Will Time be Replaced by Another Space Dimension?

world_line.thumbnail.png

What if time disappeared? Yes, it sounds like a silly question – and if the cosmos sticks to the current laws of physics – it’s a question we need never ask beyond this article. Writing this article would in itself be a waste of my time if the cosmos was that simple. But I’m hedging my bets and continuing to type, as I believe we have only just scratched the surface of the universal laws of physics; the universe is anything but simple. There may in fact be something to this crazy notion that the nature of the universe could be turned on its head should the fundamental quantity of time be transformed into another dimension of space. An idea like this falls out of the domain of classical thought, and into the realms of “braneworlds”, a view that encapsulates the 4-dimensional universe we know and love with superstrings threaded straight through…

Brane theory is a strange idea. In a nutshell, a brane (short for “membrane”) can be viewed as a sheet floating in a fifth dimension. As we can only experience three dimensional space along one dimension of time (four dimensional space-time, a.k.a. a Lorentzian universe), we cannot understand what this fifth dimension looks like, but we are fortunate to have mathematics to help us out. Mathematics can be used to describe as many dimensions as we like. Useful, as branes describe the cumulative effect of “strings” threading through many dimensions and the forces interacting to create the universe we observe in boring old three dimensional space. According to the “braneworld” view, our four dimensional cosmos may actually be embedded within a multidimensional universe – our cosmic version only uses four of the many possible dimensions.

Theorists contemplating braneworlds, such as Marc Mars at the University of Salamanca in Spain, now believe they have stumbled on an implication that could, quite literally, stop cosmologists in their tracks. The time dimension could soon be disappearing to be replaced by a fourth space dimension. Our familiar Lorentzian universe could turn Euclidean (i.e. four spatial dimensions, no time) and Mars believes the evidence for the change is staring us in the face.

One of the interesting, and intriguing, properties of these signature-changing branes is that, even though the change of signature may be conceived as a dramatical event within the brane, both the bulk and the brane can be fully smooth. In particular, observers living in the brane but assuming that their Universe is Lorentzian everywhere may be misled to interpret that a curvature singularity arises precisely at the signature change” – Marc Mars, from Is the accelerated expansion evidence of a forthcoming change of signature on the brane?.

The observed expansion of the universe (as discovered by Edwin Hubble in 1925) may in fact be a symptom of a “signature changing” brane. If our brane is mutating from time-like to space-like, observers in the Lorentzian universe should observe an expanding and accelerating universe, exactly as we are observing presently. Mars goes on to detail that this theory can explain this ever increasing expansion, whilst keeping the physical characteristics of the cosmos as we observe today, without assuming any form of dark matter or dark energy is responsible.

It is doubtful that we can ever perceive a time-less cosmos, and what would happen to the universe should time go space-like is beyond our comprehension. So, enjoy your four dimensions while they last, time could soon be running out.

Source: arXiv blog

Supercomputers Pitch in to Search for Missing Matter

2007-1206matter.thumbnail.jpg

I know, I know, you’re probably getting sick of hearing this. Astronomers have no idea what 95% of the Universe is; 70% is dark energy, and 25% is dark matter, leaving a mere 5% normal matter. But it gets worse. Astronomers can only actually account for about 60% of that regular matter (hydrogen, helium and heavier elements) – almost half of the regular matter is missing too!

I’ll repeat that, just so it’s clear. Of the 5% of the Universe that we can even understand, almost half of it is missing too.

Researchers at the University of Colorado at Boulder have used a powerful supercomputer at the San Diego Supercomputing Center to try and figure out where this missing mass could be hiding, and they think they’ve got a good place to look.

They built up a simulation of a huge chunk of Universe, 1.5 billion light-years on a side. Within this simulated Universe, they saw that much of the gas in the Universe forms into a tangled web of filaments that stretch for hundreds of million of light-years. In between these filaments are vast spherical voids without any matter.

The simulation works by modeling how material came together through gravity after the Big Bang. The simulation predicts that this missing material is hiding within gas clouds called the Warm-Hot Intergalactic Medium.

If their predictions are correct, the next generation of telescopes should be able to detect this missing mass in these hidden filaments. Some of these telescopes include the 10-metre South Pole Telescope in Antarctica and the 25-metre Cornell-Caltech Atacama Telescope (CCAT).

The South Pole Telescope will look at how the Cosmic Microwave Background Radiation is heated up as it passes through clouds of this gas. CCAT will be able to look back to periods just after the Big Bang, and see how the first large scale structures started to come together.

At least then, we’ll probably know where all that 5% of regular mass is. Dark matter and dark energy? Still a mystery.

Original Source: CU-Boulder News Release

Podcast: Questions on Inflation

2007-1029questions.thumbnail.jpg

It’s about time for a question show again, so we’ll have one last interruption to our planetary tour, to deal with the questions that arose from our inflation show. So if you still don’t understand inflation, take a listen to this week’s show and as always, send us your questions.
Click here to download the episode

Questions on Inflation – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Podcast: Inflation

2007-1015inflation.thumbnail.jpg

We interrupt this tour through the Solar System to bring you a special show to deal with one of our most complicated subjects: the Big Bang. Specifically, how it’s possible that the universe could have expanded faster than the speed of light. The theory is called the inflationary theory, and the evidence is mounting to support it. Einstein said that nothing can move faster than the speed of light, and yet astronomers think the universe expanded from a microscopic spec to become larger than the solar system, in a fraction of a second.

Click here to download the episode

Inflation – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Before the Big Bang

Researchers have developed a model of a shrinking universe that existed prior to the Big Bang. Image credit: NASA. Click to enlarge
The Big Bang describes how the Universe began as a single point 13.7 billion years ago, and has been expanding ever since, but it doesn’t explain what happened before that. Researchers from Penn State University believe that there should be traces of evidence in our current universe that could used to look back before the Big Bang. According to their research, there was a contracting universe with similar space-time geometry to our expanding universe. The universe collapsed and then “bounced” as the Big Bang.

According to Einstein’s general theory of relativity, the Big Bang represents The Beginning, the grand event at which not only matter but space-time itself was born. While classical theories offer no clues about existence before that moment, a research team at Penn State has used quantum gravitational calculations to find threads that lead to an earlier time. “General relativity can be used to describe the universe back to a point at which matter becomes so dense that its equations don’t hold up,” says Abhay Ashtekar, Holder of the Eberly Family Chair in Physics and Director of the Institute for Gravitational Physics and Geometry at Penn State. “Beyond that point, we needed to apply quantum tools that were not available to Einstein.” By combining quantum physics with general relativity, Ashtekar and two of his post-doctoral researchers, Tomasz Pawlowski and Parmpreet Singh, were able to develop a model that traces through the Big Bang to a shrinking universe that exhibits physics similar to ours.

In research reported in the current issue of Physical Review Letters, the team shows that, prior to the Big Bang, there was a contracting universe with space-time geometry that otherwise is similar to that of our current expanding universe. As gravitational forces pulled this previous universe inward, it reached a point at which the quantum properties of space-time cause gravity to become repulsive, rather than attractive. “Using quantum modifications of Einstein’s cosmological equations, we have shown that in place of a classical Big Bang there is in fact a quantum Bounce,” says Ashtekar. “We were so surprised by the finding that there is another classical, pre-Big Bang universe that we repeated the simulations with different parameter values over several months, but we found that the Big Bounce scenario is robust.”

While the general idea of another universe existing prior to the Big Bang has been proposed before, this is the first mathematical description that systematically establishes its existence and deduces properties of space-time geometry in that universe.

The research team used loop quantum gravity, a leading approach to the problem of the unification of general relativity with quantum physics, which also was pioneered at the Penn State Institute of Gravitational Physics and Geometry. In this theory, space-time geometry itself has a discrete ‘atomic’ structure and the familiar continuum is only an approximation. The fabric of space is literally woven by one-dimensional quantum threads. Near the Big-Bang, this fabric is violently torn and the quantum nature of geometry becomes important. It makes gravity strongly repulsive, giving rise to the Big Bounce.

“Our initial work assumes a homogenous model of our universe,” says Ashtekar. “However, it has given us confidence in the underlying ideas of loop quantum gravity. We will continue to refine the model to better portray the universe as we know it and to better understand the features of quantum gravity.”

The research was sponsored by the National Science Foundation, the Alexander von Humboldt Foundation, and the Penn State Eberly College of Science.

Original Source: PSU News Release