By Eric Hand of Nature magazine
Even the best pictures of a distant galaxy are a bit lopsided. But this is an attribute, not a bug. Because mass distorts space-time, light coming from distant galaxies is bent as it passes through intervening shoals of invisible matter, leaving the images of these distant objects minutely sheared and stretched.
Two astronomical surveys now scheduled to come online seek to take advantage of this effect, which is known as weak gravitational lensing. The surveys aim to use the technique to get a firmer handle on dark energy, the mysterious force that is apparently speeding up the expansion of the Universe. By observing the patterns of distortions across large swathes of sky (see 'Falling into line'), astronomers hope to map the density and distribution of dark matter, the web-like invisible scaffolding around which visible matter is thought to have first coalesced. Then, by looking at changes in this hidden web across cosmic time, they hope to discern the imprint of dark energy.
I've never liked dark energy. To me, describing dark energy is like describing negative distance: sure, you can do it mathematically, but try visualizing it.
I've always been leery of hypothesises that require exotic forms of matter or energy in order to function. Granted, I'm not a physicist and I can't propose anything better. However, I have studied philosophy and it applies here. When you consider a structure that is unimaginably massive, is constantly changing, and has been around for billions of years, complexity is not the goal.
The universe exists, and has done so for roughly 14 billion years. I think both these facts can be accepted. Now, because the universe is still here, it must be stable. If it is stable, than the rules which govern its behavior must be sufficient to guarantee its stability. Now, out of complexity comes disorder. Too many variables interacting can cause all sorts of funny things to happen.
Thus, it seems to my mind that the universe is more likely to be simple than complex. Adding exotic forms of matter and energy in order to explain things strikes me as being dangerous. Yes, sometimes it turn out to be confirmed by experiment, as in the case of quarks. However, it can lead to a trap. A theory can be so 'beautiful' and perfect mathematically that it blinds one into ignoring the evidence of the real world.
My own pet theory is that time has energy, and therefore mass. All the accumulated time of the universe lurks at the boundary, and its mass creates a pull on the center of the universe, causing expansion.