Most sci-fi stories involving time travel involve a mechanism that's incredibly rare and/or difficult to operate.

What if complete plans for a working time machine, including its power source, were published anonymously on the web, in a decentralized fashion? (Impossible to identify who published it, or from where, and thus making it impossible to go back and prevent the publication.) What if anybody could build their own, using commonly available parts and tools? 

 One could go back in time and forbid decentralization? Wait… 

 just orbit a large enough mass. time dilation is the most realistic form of time travel