Hubble Explodes Star-Formation Assumption in Globular Clusters

The Hubble Telescope found three episodes of star formation in a globular cluster.  While this announcement might make a layman yawn, what’s interesting are the expressions of grief and anguish coming from astronomers about what this does to their theories.  For many years, astronomers had prided themselves on their understanding of globular clusters.  These massive, spherical clusters formed early in the universe, it was said, and have been slowly aging till now.  This assumption appears to have been jeopardized by the observations made of giant globular NGC 2808.  Feel their pain:

• “We had never imagined that anything like this could happen,” said Giampaolo Piotto of the University of Padova in Italy and leader of the team that made the discovery.  “This is a complete shock.”
• “The standard picture of a globular cluster is that all of its stars formed at the same time, in the same place, and from the same material, and they have co-evolved for billions of years,” said team member Luigi Bedin of the European Space Agency…. “This is the cornerstone on which much of the study of stellar populations has been built.  So we were very surprised to find several distinct populations of stars in NGC 2808.”
• Finding multiple stellar populations in a globular cluster so close to home has deep cosmological implications, the researchers said.
• “We need to do our best to solve the enigma of these multiple generations of stars found in these Hubble observations so that we can understand how stars formed in distant galaxies in our early universe,” Piotto explained.
• [Science Daily]: Space telescope makes startling discovery… The Hubble Space Telescope has provided evidence representing a major upset for conventional theories that propose a single period for star birth.
• [Space.com]: The long-held belief that globular star clusters form in a single boom has been challenged by new findings.
• [New Scientist]:  “NGC 2808 was just considered a normal globular cluster and no one was expecting this ability to see three distinct stellar populations,” Piotto told New Scientist.  “This result says globular cluster stars are not as simple as we are teaching to our students.”

To be fair, the astronomers are not quite ready to take up truck driving.  “No one would make the radical step of suggesting that previous work on other clusters is no longer valid,” one of the astronomers said.  “But this discovery shows that the study of stellar populations in globular clusters now opens up in a new direction.”  If a theory this well-established can be challenged, however, it raises questions about the ability of astronomers to claim knowledge about lesser-understood phenomena.

Is science always progressive and cumulative?  Is this finding a mere adjustment?  Are astronomers converging on The Truth about the universe, despite some missteps along the way?  Or do announcements like this illustrate the tentative nature of science, and cast doubt on the ability of man by reason and fallible senses to deduce the true nature of the world?  These are profound questions in the philosophy of science.
    It appears obvious that we know more about stars and the universe than we did a hundred years ago, or two hundred.  Yet as professor Steven Goldman at Lehigh reminds us in Science Wars, almost everything we thought we knew 100 years ago has changed dramatically.  What we think the Earth is, and what we think the Universe is, and what we think an Atom is, or Space, or Time, or Matter, or Energy, bears almost no resemblance to what scientists “knew” about these things at the beginning of the 20th century.  We cannot have much assurance, therefore, that scientists 100 years in the future will not look back on the early 21st century and chuckle about how wrong we were.
    Most scientists these days are realists.  They believe in the correspondence theory of truth: i.e., that our sense impressions correspond to what is really “out there” in the world.  This is the “common sense” view most of us take for granted.  Philosophers since the Greeks have questioned this assumption, however.  For thousands of years, the greatest minds in history have debated vigorously the degree to which our senses provide knowledge about reality.  Science has, in fact, taken some of its most serious blows in recent decades.  Since the 1930s and 1960s – even into the “science wars” of the 1990s, great minds have wrestled with the “knowledge problem” in science.  Though realism tentatively holds the hill again now, some big names have challenged the objectivity of scientists.  They have pointed to the historical and social nature of science, accusing scientists of being blind to their assumptions, and asking questions that push the academic programme in certain directions and not others.  Even the logical positivists who were determined to save the objectivity of science gave up by the 1950s.

This is not to say that we must doubt what a car is, and whether we are driving down the road, or what will happen if we drive into a brick wall.  But when discussing scientific objects like a quark, or the interior of a star, or a black hole, or a species, or a population, or a gene, or global climate change, or laws of nature – and the causes of their interactions and how we explain them — scientists get onto slippery philosophical ground very quickly.  A finite number of instances cannot necessarily be extrapolated to a class.  A time sequence does not necessarily imply a cause-effect relationship.  A majority of scientists can be wrong (bandwagon fallacy).  And today’s best theory is not necessarily a good theory (Macbeth’s best-in-field fallacy).  These are just a few of the caveats that can be levied against even simple, down-to-earth explanations in our everyday experience.  The problems become even more significant in astronomy and cosmology, where the line between theory and observation is often very fuzzy.

This entry about globular clusters reminds us that scientists can never simply assume that their theories correspond to Reality with a capital R.  No matter what the textbook says, or how solid the scientific consensus appears, everything in science is subject to revision.  Some things are subject to revolution.  Whenever a scientist says “We now know,” that’s the time to get out the red flag and say, “We heard that line 100 years ago, and now look.”