In article , "Richard D.
Saam" writes:

What are the astrophysical implications
of different Hubble constants by
Planck
https://arxiv.org/abs/1502.01589
Hubble constant 67.8 +/- .9 km/s/Mpc
and by
H0LiCOW collaboration
http://shsuyu.github.io/H0LiCOW/site/
Hubble constant 71.9 +2.4 -3.0 km/s/Mpc
?

First, progress. For decades, people worried about a factor of two or
more between different measurements of the Hubble constant. Now, we are
talking about 5 per cent. Also, any "tension" assumes that the error
bars are correct. We used to have 100+/-10 and 50+/-7 or whatever. (In
these cases, not only were the error bars too large, but the
measurements themselves were wrong.)

If you have one measurement, you know the value. If you have two
different measurements, you don't. :-) So we need a third,
independent, accurate measurement of comparable precision.

Much has been written about this. Just google "tension Hubble constant
Planck" (without the quotes).

Assuming that the tension is real, there are various scenarios which
could account for it, most of which don't call the Big Bang into
question. While it is good to explore these, especially given the
history of the Hubble constant (first estimates were around 600), it is
probably more productive to wait until the tension has been confirmed or
ruled out.


[[Mod. note -- An old mariner's saying (which supports Phillip Helbig's
point): "Never go to sea with two chronometers: take either one or three".
-- jt]]