The universe is finite and far simpler than many current theories about the "big bang" - that's according to the late Professor Stephen Hawking's final work on how it all began 13.8 billion years ago.

The famed cosmologist's theory, which he worked on in collaboration with Professor Thomas Hertog of Belgium's KU Leuven, has been published two months after his death and nearly a year after it was first announced.

Modern theories of the big bang predict that our local universe came into existence with a brief burst of inflation - in other words, a tiny fraction of a second after the big bang itself, the universe expanded at an exponential rate.

It is widely believed, however, that once inflation starts, there are regions where it never stops.

Advertisement

It is thought that quantum effects can keep inflation going forever in some regions of the universe so that globally, inflation is eternal.

The observable part of our universe would then be just a hospitable pocket universe, a region in which inflation has ended and stars and galaxies formed.

"The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean," Hawking explained in one of his last interviews.

"The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse.

"But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can't be tested."

In their new paper, Hawking and Hertog say this account of eternal inflation as a theory of the big bang is wrong.

"The problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein's theory of general relativity and treats the quantum effects as small fluctuations around this," Hertog said.

"However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics.

"As a consequence, Einstein's theory breaks down in eternal inflation."

The two scientists thus predicted that our universe, on the largest scales, was reasonably smooth and globally finite, and not a fractal structure.

Hertog now planned to study the implications of the new theory on smaller scales that were within reach of our space telescopes.

He believed that primordial gravitational waves - or ripples in spacetime - generated at the exit from eternal inflation offered the most promising "smoking gun" to test the model.

Why seniors are easily distracted

Researchers have pin-pointed the region in the brain, recently revealed as the epicenter for Alzheimer's disease, that may be to blame for distraction in the elderly. Photo / 123RF
Researchers have pin-pointed the region in the brain, recently revealed as the epicenter for Alzheimer's disease, that may be to blame for distraction in the elderly. Photo / 123RF

There's an old joke about the elderly person who began one task in the morning, got distracted by hundreds of others one after another, and by evening hadn't got anything done.

Now researchers have pin-pointed the region in the brain, recently revealed as the epicenter for Alzheimer's disease, that may be to blame for distraction in the elderly.

A US study found seniors' attention shortfall is associated with the locus coeruleus, a tiny region of the brainstem that connects to many other parts of the brain, and helps focus brain activity during periods of stress or excitement.

Increased distractibility is a sign of cognitive aging - and the study found that older adults are even more susceptible to distraction under stress, or emotional arousal, indicating that the nucleus's ability to intensify focus weakens over time.

"Trying hard to complete a task increases emotional arousal, so when younger adults try hard, this should increase their ability to ignore distracting information," said Professor Mara Mather, of the University of Southern California.

"But for older adults, trying hard may make both what they are trying to focus on and other information stand out more.

"The locus coeruleus appeared to be one of the earliest sites of tau pathology - the tangles that are a hallmark of Alzheimer's disease.

"Initial signs of this pathology are evident in the locus coeruleus in most people by age 30," Mather said.

"Thus, it is critical to better understand how locus coeruleus function changes as we age."

What makes ice slippery?

While the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood. Photo / File
While the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood. Photo / File

Just in time for the first round of black ice crashes, scientists have explained what makes ice and snow so slippery - and it's a little more complicated than you might think.

And while the fact that the ice surface is slippery is widely acknowledged, it is far from being completely understood.

In 1886 Irish physicist John Joly offered the first scientific explanation for low friction on ice; when an object - such as an ice skate - touches the ice surface the local contact pressure is so high that the ice melts thereby creating a liquid water layer that lubricates the sliding.

The current consensus is that although liquid water at the ice surface does reduce sliding friction on ice, this liquid water is not melted by pressure but by frictional heat produced during sliding.

A team of German and Dutch researchers have now demonstrated that friction on ice is more complex than so far assumed.

Through macroscopic friction experiments at temperatures ranging from 0C to minus 100C, the researchers show that - surprisingly - the ice surface transforms from an extremely slippery surface at typical winter sports temperatures, to a surface with high friction at minus 100C.

To investigate further, the researchers performed spectroscopic measurements of the state of water molecules at the surface, and compared these with molecular dynamics (MD) simulations.

This combination of experiment and theory revealed that two types of water molecules exist at the ice surface: water molecules that are stuck to the underlying ice, or bound by three hydrogen bonds, and mobile water molecules bound by only two hydrogen bonds.

These mobile water molecules continuously rolled over the ice - like tiny spheres - powered by thermal vibrations.

As the temperature increased, the two species of surface molecules were interconverted: the number of mobile water molecules was increased at the expense of water molecules that are fixed to the ice surface.

Remarkably, this temperature driven change in the mobility of the topmost water molecules at the ice surface perfectly matched the temperature-dependence of the measured friction force, meaning the larger the mobility at the surface, the lower the friction, and vice versa.

The researchers therefore concluded that, rather than a thin layer of liquid water on the ice, the high mobility of the surface water molecules was responsible for the slipperiness of ice.