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 Update: 10/09 16:06 GMT by Z : A few readers have written in to point out that the article is not peer-reviewed; your mileage may vary.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

"... about to ..."

[dpilot]

So dpilot was talking with God, and God said, "To Me, a minute is like a million years, and a million years are like a minute." So dpilot said, "In a that vein, is a penny like a billion dollars, and a dollars like a penny?" God replied, "You've got it." Which led dpilot to ask of God, "Can you spare a penny?" "Sure," said God, "in just a minute..."

When you say "about to" in sports, something generally happens pretty fast.
When you say "about to" in geology, something generally happens pretty slow.
Generally speaking, saying "about to" in cosmology is to geology as geology is to sports.

But not always. At some points in time, the volcano under Yellowstone does go off. Likewise, supernovas happen, and perhaps brane changes too. But to say "about to" or "soon" is just meaningless to human scales of time.

Define "about to"?

[WibbleOnMars]

I'd like to know how they define "about to flip".

Are we talking about something they see as imminent -- could happen at any moment?
Or are we talking about geological time scales -- it'll happen in a few hundred thousand years, give or take?
Or do they mean cosmological scales -- where 'about to happen' means somewhere in the next ten or twenty million years?

Or is the whole question of when a silly thing to ask, given that they're talking about the end of time as sequential/chronological?

Consequences

[xPsi]

Ok, as others have pointed out, this "paper" is not peer reviewed. I want to make it clear that I don't personally feel slashdot is the place to debate random physics papers on the arXiv. But, being slashdot, I will ignore my own pleas for sanity. What would be the physical consequences of time suddenly becoming space-like? First, on most mesoscopic scales in our everyday life, time already appears like a spatial dimension. Newton certainly thought so and our (incorrect) intuition tells us this is the case. The degree to which special and general relativity play a role in your everyday life is a measure of how "time-like" time feels. Probably not much. Nevertheless, if time suddenly physically became space-like, physicists all over the world would know it right away. All the weird stuff in relativity like time dilation and space contraction and so on, comes from time having an opposite metric sign as space. These effects all go away if time is space-like. For example, in a typical advanced undergraduate physics lab, you might measure the lifetime of a muon that is sitting in the lab as opposed to one that is crashing down from the sky. The one coming from above (at a large fraction the speed of light) lives longer in the frame of the ground because of time dilation. Easily verified in an afternoon. But I guess no more (at least after next Thursday or whenever this is supposed to happen). Similarly, all the special relativity equations required to perform basic momentum, energy, and lifetime calculations at colliders like Fermilab, CERN, and Brookhaven would suddenly stop working. That would be a big deal and it wouldn't be a subtle thing. IMHO, it makes for great science fiction, but I'm not sure where these guys are going with it.