The “Age” Problem

The “Age” Problem

Critics relished in bashing the Big Bang theory when it appeared that there was a major conflict
between the age of the universe obtained from the expansion rate as discussed in the last chapter,
and the ages of the oldest stars in the Milky Way galaxy. The problem was that the ages of some
stars appeared to be older than the universe itself, which cannot possibly be true. This problem
arose shortly after the Hubble Space Telescope, launched in 1990, began to collect data on
distant galaxies. By carefully measuring the distances to galaxies as remote from us that light
would require 60 million years of our time to travel, and measuring how fast these galaxies are
moving away from us using the Doppler effect, we are able to determine how fast the universe is
expanding. From the expansion rate we can then determine how long the universe has been
expanding since the initial explosion we call the Big Bang. Data taken in the early 1990’s with
the Hubble Space Telescope showed that the universe appeared to be expanding faster than was
originally thought prior to these distant measurements. To avoid local variations, it is desirable
to measure the distance to galaxies much further away from us than those within a few million
years of light travel, thus the new measurements were considered to be more reliable. The faster
expansion rate implied that the universe was younger than 12 billion years old. That posed an
embarrassing problem for astronomers, since careful studies of stars within globular clusters
surrounding the Milky Way yielded ages from 13 to 15 billion years old. It appeared that the Big
Bang theory and corresponding age determinations were incompatible with our understanding of
stellar astronomy.
Cautious astronomers were not willing to toss aside the Big Bang theory quite yet, knowing that
there were additional uncertainties in the above measurements that did not allow for such a
definite conclusion. The ages of the oldest stars seemed to be quite well established. But the
expansion rate of the universe was still somewhat uncertain. Although the Hubble Space
Telescope was able to take data on stars more distant than any earth-based telescope had been
able to, it was still not certain that the distance was great enough to completely rule out
variations due to local gravitational tugs. In particular, it was well known by this time that there
is an enormously massive supercluster of galaxies known as the “Great Attractor”, which is
expected to exert significant motion on galaxies within a few hundred million years of light
travel, which includes all of the galaxies used so far in this study. What was needed was a
measurement far beyond all of our local clusters of galaxies. That finally came when a survey of
very distant supernovae, the death throes of massive stars, was made in the latter half of the
1990’s. Using only a type of supernovae having an expected brightness, we are able to
determine distances up to several billion years of light travel. From this study came two
important observations. The first was that the universe appears to be accelerating in its
expansion, which we will discuss next. The second was that the expansion rate of the universe
was more precisely determined. The resulting age of the universe is 14.5 billion years, uncertain
to 0.5 billion years [14]. By this time even more distant measurements of galaxies were
available from the Hubble Space Telescope. They were much closer to agreement with the
expansion rate determined from the distant supernovae. Thus the “age” problem of the universe
appears to be resolved and the Big Bang theory vindicated.