A theory that needed rescue

The narrative recounts three problems that cosmologists themselves identified in the original Big Bang model by the late 1970s.

The horizon problem. The Cosmic Microwave Background has the same temperature in every direction, to about one part in 100,000. In a simple Big Bang expansion, distant regions of the sky could never have been in contact to reach that agreement.

The flatness problem. The universe is extremely close to geometrically flat. Without a mechanism to tune it, the early universe would have needed to be flat to roughly one part in 10¹⁵.

The monopole problem. Grand unified theories predict that the hot early universe should have made abundant magnetic monopoles. None has ever been detected.

In 1980 Alan Guth proposed inflation, a brief burst of faster-than-light expansion that addresses all three. The narrative notes that inflation relies on a hypothesized field, the inflaton, that has not been detected. In 2014 the BICEP2 team announced a signal of primordial gravitational waves, a key inflation prediction. The signal was later attributed to dust in our own galaxy. Paul Steinhardt, one of inflation's early architects, and Anna Ijjas have since argued that the theory is flexible enough to fit almost any outcome.

RSI offers an alternative that needs no inflation. A medium in hydrostatic equilibrium is uniform because it is one substance everywhere. RSI proposes that what standard cosmology calls the Big Bang was the trough of the medium's breathing, about 13.8 billion years ago by atomic clocks, with no singularity and no beginning of everything. RSI must still derive the CMB's 2.725 K temperature, its blackbody spectrum and its acoustic peaks, and show that the trough era produces the observed light elements. The narrative then points to LIGO as positive evidence for the medium.