Direct evidence comes from the smoothness of the temperature of the cosmic microwave background, as we will discuss later. "Homogeneity" is the claim that the universe looks the same at every point.
It is harder to test directly, although some evidence comes from number counts of galaxies..
Einstein's model
The first was to suppose that the universe is homogeneous and isotropic in the large (i.e., the same everywhere on average at any instant in time), an assumption that the English astrophysicist Edward A.
Milne later elevated to an entire philosophical outlook by naming it the cosmological principle..
Homogeneity, when viewed on the largest scales, means that the average density of matter is about the same in all places in the Universe and the Universe is fairly smooth on large scales..
Einstein's model
The first was to suppose that the universe is homogeneous and isotropic in the large (i.e., the same everywhere on average at any instant in time), an assumption that the English astrophysicist Edward A.
Milne later elevated to an entire philosophical outlook by naming it the cosmological principle..
Then it follows that, since the universe appears isotropic around us, it should be isotropic around every point; and a basic theorem of geometry states that isotropy around every point implies homogeneity.
However, the opposite is not true.
Also, a Universe that is isotropic around only one point is not homogeneous..
The Universe looks statistically the same in all directions.
This, together with the hypothesis that the matter density and geometry of the Universe are smooth functions of the position, implies homogeneity and isotropy on sufficiently large scales..
Direct evidence comes from the smoothness of the temperature of the cosmic microwave background, as we will discuss later. "Homogeneity" is the claim that the universe looks the same at every point.
It is harder to test directly, although some evidence comes from number counts of galaxies..
Einstein's model
The first was to suppose that the universe is homogeneous and isotropic in the large (i.e., the same everywhere on average at any instant in time), an assumption that the English astrophysicist Edward A.
Milne later elevated to an entire philosophical outlook by naming it the cosmological principle..
Homogeneity means that the same observational evidence is available to observers at different locations in the universe ("the part of the universe which we can see is a fair sample")..
The cosmological principle implies that at a sufficiently large scale, the universe is homogeneous.
Based on N-body simulations in a ΛCDM universe, Yadav and his colleagues showed that the spatial distribution of galaxies is statistically homogeneous if averaged over scales of 260 / h Mpc or more.
Although the universe is inhomogeneous at smaller scales, according to the ΛCDM model it ought to be isotropic and statistically homogeneous on scales larger than 250 million light years.
I've read that in cosmological terms, homogeneous means that the universe "looks the same" at every point (at a given instant in time), implying that it has uniform density (on large scales) and is such that the same laws of physics apply universally.
The perfect cosmological principle is an extension of the cosmological principle, and states that the universe is homogeneous and isotropic in space and time.
In this view the universe looks the same everywhere (on the large scale), the same as it always has and always will.
