Eureka! Uh-Oh...

One of the problems astronomers and cosmologists have is figuring out how far away things are.

Not things in our solar system or things nearby -- things far away. Stars and such are light sources and ordinarily we figure a brighter light is closer to us, and vice versa. But stars vary in brightness. So something that looks very dim to us might actually be very bright but far away. Or a big cloud of whatever might be between us and it, so we see it as though we were looking through sunglasses -- only we have no idea how much light the sunglasses block.

We determine how far away closer objects are by "parallax." This describes how something appears to shift position if we look at it from one point and then move to another point and look at it again. Measure the apparent change, do some math and voila! Distance measured. Again, objects far away in space have almost no noticeable shift for about as far apart as we can distance ourselves on earth, so astronomers look at them once and then again six months later. This gives them an observational base as wide as the Earth's orbit around the sun, which is about as wide as we can manage.

The European Space Agency satellite Gaia has observed thousands of parallaxes over the past years from its orbit a million miles out from Earth, providing data for some of the most precise measurements possible. We know better than ever before how far apart things are, which makes astronomers very happy. If we know a certain kind of star is exactly so far from us and we know what it looks like, then when we find that same kind of star somewhere else we can compare brightnesses and compute a distance for the new star as well. And by "we" of course I mean astronomers, since my brain got fried several algorithms back.

This is great news for astronomers and has them quite pleased. Until it doesn't, as Natalie Wolchover writes at Quanta Magazine. Because one of the things the more precise distances tell us is that the universe's rate of expansion is faster than we thought it was, without offering any explanation as to why that might be. In other words, by answering one question scientists have posed at least one new one. Which is OK by them because they like that sort of thing -- especially when the new question apparently has no ready answer. If we figure everything out, after all, then it won't be long before boredom sets in and we don't have much of an answer for that.