Astronomers Discover a Group of Quasars 4 Billion Light Years Across

New submitter mal0rd writes "NewScientist reports a 'collection of galaxies that is a whopping four billion light years long is the biggest cosmic structure ever seen. The group is roughly one-twentieth the diameter of the observable universe – big enough to challenge a principle dating back to Einstein, that, on large scales, the universe looks the same in every direction.' For reference, Andromeda is only 2.5 million light years away."

Comments

Central limit theorem

[TapeCutter]

When Einstein said it looked the same in every direction, what he meant was that it's all governed by the same laws.

Actually it's more than that, it's also about the distribution of matter and energy on a large scale. It's assumed that matter is homogenous throughout the universe, homogenous literally means "no lumps" (above a certain size defined as "local" in your post). It's like an ideal gas, at the microscopic level you have all sorts of random "pressure" (kinetic energy of the individual atoms), at the macroscopic level there is just one pressure that is the same no matter what part of the gas you measure. This is because the macroscopic measurements are an average of all the individual microscopic pressures, the central limit theorem of statistics says that that the average of a big enough sample from a large population will always be very close to the real population average.

In other words the reason it's "odd" is that statistics says the observation can't be brushed aside as a fluke, if the distribution of quasars is lumpy then either the basic assumption of large scale homogeneity is wrong, or the observation is flawed. The OP's stupid question is by far the most insightful thing I've read about it so far, how are they defining the word "structure".