This logic leads to a cosmic history in which the universe still underwent inflation but did not necessarily continue expanding. And instead of starting with a Big Bang, time before inflation could stretch into the infinite past.
No measurement can prove whether particle masses have stayed constant because it is only possible to measure the ratio between different masses, not masses themselves. For instance, all masses on Earth are ultimately referenced to a standard kilogram sitting in a vault in France. So Wetterich’s picture is akin to saying that instead of the universe expanding, the ruler with which we measure it is shrinking, says Niayesh Afshordi, an astrophysicist at the Perimeter Institute of Theoretical Physics in Waterloo, Canada.
If particle masses have been increasing, radiation from the early universe would make it look hotter than it actually was, and distant objects would appear to be receding even if they aren’t. This would explain why the universe appears to be expanding. So Wetterich says cosmic origin theories do not need to pack all matter into one point before inflation, avoiding a singularity. The universe could have begun sparse and cold, emerging from this deep freeze only after an unimaginably long time. In this picture, he says, “you can go as far back in the past as you want, and the past is even pretty boring.”