This news came out a little while ago but I didn't cover it at the time, and it's cool enough that it deserves to be covered. I got it from my friends with NASA's Fermi satellite outreach group. I used to work on Fermi outreach before the satellite launched and was still called GLAST (Gamma-ray Large Area Space Telescope), and it was fun trying to come up with lesson plans and educational efforts based on gamma rays (the Hulk came up a lot).
Anyway, one thing Fermi can do is measure the exact time when high-energy gamma rays hit its detectors. Not too long ago, photons from a distant explosion slammed into Fermi, and it found that all these photons arrived essentially simultaneously from the event, irrespective of their energies.
So what? So, Einstein was right. Check it out for yourself:
Basically, the idea is that some quantum mechanics theories propose that space is irregular, foamy, and bumpy on incredibly small scales, and this means the speed at which photons travel may change very slightly if they are more or less energetic. The difference is so small that it takes very long trips to detect it -- imagine two cars traveling at 50 versus 50.5 kph: after a few seconds you'll hardly see any difference, but over an hour they're separated by half a kilometer. So the longer the trip, the easier it is to measure.
After 7 billion years, if those specific QM theories are right, two photons should arrive at very different times, but Fermi found that the high energy gamma rays hit Fermi less than a second after the low energy ones. This means that space really is smooth, or at smooth at scales smaller than predicted by those quantum theories. QM is still a solid model for the Universe -- after all, solar panels, computers, and nuclear bombs do work -- but this means that we need to rethink certain aspects of them.
I love hearing stuff like this. We have lots of ideas on how the Universe works, but we need observations of the Universe to know if we're traveling down the correct path or not. Fermi has shown us that some of these paths lead to dead ends, and we need to look elsewhere for our journey to continue. And I will guarantee that not only will that journey go on, but we'll find ever-more roads to investigate as we travel.