COSMO
In the literature: open
Can a nonsingular bounce reproduce all observed primordial spectra?
In plain words
Instead of inflation, the universe might have contracted and then bounced into expansion. Such models must avoid unstable or unphysical fields at the bounce while matching observations.
Precise statement
Construct a geodesically complete bouncing or ekpyrotic cosmology, free of ghost and gradient instabilities and under effective-field-theory control through the bounce, that predicts $n_s = 0.974 \pm 0.003$, $r < 0.036$ and $\mid f_{\mathrm{NL}}^{\mathrm{local}}\mid < 10$. Answer yes with an explicit model, or no with a no-go theorem for a defined class.
What would settle it
An explicit stable model with computed spectra, or a no-go theorem covering scalar-tensor bounces.
Related problems
- Special case of Did the early universe go through an inflationary phase?