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gwern comments on Open thread, July 21-27, 2014 - Less Wrong
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Comments (160)
(It's A, right?)
To some extent, 'folk physics' has already been studied a fair bit. For example, see the links at the end of http://lesswrong.com/lw/khd/confound_it_correlation_is_usually_not_causation/ about a quiz designed to measure how well people understand Newtonian mechanics and to what extent they succumb to incorrect folk physics beliefs.
If you do it in the Portal 2 engine (Portal 1 doesn't support moving portals) it seems to be A but with a slight push (google for videos).
The point is, I don't think the topology of the portals even allows for things like "conservation of momentum" to make sense (anyone can correct me here).
That's what I immediately thought, but on further thought I think it might, if you assume portals move things through some kind of force rather than by folding space itself, though something yadda yadda Dirac delta function yadda yadda, but we can assume the portals are very much heavier than the object so... Well, I'd have to work it out.
Yes, I think it can work, if when the object passes the portals the portals gets displaced by -m/M times their distance, where m is the mass of the object and M is the combined mass of the portals. (By “work” I mean it doesn't need there to be a privileged frame of reference for it to be described.)
(I'm assuming Galilean relativity; I'm not sure it can be made to work in special relativity as well.)
The link to Halloun & Hestenes 1985 no longer seems to be valid, although the 1992 paper still seems to be good.
Is this the same paper?
That was fast. But no, that seems to be an earlier paper, I meant http://generative.edb.utexas.edu/classes/knl2011fall/Halloun_Hestenes_FCI.pdf
Yes, assuming portals conserve momentum (which I believe they do in the Portal canon).
Speedy thing goes in, speedy thing comes out :-D