28
votes
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) ...
- 5,976
19
votes
Accepted
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 ...
- 37k
16
votes
Accepted
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 ...
- 37k
16
votes
Accepted
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 ...
- 146k
15
votes
Accepted
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 ...
- 36k
14
votes
Accepted
Can the Hubble constant be measured directly?
The universe doesn't expand on such small scales. In fact there is no expansion even on the scale of the local group of galaxies. It is only when you look at more distant galaxies that you see the ...
- 116k
12
votes
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 ...
- 116k
11
votes
Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?
The anthropocentric picture does not explain observations of the present and distant cosmic microwave background (CMB)?
Are we to suppose there is a large, spherical shell of optically thick gas ...
- 146k
11
votes
Accepted
How sure are we about the speed of light in vacuum in deep/far space?
The speed of light is a defined constant so cannot vary - or at least it's variation cannot be measured since it is used to define the measurement system. However $c^2 = (\mu_0 \epsilon_0)^{-1}$ and ...
- 146k
10
votes
Accepted
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 ...
- 8,313
10
votes
Accepted
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 ...
- 146k
10
votes
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 ...
- 37k
10
votes
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 ...
- 3,689
10
votes
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'...
- 201
9
votes
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 ...
- 2,523
9
votes
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, ...
- 146k
9
votes
How long has it been since dark energy started to reverse our slowdown and accelerate the expansion of the universe? 4 billion years ago? 4.5? 5?
It is likely that you or your sources are conflating two different events.
Dark energy begins to comprise the majority of the Universe's energy density about 4 billion years ago.
The expansion of the ...
- 4,260
8
votes
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 —...
- 37k
8
votes
Accepted
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 ...
- 146k
8
votes
Accepted
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 ...
- 37k
8
votes
Accepted
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 ...
- 687
7
votes
Accepted
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. ...
- 146k
7
votes
Accepted
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 ...
- 37k
7
votes
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 ...
- 10.2k
7
votes
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 ...
- 191
7
votes
Since the Hubble Constant changes over time (it's a variable parameter), why can't the conflicting values of 67.4 and 73 both be right?
You are confusing the Hubble parameter $H(t)$, which is a function of time, with the Hubble constant $H_0=H(t=\text{today})$ which is the value of the Hubble parameter today, and so of course is a ...
- 4,371
6
votes
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 ...
- 5,300
6
votes
Accepted
When was Hubble tension first noticed? When was this term first used?
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 ...
- 17.4k
6
votes
Accepted
Intuition about Hubble's Law
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 ...
- 392
6
votes
How does the hypothesis of the "inconstant Hubble constant" solve the current crisis in cosmology?
In the expanding universe the luminosity distance is related to the redshift by,
\begin{equation}
d_L=c(1+z)\int_0^z \frac{dz'}{H(z')}
\end{equation}
where $H(z')$ - is the rate of the universe ...
- 161
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