Science Fiction

[danot]

Also, the time traveller wouldn't be able to travel back to time before the first journey by all accounts. Recall hearing it somewhere.?

[woolyhead]

So what, Cyclone? You either quoted or said "the centre we observe is not really the true centre." Are you/he talking about small differences now, differences between the true centre and the one we observe? Either way we are not at the centre of the universe, like I said. So why would we see the point of creation in whichever direction we look?

Edited March 15, 2019 by woolyhead

[woodview]

50 minutes ago, woolyhead said:

So what, Cyclone? You either quoted or said "the centre we observe is not really the true centre." Are you/he talking about small differences now, differences between the true centre and the one we observe? Either way we are not at the centre of the universe, like I said. So why would we see the point of creation in whichever direction we look?

in my very limited understanding, there is no centre, but anywhere could be considered the centre, as an observer at that point. In the same way the surface of a sphere has no central point, all points are at an equal distance from it.

[woolyhead]

If you say that being at the centre of a circle is the same as being at the centre of the universe then you are assuming that we are at the centre, aren't you.  Where's the reasoning that leads to that? Of course. we know the universe has 3 special dimensions, unlike a circle but let's leave that aside for now. If you were a theoretical, lone  observer outside the universe where would you see us to be, at the centre? Why so? 

[woodview]

39 minutes ago, woolyhead said:

If you say that being at the centre of a circle is the same as being at the centre of the universe then you are assuming that we are at the centre, aren't you.  Where's the reasoning that leads to that? Of course. we know the universe has 3 special dimensions, unlike a circle but let's leave that aside for now. If you were a theoretical, lone  observer outside the universe where would you see us to be, at the centre? Why so? 

Not a circle, the surface of a sphere. The surface of a sphere has no central point, because of it's curvature. That is how space is supposed to be. But that's the end of my limited grasp.

I believe the expansion is from all points too, not from a 'central' point. I.e the big bang wasn't like a conventional explosion. It was an explosion from all points outwards, and that is the expansion now too.

[woolyhead]

The surface of a sphere has only two dimensions but if you draw a point somewhere on it you can see that other points are at various, different distances from your point,  But a sphere has three dimensions and a centre and all points on its surface are at the same distance from it.  So now the radius of the sphere is increasing as the universe expands. Why does that mean that there is no centre of the universe? The centre of the sphere is still there in your simile. 

[ANGELFIRE1]

Whoooooooooooooosh, the sound of this post flying over my head.

 

Angel1.

[apelike]

This may help understand the sphere/balloon analogy.

 

http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html

 

 

[Cyclone]

55 minutes ago, woolyhead said:

The surface of a sphere has only two dimensions but if you draw a point somewhere on it you can see that other points are at various, different distances from your point,  But a sphere has three dimensions and a centre and all points on its surface are at the same distance from it.  So now the radius of the sphere is increasing as the universe expands. Why does that mean that there is no centre of the universe? The centre of the sphere is still there in your simile. 

If the universe at some point expanded faster than the speed of light, then wherever you happen to be within it, it always appears to be the centre.  That's it.  Simples.

Assuming that the expansion was linear.

[woodview]

1 hour ago, woolyhead said:

The surface of a sphere has only two dimensions but if you draw a point somewhere on it you can see that other points are at various, different distances from your point,  But a sphere has three dimensions and a centre and all points on its surface are at the same distance from it.  So now the radius of the sphere is increasing as the universe expands. Why does that mean that there is no centre of the universe? The centre of the sphere is still there in your simile. 

It's an analogy of the accepted state of the universe. I cant explain because it's on the limit of my grasp.

The surface of a sphere is however 3d not 2d. Forget about it being a ball with a centre, the anology is related to the surface. But as mentioned above, google it, because I can't explain. Just remember lots of it is not 'common sense' because the concepts are beyond the realms of our experience.