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Why is the Hubble parameter constant for an accelerating universe?

Accelerating expansion means that the separation between two points in the universe increases at an increasing rate. The Hubble parameter is the constant of proportionality between the rate of change ...
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4 votes

In km/h, what actually is the "speed" of Andromeda away from us: cosmologically?

Andromeda is moving toward us. It isn't a peculiar motion superimposed on a cosmological recession; it's just ordinary relative motion. The FLRW geometry is not a background of expanding space on ...
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2 votes

Distance of distant galaxies

Redshift, angular-size distance, and time-since big bang are all ways of describing the distance of an object or (since distance and time are related) the time when the light was emitted. Now, you ...
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1 vote

Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?

Let's see.. suppose the ruler masses 0.001 g per meter. 1E9 ly * 0.001 g $\approxeq$ 9.5E18 kg , roughly equal to 324 Bamberga. Leaving aside the obvious questions about rigidity in the presence of ...
2 votes

Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?

I'll give it a try, and I'm perfectly willing to take my answer back if it's wrong beyond repair. The first thing I take issue with is your wording "the space surrounding the ruler expands". ...
12 votes

Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?

There is no Aristotelian/frictional force that drags things along with expanding space. The motion of objects is governed by inertia ordinary gravitation, which is an inward acceleration (note: ...
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