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/CAPCWU3JyWehP088x2qkxsh9sG2JKRKgy%3DH_wGSRuEiJNtnsthw%40mail.gmail.com.
