From Greg Egan
Tuart Hill, Western Australia
While I share Phil Bagnall’s gut feeling that time travel is impossible
(Forum, 6 July, p 45) his arguments against wormhole-based time machines are
seriously flawed. According to the models currently being studied by
relativists, no travellers from the future could arrive until the wormhole in
question has been created, so the entire era prior to the invention of wormhole
technology will remain forever out of reach. And in David Deutsch’s
multiple-worlds treatment of time travel, if there are 100 parallel worlds there
would only be 50 travellers—each one kills their “potential” grandfather
in one of the other 50 worlds—cutting the total number of time-travelling
grandsons ever born down to 50 rather than 100, an entirely unparadoxical
outcome
