Another paper in Friday's physics arXiv on using the H(z) v z plot to investigate any possible evolution of DE: Utility of observational Hubble parameter data on dark energy evolution.
From that eprint:
As discussed in the Marginal evidence for cosmic acceleration from Type Ia SNe, this paper...
Hi there! I'm having some trouble understanding Hubble's Law and Constant and would be grateful for some help.
So Hubble's Law shows that the most distant galaxies have the greatest red-shift, as they are moving away from us fastest. This shows that all galaxies are moving away from each other...
Dear PF Forum,
I know this is a very basic, basic question. But I'd like to refresh my memory.
In Hubble Law.
##V = H_0 \, D##
##H_0## is Hubble constant, aproximately ##\frac{1}{3.1E17t}##
Okayy, let's say we alter those number to an easier number.
For every 10 metres, the velocity adds 1 m/s...
I am interested in whether it is necessary to account for the effects of the Hubble Redshift in determining the rotation velocities of galaxies exhibiting keplerian motion and, in particular, whether the associated spatial expansion of the Universe is known to result in spectral shifts that...
Is there agreement here regarding the relationship between expansion of the universe from its initial conditions, entropy (2nd law), time, (and more tenuously perhaps) "evolution"?
I asked a question awhile back that was too specific I think that tried to tie the constant of expansion to the...
Homework Statement
Prove that
Homework Equations
[/B]The Attempt at a Solution
Without cosmological constant, one finds that
where w is the ratio between pressure and density.[/B]
I recently came across this claim:
"On the other hand, in certain cases even an expanding cosmology may have 0 average expansion, due to the fact that we are averaging over an infinite amount of time. "
Is this correct? can someone explain how averaging over infinity time leads to zero ...
Do I understand correctly (in general terms) or wildly incorrectly if I imagine that the constant of expansion and the second law of thermodynamics are very closely connected, or even that the constant of expansion is potentially the source of the second law?
Hi there,
This is my first post but I've been a spectator for a long time now. So I've been working on some of the basics of cosmic expansion and there is one contradiction that I came upon that I can't seem to resolve. I've looked around some of the similar threads but I couldn't find anything...
I'm interested in understanding what effect does long-term radiation and microdust exposure would do to the surface roughness of a high-precision mirror like the one on the Hubble. Since it has been on orbit for 24 years, it provides an unique opportunity to estimate accumulated environmental...
Is there any observational data available for evolution of Hubble rate? To give some context, read the dark energy FAQ by Sean Caroll here.
He says:
"If the universe is decelerating, the Hubble constant is decreasing. If the Hubble constant is increasing, the universe is accelerating. But...
if the speed of the expansion is decreasing then it would mean that the radius of the Hubble sphere is increasing because it would require more space to expand faster than the speed of light .but as you said if the speed of expansion is increasing then why is the Hubble sphere increasing and
why...
I'm looking at general relativity and particularly considering what happens at the Big Bang. I think the Friedman equation is H^2=\frac{8\pi G}{3}\rho so I see that as the matter density goes to infinity, H goes to infinity. According to this video (around 10:10), this is where the problem lies...
Is rather a question of calculus skills, but how do I get the time derivative of the Hubble parameter here in [1]? Is it the Leibnitz rule, the chain rule, some clever re-arrangement?
thank you
by Dr. Ken Croswell, author of The Alchemy of the Heavens
The Milky Way may have found a solution to its gas shortage. Astronomers had calculated that our home galaxy possesses only enough fuel to forge new stars for just a few billion more years. But scientists have now discovered that a...
There has been a flood of new data. Cosmologists have not yet settled on a new agreed value of H0. This may help lead to one.
http://arxiv.org/abs/1406.1718
The 1% Concordance Hubble Constant
C. L. Bennett (1), D. Larson (1), J. L. Weiland (1), G. Hinshaw (2) ((1) Johns Hopkins University, (2)...
Hubble’s law tells us that the velocity of distant objects increases with distance as v = Hr. Does this mean that the farther a distant object gets the more rapidly that object will recede away from us? That is, are these distant objects accelerating away from us? Can we say
v = Hr, and so...
Jorrie's calculator (Lightcone) makes cosmic history tables which tell you among other things the Hubble times in past years. For convenience let's temporarily use greek Theta Θ to stand for THubble so we don't have to write so much.
Basic facts (definitions actually) are that Θ = 1/H and the...
Hey guys,
I feel like an idiot for asking this. However, I wanted to make sure that my head was screwed on straight before I asked my old astronomy professor permission to use some of his old lecture notes.
Is gravitational redshift one of the causes of Hubble's Law? Is the Redshift of the...
Hello All,
In Carroll's there is a brief introduction to a dynamical dark energy in which the equation of motion for slowly rolling scalar field is discussed.
Then to give an idea about the mass scale of this field it is compared to the Hubble constant, saying that it has an energy of...
I did a cursory search on the forum, and I browsed Wiki...but maybe I missed it.
What is that big Flap/Door on the end of the scope.?
Is it part of the optics, or is it a protection device, or a...?
Thank You
Homework Statement
For a problem I'm doing, I am considering a universe in which k=0, and I'm told that I can consider most of the expansion to have happened during a phase when only one of the density parameters was dominant (I know which one, as well), but I don't know the scale factor or...
Hubble Sees Infant Galaxies at the Edge of the Universe
http://www.slate.com/blogs/bad_astronomy/2014/01/09/distant_galaxies_hubble_image_of_galaxies_at_the_universe_s_edge.html
Hello! This is my first post, so go easy on me! I'm working through Scott Dodelson's book Modern Cosmology http://books.google.com/books?id=3oPRxdXJexcC&pg=PA23&source=gbs_toc_r&cad=4#v=onepage&q&f=false and I am a bit confused about equation 2.85:
$$\rho_{DE} \propto e^{-3 \int^a...
Homework Statement
For a κ=0 universe with no cosmological constant, show that H(z)=H0(1+z)3/2
Homework Equations
Friedmann equation: H2=\frac{8*\pi*g}{3c^2}-\frac{κc^2}{r^2}*\frac{1}{a(t)^2}
The Attempt at a Solution
I know that R(z)=R0/(1+z) but I do not know where this comes...
Hello, everyone it seems to me that people understand how to do this problem but I am struggling to solve it.
Homework Statement
A quasar with redshift 0.3 is gravitationally lensed into two images by an elliptical galaxy at redshift 0.18. There are two images of the quasar which are separated...
How deep can Hubble Telescope see??
-I understand that the Hubble telescope can only resolve galaxies at about 13 billion years old, using gravitational lensing. I am curious, is this because the telescope does not have the power to see farther? Or is this because there are no farther...
The cosmological "Big Rip" and a shrinking Hubble radius
Doesn't an expanding universe forecast such outcomes as a faded and unobservable cmb, galaxies moving away from each other greater than the speed of light, a gravitationally unbound solar system, and eventually an observable universe...
My school textbook says that discovery of the 1a supernova was what led to the understanding that the universe expansion is accelerating
but doesn't hubble's equation already suggest that the universe would expand at an accelerating rate?
V = Hd (V = velocity, H = hubble's constant, d =...
When Hubble published that the galaxies were moving away from each other, the further away the greater redshift and the greater separation velocity, was he saying that space itself was expanding, on the basis of Einstein's general theory, or was he assuming a more or less fixed space, with...
How to derive "dark energy" density from Jorrie's Hubble radius limit
(c^4/(8 pi G))*3*(17.3e9 light years)^(-2)
Paste that in the google window, and see what you get.
When I paste that into google I get 0.5393 nanopascal, which is equivalent to
0.5393 nanojoule per cubic meter.
If the...
Hi guys, I am in a state of slight confusion! I need to know if I am getting this information right, or I have gotten something wrong somewhere!
It is to do with the Hubble constant and the Hubble law.
So 1920 Edwin Hubble estimated that the Universe was 14 Billion years Old but new...
Recently, astronomers from Caltech and Edinburgh University discovered galaxies with a redshift of 11.9. With the Hubble constant at 67.8 km/s/Mpc ( according to the most recent survey with the Planck Satellite ) this means that the galaxies are at a distance of 14.24 billion light years !
With...
1. Homework Statement
If \phi is a usual field is it possible that
H\dot{\phi}=-\partial^2\phi/{\partial x^2}
Where H is the Hubble constant and the dot denotes time derivative
2. Homework Equations
H\dot{\phi}=-\partial^2\phi/{\partial x^2}
3. The Attempt at a Solution
I tried different...
Homework Statement
r1 = t∫t1 1/a(t) dt
Use the Hubble parameter definition to change from t to a, if a(t) = a and a(t1) = 1
Homework Equations
Hubble parameter H = a' / a where a' = da/dt
The Attempt at a Solution
Start with Hubble parameter definition, and rearrange to find dt
aH =...
Vacuum metastability referenced in "Simplified chain inflation" and Hubble time
In this paper http://power.itp.ac.cn/~huangqg/Publications/JCAP-Simplified%20chain%20inflation.pdf it is referenced(Ctrl+F 'with the lifetime of the metastable vacua much shorter than the Hubble time') that basically...
In the Hubble Space Telescope, light rays from a distant celestial object
(1) first passes through an aperture window of diameter 3m
(2) incident upon, and reflected by a primary mirror of diameter 2.4m
(3) reflected by a secondary mirror of diameter 0.3m to form the final image.
For the...
According to the wikipedia entry, the latest values for the Lambda-CDM model parameters for the age of the Universe, t_0, and the Hubble constant, H_0 are
t_0 = 13.75 \pm 0.11 \times 10^9 \mbox{ years}
H_0 = 70.4 \pm 1.3 \mbox{ km s}^{-1} \mbox{Mpc}^{-1}
If you combine the errors this implies...
Hubble’s law, according to Wikipedia, says that the recession velocity of a distant object P comoving with Earth is vrec=HD where H is Hubble’s constant and D is the proper distance from Earth to P.
The Hubble sphere is the area of space in which all objects comoving with Earth have vrec less...
I'm doing a summer internship and my supervisor is currently away and uncontactable. He left me details of certain Hubble images to download and analyse asking for HST images of M31 with coordinates 00:42:52.534 +41:18:54.17 on 2006-07-15 and 2007-01-12. (YYYY-MM-DD)
The problem is that...
Hi. If we fire a rocket into space at some significant fraction of the speed of light (say 0.1c) and then switch off the engines and let it cruise indefinitely, will it appear to accelerate away from us and in effect be carried along by the Hubble flow. Given a million or a billion years would...
What must the Hubble constant be if the Universe is flat. At the Lamda CDM article on wiki it says 70.4 km/s mpc. I'm not sure if that's what it must be if the universe is flat or if that's what experiments have measured it to be, I'm 99% sure that it's the former but I want to be 100% sure...
Hubble Law - recession velcoity?
v = H0d tells us that the recession velcotiy of a galaxy is directly related to its distance from us on earth
However, as the planets move further apart, their potential energy increases (and hence kinetic energy decreases).
How do these two phenomena tie...
I understand that a Hubble diagram is a graph of recession velocity plotted against distance for distant galaxies, and shows a linear relationship. The Hubble constant is the gradient of the graph.
We are now observing extremely distant galaxies with greater than expected velocities due to...