Exponential expansion and Hubble constant

[Ranku]

I am reading conflicting interpretation of the Hubble constant in the exponentially expanding accelerating universe. Some say the Hubble constant is continuing to decrease; while others say Hubble constant is now unchanging and has become truly a constant.
Which is correct?

 

[sylas]

I am reading conflicting interpretation of the Hubble constant in the exponentially expanding accelerating universe. Some say the Hubble constant is continuing to decrease; while others say Hubble constant is now unchanging and has become truly a constant.
Which is correct?

In a pure exponential expansion, driven only by a cosmological constant, the Hubble constant remains constant.

In an accelerating expansion with some contribution from matter and some from a cosmological constant (such as our universe appears to be) the Hubble constant will continue to decrease, approaching in the limit a certain minimum value, just as the influence of the cosmological constant becomes more an more dominant over the contribution from matter.

You may be reading about these two different cases. Not all accelerating expansion is a pure exponential expansion.

Cheers -- sylas

 

[Ranku]

In a pure exponential expansion, driven only by a cosmological constant, the Hubble constant remains constant.

In an accelerating expansion with some contribution from matter and some from a cosmological constant (such as our universe appears to be) the Hubble constant will continue to decrease, approaching in the limit a certain minimum value, just as the influence of the cosmological constant becomes more an more dominant over the contribution from matter.

You may be reading about these two different cases. Not all accelerating expansion is a pure exponential expansion.

Cheers -- sylas

That clears it up. Thanks.