Physicist Colin Trafford stages a demonstration with a particle accelerator to a number of people, including Sir Henry Larnstein and Trafford's long-time friend Tom Lewis. The demonstration goes wrong and Trafford, with his same memories, finds himself in a parallel universe with significant differences from our own: John F. Kennedy is Secretary General of a still-existent League of Nations and Leslie Howard did not die in World War II because it never happened.

References:
https://en.wikipedia.org/wiki/Quest_for_Love_(1971_film)