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6

Hubble's law $$v=H_0 d,$$ relates the recession velocity $v$ of a distant object to it's physical distance $d$. Today, the physical distance coincides, by definiton, to the comoving distance $\chi \equiv d/(1+z)$, but if you want to know how fast two galaxies at a redshift of, say, $z=1$, you must plug in their physical distance at that time (and use $H(z)$,...

5

tl; dr The universe is probably infinite, but if that's the case it's impossible to verify. If the universe is finite, and small enough, and the global curvature is equal to the curvature of our observable universe, then we will be able to estimate its size. If the global curvature of the universe isn't positive, then the size of the universe is infinite, (...

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According to this paper I understood that scientists have found that redshift (z) of supernovae depends on relative distance (x) according to formula: z = 2 sinh(x)/(1 + x). And IF nothing is pushing galaxies away with force then redshift should drop linearly with decrease of distance between galaxies. But it isn't so as relationship z(x) is a nonlinear one. ...

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If like me you think the answer is C, can you explain why light should travel differently through a gravitational field to how it travels through an expanding universe? In other words, why in one case does the speed of the photon vary, while in the other case it doesn't? I think the reason is, we can take the Cosmological redshift as a Doppler redshift, ...

1

So far our estimates of the size a the Universe is from what it is expected to be (i.e. calculations) rather than what we see. But there are several problems. Age of the Universe We are pretty sure of the age of the Universe, 13.8B years old, and the time when the first light was emitted. This gives us a relatively good idea of the size of the Universe ...

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