Riess et al's findings showed that galaxies farther away are not just receding faster (as Hubble's Law already described), but that the rate of expansion itself is increasing over time. This discovery suggested the presence of a mysterious force, now called dark energy, driving this acceleration.
This was unexpected because most astronomers at the time thought the expansion should be slowing down due to gravitational attraction between galaxies.
Yes, but the article is indeed unclear about this. In particular this line:
>The farther away that galaxies were, the faster they were receding.
This is already the case in Hubble's law, which says that the velocity is proportional to the distance. Hubble's constant is the proportionality constant and thus the expansion rate.
Riess found that the Hubble constant is not constant. Instead, the expansion rate is increasing over time.
How many journalism majors did you encounter in undergrad who knew how to apply second derivatives to Physics problems? (I've given up on pop science articles - podcasts with experts interviewing experts has a much higher signal to noise ratio)
I wouldn't expect a journalist to apply second derivatives, but I would expect them to talk to physicists and accurately report what the physicists say. Of course, I have no real physics or astronomy education beyond high school, but I can recognize a textbook one-line description of Hubble's law and know that something's off when it's being attributed to a guy in 1998.
I have quite low expectations of journalists when it comes to anything technical or that requires expertise, but I do generally think highly of the Atlantic and think they are generally a lot better than average at it. I'm a disappointed in this one though.
>but that the rate of expansion itself is increasing over time.
Take for example galaxies running from us at "c". They happen to be exactly at 13.7B light years - coincidence? I don't think it is a coincidence, and some simple logic leads to conclusion that the same galaxies will be running from us at the same "c" say 300M years later - ie. then it will be "c" at 14B light years distance from us - which means that the Hubble constant is actually decreasing.
But further away galaxies are further back in time, so if the expansion is accelerating.. shouldn't they be going away at a slower speed, and the closer galaxies going away from us at a faster speed?
Riess et al's findings showed that galaxies farther away are not just receding faster (as Hubble's Law already described), but that the rate of expansion itself is increasing over time. This discovery suggested the presence of a mysterious force, now called dark energy, driving this acceleration.
This was unexpected because most astronomers at the time thought the expansion should be slowing down due to gravitational attraction between galaxies.