You have an individual who can travel backwards and forwards in time. They normally maintain an observer status but occasionally a butterfly is stepped on. Because, home is where the heart is, how does this person find their way back 'home'?
The time-travel theory I’ve been considering using is the one where the moment you CHANGE (as opposed to the minute you arrive in) the past you create an alternate timeline i.e. an alternate universe where everything is exactly the same except for that one thing, and its consequences, you changed. Is there a way (or theories at least) to differentiate between these universes; some observable physical/quantum/random feature that is in fact not exactly the same in each universe?
I understand that time-travel is all theory anyway, so the definitive answer is ‘we just don’t know’. I’m trying to figure out if I just have to resort to getting my individual to re-invent a ‘magic’ compass to get around this issue. (I use the word ‘magic’ figuratively. As far as possible my universe/s are based on the ‘magic doesn’t exist’ premise).
According to the highly unpredictable Wikipedia ‘’The actual quantum-mechanical hypothesis of parallel universes is "universes that are separated from each other by a single quantum event."’’ And seeing that “Some physicists say the multiverse is not a legitimate topic of scientific inquiry” I’d rather not ask this is the Physics SE.
NOTE: I’m not asking if it is possible to travel back and forwards through time, or if the multiverse exists etc. There is tons of research available on that. I’m also not asking about the ethics of time travel as asked here; The most interesting set of consistent rules to time travel as asked here; Or even on determining the time-paradigm of the universe you have travelled to as asked here; All great and helpful questions. The most similar question is about time travel co-ordinates as asked here which as far as I can tell was about determining where your location would be at a particular time on a single timeline. I was wondering if there have been any theories put forth on how to identify which timeline/ alternate universe you are in. If this is pretty much the whole mystery of time-travel, please stop me now and…I’ll just have to go buy a very pretty lampshade to hang on the issue, with any sales help you could provide.
For example: Let us say your observer starts at location, let us call it ‘Home’. They go back into the past to Past A. They either accidentally or purposely change something in Past A. They then try and go back to the future (sorry, I couldn’t resist). And Land in Future 1 - this isn’t their ‘home’. So they try return to the past A, but don’t quite make the same landing and land slightly after they left Past A which has since changed in some manner meaning they have actually landed in Past B. So if they try to go back to the future too (sorry, again I couldn’t resist), they would end up in future 2. It can go on like this forever, with you observer lost in time.
Another attempt at explaining my ramblings: Think of the ‘time is a tree’ analogy. From your perspective the past is set, it’s done, a solid line of events trailing back into the past. The future is dependent on choices you make, with branches splitting off at each choice. So if you travel back down the ‘trunk’ to the past, you then come across ‘existing’ other future branches of choices that were not taken in your timeline. Theoretically you could then accidentally/purposely follow these new other branches back up through time.
If your individual has a way of manipulating where they go up and down the timeline/s, and potentially swing across sideways as well (this ability and power source goes with them in each instance and they don’t have to reinvent it each time). Is there a way that they could determine what direction/location is ‘home’? Akin to smelling the air, or licking their finger to feel the direction of the wind - I’m not suggesting that the individual go around smelling the air or spending months sitting in a dusty library sifting through history books determining if indeed this or that event should have happened.
I’m thinking of the clichés, such as the red and blue and yellow universes or Earth 1, Earth 2, and presumable Earth -1 and Earth -2, etc etc ad nauseam - where the universe vibrates at a different frequency. Is there anything behind that, or is that just a massive lampshade? What other lampshade theories are out there? I only seem to remember the ‘vibration’ theory.
Oh, and also please just ignore, for now, the MASSIVE fact that if said individual had potentially the entire universe to explore throughout the various incarnations of time, why would they want to go home!
If this is too broad, please can you provide me with some pointers in how to narrow down the question (it is theoretical time travel after all!)
EDIT: Thank you for the answers so far. They have been of some help giving me some ideas and raising a few points I had forgotten about. I'm going to leave the question open for a bit longer and see if anyone else can add anything new.
I was thinking more on the universe has a Vibration trope. Vibration is an oscillation, the repetitive motion up and down across a central point. This could give me an explanation on how my time-traveller can figure out where they are in the universe. Use their 'home' time and universe as the central point.
The answer suggesting each universe having its own 'song' was actually quite nice and I may just incorporate that! Thinking of sounds, made me think of waves, which made me think of other waves such as light. The last few days I've been playing around with light being the signature or 'universe ID'. Almost like a rainbow signature (never thought I would be one for rainbows!). But I am really liking the idea. I can get my time-traveller to move across the 'rainbow' moving say from red to green which would result in 'universe' jumping, and then up and down the 'rainbow' as a function of the time-travel component. Each time a CHANGE is made, the universe splits meaning a new rainbow width can be navigated. This way you will have a unique (and infinite, yes I realise this, I'm working on it) ribbon of multicoloured light for each time and place in the universe. I know that is just a very rough outline and I haven't explained it enough. But maybe it will spark someone's imagination...
Bounty edit thank you everyone for all your answers. I'll be taking a bit from nearly all of them. As I'm having trouble deciding which is the most helpful to my question, I'll be giving the bounty to the popular Doctor Who answer. If it works for the Doctor, who am I to complain!