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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]] asks (in the title text) whether she has plans five and a half hours later. One interpretation is that these are two colleagues out for lunch, and Cueball likes her nerdy answer so much he wants to ask her out for a dinner date after work.
| + | {{incomplete|Created by a SHIFTY RED MATTER BALL - Please change this comment when editing this page. Do NOT delete this tag too soon.}} |
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| − | [[File:time by redshift.png|thumb|Redshift indicates how far in the past distant astronomical objects were as we observe them now.]]
| + | In {{w|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. 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 nearby objects. |
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| − | In {{w|observational cosmology}}, a field of astronomy, {{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 time like "in college" or "as a kid," she responds with a very precise redshift value "z=0.00000000038." This absurdly precise number is due to a highly recent event compared to the start of the universe, within the cosmologist's lifetime. The negative blueshift question in the title text is a playful way of asking about a future event, as it is approaching the speakers. Specifically it is a closer event to present day to when the cosmologist became interested in her field of study as the absolute value of z is 10^4 smaller and indicates a closer albeit future event. |
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| − | 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 2020" or "seventeen years ago", whatever may apply), 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; well within a human lifetime, though it might take a cosmologist's specific knowledge to understand this and work out the interval's value. 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.
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| − | [[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 particular cosmology, and in particular values for the Hubble constant (H₀) and the curvature of the universe, it is possible to specify a particular look-back time. For z = 0.00000000038, and a flat Lambda CDM cosmology, with H₀ = 69.32 km / (Mpc s), a value of Ω₀ of 0.2865, a cosmic background temperature of 2.725 K, the look-back time is of around 1960 days, or five and a half years, which could suggest that Ponytail started studying cosmology as part of a Ph.D. program. |
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| − | 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|Lambda-CDM model|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 about 1960 days, or 5.4 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 5.5 hours in the future. So Cueball is likely asking something like "What are you thinking of doing (later) this evening?"
| + | Negative numbers of z 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. |
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| − | The use of non-standard units of measurement has also been seen in [[2707: Astronomy Numbers]], with much larger typical redshift values previously included in [[2764: Cosmological Nostalgia Content]]. Redshift and blueshift have also been mentioned before in [[1852: Election Map]]. | + | |
| | + | 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]]. |
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| | ==Transcript== | | ==Transcript== |
| − | :[Cueball and Ponytail are sitting at a table, eating from plates in front of 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.] | + | {{incomplete transcript|Do NOT delete this tag too soon.}} |
| | + | :[Ponytail and Cueball are sitting at a table, eating dinner. The table has two cups of wine and a different dish for each person.] |
| | :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. |
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| | {{comic discussion}} | | {{comic discussion}} |
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| | [[Category:Comics featuring Cueball]] | | [[Category:Comics featuring Cueball]] |
| | [[Category:Comics featuring Ponytail]] | | [[Category:Comics featuring Ponytail]] |
| | [[Category:Cosmology]] | | [[Category:Cosmology]] |
