Information paradoxes

Woody Allen

As I have mentioned before, time travel, if it were possible, would cause many paradoxes. In a previous post I mentioned the paradox of unsourced information, which can be summarized thus:

A time traveler who lives in time 3 knows that a person A said or did something at time 2, prior to time 3. 

The traveler goes back from time 3 to time 1, prior to time 2, where he meets A. 

While they are together, the traveler suggests person A the idea of ​​doing or saying what he knows that person will do or say in the future, which has not yet taken place. 

Whose idea was it originally? Not the traveler’s, because he learned it from the history of person A at time 3. Not from person A, because the traveler suggested the idea to person A at time 1. 

The information in question has come out of nowhere, without anyone having thought it out.

The following diagram explains it.

Woody Allen, who is fascinated by time travel, made use of this paradox in his film Midnight in Paris (2011), with which he won the Oscar for best screenwriter (he was also nominated as director). He did it twice. These are the two cases of unsourced information appearing in that film:

Mark Twain

•         The protagonist, Gil Pender, who lives in the year 2010, travels back in time (we are not explained how or why) to Paris in the 1920s. There he meets writers, artists and bullfighters of the time, such as Scott Fitzgerald and his wife Zelda, Ernest Hemingway, Gertrude Stein, Cole Porter, Picasso, Dalí, Luis Buñuel, or Belmonte. At one point, Pender says this to Hemingway:

All modern American literature comes from a book by Mark Twain called Huckleberry Finn.

Pender, who, as he says at another point in the film, has read everything Hemingway wrote, knows that Hemingway used this phrase in his travel book The Green Hills of Africa (1935). By suggesting it to Hemingway, Pender is causing a paradox of unsourced information. Who should be considered the author of that phrase? Hemingway, who wrote it in a book after it was suggested by Pender? Or Pender, who read it in a book written by Hemingway?

•         The second case is more obvious, very easy to see. At another point in the film, Pender suggests to Luis Buñuel the plot of what will be one of his most famous films: The Exterminating Angel. Buñuel doesn’t understand, but Pender tells him: Don't worry, someday this will help you. Again, we have a situation of unsourced information. Who invented the plot of that movie? Buñuel, who made the film in 1962, remembering the idea Pender had offered him? Or Pender, who learned about the plot by watching Buñuel’s film?

The first time I saw Allen’s film I only detected the second case. Now, when I’ve watched it again, I have also detected the first. It turns out that I recently read Hemingway's book on Africa, which I had not read before. Reading it prompted me to rewatch the film, where I knew Hemingway appeared. And this time I did see the paradox of unsourced information, because I had recently read Hemingway’s quote.

Albert Einstein

In addition to time travel, relativity theory also gives rise to information-related paradoxes. The problem would arise if it were possible to send information faster than the speed of light. I described the paradox in another post.

These paradoxes, if they would happen, could have destructive consequences for the universe. This leads me to make the following statements:

1. Time travel is impossible.
2. Traveling or sending information faster than the speed of light is impossible.

Science fiction is one thing, physical science is another. Physicists should stop wasting their time trying to imagine how what is impossible could be possible.

The same post in Spanish

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Manuel Alfonseca