What would the effect of multiple time dimensions be on the universe?

Great Debates
1

Suppose that the universe had multiple extended time dimensions, say two, like there are three extended spatial dimensions. What would be the effect of this on the universe?

I think I can visualise it, objects just seemingly appearing out of thin air for a while and then disappearing (is this correct?), but would stars, galaxies, planets and life have developed? I’m guessing not, as the interactions between molecules needed for these things to occur would have been much rarer.

What about moving through the dimensions? How could we change through which temporal dimension we are moving through?

Finally, this is more of a GQ question, but it may be open to debate, is it thought that there are multiple temporal dimensions, perhaps curled up tightly like the extra spatial dimensions mandated by string theory, present in our universe? If not, why not?

2

I believe that current string theory requires only one time-like dimension. As to the rest, it’s too different from what we know to make even a guess without going through the math.

3

There is only one dimension of time, but there are many dimensions. In our universe, mathmatical calculations suggest that there are 10 or 26 dimensions. I am horrible at explaining things and I can’t even begin to try to explain this because it is just so insanely difficult to explain, especially how the multiple dimensions could be percieved by us, so here are some links:

More info here, here, and here. An excellent book which explains the matter is Michio Kaku’s Hyperspace.

4

I find it best when thinking about problems like this to take the approach of thinking of our universe as static 4-dimensional thing — what physicists would call a Minkowski space-time. The “present” is a three-dimensional slice of this space-time that is transversal to the time axis. “The past” is simply that portion of space-time that is on one side of this slice, while the future is on the other side.

Of course, we don’t get to choose arbitrarily which side of our present slice is “the past”. This is in contrast to the spacial dimensions, where, for example, we get to choose arbitrarily which side of the universe is “below” the spiral of our galaxy. Several things distinguish the past from the future. The one that is probably the least philosophically problematic is the arrow of entropy: the 3D slices of space-time with smaller time coordinates are the ones with lower entropy.

However, the more interesting thing that distinguishes between the past and the future is the arrow of memory: we remember the past, but we don’t remember the future. Somewhat more precisely, you can tell that time slice S[sub]1[/sub] precedes S[sub]2[/sub] on the time axis if the brain of Tyrrell McAllister in S[sub]2[/sub] contains a record of the state of the world in the vicinity of Tyrrell McAllister in S[sub]1[/sub], but not vice versa. (I said that the arrow of memory is more problematic than the arrow of entropy because it is harder to define precisely what a “record” is. But it is even harder to rigorously distinguish between cause and effect without presupposing a distinction between the past and future, so I’m staying away from the arrow of cause and effect.)

In our universe, with one temporal dimension, the past is that half of the timeline that we remember. That is, at time coordinate t[sub]0[/sub], we remember those events with time coordinates t < t[sub]0[/sub].

Now consider an entity living in a universe with two temporal dimensions. So, instead of having a timeline this entity will think of time in terms of a “timeplane”. To specify a point in time will require giving two coordinates. By analogy with the above, I suggest that at time coordinates (s[sub]0[/sub], t[sub]0[/sub]), our entity will remember those events with time coordinates (s, t) such that s < s[sub]0[/sub] and t < t[sub]0[/sub].

Whereas for us, the “past” is the left half of the timeline, to our entity, the past will be the lower left quadrant of the timeplane.

5

I was under the impression that more than one time-like dimension caused horrible things to happen.
A quick search reveals that “phenomenologically dangerous tachyonic KK graviton modes” and the like are then possible. Yet others say “there are no propagating tachyonic or negative norm states even though the extra dimension is time-like.”
Still, when I come across sentences like “It has been pointed out that in a certain class of higher-dimensional theories such as Brane World models with quasi-localized non-Abelian gauge fields the vacuum structure turns out to be trivial.”, it’s a sure sign that I need to wait until the story comes out in paperback.

6

Actually, I’m not sure of it, but I think you can also get away with having only one space-like dimension, and that the resulting universe would look like ours. But I’ll leave it to the physicists to verify that.

7

I don’t think this is a very good explanation for the universe in general, because a person from the “past” can be standing in the same place as a person from the “future”. If you considered on a personal level, i.e. individual person, proton, star, etc, then this explanation is correct.

8

kimera, I don’t understand your post at all. (Not that my own post was any less obscure.) Could you elaborate? As near as I can figure, you seem to be saying that my explanation works for individual entities, but not for the universe as a whole. But then your argument for why my explanation doesn’t work for the universe as a whole refers only to individual entities (a person from the “past” and a person from the “future”), so I’m confused.

9

It’s very strange and I will try my best shot.

Your explaination seems to imply that time is something that moves forward in set incrimates for everyone at the same rate. Time is not set though, but relative. A clock on a satellite will have slower time than than clock on the earth. When brought back down to the earth, the stationary clock will appear to be from the “future” since it is forward in time and the satellite clock will appear to be from the “past” since it is backwards in time. It is the same with people and is known as the Twins Paradox, each person has their own ‘present.’ The path of each clock, twin, muon, is plotted serparately on the Minkowski scale, instead of together.

10

What you have to keep in mind re: the twin paradox is that acceleration is not absolute motion. I think that is the key here.

11

I think a universe with many time dimensions is very different from a universe with only one. With just one dimension, we’re restricted to continuing in the same direction in time. With multiple dimensions, an object has “space” in which to “turn around” and start heading backward in time. Time simply wouldn’t behave much like time as we know it.

12

One possible problem with the classic 4-dimensional Special Relativity spacetime is that it seems to imply that the future is fixed. It is “already there”, and time is just a human perception and free will an illusion. Vonnegut’s novel Slaughterhouse Five addresses the philosophical problems with that view.

One way around this might be to postulate an additional dimension of - well on second thought it might not really be a “timelike” dimension OR a spacelike dimension. Call it a Z dimension, with space as X and time as Y. It might be akin to the multiple worlds view of Quantum Mechanics, with each slice of Z representing an alternate way particles might have progressed through time. This theory however requires something most people regard as odd or paradoxical: that the past isn’t fixed! That is, multiple possible alternate pasts could converge on an identical present, with no way to know which one was the “real” past. So counting all possible states that converge on the here and now, entropy actually increases both into the future AND the past!

13

Please note that this entirely a philosophical problem. Free will isn’t a concern for the theoretical physicists–they just want to know what explains the data most accurately.

14

i think this should be noted in response to the whole question at large, as well.

most of our interpretations of our perception are based on an assumption of a euclidian spacetime. it’s almost unavoidable with as little gravity and small relative velocities that we normally get to witness. in other geometries, there can be ways, albeit nearly infinitely more complicated, of defining metrics that explain what we see, despite the arbitrary addition of whatever dimensionality we want. at least, i think that is the case.

as a bit of a silly exercise, consider the common euclidian distance metric in three dimensions. d(p, p’) = sqrt((px - p’x)^2 + (py - p’y)^2 + (pz - p’z)^2). if we suppose p is a point in five dimensions, and we use the same metric instead of the analogous metric for five dimensions, the space wouldn’t be noticeably different from what we consider our current perception of three spatial dimensions. the definition of ‘interval’, at least in relativity, is what plays the important part here.

however, i might be talking complete nonsense here. does anyone actually understand the geometries involved in modern physics? i’m trying to struggle through it now, myself, and so far i’ve read nothing about how it relates to the quanta.