Several articles on this, here's the one from <a href="http://www.dailygalaxy.com/my_weblog/2012/06/the-greatdark-energy-debate-does-the-mysterious-anti-gravitaional-force-driving-the-universe-apart-e.html">Daily Galaxy</a> but here's the summary: For a little over a decade now we've been pretty sure the Universe is not just expanding, as we've known for nearly a century, but actually accelerating it's rate of expansion. The mysterious hypothetical thing powering this has been dubbed 'Dark Energy' and we've got basically no information on it besides effect and some various theories. The new theory detailed in the article doesn't object to the expansion, but does object to the acceleration. They believe Dark Energy is non-existent and that the apparent acceleration is caused by Time itself slowing down. And it's interesting stuff.

Okay, the stuff below in blue is a quick thumbnail on special and general relativity and Dark Energy, skip it if you're real comfortable with those:

Now, just to quickly go over known ways to slow time, there are basically 2, both dating to Einstein. The first, from Special Relativity, holds that at very high speeds, relative to an observer, your time will appear to pass more slowly. You on the other hand will see them having time pass more slowly. That is basically SR in a nutshell, velocity is distance divided by time, miles per hour, feet per second, etc, and so either distance or time must change, but you can't be aware of time changing for yourself. This is actually how we observe a lot of really short-lived particles, we get them up to such an absurdly high fraction of light speed, like 99.99999%, that they seem to live longer and we can observe them... though for them the distance from the point of their creation to the detector is actually what shrinks. Both are true, and that's Special Relativity, time slows at high velocities. General Relativity has time slow from very high accelerations or gravity, indeed the core concept of GR is that there is no difference between the two. If you take two synchronized atomic clocks sitting on the middle shelf of a bookcase, and move one down a shelf and the other up, the lower one will actually have less time pass because it is deeper into Earth's gravity well, your feet have time pass more slowly than your head, though the difference is absurdly minuscule.

Wanted to cover both of those real quick, now in this context, for this theory, it's GR that interests us. The concept behind an expanding universe - accelerating or not, is gravity, which should be dragging things back together. The Big Crunch concept which was considered until the late 90's one of the 3 possible Death Scenarios for the Universe postulated that gravity might be strong enough to drag things back eventually, that the Universe expanded in the same way a rocket flies into the sky, it eventually falls back down... or it falls into a steady orbit [not big crunch but eventual static size] or it leaves orbit never to return [eternal expansion] and none of these assumed acceleration, that of course would require monstrous amounts of energy, as Newton knew, you want to accelerate something you have to shove it along. Since the Universe appears to be doing just that, speeding up it's expansion, it needs energy to do this and we deem that 'Dark Energy'. Now we're up to date.

As mentioned, GR says that acceleration and gravity are basically identical, so there's the first ????, where there is acceleration going on time should be slowing down. The theory points out that if you can't find a force doing this, then it might be time itself slowing down and producing an apparent acceleration, uniform in all directions as we observe, because as we know, the further out in space you look the further back in time you look and if time is slowing down then it should be running faster everywhere we're looking and faster the further out you look.

So, summary complete. If you actually skipped that review then you probably guessed the basics of the theory from the title anyway so I hardly need go on Incidentally I've gone over a few articles on this today, and none mention this idea was actually brought up by the principal scientist about two years ago so it isn't brand new. Mostly just wanted it out there since it seems to have hit major papers today. It's certainly an interesting idea, Lord knows I despise Dark Energy though I'm hardly willing to jump on board with this one either. To say this would, if true, have some amusing/irritating consequences would be an understatement. One thing I feel obliged to stress, before anyone gets into philosophizing about this, is that you can never measure time slowing down for yourself, or anything with you in that same effected region [reference frame], though you can detect it in other things or by some reciprocal effect, like light blue or red shifting or in this context, presumably, generating an apparent acceleration.

So enjoy, much of the theory involves String Theory and I'm not a fan of it [not an opponent, just not a fan] so I'm not even going into that aspect of it. And here's another article on the subject, different source, same stuff.