World on a String
Toward experimental support for string theory
Download / Listen to an Audio Intro from Bill Weaver.
A while back, learned philosophers plied their trade by mixing various combinations of the four primary elements of Earth, Air, Fire and Water. Around the same A Toroidal LHC Apparatus (ATLAS) is one of six particle detector experiments currently being assembled in the Large Hadron Collider at CERN. time, healers knew that discomfort was brought about by bad vapors that were inhaled in the company of the sick or the morally unfit. In the 1600s, some malcontents suggested the existence of minuscule particles that came in many more flavors than the four basic elements and also dreamed up the heretical notion that discomfort and disease may be caused by tiny seed-like particles called “germs.” These wild speculations were broadly ridiculed while, at the same time, contritely praised for offering explanations based on invisible objects. These objects were so tiny that they could never be seen and consequently an experiment could not be devised to verify their existence. However, over the succeeding centuries, measurement technology progressed and scientists, including Robert Boyle, Antoine Lavoisier and Dmitri Mendeleev, designed experiments and theoretical advances that led to confirmation of the 117 elements we know today. Around the same time, physicians John Snow, Louis Pasteur and, later, Robert Koch laid the foundation for our modern understanding of microbiology and the pathogenic theory of medicine.
At the turn of the twentieth century, German physicist Max Planck proposed a mathematical formalism involving the notion that continuous electromagnetic waves were actually tiny, individual particles. This idea flew in the face of existing theory and was not demonstrated experimentally until 1905, when a patent clerk named Bert Einstein had the temerity to suggest Planck’s “photons” existed physically and caused the ejection of electrons from charged plates. After a flurry of experimental activity, Planck was awarded the 1918 Nobel Prize in Physics for his discovery of energy quanta, followed closely by Albert Einstein’s 1921 Nobel Prize in Physics for his explanation of the quantized photoelectric effect. Einstein went on to develop his Special Theory of Relativity that connected the concepts of energy and material in the famous equation, E=mc2, and his General Theory of Relativity that suggested the three spatial dimensions of left/right, back/forth and up/down could be combined with time to form a new kind of four-dimensional fabric known as “space-time” that could be used to explain the effects of gravity.
Planck’s initial work evolved into the discipline of quantum physics and led to the discovery of the electron, proton and neutron and the further discovery of even smaller particles having exotic names such as quarks, leptons and gauge bosons. The current Standard Model of particle physics consists of 24 elementary building blocks that cannot be decomposed into smaller pieces. Active research continues in this area, but the physicists recognize that the Standard Model is incomplete. While Einstein’s General Theory accurately describes the behavior of massive objects whose motion is controlled by gravity, and the Standard Model works well with tiny particles, there is a mismatch between the theories at the interface between large and small.
Emerging on the scene in the late 1960s, a new idea that appeared to bridge this mismatch coalesced into what is now known as “string theory.” Like the many theories before it, string theory claimed to describe tiny objects well beyond our measurement ability to detect them. The initial symmetry and elegance of the theory led some to contemplate its importance as a grand unifying “theory of everything” — and this exuberance brought out its many initial detractors.
At its core, string theory suggests that fundamental particles are not zero-dimensional points, but one-dimensional lines of vibrating energy or “strings.” These strings can be open-ended or closed loops, and the different frequencies of their vibrations permit them to combine into the various measured elementary particles. Besides the suggestion of dimensional figures instead of points, the theory further suggests these vanishingly small bundles of energy vibrate on a six-dimensional manifold whose dimensions are in addition to the four suggested by Einstein’s General Theory. Apart from the difficulty of visualizing a 10-dimensional figure, the latest developments in string theory suggest the need for an eleventh dimension. The eleventh dimension not only reconciles apparent anomalies within string theory, but also extends hope for the design of an experiment to verify the theory’s predictions.
String theory suggests that the reason why Einstein’s General Theory and the Standard Model do not mesh is because something is missing from the equations. That something is gravity or, more to the point, particles that cause the effect we describe as gravity. The Standard Model suggests the forces experienced between charged electrons and protons and between elementary particles of quarks and leptons is due to the rapid exchange of “messenger particles,” the gauge bosons. The eleventh dimension of string theory is visualized as a membrane having directions “along” and “out of.” While gauge-bosons of the Standard Model are thought to travel and exist along the membrane, the gravity-messenger particle or “graviton” is predicted to travel out of the membrane. This loss of gravitational messenger particles is calculated to reconcile the apparent weakness of gravity in comparison to the enormous strength of the other fundamental forces. The experimental plan is to generate such a violent collision between sub-atomic particles that the loss of energy due to the loss of gravitons is large enough to be measured.
An instrument designed to create these collisions was conceived in 1994 and is scheduled to go online in May 2008. The Large Hadron Collider (LHC) will be the largest instrument built by man and is located near Geneva, Switzerland, along the France-Switzerland border. It is managed by the European Organization for Nuclear Research, commonly known as CERN. The LHC represents the collaborative work of 20 member countries and nearly 8000 scientists and engineers representing over 500 universities and 80 nationalities. In addition to providing experimental research of importance to the Standard Model and perhaps string theory, the LHC is expected to generate 40,000 GBytes of data per second during each of its 20-hour experiment cycles. CERN is the birthplace of the original World Wide Web (WWW) where it was created to link its collaborators and analyze data from earlier experiments. The LHC will require new developments into grid computing and storage, as it is expected to increase by more than 10-times the current storage capacity of the WWW within one year. This fact alone has already provided experimental support for another theory — one that posits the smaller the measurement, the larger the instrument.
Bill Weaver is an associate professor in the Department of Integrated Science, Business and Technology at La Salle University. He may be contacted at editor@ScientificComputing.com.
Acronyms ATLAS A Toroidal LHC Apparatus | CERN European Organization for Nuclear Research | LHC Large Hadron Collider | WWW World Wide Web
String Theory Resources
• General Information on String Theory
• NOVA: The Elegant Universe
•P Howard J. Schnitzer, “String Theory: a theory in search of an experiment” (2003)
• CERN LHC Outreach Program
• NOVA scienceNOW Resources on CERN