Age of the Universe

The age that our group has measured of the universe is about 12 billion
years, and that’s give or take a couple of billion years.

It’s about 13 billion years, give or take about 10 percent.

Somewhere between 12 and 17 billion years.

We get an age of about 14 billion years for the universe – plus or minus
one or two billion years.

The first step was to use Hubble to measure distances to about two dozen
nearby galaxies using a class of very bright, pulsating variable stars.
And then, we used that set of galaxy distances to measure several other
methods, which allowed us to extend our scale another factor of ten in
distance farther out.

There’s a particular type of supernova for which we have determined the
actual brightness.  And having established that, if you can find these
supernovae in much more distant galaxies, by looking at how bright they
appear, you can gauge how far away they are.

Well, we’ve been studying the supernovae themselves in a lot of detail.
And by doing that, you get some clues to the ones that are a little bit
brighter and the ones that are a little bit dimmer.  That allows you to
make more accurate estimates of the distance to each one.

The different approach that our group took was to measure distances – and
therefore ages – using many different methods, so we wouldn’t put all our
eggs into one basket. And that differs from the approach of some other
groups, which, for example, might use only Type 1A supernovae.

Well, we know how fast the various bits of the universe are expanding.  So
now if we can get distances to those bits, we can calculate how long it
took to get there.

Once we’ve measured the distances to galaxies, then we can measure their
speeds or their velocities.  And that tells us how fast the universe is
expanding.  And then, just like a movie, we can run that in reverse, and
we can see how long the universe has been expanding.  And that gives us
the age.

But it might not be the right age if the universe has been speeding up over
time, or if it’s been slowing down over time, because that age assumes that
they’ve been going at constant speed. So we’ve been looking at very, very
distant supernovae – very far away, very faint – and from those, we’ve been
able to figure out that the universe has actually been speeding up, not
slowing down as many people would expect.  And that allows you to make a
more accurate estimate for the age of the universe.

Each of these methods has its own weaknesses.  The question is, which has
the least?  Now, do you gain by taking an average of several weak methods?
 Or do you pick the one that’s the least weak and use that alone?  And our
judgment was that the particular supernova method was the best way to go.

What our group did, which is somewhat different from what other groups have
done, is to measure distances – and therefore ages – using a number of
different methods.

It’s good to have a variety of them, but it’s probably good to trust the
best one.

Now, other groups have gotten slightly different answers than we have, but
that’s the way the scientific method works – to compare those results and
over time, and to iron out the differences.