Universe's watch could need winding?

[Terralthra]

The idea that time itself could cease to be in billions of years - and everything will grind to a halt - has been set out by Professor José Senovilla, Marc Mars and Raül Vera of the University of the Basque Country, Bilbao, and University of Salamanca, Spain.

The motivation for this radical end to time itself is to provide an alternative explanation for "dark energy" - the mysterious antigravitational force that has been suggested to explain a cosmic phenomenon that has baffled scientists.

A decade ago, astronomers noticed that distant supernovae - exploding stars on the very fringes of the universe - seemed to be moving faster than those nearer to the centre, suggesting that they were accelerating as they shot through space.

Dark energy was suggested as a possible means of powering this acceleration of the expansion of the cosmos.

The problem is that no-one has any idea what dark energy is or where it comes from, and theoreticians around the world have been scrambling to find out what it is, or get rid of it.

The team's proposal, which will be published in the journal Physical Review D, does away altogether with dark energy. Instead, Prof Senovilla says, the appearance of acceleration is caused by time itself gradually slowing down, like a clock that needs winding.
advertisement

"We do not say that the expansion of the universe itself is an illusion," he explains. "What we say it may be an illusion is the acceleration of this expansion - that is, the possibility that the expansion is, and has been, increasing its rate."

Instead, if time gradually slows "but we naively kept using our equations to derive the changes of the expansion with respect of 'a standard flow of time', then the simple models that we have constructed in our paper show that an "effective accelerated rate of the expansion" takes place."

While the change would be infinitesimally slow from an ordinary human perspective, from the grand perspective of cosmology - in which scientists study ancient light from suns that shone billions of years ago - this temporal slowing could be easily measured.

Astronomers are able to discern the expansion speed of the universe using the so-called "red shift" technique.

The principle is the same as that of an ambulance siren which gets higher as it comes towards the listener but lower as it moves away. Similarly, a star moving away appears redder in colour than one moving towards us.

Scientists look for exploding stars - supernovae - of certain types that provide a benchmark to work against.

However, the accuracy of these measurements depend on time remaining invariable throughout the universe.

If time is indeed slowing down, so that according to this new suggestion our solitary time dimension is slowly turning into a new space dimension, then the far-distant, ancient stars seen by cosmologists would therefore, from our perspective, look as though they were accelerating.

"Our calculations show that we would think that the expansion of the universe is accelerating," says Prof Senovilla.

The group bases its idea on one particular variant of superstring theory, a so called theory of everything, in which our universe is confined to the surface of a membrane, or brane, floating in a higher-dimensional space, known as the "bulk".

In some number of billions of years, time would cease to be time altogether - and everything will stop.

"Then everything will be frozen, like a snapshot of one instant, forever," Prof Senovilla tells New Scientist magazine. "Our planet will be long gone by then."

However, he adds that the team is only assuming there is one dimension of time. Itzhak Bars of the University of Southern California in Los Angeles has put forward the bizarre suggestion that there are two dimensions of time, not the one that we are all familiar with.

Prof Senovilla says: "One thing that is definitely not included in our models is the possibility of having more than one time dimension."

While the theory is outlandish, it is not without support. Prof Gary Gibbons, a cosmologist at Cambridge University, believes the idea has merit. "We believe that time emerged during the Big Bang, and if time can emerge, it can also disappear - that's just the reverse effect," he says.

"The wonderful thing about these explanations is that, strange as they sound, the Large Hadron Collider could provide evidence for extra dimensions in the universe," comments Dr Brian Cox of Manchester University, referring to the atom smasher in Geneva that will start up next year.

"If that happens, then these kind of theories will move out of the realm of speculation and into the mainstream."

link

[Zablorg]

I fucking hate thinking about the end of the universe. The end of me, humanity, the earth, I can deal with, but the entire of existence grinding to a halt, or running out of energy just makes me feel dead inside.

This theory of time just stopping is very interesting. In the far future, we will be able to utilize this effect to preserve foods forever!

[Edi]

If the universe exploded from the single point of origin in all directions and is expanding, then it's in one sense very much like dots painted on a deflated balloon. And when you blow the balloon full of air, it's surface stretches and expands, causing the dots to move away from each other. The further the inflation, the faster the dots move away from each other even though time is constant. Some of these issues were discussed in the thread I linked from the source of the laws of physics thread and the explanations there seemed far more convincing to me than the stuff so briefly and vaguely mentioned in this article.

[Terralthra]

I'll freely admit I'm not a cosmology expert, but it seems that the deflated balloon analogy is one attempt to explain the accelerating expansion of spacetime. The time dimension changing its rate would be another explanation - the same rate of expansion when viewed through a slowing time dimension would appear to be accelerating.

I imagine it like looking at two graphs. One is y = x^2 (arbitrary exponential growth) on standard graph paper, while the other is the line y = x plotted on graph paper with a standard y axis but the x-axis has lines drawn at log base 2 intervals. The graphs would look the same, but for entirely different reasons, and without being able to measure the rate at which time passes independent of the inertial frame, there'd be no way to tell the difference, I think.

Feel free to correct me if I'm wrong.

[Dooey Jo]

So instead of dark energy, they invent weirdo time-stopping energy? Wasn't the string theories supposed to be able to explain dark energy anyway?

[Kuroneko]

A somewhat more accurate but still easily visualizable analogy would be a curve in (t,x)-space. The curve might at some point "curve away from" the t-direction and start traveling in the x-direction only. Or, to revise the situation for a bit more accuracy, suppose the (t,x)-plane is Minkowski and the curve is at least differentiable. Then the portions of the curve for which the tangent vector is within the lightcone are timelike and those outside are spacelike.

That's what the scenario is talking about, only with a lot more dimensions and structure to go around. Instead of a plane, it's another Lorentzian manifold (the "bulk", having one temporal dimension and lots of spatial dimensions), and rather than a curve, our universe is a four-dimensional submanifold of that bulk. Apparently, they have a model in which the universe "curves away from time", i.e., stops being Lorentzian and becomes fully Euclidean. Since the metric changes signature, it must be degenerate somewhere.

Needless to say, there is very little reason to think that anything like this would actually happen. Even if string theory becomes a bit more empirically-minded, it's far from enough to have an accelerating universal expansion. In terms of the universal scale factor a, an accelerating universe means a"a/a'² is positive. Note that this doesn't mean that any of a, a', or a" diverge in finite time. If a does diverge in finite time, we get the "big rip"; what this news seems to indicate is that string theory allows for a new kind of pathology: a' diverges in finite time (and therefore so does the Hubble parameter), but a itself does not.

Internally, what happens is that dark energy density becomes infinite, but in such a way that it fails to rip everything apart before that happens. I think. If that's so, time 'stopping' would be a fairly accurate description.

[Gustav32Vasa]

This theory of time just stopping is very interesting. In the far future, we will be able to utilize this effect to preserve foods forever!

Zero Tau?