explain xkcd - User contributions [en]

3224: Centimeter Wavelengths

2026-03-26T05:10:57Z

Multiuniverse:

{{comic
| number = 3224
| date = March 25, 2026
| title = Centimeter Wavelengths
| image = centimeter_wavelengths_2x.png
| imagesize = 381x335px
| noexpand = true
| titletext = Yes, the cosmic microwave background is great, but what about the earthly microwave foreground?
}}

==Explanation==
{{incomplete|This page was created recently. Don't remove this notice too soon.}}

{{w|Cosmic microwave background radiation}} is {{w|Microwave|microwave radiation}} which permeates throughout the entire observable universe. It originated from light released during proton-electron recombination shortly after the {{w|Big Bang}}, which has since grown less energetic due to {{w|cosmological redshift}}, becoming microwave radiation which we see today. This radiation is not visible to the naked eye, but can be detected using specific radio instruments, including {{w|Super high frequency|centimeter wavelength}} antennas, which are antennas designed to make detection in the 1-10 wavelength range; the Microwave band of radio waves.

In this comic, "Penzias & Wilson" refers to American astronomers and physicists {{w|Arno Allan Penzias}} and {{w|Robert Woodrow Wilson}} who, in 1978, were awarded the Nobel Prize in Physics "for their discovery of {{w|cosmic microwave background radiation}}". The story of their discovery was that during routine experiments with the {{w|Holmdel Horn Antenna}}, a centimeter wavelength antenna, Penzias and Wilson discovered that they were detecting a static background noise that they could not explain. After "debugging" the antenna and removing all potential sources of noise, they found that this background noise was still present, leading to their accidental discovery of the cosmic microwave background radiation.

This comic is alluding to the fact that Penzias and Wilson are the only people who have won a Nobel prize from trying to debug a centimeter wavelength antenna, due to their accidental discovery of the cosmic microwave background radiation.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

:[A scatter plot graph with the Y axis of "time spent debugging centimeter-wavelength antennas" and X axis of "Nobel prizes awarded as a result". The X axis has the numbers 0 and 1 marked, while the Y axis has no numbers marked. Many dots arranged vertically appear at 0 on the X axis (zero Nobel prizes), collectively labeled as "I.T. people troubleshooting WiFi issues". A single dot appears at 1 on the X axis, vertically about 1/3 of the height of the graph up, labeled "Penzias & Wilson".]
:[Caption below the panel:]
:I just think the other people working in the field deserve at least a ''little'' recognition.

{{comic discussion}}<noinclude>

[[Category:Physics]]
[[Category:Scatter plots]]
[[Category:Comics featuring real people]]

2764: Cosmological Nostalgia Content

2023-04-18T07:28:26Z

Multiuniverse: removed a doubled up word

{{comic
| number = 2764
| date = April 17, 2023
| title = Cosmological Nostalgia Content
| image = cosmological_nostalgia_content_2x.png
| imagesize = 316x386px
| noexpand = true
| titletext = Later renouncing clickbait, Einstein called his inclusion of cosmological content in general relativity the biggest blunder of his career.
}}

==Explanation==
{{incomplete|1=Created by a Z=90s KID - What red tint around Megan. Seems invisible. Is it there? More explanation of what the click bait in the title text refers to in the context of the Einstein blunder and why that belongs in this nostalgia comic. Do NOT delete this tag too soon.}}

In cosmology Z is the symbol for {{w|Redshift|redshift}}, which is the phenomenon where photons travelling from an object that is moving away from the observer exhibits an increase in wavelength, resulting in its colour shifting towards the red end of the spectrum. Due to the accelerating expansion of the universe, objects that are further away from us are moving away from us at a faster velocity, resulting in higher redshift. As light has finite velocity, objects that are further away from us are also further back in time. Therefore, Megan is stating that only people with high redshift (Z=10) will be sufficiently further back in the past to remember when the first stars were still forming. Megan also has a red tint{{citation needed}}, indicating that she is one such Z=10 kid.

White Hat, meanwhile, is referencing the fact that the universe has {{w|Scale factor (cosmology)|three eras}}: radiation dominated, matter dominated, and dark energy dominated. As the universe expands, the density of radiation and matter decreases due to their dilution, causing the universe, which first started off being dominated by radiation, to then become dominated by matter, then by dark energy (which does not dilute as the universe expands). Dark energy dominated era, which is when "dark energy started accelerating the universe's acceleration" started around 5 billion years ago while {{w|Evolution of bacteria|bacteria evolved around 3 billion years ago}}, meaning that they evolved closer to dark energy domination than to today.

The title text refers to Einstein's inclusion of the {{w|Cosmological constant|cosmological constant}} to his theory of general relativity in order to attain a static model of the universe, which he later removed, reportedly referring to it as his "biggest blunder". Cosmological constant has, today, been generally accepted as a part of the current cosmological model, relating to the concept of dark energy.

==Transcript==
:[Megan, (with a red tint?), holds both her arms out and up while she is talking to Cueball to the left of her. To the right of Megan White Hat is holding both arms out and down while he is talking to Ponytail to the right of him.]
:Megan: Only Z=10 kids remember watching the cool dark gas that suffused the universe being eaten away by expanding bubbles of plasma around the first stars!
:White Hat: Want to feel old? Bacteria evolved closer to when dark energy started accelerating the universe's expansion than to today!

:[Caption below the panel]:
:Cosmological Nostalgia Content

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring real people]] 
[[Category:Comics to make one feel old]]
[[Category:Astronomy]]
[[Category:Biology]] 
[[Category:Clickbait]]

Talk:2764: Cosmological Nostalgia Content

2023-04-18T07:22:18Z

Multiuniverse:

When I added the transcript it broke the "Created by a BOT" tag on explanation, even though I didn't touch explanation [[Special:Contributions/172.71.151.98|172.71.151.98]] 05:30, 18 April 2023 (UTC)
:No, it was broken before your edit. Someone else changed "BOT" to "Z=90s KID". The equal sign causes problems for mediawiki, but it's been fixed now. --[[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 06:03, 18 April 2023 (UTC)
::For anyone who would benefit from a deeper explanation: 
::In the syntax for templates, equals signs come after parameter names (see [[mw:Help:Templates#Parameters|Help:Templates § Parameters]]). So, <code>Created by a Z</code> was parsed as the name of a nonexistent template parameter, and <code>90s KID - Please change this comment when editing this page. Do NOT delete this tag too soon.</code> was passed in as that parameter's value. 
::That still wouldn't necessarily be a problem. It just also left the first parameter empty. This specific template is programmed to show an error message when that happens. [[User talk:AgentMuffin|~AgentMuffin]] 06:13, 18 April 2023 (UTC)

Two times the red tint around Megan has been mentioned, in explanation and transcript... I cannot see that, no matter how much I zoon in. Is it actually there (can it be measured on the image file?) or is it just someone who wished it was like that? If it can be measrued it should be explained and if not then the mention should be deleted --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 07:13, 18 April 2023 (UTC)
:What I meant was that Megan's line art in this comic appeared more brownish/reddish to me than the line art of the other characters. Specifically, the colour hex #472425 using an online colour hex checker. --[[User:Multiuniverse|Multiuniverse]] ([[User talk:Multiuniverse|talk]]) 07:22, 18 April 2023 (UTC)

2764: Cosmological Nostalgia Content

2023-04-18T07:00:21Z

Multiuniverse: Added a short description to start of transcript

{{comic
| number = 2764
| date = April 17, 2023
| title = Cosmological Nostalgia Content
| image = cosmological_nostalgia_content_2x.png
| imagesize = 316x386px
| noexpand = true
| titletext = Later renouncing clickbait, Einstein called his inclusion of cosmological content in general relativity the biggest blunder of his career.
}}

==Explanation==
{{incomplete|1=Created by a Z=90s KID - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

In cosmology Z is the symbol for {{w|Redshift|redshift}}, which is the phenomenon where photons travelling from an object that is moving away from the observer exhibits an increase in wavelength, resulting in its colour shifting towards the red end of the spectrum. Due to the accelerating expansion of the universe, objects that are further away from us are moving away from us at a faster velocity, resulting in higher redshift. As light has finite velocity, objects that are further away from us are also further back in time. Therefore, Megan is stating that only people with high redshift (Z=10) will be sufficiently further back in the past to remember when the first stars were still forming. Megan also has a red tint indicating, indicating that she is one such Z=10 kid.

White Hat, meanwhile, is referencing the fact that the universe has {{w|Scale factor (cosmology)|three eras}}: radiation dominated, matter dominated, and dark energy dominated. As the universe expands, the density of radiation and matter decreases due to their dilution, causing the universe, which first started off being dominated by radiation, to then become dominated by matter, then by dark energy (which does not dilute as the universe expands). Dark energy dominated era, which is when "dark energy started accelerating the universe's acceleration" started around 5 billion years ago while {{w|Evolution of bacteria|bacteria evolved around 3 billion years ago}}, meaning that they evolved closer to dark energy domination than to today.

The title text refers to Einstein's inclusion of the {{w|Cosmological constant|cosmological constant}} to his theory of general relativity in order to attain a static model of the universe, which he later removed, reportedly referring to it as his "biggest blunder". Cosmological constant has, today, been generally accepted as a part of the current cosmological model, relating to the concept of dark energy.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

[Megan, with a red tint, is talking to Cueball. White Hat is talking to Ponytail.]

Megan: Only Z=10 kids remember watching the cool dark gas that suffused the universe being eaten away by expanding bubbles of plasma around the first stars!

White Hat: Want to feel old? Bacteria evolved closer to when dark energy started accelerating the universe's expansion than to today!

[Caption below the panel]: Cosmological Nostalgia Content

{{comic discussion}}

2764: Cosmological Nostalgia Content

2023-04-18T06:55:55Z

Multiuniverse:

{{comic
| number = 2764
| date = April 17, 2023
| title = Cosmological Nostalgia Content
| image = cosmological_nostalgia_content_2x.png
| imagesize = 316x386px
| noexpand = true
| titletext = Later renouncing clickbait, Einstein called his inclusion of cosmological content in general relativity the biggest blunder of his career.
}}

==Explanation==
{{incomplete|1=Created by a Z=90s KID - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

In cosmology Z is the symbol for {{w|Redshift|redshift}}, which is the phenomenon where photons travelling from an object that is moving away from the observer exhibits an increase in wavelength, resulting in its colour shifting towards the red end of the spectrum. Due to the accelerating expansion of the universe, objects that are further away from us are moving away from us at a faster velocity, resulting in higher redshift. As light has finite velocity, objects that are further away from us are also further back in time. Therefore, Megan is stating that only people with high redshift (Z=10) will be sufficiently further back in the past to remember when the first stars were still forming. Megan also has a red tint indicating, indicating that she is one such Z=10 kid.

White Hat, meanwhile, is referencing the fact that the universe has {{w|Scale factor (cosmology)|three eras}}: radiation dominated, matter dominated, and dark energy dominated. As the universe expands, the density of radiation and matter decreases due to their dilution, causing the universe, which first started off being dominated by radiation, to then become dominated by matter, then by dark energy (which does not dilute as the universe expands). Dark energy dominated era, which is when "dark energy started accelerating the universe's acceleration" started around 5 billion years ago while {{w|Evolution of bacteria|bacteria evolved around 3 billion years ago}}, meaning that they evolved closer to dark energy domination than to today.

The title text refers to Einstein's inclusion of the {{w|Cosmological constant|cosmological constant}} to his theory of general relativity in order to attain a static model of the universe, which he later removed, reportedly referring to it as his "biggest blunder". Cosmological constant has, today, been generally accepted as a part of the current cosmological model, relating to the concept of dark energy.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

Megan: Only Z=10 kids remember watching the cool dark gas that suffused the universe being eaten away by expanding bubbles of plasma around the first stars!

White Hat: Want to feel old? Bacteria evolved closer to when dark energy started accelerating the universe's expansion than to today!

[Caption below the panel]: Cosmological Nostalgia Content

{{comic discussion}}

2764: Cosmological Nostalgia Content

2023-04-18T06:50:22Z

Multiuniverse:

{{comic
| number = 2764
| date = April 17, 2023
| title = Cosmological Nostalgia Content
| image = cosmological_nostalgia_content_2x.png
| imagesize = 316x386px
| noexpand = true
| titletext = Later renouncing clickbait, Einstein called his inclusion of cosmological content in general relativity the biggest blunder of his career.
}}

==Explanation==
{{incomplete|1=Created by a Z=90s KID - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

In cosmology Z is the symbol for redshift, which is the phenomenon where photons travelling from an object that is moving away from the observer exhibits an increase in wavelength, resulting in its colour shifting towards the red end of the spectrum. Due to the accelerating expansion of the universe, objects that are further away from us are moving away from us at a faster velocity, resulting in higher redshift. As light has finite velocity, objects that are further away from us are also further back in time. Therefore, Megan is stating that only people with high redshift (Z=10) will be sufficiently further back in the past to remember when the first stars were still forming. Megan also has a red tint indicating, indicating that she is one such Z=10 kid.

White Hat, meanwhile, is referencing the fact that the universe has three eras: radiation dominated, matter dominated, and dark energy dominated. As the universe expands, the density of radiation and matter decreases due to their dilution, causing the universe, which first started off being dominated by radiation, to then become dominated by matter, then by dark energy (which does not dilute as the universe expands). Dark energy dominated era, which is when "dark energy started accelerating the universe's acceleration" started around 5 billion years ago while bacteria evolved around 3 billion years ago, meaning that they evolved closer to dark energy domination than to today.

The title text refers to Einstein's inclusion of the cosmological constant to his theory of general relativity in order to attain a static model of the universe, which he later removed, reportedly referring to it as his "biggest blunder". Cosmological constant has, today, been generally accepted as a part of the current cosmological model, relating to the concept of dark energy.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

Megan: Only Z=10 kids remember watching the cool dark gas that suffused the universe being eaten away by expanding bubbles of plasma around the first stars!

White Hat: Want to feel old? Bacteria evolved closer to when dark energy started accelerating the universe's expansion than to today!

[Caption below the panel]: Cosmological Nostalgia Content

{{comic discussion}}