explain xkcd - User contributions [en]

Talk:3097: Bridge Types

2025-06-03T15:05:27Z

172.69.224.115:

For budget overrun, see olympic stadium of Montreal, Quebec, Canada.

[[Special:Contributions/162.158.126.202|162.158.126.202]] 01:23, 3 June 2025 (UTC)

Very disappointed there's no bridge card game reference, but I guess that's not one of Randall's types of nerdiness :( [[Special:Contributions/172.71.254.203|172.71.254.203]] 01:45, 3 June 2025 (UTC)

I would like to note that cable stayed bridges, budget overrun here, are much cheaper than equivalent suspension bridges. It because they use less materials and can be built faster meaning less labor. [[Special:Contributions/172.69.58.51|172.69.58.51]] 01:50, 3 June 2025‎
:Tru dat in general, but I think that this is a reference to the {{w|Leonard_P._Zakim_Bunker_Hill_Memorial_Bridge|Zakim Bridge}} in downtown Boston, part of the {{w|Big_Dig|"Big Dig"}} project that became notorious for its budget overruns and related shenanigans. Given that Randall M. lives in Boston, that makes this panel something of an inside joke. [[Special:Contributions/172.71.147.224|172.71.147.224]] 03:15, 3 June 2025 (UTC)

The [[wikipedia:St. Louis Arch|St. Louis Arch]] is a repurposed-elevator-suspended-arch-but-without-the-base-and-wires bridge if you squint hard enough. The elevator is also fun. [[Special:Contributions/172.69.67.214|172.69.67.214]] 01:57, 3 June 2025 (UTC)

Nothing about a a [[wikipedia:Bridge circuit|bridge circuit]] or these [[Wikipedia:Bridges (disambiguation)|many]] [[wikipedia:other|other]] bridges either. Sigh. [[Special:Contributions/172.69.67.214|172.69.67.214]] 01:57, 3 June 2025 (UTC)
:And where, oh where, are Lloyd, Beau, Jeff, and Jordan? [[Special:Contributions/162.158.41.84|162.158.41.84]] 03:19, 3 June 2025 (UTC)

The L'Engle is a take off on a Wrinkle in time? But this one is in space? <small> -- [[User:162.158.91.124|162.158.91.124]] ([[User talk:162.158.91.124|talk]]) 02:26, 3 June 2025‎ <span style="color:grey; white-space:nowrap;">''(please sign your comments with <nowiki>~~</nowiki>~~)''</span></small>
:There's some space-warping in L'Engle's books. [[Special:Contributions/162.158.174.63|162.158.174.63]] 02:44, 3 June 2025 (UTC)

The "budget overrun" bridge doesn't really look like the Zakim bridge to me. It looks a lot like the Samuel Beckett Bridge in Dublin. I don't know what the budget of that bridge was, but according to wiki it cost 60 million euros, which sounds like a lot given that the bridge isn't all that long or wide. [[Special:Contributions/172.70.126.87|172.70.126.87]] 03:24, 3 June 2025 (UTC)
: Perhaps if Randall M. drew too close a likeness to the Zakim Bridge, he feared a visit from officials with lawyers and/or cement shoes. ("Only the paranoid survive ...") It seems, from a quick tour of the Internet, that words like "grandiose and overblown" are easily applied to cable-stayed bridge designs/aesthetics. I wasn't easily able to find information on budget overruns for these bridges, and see the commentator above who pointed out the lower costs overall of cable-stayed ''vs'' suspension bridges. But as a former resident of Greater Boston, I can report the pervasiveness of the Big Dig and its challenges, budgetary and otherwise, in local life and lore. [[Special:Contributions/172.68.22.108|172.68.22.108]] 04:32, 3 June 2025 (UTC)
::The cable-stayed bridge is the current darling of artists that accidentally went to engineering school, who are notorious for running over budget and behind schedule. [[User:RegularSizedGuy|RegularSizedGuy]] ([[User talk:RegularSizedGuy|talk]]) 04:40, 3 June 2025 (UTC)
: I can see the suggestion of the Beckett bridge, but in my eyes the obvious template would be [https://en.wikipedia.org/wiki/Erasmusbrug Rotterdam's Erasmus Bridge] [[User:Nachtvogel|Nachtvogel]] ([[User talk:Nachtvogel|talk]]) 06:00, 3 June 2025 (UTC)

I think the repurposed elevator should be considered a dig at Elon Musks The Boring Company, even though they tunnel rather then bridge
[[Special:Contributions/162.158.182.138|162.158.182.138]] 04:37, 3 June 2025 (UTC)

Added a bunch of explanations [[Special:Contributions/162.158.8.132|162.158.8.132]] 07:31, 3 June 2025 (UTC)

The Repurposed Elevator is actually a real thing! https://en.wikipedia.org/wiki/Schmid_Peoplemover It's not as strange as you think. It's a space effective, but too expensive solution to the problem of not making cramped railway crossroads more cramped. [[Special:Contributions/162.158.172.112|162.158.172.112]] 07:39, 3 June 2025 (UTC)
: I've added it to the list. Feel free to do such changes yourself if you know something that can contribute. --[[Special:Contributions/172.71.183.12|172.71.183.12]] 08:07, 3 June 2025 (UTC)

For the "Google Earth Bridge" remark, [https://www.fastcompany.com/90186315/the-strange-art-of-the-melting-bridges-of-google-earth this article] might work as a citation. [[User:Conster|Conster]] ([[User talk:Conster|talk]]) 07:57, 3 June 2025 (UTC)

There seem to be stick figures on each bridge, except for the Arch. Is that on phone? Maybe he's saying nobody uses arch (Linux)? Or does anyone has any other idea as to why? [[Special:Contributions/172.69.128.184|172.69.128.184]] 08:21, 3 June 2025 (UTC)

Is there a reason for the trestle bridge to have a raised deck? They were iconically used for railways, where that would not work. --[[Special:Contributions/162.158.110.59|162.158.110.59]] 09:56, 3 June 2025 (UTC)

The jump in particular feels a lot like polybridge and I love it [[Special:Contributions/172.71.167.160|172.71.167.160]] 11:27, 3 June 2025 (UTC)

== Suspended arch - tied-arch vs. through arch ==

The "suspended arch" bridge may or may not be a tied-arch bridge. Something has to stop the ends of the arch sliding outwards when there's a large load in the middle, but you can't tell what that something is from the image.

If that something is the bridge deck, being connected to the ends of the arch and under tension, than it's a tied-arch bridge (the deck ties the ends of the arch together). If that something is the arch foundations, and the deck is not under tension, then it's not a tied-arch bridge; it's just a simple through-arch bridge.

For more info on (real) bridges, [https://www.youtube.com/watch?v=DX_zkaK5PaI| Practical Engineering] --DW [[Special:Contributions/162.158.187.69|162.158.187.69]] 13:24, 3 June 2025 (UTC)

'Drawbridge' to me means a defensive bridge that crosses the moat of a castle, and can be pulled up when defending it. See, eg., my favourite castle https://en.wikipedia.org/wiki/Bodiam_Castle [[Special:Contributions/172.69.224.115|172.69.224.115]] 15:05, 3 June 2025 (UTC)

2289: Scenario 4

2025-05-22T13:46:41Z

172.69.224.115: Fixed link

{{comic
| number = 2289
| date = April 4, 2020
| title = Scenario 4
| image = sequence-four.png
| titletext = Remember, models aren't for telling you facts, they're for exploring dynamics. This model apparently explores time travel.
}}
==Explanation==
Although not directly mentioned, this comic is probably the 14th comic in a row (not counting [[2288: Collector's Edition]]) in a [[:Category:COVID-19|series of comics]] related to the {{w|COVID-19 pandemic}}. In [[2278: Scientific Briefing]], [[Megan]] and [[Cueball]] were briefing [[White Hat]] on things that were getting bad, hoping to convince him to do something about them. He chose to wait until things actually got bad. Evidently, that has happened, and now Megan and Cueball are delivering another briefing on just how much "Bad Stuff" there might be, according to their models.

In the context of the information (and misinformation) explosion associated with the COVID-19 pandemic (ongoing at the time that this comic was published), many graphs have been shown highlighting the prevalence of the disease - the number of cases at any one time and place, and the change in the number of cases over time. That being said, the graphs shown could easily apply to any number of scenarios where an upward trend is bad.

Several of these graphs have attempted to predict the future, using statistical tools ("models") to process existing data and generate a forecast. Inputs to the model(s) may include different assessments of, for example, the number of COVID-19 cases that have been recorded. Four scenarios are presented here, presumably showing what a particular model (probably only one despite the reference to "new models" in the comic) forecasts given different, unspecified, inputs. Megan and Cueball present four scenarios, only three of which are possible.

* The first, "best case" scenario recalls "flatten the curve" graphs that predict an occurrence will eventually cease to increase altogether. Using COVID-19 as an example, if strictest measures are put into place and adhered to, all those who have contracted COVID-19 will eventually be reported, and no further victims will contract it.

* The second and third scenarios are increasingly worse cases, predicting that the occurrence will continue unceasingly. Again using COVID-19 as an example, the less measures are put into place or adhered to, the more COVID-19 cases that will occur. Scenario 3 appears to indicate an exponential increase best suited to a log scale; "pretty bad" is an understatement.

* The fourth curve is not possible{{Citation needed}}, as each point along the x-axis represents a specific time point. If the curve passes the same time point twice (as it does) then this means that on a given day there were two different number of cases. E.g. on the 1st of April there would have been both 100 and 1000 people infected, which makes no sense at all. The only way to make sense of it would be by using the common trope in science fiction of time traveling creating an alternate timeline in which events are different, thus the cases could be 100 in one timeline and 1000 in a different timeline. Hence the remark, "this model explores time travel", in the title text. This is a brain cramp to visualize, and the consequences of it actually happening would be calamitous on several levels. Real modelers might encounter such "graphing errors" while they are developing their models, entering data (especially if there are time-conversion errors), and testing their functions, but persons who went so far as to present such glitches in public, except for a laugh as here, would likely be asked to hand in their modeler's cards.
** The 'time travel' remark is also suggestive of certain particle-physics phenomena captured in {{w|Feynman diagram}}s. Mathematically, an antiparticle moving forward in time looks like its equivalent particle moving backwards in time, so a particle-antiparticle annihilation or creation event could be interpreted as a single particle switching directions in time. In the context of this scenario, it is possible to read the fourth chart as predicting that the bad stuff will start traveling backwards in time as it increases, which we would see as a great quantity of "bad anti-stuff" appearing and decaying in number just as the "bad stuff" increases, until the two quantities meet at the halfway point and mutually annihilate. Even though there will be no more bad stuff after the annihilation (or time-reversal) event, particle-antiparticle annihilation releases enormous energies that might be even more catastrophic than whatever the bad stuff itself was.
** A fanciful interpretation of this otherwise uninterpretable graph is that the number of infections reached some sort of critical mass, breaking reality to begin spreading through time as well as space. Another possible interpretation may be that the number of infections become an imaginary number, as many of the common math graphs imply.

==Transcript==
:[Megan and Cueball are standing in front of a large graph, with "Time" along the horizontal axis and "Bad Stuff" along the vertical axis. The curve on the graph shows a generally shallow upward slope.]
:Megan: Our new models outline a few possible scenarios.
:Cueball: #1 is the best scenario.

:[The graph now shows a much steeper curve, before flattening out far in the future, similar to a logistic curve.]
:Megan: Scenario 2 is not so great.

:[The graph now climbs quite quickly, approximating an exponential curve.]
:Cueball: Scenario 3 would be pretty bad.

:[The graph starts curling up, like the exponential curve, but continues curving back, so that it no longer qualifies as a function, and may indicate time-travel to the past.]
:Megan: Then there is scenario 4.
:Megan: We '''''think''''' it's a graphing error.
:Cueball: If not, we '''''definitely''''' want to avoid it.

==Trivia==
*This is the first [[:Category:Saturday comics|Saturday comic]] since 2006.
**It was released on Saturday since the previous comic was the [[April Fools' Day comics|April Fools' Day comic]] for 2020.
***The release of this comic, [[2288: Collector's Edition]], had been [[2288:_Collector's_Edition#Trivia|delayed two days]] because of technical difficulties with the complex interactive nature of the comic.
***Thus the planned Wednesday release of this week was thus postponed to Friday.
****To not cheat us from the planned Friday release, this comic was thus released the day after on Saturday.

{{comic discussion}}

[[Category:COVID-19]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Charts]]
[[Category:Time travel]]