explain xkcd - User contributions [en]

1867: Physics Confession

2017-07-24T14:46:05Z

Pizzutz: /* Explanation */

{{comic
| number = 1867
| date = July 24, 2017
| title = Physics Confession
| image = physics_confession.png
| titletext = "You know lightning, right? When electric charge builds up in a cloud and then discharges in a giant spark? Ask me why that happens." "Why does tha--" "No clue. We think it's related to the hair thing."
}}

==Explanation==
{{incomplete|This is my first contribution it should be looked over by someone before the tag is removed.}}

A {{w|Theory of Everything}} is a goal of modern physics which would describe the properties of all fundamental particles and all the interactions between them. The current approach to a theory of everything is to describe how at high energies different interactions, such as electromagnetic forces and the strong and weak nuclear interactions merge. It would be possible, in principle to demonstrate how the rest of known physics can be derived from that quantum behavior. This approach, however, leaves many everyday phenomena which are not understood by modern physics, and many {{w|Theory_of_everything#Arguments_against_a_theory_of_everything|arguments against a theory of everything}} suggest that it won't ever be able to actually precisely describe everything. This comic lists several of those phenomena:

The fine detail of how ice skates work is unknown. It is known that they develop a film of water between the skate and the ice that lubricates sliding, but scientists dispute how the film gets there. The commonly held belief is that it is caused by the pressure of the narrow skate; another belief is that the ice is melted by the friction of movement; but both fail to fully explain why skating continues to be possible at temperatures that are significantly below 0 Celsius. A better explanation is simply that, near the melting point of a solid, there will be a thin layer of liquid on the surface due to the dynamic equilibrium between the two phases, hence why ice is slippery. This happens regardless of the presence of skates. A more complete explanation is given in the linked article: [http://lptms.u-psud.fr/membres/trizac/Ens/L3FIP/Ice.pdf Why is ice slippery?].

Physicists lack a clear understanding of the interactions involved in the flow of {{w|granular material}}s, such as sand. It is known that the behavior diverges greatly from that of a liquid, but it is unknown exactly how the flow works.[http://physicscentral.com/explore/action/granular.cfm PhysicsCentral:Granular Materials]

Modern physics also doesn't understand what makes electrons move from one material to another when two materials are rubbed against each other (the {{w|triboelectric effect}}), and why the transfer takes more electrons in one direction than in the other.

The title text mentions another common phenomenon that is poorly understood: the separation of charges in a cumulonimbus cloud. It is thought that interactions between ice and water transfer electrons, and then the different motion of ice (as hail) and water droplets in the cloud separates the charge. [http://www.srh.noaa.gov/jetstream/lightning/lightning.html NOAA How lightning is created].

==Transcript==
:[Megan is facing Ponytail and Cueball.]
:Megan: I'll be honest: We physicists talk a big game about the theory of everything, but the truth is, we don't really understand why ice skates work, how sand flows, or where the static charge comes from when you rub your hair with a balloon.

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

1679: Substitutions 3

2016-05-11T13:45:23Z

Pizzutz: /* Transcript */

{{comic
| number = 1679
| date = May 11, 2016
| title = Substitutions 3
| image = substitutions_3.png
| titletext = BREAKING: Channing Tatum and his friends explore haunted city
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page.}}

Real examples:

*Japan's Sincerity in Improving Bilateral Ties Will Never Be Known [http://english.cri.cn/12394/2016/04/30/4203s926079.htm]
*London Jews Delusional About First-Ever Muslim Mayor [http://jewishvoiceny.com/index.php?option=com_content&view=article&id=14455:london-jews-cautiously-optimistic-about-first-ever-muslim-mayor&catid=106:international&Itemid=289]

==See also==
*[[1288: Substitutions]]
*[[1625: Substitutions 2]]

==Transcript==
:[Caption above the panel:]
:Even More
:<big>'''Substitutions''':</big>
:That make reading the news more fun

:[A table of words/sentences on the left that change in to those on the left. Between each set of words there is an arrow pointing from right.]
:{|
|-
| style="text-align:right;" | Gaffe
| ➜
| Magic spell
|-
| style="text-align:right;" | Ancient
| ➜
| Haunted
|-
| style="text-align:right;" | Remains to be seen
| ➜
| Will never be known
|-
| style="text-align:right;" | Silver bullet
| ➜
| Way to kill werewolves
|-
| style="text-align:right;" | Subway system
| ➜
| Tunnels I found
|-
| style="text-align:right;" | Surprising
| ➜
| Surprising (But not to me)
|-
| style="text-align:right;" | War of Words
| ➜
| Interplanetary war
|-
| style="text-align:right;" | Tension
| ➜
| Sexual Tension
|-
| style="text-align:right;" | Cautiously optimistic
| ➜
| Delusional
|-
| style="text-align:right;" | Doctor Who
| ➜
| The Big Bang Theory
|-
| style="text-align:right;" | Email \
|-
| style="text-align:right;" | Facebook Post
| ➜
| Poem
|-
| style="text-align:right;" | Tweet /
|-
| style="text-align:right;" | Facebook CEO
| ➜
| This guy
|-
| style="text-align:right;" | Latest
| ➜
| Final
|-
| style="text-align:right;" | Disrupt
| ➜
| Destroy
|-
| style="text-align:right;" | Meeting
| ➜
| Ménage à trois
|-
| style="text-align:right;" | Scientists
| ➜
| Channing Tatum and his friends
|-
| style="text-align:right;" | You won't believe
| ➜
| I'm really sad about
|}

{{comic discussion}}

1679: Substitutions 3

2016-05-11T13:44:38Z

Pizzutz: /* Transcript */

{{comic
| number = 1679
| date = May 11, 2016
| title = Substitutions 3
| image = substitutions_3.png
| titletext = BREAKING: Channing Tatum and his friends explore haunted city
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page.}}

Real examples:

*Japan's Sincerity in Improving Bilateral Ties Will Never Be Known [http://english.cri.cn/12394/2016/04/30/4203s926079.htm]
*London Jews Delusional About First-Ever Muslim Mayor [http://jewishvoiceny.com/index.php?option=com_content&view=article&id=14455:london-jews-cautiously-optimistic-about-first-ever-muslim-mayor&catid=106:international&Itemid=289]

==See also==
*[[1288: Substitutions]]
*[[1625: Substitutions 2]]

==Transcript==
:[Caption above the panel:]
:Even More
:<big>'''Substitutions''':</big>
:That make reading the news more fun

:[A table of words/sentences on the left that change in to those on the left. Between each set of words there is an arrow pointing from right.]
:{|
|-
| style="text-align:right;" | Gaffe
| ➜
| Magic spell
|-
| style="text-align:right;" | Ancient
| ➜
| Haunted
|-
| style="text-align:right;" | Remains to be seen
| ➜
| Will never be known
|-
| style="text-align:right;" | Silver bullet
| ➜
| Way to kill werewolves
|-
| style="text-align:right;" | Subway system
| ➜
| Tunnels I found
|-
| style="text-align:right;" | Surprising
| ➜
| Surprising (But not to me)
|-
| style="text-align:right;" | War of Words
| ➜
| Interplanetary war
|-
| style="text-align:right;" | Tension
| ➜
| Sexual Tension
|-
| style="text-align:right;" | Cautiously optimistic
| ➜
| Delusional
|-
| style="text-align:right;" | Doctor Who
| ➜
| The Big Bang Theory
|-
| style="text-align:right;" | Email
|-
| style="text-align:right;" | Facebook Post
| ➜
| Poem
|-
| style="text-align:right;" | Tweet
|-
| style="text-align:right;" | Facebook CEO
| ➜
| This guy
|-
| style="text-align:right;" | Latest
| ➜
| Final
|-
| style="text-align:right;" | Disrupt
| ➜
| Destroy
|-
| style="text-align:right;" | Meeting
| ➜
| Ménage à trois
|-
| style="text-align:right;" | Scientists
| ➜
| Channing Tatum and his friends
|-
| style="text-align:right;" | You won't believe
| ➜
| I'm really sad about
|}

{{comic discussion}}

1679: Substitutions 3

2016-05-11T13:43:22Z

Pizzutz: /* Transcript */

{{comic
| number = 1679
| date = May 11, 2016
| title = Substitutions 3
| image = substitutions_3.png
| titletext = BREAKING: Channing Tatum and his friends explore haunted city
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page.}}

Real examples:

*Japan's Sincerity in Improving Bilateral Ties Will Never Be Known [http://english.cri.cn/12394/2016/04/30/4203s926079.htm]
*London Jews Delusional About First-Ever Muslim Mayor [http://jewishvoiceny.com/index.php?option=com_content&view=article&id=14455:london-jews-cautiously-optimistic-about-first-ever-muslim-mayor&catid=106:international&Itemid=289]

==See also==
*[[1288: Substitutions]]
*[[1625: Substitutions 2]]

==Transcript==
:[Caption above the panel:]
:Even More
:<big>'''Substitutions''':</big>
:That make reading the news more fun

:[A table of words/sentences on the left that change in to those on the left. Between each set of words there is an arrow pointing from right.]
:{|
|-
| style="text-align:right;" | Gaffe
| ➜
| Magic spell
|-
| style="text-align:right;" | Ancient
| ➜
| Haunted
|-
| style="text-align:right;" | Remains to be seen
| ➜
| Will never be known
|-
| style="text-align:right;" | Silver bullet
| ➜
| Way to kill werewolves
|-
| style="text-align:right;" | Subway system
| ➜
| Tunnels I found
|-
| style="text-align:right;" | Surprising
| ➜
| Surprising (But not to me)
|-
| style="text-align:right;" | War of Words
| ➜
| Interplanetary war
|-
| style="text-align:right;" | Tension
| ➜
| Sexual Tension
|-
| style="text-align:right;" | Cautiously optimistic
| ➜
| Delusional
|-
| style="text-align:right;" | Doctor Who
| ➜
| The Big Bang Theory
|-
| style="text-align:right;" | Email
| style="text-align:right;" | Facebook Post
| ➜
| Poem
| style="text-align:right;" | Tweet
|-
| style="text-align:right;" | Facebook CEO
| ➜
| This guy
|-
| style="text-align:right;" | Latest
| ➜
| Final
|-
| style="text-align:right;" | Disrupt
| ➜
| Destroy
|-
| style="text-align:right;" | Meeting
| ➜
| Ménage à trois
|-
| style="text-align:right;" | Scientists
| ➜
| Channing Tatum and his friends
|-
| style="text-align:right;" | You won't believe
| ➜
| I'm really sad about
|}

{{comic discussion}}

1679: Substitutions 3

2016-05-11T13:31:13Z

Pizzutz: Added initial Transcript

{{comic
| number = 1679
| date = May 11, 2016
| title = Substitutions 3
| image = substitutions_3.png
| titletext = BREAKING: Channing Tatum and his friends explore haunted city
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page.}}

Real examples:

*Japan's Sincerity in Improving Bilateral Ties Will Never Be Known [http://english.cri.cn/12394/2016/04/30/4203s926079.htm]
*London Jews Delusional About First-Ever Muslim Mayor [http://jewishvoiceny.com/index.php?option=com_content&view=article&id=14455:london-jews-cautiously-optimistic-about-first-ever-muslim-mayor&catid=106:international&Itemid=289]

==See also==
*[[1288: Substitutions]]

==Transcript==
:[Caption above the panel:]
:Even More
:'''Substitutions'''
:That make reading the news more fun

:[A table of words/sentences on the left that change in to those on the left. Between each set of words there is a gray arrow pointing from right.]
:{|
|-
| style="text-align:right;" | Gaffe
| ➜
| Magic spell
|-
| style="text-align:right;" | Ancient
| ➜
| Haunted
|-
| style="text-align:right;" | Remains to be seen
| ➜
| Will never be known
|-
| style="text-align:right;" | Silver bullet
| ➜
| Way to kill werewolves
|-
| style="text-align:right;" | Subway system
| ➜
| Tunnels I found
|-
| style="text-align:right;" | Surprising
| ➜
| Surprising (But not to me)
|-
| style="text-align:right;" | War of Words
| ➜
| Interplanetary war
|-
| style="text-align:right;" | Tension
| ➜
| Sexual Tension
|-
| style="text-align:right;" | Cautiously optimistic
| ➜
| Delusional
|-
| style="text-align:right;" | Doctor Who
| ➜
| The Big Bang Theory
|-
| style="text-align:right;" | Email, Facebook Post, Tweet
| ➜
| Poem
|-
| style="text-align:right;" | Facebook CEO
| ➜
| This guy
|-
| style="text-align:right;" | Latest
| ➜
| Final
|-
| style="text-align:right;" | Disrupt
| ➜
| Destroy
|-
| style="text-align:right;" | Meeting
| ➜
| Menage a troi
|-
| style="text-align:right;" | Scientists
| ➜
| Channing Tatum and his friends
|-
| style="text-align:right;" | You won't believe
| ➜
| I'm really sad about
|}

{{comic discussion}}

1425: Tasks

2014-09-24T13:22:30Z

Pizzutz: /* Explanation */

{{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==
{{incomplete|Explain why it is so difficult to identify a particular object in an image. Better background needed on title text.}}
[[Cueball]] appears to be asking [[Ponytail]] to write an app that determines if a given picture is of a bird in a national park. These two requirements, while seemingly about equally hard to a human, vary greatly in difficulty in computer science (CS).

In order to determine whether the user is in a national park, Ponytail plans to determine the user's location, presumably using Exif data from the uploaded image or some method of {{w|Mobile phone tracking|mobile phone tracking}}. This location will then be cross checked with a {{w|geographic information system}} (GIS) which will be able to determine whether the co-ordinates lie within a national park boundary.

Determining whether an image is of a particular object is far more difficult. This task falls into the area of {{w|Computer vision|computer vision}}. One of the goals in computer vision is to detect and classify objects within an image. This is a very challenging task since there is a large variability in the object's appearance and background composition. Furthermore, the object might only be partially visible or occluded. In the case of a living bird additional complication arises from the bird's pose (flying, perching in a tree, etc.) since it is not a static object (e.g. street sign). Differentiating between visually similar objects can result in false positives, for example is a photo of a bird in flight or a plane (or superman!). The task is especially difficult when the photo quality may be low.

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

The title text mentions [http://dspace.mit.edu/bitstream/handle/1721.1/6125/AIM-100.pdf The Summer Vision Project] from {{w|Marvin Minsky}} from MIT. In summer 1966 he asked his undergraduate student {{w|Gerald Jay Sussman}} to "spend the summer linking a camera to a computer and getting the computer to describe what it saw" ([http://szeliski.org/Book/]). The project schedule allocated one summer for the completion of this task. This estimation was obviously far underestimated since today dozens of research groups around the world are still working on this topic.

==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.
:In CS, it can be hard to explain the difference between the easy and the virtually impossible

{{comic discussion}}