Editing 2853: Redshift

{{comic
| number    = 2853
| date      = November 10, 2023
| title     = Redshift
| image     = redshift_2x.png
| imagesize = 223x264px
| noexpand  = true
| titletext = So do you have any plans for z=-0.000000000000045?
}}

==Explanation==
{{incomplete|Created by a SHIFTY RED MATTER BALL - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

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.

The joke here is that Cueball is asking Ponytail when she became interested in cosmology, and instead of giving a conventionally referenced timing, such as "in college"/"as a kid"/”in 2012”/"seven 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 speakers are getting closer to it, and would indicate (if it is Cueball again asking the question) that they both understand each other very well. As an absolute value of z is 10^4 smaller, it indicates something much closer, in the future, than the past timing was in the past.

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.

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. In the context of two apparently well-matched cosmologists getting to know each other with 'smalltalk' (of a kind; certainly with very small ''numbers''!) this probably equates to asking "So, what are thinking of doing later tonight?", after this meal (possibly a first date, if not a blind one) and perhaps some other entertainment. Or even just "Your place or mine?"...


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==
{{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?
:Ponytail: Sometime around z=0.00000000038.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Cosmology]]