Modern physics assumes the universe is the same all over... but that might not be the case. Until recently, physics held that the universe was contracting... now we're stuck with dark energy. But one moderately insane new theory could explain it all.
The discovery, just over a decade ago, that the universe is accelerating its expansion rocked astrophysics and forced theorists to invoke the existence of dark energy, a mysterious force that drove this expansion and accounted for as much as 74% of all the mass-energy in the universe. It's not exactly the most elegant solution, but it's the best explanation for the evidence currently available. For a more detailed primer on why dark energy makes more sense than all the alternatives, check out Dr. Dave Goldberg's primer.
As for the cosmological principle, which holds that the universe has the same laws of physics everywhere and the same basic structure, well... there's no evidence yet to overturn that, but there are some strange anomalies. Recent findings indicate the universe might be accelerating slightly faster in one direction than another, and some astrophysicists have actually dubbed an apparent asymmetry in the cosmic microwave background the "axis of evil" because it has such potential to wreak havoc on our understanding of physics, assuming the observations hold up.
That, however, is a very big assumption, because if these anomalies really do exist, then that opens up the possibility that the laws of physics aren't the same everywhere. What was once a relatively straightforward cosmos could become impossibly messy. And, while there's no guarantee that the universe has to be elegant, physics has so far done such a good job explaining the nature of the cosmos that we shouldn't throw it all away for such a radical alternative without very, very good evidence. We're not even close to that point just yet.
But what if there's a middle path, one that acknowledges the existence of these baffling anomalies and leaves multiple centuries worth of physics intact? That's basically the new idea put forward by Edmund Schluessel of Cardiff University. The answer, he argues, is found in gravitational waves, which are disturbances in the fabric of spacetime created by massive gravitational disturbances like colliding black holes or the Big Bang. So far, these waves are too subtle for us to have directly observed, but we're decently sure they exist — again, check out our primer for more.
Most models of the universe only incorporate gravitational waves with relatively short wavelengths, while Schluessel hypothesizes the existence of waves that are the size of the curvature of the universe, about 10 billion light-years across. The Big Bang is probably the only thing powerful enough to produce such waves — and even then, a curvature-sized wave is one hell a big thing to invoke — and Schluessel suggests they could still be slowly moving through the universe billions of years later.
The idea is that these waves would be big enough to disrupt our observation of the distant universe, but they would still be too weak for us to easily observe them directly. Waves of this magnitude could distort the cosmic microwave background, he argues, and it could even throw off the light of distant objects to make the universe appear to be accelerating when, in fact, it isn't.
That's potentially a very appealing model, because it in one fell swoop removes the need for dark energy and completely restores the cosmological principle. That's an elegant solution — except for the part where it relies on an extremely exotic form of a phenomenon whose more basic form we still only barely understand, and haven't even directly observed. Besides, while its ability to explain dark energy is a definite plus, it's still an open question whether there's really any problem with the cosmological principle — the evidence there is inconclusive at best, and the apparent anomalies may just be errors in observation.
Still, it's an intriguing hypothesis, and one that probably deserves some followup. Schuessel is optimistic that the next generation of telescopes will be powerful enough to detect evidence of these waves. But, for now, it isn't really any more elegant than the dark energy model, and it's got way less evidence backing it up.
arXiv via Technology Review. Image by Tod Strohmayer (GSFC), CXC, NASA, Illustration: Dana Berry (CXC).