The ID Report

By Robert Deyes
ARN Correspondent

In 'Heaven And Earth', a pictorial exposition of the natural world, photographer David Malin emphasized the astounding fact about man's unique position in nature- half way between the very smallest and largest things we know (Ref 1). When the world's largest particle 'smasher'- the Large Hadron Collider- is finally completed next year, it may provide a way of expanding our knowledge of the very small by unifying the two disparate realities defined by quantum physics and gravity. At least that is what String theorists hope for.

The world of quantum physics tells of a past and a future that is definable in terms of statistical probabilities and not the certainties that we attribute to a classical reality. For larger entities such as the human body, this quantum nature is lost because such objects continuously interact with the environment. The resulting so-called 'decoherence' causes larger objects to lose their quantum properties (Ref 2). But for much smaller objects such as electrons, things are rather different. Electrons become "criss-crossing waves of probability" rather than particles taking singular paths (Ref 3, p.179).

The simplest experiments in support of the quantum realm came from the Nobel Laureate Richard Feynman who showed how wave functions and interference patterns could be produced on detector screens whenever a beam emitted by a laser was split in two- an observation that could only be explained by assuming that, upon splitting, both routes had been taken by the beam (Ref 3, p.179). We now know that even when the intensity of the laser is lowered sufficiently such that single photons are emitted (one every few seconds), the interference pattern is still generated (Ref 3, p.181). Two possible histories for the path taken by the photon become reality. What we also know is that the moment some form of measuring device is placed in either of the two pathways, the interference pattern vanishes (Ref 4, p. 102). In 1997, the renowned physicists Dik Bouwmeester and Anton Zeilinger wrote of this rather strange state of affairs:

"In our everyday world, things have properties whether we care to look at them or not. Whether a given apple is red or green is independent of our checking its colour. And although most people acknowledge that quantum mechanics is very strange, thy often feel that quantum objects still have their properties- it seems to be just the clumsiness of our tools that invariably disturbs quantum objects in such a way that we cannot observe all their properties. But any seasoned quantum mechanic knows this not to be true" (Ref 5).

Expressed very simply, it is as if the photon somehow 'knows' that it is going to be measured and consequently 'decides' to go down one of the two possible pathways. As play write Michael Frayn described,

"any act of observation that attempts to determine which of the two paths the particle actually follows necessarily destroys the interference pattern phenomenon, so that the interference pattern vanishes" (Ref 4, p. 102).

One of the primary goals for modern physics is to find a theory that unifies this quantum level with the classical world defined by Newton, Maxwell and Einstein. Physics is making great strides towards a unified theory that may soon encompass these two seemingly disparate worlds under one theoretical umbrella. This theory has everything to do with the smallest unit of matter- a unit called a 'string' (Refs 6,7). The term 'string' in a cosmological context is certainly an enigmatic one and entails a rather bumpy history of excitement and disappointment for those brave physicists who have engaged in trying to realize Einstein's dream of unification. Ever since the 1920's several scientists have laid the ground work for this ambitious goal and while their efforts have so far been largely unfruitful, many believe that these efforts present us with a promise of things to come (Ref 6). According to Scientific American editor George Musser, it has been the integration of gravity into the quantum mechanistic framework that has been the greatest challenge (Ref 7).

If physicists are ever to explain what happened right at the moment that our universe came into being- a moment in which the large and the small existed together in the tiny space of the early cosmos- then a path to reconciliation of these two aspects of our physical reality must be found. In the 1970s and 80s, the unification of both of these realms became the focus of two respected scientists- John Schwarz and Michael Green- who saw string theory as, "the quantum mechanical theory of the gravitational force"(Ref 3, p. 341). Earlier studies with Schwarz' collaborator Joel Scherk, had lead to the finding of a massless particle which, they later proposed was none other than the elusive graviton (Ref 3, p.341). With the graviton- a particle that united quantum mechanics and gravity- String theory seemed poised for success.

Today String theory proposes that the vibrational patterns of strings are what determine the nature of all sub-atomic particles (Ref 8). As Princeton cosmologist Juan Maldacena elaborated, "[just] as a violin string can vibrate with different frequencies, these strings could oscillate in different ways, corresponding to the 'zoo' of particles that was observed" (Ref 8). CERN physicist John Ellis similarly described elementary particles as being different "modes of oscillation of a string" (Ref 9) while Brian Greene pictured our universe as "a string symphony vibrating matter into existence" (Ref 3, p.347). But String theory also requires the existence of space dimensions outside of the three that we experience in our everyday lives. These additional space dimensions are thought to be so small that they would have escaped detection from even the most powerful particle accelerators to-date (Refs 7; 9). Physicists to this day do not fully understand what these additional dimensions actually look like. While there have been attempts to formulate String theory within the three dimensions of space that we know of (Ref 9), most of its protagonists today concur that additional dimensions are required. Because the strings of gravity's graviton particles are thought to be free to move between these extra dimensions (Ref 3, pp.394-398), gravitons may some day soon present physicists with a window into the extra dimensions of space that String theory requires. The reason is conceptually simple and has everything to do with what scientists call the inverse square law.

The inverse square law of force tells us that a mass (A) at a distance of radius(r) from mass (D) will experience gravitational (G) and electrical (E) forces that are proportional to 1/r2 (Ref 3, pp.394-398). So for a universe many dimensions larger, this proportionality would simply increase such that in four dimensions G and E would be proportional to 1/r3, in 5 dimensions, to 1/r4 and so on (Ref 3, pp.394-398). Today the race is on to probe distances smaller than a 10th of a millimeter with the aim of detecting any deviation from the inverse square law that might indicate the presence of the additional space dimensions predicted by String theory. As astrophysicists Bernard Carr and Steven Giddings have noted, the spilling over of gravity into adjacent dimensions may provide the avenue through which String theory can truly be tested (Ref 10)

For now, no measurements on gravity have revealed any deviation from the inverse square law. But the Large Hadron Particle Collider, scheduled for completion in 2009, may change this (Ref 10). If the gravitational force really is much stronger than we observe in our three dimensional space and it is leaking out into adjacent dimensions of space as predicted, the production of tiny black holes- objects whose immense gravitational hold trap anything including light- would require much smaller amounts of energy and matter. Such a scenario would be achievable through the high-energy particle collisions that the Large Hadron Collider will be capable of (Ref 10). While Hadron has recently suffered some major technical difficulties (Ref 11) it promises much when it is finally up and running. If the planned experiments do provide evidence for gravitational spilling, we may be one step closer to achieving the String Theorists' dream of unification.

References:
1. See David Malin's discussion in Heaven and Earth: Unseen by the Naked Eye, Phaidon Press, UK, 2004

2. Michael Nielsen (2002), Rules of a Complex World, Scientific American Vol 287 (5) pp. 66-75

3. Brian Greene (2004), The Fabric of the Cosmos- Space, Time, and the Texture of Reality, Published by Alfred A. Knopf, New York, 1st Edition

4. Michael Frayn (1998), Copenhagen, Methuen Publishing Limited, London, United Kingdom

5. D.Bouwmeester and A. Zeilinger (1997), Quantum Mechanics: Atoms that agree to differ, Nature Vol 388 pp.827-829

6. Raphael Bousso and Joseph Polchinski (2004), The String Theory Landscape, Scientific American Vol 291 (3) pp. 78-87

7. George Musser (2004), Forces of the world, Unite!, Scientific American Vol 291 (3) pp. 106-107

8. Juan Maldacena (2003), Into The Fifth Dimension, Nature, Volume 423 pp. 695-696

9. John Ellis (1987), Strings in four dimensions, Nature Vol 329 pp. 488-489

10. Bernard Carr and Steven Giddings (2005) Quantum Black Holes, Scientific American, May 2005

11. Geoff Brumfiel (2008), LHC meltdown before first collision, http://www.nature.com/news/2008/080922/full/455436a.html, Volume 455, pp. 436-437