Conclusion

Let me close by suggesting that the steady state model may have lost the battle but has in fact won the war, if winning means leaving the more enduring mark on intellectual history. The debate between the Big Bang and steady state has been one of the most productive in the history of science. First, in looking for an alternative source of He production, proponents of SSM were led to examine nucleosynthesis carefully in stars, discovering the basic rules that explain the origin of the entire periodic table beyond helium, a giant achievement. Second, the most novel if off-putting feature of the steady-state theory is its spontaneous creation of matter out of nothing. With appropriate re-interpretation, this can now be seen as a forerunner of the false vacuum of inflation: both mechanisms maintain constant gravity despite expansion - both create matter and energy out of apparently nothing. Indeed, a remarkably prescient paper in 1951 by McCreaequated the matter-creation field of steady state to the Λ of GR by invoking a negative pressure, precisely the modern interpretation! The only change in the ensuing decades, it seems, is that particle physics has come up with a plausible physical mechanism for Λ, i.e., the false vacuum. Without such a prop, the proponents of steady state looked ridiculous for their time, but it now might be argued that they were merely too far ahead of their time.

In fact, it is steady-state universes, not matter-dominated universes, that are the most intensely studied of today. In addition to the inflating Universe, which was in a steady state for a brief but crucial period, evidence suggests that we may be entering another steady-state era today. This comes from measurements of the brightness of distant supernovae, which, when coupled with the size scale of irregularities in the CMB radiation, seem to imply that Λ is non-zero and repulsive. If true, we are entering another exponential expansion phase, with the generation once more of event horizons and Hawking radiation. What wholly new physical phenomena lie behind this door are as yet unknown - potentially another false vacuum, phase change, and a new hierarchy of (low-energy) physical phenomena? Who can say? At any rate, the commonly voiced predictions of the inevitable “heat-death” of the Universe may be premature if we are indeed rescued by another steady state.

Finally, I note that Linde's theory of “eternal” inflation,to be described more fully by Alan Guth this afternoon, is really also just a steady-state model in a different guise. In eternal inflation, an exponentially expanding vacuum field spawns baby universes spontaneously and sporadically in much the same fashion statistically that the classic steady state model spawned hydrogen atoms. The result is an endlessly unfolding hierarchy of universes that some have called the Meta-universe. An ensemble of such universes, if each had different physics, would provide the necessary ensemble of varied universes required by the anthropic principle, also described by John Barrow later in this volume.

In the history of modern cosmology, the only credible alternative to the Big Bang theory has been the steady-state model. I began this talk by siding firmly with the Big Bang. While my faith in our own Big Bang is undiminished, I muse on the possibility that steady-state and quasi-steady state universes unlock more and deeper secrets of fundamental physics.

Contributed by: Dr. Sandra Faber