Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: RobC on 09/08/2019 19:26:28
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I am asking this after Wendy Freedman and Adam Riess recently made their case for different expansion rates of the universe.
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I am asking this after Wendy Freedman and Adam Riess recently made their case for different expansion rates of the universe.
The Hubble constant is not a constant, but rather the inverse of the age of the universe. So if you change it, you're just positing a different age of the universe.
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Is that all?
The news item I read was headlined -- New measurements could upend the standard theory of the cosmos that has reigned since the discovery of dark energy 21 years ago.
But it did not say how.
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Is that all?
The news item I read was headlined -- New measurements could upend the standard theory of the cosmos that has reigned since the discovery of dark energy 21 years ago.
But it did not say how.
The headline is designed to drag you in. In reality, the more it would 'upend the standard theory', the more is isn't likely that it actually will. The dark energy thing didn't upend the whole standard theory at the time, but yes, nobody saw accelerated expansion coming. They were predicting a negative value. I'm not entirely aware of what case F&R are making. 21 years isn't much of a 'reign' for a theory, so upending it wouldn't be a huge thing.
Anyway, dark energy concerns the acceleration of expansion, not the expansion itself, and the Hubble 'constant' is the inverse of the age of the universe given constant expansion. So due to that acceleration (dark energy), the value is actually higher today than the inverse of the age, and thus would yield an age that is somewhat less than 13.8 billion years.
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The Hubble constant simply relates the distance to a galaxy with it's recessional velocity. You may find the abstract on the following page useful.
https://www.pnas.org/content/101/1/8 (https://www.pnas.org/content/101/1/8)
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One other thing that should be taken into account. The expansion of the universe is deduced from observation of the red shift of light from distant galaxies.
You could argue that some other process is causing this red shift, except for the fact, that at some point, it changes to indicate an accelerating expansion.
This indicates a 'change' in the Hubble constant. Which really isn't a constant at all.