The Merchant and the Alchemist's Gate
Ted Chiang
 The story follows Fuwaad ibn Abbas, a fabric merchant in the ancient city of Baghdad. It begins when he is searching for a gift to give a business associate and happens to discover a new shop in the marketplace. The shop owner, who makes and sells a variety of very interesting items, invites Fuwaad into the back workshop to see a mysterious black stone arch which serves as a gateway into the future, which the shop owner has made by the use of alchemy. Fuwaad is intrigued, and the shop owner tells him three stories of others who have traveled through the gate to meet and have conversation with their future selves. When Fuwaad learns that the shop keeper has another gate in Cairo that will allow people to travel even into the past, he makes the journey there to try to rectify a mistake he made twenty years earlier.