A centre of mass of the Universe.

[geordief]

2 hours ago, Mordred said:

Think of it this way, Our Observable universe. Key note our observable portion of the universe originated at a point smaller than an atom. However this is just the portion that makes up our Observable portion of the universe today. Now here is the trick that smaller than an atom portion now makes up the entirety of our observable universe today. We reside within that portion and everywhere we look we see within that portion. So that original smaller than an atom is our entire observable universe today. The only centre is the center of our observable portion but how much bigger the rest of the universe is we do not know. We can only measure our observable universe and never beyond it. However we are certain there is a much larger universe we can never see or measure. We can also tell it must have similar conditions in mass density to our own observable portion due to the way a homogeneous and isotropic expansion occurs.

homogeneous no preferred location ie a centre.

isotropic no preferred direction.

An explosion has a specific dynamic in that it radiates from a centre outward. this is inhomogeneous and anistropic. However measurements on how galaxies expand from one another shows no preferred direction to expansion rather it is simply a density decrease in all directions equally.

Now  center of mass. In a homogeneous and isotropic volume where the mass density is uniform, one can choose any arbitrary location. Then measure around that point and measure the same amount of mass surrounding every location. No location will have a higher gravitational potential than any other location, so one can arbitrarily choose any location as a center of mass as there is no difference between any other location in potential strength. Ie there is no discernable center of mass which would be a location of higher potential.

Is there any upper limit on the ratio of the size of the unobservable universe to that of the observable universe?

Would there be any theoretical consequences if it was infinite?

 

Can the size of this infinitely sized overall body  have an origin  which is infinitely small or it this "point smaller than the atom" some kind of a lower limit for the "origin"?

Edited June 26, 2018 by geordief

[Airbrush]

On ‎6‎/‎24‎/‎2018 at 8:43 AM, studiot said:

Think about the definition and properties of a centre of mass then come back and ask again.

IF the big bang is homogeneous and isotropic, and has a finite size (even an irregular shape), then the center of the finite size should be roughly the center of mass.  Why not?

[studiot]

1 hour ago, J.C.MacSwell said:

The present day observable universe, however you choose define it, would have a COM. Your (admittedly our) difficulty defining it, or keeping track of it, does not change that. Unlike the Universe, it conceptually would have a COM.

Why do you think it has ceased to exist? Conservation of mass and energy...the equations are different but the same principles apply in relativity as they do in Newtonian physics.

 

Quote

The present day observable universe, however you choose define it, would have a COM.

it conceptually would have a COM.

 

Unsubstantiated and therefore empty claims.

 

Quote

Unlike the Universe, it conceptually would have a COM.

 

You therefore agree that the Universe has no COM?

 

Quote

Your (admittedly our) difficulty defining it, or keeping track of it, does not change that. 

I have no difficulty defining it. I just agree that there is no COM for the observable universe either, or rather that it has no meaning.

 

No matter how small the distance of observation away, the observation take finite time to arrive so refers to the past.

I cannot observe any part of the rest of the universe in my present.

So the entire observable universe is always in the past.

Quote

Why do you think it has ceased to exist?

I don't necessarily but it would become a matter of blind faith not Science to believe it exists, before the event.

I can never prove it.

[geordief]

Is there any purely linguistic merit in (for discussions involving the universe) the use of the present tense was actually  outlawed (except for subjective purposes such as "I am right" ) since, as Studiot says  all events occur in the past?

 

So , for example the sun is not 8 light minutes away it was  whatever it was 8 minutes ago.

[taeto]

This confuses me too. It is said that the universe is 13.8B years old since BB, and the radius of the observable part is about, what, 46B light years now. So it is right to say that if you assign time t=0 to our present location, then you assign t=0 to points at the border of the observable universe as well, by saying that they have moved there "by now"? Why is it then not simply a matter of integrating density over space at time t=0 to figure out the center of gravity of the observable universe as it is "now"? What am I missing? 

[Endy0816]

Space in the Universe could loop back on itself. There would be a finite volume but no center to it.

[studiot]

3 minutes ago, taeto said:

This confuses me too. It is said that the universe is 13.8B years old since BB, and the radius of the observable part is about, what, 46B light years now. So it is right to say that if you assign time t=0 to our present location, then you assign t=0 to points at the border of the observable universe as well, by saying that they have moved there "by now"? Why is it then not simply a matter of integrating density over space at time t=0 to figure out the center of gravity of the observable universe as it is "now"? What am I missing? 

 

Ah a mathematician has noted what it says in the equations I quoted.

Integrating density over space.

But since we observe matter fleeing from us at fantastic velocities, how would me measure this 'space' relativistically and how would we assign values to the 'density'?

[taeto]

30 minutes ago, studiot said:

Integrating density over space.

But since we observe matter fleeing from us at fantastic velocities, how would me measure this 'space' relativistically and how would we assign values to the 'density'?

So this is not trivial because "density" depends on the frame. We observe an amount of matter in dilated space appearing very dense if it moves away fast? Then there could be two different measures applied to density. A "relative" measure, where we calculate the amount of matter per unit of space in our frame. Or an "absolute" measure in which we calculate the amount of matter per space in the local frame that moves with it. If we know the speed of each receding point, and assuming that the local density is known, then it should not seem that hard. For each point in space, we get a density either way, and we can integrate?

Edited June 26, 2018 by taeto

[J.C.MacSwell]

1 hour ago, studiot said:

 

 

Unsubstantiated and therefore empty claims.

 

 

You therefore agree that the Universe has no COM?

 

I have no difficulty defining it. I just agree that there is no COM for the observable universe either, or rather that it has no meaning.

 

No matter how small the distance of observation away, the observation take finite time to arrive so refers to the past.

I cannot observe any part of the rest of the universe in my present.

So the entire observable universe is always in the past.

I don't necessarily but it would become a matter of blind faith not Science to believe it exists, before the event.

I can never prove it.

To the bold yes. For reasons I have stated in all my posts in this thread.

Everything else is also my (correct I believe) interpretation of current understanding and I don't believe any of it is controversial.

If you can define a observable universe as a system it would have a COM.

I cannot observe any part of the Universe in my present but I don't take it as blind faith that the Sun still exists. I guess we will know for sure in 8 minutes whether it does/did. We will never have the same certainty about the observable universe but the principles are the same.

Edited June 26, 2018 by J.C.MacSwell

[studiot]

29 minutes ago, taeto said:

So this is not trivial because "density" depends on the frame. We observe an amount of matter in dilated space appearing very dense if it moves away fast? Then there could be two different measures applied to density. A "relative" measure, where we calculate the amount of matter per unit of space in our frame. Or an "absolute" measure in which we calculate the amount of matter per space in the local frame that moves with it. If we know the speed of each receding point, and assuming that the local density is known, then it should not seem that hard. For each point in space, we get a density either way, and we can integrate?

 

Not only that but you have to surmount the issue of when you measure the density and volume.

This is non trivial as it involves establishing relativistic simultaneity.

 

But also note one more thing from the equations.

Whilst the density may be susceptible to a local solution as a limit, the definition also involves multiplication by the 'moment' arm which includes terms the size of the Universe, and are clearly going to be subject to substantial relativistic effects.

 

J.C. MacSwell, Does this not also answer your query?

[J.C.MacSwell]

19 minutes ago, studiot said:

 

Not only that but you have to surmount the issue of when you measure the density and volume.

This is non trivial as it involves establishing relativistic simultaneity.

 

But also note one more thing from the equations.

Whilst the density may be susceptible to a local solution as a limit, the definition also involves multiplication by the 'moment' arm which includes terms the size of the Universe, and are clearly going to be subject to substantial relativistic effects.

 

J.C. MacSwell, Does this not also answer your query?

My understanding (again using that term) Is that there is an established way to do this, such that expansion effects can be set aside. (So Now is 14ish billion years ago here but also at the edge of the observable universe, regardless of how long the em radiation might take to here)

I'm not sure what query you are referring to. We seem to disagree in principle whether a COM of a system of finite size but less than the Universe is definable.

[taeto]

47 minutes ago, studiot said:

Not only that but you have to surmount the issue of when you measure the density and volume.

This is non trivial as it involves establishing relativistic simultaneity.

      I thought that simultaneity is taken into account by specifying that the measurement is taken "now", at time t=0. Which is when you look at your watch right now, and when the boundary of the observable universe is 46B LYs distant. The integral is taken over all points in spacetime that have the same value t=0. Yes, at that time you can measure density as what it is locally ( which would seem sensible), or what it looks like from our frame.

     Density and volume could be more of an issue, since volume decreases with distance, density creeps up. Possibly the density integral diverges.

[Mordred]

4 hours ago, geordief said:

Is there any upper limit on the ratio of the size of the unobservable universe to that of the observable universe?

Would there be any theoretical consequences if it was infinite?

 

Can the size of this infinitely sized overall body  have an origin  which is infinitely small or it this "point smaller than the atom" some kind of a lower limit for the "origin"?

Beyond our observable portion, its all conjecture. If one were to take the ever so slight curvature term and halt expansion. The math supports a possibility that a light ray would take 880 Billion years to arrive back at the origin. However that is only based on the ever so slight curvature term. There is no affect whether the universe is finite or infinite in terms of expansion or how our Observable universe evolves. Expansion is best described as a reduction in density, as the volume increases.

Its unknown how small the entire universe could feasibly start at  in the origin however no finite quantity can become infinite. So if the universe is infinite now then it will always be infinite in the past.

[Neil Obstat]

5 hours ago, studiot said:

 

 

Unsubstantiated and therefore empty claims.

 

 

You therefore agree that the Universe has no COM?

 

I have no difficulty defining it. I just agree that there is no COM for the observable universe either, or rather that it has no meaning.

 

No matter how small the distance of observation away, the observation take finite time to arrive so refers to the past.

I cannot observe any part of the rest of the universe in my present.

So the entire observable universe is always in the past.

Quote

J.C. MacSwell said:

Why do you think it has ceased to exist. Conservation of mass and energy...

I don't necessarily but it would become a matter of blind faith not Science to believe it exists, before the event.

I can never prove it.

Whoever designed this platform needs to get medical help. This is a nightmare. It's impossible for me to post what I want to say. I can't quote members AS THEY POSTED. The platform simply won't allow accurate quotes. It's like the system is set up to PREVENT intelligent discussion. I got a message saying my browser won't allow copy and past like that. Then the tab went blank and I had to open a new tab. This thread is moving very quickly and it's hard to keep up with it especially when I have to take all this time to post something that the system doesn't allow me to post.

Now I can't remember what I was going to say! 

Studiot, I hear you saying you can't prove that (some part of?) the historical universe (which existed in the past?) no longer exists, and it would be "a matter of blind faith not Science to believe it exists, before the event." What event? Is the "event" to which you refer "the present?"

The topic seems to be too abstract for this retarded platform to allow any reasonable discussion of it. The website is obstructing the conversation. 

The FINAL STRAW is when I try to post a reply to another person (Mordred, below) and the system merges my post with this one, such that anyone quoting this whole post will get my two different replies WITHOUT any indication that I was talking to two different people. The conversation is thereby DESTROYED with confusion, because I'm not saying to Mordred what I was saying to studiot and I am not saying to studiot what I was saying to Mordred.

 

1 hour ago, Mordred said:

It's unknown how small the entire universe could feasibly start at in the origin, however no finite quantity can become infinite. So if the universe is infinite now then it will always be [did you mean to say, "it has always been?" (present perfect tense)] infinite in the past.

All right, maybe I can deal with this much.

You said, "no finite quantity can become infinite," therefore, since the essence of the "big bang" says the entirety of the known universe was contained in a volume smaller than the nucleus of an atom, that seems to be obviously a finite entity, does it not? And since it (as it were) began as a finite entity it must continue to remain a finite entity. Consequently, the universe as it exists now and as it will ever exist in the future is equally finite as it has always been, from the beginning.

 

Edited June 26, 2018 by Neil Obstat

[studiot]

36 minutes ago, Neil Obstat said:

Whoever designed this platform needs to get medical help.

I think you have cracked it.

The designer went to get medical help and they wouldn't let him back.

I can tell you that it got worse when windows 10 came out.

 

[Neil Obstat]

5 minutes ago, studiot said:

The designer went to get medical help and they wouldn't let him back.

So the nice young men in their clean white coats came to take him away? Ha-ha? 

(They're coming to take me away, ho-ho he-he ha-ha, to the Funny Farm - where life is beautiful all the time, and I'll be happy to see those nice young men in their clean white coats and they're coming to take me away, ha ha...)

 

[beecee]

10 hours ago, Neil Obstat said:

Thank you for your reply, beecee. I'm having a hard time understanding this material. I hope you can help me! 

Please forgive me for changing the emphasis of your post I'm quoting here, because I'd like to focus on words other than the ones you had in bold and it got too messy that way.

You said, "...all of what we can know that existed, existed in a volume smaller [than] an atomic nucleus." However, you also said, "It is wrong to view the BB as an explosion emanating from any one point...," therefore, interpreted, you are distinguishing with the greatest possible emphasis between a volume smaller than an atomic nucleus and any one point, correct?

I'm sorry, but that seems to be a very clear contradiction. If you don't think it is a contradiction, can you explain why you think it's not a contradiction? 

Don't be sorry, I'm only an amateur at this game. The first thing though that I will say is read carefully the post that followed yours above by Mordred.

What I'm trying to say above is that the BB happened everywhere at once but applies to the observable portion only. As a whole though, the observable universe/spacetime is all  we can be aware of. The following may also help in understanding..... http://www.astro.ucla.edu/~wright/infpoint.html

Worth noting also that the term BB, was applied by an otherwise great astronomer named Fred Hoyle in his attempt at derision. Perhaps the BB would be better described as the big stretch.

And of course the one as yet unknown factor is whether the universe/spacetime as a whole is finite or infinite.

Edited June 26, 2018 by beecee

[J.C.MacSwell]

1 hour ago, Neil Obstat said:

 

 

All right, maybe I can deal with this much.

You said, "no finite quantity can become infinite," therefore, since the essence of the "big bang" says the entirety of the known universe was contained in a volume smaller than the nucleus of an atom, that seems to be obviously a finite entity, does it not? And since it (as it were) began as a finite entity it must continue to remain a finite entity. Consequently, the universe as it exists now and as it will ever exist in the future is equally finite as it has always been, from the beginning.

 

The known universe referred to (obviously not known at that time LOL, it's the known now as it was then) was, and therefore still is finite.

The remainder of the Universe may have been finite, or may not have been. We don't know, but the model says it would have expanded like the known part appears to have, so it would remain finite or infinite, as the case may be.

[studiot]

41 minutes ago, J.C.MacSwell said:

, "no finite quantity can become infinite,"

Why not?

Edit

Wrongly attributed to J.C. MacSwell 

Edited June 26, 2018 by studiot

[J.C.MacSwell]

21 minutes ago, studiot said:

Why not?

I didn't actually say what you just quoted me as saying, but I am assuming it is based on multiplication, not addition.

It was originally stated by Mordred and I believe it is correct in context of expansion.

Edited June 26, 2018 by J.C.MacSwell

[Neil Obstat]

34 minutes ago, J.C.MacSwell said:

The known universe referred to (obviously not known at that time LOL, it's the known now as it was then) was, and therefore still is finite.

The remainder of the Universe may have been finite, or may not have been. We don't know, but the model says it would have expanded like the known part appears to have, so it would remain finite or infinite, as the case may be.

Perhaps this conversation is a kind of "big bang" inasmuch as it could go on forever...

If the known universe had a beginning, and at that time it was unknown since there was no one around to know it yet, therefore, the unknown and the known were one and the same thing. If the unknown and the known began as one thing they would consequently continue as the same thing, since what they were was as it was when it was, as it were.

And it would remain as it was when it was, at any time in the future, when the future would refer back to its former existence, as we are doing now.

But then you have: "the remainder of the Universe may have been finite, or may not have been." This would seem to apply to the remainder of the Universe which would not have been included in the "entirety of the universe as we know it," which had been contained in a volume smaller than the nucleus of an atom "at least as far back as t+10^-43 seconds," in other words, the entirety of the universe as we know it did not include the remainder of the Universe. Correct?

 

2 hours ago, Mordred said:

Its unknown how small the entire universe could feasibly start at  in the origin however no finite quantity can become infinite. So if the universe is infinite now then it will always be infinite in the past.

Dear studiot, that was Mordred saying, "no finite quantity can become infinite," and then it was the retarded platform that put his words in someone else's mouth or whatever. 

This stuff is hard enough to keep straight, without being unsure of who said what when someone else was quoted. And of course, my replies were merged. Again.

Is this retarded platform designed to chase away members? (And They're coming to take me away Ha Ha They're coming to take me away hoho he he ha ha to the funny farm where life is beautiful all the time, and I'll be ...)

 

Edited June 26, 2018 by Neil Obstat

[J.C.MacSwell]

2 minutes ago, Neil Obstat said:

Perhaps this conversation is a kind of "big bang" inasmuch as it could go on forever...

If the known universe had a beginning, and at that time it was unknown since there was no one around to know it yet, therefore, the unknown and the known were one and the same thing. If the unknown and the known began as one thing they would consequently continue as the same thing, since what they were was as it was when it was, as it were.

And it would remain as it was when it was, at any time in the future, when the future would refer back to its former existence, as we are doing now.

But then you have: "the remainder of the Universe may have been finite, or may not have been." This would seem to apply to the remainder of the Universe which would not have been included in the "entirety of the universe as we know it," which had been contained in a volume smaller than the nucleus of an atom "at least as far back as t+10^-43 seconds," in other words, the entirety of the universe as we know it did not include the remainder of the Universe. Correct?

 

That would be correct. Your entire body but for your left foot doesn't include your left foot, but it doesn't mean your left foot is not part of your body.

[studiot]

12 minutes ago, Neil Obstat said:

 

 

Dear studiot, that was Mordred saying, "no finite quantity can become infinite," and then it was the retarded platform that put his words in someone else's mouth or whatever. 

This stuff is hard enough to keep straight, without being unsure of who said what when someone else was quoted. 

 

Yes, I apologise to J.C. MacSwell, I have just found it.

But to whoever said it I still ask the question why not?

Edited June 26, 2018 by studiot

[J.C.MacSwell]

1 minute ago, studiot said:

Yes, I apologise to J.C. MacSwell, I have just found it.

But to whoever said it I still ask the question why not?

It was originally stated by Mordred and I believe it is correct in context of expansion.

[studiot]

Again I say why not?

Have you considered Gabriel's horn?