Accelerated expanding Universe.. or not?

[sil (Steve)]

On a serious note I've always doubted the accelerated expansion model. I don't have the skills to unstand the papers or investigate my ideas, but in the end I expect it to be a misunderstanding of the data. From the observations I've heard described an apparent accelerated expansion makes perfect sense since they havent accounted for time it seems.

[Eratosthenes (Peter)]

Originally Posted by sil

On a serious note I've always doubted the accelerated expansion model. I don't have the skills to unstand the papers or investigate my ideas, but in the end I expect it to be a misunderstanding of the data. From the observations I've heard described an apparent accelerated expansion makes perfect sense since they havent accounted for time it seems.

There are physicists who think that the speed of light may not be a constant, and in fact was faster during the early stages after the Big Bang event. The horizon problem was always a challenge to the evolution of the cosmos post big bang. Inflation theory was introduced to the early periods of the Big Bang in order to tackle the Horizon problem. (this has fundamental problems in its self even though it works and is a beautiful solution to a very difficult problem)

Magueijo and others, suggest a way to test the Variable Speed of Light theory - the measurement of the spectral index. They propose a fairly accurate estimate to the spectral index = 0.96478. Current estimates from Cosmic Background radiation measurements are 0.968 - close but the small difference is critical according to Magueijo.

Lots to play out in the Big Bang theory yet as well as in Relativistic Physics - it may turn out that dc/dt is not equal to zero.

[raymo]

I have often wondered if the theorised current age of the universe is
analogous to the nano second or whatever amount of time elapses between
an explosion occurring, and the blast accelerating to its its maximum outward velocity, before beginning to slow down.
raymo

[xelasnave]

Originally Posted by raymo

I have often wondered if the theorised current age of the universe is
analogous to the nano second or whatever amount of time elapses between
an explosion occurring, and the blast accelerating to its its maximum outward velocity, before beginning to slow down.
raymo

An explosion is hideously slow compared to inflation.
From zip to at least the size of the observable universe in a trillionth of a trillionth of a trillionth of a second...as the story is told.
But I don't know I was not around to see what happened.
But if we take the time as it seems to be presented I find it hard to accept.
Alex

[sjastro]

Inflation and dark energy should not be confused for being equivalent mechanisms.
Inflation occurred in a radiation dominated Universe, lasted in the period from 10^-36 sec to 10^-32 after the Big Bang, dark energy about 6 billion years later in a matter dominated Universe and has existed ever since.

In a radiation dominated Universe the expansion characteristic of the Universe is defined as a time dependant scale factor which is different from the matter dominated Universe.
Taking this into consideration plus how the Universe eventually turned out one can calculate the duration for Inflation.
If the Inflation period was too short, the horizon problem would not be solved and the Universe would not be observed to be isotropic.
Conversely if it was too long, the Universe would take on an open or hyperbolic geometry where complex structures could not form including life itself.

As far as scientists misunderstanding the data there are two different and independent observations both of which point to dark energy.

First is the time dilation of type IA supernova light curves in distant galaxies. This a standard ruler for measuring distance.
The larger than predicted distances indicates acceleration.

Second is the flatness of the Universe itself which can only be explained by dark energy.
The evidence is provided through Baryon acoustic oscillations in the CMB (cosmic radiation background).
In the CMB plasma wants to collapse under its own gravity but is prevented by radiation pressure exerted by colliding photons.
These opposing forces create an oscillation in the plasma much like a sound wave travelling through air, and create hot and cold spot structures in the CMB.
The true size of these structures can be calculated and compared to their apparent size as measured by the observer.
Comparison of the two reveals the geometry of the Universe is flat.
https://map.gsfc.nasa.gov/mission/sg...ters_geom.html

Steven