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One problem in the standard [itex]\Lambda[/itex]CDM model is the near equality to an OOM of the densities of baryonic matter (4%), non-baryonic Dark Matter (23%) and Dark Energy (73%). The coincidence is more striking if it is realized that the proportion of DE, if due to the cosmological constant, will grow with the volume of the universe and the universe has expanded by something of the order of 10

If DE is not a cosmological constant but some form of quintessence with [itex]\omega[/itex] <,>, -1, then its density proportion will also grow or possibly shrink with cosmic expansion.

In either case the question is why should this density be in the same 'ball-park' as that of the matter content?

A second coincidence is related to this.

If the presence of DE with negative pressure is accepted it allows the universe to accelerate. A purely accelerating universe can have any age from just over Hubble time (the inverse of Hubble's constant) upwards to infinity (Such as in the Steady State model).

Without any DE acceleration, but with the presence of ordinary matter and energy with a positive pressure, the universe purely decelerates. A decelerating universe has an age less than Hubble time.

The standard model first decelerates, then massively accelerates (inflation), then decelerates through the BBN era until the recent epoch (~1 < z < 0) when it accelerates again.

So what has been the result of this deceleration/acceleration process on the age of the universe?

The present best accepted values of cosmological parameters

(using the table at http://lambda.gsfc.nasa.gov/product/map/dr2/params/lcdm_all.cfm)

H

[itex]Omega_{\Lambda}[/itex] = 0.732

[itex]Omega_{matter}[/itex] = 0.268

Feeding these values into Ned Wright's Cosmology Calculator:

The age of the universe is = 13.81 Gyrs.

But with h

Hubble Time = 13.89 Gyrs.

Strange that the age of the universe should be equal to Hubble Time to within an error of 0.6%, almost as if the universe had been expanding linearly at the same rate all the way along!

Just food for thought.

Garth

^{60}since the Planck era.If DE is not a cosmological constant but some form of quintessence with [itex]\omega[/itex] <,>, -1, then its density proportion will also grow or possibly shrink with cosmic expansion.

In either case the question is why should this density be in the same 'ball-park' as that of the matter content?

A second coincidence is related to this.

If the presence of DE with negative pressure is accepted it allows the universe to accelerate. A purely accelerating universe can have any age from just over Hubble time (the inverse of Hubble's constant) upwards to infinity (Such as in the Steady State model).

Without any DE acceleration, but with the presence of ordinary matter and energy with a positive pressure, the universe purely decelerates. A decelerating universe has an age less than Hubble time.

The standard model first decelerates, then massively accelerates (inflation), then decelerates through the BBN era until the recent epoch (~1 < z < 0) when it accelerates again.

So what has been the result of this deceleration/acceleration process on the age of the universe?

The present best accepted values of cosmological parameters

(using the table at http://lambda.gsfc.nasa.gov/product/map/dr2/params/lcdm_all.cfm)

H

_{0}= 70.4 km/sec/Mpsc[itex]Omega_{\Lambda}[/itex] = 0.732

[itex]Omega_{matter}[/itex] = 0.268

Feeding these values into Ned Wright's Cosmology Calculator:

The age of the universe is = 13.81 Gyrs.

But with h

_{100}= 0.704,Hubble Time = 13.89 Gyrs.

Strange that the age of the universe should be equal to Hubble Time to within an error of 0.6%, almost as if the universe had been expanding linearly at the same rate all the way along!

Just food for thought.

Garth

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