Isto é quase certamente O Infinitivo de Go , de John Brunner . Do resumo da trama:
For the first significant test using a live person, a diplomatic agent is Posted to a foreign embassy from the USA. The test is an abject failure: the agent, George Gunther, is unexpectedly armed and also demands a countersign upon arriving at his destination. Since nobody was instructed to provide him such a countersign, Gunther immediately assumes he's been intercepted by the enemy and shoots himself, triggering a destructive failsafe in the package of documents he was carrying. It is assumed that the Posting affected the agent's sanity. Faced with termination of the project, Dr. Justin Williams, the inventor of the technology, arranges to have himself Posted from the same embassy back to his research laboratory.
O entendimento do universo alternativo vem depois:
The problem is this: the Poster links two congruent spaces, but it searches many universes to find the best match. When all factors are accounted for, including a person's state of mind and the state of the machine itself, the best match is more likely to be found in a machine from another universe. This is how a Dr. Landini arrived that is a man descended from baboons but speaking English and coming from a world with almost exactly the same history as the one on which he arrived. Although evolution took a different track on his world, the outcome was almost exactly the same as on the world where he arrived; had it been different, he would have gone to a different universe. The person who first comes to understand this is not a scientist, but a philosopher.