Hubble's Constant

By looking at stars at different distances...

It is thought that the visible universe is about the same everywhere at any given time, and looking through the telescope is really just looking back in time.

One thing they are doing is comparing redshift with distance. There are other means of determining distance separate from redshift, called standard candles. The nearest standard candle, parallax, is calibrated by the distance of earth from the sun. Further standard candles are calibrated from closer ones where they overlap to create a calibrated series. The Hubble constant is the ratio of redshift/distance, where distance is determined by standard candles. The Hubble constant determined from greater distances give the expansion rate further in the past.

https://universe-review.ca/R02-07-candle.htm#:~:text=A%20standard%20candle%20is%20a,the%20entire%20class%20of%20objects.

It was originally assumed that expansion was slowing down over time due to gravity, but now it is apparent that the universe is expanding faster now than in the past, thought to be due to "dark energy".

All standard candles do not follow the rules,the Chandrasekhar limit,so how do we really know the distance to some of these supernova which we use as a yardstick?

How many rule-breaking "standard candles" are in the universe?If we have discovered one,there must be many n more.

Some stars (HD 140283) have been calculated to be older than the universe,so something is amiss in their measurements.They have tweaked and adjusted their measurements to agree more closely with the accepted age of the universe,but the +- could go either way,still pointing to a very,very old star.

Reminds me of the train station supervisor in the old days,that would blow the whistle at noon every day.Every day, at ten minutes to twelve,he would call the operator and ask her for the time,and adjust his watch.

Eventually they both retired,and he met her in a diner.

He thanked her for keeping his watch on time all those years.

She replied that she had been setting her watch by his whistle.

I think another means of measurement should be found.

All standard candles do not follow the rules,the Chandrasekhar limit,so how do we really know the distance to some of these supernova which we use as a yardstick?

I would assume there would be outliers. Apparently the distance accuracy is considered to be within 7%.

"The use of Type Ia supernovae to measure precise distances was pioneered by a collaboration of Chilean and US astronomers, the Calán/Tololo Supernova Survey.^[45] In a series of papers in the 1990s the survey showed that while Type Ia supernovae do not all reach the same peak luminosity, a single parameter measured from the light curve can be used to correct unreddened Type Ia supernovae to standard candle values. The original correction to standard candle value is known as the Phillips relationship^[46] and was shown by this group to be able to measure relative distances to 7% accuracy.^[47] The cause of this uniformity in peak brightness is related to the amount of nickel-56 produced in white dwarfs presumably exploding near the Chandrasekhar limit.^[48]"

https://en.wikipedia.org/wiki/Type_Ia_supernova#cite_note-explosion_model-14

Headache?I knew that head was going to give trouble the first time I saw it.

I don't see a contradiction in your post. Could you elaborate.