# Tag Info

### Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

I'm looking for some kind of observable evidence (that has been observed, or could be observed in the future) that could falsify one or the other theory. You seem to be requiring one (very high) ...
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### Does the Hubble constant depend on redshift?

Yes, definitely. The Hubble constant describes the expansion rate of the Universe, and the expansion may, in turn, may be decelerated by "regular" matter/energy, and accelerated by dark energy. It's ...
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### How is the Hubble constant determined from gravitational waves?

If you measure the gravitational waveform from an inspiralling binary, you can at any point measure the amplitude, instantaneous frequency and the rate of change of frequency. The last two give you ...
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### Latest cosmological parameters

Cosmological parameters are measured in a variety of ways, and their values will depend on which measurements you trust the most. The paper you link to (Planck Collaboration et al. 2016) with the 2015 ...
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### Why do we continue to find a discrepancy in the Hubble Constant?

To make a long story short, the measurements from Planck and the Hubble Space Telescope disagree, and the reason behind this isn't known. First, let's look at the values with the uncertainties. We ...
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### Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

We can currently only detect gravitational radiation when it is extremely intense: in the last fraction of a second. For example the first gravitational wave detection lasted less 0.15 seconds. The ...
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### Where can I find a database of galactic spectra?

The Sloan Digital Sky Survey Data Release 15 contains over 4 million spectra of both galactic and extra-galactic origin from the multi-fiber spectrographs. Of these spectra, 0.7 million came from the ...
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### Could the Hubble Constant be an artifact of the structure, and thus a way to directly measure the universes's age?

I'm a bit uncertain if I understand your question correctly, but if I do, you're asking whether or not it's a coincidence that $1/H_0$ is roughly equal to the age of the Universe. If so, the answer is ...
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### So where are these measurements of galaxies moving faster than light?

So where are these measurements of galaxies moving faster than light? They're redshift measurements. Check out the Wikipedia redshift article. It's good stuff. "we can actually observe galaxies ...
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### Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

I think StephenG is right, but I will mention one counterfactual. Suppose we observed no galaxies more than a billion light-years away, as determined by their red shifts. Say they were roughly ...
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### How is the Universe's Expansion Accelerating if the Hubble Constant is Decreasing?

The Hubble parameter is defined as the rate of change of the distance between two points in the universe, divided by the distance between those two points. The Hubble parameter is getting smaller ...
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### Does the accelerating expansion of the Universe contradict Hubble's law?

The Hubble law gives the velocity of a distant galaxy right now. A galaxy at a distance $d$ recedes at a velocity $v = H_0\,d$ right now$^\dagger$. However, the relation between $d$ and the redshift —...
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### Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?

At a distance of $d = 87\,\mathrm{Mpc}$, with a Hubble constant of roughly $H_0 = 70\,\mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{Mpc}^{-1}$ cosmological expansion should make the host galaxy UGC 11723 ...
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### Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

The duration of a gravitational wave detection is not particularly important in detecting electromagnetic counterparts, although the fact that they are not recurrent or repeating sources is. Binary ...
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### Why would a quantity like the 'Hubble contrast' be squared, then have its square root taken?

The brackets refer to the average, so $\left< x^2 \right>^{1/2}$ is the root-mean-square (RMS) of $x$. That is the square root of the mean (or average) of the square of multiple $x$s. The RMS ...
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### Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

I would like to point out another flaw in the question: the model "everything moves away from us proportionally to its distance" is not actually anthropocentric in a basic approximation. Let'...
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### Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

I'm not clear what, in this anthropocentric picture, explains the cosmic microwave background? Are we to suppose there is a large, spherical shell of optically thick gas expanding away from us faster ...
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### Interpretation of Hubble constant in SI units

Unless the expansion/contraction is periodic then the frequency is just the reciprocal of an expansion timescale. There isn't any evidence that the universe will contract again. However, if it did, ...
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### Does the accelerating expansion of the Universe contradict Hubble's law?

Hubble's law is a bit more subtle than you suppose and an expansion, whether accelerating or decelerating does not invalidate it. The distance and speed that should be used are their values now. ...
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### Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

Just a supplement to @JamesK's excellent answer. The image below (from Caltech/MIT by way of New Sciencist) shows what was detected for one collision. On the left (at the start) the blackholes orbit ...
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### If we watched extremely red-shifted galaxies near the edge of the observable universe for a very long time, how would they change? Would more appear?

tl;dr Their redshift would first decrease from $\infty$ to $\sim60$, then increase to $\infty$ again. And more eventually appear. The answer to this question is somewhat non-trivial, and will depend ...
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### Does the Hubble constant depend on redshift?

What the Hubble constant really depends on is how old was the universe at the time, but if you have a dynamical model of the universe, you can map that into z and come up with a function H(z). So in ...
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Think about it as if you were baking bread (or cake, whatever you prefer). When you bake a bread with raisins, it rises in all directions (due to the yeast). Every raisin in a rising loaf of raisin ...
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### How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?

tl;dr No, it's unfortunately not that simple. Cosmological distances The comoving distance to an object observed to have a redshift $z$ — i.e. the coordinates that expand along with the Universe — is ...
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### Hubble constant from GW events

You can't estimate Hubble's constant using the method you propose, for two reasons. (1) Redshift and luminosity distance are only linearly related by the Hubble parameter at small redshifts. (2) You ...
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### Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

I'm going to disagree with @StephenG's answer. This hypothesis is empirically falsifiable: for some other reason everything around us is physically moving away from us, and the farther things are ...
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### Light beam (1 photon) in the limited universe?

A finite universe is said to have a "closed geometry", or to be "positively curved", meaning that, in principle, you may travel in a straight line and eventually return back to your starting point. In ...
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### Did Gaia actually generate complete light curves for 212 Cepheids in other galaxies?

Am I naive to think that it is necessary to build up a nice, complete light curve with dense points in time in order to use the photometry for precision distance calculations? No, the more I read ...
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### Use of type-I a supernovae as standard candle

A type 1a supernova forms when a white dwarf grows through accretion to a certain size, at which it becomes unstable. This means that the precursor object is always a white dwarf of mass 1.39 solar ...
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Hubble tension refers to the incompatibility between different measurements of the value of the Hubble constant. These measurements are incompatible up to more than $5 \sigma$. This incompatibility ...