explain xkcd - User contributions [en]

2643: Cosmologist Gift

2022-07-10T00:31:02Z

162.158.203.22: Deleted an insult

{{comic
| number = 2643
| date = July 8, 2022
| title = Cosmologist Gift
| image = cosmologist_gift.png
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago
}}

==Explanation==
{{incomplete|Created by a MUON ON SALE, PACKAGED IN A BOX THAT A CAT MIGHT OR MIGHT NOT HAVE DIED IN- Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic shows a box labeled to indicate that it contains 30,000 fresh {{w|neutrino}}s and four zeptograms of {{w|dark matter}}. The box is intended as an inexpensive gift for a {{w|cosmologist}}. The gift giver didn't put those things in the box—both are simply passing through it, so the "gift" consists of exactly what was in the empty space it occupies. While the caption suggests this would be a good gift for a cosmologist, what they or anyone else would do with such a box is uncertain.

There are about a billion neutrinos per cubic meter throughout space, produced during the {{w|Big Bang}}.[https://physics.mit.edu/news/journal/physicsatmit_14_conrad/] However, the flux of "freshly produced" {{w|solar neutrino}}s at Earth is around 7×1010/cm2/s, yielding about 2.3 million per cubic meter, implying the box is around 13 liters, about 80% the size of a typical {{w|breadbox}}.

Four zeptograms is a minuscule mass, equal to four sextillionths of a gram, or the mass of about 200 carbon-12 atoms. There is an estimated 0.011 to 0.016 {{w|solar mass}}es of dark matter per cubic {{w|parsec}} locally to the solar system,[https://iopscience.iop.org/article/10.1088/1361-6633/ac24e7/meta] about 900 zeptograms per cubic meter, suggesting the box is closer to 4 liters. This discrepancy could imply Randall agrees with cosmologists who believe dark matter is partially composed of {{w|primordial black hole}}s,[https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.121301][https://www.sciencedirect.com/science/article/abs/pii/S2212686418301250?via%3Dihub][https://news.yale.edu/2021/12/16/black-holes-and-dark-matter-are-they-one-and-same][https://iopscience.iop.org/article/10.3847/2041-8205/823/2/L25][https://iopscience.iop.org/article/10.1088/1475-7516/2010/04/023] instead of being entirely composed of pervasive subatomic particles. A billion neutrinos have a mass of only about 2×10-12 zeptograms, at about 0.1 {{w|electron volt}}s each.

The "local source" mentioned in the title text is a pun on the commercial value of fresh, locally produced items, but here it is the Sun. It takes neutrinos not much more than 8 minutes to reach Earth once they're emitted, roughly the same time as photons. (This doesn't take into account that photons additionally take [https://news.stanford.edu/pr/97/971219neutrino.html a hundred thousand years to reach the Sun's surface] from the core where they're generated.) However, as the neutrinos have been travelling at more than 99.999% of the speed of light, they will have aged by less than two seconds,[https://www.omnicalculator.com/physics/time-dilation] and so are technically even fresher.

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

:[A picture of a box with writing on one side, saying as follows:]

:30,000 neutrinos
:Freshly produced
:Plus 4 zeptograms of dark matter

:[Caption below the panel]:
:Cosmologists are easy to shop for because you can just get them a box.

{{comic discussion}}
[[Category:Astronomy]]

1787: Voice Commands

2021-09-30T19:48:24Z

162.158.203.22: /* Explanation */

{{comic
| number = 1787
| date = January 18, 2017
| title = Voice Commands
| image = voice_commands.png
| titletext = Dvorak words may sound hard to pronounce, but studies show they actually put less stress on the vocal cords.
}}

==Explanation==
In this comic [[Cueball]] has shown [[Ponytail]] something relevant to her on his smartphone and she asks if he can send it to her. He agrees but then says something completely incomprehensible to Ponytail, but obviously his phone understands and sends the message with a beep.

The caption explains that he was speaking as though he was using a {{w|QWERTY}} keyboard layout and writing as it was a {{w|Dvorak Simplified Keyboard}}. In other words, Cueball is saying keys on a Dvorak keyboard and the phone is receiving the spaces on a QWERTY keyboard that each of Cueball's Dvorak letters uses. Cueball can be sure that nobody else will be able to use voice commands on his phone.

The sentence Cueball tells his phone translates to "Okay Google send a text" - he says it as if he were typing the sentence on a Dvorak layout with the keyboard set to a QWERTY layout. How such words would be pronounced is a mystery, as the letters in the words are merely substituted with others with no regard to phonetics; without standardized pronunciations, a speech-to-text program would be useless. To add to the confusion, one of the words in Cueball's sentence includes a semi-colon as one of its letters despite the fact that semi-colons are punctuation rather than phonemes, which only complicates the pronunciation further.

The title text is a reference to the fact that many users of Dvorak keyboards claim they may be hard to learn, but they are more movement efficient and put less stress on your fingers due to less movement. This makes little sense in the scenario set up by the comic, as speaking gibberish using oddly placed vowels would be equally difficult, if not in fact harder, on the vocal cords.{{citation needed}}

==Transcript==
:[Ponytail is looking at Cueball facing her direction, and he looks down at the smartphone he is holding in his hand.]
:Ponytail: Can you text it to me?
:Cueball: Sure!
:Cueball: ''Svat ussupd ;dlh a kdbk''
:Ponytail: ...What?
:Phone: ''*Beep*''

:[Caption under the panel:]
:Setting my phone's speech recognition to Dvorak was a pain at first, but it's more efficient in the long run.

==Trivia==
*Using a Dvorak keyboard layout on a smartphone (for actual typing, not voice commands) is possible, but the very features that make it desirable in a physical touch-typing environment are drawbacks on a swipe-enabled keyboard. A placement designed to alternate a typist's left and right hands requires the finger of a swipist to travel back and forth across the keyboard more often. Fitting commonly-used letters onto the typist's home row reduces finger movement but makes many words the swipist enters indistinguishable. On a QWERTY swipe keyboard, four English words can be entered by swiping right to left from P to T: "pot", "pit", "put", and "pout"; however, setting the layout to Dvorak causes this to happen with many more common sets of words.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Smartphones]]
[[Category:Dvorak]]

2520: Symbols

2021-09-24T20:40:51Z

162.158.203.22: Removing double transcript

{{comic
| number = 2520
| date = September 24, 2021
| title = Symbols
| image = symbols.png
| titletext = "röntgen" and "rem" are 20th-century physics terms that mean "no trespassing."
}}

==Explanation==
{{incomplete|Created by an internet argument - Please change this comment when editing this page. Do NOT delete this tag too soon. Bare-bones explanation is in, but needs much more detail.}}

This comic refers to notation commonly used in various fields of math and science.

d/dx and ∂/∂x are both used to represent derivatives in calculus and related fields. d/dx is most commonly used in introductory and basic calculus, while ∂/∂x is used when dealing with partial differential equations, a notoriously complicated topic.

ħ (pronounced 'h-bar') is a symbol used for Planck's constant, a universal constant in quantum physics equal to the energy of a photon divided by its frequency.

NA is Avogadro's number, which is used in chemistry for calculating the number of molecules in a mass of substance. As it is an extremely large number, it may lead to painful arithmetic mistakes.

μm and mK (micrometers and millikelvin) are very small units of length and temperature respectively. Any equipment that is operating in these units will be incredibly finely calibrated and thus very expensive.

nm and eV (nanometers and electronvolts) are also small units of length and energy. Nanometres in particular are commonly used to refer to wavelengths of light, and therefore might be seen when working with lasers, which you should definitely not shine in your eye.

mSv (millisieverts) are a unit of radiation exposure. Randall's comment may be referring to [https://xkcd.com/radiation/ this chart].

mg/kg and μg/kg (milligrams per kilogram and micrograms per kilogram) are units used to count the proportion of a substance that contains a certain chemical; they are equivalent to 'parts per million' and 'parts per billion' respectively. These might be found when working with particularly dangerous chemicals, where even slight exposure could lead to severe health risks.

Finally, the comic references pi and tau. Pi is defined as the ratio of a circle's circumference to its diameter, while tau is defined as pi times two. Pi is more commonly used as a circle constant and is helpful when working with areas and volumes, but proponents of tau argue that it is more useful in a pure mathematics context as it makes working with radians easier. The joke here is that whichever constant you attempt to use, it will probably be the wrong one for what you are trying to achieve.

This comic discusses different symbols found in equations, and humorously comments on their implications.
*d/dx: An undergrad is working very hard
d/dx is the symbol for a single-variable {{w|Derivative|derivative}}. This is a mathematical operation that, while difficult, is well within the reach of an undergraduate student, particularly in science. Thus, an equation with this operation would be one that would cause an undergraduate student to work very hard.

*d/dx: An undergrad is working very hard
d/dx is the symbol for a single-variable {{w|Derivative|derivative}} taken with respect to x. This is a mathematical operation that, while difficult, is well within the reach of an undergraduate student, particularly in science. Thus, an equation with this operation would be one that would cause an undergraduate student to work very hard.

*∂/∂x: A grad student is working very hard

;Re
:Reynolds number, used in modelling the flow of fluids. Fluid flow cannot usually be modelled analytically and so a numerical model is necessary.
;(Ta4 - Tb4)
:
;NA
:Avagadro's constant. If you are using this and not working in Moles there is a good chance that you will make a mistake of a factor of a power of ten. THis could create dangerous amounts of chemicals
;µm
:Micrometers are small. Any equipment that is accurate to that degree is likely to be expensive
;mK
:millikelvin are small changes in temperature, or represent very low temperatures. Equipment that uses mK is very expensive
;nm
:Describes the wavelength of laser light
;eV
:describes the energy of a particle beam
;mSv
:The amount of radiation absorbed.
;mg/kg
:The toxicity of a chemical, per kg of body mass. If it is measured in mg/kg it is quite toxic
;µg/kg
:If the chemical is measured in µg/kg it is extremely toxic
;π or τ
:τ = 2π, so it would be easy to make a mistake and use π when τ is correct.

The title text refers to two non-SI units of radiation measurement. An area with significant amounts of radiation is probably dangerous, hence the no trespassing part.

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

;d/dx
:an undergrad is working very hard
;∂/∂x
:a grad student is working very hard
;ħ
:oh wow, this is apparently a quantum thing
;Re
:someone needs to do a lot of tedious numerical work; hopefully it's not you
;(Ta4 - Tb4)
:you are at risk of skin burns
;NA
:you are probably about to make an incredibly dangerous arithmetic error
;µm
:careful, that equipment is expensive
;mK
:careful, that equipment is very expensive
;nm
:don't shine that in your eye
;eV
:definitely don't shine that in your eye
;mSv
:you are about to get into an internet argument
;mg/kg
:go wash your hands
;µg/kg
:go get in the chemical shower
;π or τ
:whatever answer you get will be wrong by a factor of exactly two

{{comic discussion}}

Talk:2520: Symbols

2021-09-24T20:40:11Z

162.158.203.22:

Great work by whomever did this, but is it possible R_e is something else? I agree that the numerical aspect makes it seem like a fluid mechanics problem, but I've never seen the Reynolds number with a subscripted e... only a regular size e, such that it is Re, not R_e. [[Special:Contributions/108.162.237.93|108.162.237.93]] 20:36, 24 September 2021 (UTC)

T to the fourth power looks like blackbody radiation, any ideas what specifically that formula represents? [[Special:Contributions/162.158.203.22|162.158.203.22]] 20:40, 24 September 2021 (UTC)

Talk:2505: News Story Reaction

2021-08-22T13:19:37Z

162.158.203.22:

It's worth mentioning that unless we're talking an industrial shredder, the Mona Lisa can't be, since unlike most stereotypical paintings, it's actually on glued together pieces of wood and not on Canvas.

Not to say that it wouldn't be damaged heavily by a band of wild rabid dogs, but not "shredded".

Why yes, I am using my art degree, why do you ask?

[[Special:Contributions/108.162.245.5|108.162.245.5]] 19:22, 20 August 2021 (UTC) Steve

: Nothing in the original says the dogs are rabid. Mind you, I would expect rabid dogs to go directly after people, not inanimate paintings. [[User:Nutster|Nutster]] ([[User talk:Nutster|talk]]) 22:07, 20 August 2021 (UTC)
:: Our dog shredded our front door once when left alone during a thunderstorm or such. There was even blood left on the broken shards of wood :-(. But I don't think Randall knew that the Mona Lisa was on wood. [[User:Baffo32|Baffo32]] ([[User talk:Baffo32|talk]]) 00:04, 21 August 2021 (UTC)

I don't have an art degree but knew that the painting was on wood. Also, it's "J.C. Penney". I'm guessing Randall was in a hurry on this one.

Pete 19:31, 20 August 2021 (UTC)

It make much more sense if the wild dogs didn't get in there by coincidence. Making it about himself would be acceptable if he was the indirect cause of the situation. Revenge successful? [[Special:Contributions/172.69.71.55|172.69.71.55]] 22:03, 20 August 2021 (UTC)

Just checking - I'm not the only one who saw this and immediately googled to see if it was an actual news story, am I? I'm so not plugged into the news that I could honestly have believed that I missed it. [[Special:Contributions/172.70.130.239|172.70.130.239]] 22:09, 20 August 2021 (UTC)
:I also cannot find anything about this. As mentioned above, the painting also cannot really be shredded, as it is on wood, rather than canvas. Edit: Can be shredded, but not really by a pack of dogs. [[User:Theusaf|theusaf]] ([[User talk:Theusaf|talk]]) 23:55, 20 August 2021 (UTC)

Uhh, WHAT? Wood can't be shredded?? Huh/ Tha's news to me . . . . [[Special:Contributions/162.158.74.198|162.158.74.198]] 00:16, 21 August 2021 (UTC)

I'm not convinced it would be THAT big loss for humanity. Sure, the original has some emotional value, but I'm sure we have plenty of backup copies. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 06:01, 21 August 2021 (UTC)

Any fule know the Jagaroth made Da Vinci paint six versions and the one in the Louvre is one of the five with Fake written on the back in felt tip by the Doctor. 08:13, 21 August 2021 (UTC)

I don't know if it's a coincidence, and if it's worth mentioning, but the Mona Lisa was stolen on 21 August 1911, almost exactly 90 years before the publication of this comic. --[[Special:Contributions/141.101.69.186|141.101.69.186]] 07:10, 21 August 2021 (UTC)
:I'm pretty sure that 2021 - 1911 equals 110 years instead of 90. [[Special:Contributions/162.158.183.158|162.158.183.158]] 09:43, 21 August 2021 (UTC)

So, the most likely news story this is referring to is the Notre Dame burning down, and then, people uploading photos of them posing in front of it in the past, and then acting as though this was a personal loss for them. Dunno why it's only being made into a comic ''now'', though. [[Special:Contributions/162.158.203.22|162.158.203.22]] 13:19, 22 August 2021 (UTC)