In 1995, with their forthcoming 15th anniversary issue in mind, The Face magazine approached Stephen Hawking and asked him for a time travel formula. They soon received the following response by fax.
(Source: The Face's former editors, Richard Benson & Johnny Davis; Image: Stephen Hawking, via.)
UNIVERSITY OF CAMBRIDGE
Department of Applied Mathematics and Theoretical Physics
Silver Street, Cambridge, England CB3 9EW
From: Sue Masey, Personal Assistant to Professor S W Hawking
To: Johnny Davis
Number of pages: 1 (Including this one)
Date 6 April 1995
Thank you for your recent fax. I do not have any equations for time travel. If I had, I would win the National Lottery every week.
S W Hawking