Hubble Definition and 278 Threads

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...

This year alone we have conflicting speeds for the Hubble Constant with 67.66 (+ or - 0.42) from the Planck Mission and 73.45 (+ or - 1.66) from the Hubble Space Telescope. The answer is simply found, and is between those figures. The furthest thing we can see (in theory) is 13.8 billion light...

New adaptive optics does an amazing job. https://cdn.eso.org/images/screen/eso1824a.jpg http://www.eso.org/public/usa/news/eso1824/ Many more hits at: https://www.google.com/search?&q=neptune+very+large+telescope

http://hubblesite.org/reference_desk/faq/answer.php.cat=topten&id=93 So, I found out that the images taken by the Hubble Space Telescope are not colored but black and white and colors are added to them later. I thought that the way you figure out what colors are present in your object(s) of...

For constant dark energy, Hubble value will eventually become asymptotic. If dark energy were dynamic and gently decreasing, what will the value of Hubble eventually become - will it asymptote or keep decreasing?

As I understand Planck has a value for Hubble as 68 kilometers per second per megaparsec and the supernova data is saying 71 . I also thought the time since the big bang (I think cosmologists are wrong to call it the age of the universe since we don't really know whether the universe did begin...

Homework Statement The star Betelgeuse is 427 lightyears from earth. Betelgeuse has a diameter 800 times that of the sun, where the diameter of the sun equals ##1.39*10^6 km##. Given that Betelgeuse has an angular resolution given by the Rayleigh Criterion of 58 nRad, is it possible for the...

Several questioners ask if the Hubble red shifts could be gravitational red shifts rather than space-expansion red shifts. I understand why the answer has generally been "no". However, can I try this variation of the question... Red-shifting is apparent mostly for distant galaxies, which are...

I may have a fundamental misunderstanding of the concept, but I was wondering, how does the accelerating expansion of the universe calculate for the time dilation in light travel? From my understanding, we know that the universe expansion is accelerating because the farthest galaxies that we...

Since the universe's expansion is accelerating, let's suppose it will expands at a higher rate of 700 km per s per megaparsec (10 times the present value) in future. Then the Hubble radius would be 430 megaparsecs (0.1 times the present value). So shouldn't the Hubble sphere contract instead...

I was just wondering what the reaction was from people and the media at the time after hubble's telescope took it's famous images? If I am not mistaken hubble's images where one of a kind showing that there where a lot of galaxies and whatnot out there. Was it advertised on the news a long...

I'm asking many questions on inflation, I hope this is the last one... If inflation is correct, our observable Universe would have been a tiny homogeneous patch before inflation started (if it started at all). The length of that initial patch is estimated to be of the order of 1 Hubble length...

Hi! Can anyone tell me what the radial BAO size method is? how do people use it to get to the H(z)? I am reading the paper "Constraints on the Dark Side of the Universe and Observational Hubble Parameter Data " by Zhang et al. and I think I am lost! Can anyone tell me very simple, how they do...

I just saw this news article on the home page of the university I'm working in: http://www.aalto.fi/en/current/news/2017-06-30/ It seems to be about a study that can potentially explain the redshift of distant stars with a mechanism that's related to the interaction of photons with the...

I'm just looking for conceptual clarification re: the relationship between matter density and the Hubble parameter in the Friedmann equation. Just for quick reference, the equation I'm looking at is H2 = 8πGρ/3 - ka-2 (I'm working through Liddle's Intro text, and for now we're ignoring the...

Is the Hubble constant decreasing over cosmological timescales?

This is the time derivative to calculate the speed which a galaxy moves away from another galaxy. I don't understand how they get from da/dt (xi − x1) to (∙a)/a a(t). (xi − x1). Could anyone explain this? vi(t) = d/dt (ri(t) − r1(t)) = d/dt a(t)(xi − x1) = da/dt (xi − x1)...

Is the energy density ##\rho## in the early universe and the Hubble scale ##H## during inflation related by the formula $$H^{4} = \frac{9}{64\pi^{2}} \frac{\rho^{2}}{M_{P}^{4}}?$$ Here, ##M_{P}## is the Planck mass. Can you suggest any resources where this is explained?

I'm trying to figure out or find how fast Earth is moving due to the Hubble constant. I'm runnng into two answers and have difficulty understanding either one. --- One answer is a number of kilometers per second per megaparsec. But that's a distance per time unit per distance unit. I don't...

EEE degree w/ phys minor. hubble's graph shows velocity increasing over distance, not time. an image 10 mil ly away is 10 mil y old (t = -d/c) the origin of hubble's graph is d=0 and t=now, not 0 older images are faster and older image means younger galaxy distance is proportional to age, which...

I have been reading in various sources that the directly measured value of Ho is high than the global value inferred by precise measurements of the CMB. The local value seems to be around 73 km/s/Mpc where as the global value inferred, assuming a flat Lamda CDM model is about 67 km/s/Mpc...

From cosmology, ##H^2 = \frac{ρ}{3M_p^2} = \frac{1}{3M_p^2}(½\dot φ^2 + ½m^2φ^2)## Suppose ##V(φ) = ½m^2φ^2## where ##ρ## = density ##M_p## = Planck mass I want to graph ##H## vs. ##φ## but there is a ##\dot φ## and I know this is a differential equation, can somebody help me what to do here?

Hello, When we assume the universe is expanding at a constant rate, we could say the age of the universe is 1/Ho. but I always feel unsure about that because 1/Ho is the distance over the velocity. However, the velocity changes over time, that is, when something is closer to us, the move slower...

I've read that Hubble is in geosynchronous orbit, but precisely what point on Earth does it remain in orbit over?

Hello! I have a question regarding the effect of the accelerated expansion of the universe on the Hubble plot (redshift over luminosity (or distance). I understand that for relatively nearby galaxies, this appears to be a linear relationship but that because of the accelerated expansion of the...

How does Hubble parameter and scale factor's derivative differ geometrically? I am reading S. Caroll's GR book. But I cannot get the full representation of these two parameters. On the book, it says How can \dot{H} and \ddot{a} be opposite of each other on the same instance if both are...

From Introduction to Cosmology by Matt Roos, he wanted to derive the Hubble parameter in terms of the scale factor. From the Friedmann's equation, ##\frac{R'^2 + kc^2}{R^2} = \frac{8πG}{3}ρ## The density parameter is ##~Ω(a) = \frac{8πG}{3H_o^2}ρ(a)~## and let ##~Ω_k = \frac{-kc^2}{H_o^2}##...

Dear PF Forum, I've been wondering about this thing. The universe's radius is 46 gly. But a galaxy in 13.8 gly from us cannot be seen because it travels faster than the speed of light. So is there a galaxy in, say, 30 billions light years away from us? But before that, I'd like to know about...

Based on my understanding, Hubble sphere is the region that contains GALAXIES receding subluminally while GALAXIES outside are receding superluminally (obviously on the border, GALAXIES recede at the speed of light). Particle horizon is the limit of what we have seen so far since the (big...

Dear PF Forum, I've been wondering about how on Earth (and I do mean it, from earth :smile:) that we know there's a galaxy 20 billions light away. Considering that https://en.wikipedia.org/wiki/Age_of_the_universe is 13.8 billions years old. But before I'm asking about Supernova Ia and Hubble...

Dear PF Forum, While learning why the net energy of the universe is zero. I've been reading about the expansion of the universe, and of course in it, Hubble Flow. https://en.wikipedia.org/wiki/Hubble's_law = 73km/s per Mega parsec https://en.wikipedia.org/wiki/Parsec = 3.26 light year. In the...

According to the paper they used 300 SNe Ia along with Cepheid variables, as a basis for determining cosmological distances. With the exception of 19 SNe Ia, which were calibrated using nearby Cepheids, the remaining 281 SNe Ia were based purely on their light curve to determine their type...

I read here, http://www.space.com/24781-big-bang-theory-alternatives-infographic.html , that, "What we call the "observable universe" (or the "Hubble Volume") is the spherical region, about 90 billion light-years in diameter, that is centered on any given observer. This is the only part of the...

I'm not talking about the well known, miss-grinding of the main mirror which was corrected long ago . This picture illustrates well , my beef with the current images ... Every image of every star has four streaks of light , this is not so noticeable in pictures of galaxies where the stars...

Is there an equation which explains how the recessional velcoity of a galaxy changes with time? Furthermore, does an equation exist that describes the universe's accelerating expansion; is it the Friedman equation?

Homework Statement I am just looking through some old notes I have from for cosmology, and there's something cropped up that i can't seem to figure out: Say I have two (or more) values for H_o each with errors such as: H_{o_1}=70^{+a+b}_{-c-d} and H_{o_2}=69^{+e+f}_{-g-h} How would I go...

"A 2.4% Determination of the Local Value of the Hubble Constant" by Riess et al has led to some excited news stories recently. I don't see it discussed anywhere here. Looking for the essence of the paper, I note three things: The two measurements considered are "the Hubble constant ... measured...

Hubble breaks the distance record, with a large jump to a redshift of 11.1 Does this mean that some of theories need revision? We do not appear to reaching a limiting value!http://sci.esa.int/hubble/57530-hubble-breaks-cosmic-distance-record-heic1604/

Dear all, Considering Einstein Hilbert lagrangian, by using Einstein field equations one can get the form of Friedman equations and consequently the Hubble parameter. I know that in f(R) models, Einstein equations get modified. However, what happens to the Friedman equation and the Hubble...

If the Universe were not expanding uniformly (i.e., at the same rate in all places), then would different places would see a different Hubble law than we do? And if If the extragalactic distance scale changed, would the Hubble constant change?

In 2008, astronomers discovered that a multi-million-solar-mass cloud named Smith's Cloud would hit the Milky Way's disk in about 27 million years. Now new Hubble observations have identified the mysterious cloud's likely origin. Link: New Scientist

I have a question regarding the exact formulation of the mechanism of Inflation. In thehttp://www.damtp.cam.ac.uk/user/db275/Cosmology/Lectures.pdf he uses ##\frac{d}{dt} \frac{1}{aH} < 0## as an definition of inflation. I see that it yields ## \ddot a > 0##, but my confusion lies in the...

I was analyzing the Hubble Ultra Deep field image and I realized that if you look at the image from a certain distance from your monitor, you can notice there is a ring of galaxies, forming a circle. The following are the HUDF image and an image where I try to show where I see the circle (it is...

Let's assume a universe like ours which after inflation expands decelerated and accelerated thereafter. How will the ratio Hubble length ##1/H## to scalefactor ##a## evolve over time? And how could one calculate the time dependence of this ratio. Any help appreciated.

RocketShip, yep that's the name I was given ironically enough. I'm not much for math but I love philosophy and critical thinking. I'll come up with ideas you come up with solutions :P my biggest interest at the moment is how to get the masses into space.

I have read that the Schwarzschild radius of a black hole with the mass-energy of the observable universe is roughly equal to the actual Hubble radius of 13.8 billion light years. And I have read that contrary to some popular esoteric interpretations such as "the universe is a black hole", "we...

Homework Statement If the energy density of the vacuum were the value 10^133 eV/m^3 , what would the value of the Hubble lookback time be for such a universe with no curvature and no other matter? Homework Equations Possible equation... ...Lookback time = ln(1+z)/H The Attempt at a Solution...

I'd like to find out how other members usually think of the Hubble rate, by preference and/or by habit. I was unsuccessful in creating a poll in Cosmology (no "add a poll" button) so I'm hoping this thread can be moved over there. Here are the options I could think of: 1. As a continuously...

From what I understand, our Hubble's sphere is just relative to Earth and has a diameter of 93 billion light years putting the edge of the observable universe at 46-47 billion light years away. So every object in space will essentially have it's own Hubble's sphere and objects near the edge of...

I have a paradox that I don't know the answer to. Special relativity has no preferred frame, but it seems like adding an exponential expansion to space introduces such a frame. The Setup Suppose we're in a universe with a much faster expansion rate, where the space between any two objects...