of the universe.

The math used in these theories is entirely meaningful and consistent; things don't get accepted into the body of mathematics if they're not. With regards to your specific concern, triangles on a sphere: non-Euclidean geometry is no less valid than Euclidean geometry, regardless of its separation from our everyday experience. It is just as consistent, just as meaningful, just as able to be applied practically in certain domains to the problem of understanding the universe.

I must say at this point that a mathematical model of the universe doesn't really tell us what the universe is -- it only gives us a framework for talking about how it appears to work (the map is not the territory). But when the model's "picture" is of a certain type of object, and that model describes reality to the precision with which our current scientific models do, then it's reasonable to tentatively assume that the picture is accurate. Of course science has a long history of abandoning one picture in favor of a better one, but still, at any given time, we work with the best pictures we have. Currently, there's a very accurate-looking picture of the universe which makes it out to be a curved 4D spacetime, and additionally to its experimental confirmation, it has a perfectly valid mathematical basis.