[Physics FAQ] -
Original by Michael Weiss.
The Twin Paradox
This hardy perennial seems to generate endless running threads on the sci.physics.*
hierarchy. This contrasts sharply with the situation among mainstream
physicists/hidebound reactionaries (take your choice), where the "paradox" has been no
more than an entertaining (and educational) exercise since it first saw the light of
It's too much to hope that this FAQ entry will change any minds, except maybe an
"undecided" or two. But perhaps it can reduce the traffic on this topic.
Read the sections as whim and mouse-clicks take you, though you might
want to read the Introduction first.
- Where we introduce our heroes, Earth-bound Terence and star-bound
Stella, and settle on a few things, like terminology. Also, the
acceleration analysis of the twin paradox.
- The Doppler Shift Analysis
- Suppose Stella and Terence each film the other's clock through
a telescope throughout the trip; when does Stella see Terence's clock
- The Spacetime Diagram Analysis
- Where we take an Olympian view, and gaze with the Fates upon
the world lines of Terence and Stella.
- The Equivalence Principle Analysis
- Pseudo-gravitational time dilation, and some matters of terminology.
- The Time Gap Objection
- Is some time simply missing from Terence's life, according to Stella?
- The Distance Dependence
- If Stella travels twice as far, does Terence age twice as fast
during her turnaround? Action at a distance!
- Too Many Analyses: a Meta Objection
- Or, the parable of the broken vase.