The Times They Are A-Changin’
Investigating whether time has more than one dimension.
September 7, 2010
University of Waterloo
A one-dimensional view is often dismissed as simplistic and narrow-minded. Thatís certainly the outlook of some physicists, who are taking this philosophy to a whole new level—by applying it to time. They argue, against conventional wisdom, that time is multi-dimensional. If they are correct, then it could help to unify general relativity and quantum mechanics.
Today, weíre almost complacent about the possibility that there may be extra dimensions of space. String theory, for example, proposes that there may be ten or more spatial dimensions, most of which are curled up so that we do not experience them everyday. The notion that time could have more than one-dimension, however, is far more jarring and physicists have been reluctant to suggest that time could move sideways as well as forwards. But the times, they are a-changiní.
"Three dimensions doesnít seem to be an essential property of space, it seems like a contingent property and could be otherwise," says FQXi member Steven Weinstein
, at the University of Waterloo, Ontario. An assistant professor of both philosophy and physics, Weinstein is open to the possibility that time could have two or more dimensions.
Part of the thinking behind this comes from attempts to unify general relativity, which governs the behavior of large-scale objects in the cosmos, and quantum mechanics, which describes particles in the subatomic world. Both theories are extremely successful in their own domains, but have so far defied attempts to be brought together under one overarching theory. A universe with three dimensions of space and one of time, it seems, is not big enough for the both of them. String theoryís extra spatial dimensions help create a bit more room, but recently some physicists have been proposing that an extra dimension of time might also be needed.
To check what a multi-time-dimensional universe would look like and if it could be compatible with the world we see around us, Weinstein and his colleagues tried to model a simple physical theory in two dimensions of time. They wanted to investigate how a standard equation describing an electromagnetic wave would be modified in a two-time-dimensional universe, but they were not sure where to begin—quite literally. Weinstein realized that he did not know how to mark off an initial time in his model: When there are multiple values for time, what is time T=0?
Weinsteinís team addressed this by attempting to see how the wave evolved as both timelines changed at once. The trouble was this made the model too wide, with too many possibilities for how the wave would grow and change. The same initial conditions could give very different final answers. By contrast, in our world we can
make predictions for how the universe evolves based on initial conditions, so it seemed that a model of two-dimensional time constructed in this particular way could not be right.
Three dimensions doesnít seem
to be an essential property
of space, so why should time
only have one dimension?
"Itís very, very hard to make a deterministic theory, where you start with data and it determines what the future will be in a reasonable way," says Walter Craig, a mathematician at McMaster University in Hailton, Ontario, Canada, who helped Weinstein make sense of his multi-time model.
Weinstein and Craig realized that a model in which the second time dimension was handled in a different way might work. Initially, they set it to zero and evolved their wave in the other dimensions of time and space. Then—to account for the extra time dimension—they stepped the initial time forward in the extra time dimension and found the data produced by the model was perfectly well-behaved. (See Weinsteinís award-winning essay in FQXiís Nature of Time contest
for more details.)
This is good news for physicists trying to build multi-dimensional time models. One such physicist is Itzhak Bars
at the University of Southern California in Los Angeles. For more than a decade, he has independently been developing a "two-time-physics" formulation, which includes a second time dimension and a fourth spatial dimension, and which grew out of his work in string theory and its extension M-theory. He believes that this extra wiggle room might help fix certain mathematical anomalies in our current understanding of particle physics.
DOUBLING-UP TIME’S DIMENSIONS
Any physicist dabbling with multiple time dimensions has to be cautious that they do not run into paradoxes, however. One problem that Bars has had to contend with is time travel
. With a whole extra dimension of time kicking around, there would seem, at least naively, to be far more freedom for particles to navigate their way sideways and then backwards in time. In his own formulation, time travel is restricted; subatomic particles and the laws of physics may be influenced by these extra-dimensions, but we are constrained to move in a "shadow" world of three spatial dimensions and one time dimension, just as shadows are restricted to a two-dimensional wall of a three-dimensional room.
Another implication of playing with multiple time dimensions is that it dramatically changes our understanding of what it means to be an observer. "Thatís a question we donít often bother to analyze when weíre doing physics," says Weinstein. "Iím localized I can go here, or here, or here, and I canít be in two places at the same time and you take all that for granted. But how do you represent experience in multiple times?"
But Bars argues that the biggest issue that Weinstein will have to look into is that his formulation is not open to "ghosts," that is, that it does not allow unphysical negative probabilities. "This is the main issue that stopped other physicists," he says.
Nonetheless, Weinstein hopes that more physicists will investigate multiple dimensions in time because the rewards in terms of unifying physics would be huge. But even if, in the end, Weinstein finds that time is simply one-dimensional, that will raise new questions. "That would be interesting too because in that way it would be essentially different from space," he says. And the philosopher in him can occupy himself with trying to work out why.
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AMIRA RAJPUT wrote on March 19, 2013
I forgot to add my name ;-) March 19, 2013 post
ANONYMOUS wrote on March 19, 2013
I agree and have experienced being in another 'space' not of this world. My soul left my body at 2 am in the morning one night, and I was conscious to the whole experience. I'm a follower of Jesus Christ and truly believe there are multiple dimensions of time. Christians are being formed into the image of Christ, learning how to obtain God's promises that were already completed in our lives, hence the problem in "trying to get" what Jesus already died to give us, keeping people stuck in...
CAREY R. CARLSON wrote on July 17, 2011
read all article comments
Causal Set Theory is fully discrete and has only time-ordering relations in it-- no spatial relations. For a reconstruction of physics using time alone as the only parameter, see the following posting.
Causal Set Theory and the Origin of Mass-ratio
The theory arises from Russell and Whitehead, who understood that the limiting velocity means that spatial relations, which are instantaneous, have no role in physics. Causal sets are the formalization of Russell's "causal skeleton"...