Starship Asterisk*

Chris Peterson wrote:So, from the instant of the Big Bang to now, nothing is moving very much, nothing was propelled, nothing felt any forces from the Big Bang.

Chris Peterson wrote:Let's go back to the balloon analogy. The universe is the surface of the balloon, so this is a 2D universe we are considering. You can stick little dots all over the surface to represent galaxies. As the balloon expands, these galaxies are getting farther apart. But are they moving? You could argue that they are not. If you were perched on one of those dots, you'd feel no forces in the plane of your universe. No acceleration, even if the expansion rate was not uniform. Of course, from our vantage point we understand that you'd feel a force in what we'd call the vertical or radial direction... but that direction isn't accessible to those living on the balloon, because they only perceive two dimensions. And if you look at what direction the dots are actually traveling, it isn't a direction along the surface, but is in a straight line away from the center of the balloon- a point that isn't even in that spatial universe.

Now, if you can, extend the analogy to our own Universe. We inhabit the 3D surface of a 4D universe. Distant objects aren't really moving with respect to each other (except in a minor, non-cosmological way). What's happening is that the Universe is expanding, and all these essentially stationary objects are staying in place. The only direction anything is moving is away from the 4D center of the Universe- the point where t=0. We are moving on the radial (time) axis of the Universe. We don't feel any forces on this axis. We can't see along this axis ("outward", the direction we are expanding, is the future; "inward", the direction we came from, is the past).

So, from the instant of the Big Bang to now, nothing is moving very much, nothing was propelled, nothing felt any forces from the BB.

dougettinger wrote:I am trying to enhance your balloon analogy. The 3D surface that you refer to can be considered as the skin of the balloon that has a thickness of the "observable" universe. If not for gravity, all matter inside this 3D surface would be expanding uniformly. We do not know the age of the overall universe; we only speculate the age of the "observable" universe. Is this a further enhancement ?

I now add another thought experiment only for your enjoyment. Your balloon analogy is an excellent way to explain how each and every bundle of matter expands in a similar fashion - such as stars, planets, and our own bodies. I believe that our thinking is still very self-centered in believing that only galaxies expand in this manner.

dougettinger wrote:Depending on our perspective the dividing lines between space, energy, and matter are very fuzzy.

dougettinger wrote:The explanation for space expanding at an increasing rate is Dark Energy. So what is the connection then between space and energy ? Is Dark Energy a misnomer ?

dougettinger wrote:So how do cosmologists compute the percentages of Dark Energy being 72% and Dark Matter & regular matter as 28%?

The idea that Dark Energy pervades all of expanding space is unavoidable.

dougettinger wrote:What kind of calculations based on the WMAP data are used.

I believe that space, or the voids between matter, or hard vaccuum, or the separations between galaxies, or whatever you wish to call it - is filled with energy.

Chris Peterson wrote:One major view of dark energy is that it uniformly fills space in this way (at an extremely low density). The other view is that while its density is uniform on a large scale, it is locally distributed. If the second view is correct, there may be no dark energy at all in the space within atoms, for example.

I think it is a mistake to "believe" either of these. Both are valid ideas, subject to test, but not yet tested. Either may turn out to be correct, or given how little is known about dark energy, neither. This is a good time to keep an open mind and wait for more data.