A misremembered episode

The Big Bang won.  But not the way it’s normally presented.

Our astronomer has been pondering an episode in the history of his science from the last century: the contending cosmological theories of the Big Bang and the Steady State.  They are often presented as a textbook case in the philosophy of science, in which two theories are formulated, then tested against observations, and one chosen.  In the end, the detection of the Cosmic Microwave Background (CMB) led to the elimination of the Steady State, and the Big Bang won.  It was not quite so simple, and there are aspects about the process that we think are worth bringing out.

The basic observational data began to come in from the 1930s: spectra of almost all galaxies showed a red shift, and the farther away they were, the greater the red shift.  If we interpret the red shift as being due to motion, galaxies are moving away from each other.  This is the “expansion of the universe,” a phrase that’s often misinterpreted, but we won’t go into that here.

Plugged into Einstein’s General Relativity (still fairly new, but gaining acceptance), this meant that everything was closer together earlier.  And if you traced the equations back far enough (billions of years), the universe must have been a very different place: hot and dense; and that also implied a finite age of the universe.  The model was the hot Big Bang.

In contrast to this, however, some astronomers produced the Steady State model.  In this, matter was created from nothing (it would not actually take very much) so that the average density stayed the same over time.  The universe would always look the same, no matter where or when you were; this was the Perfect Cosmological Principle.

For a long time actual observations were unable to distinguish between the two models, and we notice arguments based on philosophical principles.  The Perfect Cosmological Principle was one; now something similar is called the Copernican Principle: we are not allowed to be in some special place, as the geocentric Earth was.  The Steady State supporters extended it to time.  One of them asserted that, if the Big Bang people allowed parts of the universe (density, temperature) to change, they must allow everything to change.  (We don’t find that argument convincing.)  Finally, they pointed out that the Steady State mathematics had all been worked out, and so was scientifically testable.  The Big Bang was kind of incoherent at the start, partly due to inadequacies in nuclear physics.

And indeed the original Big Bang turned out to be wrong in almost all details, while somehow eventually being correct overall.  For instance, the first matter in the universe would be made of extremely dense, large nuclei, larger than anything seen now, which would fission and create energy.  The current picture is that the original stuff was mostly hydrogen, the lightest element, with some helium and a smidgen of lithium.  But many astronomers were uncomfortable with the way the Steady State postulated something called the c-field, unlike any known entity, and did away with the conservation of energy.

The CMB (detected in 1965) was not the “crucial experiment” beloved of philosophers of science, either.  Opinion among astronomers had been turning against the Steady State for a while, based on something called faint source counts that we’re not going to try to explain.  Indeed, one of the last Steady State supporters was trying to explain the CMB in the 1990s as being due to whiskers of iron in the atmospheres of cool stars.

What do we conclude?  That principles are a weak argument.  (On of our grad school teachers remarked, “Any time someone talks about principles in mathematical physics, he’s trying to pull a fast one.”)  That a theory can be almost all wrong at the outset, but eventually come right.  And with the myriad of strangely-behaving things invented in mathematical physics since the 1980s, no one would bat an eye at the c-field nowadays.