Question about Cosmology

[Johnny5]

I want to know whether or not the universe has a center of mass. Is there any experimental fact that dictates that the universe must have one?

 

Thank you

[Pangloss]

You may wish to read this thread and check out the corresponding article at Scientific American this month (there's a link to it in that thread):

 

http://www.scienceforums.net/forums/showthread.php?t=9310

 

It may not answer your question directly but you may not need to ask the question anymore after reading some of their disambiguational points.

[Johnny5]

Thank you Pangloss, but my question really wasn't answered.

 

I just want to know whether or not the universe has a center. It exploded into pure vacuum, so I think there is one, but how would you go about proving that it has one experimentally. <-- That's the question I want answered.

 

Thank you

[Severian]

I just want to know whether or not the universe has a center. It exploded into pure vacuum' date=' so I think there is one, but how would you go about proving that it has one experimentally. <-- That's the question I want answered.

[/quote']

 

It really depends how you define 'universe'. In one sense, the universe is the set of measurements that you or I can make. Clearly that set is centered around you or I, so the universe has a centre!

 

However, in more reasonable scientific convention, no the universe has no centre. The Big Bang happened everywhere at once.

[Johnny5]

However' date=' in more reasonable scientific convention, no the universe has no centre. The Big Bang happened everywhere at once.[/quote']

 

I regard this as patently absurd, without any argument for my position whatsoever. I am willing to construct one ad hoc though.

 

Space is infinite. The big bang had a finite amount of energy, and so represented a finite amount of mass. You cannot spread out a finite amount of mass over an infinite amount of space, can't be done.

 

J5

 

If what you said is true, then the density of the universe would be equal to a finite number, divided by an infinite number, which (though it isnt even really a number) would be equal to zero.

[Severian]

I regard this as patently absurd' date=' without any argument for my position whatsoever. I am willing to construct one ad hoc though.

 

Space is infinite. The big bang had a finite amount of energy, and so represented a finite amount of mass. You cannot spread out a finite amount of mass over an infinite amount of space, can't be done.

[/quote']

 

Why does the amount of energy need to be finite? Can you measure it? No you can't - you can measure the energy density but that is not the same thing. In fact, if space-time is infinite (and measurements seem to indicate that it is) then it is unresonable for the energy content not to be infinite too.

[Newtonian]

I regard this as patently absurd' date=' without any argument for my position whatsoever. I am willing to construct one ad hoc though.

 

Space is infinite. The big bang had a finite amount of energy, and so represented a finite amount of mass. You cannot spread out a finite amount of mass over an infinite amount of space, can't be done.

[/quote']

You might like this then.http://www.space.com/businesstechnology/blacklight_power_000522.html

[swansont]

Thank you Pangloss' date=' but my question really wasn't answered.

 

I just want to know whether or not the universe has a center. It exploded into pure vacuum (...)[/quote']

 

I don't think that's a valid representation of the Big Bang.

[Johnny5]

You might like this then.[url']http://www.space.com/businesstechnology/blacklight_power_000522.html[/url]

 

I don't like the hydrino idea, the originator of it has no understanding of physics, he was a doctor, not a physicist. Night and day. I've seen the blacklight thing before, I pay no attention to it, I don't waste my time with it. I am positive that if i were to ask him simple questions, he would get them wrong.

 

But thank you for showing me the link. I don't really see how any of this gets to the heart of the matter though, which is does the universe have a center of inertia or not. Why doesn't anyone seem to 'know' the answer?

 

Regards

[Johnny5]

I don't think that's a valid representation of the Big Bang.

 

Why on earth not? It makes total intuitive sense, it's practically obvious to me now. I guess you could say that in my model, vacuum cannot be created, hence was always there. Using that model of vacuum, it makes sense to say that somewhere in the universe is the center of mass of the universe.

 

Regards

[Johnny5]

Why does the amount of energy need to be finite? Can you measure it? No you can't - you can measure the energy density but that is not the same thing. In fact, if space-time is infinite (and measurements seem to indicate that it is) then it is unresonable for the energy content not to be infinite too.

 

The number of bodies is finite, the inertial mass per body is finite, hence the total inertial mass of the universe is finite, hence the total energy is finite.

 

Regards

[Severian]

The number of bodies is finite' date=' the inertial mass per body is finite, hence the total inertial mass of the universe is finite, hence the total energy is finite.

[/quote']

 

Let's start with the first statement. Why is the number of bodies finite?

[Johnny5]

Why does the amount of energy need to be finite? Can you measure it? No you can't - you can measure the energy density but that is not the same thing. In fact, if space-time is infinite (and measurements seem to indicate that it is) then it is unresonable for the energy content not to be infinite too.

 

What do you mean when you say that space-time is infinite?

 

Regards

[5614]

What do you mean when you say that space-time is infinite?

I can only make an assumption, but I would assume he meant that the universe is infinite, as space-time is (effectively) the universe.

[Johnny5]

I can only make an assumption, but I would assume he meant that the universe is infinite, as space-time is (effectively) the universe.

 

I assume that's what he meant too. But why didn't he just say that 'time' is infinite, without referece to space. That 'time' is infinite is obvious. I interpret that as meaning that relative motion cannot cease. (Newtons laws have this, thermodynamics has this).

 

That time is 'infinite' (really unbounded) can be inferred from very basic observations about the macroscopic behavior of the universe, and here i am treating time separately from space.

 

Aside: That space is infinite is obvious, because we are not enclosed inside some infinite solid shell.

 

I don't mean to quibble, its just that when I read that "spacetime" is infinite, my first thought was, "of course relative motion cannot cease".

 

Regards

[swansont]

Why on earth not? It makes total intuitive sense' date=' it's practically obvious to me now. I guess you could say that in my model, vacuum cannot be created, hence was always there. Using that model of vacuum, it makes sense to say that somewhere in the universe is the center of mass of the universe.

[/quote']

 

The big bang was not an explosion in space, it was an explosion of space - it created space. That's why it happened everywhere at once.

[Johnny5]

The big bang was not an explosion in space, it was an explosion of space - it created space. That's why it happened everywhere at once.

 

Space isn't a tangible thing to be created.

The big bang was most definitely an explosion in space.

 

The reason I am right has to due with the impedance of the vacuum, it's literally zero. And I don't mean electrical impedance, and I don't mean our local vacuum, which isn't a true vacuum.

 

 

Regards

 

PS: If I'm wrong prove it to me.

[Tom Mattson]

Space isn't a tangible thing to be created.

The big bang was most definitely an explosion in space.

 

I agree that space isn't a thing' date=' but your conclusion simply does not follow from that fact. Your view seems to stem from treating space as a container in which physical objects move around in. This view is rooted in the assumption that, if you took the objects away, the containing space would remain.

 

Is that your basic position?

 

The reason I am right has to due with the impedance of the vacuum, it's literally zero. And I don't mean electrical impedance, and I don't mean our local vacuum, which isn't a true vacuum.

 

PS: If I'm wrong prove it to me.

 

You seem to hold a double standard. Your "reason" does not logically necessitate your position, and yet you seem to insist on a proof from anyone who disagrees with it. Why are your bald assertions more acceptable than anyone else's?

[J.C.MacSwell]

I agree that space isn't a thing, ?

 

Why is space not a "thing"?

 

Is space-time a thing?

[Johnny5]

I agree that space isn't a thing' date=' but your conclusion simply does not follow from that fact. Your view seems to stem from treating space as a container in which physical objects move around in. This view is rooted in the assumption that, if you took the objects away, the containing space would remain.

 

Is that your basic position?

[/quote']

 

It most certainly is.

 

Regards

[Johnny5]

You seem to hold a double standard. Your "reason" does not logically necessitate your position, and yet you seem to insist on a proof from anyone who disagrees with it. Why are your bald assertions more acceptable than anyone else's?

 

You are right, that reason doesn't logically necessitate that position. You are absolutely right.

 

Ok I guess I will have to show you my real argument, though I don't want it ridiculed because I like it.

 

Suppose that space could be created. Therefore, points in a coordinate system could move relative to one another. If a point in a coordinate system could move in a coordinate system, then two points in the coordinate system would simultaneously be located at one point in the coordinate system, whence 1=2. Therefore, locations in the vaccum cannot be created.

 

That was my secret argument for maintaining my position.

 

Regards

[J.C.MacSwell]

You are right' date=' that reason doesn't logically necessitate that position. You are absolutely right.

 

Ok I guess I will have to show you my real argument, though I don't want it ridiculed because I like it.

 

Suppose that space could be created. Therefore, points in a coordinate system could move relative to one another. If a point in a coordinate system could move in a coordinate system, then two points in the coordinate system would simultaneously be located at one point in the coordinate system, whence 1=2. [b']Therefore, locations in the vaccum cannot be created.[/b]

That was my secret argument for maintaining my position.

 

Regards

 

I think your conclusion is wrong and one can equal two using the assumptions you proposed.

[Johnny5]

I think your conclusion is wrong and one can[/b'] equal two using the assumptions you proposed.

 

No, one cannot equal two, this has nothing to do with assumptions.

 

My conclusions about the vacuum are reached by using what I might as well call spatio-temporal logic. Logicians are still working out the details of temporal logic, physicists have actually worked out spatio-temporal logic. In a way, that's what reasoning about motion leads to.

 

Regards

[J.C.MacSwell]

No' date=' one cannot equal two, this has nothing to do with assumptions.

 

My conclusions about the vacuum are reached by using what I might as well call spatio-temporal logic. Logicians are still working out the details of temporal logic, physicists have actually worked out spatio-temporal logic. In a way, that's what reasoning about motion leads to.

 

Regards[/quote']

 

2 nickels =1 dime, it's all about assumptions

[Tom Mattson]

Tom Mattson: Is that (edit: the container view of space) your basic position?

 

Johnny5: It most certainly is.

 

That's what I thought. I also think that position is completely untenable.

 

There is no sensible way to talk about locations in space in the absence of physical objects. Take away all physical objects in the universe, and there is no way you can point somewhere and say, "There's where Earth used to be".

 

I think that a much more sensible conception of space is the relational view, which states that space does not exist apart from the spatial relationships which physical objects bear relative to one another. Take away the objects, and you take away their spatial relationship.

 

This is not only more attractive logically, it also has its advantages scientifically, being more in harmony with General Relativity.