Dark Flow

The known universe is about 27.4 billion light years across. It’s thought that the universe is bigger than that, possibly a lot bigger, but we can’t see farther than 13.7 billion light years in any direction. Our knowable universe is limited by the speed of light and how far it could travel since the Big Bang, 13.7 billion years ago. Since light travels one light year per year, that limits us to a radius of 13.7 billion light years.

That’s pretty big. If it’s all we can see with no way to ever see beyond, who’s to say there is anything else? If we’re to be limited to this, admittedly enormous, bubble of space and time, is there any point in wondering if there’s anything else out there? Of course there is. Even if it’s impossibly out of reach we will reach for it. We humans, as soon as we’re shown our boundaries, will try to see beyond them.

Astronomers think they might have done just that. How do they infer that there is more to the universe than we can see? They do it by detecting its effect on what we can see. Two ways of doing that seem to show positive results. One is the motion of large swaths of galaxies and the other is a peculiar imbalance in the symmetry of space.

The flow of galaxies is called Dark Flow by some, in keeping with other great unknowns such as Dark Matter and Dark Energy. It was found in a survey of galaxy clusters, huge gravitationally bound congregations of hundreds or thousands of galaxies, in an area about two billion light years across. They all appear to be moving in the same direction at about a thousand kilometers per second. The implication of that much matter moving at high speed toward the same point is that there isn’t enough matter in the observable universe to account for the gravitational attraction required. It suggests huge concentrations of matter beyond the known universe drawing our galaxies away.

The peculiar asymmetry, the second effect, is found in the cosmic microwave background(CMB) radiation that fills space. The CMB is the cold, fading glow left over from the extreme heat of the Big Bang. It’s observed more or less evenly spread everywhere, with small fluctuations. In theory even the fluctuations should be evenly distributed, but they’re not. They’re about ten percent more numerous on one side of the sky than the other. This suggests that the observable universe’s structure is affected, distorted or sloped in some way, by other structures much larger than everything we can see.

The “whole” universe, of which our observable bubble is just a small part, would have to be very big. So much bigger that there wouldn’t be room in this article to write out how much bigger. It’s no wonder it affects the part we can observe.

rjb