There is a straightforward way, in principle, to measure these two types of curvature. A slowly-moving object (like a planet moving around the Sun) is influenced by the curvature of time, but not by the curvature of space. (That sounds backwards, but keep in mind that “slowly-moving” is equivalent to “moves more through time than through space,” so the curvature of time is more important.) But light, which moves as fast as you can, is pushed around equally by the two types of curvature. So all you have to do is, for example, compare the gravitational field felt by slowly-moving objects to that felt by a passing light ray. GR predicts that they should, in a well-defined sense, be the same.
We’ve done this in the Solar System, of course, and everything is fine. But it’s always possible that some deviation from Einstein shows up at much larger distance and weaker gravitational fields than we have access to in our local neighborhood. That’s basically what Rachel’s paper does, considering different measures of the statistical properties of large-scale structure and comparing them to the predictions of a phenomenological model of the gravitational field. A crucial role is played by gravitational lensing, since that’s where the deflection of light comes in.
Archive for October 13th, 2009
Travel has become difficult. Last year, a bureaucratic snafu not only denied me a trip to a conference in Hawaii, but it happened late enough that it kept me from scheduling an alternate trip to DAMOP. I spent the last week with the flu, which forced me to cancel a long-weekend trip to visit some college buddies, and now my plan to give a talk at an AAPT conference has been shot down. The government is operating under a continuing resolution, rather than an actual budget, and apparently this means there is a moratorium on this kind of travel. Not going on work-sponsored travel would essentially mean I couldn’t talk about results from work, which was going to be half of my talk. I’d be limited to talking about things that you could pick up on the streetcorner (but don’t do that … you never really know if that information is any good). Meh. Maybe this is a conspiracy.