The A theory holds that only the present time (and everything at that time) exists. Therefore any time other than the present time is not an available travel destination. This appears to rule out the possibility of time travel according to the A theory
However, there is one caveat, which is that the present time is always moving into the future.. — Luke
I don't see why presentism as such should be inimical to other kinds of time travel, proceeding at different rates than the normal forward rate. — SophistiCat
Suppose that the metaphysics behind the A theory of time is correct, is it possible to travel to the year 2024 (or the "future") or the year 2000 (or the "past") or does time travel require the B theory of time to be correct? — Walter Pound
It degenerated into the usualy discussion of what eternalism is rather than its implications. — noAxioms
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Time travel isn't possible period. — Terrapin Station
You need presentism of course. Travel isn't possible at all in eternalism, given the usual A-definition of 'travel'. — noAxioms
I presume you ride the 'now' into the future. That's how it worked. To travel to the past, I suppose you'd have to get time to go the other way, and still be able to ride it, but leaving everybody else behind.Thinking a bit more about this, if now is an objective fact on presentism, and the Time Traveler is transported some ways into the past or the future, what happens with the now? — SophistiCat
I always wondered what meaning there is being a unit of X per X, which seems to reduce to just unitless '1'. On the other hand, our clocks are dilated mostly due to the gravity well in which we find ourselves, so maybe the rate is still unitless, but still less than 1. How much less is an eye-opening exercise.normal "time travel" when everyone moves forward into the future in lockstep at 1 second per second — SophistiCat
There are certain space-time structures that make time-travel possible, i — Inis
Not any spacetime structure that's correct, though. I'm not saying that it's not a popular belief that time travel is possible, but the belief rests on not understanding what time really is. — Terrapin Station
According to you, time doesn't pass at all, according to presentism. That can't be right. And I don't mean that in the sense that presentism can't be right, but in the sense that your construal of presentism can't be right. — SophistiCat
I presume you ride the 'now' into the future. That's how it worked. To travel to the past, I suppose you'd have to get time to go the other way, and still be able to ride it, but leaving everybody else behind. — noAxioms
In more objective terms, I think time travel to the past would be to cause an instance of 'yourself' to exist at time X, but with memory of time Y, with Y > X. This is pretty easy to do in theory in the forward direction, but not so much backwards, being a violation of the principle of locality. — noAxioms
I always wondered what meaning there is being a unit of X per X, which seems to reduce to just unitless '1'. On the other hand, our clocks are dilated mostly due to the gravity well in which we find ourselves, so maybe the rate is still unitless, but still less than 1. How much less is an eye-opening exercise. — noAxioms
Well, they 'rewind' along with the rest of 'history', which isn't even a violation of physics. Only what you (the 'traveler') are doing is a violation."I presume you ride the 'now' into the future. That's how it worked. To travel to the past, I suppose you'd have to get time to go the other way, and still be able to ride it, but leaving everybody else behind."
— noAxioms
This works for the Traveler, but what about the rest of us? What happens to us and our now when the Traveler departs into the future or the past, and now departs with him? — SophistiCat
Pretty much the standard depiction, yes. I think Back to the Future did almost exactly this.We can imagine a world in which, in the year 2019, you stepped into the time machine and suddenly disappeared. Earlier, in the year 1919, an exact copy of you as of 2019 suddenly appeared in a field, fooled around for, say, a week, and then disappeared. Meanwhile, in the year 2019, five minutes after vanishing in the time machine, you reappear, having the memories and other physical changes that your copy had in 1919 at the time of disappearance.
I think it very much counts if there is a guy in 1919 with memory of 2019. The way you tell the story puts emphasis where the storyteller wants it, but there would be little dispute of time travel to somebody with such memories in 1919, however little he might be able to convince the locals there.We could tell the same story chronologically, without jumping back and forth between 2019 and 1919. The reason we usually tell these stories achronologically is to emphasize causal connections. But in this telling there are no anomalous causal connections between the past and the future - and that is why it does not count as time travel. Time travel is all about anomalous causality.
I think it's important to remember that the motivation, the main selling point of presentism is this inescapable subjective perception of being in time - and that includes both the instantaneous now and its temporal progress. However we choose to formalize and articulate presentism, we shouldn't lose track of those basic intuitions, else this turns into a sterile formal exercise. — SophistiCat
I agree, and I've never said otherwise. What I've said is that, according to my view of presentism, no other times but the present time exist, and time travel can only be viewed from an eternalist or B theory perspective of time. — Luke
How about doing a simple time dilation experiment? Synchronise atomic clocks, and take one on a flight around the world. When the clocks are reunited, they no longer agree on the time. How is that possible under presentism? — Inis
Are both clocks at the present when they are reunited? The time displayed on the clocks is irrelevant to presentism, so long as the clocks always remain at the present. — Metaphysician Undercover
That has been done many different times and many different ways and the result is the same, clocks run at different rates under the influence of gravity and acceleration. The time reading on a clock however has nothing to do with presentism. Time is not fundamental, what is fundamental is change and process, and the rate at which a clock runs, or humans age, varies with gravity and acceleration. There is a fundamental misunderstanding about what time is (a derived concept from change) and what clocks do (they are processes that run at different rates under different conditions).How about doing a simple time dilation experiment? Synchronise atomic clocks, and take one on a flight around the world. When the clocks are reunited, they no longer agree on the time. How is that possible under presentism? — Inis
That has been done many different times and many different ways and the result is the same, clocks run at different rates under the influence of gravity and acceleration. The time reading on a clock however has nothing to do with presentism. Time is not fundamental, what is fundamental is change and process, and the rate at which a clock runs, or humans age, varies with gravity and acceleration. There is a fundamental misunderstanding about what time is (a derived concept from change) and what clocks do (they are processes that run at different rates under different conditions). — prothero
Clocks around the world have 24 different times representing the different time zones. Before agreement clocks in different towns had different times, rail travel made synchronizing clocks necessary, etc. The time reading on any particular clock has nothing to do with presentism or with the philosophical notion of time. — prothero
Well, they 'rewind' along with the rest of 'history', which isn't even a violation of physics. Only what you (the 'traveler') are doing is a violation. — noAxioms
What I've said is that, according to my view of presentism, no other times but the present time exist, and time travel can only be viewed from an eternalist or B theory perspective of time. — Luke
No times but the present exist, and wherever the present is, that is what exists. Yesterday the present was thataway, and now the present is thisaway. Nothing about presentism says that the present has to stay in one place — SophistiCat
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