Time Travel and portals...

 https://en.wikipedia.org/wiki/The_Time_Machine_(1960_film)#Plot

https://timemachine.fandom.com/wiki/The_Time_Machine_(1960_Film)

https://www.britannica.com/topic/The-Time-Machine-film-1960

https://www.thisisbarry.com/film/most-interesting-mechanics-of-time-travel-in-films

https://theconversation.com/can-we-time-travel-a-theoretical-physicist-provides-some-answers

DD is as much about portals as it is about time travel.

http://www.donniedarko.org.uk/philosphy-of-time-travel , https://iep.utm.edu/timetravel

https://www.goodreads.com/en/book/show/31509348-the-philosophy-of-time-travel

http://ddarko.weebly.com/the-philosophy-of-time-travel.html

The+Source+Code+of+Donnie+Darko, these two movies a decade apart that feature the protagonist shifting into another timeline. 

Everything Wrong With Donnie Darko https://www.youtube.com/watch?v=7kG7UVcvKao 

Although anyone can find various flaws in the movie, the overall premise of the DD story is still fascinating and fantastic. 

https://timetravelnexus.com/popcorn-paradoxes-the-philosophy-of-time-travel  "During many of the visions with Frank when we see images of Donnie’s eyes, we also see computer code scrolling over the imagery.  The most likely explanation for this (in the context of the movie) is that the movie takes place within a simulated reality."

https://borg.com/2011/08/27/on-video-source-code-more-than-meets-the-eye

https://www.thereviewgeek.com/10movies-sourcecode

https://thedigitallabyrinth.blogspot.com/search?q=Time+portals+and+other+things

https://thedigitallabyrinth.blogspot.com/search?q=Time+Travel