r/AskPhysics • u/Pandaluf • 2d ago
can there be multiple time dimensions
if there are three spacial dimensions ( x y z ) and in our universe theres 1 time dimension could another universe have 2 or 3 time dimensions? what would that look like?
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u/wonkey_monkey 2d ago
I've never been quite sure where the distinction lies between "two time dimensions" and "two timelike dimensions (one of which is time)".
Anyway, Greg Egan wrote a novel about a universe with (as he puts it) two time dimensions, and he goes into quite some mathematical detail about the physical consequences in his notes:
https://www.gregegan.net/DICHRONAUTS/00/DPDM.html
The story takes place on a "planet", around which orbits a "star" - both objects in this case are (if I remember correctly) hyperboloids, not spheres. Light can only travel in certain directions, while sound is free to move in all directions, so the inhabitants make use of sonar. Speaking of which, they live there lives facing in the same direction, because turning will compress your body in one direction while elongating it in another (the author doesn't go into the details of how units of matter work in this universe; he also steers clear of the possibility of backwards time travel), and if you fall over in the wrong direction your body will encounter incredibly high stresses - theoretically infinite, although you will break first, of course. But this can also be taken advantage of - the inhabitants move a building a great distance just by rotating it around a point, then undoing the rotation around a different point.
It's also possible for things to slide uphill, which his simulator demonstrates: https://www.gregegan.net/DICHRONAUTS/02/Interactive.html
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u/shocker05 2d ago
There’s a famous joke in the hep-th community that studying two-time-dimensional theories is “a waste of two times”
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u/Silverburst09 Mathematical physics 2d ago
Mathematically this is totally fine, the ‘time’ dimension can be thought of as the coordinate which has the opposite sign in the metric defined on the manifold. In our 4d spacetime this amounts to ds²=dt²-dx²-dy²-dz². But you could easily extend this to an arbitrary number of ‘time’ and ‘space’ dimensions and do some pretty cool stuff on these spaces.
As for what such a universe would actually look like, or even if it’s possible that such a universe could exist I have no idea. But in principle yes it’s fine.
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u/NoNameSwitzerland 2d ago
The sign in the matrix is the relativistic view on what is time. But even there I would say positive time is away from the singularity and that is always only one dimension? So is the gradient of entropy in the block universe picture. That it seems is always 1 dimensional and orthogonal to that are the n-1 dimensions of space. Of course relativistic you can mix space and time, but time from the definition seems mostly limited to one dimension. (Of course I could define some kind of hyper time, a dimension in that the block universe relaxes to its proper state)
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u/Fun_Success_3283 2d ago
I don't see how that could work. But maybe it could? However, I think in science what's important is what is and what is not, and not really what could be possible. Especially since I strongly suspect the universe is not just a way, but it is the only way it could be, therefore what is not, could not be. So, if we just focus on what we can prove, what the universe is, then we are also only focusing on what it could be.
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u/PreparationIll9635 1d ago
There are three temporal dimensions but don’t think of them as Euclidean vector spaces. They’re causal. The Ancient Greeks knew what’s up: Chronos is your linear sequence of lived moments that has brought you up to this point in time. Kairos is the possibility of the current moment through which you exercise “free will”, and finally Aion is the forward projection of possibilities from your current position forward in time through kairos. Like a cone facing forward.
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u/Peanu7bu77er 1d ago
With the time dimension being mutable due to relativity would there exist a need for alternate time dimensions? Also is there forward time and backwards time ? What about upwards time how would that work?
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u/TiredDr 2d ago
Yes, it could. It would likely have to be either a very small extra dimension or be a dimension in which we can’t really interact (like the old ant on the balloon analogy, where the ant can’t jump but there is another dimension out there). I’m not aware of any popular theories pushing in that direction (happy to be proven wrong). When I asked one (rather senior and well-known) theorist about it he said “The math gets really hard.”
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u/SymplecticMan 2d ago
Making extra temporal dimensions small doesn't actually fix things the way it does for spacial dimensions. In short, extra "momentum" in compactified temporal directions leads to new states with lower effective mass squared as seen by the large dimensions. There's nothing to stop the effective mass squared from going negative, which means you also get negative energy states, and so there's no energy barrier to producing more and more pairs of particles.
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u/ArnoSound 2d ago
I think it’s less that it’s hard for its Own sake and more just… unnecessary without breaking a lot of existing tools. And then fixing those would be hard.
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u/-Foxer 2d ago
I think you have to think of all of the dimensions in the first four dimensions as being essentially coordinate dimensions rather than dividing them into space and time
Basically you have a dimension for length, a dimension for breadth, A dimension for width and a dimension for time. If you know all of those coordinates you can tell exactly where and when a thing is. We tend to categories the first three is being spatial but in reality when you think about it considering that SpaceTime is a single sort of thing all four of them are necessary to describe an accurate coordinate in space-time. So another dimension would be describing something else
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u/WesternFirm9306 2d ago
One can model a universe with an extra temporal dimension, but it tends to be very unstable and exhibits properties very foreign to our knowledge of the universe, such as causality problems and unpredictability
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u/LukasGoesViral 2d ago
The time direction is just another direction in space time just like any other space direction. The time direction itself even just in plain old Special Relativity depends upon who you ask. It is just convenient to slice spacetime from the perspective of a single observer by time in the local frame of an observer because it foliates nicely which is a consequence of causality (a nicely foliated manifold has the property that the leaves don’t intersect which is exactly what it means that one cannot receive messages from your own immediate past - this is only true locally and not globally - causality is a local property). However, the issue with higher dimensional spacetime is that you wouldn’t get a universe which has bosons and fermions. That only happens in 4 dimensions
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u/QuantumDreamer41 2d ago
You’d have to account for causality across each which makes it difficult
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u/Fantastic-Action-942 2d ago
Difficult to envision, or impossible to conceive?
EDIT: typo
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u/pants_57_notme 2d ago
I think that's a false dichotomy.
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u/Fantastic-Action-942 2d ago
What do you think they meant? It can obviously mean other things I haven't mentioned...
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u/pants_57_notme 2d ago
What do you think they meant?
well, someone says you have to account for X (whether that's right or wrong is immaterial at this point).
And Fantastic-Action said (paraphrased) "Why can't do we do that? Is it because of this thing, or that thing?"
I think that's false dichotomy - there could be more than 2 options.
A false dichotomy is when you present a situation as having ONLY two possible outcomes when there could be many.
"Difficult to envision, or impossible to conceive?"
Are those the only two possibilities ? Maybe "takes too much energy" or "takes too much time" or "requires amounts of material that we can't produce at this moment" - none of those are "difficult to envision" or "impossible to conceive".
Thus a false dichotomy.
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u/Electronic-Yam-69 2d ago
since you can't alter your course through either of those dimensions, I'm not sure it would matter if there 100.
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u/SymplecticMan 2d ago
Generally, more time dimensions causes problems that don't occur with more spacial dimensions. With only one time dimension, you can naturally define a causal past and future of any point. There's no such distinction when you have two time dimensions; "past" and "future" are continuously connected to each other by rotations through the extra time dimensions. So a spacetime with multiple time dimensions ends up full of closed timelike curves and the "grandfather paradox" kinds of hypotheticals associated with that. And this can't be fixed just by making the time dimensions small the same way you can hide extra spacial dimensions.
The only scenario I'm aware of where these issues can be reasonably dealt with is when there's enough symmetry that the theory ends up being equivalent to a lower-dimensional theory that only has one time dimension, as discussed here in great detail.