Stationary Centre of Universe Defined?

[AntiTelharsic]

I certainly don’t accept everything that my doctor, dentist, lawyer (especially), etc tells me. Do you?

If my doctor told me something which was beyond my understanding (something which I am perfectly willing to stipulate could happen) then I might seek a second or third opinion, and in the end defer to expert judgment.

How many opinions would you need in such a situation? How many would you require from physicists?

 

[JFrankA]

No. It's a singularity; nothing much can be said about it.



The entire 3-dimensional space expands uniformly with time. If you insist you can think of it expanding into a 4th spatial direction (so there are 4 spatial dimensions and one time). If you do think of it that way there is a center, but it's not part of the universe (think of the surface of the earth - there's a center to the earth, but it's not part of the surface).



At every moment of time after the big bang they've been arranged like that (at least assuming they aren't moving relative to each other apart from the expansion of space). If you're asking why they started off like that, the answer is that no one knows. We don't understand what physics, if any, set up the "initial" conditions at the big bang (or even if it was truly the beginning).

Actually, this quote from Sol explained it perfectly to me.


(Thank you, Sol, by the way. )

 

[ynot]

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 didn’t say that non-Euclidean geometry is less valid than Euclidean geometry. I don’t agree that non-Euclidean geometry is particularly separated from our everyday experience either. At least not for myself as I have no problem with 3D concepts. My Point was that I don’t think it’s valid (or helpful) to use Euclidean language for non-Euclidean geometry.

 

[Towlie]

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.

But it's not a "claim", it's a scientific theory. As such, it's not right or wrong, it's only superior or inferior to competing scientific theories in how well it describes observations and makes predictions. The parallel you imply between "scientific and paranormal claims" simply does not exist.

 

[ynot]

If my doctor told me something which was beyond my understanding (something which I am perfectly willing to stipulate could happen) then I might seek a second or third opinion, and in the end defer to expert judgment.

How many opinions would you need in such a situation? How many would you require from physicists?

Don’t think it’s valid to compare the “nuts and bolts” diagnosis of a doctors with the theoretical mathematics of physicists.

 

[AntiTelharsic]

My Point was that I don’t think it’s valid (or helpful) to use Euclidean language for non-Euclidean geometry.

Mathematicians do re-use terminology, where there are sufficient similarities to warrant it despite differences, and as a matter of convenience. Your position is valid, I suppose, but it seems that you were disagreeing less with terminology than with basic concept.

 

[AntiTelharsic]

Don’t think it’s valid to compare the “nuts and bolts” diagnosis of a doctors with the theoretical mathematics of physicists.

Nuts and bolts of the human body, nuts and bolts of the universe. Each requires a good many years of specialized education to be able to think about / work with meaningfully, and that means laymen in each case must defer to the judgment of the experts. There are matters of medical science which are considered factual by professional consensus, and the same is true of physics. Each field has its crackpot deniers. I don't think they're different enough in essence to invalidate the comparison for our purposes here.

 

[AntiTelharsic]

I should also add to those points that the experimental tests which General Relativity has passed are as practical and repeatable as any in medical science: clocks run at different rates at different positions in a gravitational field; light follows curved paths in the vicinity of mass; these things and many more were predicted on the basis that they're what we would expect to see if Einstein was right and the universe is a curved four-dimensional spacetime.

We can experiment with the universe as a whole just as we can with human physiology, so again, I think the comparison is valid, and it doesn't seem reasonable to accept the position of medical science on topics outside your expertise, and not accept the position of physicists.

 

[Foster Zygote]

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.

People like Albert Einstein, Hermann Minkowski, Hendrik Lorentz, Henri Poincaré, Carl Sagan, Stephen Hawking and Michio Kaku disagree with you so I don't think it can be so casually dismissed as "ludicrous woo".

Let me see if I can't lay it out in a bit more detail: First of all, current models for the structure of the universe suggest that there are a good bit more than three spatial dimensions at play. The problem is that it is practically impossible for us to visualize dimensions beyond the three (four, actually, including time) that we think in.

We can describe the fourth dimension rather easily. Define a point in space, then expand that point to a 10 cm line segment. That is one dimensional space consisting of length only. Even if it loops around on itself it is still a closed one dimensional space, but it is now without any internal boundary. It is finite but boundless within its single dimension. A one dimensional inhabitant could set off in one direction and return to its starting point from the opposite direction.

Now let's define a two dimensional space. Go back to our original point and draw a 10 cm line segment radiating from the original point at a 90 degree angle to the first segment. We have now defined a two dimensional space with length and width only. If we wrap it around on itself into a sphere we have the same situation as we did with the one dimensional ring. The space is two dimensional, yet it is boundless and finite. "Mr. Square" could set out in one direction looking for the end of the universe and discover that after traveling a certain distance he will come back to his starting point from the opposite direction.

Now lets move on to three dimensions. The model is the same: we take our original point and draw another line segment radiating from it at 90 degrees to both of our earlier lines. We squared one dimension and got two, then we squared two and got three. Now we have a space that is 10 cm in length, 10 cm in width and 10 cm in height. We have a tree dimensional cube.

But can we wrap the cube around upon itself in the same way as the line and the square? The answer is "yes", but we can't visualize it. Why not? Because we would have to be able to visualize a point with four lines radiating from it with each line at 90 to the other three. That is the fourth dimension put very simply. If we could fold the cube around in the fourth dimension, just as we folded the line into the second dimension to make a ring and folded the square into the third dimension to make a sphere, we would have a space in which a traveler could set off in any direction and return to the point of origin without ever turning or reversing. But again, we can't visualize it. If you've ever noticed Paulhoff's avatar then you have seen a representation of the three dimensional shadow of a four dimensional cube (a hypercube for short) rotating in space. Just as a three dimensional object casts a two dimensional shadow on a surface, a hypercube will cast a three dimensional shadow in three dimensional space. A real hypercube would look like Paulhoff's avatar, but all the line segments would be the same length and all the angles would be 90 degrees.

This inability to visualize higher dimensions (and yes, you can square the hypercube) is the reason that we have to resort to analogies based on two dimensions. This isn't even a new concept. One of the most famous examples being the 1884 book Flatland: A Romance of Many Dimensions by Edwin Abbott Abbott (yes, Abbott squared). It contains a lot of contemporary social satire, but the basic model is still considered very valid. I suggest doing a bit of reading on the subject of flatland in general. You may learn some fascinating things. For example: a sealed cube is actually wide open to four dimensional space, just as a sealed square (at least, so seeming to a Flatlander) is open to three dimensional space.

This is far from a comprehensive explanation, but I think you can get the basic drift from it.

 

[AntiTelharsic]

I don’t agree that non-Euclidean geometry is particularly separated from our everyday experience either. At least not for myself as I have no problem with 3D concepts.

Euclidean geometry is "flat" geometry, and non-Euclidean geometry is "non-flat" geometry, in any dimension, so this was about wacky triangles and not about 3D.

Edited to add...

For instance, your triangle-on-a-sphere really exists in a non-Euclidean 2-space, and we don't need a sphere in 3D in order to deal with it (as suggested in my earlier post about how we can consider just the intrinsic metric properties of a space without needing to embed it in a larger space).

 

[Brian-M]

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.

Isn't that entierly self-referential, or are you trying to make a point that the universe has undergone a sum total of zero acceleration since it was just a singularity?

Or are you saying that we should use the original position of the singularity as a point of reference? This might be a bit hard to do, as the entire universe is the original position of the singularity.

 

[ynot]

Isn't that entierly self-referential, or are you trying to make a point that the universe has undergone a sum total of zero acceleration since it was just a singularity?

No.

Or are you saying that we should use the original position of the singularity as a point of reference? This might be a bit hard to do, as the entire universe is the original position of the singularity.

Yes.

If the Universe has expanded from the singularity then surely it’s spatially larger than the singularity. The Universe would be concentric to the singularity but it would have a greater spacial dimension. Everything that has spatially expanded from the position of the singularity is no longer in the spatial position of the singularity

 

[Hokulele]

If the Universe has expanded from the singularity then surely it’s spatially larger than the singularity. The Universe would occupy the same centre position as the singularity but not the same spatial position.

I think the biggest problem with the way you are approaching this is the use of the word "expanded". Are you thinking of this as being similar to a balloon expanding as it is inflated?


ETA: I quoted you before your edit, and I am too lazy to change it. Hopefully people will figure it out.

 

[ynot]

I think the biggest problem with the way you are approaching this is the use of the word "expanded". Are you thinking of this as being similar to a balloon expanding as it is inflated?


ETA: I quoted you before your edit, and I am too lazy to change it. Hopefully people will figure it out.

Sorry about that. I’m running out of time and am rushing things.

Will be traveling all next week so may not have time to post much.

I'm using "expanded" as becoming spatially larger. Things aren't expanded they are becoming further apart. If this is wrong what is correct?

 

[AntiTelharsic]

If the Universe has expanded from the singularity then surely it’s spatially larger than the singularity. The Universe would be concentric to the singularity but it would have a greater spacial dimension.

It sounds like you're suggesting the existence of points outside the universe; space outside of space. Either that, or you're suggesting that all matter in the universe started at a single point in an already existing space and then started moving away from it. Neither of these is consistent with modern scientific models.

 

[ynot]

It sounds like you're suggesting the existence of points outside the universe; space outside of space. Either that, or you're suggesting that all matter in the universe started at a single point in an already existing space and then started moving away from it. Neither of these is consistent with modern scientific models.

Is an expanding Universe getting spatially larger?

 

[AntiTelharsic]

Is an expanding Universe getting spatially larger?

Yes, but not in the way you seem to be thinking. The "expanding universe" is a four-dimensional object comprising three dimensions of space, and one of time, and that's all there is. It's not expanding into any larger "space", and at the beginning the entire thing occupied the point of the singularity; the singularity was not a point within the thing, but the state of the entire thing itself, from which the entire thing grew. Every point in the universe today was once the same point, and there's no outside.

Edited for clarity.

 

[shadron]

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 - all the "places" possible (that is, all space) is in the singularity at the point of the BB. There are no places outside it.

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.

You don't get it. The universe is all the places that there are. "The very point they all expand from" is all of space, just as your first answer told you. The "stationary center" grew to be all space.

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.

Why the heck not? Analogies aren't woo; they are supposed to be simplifications of some reality into a model that can be better understood. They are not the reality that they stand in for, but they are no more woo than Newton's abstract Law of Universal Gravitation is. The analogies given above are all valid analogies; they merely have deleted one of more dimensions in order to reduce the understanding down to three dimensions that you can easily understand. There is nothing wrong with them as analogies, and your difficulty in comprehension merely means you don't know what an analogy is or what it is for.

The picture here: http://en.wikipedia.org/wiki/File:CMB_Timeline75.jpg is an analogy of the Big Bang and subsequent history in which one spatial dimension is removed in order to show the remaining spatial dimensions and the time dimension (And that is subsequently projected onto the two dimensions of the sheet or screen). It is not inaccurate (or woo) simply because it is an abstraction.

 

[Hokulele]

Sorry about that. I’m running out of time and am rushing things.

Will be traveling all next week so may not have time to post much.

No worries, this is an interesting thread with or without you.

I'm using "expanded" as becoming spatially larger. Things aren't expanded they are becoming further apart. If this is wrong what is correct?

That implies that it is larger relative to something else or relative to surrounding space. Things are becoming further apart, but only relative to each other (in most cases), not relative to some outside standard.

To explain this using a non-spatial dimension, if you were approaching a black hole and I was sitting here watching you, to me, it would appear that you are essentially slowing down. In other words, I would find myself aging at the normal pace (*sigh*), but you wouldn't be. To you, time appears to be running at the same pace it always has. Which is the "correct" time?

In other words, there is no linear universal spatial center, just as there is no linear universal time. It is all relative to your frame of reference. If you do not believe my words, take a look at how GPS receivers work as this time dilation effect is pretty much built into them. There really is some solid evidence to support my claim.

On a positive note, it would be correct to state that you are the center of the universe. As am I.

 

[ynot]

Yes, but not in the way you seem to be thinking. The "expanding universe" is a four-dimensional object comprising three dimensions of space, and one of time, and that's all there is. It's not expanding into any larger "space", and at the beginning the entire thing occupied the point of the singularity; the singularity was not a point within the thing, but the state of the entire thing itself, from which the entire thing grew. Every point in the universe today was once the same point, and there's no outside.
Edited for clarity.

I asked if the Universe is getting spatially larger. I don’t accept time as a spatial dimension. Is the expanding Universe becoming 3 dimensionally larger?

Unless every point in the Universe is still the same point then every point in the Universe must be a different point with a different relative location to all other points.