Poll – The Hubble Constant: High or Low?
Given yesterday’s news from the Atacama Cosmology Telescope, among other things suggesting a low value of the Hubble constant of around 67.6 km s-1 Mpc-1, it might be fun to run another totally unscientific poll about which of the two Hubble constant camps has the most support in the community. The two camps are:
- A `high’ value H0 ~ 73.5 ± 1.5 km s-1 Mpc-1 (as favoured by most stellar distance indicators, i.e. `local’ measurements).
- A `low’ value H0 ~ 67.5 ± 0.5 km s-1 Mpc-1 (as favoured by most `cosmological’ estimates, e.g. cosmic microwave background fluctuations).
Of course you might also believe that both are wrong and the `true’ result lies outside both error regions but I’d like to focus on these two possibilities, so the question is posed assuming that one of them is right, which one is that most likely to be. In your opinion. Humble or otherwise.
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In the Dark 
July 17, 2020 at 10:43 am
I voted low. Why? Historically, local measurements have been problematic, as the old debate of 50 vs. 100 shows, with some people, even some readers of this blog, seriously suggesting a Hubble constant as low as 30*. So it wouldn’t surprise me if there is some subtle effect affecting the local measurements—neither new physics nor some departure from F(L)RW, but rather some overlooked aspect of the analysis. There have been a few papers on such possibilities recently.
I tend to trust the CMB estimates because, despite the huge amount of data now available from the CMB, there have been essentially no revisions to the standard model necessary as a result of new data; what has happened is that the handful of parameters people were talking about even before the first peak had been seen are now known much more precisely, but no new ones have had to be introduced. Thus, I think that the Hubble-constant measurement from the CMB is probably OK.
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*Not so much because they believe(d) that observations suggest that, but rather because it would make some other things easier to understand.
July 17, 2020 at 12:18 pm
I voted high because there is less interpolation of data in that method – but it will be interesting if it turns out that there is a new systematic error in distance we don’t know about
July 17, 2020 at 12:27 pm
I’m not going to say which way I voted until we find out which one is right.
July 17, 2020 at 12:40 pm
smiley!
July 21, 2020 at 2:47 pm
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July 22, 2020 at 3:52 pm
Not surprisingly, I voted low.