Time Dimension To Become Space-like

KentuckyFC writes "The Universe is about to flip from having three dimensions of space and one of time to having four dimensions of space. That's the conclusion of a group of Spanish astrophysicists who have calculated that observers inside such a Universe would see it expanding and accelerating away from them just before the flip (abstract, full paper pdf on the physics arXiv). 'We show that regular changes of signature on brane-worlds in AdS bulks may account for some types of the recently fashionable sudden singularities. Therefore, the fact that the Universe seems to approach a future sudden singularity at an accelerated rate of expansion might simply be an indication that our braneworld is about to change from Lorentzian to Euclidean signature. Both the brane and the bulk remain fully regular everywhere.'" Update: 10/09 16:06 GMT by Z : A few readers have written in to point out that the article is not peer-reviewed; your mileage may vary.

Comments

But what does that mean?

[downix]

If time becomes space-like, what would that mean for us? Would we be able to transverse time as easily as space? Would time itself become irrelevent as we could look "forwards"? Will the cubs win the world series? These important questions have to be answered!

Re:But what does that mean?

[inviolet]

> Would we be able to transverse time as easily as space?
Yes!

> Would time itself become irrelevent as we could look "forwards"?
Yes!

In "Slaughterhouse Five", Vonnegut wrote about creatures who perceived time as a geometric dimension. They could perceive their entire lives as a wide landscape, stretching from past to present to future... and they could move freely within it, to relive the better moments and fast-forward over the unpleasant ones.

One of the implications that these creatures could see, but which we could not, is that the universe can only play out one way. Whatever happens, has always happened, and always will happen, it is unavoidable. The creatures could see their future with absolute certainty, and so they knew that choice is an illusion (or, in my understanding, a mis-connotated word that belongs in the realm of epistemology rather than of metaphysics).

In any case, if the universe experiences this sort of "signature change", then we'll never know it. Consciousness will abruptly cease, like a paused DVD player or a saved Diablo game, waiting forever for time to resume. But, a new sort of consciousness could arise, to which physical movement is the equivalent of temporal progression. Somehow, if it could gather information and then ruminate upon it, by means of movement rather than time, it could become self-aware.

Re:But what does that mean?

[kalirion]

This allows from freedom of choice because you can move all over the realm of time.

But you'd have no control over where in the realm of time you choose to move any more than you have control where in space you choose to move. You can will what to do, but you can't will what to will.

Re:But what does that mean?

[jeffasselin]

The existence of 3 dimensions of time is one of the suggestions of quantum gravity.

Also, why does time seem to flow into a single direction? Most of the equations of physics work fine both ways, but time only appears to flow in a single direction, only its "pace" changes. The best explanation is that there's a breaking of symmetry, a process which for some reason only occurs in one direction of the time dimension(s). The only such process we can observe at this time is entropy. In a closed system, it always increases, it can never decrease. So entropy seems to be linked to time in some intricate way, or maybe it's actually an extra time dimension linked to the first in some way. So what happens if time changes into a space dimension? What does that even MEAN? The only significant difference between time and space is that single direction in which time flows, so does it mean the second law of thermodynamics will stop applying? The flow of entropy will reverse or break its link to the time dimension? This would not necessarily be so "bad" but it would completely break down most of the laws of physics that depend on this phenomenon, thus destroying the universe, no?

Re:But what does that mean?

[Ashtead]

"Look" at all? Won't electromagnetism fail at this point too when the photons stop dead, so there won't be anyone left to look for or at anything? Not that there would be any way to see anything either. After all, it is electromagnetism that really holds atoms, molecules, and thus people, planets, and stars together ...

Will it look like the langoliers finishing off the reality starting at one edge, or will it be like the encounter with the Boojum "softly and suddenly vanish away"?

Or maybe it just will be a party lasting indefinitely at a restaurant at the end of the universe.

Re:But what does that mean?

[kalirion]

In "Slaughterhouse Five", Vonnegut wrote about creatures who perceived time as a geometric dimension. They could perceive their entire lives as a wide landscape, stretching from past to present to future... and they could move freely within it, to relive the better moments and fast-forward over the unpleasant ones.

Movement is change, and change requires time. To move from one time to another, you need some kind of "metatime". To move through that, you'd need "metametatime" and so forth. Without change, you can't decide to "relive" the better moments because you've already lived them, are currently living them, and will always live them. You'd either exist everytime through your life "simultaneously" or just in the same moment. With metatime your existence would still be linear, no matter how many jumps and zigzags you make through ordinary time. Say you time travel 1985 -> 1955 -> 1985 -> 2015 -> 1985 -> 1955 -> 1885. That would be your linear metatime progression, and that's the one your memories will follow.

Anyway, that's the only way it would make sense to me :)

Re:But what does that mean?

[kalirion]

You're absolutely right. There is an underlying assumption that right now we are moving linearly through time. However you have to consider that if we were bouncing around, it wouldn't make any difference to us. I mean, what's doing the bouncing? At each point, as you've said, we have our memories of the past and not the future. As far as I'm concerned, that is me, the memories, the remembered experiences, whatever the current state is. Past bounces and future bounces would have zero affect on the present. It's always the current bounce that would matter and nothing else.

To take it further, The memories present in each bounce could be completely unrelated to any events at any time. There might be no cause and effect at all, rendering "past" and "future" meaningless terms.

Hell, instead of bouncing around, we could be stuck within the same moment and not know the difference. That's what might happen when time is gone, and it "already" might be. Might "always" have been in fact.

Re:But what does that mean?

[Anonymous Coward]

We are entirely physical,

Correct.

deterministic

Incorrect. The particles comprising our bodies can only be determined within a probability distribution, with the Heisenberg uncertainty principle providing the lower limit to observation.

machines.

Re:But what does that mean?

[ultranova]

The only such process we can observe at this time is entropy. In a closed system, it always increases, it can never decrease.

In a closed system entropy can and does decrease from time to time. It is simply much more likely to increase, due to there being more possible states with high entropy than there are states with low entropy in known physical systems, and the likelihood of it decreasing in a given period decreases sharply as the complexity of the system grows. It never goes to zero, thought.

A classical example is a box with two separate gasses, initially separated by a dividing wall. If the wall is removed, the gasses will mix, eventually spreading equally to every part of the box. However, suppose that the box only contains a single molecule of both gasses. It is certainly possible, and even likely, that both molecules happen to be at their initial side of the box, and both gassed therefore separated back to their own sides, at some future point. Add another molecule to both gassed, and you'll have to wait a bit longer for all four to be at their initial sides, but still not too long. A third molecule, and it takes longer still, then fourth, fifth and so on.

The more molecules you add, the longer you'll have to wait. However, no matter how many molecules there are in the box, given a long enough time, the gasses will separate, simply due to random motion of the molecules happenign to take all the molecules of one gas to one side of the box at the same time, and all the molecules of the other gas to the other side at the same time.

It will take almost, but not quite, forever, but that's a far cry from "never".

So how does this affect us?

[icebrain]

So what does this mean for us, exactly? Would we still perceive things as we do now (only with some relativistic stuff changing), or does everything suddenly go nuts? FTL travel, maybe?

And mostly-OT but seemed related: I remember a couple of SF short stories about something like this... one was "Mimsy were the Bogroves" or something like that, where two kids discover 4-dimensional toys from the future, then read "Jabberwocky" and figure out how to move in time.

The other one was about a kid who befriends a neighbor working in 4-D stuff. The kid (because he's young and has an open mind or something) learns to move about in that dimension as well, and communicate with creatures living in other dimensions. Don't remember the title of that one, thoguh.

Re:Explanation?

[xPsi]

Lets say I told you we had two spatial dimensions. You would imagine a plane with perpendicular x-y axes everyone knows and loves. If I asked you to draw the set of points that were equidistant from the origin, you would probably assume the geometry was Euclidian and would probably instinctively draw a circle (a good guess!). It is commonplace to hear "time is the fourth dimension." As first pass to visualize this, you might try to draw a two dimensional space-time plot: an x axis and a perpendicular time axis in a plane. If I then asked you to draw all the points equidistant from the origin, you would probably again draw a circle in this x-t plane. It seems to make sense, but is only true of time is a "space-like" dimension like "y" in the x-y plane. This is way Newton thought of things and it seems to be what the authors of the paper are advocating. But, unbeknownst to some people who cite "time as the fourth dimension," according to the theory of relativity, the set of equidistant points from the origin on a x-t graph would actually be hyperbole, not circles. This is because in relativity space-time is a Minkowski geometry, not Euclidian. All the weird stuff in special relativity like time dilation and length contraction come about because of this weird geometry. In fancier language, time has an opposite sign than space in the metric. The metric determines how distances are calculated in a given geometry. If time has the same sign as space in the metric, then space-time becomes Euclidian and one would say that time was a space-like. The article is probably extra confusing to non-physics people because most probably didn't know time wasn't space-like to begin with.

Hope not.

[mattr]

I knew 3 answers to the Fermi Paradox. Either intelligence quickly builds into quiet-looking shells like in Charlie Stross' Accelerando, or by virtue of being conscious we humans have somehow carved out a light cone or domain excluding other intelligences, some wierd cocoon: it is impossible physically to communicate because other domains have other physics. There's a neat scifi story about that too. The third is a land mine in physics, waiting for young civilizations to liberate enough power to fry them. Heinlein did that one, it's a nasty one. Now a fourth: the universe really is out to get us. Not just out to get aggressive monkeys that want to learn high-energy physics, but even to the point of making a state flip ever so often. I think this last one (today's news) is pretty unlikely to happen any time soon but nevertheless it is a future killer, something harder to understand than the burning out of the stars in the far future. None of these are very nice ideas but I hope some physicists will step up to answering what the latest theory says about when it might happen and whether it could operate on a patchwork basis, killing other civilizations while our planet was still cooling.

Re:Hope not.

[Ristol]

All wrong. See, in the future, we're gonna create robots whose only goals are the well-being of humanity. They'll eventually realize that it would benefit us if we were the only intelligent race in the galaxy. So when they eventually become omnipotent, they'll travel back in time and 'choose' a universe for us in which Earth hosts the only life-forms.
Seriously, I read it in a book!

My crude guess

[khallow]

It appears to me that this is a purely mathematical result. They are basically saying that an anti-de sitter bulk, the interior of anti de Sitter (AdS) space which is a constant negatively curved (or constant positive cosmological constant) with one time-like dimension (Lorentzian space) can be glued to a euclidean space smoothly along the boundary of the two spaces. Classically, this is of little relevance since time-based trajectories would stop at the boundary (either take infinite time to arrive or the system would "rip" itself apart at the boundary). Instead there could be (though not addressed in the paper) observable quantum effects from having something past the boundary even if it is purely spatial. Space-time states might extend over the boudary into this other space. So you might end up with the strange situation where parts of the universe are interacting beyond the end of time.

This paper doesn't tell you whether that occurs or not. But it does indicate that it is possible for quantum systems to have both Lorentzian and Euclidean space components seamlessly connected.

Time speeding up

[Skevin]

When I first heard that the rate of the universe's expansion was actually accelerating, I came up with a weird hypothesis after a few days...

Time in our frame of reference is slowing down.

The only way that seemed possible was if we were traveling at speeds close to c, but that didn't sound feasible since we were observing objects that were moving away from us, in all directions. Then another weird thought occurred to me...

Our observed universe is self-contained within the event horizon of a giant black hole.

We're closer to the singularity, and accelerating towards it faster than objects closer to the edge of the event horizon. Time will move slower for us, and far away objects will appear to speed up. An outside observer (if such a thing could possibly exist) would perceive our universe as shrinking, but in our current frame of reference, we still think of it as expanding.

One other observation that lends to this possibility is the fact that we have not seen evidence of other "Big Bangs" or other "Universes". If the Big Bang happened once, shouldn't it be a repeatable occurrence in the limitless void of space?

Okay, that's my rant. You can slap the straitjacket on me now and ship me off to the funny farm.

Solomon Chang

Re:Time speeding up

[addbo]

Interesting when I took astronomy in University I had the same hypothesis that the Universe itself is a black hole.

One of the unintuitive properties of a black hole is that as mass increases the average density inside the Schwarschild radius decreases... even though the radius itself increases. Anyways as Mass goes to infinity, Density inside the Schwarschild radius goes to Zero and of course the Radius goes to infinity.

The radius of the known Universe along with the mass that is hypothesized almost satisfy the Schwarschild radius equation and is only off by a factor of 2 or 3.(Which isn't much in Astronomy)

Re:Mayan Calender

[MarsDefenseMinister]

That particular problem can be solved by defining time as a big rubber band that *doesn't* break. Simple.

Re:Assumptions

[ShieldW0lf]

If the universe isn't infinite, but just gigantic, and there are multiple dimensions, rather than just one, and time branches into multiple dimensions in response to possibilities, one dead cat and one live cat instead of one cat floating in an indeterminate state, then that would imply that the universe is a finite set, time is a path through permutations of that set, and time travel would consist of mapping these permutations to a degree that one is able to follow non-obvious and improbable paths through the set.

Re:Mayan Calender

[eclipz]

I am also not a professional. However...

The paper describes the time dimension heading toward a singularity. So, we'll get the universe rapidly expanding outward faster and faster. However, there will be a point at which there is a "big freeze", where time will stop. However, there is no 'experience' of time stopping. Instead, we would experience time as normal as we are attached to it, and would have no clue that we can go no further. There is a very interesting description of this in "Einstein's Dreams".

So, putting it into your explaination, all that spaghetti rotating in the forth dimension would keep doing so. Only an observer *outside* of time could ever see the change in the brane-space and only they would ever see the stuck versions of ourselves at the point of the signature change.