A wristwatch worn
by a particle of light
would not tick a-tall.
(-- after Brian Greene; slightly modified, to please the Muse)
Dr. Greene delivers himself of this epigram, in the course of explaining that we
each of us, all of us,
even Achilles and the tortoise,
move equally at the speed of light.
To be sure, in a Pickwickian sense (dividing our motion between space and time).