FlatEarth":3bl2jac8 said:
And so we have come full circle! The idea that we need a force or energy to drive expansion is what I believe to be incorrect.
You keep confusing expansion, which was one of the initial conditions of the Big Bang, with
accelerating expansion, which requires a separate cause. I am talking about the
acceleration of that expansion, which is the reason dark energy is required.
FlatEarth":3bl2jac8 said:
Analogous to gravity not actually being force but a distortion in space-time, the expansion of space-time is not force-driven. Remember that the galaxies are really not moving through space but are more or less in a fixed position as space-time expands around them, and this expansion is always accelerating. Einstein was right to drop the c constant!
I see where you are going wrong now - you misunderstand what accelerating expansion means. Do you think it is the fact that the further away a galaxy is, the faster it is receding, means the expansion is accelerating? If so, you are incorrect!
The increase in recession speed with distance comes from expansion, whatever the expansion is doing, even if it is decelerating.
Let's make a model.
Now to model an expanding space we need to assign coordinates within that space. For the moment, forget about any edges to that space, we don't need edges, we just need coordinates in order to measure the expansion of space. Galaxies come later, so for now just imagine a 3 dimensional grid. At each grid intersection we will assign a coordinate, a point, a dot. Let's say each intersection point is 1 meter apart.
Put yourself on a point somewhere in this space. Whatever axis you look along you see neighbouring points 1, 2, 3, 4, 5 etc meters away, receding off into the distance. Then we introduce some expansion. Let's say the space grows to 10 times its original size in 1 second! That seems fast perhaps, but this is just a model with easy numbers. The key thing to remember is that
the grid expands with the space.
So, here we are, still sitting on our point (but it could have been any point) 1 second later. Now lets look along an axis. We see those neighbouring points are now 10, 20, 30, 40, 50 etc meters away. The space increased to 10 times its original size, and so did the distance between each intersection point on that grid.
Our nearest neighbouring point has receded from 1 to 10 meters in 1 second, so it has receded at 9 meters per second. The next point away has receded from 2 to 20 meters in 1 second, so that point receded at 18 meters per second. The fifth point has moved from 5 to 50 meters away in 1 second, so that one has receded at 45 meters per second. The further away you look, the faster a point will seem to have receded!
And
the view would be the same, whatever viewpoint you choose in the grid! There is no "centre" of expansion, no origin point within that grid - the whole thing, the whole space has expanded from something where the spaces between things were really small to something where the spaces between things are much larger. The expansion of that space has carried matter and energy along for the ride.
Remember I said the grid of points receded off into the distance.. well a point that was initially 33,000,000 meters away will have moved away to 330,000,000 meters in 1 one second, meaning that it has receded at 300,000,000 meters per second - the speed of light! Any point initially more distant than 33,000,000 meters away from another point will have receded from that point faster than the speed of light. That is the distance were an object recedes at light speed in this "little" model of expansion. If you look at a point that has receded at the speed of light, then from that point, the point
you are on has receded at the speed of light. But no object would be moving through space faster than light, no photon would ever overtake another photon, it all just gets carried along by the cosmic flow.
The above simply describes a constant rate of expansion. The further away you look, the faster an object recedes, and the relationship is linear.
Now then, if the rate of expansion were to be accelerating, then we would observe those closer grid boxes would be getting slightly larger, compared to the distant ones. Put into normal terms, it was the observation that as we looked at
closer and closer supernovae, they were further away than we thought they should be, relative to the distant supernovae, if the expansion were still decelerating like we had originally thought. This is because we see the distances between the distant objects as they were before the acceleration started, 5 billion years ago. The relationship is not linear, as the rate of expansion has changed.
In an expanding universe, the further you look the faster an object recedes. If that expansion is accelerating, the closer you look, the further away an object would be in relation to where it should be if the rate had remained constant. If you plot the recession speeds, with constant expansion the line is straight, with decelerating expansion the line curves one way and with accelerating expansion it curves the other. But the recession speed is always increasing along that line, in all three cases.
I hope this clears up the big difference between increasing recession speeds over distance, and the acceleration of the expansion.
FlatEarth":3bl2jac8 said:
SpeedFreek":3bl2jac8 said:
A universe infinite in extent is still one of the valid possibilities, but most cosmologists tend towards a universe that is finite but has no edge, like the 3-Torus.
This is the universe I picture when stating that it has a center. I never said we could find that center!
Whether I am right or wrong on either point, I think it's important that the scientific community continues to challenge and question what has become accepted as indisputable fact. Perhaps experiments at the LHC will uncover new evidence that will force some of these pillars of truths to be reconsidered. Whatever happens, God I hope they don't find dark energy! :shock:
The "geometric" centre of the 3-Torus is in a different dimension! All we are concerned about is the three-dimensional surface of that torus, which has no edge or centre. Wrap my grid model from above onto the surface of that 3-Torus and hopefully you will see what I mean. No part of our universe is in the hole in the centre of the Torus - it is a four dimensional shape!