It’s easy, relatively speaking, to develop an intuition for higher spatial dimensions, usually by induction on familiar lower-dimensional spaces. But I’m having difficulty envisioning a universe with multiple dimensions of time. Even if such a thing may not be real or possible, it seems like a good intellectual exercise. Can anyone offer an illustrative example?
2$\begingroup$ This is very very very far off from real physics, We have only one time dimension as far as we know. Why would you try to build an intuition into this? $\endgroup$– PrathyushNov 3, 2012 at 2:55
7$\begingroup$ @Prathyush see Qmechanic's nice answer, which is about serious physics (+1) ;-). It is (at least up to now) not forbidden to think and talk about physics that could be valid and most relevant at higher (not yet directly experimentally accessible) energy scales and that differs from the effective physical laws we observe at our low energy "everyday scales" ! $\endgroup$– DilatonNov 3, 2012 at 10:48
$\begingroup$ I asked a similar question as a comment on a previous question. It was a rather uninformed comment, as I saw 3+1 dimensions being addressed as a matrix with diagonal elements, I only asked why not two, as opposed to one, may be negative. I got a good response, apparently a trace of zero has bad implications, so I guess a possibility left is $diag(-1,-1,1,1,1)$, but again, I'm just making this all up physics.stackexchange.com/q/13451 $\endgroup$– Alan RomingerNov 7, 2012 at 15:40
$\begingroup$ I've got a kind of sub-question to piggy back on this: If everything's relative aren't people experiencing different time effects in the same universe when one is moving much faster than the other? Arent the two subjects experiencing different "times"? $\endgroup$– LenFeb 15, 2018 at 16:55
Several authors (in particular Itzhak Bars) have written papers about two-time-physics that should help build intuition for the topic.
Infinitely many 'times' appear in integrable systems.
F-Theory, which is a 12 dimensional theory, has been described as having extra temporal dimensions, however see Wikipedia.
Theories can be formulated in any number of space-time dimensions. Examples of multidimensional theories:
F-theory, 12d theory with two times.
S-theory, 13d theory with three times.
Kalitzin's relativity with r-times or even infinite-dimensional times (the latter much less developed) was studied.
Indeed, I think to remember some people tried to understand quantum mechanics in a multitemporal set-up.
In philosophy, some people studied three-dimensional time theories. These times are called time, hyparxis and eternity.
If you are happy to focus on the intuitive without worrying about too much maths, the classic work on multiple time dimensions in physics must surely be J W Dunne's The Serial Universe - the second edition, published in 1942, is shorter and (comparatively) more readable. It was the sequel to his bestseller An Experiment with Time and elaborated on the role of the observer in modern physics. His regress of multiple time dimensions was inhabited by a similar regress of observers, thus (in retrospect) proffering a solution to the Schroedinger's Cat + Wigner's Friend regress of discrete real observers.
$\begingroup$ I agree that An Experiment with Time is a fascinating book, but "Mainstream scientific opinion remains that, while Dunne was an entertaining writer, there is no scientific evidence for either dream precognition or more than one time dimension and his arguments do not convince". $\endgroup$– PM 2RingFeb 6, 2020 at 12:34
$\begingroup$ At the time, mainstream science was split. See for example Herbert Dingle's contemporary commentaries in Nature. After WWII Dunne was largely forgotten and today's mainstream scientific opinion has barely even heard of him. Suffice to say that his case at least contains some intriguing ideas. (BTW, is it not the custom here to cite Wikipedia when you quote directly from it, especially when I wrote part of your quote and added a citation in support of it? I do not post here from ignorance or prejudice!) $\endgroup$ Feb 6, 2020 at 13:44
I have been a self-guided student of theoretical physics for over 30 years. I don't have any formal training. I have been working on a model of our universe ever since I purchased and read Dr dr Michio Kaku book "hyperspace" in high school 25+ years ago. My model utilizes multiple dimensions of space time. It is still a work in progress. The assumption that my model is built of is this: Because spacetime is an inseparable entity it is assumed that space and time are proportionate to each other. What that means is, as space expands in dimensions, so too does time. So rather than with 5 spatial dimensions there is just one dimension of time there ate two axis of time. 6 dimensions of space 3 of time, [7D 4t], [8D 5t]. Lets just say time gets really really weird when you get to 4t and above. at one point you end up having a prime observer in two separate timelines within the same 3D space. Nuts! Another implication that is poking its head out is that energy density is relative to spacetime/matter-energy. That is, energy density determines the number of space time dimensions. There might be some explanation to the hyper expansion of our univers right after the big bang. This is still just a work in progress and no ware near complete. But some interesting hints at the possible nature of our univers.
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$\begingroup$ Please remember the rules of this site: no personal theories. $\endgroup$– MiyaseMay 27, 2022 at 6:55
$\begingroup$ Is it possible that in general relativity there are $2n+1$ possible times for n test particles. The eigentime of each particle, the parametric time of their geodesics and the coordinate time. $\endgroup$– Cretin2May 27, 2022 at 7:09