number called the Hubble Constant, named
after the first astronomer to measure it.
But as both sides get more precise data, it’s
becoming clear that the answers disagree.
This is sometimes called the “Hubble
tension”; other times it’s called a “crisis in
the cosmos”.
So, what’s the solution? It may be
that one side is making a mistake in its
data analysis. Or perhaps missing some
important bit of astrophysical data that
would lead to a different result. The only
other possibility is that both measurements
are essentially correct, but they’re not
actually measuring the same thing, which
would mean our big picture is incomplete,
and the evolution of the cosmos is more
complicated than we thought.
Based on the headlines, you’d think that
this last possibility would be the nightmare
case. It would, after all, mean that the very
precise accounting we’ve made of the
makeup and/or evolution of the Universe
was never correct, and we’ve been missing
something important all this time.
But from an astronomer’s viewpoint,
it’s less of a nightmare and more of a dream
come true.
Our current picture of the cosmos has so
far been beautifully, frustratingly consistent
with every measurement we’ve thrown at it.
This so-called Concordance Cosmology has
passed every observational test, painting
for us a precise picture of exactly what the
Universe is made of, and in what quantities.
Even general relativity, a theory of gravity
first written down by Einstein in 1915, has
yet to show any cracks.
In science, when everything works as
expected, it might be personally satisfying,but it doesn’t give you any hint as to how
to make your theories better. Cosmology
is in desperate need of just such a clue,
in part because the two most important
components of the cosmos, dark matter and
dark energy, are so far entirely unexplained.
We don’t know yet what the solution
to the Hubble tension will be. It’s entirely
possible that it will turn out to be an
unaccounted-for fluke of stellar evolution,
or some glitch in a data analysis pipeline,
rather than bona fide new physics. But
whether or not this “crisis” leads us on
a path to a better understanding of the
cosmos, we’ll keep hoping to see something
truly unexpected in the data – something
weird that will tell us where to go next.
As Irish comedian Dara Ó Briain once
said, “Science knows it doesn’t know
everything. Otherwise, it would stop”.Our current picture of the
cosmos has so far been
beautifully, frustratingly
consistent
THE NEXT BEST THING
Issue 86 COSMOS – 25