I know this question has been asked before and I have read and understand the answers however imo none of them still imply that backward time travel is possible.
I understand moving forward in time easily, it’s the backwards in time I don’t get; I just don’t think it is possible, even in theory. I think where I might be getting it wrong (if I am) is my perception of what time travel is so let me clear that up first.
I think what most non-scientific people (me) believe backward time travel is, is what we see in the movies – that is you can travel backwards in time to specific timeline and interact with it, potentially changing the course of some events. They key phrase here is “interacting with it” as in somehow change it or influence the future.
I am going to reference this question here and the answers proposed, I will build on them and their examples.
Every explanation so far I’ve read (inc link above) about backwards time travel always hinges on the speed of light, light cones and that you must travel faster than light to achieve it. However, from what I take away from these explanations is that it only “appears” as though (as in “observed”) backwards time travel was achieved, to me this not true time travel (or what my definition is of it). The best way to demonstrate my point is with an example so let’s expand on the great explanation already provided by the last poster from the link above (you don't need to read all answers just the last one right at the bottom by Andrew Steane).
In the last diagram he gives an example of us seeing someone or some event BEFORE they were born, then later seeing them born (read the whole thing first to get the context). But imo this is not time travel, the same events occurred in the correct order (A then B then C), it’s just that due to said object (the person or ship) traveling faster than light we OBSERVED event B first. So essentially we viewed these events out of order…but they STILL OCCURRED in the correct order of a,b,c. So my first question here is, is my understanding here correct or not?
Assume I am correct with the above. What this means is that, at best we can only ever observe past events, we cannot interact with them, influence them or change them. To illustrate this let’s use the last diagram but change it slightly. Let’s say said person did some terrible event at point B (which we “observe” first), then we view event A after (the birth of the person). We could (if we could travel fast enough) witness event B then travel to before event A using FTL to stop the birth/kill them and therefore prevent event B (according to the posters explanation). However, this statement is not true because event A already occurred, you just haven’t seen it yet. if we were to travel to where event A occurred in the hopes of stopping it (after seeing event B), we would find it still occurred no matter how fast we travelled. So, in other words we can’t go really go back in time – or at least in the concept of my understanding and what I believe is the concept of time travel (interacting with past event or changing it). So, in the last statement where he said:
“Now we have that someone or something born at A then went off to B and came back to C where they were present before their own birth.”
It isn’t true, you just observed it that way.
So to summarise, when we talk about “backward time travel” in the scientific definition of it - is it really just that we are observing events out of sync (in layman’s terms) if we use FTL or is it really possible (theoretically) to actually go back and interact with a past event? if yes, how?
Also, I know there are other things at play here like causality and possible other theories like multi-dimensional timelines. For the sake of keeping it as simple as possible I’d like to not discuss them at this point, maybe later after I grasp the above!