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Comment by pdonis | Hacker News Reader

> To me, this says a lot more about the expansion of the universe, in that we have an ever smaller window into the observable universe

I don't think that's what the actual paper is saying. The "stellar mass density" it talks about is by definition homogeneous across the entire universe; it's not something that is affected by how much of the entire universe we can actually see.

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“Observed locally” seems to be doing a lot of heavy lifting if I read things right.

If the observable universe is say 1/300th of the total, wouldn’t this actually represent an increase?

We can only make direct observations of stellar mass density locally. We have no direct way of knowing what the stellar mass density is "now" a billion light years away; all we can see is what it was a billion years ago. We have to reconstruct what things are like "now" elsewhere based on past data, which is all we can see.

That makes sense, but isn’t it at least more likely than not that there is relatively normal distribution?

> isn’t it at least more likely than not that there is relatively normal distribution?

No, because that would make our particular spatial location in the universe special, and that is an additional hypothesis that would require some kind of evidence in its favor, and we have none. The simplest hypothesis is that the universe is pretty much the same everywhere, and that means the average stellar density "now" should be pretty much the same everywhere.

That’s what I meant by normal distribution :)

Ah, ok. I was interpreting "normal distribution" in the sense that term is used in statistics, as "Gaussian centered on our spatial location".

This type of casualty is to be expected when a word like 'normal' takes on a technical definition :)

That's a uniform distribution

> If the observable universe is say 1/300th of the total, wouldn’t this actually represent an increase?

I'm not sure what you mean.

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