Is Hubble Constant Really Constant?

[jayaramas]

i think Hubble constant is not a constant because of relativistic speeds of galaxies. is it?

 

[cepheid]

i think Hubble constant is not a constant because of relativistic speeds of galaxies. is it?

You're right that the thing we call the Hubble parameter, H, which relates recessional velocity to proper distance, is not constant. It changes with time, and so it can be expressed as a function H(t). However, your reason is wrong: it has nothing to do with "relativistic speed" of galaxies. It changes with time in a manner determined by the Friedmann equations, which describe the large-scale dynamics of the universe in terms of its matter and energy content.

The thing we we call the Hubble constant, H₀, is the value of the Hubble parameter NOW. This is, in fact, a constant.

Note that although H changes with time, it is constant throughout space (i.e. it does not vary with location). Therefore, H is the same everywhere at any given instant.

 

[jayaramas]

this is not the correct answer!. what is NOW ? this indicates lack of understanding of theory of reletivity

 

[Chronos]

Asking a question you already 'know' the answer to is commonly referred to as trolling. Of course, that is not an issue in this case. I suggest a refresher course on the concept of 'NOW'.

 

[twofish-quant]

this is not the correct answer!. what is NOW ?

The space time coordinate of the current location.

This indicates lack of understanding of theory of reletivity

Be very careful on this forum with asserting that people don't understand things.

 

[jayaramas]

sorry. what i mean is that the distant galaxy is not moving at calculated speed NOW but is was moving like that long back!