Spoilers for a 22 year old show and 25 year old movie.

'How many loops could a time loop loop if a time loop could loop time?'

As FGP has reminded me, the main problem with time travel is causality. During her recent Friday Physics invitational, I asked about the ending of Back To The Future 2. Doc travels 80 years into the past and moments later, Marty receives a letter from him. This is fascinating. Though mere moments pass, the letter has existed at Western Union for the entire time, and is indeed, 80 years old!

Advertisement

In ST:TNG-Times Arrow, the away team arrives in the mid 1800's from the 24th century. This is important because although the team does indeed get back home, we know the intervening time does exist and does not "catch up" to the present instantaneously.

Underneath a San Francisco cavern, a surprising discovery is made. Along with glasses, a revolver and a gold watch lay a robotic head. Upon study, it is determined the head is 500 years old and is indeed that of Lt. Commander Data. Further analysis determines fossil evidence on the head could only have come from one location, Devidea II. At the planet, during the away mission to study a temporal disturbance, the team is transported to San Francisco in the mid 1800's. During a scuffle with a Devidean underneath a San Francisco cavern, Data grabs his 'walking cane' and the energy within unleashes at once and Data's head is on the floor. The team returns home with Data's body and attaches the 500 year old head found earlier. [First loop.]

However, we know the intervening time exists.

Underneath a San Francisco cavern, a surprising discovery is made. Along with glasses, a revolver and a gold watch lay a robotic head. Upon study, it is determined the head is 1000 years old and is indeed that of Lt. Commander Data. Further analysis determines fossil evidence on the head could only have come from one location, Devidea II. At the planet, during the away mission to study a temporal disturbance, the team is transported to San Francisco in the mid 1800's. During a scuffle with a Devidean underneath a San Francisco cavern, Data grabs his 'walking cane' and the energy within unleashes at once and Data's head is on the floor. The team returns home with Data's body and attaches the 1000 year old head found earlier. [Second loop.]

Advertisement

Underneath a San Francisco cavern, a surprising discovery is made. Along with glasses, a revolver and a gold watch lay a robotic head. Upon study, it is determined the head is 1500 years old and is indeed that of Lt. Commander Data. Further analysis determines fossil evidence on the head could only have come from one location, Devidea II. At the planet, during the away mission to study a temporal disturbance, the team is transported to San Francisco in the mid 1800's. During a scuffle with a Devidean underneath a San Francisco cavern, Data grabs his 'walking cane' and the energy within unleashes at once and Data's head is on the floor. The team returns home with Data's body and attaches the 1500 year old head found earlier. [Third loop.]

And so on and so on until finally…

Underneath a San Francisco cavern, a surprising discovery is made. Along with glasses, a revolver and a gold watch lay a Bitanium Oxide compound, roughly the shape of a human head. Upon study, it is carbon dated to be over ten thousand years old. Further analysis is indeterminate.

Lt. Commander Data fades from existence and no one on The Enterprise remembers him. [Last Loop]