# 1473: Location Sharing

 Location Sharing Title text: Our phones must have great angular momentum sensors because the compasses really suck.

## Explanation

 This explanation may be incomplete or incorrect: First draft.If you can address this issue, please edit the page! Thanks.

In this comic, Megan is visiting a website on her mobile phone. After loading it, the website asks for her location, which Megan gives. 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 her location with such an entity. An example of which is a weather app which would need your location in order to find the correct forecast.

Megan is then asked her momentum, which she denies. The joke is based off of the Uncertainty Principle, which, in physics, states that one cannot know exactly the location and momentum of an electron. This principle was previously referenced directly in XKCD comic 824, and as a topic for discussion in XKCD comics 1404 and 1416. In the context of the comic, Megan acknowledges the website's attempt to violate the uncertainty principle by saying "nice try".

The title text refers to the inclusion of accelerometers in modern cell phones, mostly to detect when the phone is tilted, but also used in a few mobile games. Modern phones also include varied technologies (such as GPS) to pinpoint the user's location, with varying degrees of accuracy. Randall suggests this poor accuracy is due to the accelerometers being too good. (If both the accelerometers and the location sensors were completely accurate, it would violate the uncertainty principle.)

## Transcript

First Slide: This website wants to know your location Two buttons: "Allow" on left and "Deny" on right Allow is highlighted

Second Slide: No text

Third Slide: This website wants to know your momentum Two buttons: "Allow" on left and "Deny" on right Deny is highlighted

"Nice Try"

# Discussion

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. 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 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. 108.162.254.57 08:53, 14 January 2015 (UTC)
You're such a Bohr. --108.162.216.30 11:54, 18 January 2015 (UTC)
I genuinely cannot believe you made that joke.173.245.50.107 04:35, 28 February 2015 (UTC)

She does not want the website to calculate her mass and therefore her weight. It has nothing to do with the uncertainty principle -- Saints22 (talk) (please sign your comments with ~~~~)

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. --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. 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". --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. --Kynde (talk) 10:33, 14 January 2015 (UTC)
No, the highlighted buttons are definitely meant to be preselected. Megan pushes a button on the second panel, and then the website shows the page where denying the momentum is preselected. 108.162.254.47 (talk) (please sign your comments with ~~~~)
True! Thats exactly how I understand this comic. The website wants to know her location. She denies. Then the website tries to trick her in wanting to be forced not to know her exact momentum - so in turn to be able to know her exact location anyway. 108.162.254.47 (talk) (please sign your comments with ~~~~)
I think you're right. Her thumb is definitely only extended in panel 2, and, going back, it looks like the highlight is supposed to be this sort of window, although I have no idea what it looks like on mobile. Also, the "beat" panel makes more sense with this explanation, since it's actually an action panel instead of suggesting a weird gap between the two requests. It certainly makes more sense than the article asking for her momentum after already having her position, since measuring momentum would decrease their certainty of subatomic Megan's position. And it's definitely about the uncertainty principle, given: 1. This is Randall; he's way more likely to do a comic about a principle of particle physics than one about women not wanting people to know their weight, and 2. The alt text is about the uncertainty principle. 199.27.128.237 05:31, 16 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"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. 173.245.54.204 13:29, 14 January 2015 (UTC)
"Females" is shorter than "women and girls". 108.162.221.201 14:54, 14 January 2015 (UTC)
Yes, some people are determined to be offended. Unfortunate. 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...-- Brettpeirce (talk) 19:57, 14 January 2015 (UTC)
A "woman" is a person; "female" is a sex. "Females" in this context is as rude as calling grown women "girls." 108.162.216.36 03:45, 16 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. 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). --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. --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! ;) 141.101.98.191 16:28, 14 January 2015 (UTC)

My goodness, yes! What a lot of seriousness has found its way into this discussion! How could anyone miss the humo[u]r in the personification of a subatomic particle as a Megan?Taibhse (talk) 04:23, 15 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 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. 173.245.52.142 17:45, 14 January 2015 (UTC)

The way I read this, by knowing her current location AND momentum (ignoring the uncertainty principle thing for the moment) it becomes possible to predict where whe'll be in the future, which would open up all sorts of ... 'interesting' marketing opportunities for the app maker. Megan doesn't mind the app knowing where she *is*, but doesn't want it to know where she's *going*, and so rejects the second seemingly innocent question. Maybe? 108.162.249.205 (talk) (please sign your comments with ~~~~)

I agree. It is not about the uncertainty principle, but about predicting future locations with the momentum, or future orientations with the angular speed from the gyroscope. It would NOT violate Heisenberg to measure two (not conjugating) physical parameters with bad accuracy (only the other way round). The argument goes: The phone can measure the orientation quite well despite of the bad compass. So its only option is using the gyroscope and integrating its angular speeds over time. The initial value can come from the GPS, the compass (offset error, if it is really so bad) or from an initialization in the factory (then the gyroscope has to function exceptionally well, but this could be the joke). Sebastian --108.162.254.56 14:15, 15 January 2015 (UTC)

+1 for this being about the uncertainty principle. Frankly, I'm surprised there's any controversy (many of the alternative explanations offered seem very unlikely, quite apart from anything else): if there's any ambiguity in the cartoon itself, surely the title text (by riffing on another pair of conjugate variables) clears that up? 141.101.98.169 10:47, 16 January 2015 (UTC)

Paragraph 4 is kind of a stretch. I highly doubt that was Randall's intention, or that it even crossed his mind.
-Sensorfire (talk) 02:19, 15 August 2018 (UTC)

It might be as well a reference to classical mechanics and its determinism. If one knew both Megan's location and momentum he would be able to get to know all her future (i.e. her trajectory in state space) appyling the laws of mechanics so she denies to keep herself safe. 172.69.194.22 21:26, 6 November 2019 (UTC)