Whatever else, if we went back and killed Hitler when he was a baby, we might all still be enjoying the aesthetic design of the swastika, and Hipsters the world over might all be sporting toothbrush mustaches.
I find the many world theory absolutely depressing. It removes any hint of free will (I don’t believe in free will, but I believe that I’m the physical process that determines my actions) and even the hope of randomness, since every single thing we can do, we will do, every single thing that can happen to us, will happen to us, every single possible future will take place. I will thrown myself out of the window in five minutes, I will also drink a full glass of vinegar and sing the Orfeo of Monteverdi. China will launch a missile on Paris and a stranger will knock at my door to offer me a suitcase full of € 500 bills.
On top of it, the idea sometimes advanced that in a many world…multiverse… we will live forever makes complete sense to me. Which is not exactly an uplifting concept, because it doesn’t guarantee a healthy and pleasant life, at the contrary (while you’re dying from cancer, some freak event keeps you alive, but still on the verge of death is more or less how it would work for the overwhelming majority of future “you”), and you’re going to still be around during the umpteenth billions of years during which the universe will slowly get dark and “dies”. The only positive point is that the vast majority of “me” will be unconscious most of the time but…some won’t :eek:
this reminds me of a what if that was in a scholastic history magazine
it was “what if the great depression never happened” and it was postulated that tech wise wed be in the mid 80s germany and eastern Europe thewould be equilivent of todays japan and china thered be no Nazis because things would be outsourced to them and every one would have jobs and money (hitler would be the artist he wanted to be and considered “eccentric”)
ww2 would be a few atomic bombs lobbed to the ussr and be over in mere weeks
but since thered be none of the infrastructure building the depression and ww2 spawned wed be at the same spot we were in the teens and 20s ……and in a permanent semi recession…
I really wanted that Urban Seamripper job. 
I personally hate the mutil-verse theory. Larry Niven put it best (from memory): Remember that decision you had to make that was really important? How hard you agonized over it? Well, an infinite number of you decided the exact opposite. And an infinite number of you still haven’t decided!
If every decision choice goes both ways, there’s no point to anything. But actions DO have consequences. As messed up as our universe may be, realize there would be an infinite number where everyone is a violent criminal.
I’m of the opinion that anything other than extreme time travel interventions will basically regress to the mean. If you butterfly away Einstein, then someone else comes up with relativity. If our universe is the middle of the bell curve, the new universe won’t be exactly the same, but it will likely not be standard deviations away.
I think Einstein might not be the best example. Relativity was not like many other independent discoveries or inventions. Somebody might have come up with relativity but it could have taken years–and then maybe the atomic bomb would not have been available for WWII.
Someone else would have come up with Special Relativity, at most a couple of years after Einstein did. General Relativity, however, would probably have taken decades.
I think people confuse the general and the specific.
Killing Hitler might still lead to a reality where WWII happened, nuclear weapons were invented, General relativity was theorized, the cold war happened, and some buffoon was elected President in 2016.
But everyone will be different. Different people will have lived and died. Time travel to 1920 kill Hitler and return and it is near 100% that no one will ever have heard of you. Your parents will have never met. Your office and job might be there, but no one you know will be working there.
I agree generally with JAQ, but I would add that although technology might be similar, every movie, song, novel, and artwork would be different. And that would feel like a very different society. I think over time, that would cause the cultural differences to pile up more and more.
Damnit, someone find that person and stop them. But why was the butterfly hunting the dinosaur? Were butterflies that ferocious in the Cretaceous that they hunted down and killed dinos?
That last is probably reason enough not to prevent WWII. Sorry Jews, we’re not undoing the Holocaust this year.
Rereading your OP, I think you are right that time travel would cause more people to be born to different people. I think I was responding to the general case of butterfly effect causing amplified changes as time goes on whereas I think the changes of the butterfly effect will tend to converge back to normal as time goes on. To be fair, I think a few others were responding in the same manner.
If this is aimed at me, earlier posts addressed the general case, including your own about how we might not have nuclear weapons and have jobs like mystellogist. I do not feel it was off topic.
Not directly at you, sorry. I just wanted to clarify that if time tracks back to what is “normal”, with all the major events happening more or less the same, all the people will still be different. Like, we’d still have a buffoon narcissistic President, but it wouldn’t be trump.
Timeline for who?
My problem with “time travel” speculation is that it never really answers the question that if one can visit any point on the timeline as if they were traveling to another city or country, what makes “right now” any more or less significant than any other point in time?
To put it another way, why would the timeline restart for everyone in 2018 just because some traveler went back to 1942?
In which case we would know about time travel, but we don’t, so it isn’t.
If I may attempt this:
Assume a deterministic universe (free will is possible. Closed time loops (I travel in time, kill my grandfather but unknowingly sleep with my grandmother and fathering my own dad, then when I return nothing has actually changed except my knowledge is increased about my own origin).
The second a time traveler steps into the past, that past is now changed from what it was. Before time travel existed, what is known as the original timeline progressed as we all remember it here and now. But I invent a time machine and go back to 1942. By doing anything at all, I have changed the original timeline. Even if the affect was minuscule I have made a difference. Average people may not notice if I spit at the South Pole and left, but the Universe knows. And it has an effect.
For the duration of my trip, the universe had more mass. Technically, it had duplicate mass. All the mass in me and my time machine already existed in the universe, and was already somewhere there in 1942. As I breathe in and out, and slough off skin cells, and dust falls on me, some atoms get left behind, and some atoms come back to the future with me.
These atoms that weren’t there before, and those atoms that should have been there, will interact with other atoms in tiny ways, but tiny changes add up. This is the butterfly effect. The CO2 I breathe out bumps some air which causes even bigger changes until whammo giant lizards roam 2018 and donuts fall from the sky like rain. More or less.
Now, to your question: “why would the timeline restart for everyone in 2018 just because some traveler went back to 1942?” The answer is, the timeline didn’t restart in 2018, the timeline restarted the instant my time machine arrived. Everything that was in the original timeline between 1942 and the present all of a sudden “never happened”. It’s gone, or more precisely, it never was there to begin with. The universe now “runs” along a different path. That path can be very similar, even indistinguishable to a hypothetical observer “outside of time”, but it IS different. And even worse, it can never be recreated! It is gone forever. The new timeline has replaced it.
And it doesn’t matter if in the new timeline I never get born, or invent time travel. After returning to 2018, I still exist. But I have no connection to the new timeline. I was not born in it. None of the atoms in my body or time machine came from it. Even if the new timeline is close enough to the original that my parents met, fell in love, married, had a kid with my same name who invented a time machine, he’s not me!
This is the crux of the problem of changing the past. You also change everything, from that point until the end of the universe! That’s a lot of power.
Familiar pop culture examples in the next post.
Back to the Future (original).
When Doc Brown sends Marty back, starting from when he runs over old man Peabody’s pine trees and culminating when he leaves as the lightning strikes the clocktower, everything in the future that he goes back to is different. He has no connection to that universe at all!
Note: the Marty we know has loser parents and no car. When he returns his parents are hip and cool and successful, and he has a new truck. Despite him apparently being indistinguishable from new Marty, he isn’t new Marty. And these are not his parents. Someday, someone’s going to notice, because he won’t know crucial details from the changed universe. Original Marty is lucky his parents didn’t move to a new house, because he’d be literally lost. Marty is from outside the universe of the end of the movie.
Not only that, you should ask yourself, what happened to new Marty? Marty who grew up with new parents, which a cool girlfriend and a new truck, is…gone! Where did he go?
Let’s say that he was a better driver (he has a truck and all) and simply goes back to 1955, looks around and comes back. He is the rightful heir, as it were, to the life original Marty is usurping. And he’s going to want it back. But, why hasn’t he returned? More on that in a bit.
Look at the movie closely - when Marty is in Courthouse Square in the beginning of the movie and gets the “Save the Clocktower!” flyer, you can see that the ledge under the clock is not broken. When Marty returns, the ledge is clearly broken. He is in the new timeline.
When Doc is shot by the Libyans (at Twin Pines Mall), he is quite clearly not wearing a bullet proof vest. When Marty returns to Lone Pine Mall, Doc is wearing the vest. This is the new timeline.
So Marty traveling to 1955 has completely “poofed” his entire history out of existence, and replaced it with the new, mostly-indistinguishable but still different, timeline of the end of the movie. It is gone, and cannot be recovered.
But what of new Marty?
He traveled to the 1955 that he grew up from. The one where his parents were manipulated into eventually marrying by the influence of the stranger “Calvin Klein”, who showed up for a week and then disappeared, never to be heard from again. During all of new Marty’s childhood, the clocktower ledge was broken.
If new Marty had driven out to the location of his house, he would have found a Delorean under some bushes, which would have been quite perplexing, to say the least. Had he gone to school and checked out his parents, there is a great chance he would have met original Marty, aka Calvin.
But did he? Who knows, because his story ends. Maybe new Doc’s time calculations were not as good (he cut corners, because he already knew time travel worked, so he never double checked the math, let’s say), and he went…no where. It would explain one important thing.
And that is, why didn’t new Marty also create a new timeline? His mere presence in 1955 should have “never happened” his own timeline and replaced it with a new one. And original marty’s timeline, and the timeline we see at the end of the movie, both would have been “never happened” away and replaced with the new timeline created by new Marty in 1955. That is, if he made it.
Sad to say, I think new Marty died outside of time. Or accidentally got sent to the year 11995555, where his impact on the timeline would only go forward from that point. And with no plutonium, he is doomed to live out the rest of his (now short) life in the ruined wasteland that Earth had become.
We see “new” Marty jump back to 1955 in the parking lot of Lone Pines Mall.
Yes, but where did he go? And more importantly, why didn’t he come back?