Editing 2853: Redshift
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==Explanation== | ==Explanation== | ||
− | In this comic, [[Ponytail]] is using cosmological terms to answer that she first got interested in early universe cosmology 5.4 years ago, to which [[Cueball]] | + | {{incomplete|Created by a HYPERGEOMETRIC INTEGRAL SOLUTION. Do NOT delete this tag too soon.}} |
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+ | In this comic, [[Ponytail]] is using cosmological terms to answer that she first got interested in early universe cosmology 5.4 years ago, to which [[Cueball]] replies in in the title text, essentially asking whether she has plans five and a half hours later. | ||
[[File:time by redshift.png|thumb|Redshift indicates how far in the past distant astronomical objects were as we observe them now.]] | [[File:time by redshift.png|thumb|Redshift indicates how far in the past distant astronomical objects were as we observe them now.]] | ||
− | In | + | In cosmology, {{w|redshift}} refers to the way that light from distant objects in the universe is stretched out, making it appear more red than it would otherwise. This occurs because the universe is expanding, and as a result, light waves are stretched as they travel through space. The {{w|Redshift#Redshift formulae|"z" value}} is a dimensionless measure of the redshift: the observed wavelength minus the expected wavelength, divided by the expected wavelength. A higher "z" value, or redshift, corresponds to earlier times in the history of the universe. This is because as the universe expands, light from distant galaxies is stretched to longer, redder wavelengths as it travels towards us. The further away a galaxy is, the longer its light has been traveling, and thus the more the universe has expanded since that light began its journey. Therefore, a higher redshift indicates a galaxy that is further away and that the light we see from it left when the universe was younger. Conversely, a lower redshift means the light has traveled a shorter distance and time, indicating a more recent epoch in the history of the universe. Negative values of "z" indicate a blueshift, which indicate objects that are approaching the observer, generally used in cosmological work to calculate rotation speeds of closer objects. |
− | The joke here is that Cueball is asking Ponytail when she became interested in cosmology, and instead of giving a conventionally referenced time | + | The joke here is that Cueball is asking Ponytail when she became interested in cosmology, and instead of giving a conventionally referenced time such as "in college", "as a kid", "in 2018", or "five years ago", she responds with a redshift value "z=0.00000000038". This very small number corresponds to a very recent event compared to the start of the universe; indeed, well within a cosmologist's lifetime, though it might take a cosmologist's rather specific knowledge to understand this and work it out. The negative blueshift question in the title text is a playful way of similarly asking about a future event. As the absolute value of the negative z is about ten thousand times smaller, it indicates a much closer event in the future. |
[[File:LookBackFromRedshiftEqns.png|thumb|right|Calculation of look-back time is based on redshift, the {{w|Hubble parameter}} H<sub>0</sub>, and the {{w|Lambda-CDM model#Parameters|cosmological parameter}}s for mass Ω<sub>m</sub> and {{w|dark energy}} Ω<sub>Λ</sub>. The [https://www.researchgate.net/profile/Michael-Wade-5/publication/302632920/figure/fig2/AS:751645805789184@1556217733527/Then-a-Miracle-Occurs-Copyrighted-artwork-by-Sydney-Harris-Inc-All-materials-used-with_W640.jpg suprisingly extant] closed-form solution of the integral includes the special Gaussian {{w|hypergeometric function}} <sub>2</sub>''F''<sub>1</sub>.]] | [[File:LookBackFromRedshiftEqns.png|thumb|right|Calculation of look-back time is based on redshift, the {{w|Hubble parameter}} H<sub>0</sub>, and the {{w|Lambda-CDM model#Parameters|cosmological parameter}}s for mass Ω<sub>m</sub> and {{w|dark energy}} Ω<sub>Λ</sub>. The [https://www.researchgate.net/profile/Michael-Wade-5/publication/302632920/figure/fig2/AS:751645805789184@1556217733527/Then-a-Miracle-Occurs-Copyrighted-artwork-by-Sydney-Harris-Inc-All-materials-used-with_W640.jpg suprisingly extant] closed-form solution of the integral includes the special Gaussian {{w|hypergeometric function}} <sub>2</sub>''F''<sub>1</sub>.]] | ||
− | Assuming a given cosmology, its {{w|Shape of the universe|curvature}}, and a value for the {{w|Hubble's law#Interpretation|Hubble parameter}} H<sub>0</sub> (also called the Hubble constant), it is possible to derive a specific look-back time for any given redshift value. For z=0.00000000038, a flat {{w | + | Assuming a given {{w|cosmology}}, its {{w|Shape of the universe|curvature}}, and a particular value for the {{w|Hubble's law#Interpretation|Hubble parameter}} H<sub>0</sub> (also called the Hubble constant), it is possible to derive a specific look-back time for any given redshift value. For z=0.00000000038, a flat {{w|Lambda-CDM cosmological model}} with H<sub>0</sub> = 69.32 km / Mpc / s (a reasonable medium between {{w|Hubble's law#Hubble tension|the disparate "crisis in cosmology" values for the Hubble parameter}}), a value of Ω<sub>0</sub> of 0.2865, and a cosmic background temperature of 2.725 K, the look-back time is of around 1960 days, or about five and a half years, which could suggest that Ponytail started studying cosmology as part of a Ph.D. program. Negative numbers of z, such as in the title text, would indicate a "look-forward" time, or a time in the future, and the same model indicates that z=-0.000000000000045 corresponds to about 5.5 hours in the future. It might be like asking "So, what are you thinking of doing this evening?" |
− | The use of non-standard units of measurement has also been seen in [[2707: Astronomy Numbers]], with | + | The use of non-standard units of measurement has also been seen in [[2707: Astronomy Numbers]], with (higher) redshift values previously visited as a part of [[2764: Cosmological Nostalgia Content]]. Redshift and blueshift have been mentioned before in [[1852: Election Map]]. |
==Transcript== | ==Transcript== | ||
− | :[Cueball and Ponytail are sitting at a table, eating from plates in front | + | :[Cueball and Ponytail are sitting at a table, eating from plates in front om them, Cueball using both hands with cutlery, Ponytail only holding cutlery in one hand, the other hand lying on her lap. Each has a wine glass standing on the table between the plates.] |
:Cueball: So, when did you first get interested in early universe cosmology? | :Cueball: So, when did you first get interested in early universe cosmology? | ||
:Ponytail: Sometime around z=0.00000000038. | :Ponytail: Sometime around z=0.00000000038. |