Caught up in string

Is this the dawning of a `second revolution' in string theory? Supporters say it's a unified theory of physics. Others say it is all philosophy. By Dan Falk

Just as the world of fashion cycles around various vogues, so in science theories come and go in terms of their popularity. Just as flared trousers have come in, gone out and come back, so string theory has ebbed and, now, flowed back in to the mainstream.

Many people have heard of string theory, but few can really describe it. Simply put, it is one of the candidates to produce an all-encompassing "theory of everything" - a single theory that can explain the observed behaviour of the physical universe, from quarks to quasars.

Presently, physical science rests on two tremendously successful but separate theories. The first is Einstein's theory of gravity, known as general relativity, which describes the behaviour of matter over large distances. The other is quantum mechanics, which governs the sub-atomic world. So far, like an unwilling bride and groom resisting a forced marriage, the two have defied all attempts at unification.

But in the past two years more and more scientists have begun to take string theory seriously, thinking it has begun to offer a glimpse of what that fiery marriage might be like. The theory itself is a mathematical framework, in which matter is represented by tiny, one-dimensional loops of string rather than particles. It is, fundamentally, a quantum theory. But at the same time, supporters say that gravity emerges as a natural feature of the string representation. Proponents believe it's the best bet for a unified theory of physics.

The strings at the heart of the theory are unimaginably small - some hundred million million million (1020) times smaller than an atomic nucleus. According to the theory, as these strings vibrate they give rise to the properties of the various observed particles - just as a violin string, depending on the way it vibrates, can produce a range of musical notes. A string vibrating a certain way, for example, could appear as an electron; another mode of vibration might give rise to a photon of light.

The roots of string theory go back several decades; in fact, it had somewhat of a heyday in the early Eighties, when supporters first hailed it as a possible "theory of everything". About 10 years ago, however, string theory seemed to have gone limp. It had become tangled in a mess of mathematics, and made few predictions that could be independently tested. To compound the difficulty, it seemed to split up into five theories rather than one.

But a series of advances over the past 18 months has put strings back in the spotlight. Supporters are calling it the "second revolution" in string theory.

The most remarkable find came last June, in a discovery that brought string theorists face to face with a problem from the front lines of modern cosmology. At centre stage are the ultra-dense remnants of collapsed stars, known as black holes. For the first time, researchers showed how to count what are called the quantum states of a black hole - a measure of how these esoteric objects are structured on a microscopic scale. When the calculation was carried out and the result agreed with a prediction made by Cambridge physicist Stephen Hawking, using a different method in the mid-Seventies, it was hailed as a triumph for string theory.

A second advance has been the discovery that the five versions of string theory that once prevailed are, in fact, equivalent. They are now recognised as different formulations of the same mathematical structure.

With these developments, many of those who were once ready to bury string theory have now come to praise it - and that includes Hawking himself. Just two years ago, he dismissed the theory as "pretty pathetic", but at a conference in Chicago in December, Hawking devoted a substantial portion of his talk to the intricacies of string theory. He stopped short of an all-out endorsement, but he was impressed with the new quantum-state result, describing it as the first "credible mechanism" for explaining the microscopic structure of black holes. The quantum-state measurement has made a deep impression on many scientists. "That is such a remarkable confirmation, emerging from a very different concept ... that there has to be something right about it," says Stuart Shapiro, an astronomer and physicist at the University of Illinois. "String theory, if it's not the final quantum theory of gravity, is on the right track - it has the seeds of something true. And I say that as a long-time sceptic of exotic theories."

Martin Rees, an astrophysicist at Cambridge and Britain's current Astronomer Royal, concurs: "It certainly seems clear that it's the most fruitful approach to the idea of understanding the relationship between the different forces - to relate gravity, electric forces, and nuclear forces, and lead toward a unified theory. And if it does succeed, it will be of course a fantastic development in understanding the world."

While the potential of string theory seems immense, it has a number of hurdles to clear before it can reach widespread acceptance. Most importantly, it has yet to be tested against direct observation. In fact, the energy required for such a test is far beyond the capability of even the largest particle accelerators. Critics of the theory say it is not "falsifiable" - that is, it cannot be shown to be wrong - and therefore is not a genuine scientific theory.

"If you can't show it's wrong, it's not science - it's merely philosophy or mathematics," says Glenn Starkman, a particle physicist and cosmologist at Case Western Reserve University in Ohio. String theory, he says, is beginning to solve theoretical problems, but is still a long way from experimental verification. And that, Starkman says, is "what holds many people back from being true believers".

For Roger Penrose, a mathematical physicist at Oxford, even the black hole calculation should be taken with a grain of salt. "I think it's a common phenomenon in physics that you're working away at something, and something works better than you expect, and you say, `gosh, it's a miracle - there must be some real truth hiding behind there.' And there may well be, but that doesn't mean it's a theory, as it stands."

One of the string theorists' more pressing tasks is the job of simplifying their work, which remains so mathematically complex that few outside the field can comprehend it. Edward Witten, a leading string theorist and physicist at Princeton's Institute for Advanced Study, says he looks forward to the day when string theory will be taught to undergraduates, as the basics of quantum mechanics and relativity are today.

For now, the theoreticians will continue to take their calculations where no mathematics has gone before. Their great challenge is to convince outsiders that their equations actually describe the real world. Only then will it be possible to decide if a "theory of everything" is truly on the horizon - or if it's just another phase of scientific fashionn

Dan Falk is a science journalist based in Toronto, Canada.

PROMOTED VIDEO
News
ebooksAn unforgettable anthology of contemporary reportage
Life and Style
Britons buy more than 30 million handsets each year, keeping them for an average of 18 months
tech
Arts and Entertainment
Alloysious Massaquoi, 'G' Hastings and Kayus Bankole of Young Fathers are the surprise winners of this year's Mercury Music Prize
musicThe surprise winners of the Mercury Prize – and a very brief acceptance speech
Arts and Entertainment
TV Presenters Ant McPartlin and Dec Donnelly. Winners of the 'Entertainment Programme' award for 'Ant and Dec's Saturday Night Takeaway'
musicAnt and Dec confirmed as hosts of next year's Brit Awards
Arts and Entertainment
Orson Welles made Citizen Kane at 25, and battled with Hollywood film studios thereafter
film
News
video
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Primary Teachers Required in King's Lynn

Negotiable: Randstad Education Cambridge: Primary Teachers needed in King's Ly...

Primary Teachers needed in Ely

Negotiable: Randstad Education Cambridge: Primary Teacher needed in the Ely ar...

Teaching Assistant to work with Autistic students

£60 - £65 per day: Randstad Education Leicester: Randstad Education Leicester ...

KS2 Teacher

Negotiable: Randstad Education Cambridge: KS2 Teacher needed in Peterborough a...

Day In a Page

Isis in Syria: A general reveals the lack of communication with the US - and his country's awkward relationship with their allies-by-default

A Syrian general speaks

A senior officer of Bashar al-Assad’s regime talks to Robert Fisk about his army’s brutal struggle with Isis, in a dirty war whose challenges include widespread atrocities
‘A bit of a shock...’ Cambridge economist with Glasgow roots becomes Zambia’s acting President

‘A bit of a shock...’ Economist with Glasgow roots becomes Zambia’s acting President

Guy Scott's predecessor, Michael Sata, died in a London hospital this week after a lengthy illness
Fall of the Berlin Wall: History catches up with Erich Honecker - the East German leader who praised the Iron Curtain and claimed it prevented a Third World War

Fall of the Berlin Wall

History catches up with Erich Honecker - the East German leader who praised the Iron Curtain and claimed it prevented a Third World War
How to turn your mobile phone into easy money

Turn your mobile phone into easy money

There are 90 million unused mobiles in the UK, which would be worth £7bn if we cashed them in, says David Crookes
Independent writers remember their Saturday jobs:

Independent writers remember their Saturday jobs

"I have never regarded anything I have done in "the media" as a proper job"
Lyricist Richard Thomas shares his 11-step recipe for creating a hit West End musical

11-step recipe for creating a West End hit

Richard Thomas, the lyricist behind the Jerry Springer and Anna Nicole Smith operas, explains how Bob Dylan, 'Breaking Bad' and even Noam Chomsky inspired his songbook for the new musical 'Made in Dagenham'
Tonke Dragt's The Letter for the King has finally been translated into English ... 50 years on

Buried treasure: The Letter for the King

The coming-of-age tale about a boy and his mission to save a mythical kingdom has sold a million copies since it was written by an eccentric Dutchwoman in 1962. Yet until last year, no one had read it in English
Can instilling a sense of entrepreneurship in pupils have a positive effect on their learning?

The school that means business

Richard Garner heads to Lancashire, where developing the 'dragons' of the future is also helping one community academy to achieve its educational goals
10 best tablets

The world in your pocket: 10 best tablets

They’re thin, they’re light, you can use them for work on the move or keeping entertained
Lutz Pfannenstiel: The goalkeeper who gave up Bayern Munich for the Crazy Gang, Bradford and a whirlwind trawl across continents

Lutz Pfannenstiel interview

The goalkeeper who gave up Bayern Munich for the Crazy Gang, Bradford and a whirlwind trawl across continents
Pete Jenson: Popular Jürgen Klopp can reignite Borussia Dortmund’s season with visit to Bayern Munich

Pete Jenson's a Different League

Popular Klopp can reignite Dortmund’s season with visit to Bayern
John Cantlie video proves that Isis expects victory in Kobani

Cantlie video proves that Isis expects victory in Kobani

The use of the British hostage demonstrates once again the militants' skill and originality in conducting a propaganda war, says Patrick Cockburn
The killer instinct: The man who helps students spot potential murderers

The killer instinct

Phil Chalmers travels the US warning students how to spot possible future murderers, but can his contentious methods really stop the bloodshed?
Clothing the gap: A new exhibition celebrates women who stood apart from the fashion herd

Clothing the gap

A new exhibition celebrates women who stood apart from the fashion herd
Fall of the Berlin Wall: Goodbye to all that - the lost world beyond the Iron Curtain

The Fall of the Berlin Wall

Goodbye to all that - the lost world beyond the Iron Curtain