Rewritten, or Why Time Travel With the Intent to Change is Impossible

[AlmostEternity]

With many time travel books or movies, I find that the protagonist is either traveling back in time to change something or trying to stop a change to time. But in real life, if time travel ever becomes real, either situation would be impossible to cause simply because it would create a paradox if it were fixed, much like if you were to prevent your own birth by killing a relative.

Simply put, a rule that would seriously inhibit time travel in a way that many people dream is that you can not do something that eliminates the entire reason you left your present in the first place. Because then you would never had a reason to leave.

Therefore, you can't do these things:

• Travel back in time with the intent to murder a certain figure; for example, Hitler.
• Go back in time to save a family member from being killed. In consequence, all those books where the inventor of time travel creates the time machine with the intent to revive a family member and succeeding in any way would be impossible. This would also prevent someone from going back in time and saving President Lincoln from being assassinated. HOWEVER, this DOES NOT prevent time travel from being created due to such a motive. It's just that those reasons would remain unrealized.
• You can't go back in time to stop an event from occurring. So no saving every person on the Titanic or preventing it from sinking.
• You can't go and stop someone from doing something.

Yet this is somewhat of a slippery slope. The line between what can and can't be done is a thin one. It would technically still be possible to do things by accident. You could go back in time and accidentally run over Albert Einstein with a horse and buggy, and be none the wiser(although I doubt few would mistake Albert Einstein upon first sight). But who knows what the consequences would be.
This all somewhat ignores the possibility of alternate dimensions, which I might get back to later when I feel like typing out an essay in these forums.

I don't know if someone else has thought or come up with this, but I find it pretty interesting.

 

[Cthulhu.Science]

The introduction in this book covers that problem.

How to Invent Everything: A Survival Guide for the Stranded Time Traveler​

I'm going from memory but as I recall the introduction includes some very important information about the time machine that you rent from the time machine rental company that supposedly wrote the book.

When you time travel with their machine you create a new Universe that includes an Earth (where you arrive) that is exactly as Earth was at the time selected. Thus each trip creates a new universe. They also point out that they have on their staff a highly skilled team of ethicists who have done the deep analysis and have determined that creating all of these new universes is perfectly ethical.

​

 

[Yozh]

Time travel stories usually build some internal logical "rules" into the narrative, but any of these fail under deep analysis.

At a most basic level, such tales nearly universally posits some method for a human being to "travel" through time while still retaining the mental and physical state they enjoyed at the time of outset. That is, the typical "time travel" story would involve the time traveller today (Let's signify then by TimeTravellerV15.01.2025) travelling back to make some observation or change in the past, let's say just one week ago. In the typical story, TimeTravellerV15.01.2025 is maneuvering around the time and space of January 8, 2025, and maybe trying to avoid running into their contemporary self (TimeTravellerV.08.01.2025) or else they are back in the body of TimeTravellerV.08.01.2025, but with the knowledge and consciousness of TimeTravellerV15.01.2025. But how is it that TimeTravellerV.15.01.2025 exists at all on January 8, 2025? Would they not just become TimeTravellerV08.01.2025 upon arrival at January 8, 2025? Positing otherwise is like expecting a person could travel through space unaffected by local conditions-- that I could step outside my door in winter and not feel cold, or jump in a lake and not get wet.

But does any of that matter in a given story? The point of most time travel stories is philosophical exploration of alternative histories or hypothetical futures, relying on some willing suspension of disbelief by the reader.

 

[Astro Pen]

The past is locked in because the 'now' is a point of quantum resolutions. The collapse of quantum probability. The past has zero alternative probabilities. The future, on the other hand is currently open, which is why it "feels" like we can control things. Of course we can't, there are just a quadrillion unpredictable quantum dice rolls every microsecond.
(I realise that this doesn't make for exciting SF )

 

[Christine Wheelwright]

Original poster suggests you can't change major things (like killing Hitler). But in fact, if you went back and moved even a blade of grass you would significantly change the future. This is the well known 'butterfly effect' where the flapping of the wings of a butterfly can cause a storm in the other hemisphere.
I always think the old 'game of life' is interesting as it shows that - with the smallest difference in starting conditions - a system can develop completely differently after just a few iterations.

Play John Conway’s Game of Life

Play the Game of Life online, a single player game invented in 1970 by Cambridge mathematician John Conway.

playgameoflife.com

 

[Harpo]

In fiction anything is possible. The story that first got me interested in time travel involved Hitler being the time traveller. He goes back to meet Napoleon, Napoleon realises how bad Hitler is, and abandons him in the distant past.
Entertaining nonsense, but so are Dr Who, Star Wars, Lord Of The Rings, etc etc etc.

 

[Astro Pen]

Original poster suggests you can't change major things (like killing Hitler). But in fact, if you went back and moved even a blade of grass you would significantly change the future. This is the well known 'butterfly effect' where the flapping of the wings of a butterfly can cause a storm in the other hemisphere.
I always think the old 'game of life' is interesting as it shows that - with the smallest difference in starting conditions - a system can develop completely differently after just a few iterations.

Play John Conway’s Game of Life

Play the Game of Life online, a single player game invented in 1970 by Cambridge mathematician John Conway.

playgameoflife.com

I've always been sceptical of that claim. Butterflies take off in their millions every day without starting storms.
That's the trouble with 'pop science'.

 

[Cthulhu.Science]

I've always been sceptical of that claim. Butterflies take off in their millions every day without starting storms.
That's the trouble with 'pop science'.

I understand the sentiment, but do we know that for certain???

Maybe all storms are the results of flying butterflies.

Fun with fiction.

 

[Cthulhu.Science]

Original poster suggests you can't change major things (like killing Hitler). But in fact, if you went back and moved even a blade of grass you would significantly change the future. This is the well known 'butterfly effect' where the flapping of the wings of a butterfly can cause a storm in the other hemisphere.
I always think the old 'game of life' is interesting as it shows that - with the smallest difference in starting conditions - a system can develop completely differently after just a few iterations.

Play John Conway’s Game of Life

Play the Game of Life online, a single player game invented in 1970 by Cambridge mathematician John Conway.

playgameoflife.com

Isn't all alt-history fiction just time traveler changing something -- just without the time traveler?
The author is the time traveler...

Wait. Doesn't that make all Fiction essentially time-traveler fiction?

 

[Christine Wheelwright]

I've always been sceptical of that claim. Butterflies take off in their millions every day without starting storms.
That's the trouble with 'pop science'.

Oh, the butterfly effect is a very real thing, solidly grounded in physics. The smallest effects completely change the future (like missing a train in the movie). Not much effect in the following minutes but more and more as time goes by. Two people don't meet due to the slightest fluke, the slightest change in the starting conditions. They don't get married and have kids. Their kids never exist to have kids. 500 years later, over a million people don't exist (who would otherwise have done so). A million different people exist. And then there is the effect all those people have on the lives of others. The world is a different place, all down to that ridiculous tiny change in the starting conditions. For sure it works on the scale of a butterfly flapping its wings. The system is too complex to model (there could be a trillion insects flapping their wings), but remove one of them and a storm destined to occur in 50 years time may not occur.

 

[Astro Pen]

Ok, so would we reduce storms globally by eradicating butterflies?

 

[Harpo]

Ok, so would we reduce storms globally by eradicating butterflies?

No, because the same applies to anything else that causes any change in any wind. Such as me going for a walk, or any car driver slowing down or speeding up.

 

[Astro Pen]

No, because the same applies to anything else that causes any change in any wind. Such as me going for a walk, or any car driver slowing down or speeding up.

Exactly.

 

[Elckerlyc]

When you travel to the past, you've already been there. Because it happened in the past, right? Looking at it from your starting-point - the Now - as most stories do, is therefor misleading and results in weird plots.
I am a Novikov proponent.

From Wikipedia:
The Novikov self-consistency principle, named after Igor Dmitrievich Novikov, states that any actions taken by a time traveller or by an object that travels back in time were part of history all along, and therefore it is impossible for the time traveller to "change" history in any way.

 

[Harpo]

It’s not impossible at all, it just requires a new perspective.

Time traveller: “I went back in time and saved Keanu Reeves’ life.”
Traveller’s neighbour: “Keanu Reeves didn’t die, he’s alive”
Time traveller: “you’re welcome”

 

[Cthulhu.Science]

Ok, so would we reduce storms globally by eradicating butterflies?

Maybe butterflies and bees flying around actually reduces the number of storms.

There is a correlation between a reduction in the number of bees and butterflies and an increase in storms.

Correlation ALWAYS equals causation, right?

 

[Venusian Broon]

Firstly we don't have a clue about the nature of time. There are many theories on what Time is. Even if it really exists (in the sense that it is an objective thing). It may just be an artefact of our minds.

Secondly. Actually...some theories of time have solutions for time-travel that are logically consistent and do not produce paradoxes. Whether or not they are practical in real life is another question. But as SF writers we don't really care too much about it being practical for our stories.

Thirdly I am having fun in my current WiP with one such solution. I think it all works out consistently However, it's been taking a long time for me to get it out. Maybe future me could just post the completed manuscript...

 

[Elckerlyc]

It’s not impossible at all, it just requires a new perspective.

Time traveller: “I went back in time and saved Keanu Reeves’ life.”
Traveller’s neighbour: “Keanu Reeves didn’t die, he’s alive”
Time traveller: “you’re welcome”

But did he change history? No, he just happened to be there and then to save Keanu Reeves life. Keanu never died. He might have been if the Time traveller had not traveled back in time. His travels mattered, but didn't change anything.

 

[paranoid marvin]

Time is an invention by humans to describe the period between things happening. Once something has happened, it can't unhappen, no matter how much we would sometimes like it to.

Are there ways of viewing the past? Yes there are, and not just recording devices.Theoretically, you could stand on a planet 1,000 light years away and see things that happened 1,000 years ago. So if you developed a spacecraft that travelled faster than light you , you could travel to a place x light years from Earth, whip out your telescope and see the Battle of Hastings, the Sack of Rome, the building of the pyramids.

You couldn't interact with it in any way, but you could (theoretically) answer many of history's mysteries.

 

[paranoid marvin]

But did he change history? No, he just happened to be there and then to save Keanu Reeves life. Keanu never died. He might have been if the Time traveller had not traveled back in time. His travels mattered, but didn't change anything.

It's a bit like that episode of Quantum Leap, when Sam travels back to JFK's assassination. He doesn't prevent Kennedy's death, and bemoans the fact that this time he failed. Then he is told no, your mission was to save Jackie. So obviously in Sam's original timeline they both died, now only the President had.