explain xkcd - User contributions [en]

Talk:1473: Location Sharing

2015-01-14T20:36:44Z

ChristGoldman:

It's a reference to the Uncertainty Principle, a property of quantum mechanics that states that position and momentum cannot be known at the same time.
[[Special:Contributions/199.27.133.98|199.27.133.98]] 05:20, 14 January 2015 (UTC)

I may be thinking too much into this, but couldn't she also not want the website to know her mass? Momentum is Mass*Velocity, and Velocity can be derived from change in position [[Special:Contributions/173.245.56.159|173.245.56.159]] 05:34, 14 January 2015 (UTC)
:That was my understanding, too. Moreover, I don't see any humor in applying the uncertainity principle to macroscopic objects. [[Special:Contributions/108.162.254.57|108.162.254.57]] 08:53, 14 January 2015 (UTC)

Angular momentum sensors - a.k.a. gyros, not accelerometers. {{unsigned ip|141.101.80.109}}

She does not want the website to calculate her mass and therefore her weight. It has nothing to do with the uncertainty principle {{unsigned|Saints22}}
:I disagree. Of course it is funny idea that she says nice try as if the website had interest in her weight. But since you cannot calculate mass from position and momentum your ideas makes no sense. You need the velocity and the momentum to calculate the mass. So even though they could have both position and momentum they would still not know her mass. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 10:33, 14 January 2015 (UTC)
::Unless, of course, the permission given by Megan to determine her location is persistent and lasts for at least two consecutive polls for location, which would enable the recipient to compute the velocity out of two locations and time between the polls. [[User:Nyq|Nyq]] ([[User talk:Nyq|talk]]) 13:12, 14 January 2015 (UTC)

I do not not think that Megan allows the website to access her location. The website wants her to, that's why the button is highlighted and blinking. In the beat panel, Megan presumably denies. The website then asks for momentum and wants Megan to deny the request (by highlighting "Deny"), so that, according to the uncertainty principle, they can still get her location (which is what they wanted all along). However, Megan sees through this trick and acknowledges its cleverness with a "Nice try". --[[Special:Contributions/108.162.254.134|108.162.254.134]] 10:27, 14 January 2015 (UTC)
:No I disagree. Of course the highlighted button is the one Megan pushes. And just because you do not know the momentum does not automatically give you the location. You just can't know both without a given uncertainty. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 10:33, 14 January 2015 (UTC)

What's with the persistent "females"? Would make sense in biology talk, but it's really weird when what you mean is "women"[[Special:Contributions/141.101.104.185|141.101.104.185]] 13:14, 14 January 2015 (UTC)
:: I'd suggest that it is just about avoidance: some might take 'women' as having negative derogative connotations in this context, whereas females is unarguably accurate. [[Special:Contributions/173.245.54.204|173.245.54.204]] 13:29, 14 January 2015 (UTC)
:::"Females" is shorter than "women and girls". [[Special:Contributions/108.162.221.201|108.162.221.201]] 14:54, 14 January 2015 (UTC)
::: Yes, some people are determined to be offended. Unfortunate. [[Special:Contributions/173.245.54.152|173.245.54.152]] 19:52, 14 January 2015 (UTC)
::: For the sake of accuracy, I move that we should really say something more along the lines of "living female homo sapiens organisms" - so that we can exclude the countless other female eukaryotes we know so little about socialogically, and/or the otherwise dead or nonexistent homo sapiens or their representations? I mean, come on! "Females" is sooooo nonspecific...-- [[User:Brettpeirce|Brettpeirce]] ([[User talk:Brettpeirce|talk]]) 19:57, 14 January 2015 (UTC)
:: The name of the academic field of the study of women's perspectives in most public universities is, "Gender, Sexuality, and Women's Studies." "Women" is the correct academic term for the discussion of women. [[User:ChristGoldman|ChristGoldman]] ([[User talk:ChristGoldman|talk]]) 20:36, 14 January 2015 (UTC)

There's some confusion over the sensors. GPS is used to determine the device's position on Earth, but not its orientation. An accelerometer may be used to determine a phone's orientation in terms of flat/portrait/landscape, but not in which direction in terms of north/south. The magnetometer can measure magnetic forces, but isn't enough to determine north (because of inclination). To measure magnetic north, you need to combine data from accelerometer and magnetometer, which gets a working, but quite unsteady compass. These sensors (GPS, accelerometer, magnetometer) are available on most current smart phones. Better devices also include a gyroscope, which measures angular momentum, but no absolute angle towards the horizon and/or north. A gyroscope may be used to improve the stability of the accelerometer/magnetometer compass (but requires a good algorithm which I'm still looking for). Knowing this, the title text is disputable, because devices without gyro aren't actually able to provide a steady compass, while those with gyro are (although there are apps which don't use the gyro even when available, so they won't get a fast, steady compass anyway). --[[User:SlashMe|SlashMe]] ([[User talk:SlashMe|talk]]) 15:24, 14 January 2015 (UTC)

It seems to me that the paragraph explaining mass and weight is too complicated and overly long, and the hypothesis that the app is trying to steal this information unrelated to the comic, or rather, wild speculative extrapolations of logic and meaning. Likewise, the sentences on how the accelerometer may be used to guess passwords seems to me to be unfounded in science. The uncertainty principle is the clear main theme of this comic. --[[User:Canned Soul|Canned Soul]] ([[User talk:Canned Soul|talk]]) 16:03, 14 January 2015 (UTC)

Added one word to make it "An example is a weather app which would need your location in order to '''automatically''' find the correct forecast." It's often trivial to manually get forecasts (or other services, like "nearest branch of a shop that has your desired item in stock") for a current location, just so as long as /you/ know where you are... (I don't turn on my GPS unless I'm actually wanting to use it for something, and don't like websites knowing these things just because they ask for them in the background. Go away, Google Location Services... and why does it grey-out the "Don't share information" hotspot when I've ticked the "Don't ask me again" and only lets me continually refuse ''manually''!? Which I do on principle!!) I keep a variety of common home/away locations on permalink in my favourite weather forecast app and know I can easily add another at a moment's notice when I ''want'' to. (And, the beauty is, I don't even need to be there at the time, just perhaps ''planning'' to go!)

Plus, to the "I don't see any humor in applying the uncertainity principle to macroscopic objects." person, above, please pass by your local XKCD offices at the first opportunity in order to hand back your XKCD Membership Card. You're obviously not one of us! ;) [[Special:Contributions/141.101.98.191|141.101.98.191]] 16:28, 14 January 2015 (UTC)

Per the explanation: "Randall suggests the poor accuracy of the compasses in mobile phones (measuring the angular position) is due to the gyroscopes being too good. (If both the gyroscope and the compasses were completely accurate, it would violate the uncertainty principle)."
The compass points in a particular direction but tells you nothing about location or momentum. How would it be involved in any violation of Uncertainty? The gyroscope and GPS I could see, maybe. But the compass? I don't see how it combined with anything could involve Uncertainty. - Equinox [[Special:Contributions/199.27.128.117|199.27.128.117]] 16:46, 14 January 2015 (UTC)
: The Uncertainty Principle extends to other pairs of conjugate variables besides the well-known pair of position and momentum. One of these pairs is orientation and angular momentum. [[Special:Contributions/173.245.52.142|173.245.52.142]] 17:45, 14 January 2015 (UTC)

Talk:1473: Location Sharing

2015-01-14T20:36:12Z

ChristGoldman:

It's a reference to the Uncertainty Principle, a property of quantum mechanics that states that position and momentum cannot be known at the same time.
[[Special:Contributions/199.27.133.98|199.27.133.98]] 05:20, 14 January 2015 (UTC)

I may be thinking too much into this, but couldn't she also not want the website to know her mass? Momentum is Mass*Velocity, and Velocity can be derived from change in position [[Special:Contributions/173.245.56.159|173.245.56.159]] 05:34, 14 January 2015 (UTC)
:That was my understanding, too. Moreover, I don't see any humor in applying the uncertainity principle to macroscopic objects. [[Special:Contributions/108.162.254.57|108.162.254.57]] 08:53, 14 January 2015 (UTC)

Angular momentum sensors - a.k.a. gyros, not accelerometers. {{unsigned ip|141.101.80.109}}

She does not want the website to calculate her mass and therefore her weight. It has nothing to do with the uncertainty principle {{unsigned|Saints22}}
:I disagree. Of course it is funny idea that she says nice try as if the website had interest in her weight. But since you cannot calculate mass from position and momentum your ideas makes no sense. You need the velocity and the momentum to calculate the mass. So even though they could have both position and momentum they would still not know her mass. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 10:33, 14 January 2015 (UTC)
::Unless, of course, the permission given by Megan to determine her location is persistent and lasts for at least two consecutive polls for location, which would enable the recipient to compute the velocity out of two locations and time between the polls. [[User:Nyq|Nyq]] ([[User talk:Nyq|talk]]) 13:12, 14 January 2015 (UTC)

I do not not think that Megan allows the website to access her location. The website wants her to, that's why the button is highlighted and blinking. In the beat panel, Megan presumably denies. The website then asks for momentum and wants Megan to deny the request (by highlighting "Deny"), so that, according to the uncertainty principle, they can still get her location (which is what they wanted all along). However, Megan sees through this trick and acknowledges its cleverness with a "Nice try". --[[Special:Contributions/108.162.254.134|108.162.254.134]] 10:27, 14 January 2015 (UTC)
:No I disagree. Of course the highlighted button is the one Megan pushes. And just because you do not know the momentum does not automatically give you the location. You just can't know both without a given uncertainty. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 10:33, 14 January 2015 (UTC)

What's with the persistent "females"? Would make sense in biology talk, but it's really weird when what you mean is "women"[[Special:Contributions/141.101.104.185|141.101.104.185]] 13:14, 14 January 2015 (UTC)
:: I'd suggest that it is just about avoidance: some might take 'women' as having negative derogative connotations in this context, whereas females is unarguably accurate. [[Special:Contributions/173.245.54.204|173.245.54.204]] 13:29, 14 January 2015 (UTC)
:::"Females" is shorter than "women and girls". [[Special:Contributions/108.162.221.201|108.162.221.201]] 14:54, 14 January 2015 (UTC)
::: Yes, some people are determined to be offended. Unfortunate. [[Special:Contributions/173.245.54.152|173.245.54.152]] 19:52, 14 January 2015 (UTC)
::: For the sake of accuracy, I move that we should really say something more along the lines of "living female homo sapiens organisms" - so that we can exclude the countless other female eukaryotes we know so little about socialogically, and/or the otherwise dead or nonexistent homo sapiens or their representations? I mean, come on! "Females" is sooooo nonspecific...-- [[User:Brettpeirce|Brettpeirce]] ([[User talk:Brettpeirce|talk]]) 19:57, 14 January 2015 (UTC)
:: The name of the academic field of the study of women's perspectives in most public universities is, "Gender, Sexuality, and Women's Studies." "Women" is the correct academic term for the discussion of women.

There's some confusion over the sensors. GPS is used to determine the device's position on Earth, but not its orientation. An accelerometer may be used to determine a phone's orientation in terms of flat/portrait/landscape, but not in which direction in terms of north/south. The magnetometer can measure magnetic forces, but isn't enough to determine north (because of inclination). To measure magnetic north, you need to combine data from accelerometer and magnetometer, which gets a working, but quite unsteady compass. These sensors (GPS, accelerometer, magnetometer) are available on most current smart phones. Better devices also include a gyroscope, which measures angular momentum, but no absolute angle towards the horizon and/or north. A gyroscope may be used to improve the stability of the accelerometer/magnetometer compass (but requires a good algorithm which I'm still looking for). Knowing this, the title text is disputable, because devices without gyro aren't actually able to provide a steady compass, while those with gyro are (although there are apps which don't use the gyro even when available, so they won't get a fast, steady compass anyway). --[[User:SlashMe|SlashMe]] ([[User talk:SlashMe|talk]]) 15:24, 14 January 2015 (UTC)

It seems to me that the paragraph explaining mass and weight is too complicated and overly long, and the hypothesis that the app is trying to steal this information unrelated to the comic, or rather, wild speculative extrapolations of logic and meaning. Likewise, the sentences on how the accelerometer may be used to guess passwords seems to me to be unfounded in science. The uncertainty principle is the clear main theme of this comic. --[[User:Canned Soul|Canned Soul]] ([[User talk:Canned Soul|talk]]) 16:03, 14 January 2015 (UTC)

Added one word to make it "An example is a weather app which would need your location in order to '''automatically''' find the correct forecast." It's often trivial to manually get forecasts (or other services, like "nearest branch of a shop that has your desired item in stock") for a current location, just so as long as /you/ know where you are... (I don't turn on my GPS unless I'm actually wanting to use it for something, and don't like websites knowing these things just because they ask for them in the background. Go away, Google Location Services... and why does it grey-out the "Don't share information" hotspot when I've ticked the "Don't ask me again" and only lets me continually refuse ''manually''!? Which I do on principle!!) I keep a variety of common home/away locations on permalink in my favourite weather forecast app and know I can easily add another at a moment's notice when I ''want'' to. (And, the beauty is, I don't even need to be there at the time, just perhaps ''planning'' to go!)

Plus, to the "I don't see any humor in applying the uncertainity principle to macroscopic objects." person, above, please pass by your local XKCD offices at the first opportunity in order to hand back your XKCD Membership Card. You're obviously not one of us! ;) [[Special:Contributions/141.101.98.191|141.101.98.191]] 16:28, 14 January 2015 (UTC)

Per the explanation: "Randall suggests the poor accuracy of the compasses in mobile phones (measuring the angular position) is due to the gyroscopes being too good. (If both the gyroscope and the compasses were completely accurate, it would violate the uncertainty principle)."
The compass points in a particular direction but tells you nothing about location or momentum. How would it be involved in any violation of Uncertainty? The gyroscope and GPS I could see, maybe. But the compass? I don't see how it combined with anything could involve Uncertainty. - Equinox [[Special:Contributions/199.27.128.117|199.27.128.117]] 16:46, 14 January 2015 (UTC)
: The Uncertainty Principle extends to other pairs of conjugate variables besides the well-known pair of position and momentum. One of these pairs is orientation and angular momentum. [[Special:Contributions/173.245.52.142|173.245.52.142]] 17:45, 14 January 2015 (UTC)

1473: Location Sharing

2015-01-14T20:31:28Z

ChristGoldman: Edited the sentence, "The tendency to keep their weight secret[...]," for gender perspective and objectivity.

{{comic
| number = 1473
| date = January 14, 2015
| title = Location Sharing
| image = location_sharing.png
| titletext = Our phones must have great angular momentum sensors because the compasses really suck.
}}

==Explanation==
{{incomplete|First draft.}}

In this comic, [[Megan]] is visiting a website on her mobile phone. After loading it, the website {{w|Location-based service|asks for her location}}, which Megan permits the phone to give. The choice between allowing or denying a website or app access to certain information is common among smartphones. The term "location sharing" specifically refers to when a smartphone user shares their location with such an entity. An example is a weather app which would need your location in order to automatically find the correct forecast.

Megan is then asked her {{w|momentum}}, which she denies. The joke is based off of the Heisenberg {{w|uncertainty principle}}, which, in quantum mechanics, states that one cannot accurately know both the location and momentum of any particle simultaneously. However, since Megan is not a microscopic particle, it doesn't make any sense to say the the app is trying to violate Heisenberg's principle.

The ramifications of the uncertainty principle being violated in this context are unknown, but the comic might be alluding to security problems that appear if an untrusted application is given access to momentum data generated by the gyroscope. Access to gyroscope data can be used for reading passwords entered into the on-screen keyboard or even guessing keyboard strokes on a keyboard lying on the same table as the phone.

It could also be an attempt to get [[Megan]] to unwillingly reveal her weight (mass to be more exact), as the mass can be inferred by dividing the momentum by velocity (the velocity in turn can be obtained by observing the change of the location over time). In order to be feasible, the location must be polled at least twice, as at least two location points are necessary to compute the velocity. It is a stereotype in many Western cultures that women tend to keep their weight secret. The stereotype implies that women tend to obsess about controlling (and not revealing) their weight in order to conform to societal and sexual pressure.

The title text refers to the inclusion of {{w|gyroscope}}s in modern cell phones that measure angular momentum, mostly to detect when the phone is tilted, but also used in a few mobile games. Randall suggests the poor accuracy of the compasses in mobile phones (measuring the angular position) is due to the gyroscopes being too good. (If both the gyroscope and the compasses were completely accurate to a subatomic scale, it would violate the uncertainty principle). Modern phones also include varied technologies (such as GPS) to pinpoint the user's location, with varying degrees of accuracy.

The uncertainty principle has previously been referenced in [[824: Guest Week: Bill Amend (FoxTrot)]]. It has also been discussed in relation to the two comics [[1404: Quantum Vacuum Virtual Plasma]] and [[1416: Pixels]].

==Transcript==
:[Megan is holding her phone. Above her is the text she can see on the screen:]
:This website wants to know your location.
:[Two buttons are below this text. The first is white with a black frame and black text. The second (the chosen button) also has a black frame, but inside the frame is a black rectangle with white text. Around the chosen button are small lines indication rays.]
:Deny
:'''Allow'''

:[Megan is holding her phone.]

:[Megan is holding her phone. Above her is again the text she can see on the screen.]
:This website wants to know your momentum.
:[Two buttons are below this text. The first (the chosen button) has a black frame, but inside the frame is a black rectangle with white text. The second is white with a black frame and black text. Around the chosen button are small lines indication rays.]
:'''Deny'''
:Allow

:Megan: Nice try.

{{comic discussion}}
[[Category:Comics featuring Megan]]