Hubble Definition and 271 Threads

According to Hubble's law, galaxies are moving away from Earth at a speed proportional to their distance. In other words, the further away they are, the faster they move away from the Earth. The speed of galaxies is determined by their redshift. Based on this law, some scientists have come to...

A few years back there was an issue called the Hubble tension where the observations were nor matching up to predictions when looking at the Early and late time data. I had heard that one possible explanation is due to our being in an underdense region but have also read a counter paper to...

Einstein's equations in general relativity indicate that the universe is expanding. Einstein himself believed that the universe should be stable so he introduced a correction to his equations which made for a static universe. He later admitted that was his biggest blunder. Hubble proved by...

Dr. Smethurst summarizes the latest results of the DESI collaboration. What I found especially interesting is that the current value of the Hubble constant that they obtained from baryon acoustic oscillations is in good agreement with the value obtained from Lamda-CDM using Planck data.

I don't understand the discovery of "accelerating expansion" in 1998 (hence the postulate of dark energy, etc..), because Hubble's old law already described exponentially accelerating expansion in 1929, right?

Dr. Becky Smethurst provides a summary of the latest analysis of JWST data by Freedman et al., indicating that there's no statistically significant discrepancy between the value of the Hubble constant thus obtained and the value obtained from Lambda-CDM using Planck data.

Scolnic et al have put out a new preprint with an updated value for the Hubble constant as measured from the Tip of the Red Giant Branch: https://arxiv.org/abs/2304.06693

From NASA: https://www.nasa.gov/feature/goddard/2023/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars "We think we're seeing a wake behind the black hole where the gas cools and is able to form stars. So, we're looking at star formation trailing the black hole," said Pieter...

The GR predictions for the universe's size are those of fig.a. Whereas the Hubble expansion is exponential, fig.b. How are the two reconciled?

In the last chapter of Schutz devoted to Cosmology, Schutz writes So it seems that in 1985 it was assumed as obvious that the recession speed could not exceed ##c##. The consensus seems to have swiftly changed. When did that happen? Was it debated at all?

Spacetime expands at an accelerated rate and the particles with movement associated to this expansion are coupled to the Hubble flow. In many papers that I've read, objects coupled to the Hubble flow are treated as if they have some velocity and kinetic energy associated with it.However, can...

This graph shows ##H## as a function of time related to the L-CDM model. Do we (@Jorrie) have similar graphs e.g. for ##\Lambda=0##; ##k=-1## critical, ##\Lambda=0##; ##k=0## open, ##\Lambda=0##; ##k=+1## closed? That would be great, thanks in advance.

From NASA.gov Mar 30, 2022 Record Broken: Hubble Spots Farthest Star Ever Seen. NASA’s Hubble Space Telescope has established an extraordinary new benchmark: detecting the light of a star that existed within the first billion years after the universe’s birth in the big bang – the farthest...

If there were humans on Earth 2.5 billion years ago (universe 20% younger) and they had today's equipment , would they measure the Hubble constant smaller, larger or the same?

One recent example of a thread discussing flat or not is: https://www.physicsforums.com/threads/could-the-universe-be-infinite.1011228/ . I found an interesting 2021 article regarding the Hubble constant tension...

[Moderator's note: Spin off from previous thread due to topic change.] It's my understanding that Edwin Hubble used the Hooker telescope to measure the red shift of galaxies only within the Local Group of galaxies to determine that the universe was expanding. As we see here...

(P.S! this is an open question, feel free to answer)

By analyzing 91,742 reported extra-galactic distances and their one sigma uncertainties for 14,560 galaxies, it was found that pairs of reported extra-galactic distances of the same galaxy differ from each other by 2.07 the reported uncertainties on average. In my opinion, this indicates that...

I first saw note of this about a week ago and I don't think it has gotten enough attention: https://www.cnn.com/2021/06/30/opinions/hubble-telescope-glitch-opinion-lincoln/index.html While I don't want to eulogize too soon, I'm wondering where the HST ranks in the annals of the most...

Consider a celestial object distance d1 away from an observer, receding at v1=H0d1, Fig.a. And the same object at some time later, now at distance d2 and receding at higher speed v2=H0d2, Fig.b -- 1) where does the accelerating force come from? 2) the resulting universe-size vs time...

The general form of Hubble’s law for a given cosmological time t is given by, v = H(t)D, (1) where v is the recession velocity of an object, D is its proper distance, and H(t) is the Hubble parameter at t. To get the H vs. t plot based on the ΛCDM model, we can use the following steps...

Hubble deep field allowed us to study galaxy evolution from 500 million years onward. Based on my (limited) understanding, I would expect ancient galaxies to contain fewer heavy elements and to have a more "juvenile" appearance, as compared to modern galaxies. Have we actually observed these...

honestly just need some help here i understand the physics just not how to code it or the syntax of python

Here's the problem: It is more common to define the “effective number of relativistic degrees of freedom” by writing the total radiation energy as ρR = ργ + ρν + ρe± = (π^2/30) g∗*T^4 , where g∗ = 2 + 7/8(6 + 4) = 43/4 . (1.52) With this, the expansion rate during the radiation era is given by...

Just curious. We can't figure out Earth's speed of travel through the universe due to the Hubble constant because that would be measured from the center of the universe and the center is located somewhere unknown to us except that it is beyond what we can perceive, i.e., more than about 63 Gly...

Consider the Hubble horizon as the proper distance over which Hubble expansion equals c, so that you are in the center of a Hubble sphere with a radius of about 13.5 billion light-years. As you approach light speed in any direction, does the Hubble horizon draw closer in that direction due to...

Why does the term observerable universe have any meaning outside of observers on earth? From earth, the observable universe is the universe 13.8 billion light years away in every direction which is large but a finite distance. Say there's a galaxy near the edge of our observable universe...

A new report based on Hubble Space Telescope observations is a big deal because it presents a new and independent apparent disparity between the lambdaCDM predictions for dark matter phenomena in galactic clusters and what is observed via gravitational lensing. The paper and its summary and...

Since distances increase, their first derivative which is velocity (Hubble constant) should be positive if not increasing too. Accelerated expansion needs the velocity to increase. What about the third derivative which is acceleration? An accelerated universe could have third derivative (called...

Had to Google Flocculent, adjective having or resembling tufts of wool. "the first snows of winter lay thick and flocculent" having a loosely clumped texture. "a brown flocculent precipitate"...

What has Hubble seen on your birthday? https://www.nasa.gov/content/goddard/what-did-hubble-see-on-your-birthday

It has been proposed the Hubble tension can be solved if we assume our galaxy is located in a giant void (such as KBC). I am confused at this point. If we were living in a giant void, we should have measured the Hubble constant lower. Since when the light passes an underdense region it gets...

There has been a lot of Hubble Tension questions and I know its kind of boring ( maybe for some people) but this seems interesting. I find this article https://arxiv.org/pdf/1911.06456.pdf It claims that "The results are shown in Figure 1 which makes it evident that the derived value of...

This paper just came out with a new measurement of the Hubble constant based on the technique of gamma ray attenuation. The result is consistent with the lower (CMB-based) value. Interestingly, they also do a joint analysis of several non-CMB techniques (BAO+BBN+SN+γ-ray attenuation), and find...

This question will sound mostly stupid but anyways. We see that galaxies have some velocity due to the Hubble law. Let's take an object that has a recessional velocity of ##v##. In SR case assuming the universe is nearly flat, can we say that the galaxy gains mass relative to us ? I guess in...

Imagine a Universe where the Hubble parameter is truly a constant, in both space and time. How much smaller would such a Universe be 14 billion years ago compared to today? Using the Hubble parameter in terms of scale factor: ##H(t) = \frac{\dot{a}}{a}## leads to the differential equation...

I just saw a new paper on measuring the Hubble Parameter : https://arxiv.org/pdf/1908.06060.pdf It seems they are agreeing with Planck which I understand would speak largely against the idea of new physics from the Hubble tension. However it says +14 and -7 next to the estimate. I presume...

The Hubble tension or Hubble discrepancy is a contradiction between the Hubble constant as measured today, and the Hubble constant as measured in the early universe and extrapolated to today. @mfb recently listed the relevant measurements. There are some threads about this in the Cosmology...

Interesting paper on the arXiv today. The authors claim that there is observational evidence that we live in a region with slightly lower density than the universe average, just by chance. Taking this into account can explain as much as 5.5% of the discrepancy in the Hubble constant between...

Hubble constants (HCs) have been estimated based on the CMB, on Cepheid variables, gravitationally lensed quasars, Type 1 supernovae, and red giant luminosity. Not all agree within their estimated error bounds. This has been represented by some as a conundrum. Is it? The mean age of the...

The collaboration with the questionable acronym improved their measurement with a joint analysis of the whole dataset of six gravitationally lensed quasars. Measurements based on supernovae (measuring the Hubble constant "now") and measurements based on the cosmic microwave background (needing...

The Hubble telescope was able to capture images of the edges of our visible universe in its deep space photos. These were among its most breathtaking pictures. They show galaxies from about 14 billion light years away, as well as in the past, from the very beginning of time and space in our...

On Ned Wright's pages one can find this graph: plotting some supernova data against different expansion models. The main thing here that gives me a pause is the linear relationship for the closed universe with ##\Omega##=2 (red line). There doesn't seem to be any weird scaling involved. What is...

How can I calculate the Hubble Parameter in time. I know that it decreases in time and approaches to some constant value but I am not sure to what value, Is there any graph for that ?

Not much known yet, NASA is assembling a team to look into it. The Wide Field Camera 3 is the camera used for most off the "pretty pictures". https://www.nasa.gov/feature/goddard/2019/wide-field-camera-3-anomaly-on-hubble-space-telescope

Homework Statement Estimate how long a galaxy in the Coma cluster would take to travel from one side of the cluster to the other. Assume that the galaxy moves with a constant speed equal to the cluster’s radial velocity dispersion. How does this compare with the Hubble time, t H ? What can you...

i got a bit lost in the responses to my last question so I am guessing this one is really going to be beyond me. Assumptions I have used for my questions are: · Speed of light = 299792.458 km/s · Hubble constant = 71 km/s/Mpc (I know about the tension of H0 being 68 and 73 but...

In the last years a discrepancy between two methods to measure the Hubble constant appeared. Measurements based on redshift and the cosmic distance ladder produced results of about 73 km/(s*Mpc) while measurements based on the cosmic microwave background lead to results of about 68 km/(s*Mpc)...

this graph: http://www.pnas.org/content/pnas/112/11/3173/F1.large.jpg?width=800&height=600&carousel=1 from: http://www.pnas.org/content/112/11/3173 can be found on many sites. the origin is D=0 and t=0. cosmology claims the universe is accelerating over time. the graph shows acceleration over...

From this link https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations#Measured_observables_of_dark_energy , I can't get this relation : ##c\Delta z = H(z)\Delta \chi\quad\quad(1)## with ##z## redshift, ##H(z)## Hubble constant at redshift = ##z## and ##\chi## radial coordinates. One...