AFAICT, the approaching rod is shortened. Possibly I don't understand your argument, but it directly contradicts my understanding of SR. AG
On Saturday, September 7, 2024 at 7:46:16 PM UTC-6 Jesse Mazer wrote: > Again, are you talking about visual contraction, or contraction in terms > of simultaneous measurements of both ends in your reference frame? If the > former the approaching rod appears elongated rather than contracted (it > says so on the Terrell rotation page), if the latter then the rod is > contracted by the gamma factor regardless of whether it's moving towards > you or away from you (assuming that either way its velocity vector is > parallel to the line between the two ends). > > On Sat, Sep 7, 2024 at 6:41 PM Alan Grayson <[email protected]> wrote: > >> It's the *approaching *rod that is contracted, say the distance to the >> Andromeda galaxy as the observer is approaching it. But what if the >> observer is receding from Andromeda? How is the problem modeled in this >> situation, where the observer doesn't see the ends of some rod? Your second >> link might have the solution. AG >> >> On Saturday, September 7, 2024 at 4:18:24 PM UTC-6 Jesse Mazer wrote: >> >>> Answer depends on whether you are talking about how the rod looks >>> visually to them (in which case a receding rod appears contracted but an >>> approaching rod appears elongated, see >>> https://en.wikipedia.org/wiki/Terrell_rotation ) or if you are talking >>> about how they assign coordinates to the rod in their own rest frame, using >>> a system of rulers and clocks which are at rest and synchronized relative >>> to themselves (like in the illustration at >>> https://faraday.physics.utoronto.ca/GeneralInterest/Harrison/SpecRel/SpecRel.html#Exploring >>> >>> with synchronization based on the procedure described at >>> https://en.wikipedia.org/wiki/Einstein_synchronisation ), which was >>> what Einstein was concerned with in his original SR paper. In terms of the >>> latter, if they measure the back end and front end of the moving rod >>> simultaneously using their own clocks and rulers, they will always find the >>> distance to be shrunk by the gamma factor regardless of whether it's moving >>> towards or away from them. >>> >>> On Sat, Sep 7, 2024 at 3:25 AM Alan Grayson <[email protected]> wrote: >>> >>>> For an observer moving toward a rod of some fixed length in a rest >>>> frame, the rod shrinks, but what happens when the observer is moving >>>> *away* from the rod, given that the gamma factor remains unchanged? >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Everything List" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/everything-list/02981fe3-8c92-41e4-aa3c-98b57be89e54n%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/everything-list/02981fe3-8c92-41e4-aa3c-98b57be89e54n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "Everything List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/everything-list/9b485ffe-d1d6-4338-8775-5db979608277n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/everything-list/9b485ffe-d1d6-4338-8775-5db979608277n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/42f90ed5-15e9-43ba-a9e4-151d8b2f3ad9n%40googlegroups.com.
