In response to the call for uncomfortable questions, Jason Failes asks:
What’s the best evidence for the Big Bang theory?
The more I read about it (25 years ago to present), the more contrived, ad hoc, and retro-dictive it seems.
At this point, what would falsify the Big Bang theory?
What would falsify the Big Bang? Jesus Christ his own self turning up at the American Astronomical Society meeting, turning water to wine, and giving a talk titled “What Big Bang? How I Hoaxed You All.”
OK, that’s pretty flippant, but my understanding of the matter is that the evidence supporting the current cosmological model is simply overwhelming. The measured redshifts of distant galaxies correspond very nicely to Hubble’s Law, the cosmic microwave background radiation is at a temperature that fits perfectly (and, it should be noted, Ralph Alpher predicted the existence and temperature of the microwave background to within a factor of 2 in the late 1940’s, nearly twenty years before it was discovered, so it’s not all “retro-dictive”), observed abundances of light elements are right where you would expect, etc.
The only observation that isn’t entirely consistent with a fairly straightforward variant of the original Big Bang idea is “dark energy,” which manifests as an apparent acceleration of the expansion of the universe. That’s a significant gap, to be sure, but it’s still a recent discovery as such things go, and I’m not aware of any astronomers who believe it represents an insuperable obstacle for Big Bang cosmology.
The tendentious phrasing of the question suggests a belief in some other alternative, but I’m not aware of any alternative theory that is taken seriously by anybody in the field. The evidence supporting the current Big Bang model is compelling enough that falsifying it would require something not far short of an authenticated miracle.