explain xkcd - User contributions [en]

3097: Bridge Types

2025-06-03T14:42:28Z

172.68.22.108:

{{comic
| number = 3097
| date = June 2, 2025
| title = Bridge Types
| image = bridge_types_2x.png
| imagesize = 740x581px
| noexpand = true
| titletext = Pontoon bridges are just linear open-sided waterbeds.
}}

==Explanation==
{{incomplete|This page was recently created by a TESSERACT BRIDGE ABUTMENT. Don't remove this notice too soon.}}
This comic shows, in a four-by-four grid of images, a series of bridge types. The first two rows of images are of authentic bridge types, whereas those in the last two rows are progressively more absurd. At first glance, the joke lies in the progression of bridge types from simple to realistically complex to totally bogus.

{| class="wikitable"
!Label
!style="width:7em;"|Status
!Type
!Notes
|-
|Plank
|Real
|{{w|Beam bridge}}
|A straightforward piece of solid material (in this case, made of solid wood, but there are {{w|Clapper bridge|other materials}}) is the most basic form of bridge, and generally the easiest to construct, but also the weakest. Consequently, such bridges are only suitable for small spans and light weights (such as a footbridge over a stream).
|-
|Rope
|Real
|{{w|Simple suspension bridge}}
|Rope bridges consist of several lengths of rope anchored on both sides of the span. Typically, one or more ropes will be intended to support the crossing load (possibly with boards or some other walkway between them), and additional ropes will act as handrails, reducing the risk of falling. These are typically only intended for foot traffic, due to their light construction and lack of rigidity. Because of the simple materials and relative ease of construction, they're often used as improvised bridges.
|-
|Truss
|Real
|{{w|Truss bridge}}
|A truss is a common type of framework consisting of supports connected in a series of triangles which provide support for a load. This design provides significant strength and rigidity with minimal material and weight. A truss bridge can either have the truss above the bridge platform (as in the drawing) or underneath it (also known as a deck truss). This is the first bridge type on this list which is commonly used for vehicle traffic.
|-
|Trestle
|Real
|{{w|Trestle bridge}}
|A trestle bridge is held up by supports reaching all the way to the ground beneath. Typically at least some of the supports will slope outward to give a larger base of support. Once common for railroads, these are less popular nowadays, but are still seen in certain areas and applications.
|-
|Arch
|Real
|{{w|Arch bridge}}
|Arches are one of the oldest kinds of bridges for carrying significant loads. They can be made out of rock or metal. Each span consists of an arch resting on supports. Simple arch bridges rest on both sides of a river or other gap, but longer bridges (as in the drawing) will have intermediate pillars to support multiple arches. The arches distribute the load, allowing a relatively small number of pillar to support weight across the entire deck of the bridge.
|-
|Suspended Arch
|Real
|{{w|Tied-arch bridge}}
|Tied arch bridges use a similar concept as arch bridges, but the arch is instead positioned overhead, with the deck supported by suspended cables. Such bridges may use a single arch (as in the drawing) or multiple arches in succession.
|-
|Draw
|Real
|{{w|Drawbridge}}
|Drawbridges are used to allow ships to pass through obstacles like bridges. They use a cable to pull up one or both sides of the bridge to create enough height clearance for vessels to pass through.
|-
|Suspension
|Real
|{{w|Suspension bridge}}
|A suspension bridge suspends its deck with cables or rods from a cable linked to a pillar and a point a certain distance from each pillar
|-
|Filler
|Real method of maintaining {{w|Grade (slope)|grade}}, not really a 'bridge'
|{{w|Embankment (earthworks)|Embankment}}, {{w|Causeway}} or even a {{w|Dam}}
|Serves the purpose of allowing travel across the gap, but by removing (or {{w|Culvert|mostly removing}}) passage through the gap itself. By filling the gap with hard, irregular material (most commonly rocks), support can be provided, while still allowing water to flow through the gaps. Due to the generally small size of the gaps, generally only slow-flowing water can reliably get through.
|-
|Budget Overrun
|Real (Absurd Name)
|{{w|Cable-stayed bridge}}
|Specifically, the pictured bridge is a {{w|cantilever spar cable-stayed bridge}}, similar in appearance to the {{w|Samuel Beckett Bridge}}. Many bridges in this category suffer severe cost overruns. Randall may be drawing upon his local knowledge of the {{w|Leonard P. Zakim Bunker Hill Memorial Bridge|Zakim Bridge}} in downtown Boston's {{w|Big Dig}}, also strongly associated with cost overruns.
|-
|Jump
|Not Real
|N/A
|A "bridge" that looks like it belongs in a skatepark. Iconically featured in {{w|The Dukes of Hazzard}} TV show.
|-
|Halfhearted
|Real
|[https://www.archdaily.com/184921/moses-bridge-road-architecten Moses bridge]
|Such a bridge exists at the {{w|Fort de Roovere}} in Halsteren, Netherlands. The bridge in the comic might still require stairs. The concept may have been inspired, in part, by [https://www.fastcompany.com/90186315/the-strange-art-of-the-melting-bridges-of-google-earth an artifact in Google Earth software].
|-
|Waterbed
|Not a bridge
|{{w|Waterbed}}
|Rather than a bridge, it is more like another version of a causeway (see 'Filler') using trapped water to maintain the upper surface.
Named for a 'mattress' type, which is usually a raised surface ''on top of'' a piece of bedframe, with an unusual approach to padding and comfort.
|-
|L'Engle
|Not Real
|[https://www.refinery29.com/en-us/2018/03/192728/tesseract-definition-wrinkle-in-time-space-dimension Tesseract AWIT] not {{w|Tesseract|Tesseract (geometry)}}
|References {{w|A Wrinkle In Time}} by Madeleine L'Engle. Characters cross great distances by "tessering", moving via a tesseract through a higher dimension which essentially brings the two ends of the journey together from the perspective of the traveler. The image shows the two ends of the gap being brought together, with the gap apparently crumpled in between them.
|-
|Fun
|Not Real
|
|It is a loop-de-loop, possible allusion to [[2935: Ocean Loop]].
|-
|Repurposed Elevator
|Real, but not as displayed
|Horizontal elevator / {{w|People mover|People mover}}
|There are various implementations of such designs, the best-known one is probably the {{w|Schmid Peoplemover|Schmid Peoplemover}}.
However, unlike a regular people mover, where the door stays upright, the image shows a regular elevator that has been rotated 90 degrees.
|-
|''(Title text)''
|Real
|{{w|Pontoon bridge}}
|Pontoon bridges are described as a series of fictitious "waterbed bridges", as shown above, but constructed without sides. This would mean that that the 'bed'-supporting water flows in one side and out the other, if there is any passage or tidal flow of water. It may technically mean that you cannot cross {{w|The Same River Twice|the same bridge twice}}.
Pontoons rely upon buoyancy, either of the whole deck or distinct floating elements, whereas an enclosed "waterbed" bridge would rely upon the strength of the membrane to keep the mass of water within it, and thus the deck above that mass.
|}

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

:[A 4x4 matrix of 16 ways to cross the same rectangular hole in the ground]

:Plank [shows a plank laid over the hole]

:Rope [shows a rope bridge with rope guardrail]

:Truss [shows a truss bridge with a triangular truss above the bridge deck]

:Trestle [shows a trestle bridge]

:Arch [shows stone arches supporting a straight deck]

:Suspended Arch [shows a single arch, with the bridge deck suspended from it]

:Draw [shows a truss bridge, with one half opened like an unrealistic draw bridge]

:Suspension [shows the bridge deck suspended from a cable strung between two pillars and the shores]

:Filler [shows the hole filled with dirt and stones]

:Budget Overrun [shows a bridge deck suspended by cables from an artistically shaped pillar]

:Jump [shows two ramps at the edges of the hole, and a skateboarder jumping across the hole]

:Halfhearted [shows a ramp at each side of the hole that leads down to the bottom]

:Waterbed [shows the hole filled with water, two fish and an octopus, a wobbly covering, and two stick figures crossing]

:L'Engle [shows the hole warped such that the opposite shores meet]

:Fun [shows a loop-de-loop rollercoaster bridging the hole, and a skateboarder using it to get across]

:Repurposed Elevator [shows an elevator tower, rotated sideways as a whole, laid across the hole. 2 stick figures using the elevator are also rotated.]

{{comic discussion}}<noinclude>

[[Category:Engineering]]
[[Category:Comics featuring Cueball]]
[[Category:Multiple Cueballs]]
[[Category:Animals]]

Talk:3097: Bridge Types

2025-06-03T04:32:29Z

172.68.22.108:

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? -- [[User:162.158.91.124|162.158.91.124]] ([[User talk:162.158.91.124|talk]]) 02:26, 3 June 2025‎ ''(please sign your comments with <nowiki>~~</nowiki>~~)''
: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)

3096: Check Engine

2025-05-31T16:29:55Z

172.68.22.108:

{{comic
| number = 3096
| date = May 30, 2025
| title = Check Engine
| image = check_engine_2x.png
| imagesize = 331x383px
| noexpand = true
| titletext = They say it's probably safe to keep orbiting for a while, but if it stays on or starts flashing we might have to call someone.
}}

==Explanation==
{{incomplete|This page was created by SOL'S PIT CREW. Don't remove this notice too soon.}}
{{w|Sunspot|Sunspots}} are temporary, relatively small, darker (because cooler) regions on the surface of Sol (Earth's Sun). The number of sunspots that can be observed varies over an approximately 11-year cycle. The current cycle is {{w|Solar_cycle_25|the 25th since reckoning began in 1755}}.

The joke in this comic is that the sunspot array shown has taken the form of a {{w|Check_engine_light|"Check engine light"}}, found on the instrument panel of most automobiles. The illumination of this light means that the automobile's onboard computer has detected an engine malfunction, which should be checked out by an experienced mechanic. For such a signal to appear among the nuclear fires and plasma of Sol would most certainly be of concern to astronomers.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:["Check Engine" warning light (from a car's dashboard) is shown on the surface of the Sun]

:[Caption below the panel:]
:This new sunspot cluster has raised concern among astronomers

{{comic discussion}}<noinclude>
[[Category:Comics with color]]
[[Category:Astronomy]]

3095: Archaea

2025-05-30T02:07:27Z

172.68.22.108:

{{comic
| number = 3095
| date = May 28, 2025
| title = Archaea
| image = archaea_2x.png
| imagesize = 404x412px
| noexpand = true
| titletext = Under the two-domain system, anyone who punches you is technically an Archaean pathogen.
}}

==Explanation==
{{incomplete|This page was created by an Archean pathogen. Don't remove this notice too soon.}}
{{w|Archaea}} is one of the three main lineages (domains) of free-living lifeforms. The other two are {{w|Bacteria}} and {{w|Eukaryote|Eukaryota}}. Organisms within Archaea and Bacteria are {{w|Prokaryote|prokaryotes}}, and were treated as a single domain until the Archaea were split off in the 1970s.

The bacterial and eukaryotic domains each contain numerous species that cause human disease (are pathogens). However, to date, no species of Archaea has been unequivocally shown to be a human pathogen. Whether such pathogens exist, and if they do, why they are rare and have low impact, are [https://microbiologysociety.org/blog/why-dont-archaea-cause-disease.html matters of debate].

The joke in this comic is that one or more strains of Archaea, being cultivated in a laboratory, overheard a conversation among three human scientists (represented by [[Cueball]], [[Megan]], and [[White Hat]]). Perhaps taking offense at Megan's disparaging comments, perhaps considering it as a challenge, the eavesdropping culture resolves to become a human pathogen.

The caption reports this as "bad news" for humanity. It may turn out that they always had the ''potential'' to harm humans, but had never tried to (for any number of reasons).

Most of the species of Archaea that were known, at the time that the domain was recognized and for some time thereafter, were {{w|Methanogen|methanogens}}, cells that require anaerobic conditions for life and emit methane as a byproduct, or {{w|Methanotroph|methanotrophs}}, cells that use methane (also anaerobically) as a carbon source ("food"). Methanogens and methanotrophs are common in the guts of humans and other animals, therefore have proximity to human cells and opportunity to infect them — hence (the inappropriate anthropomorphism aside) their indignance at Megan's comment, especially since neither group contains methane "breathers". Archaea are now known from many different environments, including aerobic ones, so do not have the limited metabolic options that one might assume that they do from Megan's statement. Megan calls them ”gross methane breathers” and believes they are too weird and incompetent. If the Archaea could actually understand this, no wonder they became offended and would like to prove what they could do to us.

"Archaea has" in the caption is a debatable grammar, as it denotes that a lineage (a branch of a phylogenetic tree) has become pathogenic. "Archaeans have" could have been better, but contrast with statements using "humanity is", compared with "humanity are" for the linguistic and contextual complications involved.

The title text alludes to the hypothesis that the domain Eukaryota arose from within the domain Archaea, allowing for a {{w|two-domain system}} which classifies everything into Bacteria and Archaea, with Eukaryota being included as a sub-division of Archaea. Since humans belong within Eukaryota (i.e. being not Bacteria), by extension they would belong to the Archaea split. A human attacker of another human could therefore be considered both a pathogen and an archaeon. The same would be true of an attack by any other animal.

==Transcript==
:[Cueball, Megan, and White Hat are standing in a lab in front of a root-like phylogeny diagram, looking at it. Behind them is a desk with a microscope on it. There is a pile of items behind it and one item in front. From the plate on the microscope where the sample is, there is a star burst and a line going up to the text said by the sample.]
:Cueball: It's weird how, despite being one of the main branches of the tree of life, no Archaea species are known to cause disease in humans.
:Megan: Personally, I think it's because those gross methane breathers are too weird and incompetent to figure out how to hurt us even if they wanted to.
:Archaea sample: ''Hey!''

:[Caption below the panel:]
:Bad news: After overhearing a conversation in our lab, Archaea has finally started harming humans.

{{comic discussion}}<noinclude>

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring White Hat]]
[[Category:Biology]]

3090: Sail Physics

2025-05-17T20:50:53Z

172.68.22.108: /* Explanation */ not clear that friction plays a role

{{comic
| number = 3090
| date = May 16, 2025
| title = Sail Physics
| image = sail_physics_2x.png
| imagesize = 699x263px
| noexpand = true
| titletext = Turning in other directions can be accomplished by using a magnetized centerboard and ocean currents, since a current flowing through a magnetic field induces a Laplace force.
}}

==Explanation==
{{incomplete|This page was created by a wind-blown electron. Don't remove this notice too soon.}}

This comic starts off looking like a straightforward explanation of how sailboats can travel upwind — a topic that continues to spark debate and refinement in physics circles. However, it quickly veers into a completely fictional and incorrect theory involving triboelectric charging and the {{w|Lorentz force}}, rather than referencing real mechanisms like {{w|airfoil|aerodynamic lift}}.

This humor works at another level — most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature. So one unaware of sailing mechanics may start to explain the situation with electromagnetism, and could come to this line of thinking, but it is wrong. If we are to consider this, we find that either no force is appearing in the direction shown, or very little.

{{w|Triboelectric effect|Triboelectric effect}} is acquisition of "static" electric charge by rubbing between two objects, which in turn depends on effective interaction surface area. The charge imparted to light items, such as toy balloons or scraps of tissue, can be sufficient to overcome gravitational force.

For a sailboat, the charge acquired would be very small. There is more charge generated due to the running of the boat through water, in a realistic situation.

Following on from the initial assumption, however, the comic assumes motion in a downstream direction, effectively due to normal forces on the sail. Further, the comic applies this motion as of that of a charged object in Earth's magnetic field. If we are to consider this magnetic field to be roughly parallel to Earth's surface, which would be true for situations close to the equator (as Earth's magnetic field is effectively that of dipole bar magnet, which is roughly aligned with our planetary rotational axis). The net Lorentz force on the boat would be F = qvB, and since both velocity of both and magnetic field lines are in the same plane (as viewed in the above sketches, in a top-down manner), then the force would be perpendicular to the plane. That is, along the direction of gravity for the boat, which will not cause any motion in plane. If we consider magnetic field lines to be perpendicular to Earth's surface (close to poles), even then the magnitude of the force is very small. If we consider a net charge of 1 coulomb across the boat (which is an extremely high amount of charge, at which point, the charge would try to accumulate on sharp objects, and due to this high charge density, either charge will leave the boat through coronal discharge, or the sharp objects would start to break from the boat (this is due to high self electrostatic energy, which is roughly proportional to square of charge density divided by radius of curvature of object, if the bonding between object is not strong enough, then this electrostatic energy can overcome this bonding energy), assuming that this charge does not cause the ship to break or the charge to leak out to water body, as the charge would like to spread to minimise the electrostatic energy), and if we consider field strength of order 0.0001 Tesla (close to typical values on surface), and take wind speeds of 10000 m/s (also very high) then the net force on ship would be 1 N, which for a boat of mass 10 kg (less for a typical boat, but is appropriate for a makeshift raft) cause a net acceleration of 0.1 m/s^2. Which is not tiny, but due to friction across the boat, would be cancelled out (by 1 or 2 orders of magnitude). This is considering the best possible case. For more reasonable charge values, this force would be about a trillion times weaker, and hence this will not cause any practical motion.{{citation needed}}

If the described effect were actually significant, it wouldn't always make boats turn upwind. A positively charged boat would turn counter-clockwise on the northern hemisphere, where the magnetic field points down, and clockwise on the southern hemisphere, where the magnetic field points up. Thus it would turn upwind or downwind depending on which side of the boat faces the wind. A negatively charged boat would turn in the opposite direction. To beat to windward it would be necessary to switch between two sails made of different materials – one sail to accumulate a positive charge, and another to accumulate a negative charge.

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

[Panel 1]

How sailboats use physics to sail upwind:

[A schematic boat with a sail is shown (top-down view). Winds shown with directional arrows, pointing in the direction of the sail (going towards 4:30 on a clock face).]

[Panel 2]

1. Wind passing over the sail strips away electrons via the triboelectric effect.

[Schematic similar to panel 1, but with charged ions shown across both sides of the sail, representing the triboelectric effect.]

[Panel 3]

2. The positively charged boat is blown downwind; its movement in Earth's magnetic field produces a Lorentz force.

[The same schematic, except a force vector is shown in the direction of the wind, and a perpendicular force vector (along 1:30 on a clock face) is shown with a dashed arrow.]

[Panel 4]

3. The Lorentz force acts perpendicular to the direction of motion, redirecting the boat upwind.

[A net force vector is shown perpendicular to the downstream vector.]

{{comic discussion}}<noinclude>

3090: Sail Physics

2025-05-17T20:46:56Z

172.68.22.108: /* Explanation */ wikilink lorentz, split part of long paragraph; simplify

{{comic
| number = 3090
| date = May 16, 2025
| title = Sail Physics
| image = sail_physics_2x.png
| imagesize = 699x263px
| noexpand = true
| titletext = Turning in other directions can be accomplished by using a magnetized centerboard and ocean currents, since a current flowing through a magnetic field induces a Laplace force.
}}

==Explanation==
{{incomplete|This page was created by a wind-blown electron. Don't remove this notice too soon.}}

This comic starts off looking like a straightforward explanation of how sailboats can travel upwind — a topic that continues to spark debate and refinement in physics circles. However, it quickly veers into a completely fictional and incorrect theory involving triboelectric charging and the {{w|Lorentz force}}, rather than referencing real mechanisms like {{w|airfoil|aerodynamic lift}}.

This humor works at another level — most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature. So one unaware of sailing mechanics may start to explain the situation with electromagnetism, and could come to this line of thinking, but it is wrong. If we are to consider this, we find that either no force is appearing in the direction shown, or very little.

{{w|Triboelectric effect|Triboelectric effect}} is acquisition of "static" electric charge by friction between two objects,{{cn}} which in turn depends on effective interaction surface area. The charge imparted to light items, such as toy balloons or scraps of tissue, can be sufficient to overcome gravitational force.

For a sailboat, the charge acquired would be very small. There is more charge generated due to the running of the boat through water, in a realistic situation.

Following on from the initial assumption, however, the comic assumes motion in a downstream direction, effectively due to normal forces on the sail. Further, the comic applies this motion as of that of a charged object in Earth's magnetic field. If we are to consider this magnetic field to be roughly parallel to Earth's surface, which would be true for situations close to the equator (as Earth's magnetic field is effectively that of dipole bar magnet, which is roughly aligned with our planetary rotational axis). The net Lorentz force on the boat would be F = qvB, and since both velocity of both and magnetic field lines are in the same plane (as viewed in the above sketches, in a top-down manner), then the force would be perpendicular to the plane. That is, along the direction of gravity for the boat, which will not cause any motion in plane. If we consider magnetic field lines to be perpendicular to Earth's surface (close to poles), even then the magnitude of the force is very small. If we consider a net charge of 1 coulomb across the boat (which is an extremely high amount of charge, at which point, the charge would try to accumulate on sharp objects, and due to this high charge density, either charge will leave the boat through coronal discharge, or the sharp objects would start to break from the boat (this is due to high self electrostatic energy, which is roughly proportional to square of charge density divided by radius of curvature of object, if the bonding between object is not strong enough, then this electrostatic energy can overcome this bonding energy), assuming that this charge does not cause the ship to break or the charge to leak out to water body, as the charge would like to spread to minimise the electrostatic energy), and if we consider field strength of order 0.0001 Tesla (close to typical values on surface), and take wind speeds of 10000 m/s (also very high) then the net force on ship would be 1 N, which for a boat of mass 10 kg (less for a typical boat, but is appropriate for a makeshift raft) cause a net acceleration of 0.1 m/s^2. Which is not tiny, but due to friction across the boat, would be cancelled out (by 1 or 2 orders of magnitude). This is considering the best possible case. For more reasonable charge values, this force would be about a trillion times weaker, and hence this will not cause any practical motion.{{citation needed}}

If the described effect were actually significant, it wouldn't always make boats turn upwind. A positively charged boat would turn counter-clockwise on the northern hemisphere, where the magnetic field points down, and clockwise on the southern hemisphere, where the magnetic field points up. Thus it would turn upwind or downwind depending on which side of the boat faces the wind. A negatively charged boat would turn in the opposite direction. To beat to windward it would be necessary to switch between two sails made of different materials – one sail to accumulate a positive charge, and another to accumulate a negative charge.

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

[Panel 1]

How sailboats use physics to sail upwind:

[A schematic boat with a sail is shown (top-down view). Winds shown with directional arrows, pointing in the direction of the sail (going towards 4:30 on a clock face).]

[Panel 2]

1. Wind passing over the sail strips away electrons via the triboelectric effect.

[Schematic similar to panel 1, but with charged ions shown across both sides of the sail, representing the triboelectric effect.]

[Panel 3]

2. The positively charged boat is blown downwind; its movement in Earth's magnetic field produces a Lorentz force.

[The same schematic, except a force vector is shown in the direction of the wind, and a perpendicular force vector (along 1:30 on a clock face) is shown with a dashed arrow.]

[Panel 4]

3. The Lorentz force acts perpendicular to the direction of motion, redirecting the boat upwind.

[A net force vector is shown perpendicular to the downstream vector.]

{{comic discussion}}<noinclude>

2576: Control Group

2025-05-05T10:18:45Z

172.68.22.108:

{{comic
| number = 2576
| date = February 2, 2022
| title = Control Group
| image = control_group.png
| titletext = Placeble 228 x/6 ⬜⬜⬜⬜⬜ ⬜⬜⬜⬜⬜ ⬜⬜⬜⬜⬜ ⬜⬜⬜⬜⬜ ⬜⬜⬜⬜⬜ ⬜⬜⬜⬜⬜
}}

==Explanation==
{{w|Wordle}} is a web-based word puzzle game that was especially popular when this comic was released. In the comic, [[Ponytail]] asks [[Cueball]] whether he's playing the game; Cueball replies that he isn't, because he's "in the control group". In scientific studies, the {{w|control group}} stands in opposition to the treatment group; whereas the treatment group receives the experimental "treatment", the control group does not, instead receiving a {{w|placebo}} or nothing at all. This is done to establish a baseline—what would happen without intervention—against which the result of the experimental treatment is compared later.

When Cueball replies that he's "in the control group", this implies that Ponytail and other Wordle players are part of a "treatment" group. This implies that playing Wordle may have some long-term effects worth studying.
Jokingly, this may also imply that Wordle is some sort of {{w|social experiment}}, perhaps a [https://knowyourmeme.com/memes/sociological-study-conducted-by-harvard-university sociological study conducted by Harvard]. As noted in the caption to the comic, [[Randall]] has been using this line as his new all-purpose excuse when he is not doing something. It's a clever way of saying that you're determined not to take part, as a control group requires him to avoid it. Mind control studies can also be nonconsensual experiments that massively impact public behavior.

More realistically, Cueball may be part of a real market research control group, which was not exposed to advertisements and memes supporting the game or anything associated with the game. Market research studies have been common since the advent of advertising.

The title text is a parody of emoji-based Wordle's sharing feature, which users have been [https://twitter.com/search?q=wordle&f=live posting on Twitter] or other social media platforms to show their success or failure at the game. The title text shows a 5x6 grid, but calls it "Placeble" (a {{w|portmanteau}} of Placebo and Wordle) and has a number after it, suggesting that not only is the game a social experiment, but that a "placebo version" is being given to the control group. In the real Wordle sharing feature, the number represents the current day's game. On the date this comic was released, the Wordle website itself was on game 228, matching the number in the title text. Randall's placebo version of Wordle has blank/incorrect squares and has a score of "x/6" which is a loss in Wordle — unsuccessful after the maximum 6 tries. A potential candidate for a "Placeble" might be [https://qntm.org/files/absurdle/absurdle.html Absurdle], although it does not automatically end after 6 tries.

==Transcript==
:[Ponytail is looking at her smartphone which she is holding in her hand, while she is talking to Cueball.]
:Ponytail: Are you playing Wordle?
:Cueball: No, I'm in the control group.

:[Caption below the panel:]
:My new all-purpose excuse for when I'm not doing something

==Trivia==
The image for this comic had a much larger size than normal, because Randall used the same file for both the normal "double-sized" image and the "regular" size. This resulted in [https://web.archive.org/web/20220203020828/https://xkcd.com/ the comic breaking the boundaries of the website]. This was fixed on [https://web.archive.org/web/20220208211028/https://xkcd.com/2576/ February 8th, 2022], when he updated the comic to make the [https://xkcd.com/2576 image on xkcd.com] the same size as other comics. Later, something similar happened with [[2599: Spacecraft Debris Odds Ratio]], when Randall changed the original comic, and made both images the same size.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Portmanteau]]
[[Category:Comics edited after their publication]]
[[Category:Scientific research]]
[[Category:Emoji]]

1425: Tasks

2025-04-24T04:37:05Z

172.68.22.108: /* Explanation */ remove extra words

{{comic
| number = 1425
| date = September 24, 2014
| title = Tasks
| image = tasks.png
| titletext = In the 60s, Marvin Minsky assigned a couple of undergrads to spend the summer programming a computer to use a camera to identify objects in a scene. He figured they'd have the problem solved by the end of the summer. Half a century later, we're still working on it.
}}

==Explanation==
[[Cueball]] appears to be asking [[Ponytail]] to write an app that determines if a given picture is (1) taken in a {{w|national park}}, and (2) a picture of a bird. The first question is generally harder for a human to answer, but easy for an app that has access to location information and a {{w|geographic information system}} (GIS). The second one is easy for a human but much harder for a computer. This illustrates {{w|Moravec's paradox}} from the 1980s in a modern context. By the 1950s computers were useful for tasks like {{w|trajectory optimization}}, {{w|automated theorem proving|generating novel mathematical proofs}}, and {{w|English_draughts#Computer_players|the game of checkers}}, so such high-level computation and reasoning tasks that were hard for humans turned out to be relatively easy for them. On the other hand, it turns out to be hard to "give them the skills of a one-year-old when it comes to perception", as Moravec wrote.

In order to determine whether the user is in a national park, Ponytail plans to determine the user's location using the location tracking receivers which are common in to many devices. These provide location information using nearby radio sources, such as cell phone towers or WiFi hotspots, or the positions of satellites supplied by a {{w|Global Positioning System|GPS}} receiver. This location will then be checked with a {{w|geographic information system}} (GIS) which will determine whether the photographer is in a national park.

Determining whether an image is of a given kind of natural object is far more difficult. This task falls into the area of {{w|computer vision}}. One of the goals in computer vision is to detect and classify objects within an image.

Humans use size, focus, edge-assignment, movement (of both the subject and the observer), and stereoscopic vision when looking at a scene (not a picture of a thing, but the thing itself) to discern individual objects and then {{w|Figure-ground (perception)|categorize them as foreground or background}}. Sound may also assist in locating and identifying objects. An app could use these techniques, as well as additional senses, such as distance to the subject and light outside our visual spectrum.

Identifying objects in a photograph is harder. A photograph is a static, usually monoscopic image that can only provide size and edge-assignment clues. Humans are only able to discern objects from background in photographs by comparing the photo against all of the things they've seen and everything they've learned about those things over the course of their life and {{w|Visual perception|identifying matching patterns}}.

The quality of the photograph will have an impact on a computer's ability to match patterns. For example, the object in the photograph might be partially visible or occluded. In the case of a living bird, additional complications arise from the variations among individual birds of the same species and differences in pose (flying, perching in a tree, etc.). Differentiating between visually similar objects can result in false positives. For example, is it a photo of a [[1792: Bird/Plane/Superman|bird in flight or a plane <s>(or superman!)</s>]]? Ponytail's estimate of 5 years may be overly optimistic (see [[678: Researcher Translation]]).

The state-of-the-art algorithms for solving this kind of task (as of this comic's publishing) use local features (e.g. {{w|Scale-invariant feature transform|SIFT}} or {{w|Speeded up robust features|SURF}} in combination with a {{w|support vector machine}}) or a {{w|convolutional neural network}}.

The subtitle refers to "CS", a common abbreviation for "{{w|Computer Science}}", of which {{w|artificial intelligence}} and {{w|computer vision}} are sub-disciplines.

The title text mentions [http://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-100.pdf The Summer Vision Project] and {{w|Marvin Minsky}} of MIT. In the summer of 1966, he asked his undergraduate student {{w|Gerald Jay Sussman}} to [http://szeliski.org/Book/ "spend the summer linking a camera to a computer and getting the computer to describe what it saw"]. {{w|Seymour Papert}} drafted the plan, and it seems that Sussman was joined by {{w|Bill Gosper}}, {{w|Richard Greenblatt (programmer)|Richard Greenblatt}}, {{w|Leslie Lamport}}, Adolfo Guzman, Michael Speciner, John White, Benjamin, and Henneman - in case the multiple Wikipedia links don't give it away, know that this is a sizable cross-section of the AI researchers of the period. The project schedule allocated one summer for the completion of this task. The required time was obviously significantly underestimated, since dozens of research groups around the world are still working on this topic today.

A month after this comic came out, {{w|Flickr}} [http://code.flickr.net/2014/10/20/introducing-flickr-park-or-bird/ responded] with a [http://parkorbird.flickr.com/ prototype online tool] to do something similar to what the comic describes, using its automated-tagging software. According to them, the bird solution "took us less than 5 years to build, though it's definitely a hard problem, and we've still got room for improvement".

Now, years later, the second problem of detecting birds (or any other objects) in the image has also turned into a relatively easy application of existing technologies. Image classification neural networks are readily available. Many groups have put in the years of research (with teams of computer scientists) into the problem of computer vision, and thanks to recent breakthroughs in neural net architectures.

==Transcript==
:[Ponytail sitting at a computer with Cueball standing behind her.]
:Cueball: When a user takes a photo, the app should check whether they're in a national park...
:Ponytail: Sure, easy GIS lookup. Gimme a few hours.
:Cueball: ...and check whether the photo is of a bird.
:Ponytail: I'll need a research team and five years.

:[Caption below the panel:]
:In CS, it can be hard to explain the difference between the easy and the virtually impossible.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Artificial Intelligence]]
[[Category:Programming]]
[[Category:Photography]]
[[Category:Comics featuring real people]]

1425: Tasks

2025-04-24T04:34:59Z

172.68.22.108: /* Explanation */ move GPS, remove excess words, more on positioning systems

{{comic
| number = 1425
| date = September 24, 2014
| title = Tasks
| image = tasks.png
| titletext = In the 60s, Marvin Minsky assigned a couple of undergrads to spend the summer programming a computer to use a camera to identify objects in a scene. He figured they'd have the problem solved by the end of the summer. Half a century later, we're still working on it.
}}

==Explanation==
[[Cueball]] appears to be asking [[Ponytail]] to write an app that determines if a given picture is (1) taken in a {{w|national park}}, and (2) a picture of a bird. The first question is generally harder for a human to answer, but easy for an app that has access to location information and a {{w|geographic information system}} (GIS). The second one is easy for a human but much harder for a computer. This illustrates {{w|Moravec's paradox}} from the 1980s in a modern context. By the 1950s computers were useful for tasks like {{w|trajectory optimization}}, {{w|automated theorem proving|generating novel mathematical proofs}}, and {{w|English_draughts#Computer_players|the game of checkers}}, so such high-level computation and reasoning tasks that were hard for humans turned out to be relatively easy for them. On the other hand, it turns out to be hard to "give them the skills of a one-year-old when it comes to perception", as Moravec wrote.

In order to determine whether the user is in a national park, Ponytail plans to determine the user's location using the location tracking receivers which are common in to many devices. These provide location information using nearby radio sources, such as cell phone towers or WiFi hotspots, or the positions of satellites supplied by a {{w|Global Positioning System|GPS}} receiver. This location will then be checked with a {{w|geographic information system}} (GIS) which will determine whether the photographer is in a national park.

Determining whether an image is of a given kind of natural object is far more difficult. This task falls into the area of {{w|computer vision}}. One of the goals in computer vision is to detect and classify objects within an image.

Humans use size, focus, edge-assignment, movement (of both the subject and the observer), and stereoscopic vision when looking at a scene (not a picture of a thing, but the thing itself) to discern individual objects and then {{w|Figure-ground (perception)|categorize them as foreground or background}}. Sound may also assist in locating and identifying objects. An app could use these techniques, as well as additional information, such as additional senses, such as distance to the subject and light outside our visual spectrum.

Identifying objects in a photograph is harder. A photograph is a static, usually monoscopic image that can only provide size and edge-assignment clues. Humans are only able to discern objects from background in photographs by comparing the photo against all of the things they've seen and everything they've learned about those things over the course of their life and {{w|Visual perception|identifying matching patterns}}.

The quality of the photograph will have an impact on a computer's ability to match patterns. For example, the object in the photograph might be partially visible or occluded. In the case of a living bird, additional complications arise from the variations among individual birds of the same species and differences in pose (flying, perching in a tree, etc.). Differentiating between visually similar objects can result in false positives. For example, is it a photo of a [[1792: Bird/Plane/Superman|bird in flight or a plane <s>(or superman!)</s>]]? Ponytail's estimate of 5 years may be overly optimistic (see [[678: Researcher Translation]]).

The state-of-the-art algorithms for solving this kind of task (as of this comic's publishing) use local features (e.g. {{w|Scale-invariant feature transform|SIFT}} or {{w|Speeded up robust features|SURF}} in combination with a {{w|support vector machine}}) or a {{w|convolutional neural network}}.

The subtitle refers to "CS", a common abbreviation for "{{w|Computer Science}}", of which {{w|artificial intelligence}} and {{w|computer vision}} are sub-disciplines.

The title text mentions [http://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-100.pdf The Summer Vision Project] and {{w|Marvin Minsky}} of MIT. In the summer of 1966, he asked his undergraduate student {{w|Gerald Jay Sussman}} to [http://szeliski.org/Book/ "spend the summer linking a camera to a computer and getting the computer to describe what it saw"]. {{w|Seymour Papert}} drafted the plan, and it seems that Sussman was joined by {{w|Bill Gosper}}, {{w|Richard Greenblatt (programmer)|Richard Greenblatt}}, {{w|Leslie Lamport}}, Adolfo Guzman, Michael Speciner, John White, Benjamin, and Henneman - in case the multiple Wikipedia links don't give it away, know that this is a sizable cross-section of the AI researchers of the period. The project schedule allocated one summer for the completion of this task. The required time was obviously significantly underestimated, since dozens of research groups around the world are still working on this topic today.

A month after this comic came out, {{w|Flickr}} [http://code.flickr.net/2014/10/20/introducing-flickr-park-or-bird/ responded] with a [http://parkorbird.flickr.com/ prototype online tool] to do something similar to what the comic describes, using its automated-tagging software. According to them, the bird solution "took us less than 5 years to build, though it's definitely a hard problem, and we've still got room for improvement".

Now, years later, the second problem of detecting birds (or any other objects) in the image has also turned into a relatively easy application of existing technologies. Image classification neural networks are readily available. Many groups have put in the years of research (with teams of computer scientists) into the problem of computer vision, and thanks to recent breakthroughs in neural net architectures.

==Transcript==
:[Ponytail sitting at a computer with Cueball standing behind her.]
:Cueball: When a user takes a photo, the app should check whether they're in a national park...
:Ponytail: Sure, easy GIS lookup. Gimme a few hours.
:Cueball: ...and check whether the photo is of a bird.
:Ponytail: I'll need a research team and five years.

:[Caption below the panel:]
:In CS, it can be hard to explain the difference between the easy and the virtually impossible.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Artificial Intelligence]]
[[Category:Programming]]
[[Category:Photography]]
[[Category:Comics featuring real people]]

1425: Tasks

2025-04-24T04:15:58Z

172.68.22.108: /* Explanation */ location - GPS or other positioning (GLONAS, wifi, ...)

{{comic
| number = 1425
| date = September 24, 2014
| title = Tasks
| image = tasks.png
| titletext = In the 60s, Marvin Minsky assigned a couple of undergrads to spend the summer programming a computer to use a camera to identify objects in a scene. He figured they'd have the problem solved by the end of the summer. Half a century later, we're still working on it.
}}

==Explanation==
[[Cueball]] appears to be asking [[Ponytail]] to write an app that determines if a given picture is (1) taken in a national park, and (2) a picture of a bird. The first question is generally harder for a human to answer, but easy for an app that has access to location information, such as supplied by a {{w|Global Positioning System|GPS}} receiver or other positioning network, and a {{w|geographic information system}} (GIS). The second one is easy for a human but much harder for a computer. This illustrates {{w|Moravec's paradox}} from the 1980s in a modern context. By the 1950s computers were useful for tasks like {{w|trajectory optimization}}, {{w|automated theorem proving|generating novel mathematical proofs}}, and {{w|English_draughts#Computer_players|the game of checkers}}, so such high-level computation and reasoning tasks that were hard for humans turned out to be relatively easy for them. On the other hand, it turns out to be hard to "give them the skills of a one-year-old when it comes to perception", as Moravec wrote.

In order to determine whether the user is in a national park, Ponytail plans to determine the user's location using the mobile device. This location will then be cross checked with a {{w|geographic information system}} (GIS) which will be able to determine whether the coordinates lie within a national park boundary.

Determining whether an image is of a given kind of natural object is far more difficult. This task falls into the area of {{w|computer vision}}. One of the goals in computer vision is to detect and classify objects within an image. This is a very challenging task for a number of reasons.

Humans use size, focus, edge-assignment, movement (of both the subject and the observer), and stereoscopic vision when looking at a scene (not a picture of a thing, but the thing itself) to discern individual objects and then {{w|Figure-ground (perception)|categorize them as foreground or background}}. Sound may also assist in locating and identifying objects. An app could use these techniques, as well as additional information, such as distance to the subject and observations of light outside our visual spectrum.

Identifying objects in a photograph is harder. A photograph is a static, usually monoscopic image that can only provide size and edge-assignment clues. Humans are only able to discern objects from background in photographs by comparing the photo against all of the things they've seen and everything they've learned about those things over the course of their life and {{w|Visual perception|identifying matching patterns}}.

The quality of the photograph will have an impact on a computer's ability to match patterns. For example, the object in the photograph might be partially visible or occluded. In the case of a living bird, additional complications arise from the variations among individual birds of the same species and differences in pose (flying, perching in a tree, etc.). Differentiating between visually similar objects can result in false positives. For example, is it a photo of a [[1792: Bird/Plane/Superman|bird in flight or a plane <s>(or superman!)</s>]]? Ponytail's estimate of 5 years may be overly optimistic (see [[678: Researcher Translation]]).

The state-of-the-art algorithms for solving this kind of task (as of this comic's publishing) use local features (e.g. {{w|Scale-invariant feature transform|SIFT}} or {{w|Speeded up robust features|SURF}} in combination with a {{w|support vector machine}}) or a {{w|convolutional neural network}}.

The subtitle refers to "CS", a common abbreviation for "{{w|Computer Science}}", of which {{w|artificial intelligence}} and {{w|computer vision}} are sub-disciplines.

The title text mentions [http://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-100.pdf The Summer Vision Project] and {{w|Marvin Minsky}} of MIT. In the summer of 1966, he asked his undergraduate student {{w|Gerald Jay Sussman}} to [http://szeliski.org/Book/ "spend the summer linking a camera to a computer and getting the computer to describe what it saw"]. {{w|Seymour Papert}} drafted the plan, and it seems that Sussman was joined by {{w|Bill Gosper}}, {{w|Richard Greenblatt (programmer)|Richard Greenblatt}}, {{w|Leslie Lamport}}, Adolfo Guzman, Michael Speciner, John White, Benjamin, and Henneman - in case the multiple Wikipedia links don't give it away, know that this is a sizable cross-section of the AI researchers of the period. The project schedule allocated one summer for the completion of this task. The required time was obviously significantly underestimated, since dozens of research groups around the world are still working on this topic today.

A month after this comic came out, {{w|Flickr}} [http://code.flickr.net/2014/10/20/introducing-flickr-park-or-bird/ responded] with a [http://parkorbird.flickr.com/ prototype online tool] to do something similar to what the comic describes, using its automated-tagging software. According to them, the bird solution "took us less than 5 years to build, though it's definitely a hard problem, and we've still got room for improvement".

Now, years later, the second problem of detecting birds (or any other objects) in the image has also turned into a relatively easy application of existing technologies. Image classification neural networks are readily available. Many groups have put in the years of research (with teams of computer scientists) into the problem of computer vision, and thanks to recent breakthroughs in neural net architectures.

==Transcript==
:[Ponytail sitting at a computer with Cueball standing behind her.]
:Cueball: When a user takes a photo, the app should check whether they're in a national park...
:Ponytail: Sure, easy GIS lookup. Gimme a few hours.
:Cueball: ...and check whether the photo is of a bird.
:Ponytail: I'll need a research team and five years.

:[Caption below the panel:]
:In CS, it can be hard to explain the difference between the easy and the virtually impossible.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Artificial Intelligence]]
[[Category:Programming]]
[[Category:Photography]]
[[Category:Comics featuring real people]]

1425: Tasks

2025-04-24T04:09:07Z

172.68.22.108: /* Explanation */ we also use sound and focal distance. More clearly differentiate the image understanding from the more general problem posed in the comic

{{comic
| number = 1425
| date = September 24, 2014
| title = Tasks
| image = tasks.png
| titletext = In the 60s, Marvin Minsky assigned a couple of undergrads to spend the summer programming a computer to use a camera to identify objects in a scene. He figured they'd have the problem solved by the end of the summer. Half a century later, we're still working on it.
}}

==Explanation==
[[Cueball]] appears to be asking [[Ponytail]] to write an app that determines if a given picture is (1) taken in a national park, and (2) a picture of a bird. The first question is generally harder for a human to answer, but easy for an app that has access to location information and a {{w|geographic information system}} (GIS). The second one is easy for a human but much harder for a computer. This illustrates {{w|Moravec's paradox}} from the 1980s in a modern context. By the 1950s computers were useful for tasks like {{w|trajectory optimization}}, {{w|automated theorem proving|generating novel mathematical proofs}}, and {{w|English_draughts#Computer_players|the game of checkers}}, so such high-level computation and reasoning tasks that were hard for humans turned out to be relatively easy for them. On the other hand, it turns out to be hard to "give them the skills of a one-year-old when it comes to perception", as Moravec wrote.

In order to determine whether the user is in a national park, Ponytail plans to determine the user's location using the mobile device. This location will then be cross checked with a {{w|geographic information system}} (GIS) which will be able to determine whether the coordinates lie within a national park boundary.

Determining whether an image is of a given kind of natural object is far more difficult. This task falls into the area of {{w|computer vision}}. One of the goals in computer vision is to detect and classify objects within an image. This is a very challenging task for a number of reasons.

Humans use size, focus, edge-assignment, movement (of both the subject and the observer), and stereoscopic vision when looking at a scene (not a picture of a thing, but the thing itself) to discern individual objects and then {{w|Figure-ground (perception)|categorize them as foreground or background}}. Sound may also assist in locating and identifying objects. An app could use these techniques, as well as additional information, such as distance to the subject and observations of light outside our visual spectrum.

Identifying objects in a photograph is harder. A photograph is a static, usually monoscopic image that can only provide size and edge-assignment clues. Humans are only able to discern objects from background in photographs by comparing the photo against all of the things they've seen and everything they've learned about those things over the course of their life and {{w|Visual perception|identifying matching patterns}}.

The quality of the photograph will have an impact on a computer's ability to match patterns. For example, the object in the photograph might be partially visible or occluded. In the case of a living bird, additional complications arise from the variations among individual birds of the same species and differences in pose (flying, perching in a tree, etc.). Differentiating between visually similar objects can result in false positives. For example, is it a photo of a [[1792: Bird/Plane/Superman|bird in flight or a plane <s>(or superman!)</s>]]? Ponytail's estimate of 5 years may be overly optimistic (see [[678: Researcher Translation]]).

The state-of-the-art algorithms for solving this kind of task (as of this comic's publishing) use local features (e.g. {{w|Scale-invariant feature transform|SIFT}} or {{w|Speeded up robust features|SURF}} in combination with a {{w|support vector machine}}) or a {{w|convolutional neural network}}.

The subtitle refers to "CS", a common abbreviation for "{{w|Computer Science}}", of which {{w|artificial intelligence}} and {{w|computer vision}} are sub-disciplines.

The title text mentions [http://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-100.pdf The Summer Vision Project] and {{w|Marvin Minsky}} of MIT. In the summer of 1966, he asked his undergraduate student {{w|Gerald Jay Sussman}} to [http://szeliski.org/Book/ "spend the summer linking a camera to a computer and getting the computer to describe what it saw"]. {{w|Seymour Papert}} drafted the plan, and it seems that Sussman was joined by {{w|Bill Gosper}}, {{w|Richard Greenblatt (programmer)|Richard Greenblatt}}, {{w|Leslie Lamport}}, Adolfo Guzman, Michael Speciner, John White, Benjamin, and Henneman - in case the multiple Wikipedia links don't give it away, know that this is a sizable cross-section of the AI researchers of the period. The project schedule allocated one summer for the completion of this task. The required time was obviously significantly underestimated, since dozens of research groups around the world are still working on this topic today.

A month after this comic came out, {{w|Flickr}} [http://code.flickr.net/2014/10/20/introducing-flickr-park-or-bird/ responded] with a [http://parkorbird.flickr.com/ prototype online tool] to do something similar to what the comic describes, using its automated-tagging software. According to them, the bird solution "took us less than 5 years to build, though it's definitely a hard problem, and we've still got room for improvement".

Now, years later, the second problem of detecting birds (or any other objects) in the image has also turned into a relatively easy application of existing technologies. Image classification neural networks are readily available. Many groups have put in the years of research (with teams of computer scientists) into the problem of computer vision, and thanks to recent breakthroughs in neural net architectures.

==Transcript==
:[Ponytail sitting at a computer with Cueball standing behind her.]
:Cueball: When a user takes a photo, the app should check whether they're in a national park...
:Ponytail: Sure, easy GIS lookup. Gimme a few hours.
:Cueball: ...and check whether the photo is of a bird.
:Ponytail: I'll need a research team and five years.

:[Caption below the panel:]
:In CS, it can be hard to explain the difference between the easy and the virtually impossible.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Artificial Intelligence]]
[[Category:Programming]]
[[Category:Photography]]
[[Category:Comics featuring real people]]

Talk:1425: Tasks

2025-04-24T03:56:01Z

172.68.22.108: problem presented in the comic was never just find a bird in a static photo

the source of title text maybe is Szeliski, ''Computer Vision: Algorithms and Applications'' (2010), p. 10. --[[User:Valepert|valepert]] ([[User talk:Valepert|talk]]) 06:59, 24 September 2014 (UTC)

[http://www.wired.com/2012/06/google-x-neural-network/ Google’s Artificial Brain Learns to Find Cat Videos] might be useful as a description of the problem [[Special:Contributions/108.162.250.219|108.162.250.219]] 08:34, 24 September 2014 (UTC)

:Sorry for editing your comment but external links have different syntax that internal links so it wasn't working. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 11:21, 24 September 2014 (UTC)

Nice Superman joke there, Pudder! --[[Special:Contributions/141.101.99.49|141.101.99.49]] 10:26, 24 September 2014 (UTC)
:It had been removed in an edit, so I shoehorned in back in :P --[[User:Pudder|Pudder]] ([[User talk:Pudder|talk]]) 12:25, 24 September 2014 (UTC)
Isn't there an xkcd where the estimate of 5 years of work is equivalent to "might take forever?" [[User:Rtanenbaum|Rtanenbaum]] ([[User talk:Rtanenbaum|talk]]) 13:16, 24 September 2014 (UTC)
:I'm pretty sure you're refering to 678. [[Special:Contributions/173.245.52.132|173.245.52.132]] 15:00, 25 September 2014 (UTC)

The link in the description is to a document by {{w|Seymour Papert}} and the [http://books.google.com/books/about/The_Summer_Vision_Project.html?id=qOh7NwAACAAJ book] on the project is also by Papert. Is there any contemporary evidence that it was actually Minsky who assigned the project? I think he just got interested in it later. 14:17, 24 September 2014 (UTC)

[http://xkcd.com/678/ 678: Researcher Translation] is probably what you're thinking of, Rtanenbaum. [[User:Ndgeek|Ndgeek]] ([[User talk:Ndgeek|talk]]) 17:44, 24 September 2014 (UTC)

Is it possible that Randall's selection of bird rather than another naturally occurring object is a subtle reference to the Birdsnap app (http://engineering.columbia.edu/it-crow-or-raven-new-birdsnap-app-will-tell-you-0) which has solved some of the aspects of this problem? [[Special:Contributions/173.245.48.137|173.245.48.137]] 22:02, 27 September 2014 (UTC)

Hopefully I can add that this also seems to make reference to the U.S. Forest Service intention to make everyone have a permit to take pics, etc., in national parks. https://www.yahoo.com/travel/dont-take-that-picture-the-u-s-forest-service-might-98484656432.html {{unsigned ip|108.162.216.21}}

Post the picture to an online forum, say it's a bird, if it's not everyone will correct you as per http://xkcd.com/386/, so scrape forum and if there's a lot of attention it's not a bird, if there isn't much attention it probably is a bird. [[Special:Contributions/141.101.99.78|141.101.99.78]] 23:06, 3 October 2014 (UTC)

A dev team at Flickr took this comic as a challenge, and set up a PoC at http://parkorbird.flickr.com/ (that seems to work fairly well). --[[Special:Contributions/108.162.210.135|108.162.210.135]] 20:08, 20 October 2014 (UTC)
:I was duly impressed. It doesn't recognize big bird very well, though. ;) [[User:Suspender guy|Suspender guy]] ([[User talk:Suspender guy|talk]]) 20:26, 17 February 2016 (UTC)

A 'picture of a bird' from a CS perspective is a reverse engineering problem. The picture is a 2 dimensional rendering of a 3-dimensional world and a 'bird' is a 3-dimensional object. It takes years for the mind of a newborn human to be able to recognize a majority of objects based on their 'first look' at a stereoscopic (two-eyes) image presented by their visual cortex. The software equivalency of this would be to create a 3 dimensional representation of objects and create a linear-algebra algorithm that can define the statistical probability that any given shape is within a certain degree of exclusion a matrix representation of the target shape (area) of the 3 dimensional object (bird) based on distance (using spacial reconstruction). It's not impossible, it's just really really hard. - nerd answer {{unsigned ip|173.245.54.166}}
:To be honest I don't think it is impossible to replicate any function of human intelligence and mental capacity on a computer system. It just requires sufficient processing ability, appropriate hardware, and of course, an understanding of how humans do it in the first place. -Pennpenn [[Special:Contributions/108.162.250.162|108.162.250.162]] 03:29, 17 September 2015 (UTC)

Or just give Google a little less than two years, and they'll make [https://cloud.google.com/vision/ Google Cloud Vision API] for you [[User:Gpk|Gpk]] ([[User talk:Gpk|talk]]) 20:39, 13 June 2016 (UTC)

I read somewhere that when you ask CS/IT specialist for a probable ETA for solving an interesting problem, you need to multiply the given time to the ETA by 4 and take the next larger unit (a minute becomes 4 hours, an hour becomes 4 days etc.). Can't find the source of that though. [[Special:Contributions/141.101.70.229|141.101.70.229]] 15:47, 12 September 2016 (UTC)

== GIS being "easy" ==

All these years later, I still struggle with the classification of "are we in a national park" as "easy"..

It 'only' requires a functioning GPS-system. A military super-project, whose [https://nation.time.com/2012/05/21/how-much-does-gps-cost/ initial setup cost 12 billion], still costs ~2 million a day, and whose principles of operation depend on [https://skeptics.stackexchange.com/questions/20230/does-gps-use-general-relativity both special '''and''' general relativity] for correctness.
And that's ''before'' we add the record-keeping and (internet?)logistics involved with providing each phone an accurate GIS-database. The OpenStreetMap (most likely free/gratis source of this type of data, for a cheap app) is a massive undertaking!

(sarcasm on) GIS-lookup sure is easy! Only took a minor Manhattan-project, a literal Einstein, and an army of internet volunteers to solve!(sarcasm off)

(I'm leaving out mobile internet access while in said National Parks (Telecom operators are among the wealthiest companies in the world, and those phone-towers-disguised-like-trees don't come cheap...), because the App would probably be shipped with a hardcoded park-database, not do live queries.)

-- Jules @ [[Special:Contributions/162.158.91.77|162.158.91.77]] 08:13, 18 May 2020 (UTC)

:This is about implementation of something existing, not inventing it from scratch. The use of the word "app" implies, that this comic is happening in the smartphone area, so GPS on phones should be a regular thing. --[[User:Lupo|Lupo]] ([[User talk:Lupo|talk]]) 09:57, 18 May 2020 (UTC)

:: "app" sets the real-world context, but the punchline is about the comparative hardness '''in CS'''.
:: For the pragmatic app-developer, "previously solved" equals "easy"; for a doctorate in computational theory, it doesn't :-)
:: -- Jules @ [[Special:Contributions/162.158.91.77|162.158.91.77]] 12:16, 18 May 2020 (UTC)
:::That might be true, but this comic is definitely about developing an app, so it doesn't matter if GPS involves complicated hard- and software setups outside of the app or not. And unless you focus on the theoretical work also for a computer scientist, it is easy to use established GPS methods. --[[User:Lupo|Lupo]] ([[User talk:Lupo|talk]]) 12:45, 18 May 2020 (UTC)

now deep learning is common you not need research team and five years anymore

:And it took about five years since the comic was posted to get to that point...

This comic is referring to doing a GIS lookup which is a glorified sql Query which has nothing to do with GPS and the the USGS spatial data a GIS database is commonly populated with is not derived from GPS information anyway. A GIS Lookup IS easy. Gathering the spatial data is difficult, though as previously mentioned its already widely and freely available for use. --[[User:PlatterMonkous|PlatterMonkous]]
:The GIS data is being looked at to determine if GPS-derived metadata lies within one of its boundaries, surely? Without GPS, the query has no sensible question to ask.
:(Then again, none of my own pictures have that sort of EXIF information. Either they're taken on a 'dumb' digital camera, that doesn't have inbuilt GPS, or even ''if'' they're done via my GPS+Camera-equipped tablet (rare) I've likely not allowed the one to be fed data that the other one knows. If it's even turned on. But the comic scenario clearly assumes otherwise.) [[Special:Contributions/172.70.86.62|172.70.86.62]] 20:21, 10 November 2022 (UTC)

I think that, like in a number of other comic explanations, the explanation of the humour has given way to the technical exposition of the situation. What made me chuckle about this comic is the old adage in the software industry that: ''It takes 5% of the time to implement the first 95%, but 95% of time to complete the last 5%''. Even when experienced programmers correctly identify the difficult element of a problem and attempt to compensate for that difficulty in their implementation schedules, they can still be ''wildly'' off the mark. In this case, 60 years and counting... [[Special:Contributions/172.71.94.28|172.71.94.28]] 10:55, 9 August 2023 (UTC)

The year is 2024, and there is an ArsTechnica article about the problem in this comic now being solved. https://arstechnica.com/information-technology/2024/01/famous-xkcd-comic-comes-full-circle-with-ai-bird-identifying-binoculars/ [[Special:Contributions/172.70.210.41|172.70.210.41]] 22:24, 17 January 2024 (UTC)
:Updated to add credit where credit is due, the research team in our reality that created the technology is the Cornell Lab of Ornithology in the Center for Avian Population Studies and Macaulay Library: https://ebird.org/about/staff -- No doubt if Ponytail was the lead the staff could've done it in half the time! [[Special:Contributions/162.158.90.24|162.158.90.24]] 22:32, 17 January 2024 (UTC)

The rewrite of the explanation is really long overdue! If it's hard to start from scratch, someone could request GPT-4 to make a plan on how to update the article, and then use the ideas for inspiration {{unsigned ip|162.158.151.152|20:44, 13 March 2024}}
:If you think it could do with a rewrite, rewrite it yourself. (Stay away from GPT, though, still likely to give an unsatisfactory explanation. If not downright hallucinating.) [[Special:Contributions/172.70.86.179|172.70.86.179]] 21:01, 13 March 2024 (UTC)

The explanation of bird identification assumed that a static picture was all the information available to the app. There is no reason the app can't use additional data for this problem (as it does for problem 1). There are various ways the App could estimating range (stereo pictures, series of images with different focal lengths, distance sensors). Could use images beyond the visible range. Could use multiple frames or moving images to figure parallax, and help differentiate static from moving objects. (Sensors in the camera could indicate how the camera moved to inform interpretation of time based imaging.) All of these techniques were possible when the comic was posted, although they present interesting problems. I updated the explanation to try to expand the possibilities. Put in this comment in case what I put in the explanation wasn't clear. [[Special:Contributions/172.68.22.108|172.68.22.108]] 03:56, 24 April 2025 (UTC)

3079: Air Fact

2025-04-21T19:14:33Z

172.68.22.108:

{{comic
| number = 3079
| date = April 21, 2025
| title = Air Fact
| image = air_fact_2x.png
| imagesize = 250x394px
| noexpand = true
| titletext = 'Wow, that must be why you swallow so many of them per year!' 'No, that's spiders. You swallow WAY more ants.'
}}

==Explanation==
{{incomplete|This page was created by a MICROSCOPIC ANT and contains only microscopic text. Don't remove this notice too soon.}}
Microbiologist [[Megan]] tells [[Cueball]] that every cubic meter of air contains thousands of microscopic ants. This, ironically, is a tall tale. Adult workers in some species of the genus {{w|Carebara|Carebara}}, the [https://www.guinnessworldrecords.com/world-records/341603-smallest-ant-species smallest known ants], can be 0.8 millimeters long, which is just below the 1.0 millimeter upper bound of "microscopic". It is therefore possible (barely) for an air sample to contain microscopic ants. However, given the subterranean, cryptic habitats typical of Carebara species, it is highly unlikely that these ants would appear in any, never mind every, air sample.

Initially incredulous, Cueball accepts Megan's fib as a fact, because he doesn't have any easy way of take samples of air and assess what these samples contain.

There are indeed microorganisms floating in the air, and getting air samples that will allow these microorganisms to be identified and quantified is indeed hard. [https://www.btpm.org/health-wellness/2018-05-23/allergy-season-is-back-but-how-do-we-know-whats-in-the-air Methods, with specialized collecting devices, exist] that take (one hopes) known volumes of air and deposit the particles contained in that air onto sticky surfaces, which are then viewed under the microscope, or onto culture media which are then incubated. The methods are time-consuming and dependent on specialized knowledge (e.g., the identification of pollen grains or spores by surface features under the microscope), and are subject to numerous biases. For example, "sticky surface" methods will likely miss bacteria, and fail to identify 'nondescript' objects, whereas culture-based methods will not detect anything that will not grow on the selected media. The joke is that microbiologists are tempted to make up stories about what's in the air, because most people lack the data or skills to fact-check the stories.

In the comic, Megan presumably sampled a 10 cubic centimeter space of air and found 1 microbe (e.g. a bacterium, a mold spore, a protozoan cyst) in it. If she assumed that this was a representative sample, Megan could extrapolate from this datum to say that there are 10,000 microbes (which she then calls "ants") for every 1 cubic meter (1,000,000 cubic centimeters). Randall Monroe has made comics about dubious extrapolations: [[605]], but in this case, Megan's number is [https://pmc.ncbi.nlm.nih.gov/articles/PMC4515362/ within the range of microbial counts] that have been made in various indoor and outdoor environments.

The title text refers to the commonly believed myth that [https://www.bbc.com/news/uk-england-beds-bucks-herts-66319172 people swallow 8 spiders a year in their sleep]. Though commonly quoted, [https://www.scientificamerican.com/article/fact-or-fiction-people-swallow-8-spiders-a-year-while-they-sleep1/ it has no basis in fact].

==Transcript==
:[Megan, with her palm out, is talking to Cueball.]
:Megan: Did you know that every cubic meter of air contains over 10,000 microscopic ants?
:Cueball: Wow, really?
:Cueball: I had no idea.

:[Caption below the panel:]
:The fact that taking air samples is hard presents microbiologists with a constant temptation.

{{comic discussion}}

[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Biology]]
[[Category:Ants]]
[[Category:Spiders]]