The Steady State Theory represents a significant historical model in cosmology. While largely supplanted today, it presented a compelling view of a cosmos that, despite its expansion, maintained a consistent appearance over vast spans of time, contrasting with models of a universe evolving from a singular, denser state.
Defining the Steady State Universe
The Steady State Theory proposed that the universe is infinite in both space and time, possessing no beginning or end. A central tenet was the “perfect cosmological principle,” which posited that the universe appears the same in all directions, locations, and at all times. This meant that, on a large scale, the average density and arrangement of galaxies would remain constant. To reconcile an expanding universe with constant average density, the theory introduced the concept of continuous creation of matter. As galaxies moved apart due to expansion, new hydrogen atoms were thought to spontaneously appear throughout space. This newly created matter would then condense, forming new stars and galaxies, preserving the universe’s unchanging appearance.
The Theory’s Origins
The Steady State Theory was primarily developed in 1948 by British scientists Hermann Bondi, Thomas Gold, and Fred Hoyle. Their work emerged during a period of active debate in the mid-20th century, as the Big Bang hypothesis also gained consideration. Bondi, Gold, and Hoyle sought an alternative framework that avoided a singular creation event, proposing a model where the universe’s properties remained uniform across cosmic time, even as it expanded. Fred Hoyle, a notable advocate, even coined the term “Big Bang” for the rival theory in a mildly derisive manner during a radio broadcast.
Key Predictions and Confronting Observations
The Steady State Theory predicted that the universe should exhibit no evolutionary changes when observed over cosmic distances. This meant that distant, and therefore older, regions of the universe should appear statistically similar to nearby, more recent regions. The distribution and types of galaxies, for example, were expected to be uniform throughout space and time.
However, observational evidence that emerged in the 1960s began to challenge these predictions directly. The discovery of quasars in the early 1960s posed a significant problem. These extremely luminous objects were found predominantly at great distances, implying they existed in the early universe. Their high redshifts indicated they were very far away, suggesting the universe was different in the past, with these energetic objects being far more common then than they are today.
A discovery that further contradicted the Steady State model was the cosmic microwave background (CMB) radiation. In 1964, Arno Penzias and Robert Wilson detected a persistent, uniform microwave signal coming from all directions in space. This pervasive background radiation was later interpreted as a remnant glow from a hot, dense early universe. This was a direct prediction of the Big Bang model, but inexplicable within the Steady State framework.
The observed cosmic abundances of light elements like hydrogen, helium, and lithium provided additional evidence against the Steady State Theory. The proportions of these elements align well with predictions from Big Bang nucleosynthesis. The Steady State model, which proposed that all elements were synthesized within stars through continuous creation, struggled to account for these primordial ratios. Observations of galaxy evolution also showed that distant galaxies appear different from nearby ones, indicating that galaxies have changed over cosmic time.
Why the Theory Was Supplanted
New observational evidence, particularly the discovery of the cosmic microwave background radiation, led to the Steady State Theory’s decline. The CMB provided strong support for a universe that began in a hot, dense state and has been expanding and cooling ever since. This observation was a key prediction of the Big Bang model and could not be adequately explained by the Steady State Theory.
While the Steady State Theory was a scientifically valid hypothesis that stimulated cosmological research, it ultimately could not withstand the scrutiny of empirical data. The consistent findings from quasar distributions, light element abundances, and the universal microwave background radiation presented insurmountable challenges. As a result, the scientific community largely shifted its consensus towards the Big Bang model, which offered a more consistent explanation for the observed universe.