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Australian Study Backs Major Assumption of Cosmology
cylonlover writes "In mankind's attempts to gain some understanding of this marvelous place in which we live, we have slowly come to accept some principles to help guide our search. One such principle is that the Universe, on a large enough scale, is homogeneous, meaning that one part looks pretty much like another. Recent studies by a group of Australian researchers have established that, on sizes greater than about 250 million light years (Mly), the Universe is indeed statistically homogeneous, thereby reinforcing this cosmological principle."
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So the laws of physics still hold in Australia at least.
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(and, shouldnt that be a unit of volume, not length?)
When talking in terms of scale, it's generally better to use fundamental units, not derived ones. Volume is derived from length (length^3), so a volume scale is inherently a length scale, but less precise. If you were to use a volume scale, say 250Mly^3, then that could mean different averages looking in different directions (i.e. the universe is homogenous every 250kly looking up, every 10ly looking left, and every 100ly looking forward). Just using a length scale ensures all 3 dimensions are covered equally.
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So, does that mean there is atleast one Earthlike planet with life on it every 250 million light years?
No. Statistics don't work that way. It might mean there is, on average, one Earthlike planet per given volume of space, but certainly no "at least" guarantee, and indeed if the average is that low, there will be many instances of zero in said volume.
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More to the point would we recognize intelligent life even if it was in front of our face.
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Most comments seem to be vying for most funny, but if you do happen to care about visualizing the scale, the distance to our closest full-sized galactic neighbor, the Andromeda Galaxy is 2.5 Mly. That is 1% of the homogeneity scale cited by the article. So, they are saying that things seem smooth averaged over scales merely 100 times bigger than the distance to the nearest extra-galactic clump which is sized comparably to The Milky Way. That's actually pretty smooth, in context.
...an argument often made right here on Earth.
None. Although you might see people from time to time, they are most likely products of your imagination. Simple mathematics tells us that the population of the Universe must be zero. Why? Well given that the volume of the universe is infinite there must be an infinite number of worlds. But not all of them are populated; therefore only a finite number are. Any finite number divided by infinity is as close to zero as makes no odds, therefore we can round the average population of the Universe to zero, and so the total population must be zero.
For scale:
Milky way diameter ~ 0.11 Mly,
Local Group (Milky way, Andromeda, etc...) diameter ~ 10 Mly,
Virgo Supercluster diameter ~ 100 Mly.
The existence of superclusters is part of why local homogeneity is not observed. However, the claim is only that any given region of about 250 Mly is on average about the same as any other region of the same size. So, even if that homogeneity holds true as you reduce scale (i.e. look for an average Earth) there's still a huge difference in thinking that you've got AC posters on alt-Earth asking about their alt-Australian universe homogeneity study. Besides, the frequency of Earth like planets should be signnificantly higher within our own statistically homogeneous region, but we still haven't had cookies dropped off from our older-to-the-hood neighbors. Check out the Fermi Paradox for fun reading.
Actually - there's some discussion to having been visited in prehistory and early history earth, but that's a subject for an alt. and not an alt-
;)
There's a reason that we use volume as a dimension......volume doesn't depend on shape.
There's a reason that we don't use volume as a measure of scale - volume doesn't depend on shape. That's my entire point. When you're dealing with scale, it doesn't matter if it's a sphere or a cube, because we're dealing with statistical averages, not defined physical limits. The difference between a sphere and a cube of D=S is dwarfed by the difference between a sphere and a hugely-eccentric ellipsoid of equal volumes. The point is homeogeneity. We want to be clear that the average pointing one direction is the same as the average pointing another direction. You can't do that with volume.
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Until the Billion light-year across VOID is explained, this article makes no sense! http://www.newscientist.com/article/dn12546-biggest-void-in-space-is-1-billion-light-years-across.html
It's still an assumption. If the universe is infinite, then this observation says nothing about the non-observable universe. Any statements about the non-observable portions are purely assumptions.
It was pretty much ruled out by the cosmic background microwave radiation surveys. Because that's a point-in-time snapshot of the universe, seeing the same stuff repeated in layers would really stand out. The visible universe is a subset of the universe.
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