From Felix Tymcik:

Re: Gaping “hole” in the cosmos found (Aug. 23): logic dictates that outcome equals input, as far as I understand it. If rays actually leave a cluster of galaxies with a slightly higher potential than they entered with, as stated in the second last paragraph, that would mean that dark energy works selectively – by greasing the way out (by shielding off gravity) but not influencing incoming rays.

Did I get that right?