Discovering the Paradox of Being Your Own Grandfather in Futurama

[WCOLtd]

In a slightly disturbing episode of futurama, Fry (the main character) goes back in time and through a series of disturbing events discovers he is his own grandfather.

If you think about the situation, you can go in a perpetual loop trying to figure out the causality. He went back in time because he was born and he was born because he went back in time. In other words, he necessitated his own existence.

I thought this was an interesting concept - where the causality is ambiguous.

Is this situation observed in physics?

 

[Pengwuino]

No. It's a cartoon.

 

[pervect]

Obserbed in physics? No. But people do worry about the existence of closed timelike curves in GR, often with a desire to rule them out. But so far nobody's been quite able to rule them out. Which is quite a long ways away from having observed them...

 

[bcrowell]

The science-fictional idea dates back at least as far as a 1958 story by Robert Heinlein: http://en.wikipedia.org/wiki/—All_You_Zombies—

As pervect has noted, closed timelike curves (CTCs) are a subject that has been studied extensively in general relativity:
http://en.wikipedia.org/wiki/Closed_timelike_curve
http://en.wikipedia.org/wiki/Chronology_protection_conjecture

A good popularization: Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time by J. Richard Gott

CTCs are not necessarily paradoxical:
Friedman, Cauchy problem in spacetimes with closed timelike curves, http://authors.library.caltech.edu/3737/
Echeverria, Billiard balls in wormhole spacetimes with closed timelike curves: Classical theory, http://authors.library.caltech.edu/6469/

 

[Bill_K]

There was also a story ca 1956 called "Z", by Charles Fontenay, which avoided closed timelike curves, achieving time-travel via pair creation. A lightning bolt hits a tree, and a man and woman emerge, apparently unharmed. As time passes the man ages normally, but the woman grows progressively younger. Eventually she becomes the same age as her son, at which point mother and son disappear in a second explosion. The punchline is that mother, father and son were all the same person, and the explosions had caused his/her/its timeline to reverse. (For some reason, traveling backwards in time turns you into a woman.)

 

[George Jones]

A good popularization: Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time by J. Richard Gott

Another good popularization:

BadFish, you might be interested in an excellent, non-technical reference on time travel, the second edition (make sure that it's the second edition) of Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction by Paul Nahin. This is a wonderful book that is written for the educated layperson.

https://www.amazon.com/dp/0387985719/?tag=pfamazon01-20.

Physicist (and relativist) Kip Thorne wrote a foreword for the second edition of this book, and here's a quote from this foreword: "It now is not only the most complete documentation of time travel in science fiction; it is also the most thorough review of serious scientific literature on the subject - a review that, remarkably, is scientifically accurate and at the same time largely accessible to a broad audience of nonspecialists."