posted by: Tom Loughran
Maybe you’ve seen the picture: the best image we have of the cosmic microwave background radiation, from the Planck mission. This newest image of the oldest things is creating a bit of stir. It’s important to know something about why.
Cosmic microwave background radiation is the observable limit of the light that is emitted from the big bang. For most of us this has an unfamiliar ring, but it’s not so hard to grasp. When we catch a glimpse of the sun, light has just traveled the ~93 million miles to reach us, which took about 8 minutes. As we look further out–to the nearest star, say–it takes light longer (about four years) to cover the distance. But it turns out that the space over which that light is traveling is actually stretching: we know this from watching the chemical signatures in the light, which shift with distance in just the way that sound waves stretch (and seem lower in pitch) when their source (say, an ambulance) is moving away from us. Our speeding away from the source makes the wavelength of light more red when we detect it, just as sound waves seem lower when their source is fleeing; we call this change in light “red shift.” The upper limit of red-shifted light is from the oldest, furthest-away sources. These sources–like points on opposite ends of a balloon while it is being blow up–are fleeing every other point on the balloon most rapidly, and are stretched into longer wavelengths, in the microwave region.
This oldest, most red-shifted light from the big bang is the cosmic microwave background radiation. And it’s not behaving quite as the standard model of cosmology–what most scientists accept as pretty well established–predicted that it would. In many ways, that’s a bit misleading: it behaves as expected in a great many respects. But not in all. Watch the short video below to find out more. And stay tuned: Planck is still taking data, and what it has already delivered has stirred a flurry of scientific activity. It’s worth stretching a bit to follow the conversation.