Lemur 866*, that explains the issue of a return trip, you’d have to go back in time after going forward to meet yourself in the future, and you’d have to remember that you did it in the future. That’s still not what I’m considering.
First, is traveling to another universe a time travel issue at all? In another universe you can’t meet your past, current, or future self in another universe, just somebody very much like you or even identical to you. We all want to go back in time and kill baby Hitler but I’d prefer to do it in this universe. I’ll be happy to do it for some other universe, but I don’t know how to tell if that’s even time travel. In some other universe baby Hitler might be born today, whatever today means across universes.
So let’s look at time travel in our own universe, whether or not I return, whether or not I meet myself, if I jump to 9/5/2018 right now and write down tomorrow’s Mega millions winning numbers they should be the same numbers you will see winning tomorrow and in the note I left you. How could my time travel not fix in stone the future for you if we stay within the same universe?
That’s the problem with alternate universe theories of time travel.
You don’t really make a machine that transports you to another universe. There just is another universe in which you spontaneously appear. This will happen with or without your time machine.
All your time machine is, in this case, is a few dials and nobs that aren’t hooked up to anything, along with a disintegration ray that kills you.
But you didn’t go into my future and then write down the answer.
If I go to Tau Ceti and back and it takes 22 years, and when I get back I notice that the Cubs win the World Series in 2040, and write that fact down, have I discovered that the future is fixed?
Maybe the future is fixed, maybe it isn’t. But if we rule out time travel into the past, we can all agree that the past is fixed, right? Ronald Reagan became president in 1980. He still became president in 1980 when 1984 rolled around. He still became president in 1980 when 2008 rolled around. And he still became president in 1980 when I woke up this morning September 4th, 2018. And he will still have became president in 1980 after my trip to Tau Ceti and back.
Now, was Reagan going to become president in 1980 back in 1958? Beats me. But if I had gotten into my spaceship in 1958 and blasted off for Tau Ceti and returned in 1980 to find that Reagan is now president, what have I proved? That in the 22 years while I was gone events unfolded, and when I get home I find that Reagan is president. My time travel doesn’t fix the future for the people in 1958, the unfolding events of the universe as they occur are what fixes the future as it becomes the past.
We only discover if everything in the future is fixed if we’re allowed to travel into the past. Traveling into the future doesn’t tell us anything, because we already all do that every second of every day. It doesn’t matter if you travel into the future by cryogenic suspension, relativistic time dilation, stasis fields, orbiting too close to a black hole, or going through a wormhole. You’re now in what was the future, but that future become the present the second you arrive there. I mean then.
Duplicator rays establish some metaphysical shenanigans, but don’t make a bit of difference to predestination paradoxes. Yes, if you duplicated yourself, and then sent the duplicate on a NAFAL trip to Tau Ceti, that duplicate would return home in 22 years and shake your hand only 22 minutes older than when he left. And? There’s no paradox here, just magic duplication.
It’s the “in the note I left you” part that makes a return trip. Even though you, yourself, did not return to the past, you sent information back.
If you are able to do that, and the numbers do match, then yeah, that indicates a “fixed in stone” future and past.
The very most likely scenario is that time travel is just impossible, flat out, so that gives no indication as to whether the future or past is fixed.
The “slightly” less likely scenario is that you can travel to the past, but doing so changes it. Like traveling up a river against the current. Doing that changes the way the water flows past a particular point on the bank. If you travel to tomorrow and write down the winning mega numbers for me, but when I get to tomorrow they are no longer winners, that would indicate that we live in a universe without a fixed past or future.
The most unlikely scenario (IMHO) is that time travel is possible, and that the future and past are fixed. If you travel to the past, you can’t change anything. You may even be a participant in past events, but you always were. You tried to kill Hitler, but were accidentally tripped by another time traveler also trying to kill Hitler. This is the one that creates all the paradoxes if both assertions are assumed to be true.
I’m not saying the entire future would be fixed, not for all time or beyond the part of the universe I can observe. I think it’s like peeking at that cat, once I’ve traveled to the future what I can observe there tomorrow, and I reach tommorow a second from now, you will have to see 24 hours later unless we have ended up in different universes.
Yes. You travel 22 years into the future and peek at the cat in the box, and write down whether it is alive or dead. Then I, who have been sitting here on Earth for 22 years like a chump, also peek into the box and write down whether the cat is alive or dead. And when we compare notes, the notes match! We both saw the same thing! And the reason we saw the same thing is because…we saw the same thing? Yes, yes it is.
Your seeing that the cat was alive or dead didn’t fix the cat into that alive or dead state for me. The cat being either alive or dead is what did that. You saw the cat was dead, I saw the cat was dead, and that was because the cat was dead.
No you didn’t. This is your problem. You didn’t arrive in 2040 to look in that box before I did. We both arrive in 2040 at exactly the same time. You experienced less time on your watch, sure. But you can’t arrive in 2040 until 2040, just like I can’t arrive in 2040 until 2040.
Yes, but but only if you have ended up in the same universe I time traveled to. I’m not there looking at the cat when you get there, if I didn’t time travel again I’d be 22 years older and probably dead by the time you got there You would be seeing a note I had written 22 years earlier for me.
I understand we can’t talk about simultainity in terms of time travel easily, but looking at our watches, I determined that cat’s fate before you even reached that time, and without traveling to another universe you will have to see the same fate after a lot of time has passed on your watch.
Or just consider a return trip. If I traveled to the future if this universe, and back to right now in this universe, I can tell you what happens to that cat but you can’t see it for yourself for 22 years.
(How bout we stick to 24 hours so I have a better chance of being alive?)
The reason I keep talking about 22 years is that Tau Ceti is 11 light years away, and so if you travel nearly as fast as light that’s how long it would take you to travel to Tau Ceti and back.
The reason I keep harping on this trip to Tau Ceti is that I think it clarifies some of your objections to time travel into the future.
It is absolutely an established physical fact that if you took a NAFAL trip to Tau Ceti and back, you would be gone for 22 years, but according to the internal clocks on your spaceship it took much less time. How much less time depends on how “nearly” that “nearly” was. So I just set your speed at whatever speed it would take for you to experience 22 minutes on your internal timeline.
If you’re off on your trip while I sit here on Earth, our clocks don’t agree. It’s only when you arrive back on Earth that we agree who experienced a slower clock and who experienced a faster clock.
Do you agree that if you traveled on a trip to Tau Ceti and back, and the trip took 22 years, when you arrive back on Earth you’re at the time on Earth that the people on Earth are at? It doesn’t make sense to insist that you’re 22 years in the future, because when you step out to shake my hand we’re both in the present. I’m not in the past, you’re not in the future. If we can shake hands we’re both in the present.
I have no idea how alternate universes work. That’s above my pay grade. But I can tell you with absolute confidence that if you travel 22 years into the future in this universe, when you get there, you’ll be in the present.
That is overly simplistic. The past is a sort of probability macadam, where the lower parts (further away in spacetime) are more diffusely effective. The assumption that the dynamics of causality are precisely mechanistic is unfounded. Reality is not a doohickus, it is an amorphality where altering some given cause may not have the pinball-type knock-on effects that a clockwork universe would presume.
How do I know this? I do not, but neither do you know the opposite. Causality and temporal discontinuity is a poorly studied discipline.
