Jerry said: "The only exacting proof that the cosmic redshift is caused by relativistic expansion is the time-dilation measured in supernova light-curves. The theory redshifting is caused by relativistic expansion is completely dependent upon the theory that type Ia supernova events are caused by a white dwarf star accreting matter to a critical mass and exploding within a narrow range of light-curve widths and ~0.6 absolute magnitudes."

Righ now we are limited in our ability to do astrophysics by the fact that all of our information about distant objects comes from electromagnetic waves. Actually, if and when gravitational waves from distant sources are detected they will provide independent confirmation of the expansion of the Universe. Once gravitational waves are used in tandem with electromagnetic waves to do cosmology it will be harder and harder to deny the expansion of the Universe. In fact, here is a paper which talks about gravitational wave measurements from distant sources being used to determine the hubble constant: "Determining the Hubble constant from gravitational wave observations" by Bernard F. Schutz

Abstract

"I report here how gravitational wave observations can be used to determine the Hubble constant, H 0. The nearly monochromatic gravitational waves emitted by the decaying orbit of an ultra−compact, two−neutron−star binary system just before the stars coalesce are very likely to be detected by the kilometre−sized interferometric gravitational wave antennas now being designed1−4. The signal is easily identified and contains enough information to determine the absolute distance to the binary, independently of any assumptions about the masses of the stars. Ten events out to 100 Mpc may suffice to measure the Hubble constant to 3% accuracy."

Due to, as Nereid so aptly puts it, Jerry's "anti-confirmation bias on steroids" Jerry will surely be much displeased if and when dark matter particles are discovered. He will be even more irked if the directly measured abundance of dark matter particles ends up matching the implied abundance as inferred from the CMB, galaxy cluster data, lensing, and supernovae observations. The direct detection of dark matter will largely make Jerry-like radical skepticism when it comes to cosmology even less tenable. Right now Jerry et al use our current ignorance of dark matter as an example of how cosmologists invent "theoretical entities" in an epicyclical manner to make up for the shortcomings of their existing theories. Once dark matter is discovered, if it is, Jerry will be forced to eat his words and his type of snide superiority-laden skepticism will become even more out of fashion than it already is.

So, the direct detection of gravitational waves and the direct detection of dark matter will both be sad days for Jerry. Of course, I am sure he'll fall back on the same kind of petty what if pigs could fly skepticism that he uses right now to try debunk the evidence, as there are people who right now dispute the roundness of the Earth (e.g. the Flat Earth Society), anthropogenic climate change, and the fact that the Earth revovles around the Sun. Except, the direct detection of these "free parameters" or "theoretical entities" will make Jerry's position even more untenable. Hence the title of this post, Jerry's worst nightmare. We shall see.