# Talk:1473: Location Sharing

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)

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)

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)

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)

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)