Where Is The Center Of The Big Bang Universe?

[Skeptic Ginger]

The surface of a sphere. The universe.

There two.

Paul

The current thought is the Universe has no boundaries. But it isn't the only possibility.

I object to it being the foregone conclusion as if no other options were possible. But we cannot see the Universe in real time. We are limited by the time it takes to see across the Universe.

 

[Paulhoff]

The current thought is the Universe has no boundaries. But it isn't the only possibility.

I object to it being the foregone conclusion as if no other options were possible. But we cannot see the Universe in real time. We are limited by the time it takes to see across the Universe.

The Universe has no boundaries, to say it does would mean there was something else outside of the universe, so without any other proof of that, the only other possibility is magical thinking, which means, make anything up that you want.

Paul

 

[Skeptic Ginger]

Well, that is the current dogma, Paul. For whatever reason people seem to think if one challenges that assumption it means they don't understand it. I understand it and I challenge it. Unlike god beliefs where there is evidence they are human constructs making the question of the existence of gods not equally yes or no, in the case of whether the Universe is all or is not all, there is not evidence which makes that question weighted more toward yes. We cannot see outside the Universe, but that doesn't provide evidence there is not an 'outside'.

So the burden of proof is not with either proposition over the other.

 

[Skeptic Ginger]

Which is the answer then, if one crossed the Universe with time stopped, would you return to where you left or go on forever? There is no consensus, is there? So how can anyone be certain of the shape/form of the Universe or whether or not it is all there is?

This is not the equivalent of magical thinking because we know that what we can observe is limited. If we could see everything, then speculating there was something else would be magical thinking. But if we know that we cannot see everything, then any speculation there is no more or there is more is equally valid.

 

[Paulhoff]

Well, that is the current dogma, Paul.

I don't see it as a dogma that all, I am open to ideas, but then I know that they are only ideas and not magic.

Paul

 

[Reality Check]

Which is the answer then, if one crossed the Universe with time stopped, would you return to where you left or go on forever? There is no consensus, is there? So how can anyone be certain of the shape/form of the Universe or whether or not it is all there is?

This is not the equivalent of magical thinking because we know that what we can observe is limited. If we could see everything, then speculating there was something else would be magical thinking. But if we know that we cannot see everything, then any speculation there is no more or there is more is equally valid.

The problem is that you cannot cross the universe with time stopped. In order to move you need a velocity. Velocity = change in distance divided by change in time. If there is no change in time then velocity has no meaning and thus movement has no meaning.

If this is a thought experiment then it tells you nothing about the shape of the universe. You instantly get back to where you started or an infinite distance away, there is no path to your movement and no information about the universe through wihich you "travelled".

 

[ynot]

The problem is that you cannot cross the universe with time stopped. In order to move you need a velocity. Velocity = change in distance divided by change in time. If there is no change in time then velocity has no meaning and thus movement has no meaning.

If this is a thought experiment then it tells you nothing about the shape of the universe. You instantly get back to where you started or an infinite distance away, there is no path to your movement and no information about the universe through wihich you "travelled".

But let’s pretend (one of those impossible analogies) that we could travel around the universe with time stopped for everything but us, and we could get an impossible omnipresent view of the universe. We would get a view of the universe in “real time”, as it exists at a particular “instance of existence“. In other words, as it actually exists and not as we observe it time delayed.

 

[sol invictus]

Please give an expample of an actual thing that is finite but has no boundaries.

You were given an 2D example. In 3D, a 3-sphere, a 3-torus, or any other of an extremely large (and not fully characterized) infinite family of compact 3-manifolds. The boundary of any 4-manifold.

I could cut a sentence of yours in half and call it false also. Try reading what I actually posted.


"unless it loops back on itself which I included as one of the three options"

Sorry - I didn't mean to misrepresent what you said. With the next sentence added, the statement is still at best only kind of correct.

Which is the answer then, if one crossed the Universe with time stopped, would you return to where you left or go on forever? There is no consensus, is there? So how can anyone be certain of the shape/form of the Universe or whether or not it is all there is?

We don't know, as I've said many times. Of the three possibilities, the flat universe is the simplest and is also consistent with data, so it's favored.

You can question the assumptions I used to come to the conclusion that there are only three possibilities - and please go ahead, and we can discuss them - but you cannot question the conclusion itself (or if you do, you will be wrong).

The problem is that you cannot cross the universe with time stopped. In order to move you need a velocity. Velocity = change in distance divided by change in time. If there is no change in time then velocity has no meaning and thus movement has no meaning.

If this is a thought experiment then it tells you nothing about the shape of the universe. You instantly get back to where you started or an infinite distance away, there is no path to your movement and no information about the universe through wihich you "travelled".

Actually I disagree with you. While I wouldn't phrase skeptigirl's question quite the way she did, it remains a perfectly valid question.

 

[ynot]

You were given an 2D example. In 3D, a 3-sphere, a 3-torus, or any other of an extremely large (and not fully characterized) infinite family of compact 3-manifolds. The boundary of any 4-manifold.

Are you saying that these are “actual things” that you can provide non-mathematical physical examples of?

 

[sol invictus]

Are you saying that these are “actual things” that you can provide non-mathematical physical examples of?

I don't know what you're talking about, nor am I interested in trying to find out.

 

[Reality Check]

Which is the answer then, if one crossed the Universe with time stopped, would you return to where you left or go on forever? There is no consensus, is there? So how can anyone be certain of the shape/form of the Universe or whether or not it is all there is?

This is not the equivalent of magical thinking because we know that what we can observe is limited. If we could see everything, then speculating there was something else would be magical thinking. But if we know that we cannot see everything, then any speculation there is no more or there is more is equally valid.

My last answer assumed actual physical movement. Perhaps a better answer is:
If the universe has boundaries then crossing the universe with time stopped will result in returning to the starting point.
If the universe does not have boundaries then crossing the universe with time stopped will not result in returning to the starting point.

The theories that we have about the shape/form of the universe (I suggest that you read the Wikipedia article) are:
The local geometry in the observable universe is either flat, spherical or hyperbolic. Observations suggest a flat universe:

Astronomical measurements of both matter-energy density of the universe and spacetime intervals using supernova events constrain the spatial curvature to be very close to zero

So the current local answer is that if one crossed the Universe with time stopped then one would go on forever.

The global geometry of the entire universe is less certain. The local geometry provides constraints on the global geometry but does not determine it.

 

[ynot]

If the universe has boundaries then crossing the universe with time stopped will result in returning to the starting point.

Or reaching a boundary.

 

[sol invictus]

My last answer assumed actual physical movement. Perhaps a better answer is:
If the universe has boundaries then crossing the universe with time stopped will result in returning to the starting point.
If the universe does not have boundaries then crossing the universe with time stopped will not result in returning to the starting point.

You're not using these terms in a standard way, which may be adding to the confusion here.

A manifold with boundary means a space with an edge. For example, a thin disk is a 2-manifold (a 2 dimensional space) with an edge. If you take two disks, puff them out a little, and then glue them together along their edges, you get a 2-sphere (like the surface of the earth). That's an example of a compact (meaning finite area) 2-manifold without boundary.

The same construction works just fine in 3 dimensions. Take a three dimensional solid ball. That has a boundary (a 2-sphere - if the ball is the earth, the boundary is the surface of the earth). So that's a 3-manifold with boundary (it's called a 3-ball, and the thin disk is a 2-ball).

Now take two such balls, and glue them together along their boundary in such a way that their volumes do not intersect (which is obviously impossible in three flat dimensions, but Einstein's theory allows for spacetime curvature, which makes it not just possible but required sometimes). That's a 3-sphere, and it's one of the three possible geometries the spatial universe may have.

 

[MattusMaximus]

But let’s pretend (one of those impossible analogies) that we could travel around the universe with time stopped for everything but us, and we could get an impossible omnipresent view of the universe. We would get a view of the universe in “real time”, as it exists at a particular “instance of existence“. In other words, as it actually exists and not as we observe it time delayed.

This is a big problem... you are viewing time in the classical Newtonian sense of measuring "real" or "actual" time from an absolute reference frame. The problem is that no such reference frame exists, and we know this to be true from modern relativity theory.

This is one of the biggest physics misconceptions ever, and until you and others can get past it you aren't going to make much progress on your understanding of this subject matter.

It's not an insult, just a statement of fact. You have to be willing to understand the physical theories involved instead of relying upon your "common sense" notions of time...

... which are dead wrong.

ETA: To get started on this, I suggest reading this section of the Wikipedia entry on "Time"...

http://en.wikipedia.org/wiki/Time#Time_in_the_physical_sciences

Many people think time is a simple thing, but it isn't. It is very complex, and attempting to insist that the universe behaves according to our "common sense" notions of time is like trying to squeeze blood from a stone.

 

[sol invictus]

This is a big problem... you are viewing time in the classical Newtonian sense of measuring "real" or "actual" time from an absolute reference frame. The problem is that no such reference frame exists, and we know this to be true from modern relativity theory.

Just a minor comment on that: the situation in cosmology is a little different than in special relativity. In cosmology the standard assumption (which is well-motivated by data) is that the universe is homogeneous and isotropic in space.* But that assumption requires there be a special, preferred reference frame - namely the one in which the constant time slices are homogeneous and isotropic. (An observer at rest in that frame, as the earth nearly is, is said to be comoving with the Hubble flow.) Given that the universe picks a preferred time coordinate for us, it's perfectly reasonable to ask what the geometry of the space transverse to that time coordinate is.


*It is not homogeneous and isotropic in spacetime - such spacetimes are called maximally symmetric and do not have big bangs or any non-trivial cosmological evolution. Put another way, our universe is not Lorentz invariant - only the vacuum (completely empty space) is Lorentz invariant on large scales.

 

[RecoveringYuppy]

But that assumption requires there be a special, preferred reference frame - namely the one in which the constant time slices are homogeneous and isotropic. (An observer at rest in that frame, as the earth nearly is, is said to be comoving with the Hubble flow.) Given that the universe picks a preferred time coordinate for us, it's perfectly reasonable to ask what the geometry of the space transverse to that time coordinate is.

I was hoping someone would pick apart this post. Does it make sense to imagine a coordinate system where time is measured by a system of clocks that each continuously observe the CMB as isotropic? And is that similar to what you are describing?

 

[ynot]

This is a big problem... you are viewing time in the classical Newtonian sense of measuring "real" or "actual" time from an absolute reference frame. The problem is that no such reference frame exists, and we know this to be true from modern relativity theory.

This is one of the biggest physics misconceptions ever, and until you and others can get past it you aren't going to make much progress on your understanding of this subject matter.

It's not an insult, just a statement of fact. You have to be willing to understand the physical theories involved instead of relying upon your "common sense" notions of time...

... which are dead wrong.

ETA: To get started on this, I suggest reading this section of the Wikipedia entry on "Time"...

http://en.wikipedia.org/wiki/Time#Time_in_the_physical_sciences

Many people think time is a simple thing, but it isn't. It is very complex, and attempting to insist that the universe behaves according to our "common sense" notions of time is like trying to squeeze blood from a stone.

Actually I’m not viewing time at all. In fact I’m taking a theoretical omnipresent view of the universe completely without time. By “real time” I meant as opposed to “delayed time”. I observe my hand in “real time” (virtually as it is). I observe a distant star in “delayed time” (as it was). To put it another way, an omnipresent view would observe everything in the universe occurring at the same time (hand and star simultaneously as they are). Perhaps I should have said “no time”.

Thanks for the link but I've already read the page several times before.

 

[steenkh]

I can understand that the universe can be finite and without boundaries, but I cannot understand that the universe can be finite, without boundaries and flat. It seems to me that a flat universe needs to be infinite.

There is also the question of the finite amount of matter in the the universe: If we could travel infinitely in one direction, and still encounter matter at every stage on the way, there has to be an infinite amount of matter, or we would have encountered the same matter twice, which should be impossible in a flat universe.

What is wrong in my reasoning?

 

[sol invictus]

I can understand that the universe can be finite and without boundaries, but I cannot understand that the universe can be finite, without boundaries and flat. It seems to me that a flat universe needs to be infinite.

It is, normally. Of the three standard cosmologies, it's only the closed universe that's finite.

However (and this is not standard, but it's perfectly consistent) one can take the flat universe and "compactify" each of the three spatial directions independently. That gives you something called a 3-torus.

Ever play a video game where, when you go off the edge of the screen, you wrap around and appear on the opposite side? That's a 2-torus - a 2D analogue of a 3-torus, and both a 2 and 3-torus are flat in the sense that they have zero spatial curvature. Put another way, unlike a flat map of the earth, there is no distortion or stretching when you represent the 2-torus in that video game using a flat screen.

 

[Paulhoff]

If we could travel infinitely in one direction, and still encounter matter at every stage on the way, there has to be an infinite amount of matter, or we would have encountered the same matter twice, which should be impossible in a flat universe.

What is wrong in my reasoning?

First, the universe is no longer flat, it is an open system, it is speeding up has of about 9 billion years ago.

http://www.sciencenews.org/articles/20000212/bob1.asp

Paul