Weird Sci­ence

Weekend Herald - - Science & Tech - With Her­ald sci­ence writer Jamie Mor­ton @jamien­zher­ald

Hawk­ing’s fi­nal the­ory on the uni­verse

The uni­verse is fi­nite and far sim­pler than many 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 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.

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.

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.

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.

Why se­niors are eas­ily dis­tracted

Re­searchers have pin-pointed the re­gion in the brain, re­cently re­vealed as the epi­cen­tre 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 brain stem 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 age­ing — and the study found that older adults are even more susceptible to dis­trac­tion un­der stress, or emo­tional arousal, in­di­cat­ing that the 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?

Sci­en­tists have ex­plained what makes ice and snow so slip­pery — and it’s a lit­tle more com­pli­cated than you might think.

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 -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 -100C.

The re­searchers say 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.

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 tem­per­a­ture­de­pen­dence 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.

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