Implications for the Hubble tension from the ages of the oldest astrophysical objects

We use the ages of old astrophysical objects (OAO) in the redshift range 0 less than or similar to z less than or similar to 8 as stringent tests of the late-time cosmic expansion history. Since the age of the Universe at any redshift is inversely proportional to H-0, requiring that the Universe be older than the oldest objects it contains at any redshift, provides an upper limit on H-0. Using a combination of galaxies imaged from the CANDELS program and various high-z quasars, we construct an age-redshift diagram of greater than or similar to 100 OAO up to z similar to 8. Assuming the Lambda CDM model at late times, we find the 95% confidence level upper limit H-0 < 73.2 km/s/Mpc, in slight disagreement with a host of local H-0 measurements. Taken at face value, and assuming that the OAO ages are reliable, this suggests that ultimately a combination of pre- and post-recombination (z less than or similar to 10) new physics might be required to reconcile cosmic ages with early-time and local H-0 measurements. In the context of the Hubble tension, our results motivate the study of either a) combined global pre-and post-recombination modifications to Lambda CDM, or b) local new physics which only affects the local H-0 measurements. (C) 2022 Elsevier B.V. All rights reserved.