This is the
talk page for discussing improvements to the
Redshift article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Archives:
Index,
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11Auto-archiving period: 90 days
![]() |
![]() | Redshift is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. Even so, if you can update or improve it, please do so. | ||||||||||||||||||||||||||||||
![]() | This article appeared on Wikipedia's Main Page as Today's featured article on December 29, 2006. | ||||||||||||||||||||||||||||||
|
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||||||||||||||||||||||
|
Index
1,
2,
3,
4,
5,
6,
7,
8,
9,
10 11 |
|
This page has archives. Sections older than 90 days may be automatically archived by Lowercase sigmabot III when more than 3 sections are present. |
![]() | This article links to one or more target anchors that no longer exist.
Please help fix the broken anchors. You can remove this template after fixing the problems. |
Reporting errors |
The lead says, "Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena." But then it would be true that gravitational waves are subject to redshifting by gravitational potentials. Is this true? Praemonitus ( talk) 18:07, 28 October 2023 (UTC)
Hi @ Parejkoj: regarding [1], could you please give me more actionable criticism than "not sure these are a good fit"? I worked hard to make charts the lay readership can actually use when interpreting the groundswell of very early JWST observations filling the news these days. The existing proper distance plot you favor goes to z=10,000 so fully half of it will almost certainly never correspond to any observations, and the log scale axes aren't at all layperson friendly. My charts are designed to do what laypeople readers are most likely going to want to do when they read a z number, and do it clearly and easily. I am most interested in learning how you think they may be improved.
As for the equations, there are already no fewer than thirty-six display equations in this article, including lengthy integral solution derivations which have nothing practical to do with redshifts. Let me ask you, if someone gives you a redshift value, and asks you to calculate something with it, the age of the universe or lookback time is likely to be pretty high up on the list of possibilities, right? None of the 36 display equations already in this article allow you to calculate those; mine do.
Can we agree to delete the AP calculus derivations instead of the math which is immediately useful for values of the subject of the article? Sandizer ( talk) 02:24, 16 November 2023 (UTC)
To derive the age of the universe from redshift, numeric integration or its closed-form solution involving the special Gaussian hypergeometric function 2F1 may be used. For early objects, this relationship is calculated using the cosmological parameters for mass Ωm and dark energy ΩΛ, in addition to redshift and the Hubble parameter H0.
Or in Python,
from scipy.special import hyp2f1 # hypergeometric function 2F1 is in integral solution
H0 = 69.32 # Hubble parameter, median of disparate approxiamations
Om = 0.317 # Density parameter for matter Omega_mass from arxiv:1406.1718.pdf p. 8
OL = 1.0 - Om - 0.4165/(H0**2) # set parameter for dark energy density Omega_Lambda
# to a flat curvature, from https://www.astro.ucla.edu/~wright/CC.python
# (on https://www.astro.ucla.edu/~wright/CosmoCalc.html which see)
# Age of universe at redshift z as a closed-form solution to its integral definition,
def age_at_z(z): # ...which is 27 times faster than the original numeric integration
hypergeom = hyp2f1(0.5, 0.5, 1.5, -OL / (Om * (z + 1)**3))
return (2/3) * hypergeom / (Om**0.5 * (z + 1)**1.5) * (977.8 / H0) # 977.8 for Gyr
Lookback time is the age of the observation subtracted from the present age of the universe:
is not the right word for two descriptions of the same thing changing correspondingly. 184.97.176.97 ( talk) 03:06, 12 December 2023 (UTC)
This is the
talk page for discussing improvements to the
Redshift article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Archives:
Index,
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11Auto-archiving period: 90 days
![]() |
![]() | Redshift is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. Even so, if you can update or improve it, please do so. | ||||||||||||||||||||||||||||||
![]() | This article appeared on Wikipedia's Main Page as Today's featured article on December 29, 2006. | ||||||||||||||||||||||||||||||
|
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||||||||||||||||||||||
|
Index
1,
2,
3,
4,
5,
6,
7,
8,
9,
10 11 |
|
This page has archives. Sections older than 90 days may be automatically archived by Lowercase sigmabot III when more than 3 sections are present. |
![]() | This article links to one or more target anchors that no longer exist.
Please help fix the broken anchors. You can remove this template after fixing the problems. |
Reporting errors |
The lead says, "Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena." But then it would be true that gravitational waves are subject to redshifting by gravitational potentials. Is this true? Praemonitus ( talk) 18:07, 28 October 2023 (UTC)
Hi @ Parejkoj: regarding [1], could you please give me more actionable criticism than "not sure these are a good fit"? I worked hard to make charts the lay readership can actually use when interpreting the groundswell of very early JWST observations filling the news these days. The existing proper distance plot you favor goes to z=10,000 so fully half of it will almost certainly never correspond to any observations, and the log scale axes aren't at all layperson friendly. My charts are designed to do what laypeople readers are most likely going to want to do when they read a z number, and do it clearly and easily. I am most interested in learning how you think they may be improved.
As for the equations, there are already no fewer than thirty-six display equations in this article, including lengthy integral solution derivations which have nothing practical to do with redshifts. Let me ask you, if someone gives you a redshift value, and asks you to calculate something with it, the age of the universe or lookback time is likely to be pretty high up on the list of possibilities, right? None of the 36 display equations already in this article allow you to calculate those; mine do.
Can we agree to delete the AP calculus derivations instead of the math which is immediately useful for values of the subject of the article? Sandizer ( talk) 02:24, 16 November 2023 (UTC)
To derive the age of the universe from redshift, numeric integration or its closed-form solution involving the special Gaussian hypergeometric function 2F1 may be used. For early objects, this relationship is calculated using the cosmological parameters for mass Ωm and dark energy ΩΛ, in addition to redshift and the Hubble parameter H0.
Or in Python,
from scipy.special import hyp2f1 # hypergeometric function 2F1 is in integral solution
H0 = 69.32 # Hubble parameter, median of disparate approxiamations
Om = 0.317 # Density parameter for matter Omega_mass from arxiv:1406.1718.pdf p. 8
OL = 1.0 - Om - 0.4165/(H0**2) # set parameter for dark energy density Omega_Lambda
# to a flat curvature, from https://www.astro.ucla.edu/~wright/CC.python
# (on https://www.astro.ucla.edu/~wright/CosmoCalc.html which see)
# Age of universe at redshift z as a closed-form solution to its integral definition,
def age_at_z(z): # ...which is 27 times faster than the original numeric integration
hypergeom = hyp2f1(0.5, 0.5, 1.5, -OL / (Om * (z + 1)**3))
return (2/3) * hypergeom / (Om**0.5 * (z + 1)**1.5) * (977.8 / H0) # 977.8 for Gyr
Lookback time is the age of the observation subtracted from the present age of the universe:
is not the right word for two descriptions of the same thing changing correspondingly. 184.97.176.97 ( talk) 03:06, 12 December 2023 (UTC)