This doesn’t mean you would know it was slower if you were there at the time. A second would still feel like a second. But, relative to us, it was five times slower.
This doesn’t mean you would know it was slower if you were there at the time. A second would still feel like a second. But, relative to us, it was five times slower.
Oh, ok! They are just talking about normal relativistic/doppler time dilation then. The headline makes it sound as if they found an exotic source of time distortion in early universe, maybe something similar to “cosmic inflation”? But they just created an alternative way to measure timerate using quasars and statistics, to supplement already existing measurements using redshift of supernovas. Indeed the very existence of redshift itself is proof that what you are seeing is happening slower than realtime for you, because there is no sensible way to alter the spectral lines otherwise. About half of the magnitude of the distortion is classical doppler shift, and half is actual relativistic slowdown of time.
Can’t read the full paper, but it seems their observations reach redshift z=~5 at ~10% universe age. Stars and galaxies already existed, so the article headline saying “soon after the Big Bang” is a bit of a misnomer.