Universe expanding...

[Externet]

Hi.

Where in the universe is the point all galaxies, planets, celestial bodies are moving away from in their expansive motion ?   Is that point consistently the one and only same for all constellations ?  Is there any curving/bent trajectory ?

Am sorry for the poor wording.

[swansont]

All points.

Other than local motion, the expansion is there for every point.

[StringJunky]

The 'centre' is wherever the observer is, and every other galaxy not gravitationally bound to their galaxy moves away. The apparent velocity  they move away at increases with distance and causes an increasing redshift.

[Externet]

Thanks.  

Now am done scratching my head...

 If Betelgeuse explodes tomorrow, its 'little bang' will spit matter expanding in all directions away from wherever in the Orion constellation it is today.  That will be its point from where it expands.  How does the "All points" refer to it if you are observing it from planet earth or observing it from Antares at Scorpius ?

[swansont]

An exploding star is not an analogue of the big bang

[beecee]

32 minutes ago, Externet said:

Thanks.  

Now am done scratching my head...

 If Betelgeuse explodes tomorrow, its 'little bang' will spit matter expanding in all directions away from wherever in the Orion constellation it is today.  That will be its point from where it expands.  How does the "All points" refer to it if you are observing it from planet earth or observing it from Antares at Scorpius ?

When Betelgeuse goes supernova, it will simply spew its enriched guts of elements into space. It will in all likelyhood leave a BH in its place, and in the course of time, gravity may condense the enriched guts from the original star, to ignite another generation star.  This is nothing like the BB, which was the evolution of space and time. There was no matter at the BB. 

4 hours ago, StringJunky said:

The 'centre' is wherever the observer is, and every other galaxy not gravitationally bound to their galaxy moves away. The apparent velocity  they move away at increases with distance and causes an increasing redshift.

This is an important point. The only center one can logically speak of with regarding an expanding universe, is the center of one's observable universe as String Junky says, emanating out in all directions from a particular point. This follows from the fact that the BB occurred in all of spacetime, as all of spacetime was confined to within the size of an atomic nucleus. Best analogy is claiming any center on the surface of an inflating balloon...the 2 dimensional surface, representing 4 dimensional spacetime.

[QuantumT]

If the universe has the geometrical shape of a balloons surface, a hollow sphere, does it then have a true vacuum in the middle?

Sorry if my question is stupid, but the shape itself is something I've always wondered about. Please don't downrate me.

Edited February 18, 2021 by QuantumT

[beecee]

29 minutes ago, QuantumT said:

If the universe has the geometrical shape of a balloons surface, a hollow sphere, does it then have a true vacuum in the middle?

Sorry if my question is stupid, but the shape itself is something I've always wondered about. Please don't downrate me.

No stupid questions. The 2D surface of the balloon represents the 3 spatial and 1 time dimension of spacetime. It is an analogy based on the BB, where all of spacetime was squeezed to within the volume of an atomic nucleus...there is no outside to speak of...no inside, no "before time" and no "before space" as we know them. Remember the BB is not a theory on how the universe/space/time started, it is a theory of the evolution of spacetime from t+10-43 seconds...before that, our models and theories fail us.

 

I'm only an amateur at this game though so any errors, or modifications welcome.

Edited February 18, 2021 by beecee

[QuantumT]

3 minutes ago, beecee said:

No stupid questions. The 2D surface of the balloon represents the 3 spatial and 1 time dimension of spacetime. It is an analogy based on the BB, where all of spacetime was squeezed to within the volume of an atomic nucleus...there is no outside to speak of...no inside, no "before time" and no "before space" as we know them. Remember the BB is not a theory on how the universe/space/time started, it is a theory of the evolution of spacetime from t+10-43 seconds...before that, our models and theories fail us.

Thank you! So the universe, as a whole, has no geometry?

[beecee]

1 minute ago, QuantumT said:

Thank you! So the universe, as a whole, has no geometry?

The universe is topologically flat to within small error bars. The balloon analogy explains why we can never claim a center, other then the center of our personal observational universe.

Those small error bars though, may prevent us seeing a closed universe shape...much as a straight line is possible to be an arc of a much larger sphere/circle.

 

or possibly 

https://www.forbes.com/sites/startswithabang/2019/11/23/ask-ethan-could-the-shape-of-our-universe-be-closed-instead-of-flat/?sh=4d41fb32e038

In a hypertorus model of the Universe, motion in a straight line will return you to your original location, even in an uncurved (flat) spacetime. The Universe could also be closed and positively curved: like a hypersphere. A new analysis has challenged our conventional thinking on a flat Universe, but does it hold up under scrutiny?

 

[zapatos]

9 hours ago, Externet said:

Thanks.  

Now am done scratching my head...

 If Betelgeuse explodes tomorrow, its 'little bang' will spit matter expanding in all directions away from wherever in the Orion constellation it is today.  That will be its point from where it expands.  How does the "All points" refer to it if you are observing it from planet earth or observing it from Antares at Scorpius ?

Don't think of the BB as an explosion from a central location as that is not what is happening. Think instead of a loaf of raisin bread. When the bread first begins baking all the raisins are 1 cm apart. As the bread expands every raisin moves further away from the raisins closest to it. It doesn't matter which raisin you are observing this expansion from, all raisins see all the other raisins moving away from it; that is, they all look as if they are in the center of the expansion.

[MigL]

Unfortunately Zap, whenever you use one of these analogies, people always ask "What's the space inside the balloon ?" or " What is the raisin bread expanding into ?"

I would assume that anyone on this forum has a little bit of scientific inclination, and knows how to do an internet search.
Give them the actual explanation; separation between things, at very large scales, is increasing.
And that is happening all through the universe, so there is no inside or outside of an 'expansion'.

 

That last picture you presented of the 'doughnut' shaped universe is more than a little misleading, BeeCee.
A flat sheet of paper cannot be rolled up into that shape in three dimensions.
The inside ( next to the hole ) will have negative curvature, while the outside * large circumference ) will have positive curvature.

A better way to imagine the concept of  a hypertorus is the old Asteroids video game; but it is hard ( impossible ? ) to illustrate in 3D.
The flat video screen is 'rolled up' in four dimensions, such that the top edge identifies with the bottom edge, and independently, the left edge is 'rolled up' to meet the right edge.
In three dimensions you would see spaceships disappear off the right side of the flat screen, and re-appear on the left side.
Similarly for the top and botton edges of the flat screen.

Edited February 18, 2021 by MigL

[zapatos]

55 minutes ago, MigL said:

Unfortunately Zap, whenever you use one of these analogies, people always ask "What's the space inside the balloon ?" or " What is the raisin bread expanding into ?"

 

I agree. However, on occasion I notice a disconnect between an OP and the people attempting to help him. Sometimes (maybe not time, don't want to make assumptions about Externet) a person will ask an elementary school type question and get a grad school type answer which doesn't really help them. Analogies are sometimes just the answer a person was looking for.

Edited February 18, 2021 by zapatos