So far this week we have Em taking a round-trip to planet Noether at half the speed of light. Upon her return she discovers that, while she’s aged 23.8 years, Al (who stayed home on Earth babysitting Theories) has aged 27. It took her well over twenty years to do it, but Em effectively traveled 3.2 years into the future.
Last time we saw that — so long as Em is in constant motion — there is symmetry between Al and Em with regard to who is moving and who isn’t. Both can claim the other is (or they are). Both views are valid. Until Em stops. Or starts, for that matter.
Today we look at Em’s “time shadow” — it’s a key to the puzzle!
This is an eXtra post in the Special Relativity series. It explores a sub-topic in detail that may not be of interest to most readers — either the detail or the sub-topic itself. The purpose of the post is to pre-answer, or serve as a reference for, obvious questions that the technically astute might ask (often questions I once asked).
This article is about the acceleration and deceleration that seems required in the Twins Paradox illustration. Some even refuse to accept the illustration as valid under the belief that changing speed significantly alters the picture.
Here I try to show how we can completely ignore it.