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MaximT

Is the Earth close to the center of the Universe ?

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Our best scientist claimed that a long time ago. Is this still true?

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Nope it's only the centre of our observation. There is no centre of the universe.

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Just now, MaximT said:

Our best scientist claimed that a long time ago. Is this still true?

Who is "our best scientist"? And where did the they claim this?

The universe, in current models, has no centre.

However, the Earth is the centre of the observable universe, by definition. Every position in space is the centre of the universe observable from that point. (Which is why there is no centre.)

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Ok, now I understand that the light observation, is equal in every direction...

3 minutes ago, Strange said:

Who is "our best scientist"? And where did the they claim this?

Hawking, did, but maybe bad citation, sorry… Did you read his thesis ?

Edited by MaximT

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More often than not they forget to mention Observable universe.

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Invalidated by Planck measurements. The universe is close to flat but universe geometry refers to the geodesic paths not the actual 3d shape. Two parallel beams will neither converge or diverge in a perfect flat geometry  they will converge for positive curvature or diverge in negative curvature.

CMB measurements allows us to test the curvature term

Edited by Mordred

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7 minutes ago, Mordred said:

The universe is close to flat

Base on actual measurement, the surface of that flat universe, would be seriously huge :)

 

image.thumb.png.15b9edd1e0ae22ba425ef64095d8611d.png

Edited by MaximT

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Not if you properly understand what is curved under universe geometry.

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1 minute ago, Mordred said:

Not if you properly understand what is curved under universe geometry.

I do not, could you explain?

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They are referring to spacetime curvature of the freefall paths. In the case of photons it is the null geodesic that becomes curved not the spatial volume.

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17 hours ago, Mordred said:

They are referring to spacetime curvature of the freefall paths. In the case of photons it is the null geodesic that becomes curved not the spatial volume.

Could you please explain what you mean by "In the case of photons it is the null geodesic that becomes curved not the spatial volume" in plain English?  Thank you.

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Think of it this way our observable universe is a sphere. The volume around a star or planet obviously isn't flat or curved. As gravitational potential falls off at r^2. If you were to draw field lines you would end up with the gravitational potential from a centre of mass being spherical for any given value.

So what is really meant by curved or flat spacetime. Obviously we are not describing the potential gravity distribution nor are we talking about a physical shape for lack of a better description.

In essence we are talking about the geodesics and particle paths due to spacetime. Take the statement mass tells spacetime how to curve. Mass is resistance to inertia change. This tells us were dealing with the energy momentum relations under coordinates {ct,x,y,z}.

Now massless particles follow a particular type of geodesic  {null}. In flat spacetime if you took several parallel beams of light those beams will neither diverge or converge. They will remain parallel. Spacetime is flat in this case, however if you took those same beams in curved spacetime the will either converge or diverge. Positive curvature being the former.

Now for a massive falling object. If you take two objects in flat spacetime with equivalent momentum and parallel direction. In flat spacetime those paths will remain parallel.

Now let's use a curved example. Take two objects and drop them from some radius from Earth. As they approach the Centre of mass the distance between the two dropped objects will converge. You have in this example positive curvature. 

So it is the paths taken by objects with momentum that is either straight or curved. (Follows the principle of least action). The geodesics that the object or particle follows is what is described by spacetime curvature. The more curved a path an object must follow the longer the interval will be to arrive at the receiver.

This also applies to the Feymann path integrals. The paths chosen will affect reaction and interaction times. (If you think about that one can better understand aging and how time itself varies). Granted you must include all particle interactions. Helps to remember we give time units of length by describing time as an interval using (ct) the length contraction itself allows c to remain constant while x is the particle vector direction. The length between individual units of x will be determined by how the interval is affected by the gamma factor of the Lorentz transforms.

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On 1/16/2020 at 11:30 PM, MaximT said:

Our best scientist claimed that a long time ago. Is this still true?

 

On 1/18/2020 at 6:46 PM, Mordred said:

 

Snip<  . . . . . . . .So it is the paths taken by objects with momentum that is either straight or curved. (Follows the principle of least action). The geodesics that the object or particle follows is what is described by spacetime curvature. The more curved a path an object must follow the longer the interval will be to arrive at the receiver.............>

I often find myself wondering if there’s an accepted definition for the term ‘taken’ in these contexts. Do we mean something as simple as ‘measured’ ?

Edited by Strange
fixed quotes

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10 minutes ago, Dissily Mordentroge said:

 

I often find myself wondering if there’s an accepted definition for the term ‘taken’ in these contexts. Do we mean something as simple as ‘measured’ ?

In this case, "taken" means the path that the object ... uhm ... takes... I mean "follows" ... or goes along.

We might calculate the path we expect an object to take, or we might measure the path an object takes (to check our calculation). But the object is not measuring it. 

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4 minutes ago, Strange said:

In this case, "taken" means the path that the object ... uhm ... takes... I mean "follows" ... or goes along.

We might calculate the path we expect an object to take, or we might measure the path an object takes (to check our calculation). But the object is not measuring it. 

Fair enough and simple enough. My question I suppose derived from often having the feeling when ‘taken’ is used as reference to a path the writer appears to be implying something like

‘chosen’. But let’s not go there or we’ll be wollowing in a discussion of the quantum and consciousness.

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2 minutes ago, Dissily Mordentroge said:

Fair enough and simple enough. My question I suppose derived from often having the feeling when ‘taken’ is used as reference to a path the writer appears to be implying something like

‘chosen’. But let’s not go there or we’ll be wollowing in a discussion of the quantum and consciousness.

There is the problem that a lot of normal words imply that sort of conscious action, purely because we normally use them for human activity and extend them to inanimate objects by metaphor. And, I suppose, because we say things like "I took the shortest route home" it can imply some sort of choice. But, when it comes to any of the non-biological sciences, such conscious action is never implied.

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IF our universe, or more precisely big bang, was finite in size (IF it has a finite length, width, and depth), then the Earth would have a location relative to the center of the finite-sized universe.  Maybe not the center, but the Earth would have coordinates of x, y, & z axes, measured from the true center of the universe.   Right?

Edited by Airbrush

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On 1/24/2020 at 3:39 AM, Airbrush said:

IF our universe, or more precisely big bang, was finite in size (IF it has a finite length, width, and depth), then the Earth would have a location relative to the center of the finite-sized universe.  Maybe not the center, but the Earth would have coordinates of x, y, & z axes, measured from the true center of the universe.   Right?

Somehow discussions of this nature remind me we’re all in some way only dancing around the deck of the Titanic just before - - - - - - - 

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On ‎1‎/‎23‎/‎2020 at 11:39 AM, Airbrush said:

IF our universe, or more precisely big bang, was finite in size (IF it has a finite length, width, and depth), then the Earth would have a location relative to the center of the finite-sized universe.  Maybe not the center, but the Earth would have coordinates of x, y, & z axes, measured from the true center of the universe.   Right?

Not right.
In your example the finite Universe is 'bounded'.
What happens at the boundary ?
Is there a physical barrier there ?
What keeps the contents of our Universe from escaping into whatever lies beyond ?
If you stick your arm past the boundary, does it go to another Universe ?
Or does it 'extend' our Universe, since Universe means "all there is" ?

A finite, UNBOUNDED Universe, on the other hand, has the properties of a finite size, but no 'edge'.
Somewhat like the Earth's surface ( a 2Dimensional analogy ) is finite, yet you can travel as far as you like without reaching an edge.
Our 3dimensional Universe would be the 'surface' of a 4Dimensional hypersphere ( just one possible model ), where the 'surface' has a 'thickness' which also curves around to meet itself ( yes, 4D is very hard to describe verbally using 3D language ).

The Earth's SURFACE ( not the Earth's volume ) has no center, why would the 'surface' of the hypersphere ?

Edited by MigL

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1 hour ago, MigL said:

Not right.
In your example the finite Universe is 'bounded'.
What happens at the boundary ?
Is there a physical barrier there ?

My example is no more "bounded" than a galaxy is bounded.  My example is a multiverse of big bangs that are separated by much vaster distances than you can imagine.  Each big bang is expanding at billions of times light speed, but they are so far apart that they don't collide (or maybe some do).  There is no boundary at the edge of each big bang.  There is just a fuzzy region that gets less and less dense, like at the edge of a galaxy, until there is a perfect vacuum between big bangs, for googols of light years.  Each big bang has a finite size, although it is expanding rapidly, so you can calculate a center to it at any moment.

Edited by Airbrush

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12 minutes ago, Airbrush said:

My example is no more "bounded" than a galaxy is bounded.  My example is a multiverse of big bangs that are separated by much vaster distances than you can imagine.  Each big bang is expanding at billions of times light speed, but they are so far apart that they don't collide (or maybe some do).  There is no boundary at the edge of each big bang.  There is just a fuzzy region that gets less and less dense, like at the edge of a galaxy, until there is a perfect vacuum between big bangs, for googols of light years.  Each big bang has a finite size, although it is expanding rapidly, so you can calculate a center to it at any moment.

Turtles. It's just another regression series that never ends.

Edited by StringJunky

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18 minutes ago, Airbrush said:

My example is no more "bounded" than a galaxy is bounded.  My example is a multiverse of big bangs that are separated by much vaster distances than you can imagine.  Each big bang is expanding at billions of times light speed, but they are so far apart that they don't collide (or maybe some do).  There is no boundary at the edge of each big bang.  There is just a fuzzy region that gets less and less dense, like at the edge of a galaxy, until there is a perfect vacuum between big bangs, for googols of light years.  Each big bang has a finite size, although it is expanding rapidly, so you can calculate a center to it at any moment.

This sounds something like the "eternal inflation" hypothesis.

I am not sure if each of these "big bang bubbles" you describe are considered to be unbounded or not. 

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On 1/17/2020 at 9:30 AM, MaximT said:

Our best scientist claimed that a long time ago. Is this still true?

As others have informed you, the only centre of any universe, is that of our observable  universe. An Alien on the edge of our observable universe, would also be the centre of his or her observable universe.

It has been shown [MAXIMA, Boomerang, WMAP experiments] that our universe is flat to within small tolerances. That flatness does not give us with any certainty, an answer to the question re the universe being infinite or finite, when we consider exotic geometries like a torus.

Been off grid for a while fellas and a busy little beaver but havn't as yet kicked the bucket!!!

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5 hours ago, beecee said:

havn't as yet kicked the bucket!!!

Yeah, sometimes 'life happens' and you gotta take a break.
Good to have you back.

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