The Royal Society

2011 Summer Science Exhibition

A Cafe of String and Science

"There was no question too challenging for an honest answer.  One member of the audience asked what had existed before the Big Bang."

Who wants to know about string theory? 

Judging from the packed tent at the 2011 Royal Society Summer Science Exhibition, the answer was a lot of people!

The first Cafe Scientifique of the week drew a tent full of people to hear Dr. David Tong, Research Fellow of the Royal Society and theoretical physicist of Cambridge University, deliver an energetic introduction to the strangely named theory.  Prior to the event, Dr. Tong admitted he had never done a Cafe Scientifique before, but was looking forward to the experience and hoped he could deliver a broad understanding of what string theory was, and how it may be explored in the near future.

The event was hosted by space scientist Dr. Maggie Alderin­-Pocock, who deftly directed dialogue while handling her lively young toddler.  Asked to describe her impression of Cafe Scientifique events, Dr. Maggie said she enjoyed the informal nature and interaction in the events and was looking forward to learning about string theory herself.

Dr. Tong began the event by tackling what string theory was, how it related to other areas of physics, and what developments we could look forward to in the future, thanks to the Large Hadron Collider.  He gave a neat summary of string theory’s fundamental postulate­ “If you could look inside any particle­ really closely, as far down as you could­ what you would find is a single loop of string,” ­ and explained that according to the theory, different fundamental particles of matter were the result of different ranges of string vibrations.  

An audience member asked what the string was made out of.  Dr. Tong gave him three possibilities­ fundamental building blocks, infinitely smaller particles, or simply pure energy.

String theory gained a colourful personality as Dr. Tong described it variously as “a speculative but highly promising idea for the ultimate laws of physics”, a “fairly ludicrous idea” born in the ‘70s, the mathematical product of around 15 years challenging work, and most strikingly­ “A tiny equation that contains every law of physics that mankind has ever discovered throughout history.”  The theory combines physics theories and is the next step from the Standard Model of particle physics, which outlines the motions and properties of particles.  The Standard Model was also personalised by Dr. Tong as “The pinnacle of scientific achievement, marred only by a bland name!”

But is string theory too good to be true?  Dr. Tong confessed that in part, this has always been the case.  Although the mathematics behind this conceptually vivid theory works well, the inability to experimentally test string theory has always been an enduring problem.

Nonetheless, he pointed out that it was the Ancient Greeks who had first proposed the existence of atoms, which have only become visible in the modern age of powerful scanning microscopes.  This brought us nicely to the topic of the world's latest piece of scientific kit and technological crowning glory, the Large Hadron Collider.

One of the most striking predictions of string theory is that there are extra dimensions in our world­ and if so, the Large Hadron Collider is expected to show evidence of them.  Reassuringly, Dr. Tong said he felt confident that the LHC would produce exciting evidence for or against string theory within one or two years.

Though Dr. Tong confessed that he believed string theory was missing some key elements, he also described it as the only credible solution to dark energy, which accounts for 75% of energy in the universe and which is currently hidden.  As an aside on that topic, Dr. Tong cheerfully admitted that the current quantum theory has its own calculations and candidates for dark energy, but that calculations come out wrong by, oh, roughly 20 billion...

He also described an exciting and alternative theory to look for evidence of strings, a theory which he had helped personally develop.  Extreme conditions are needed to see strings, and the collisions of the LHC will not be strong enough to make strings themselves visible.  So what about the Big Bang?  Dr. Tong explained that the extra dimensions of string theory may be visible in the ‘fireball’ imprint of the Big Bang, otherwise known as cosmic background radiation, and this is measurable by satellite in exquisite detail.  The evidence for this theory could be being collected right now by the recently launched Planck satellite, currently 3 million kilometres from Earth.

“There’s something kind of miraculous about this.  That someone like me can sit in an office with a pen and paper musing about what happened 13.7 billion years ago, but we actually know whether this is right or wrong,” Dr. Tong commented happily, touching right on one of the best points of modern physics.

An audience member questioned if strings might have been caught and stretched out across the universe during the Big Bang explosion­ and the answer was yes.  One day, they may be discovered just like this.

Further questions probed the nature of the extra dimensions... 

"Current thinking says there are 10 or 11..."

...what the Higgs boson actually is... 

"Invisible treacle’ that slows down particles and generates mass."

 ...and whether string theory has anything to add on the philosophical question of free will?

"No."

There was no question too challenging for an honest answer.  One member of the audience asked what had existed before the Big Bang.

Dr. Tong answered without hesitation.  “That’s easy to answer.  We have no idea!”

Expounding further on this, Dr. Tong rearranged the common perception of the Big Bang Theory.  The theory outlines the sudden expansion of the universe 13.7 billion years ago, but it doesn’t say what started it, or why it happened. Tantalisingly, it could be string theory which will answer those questions.

Time ran out before the questions could, but Dr. Tong was content to remain behind and chat further.

“I’ll happily stay behind until I’ve exhausted you all,” he said cheerfully, and the eager crowd moved in.


Blog article about a cafe scientifique event on String Theory
Originally posted here ­
http://blogs.royalsociety.org/science­live/2011/07/20/a­cafe­of­string­and­science/