Think of a guitar string that has been tuned by stretching the string under tension across the guitar. Depending on how the string is plucked and how much tension is in the string, different musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension.
In a similar manner, in string theory, the elementary particles we observe in particle accelerators could be thought of as the “musical notes” or excitation modes of elementary strings.
In string theory, as in guitar playing, the string must be stretched under tension in order to become excited. However, the strings in string theory are floating in spacetime, they aren’t tied down to a guitar. Nonetheless, they have tension. The string tension in string theory is denoted by the quantity 1/(2 p a’), where a’ is pronounced “alpha prime” and is equal to the square of the string length scale.
If string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. Unfortunately, this means that strings are way too small to see by current or expected particle physics technology (or financing!!) and so string theorists must devise more clever methods to test the theory than just looking for little strings in particle experiments.
String theories are classified according to whether or not the strings are required to be closed loops, and whether or not the particle spectrum includes fermions. In order to include fermions in string theory, there must be a special kind of symmetry called supersymmetry, which means for every boson (particle that transmits a force) there is a corresponding fermion (particle that makes up matter). So supersymmetry relates the particles that transmit forces to the particles that make up matter.
Supersymmetric partners to to currently known particles have not been observed in particle experiments, but theorists believe this is because supersymmetric particles are too massive to be detected at current accelerators. Particle accelerators could be on the verge of finding evidence for high energy supersymmetry in the next decade. Evidence for supersymmetry at high energy would be compelling evidence that string theory was a good mathematical model for Nature at the smallest distance scales.
The holographic paradigm is joining of two concepts that were developed independently:
- That the universe is in some sense a holographic structure — proposed by David Bohm
- That consciousness is dependent on holographic structure — proposed by Karl Pribram
This paradigm posits that theories utilizing holographic structures may lead to a unified understanding of consciousness and the universe.The physicist David Bohm, who died in 1992, developed a sophisticated approach to this concept of the universe, which he termed ‘undivided wholeness’. Bohm outlined his approach in the classic 1980 book, ‘Wholeness and the Implicate Order’. He used the analogy of the hologram to illustrate the concept of undivided wholeness. A hologram is a special kind of photographic plate produced with the highly coherent light of a laser source, i.e. light which is all of the same frequency and which does not disperse. Whereas an ordinary photographic plate records a flat image of an illuminated object, a hologram provides a three-dimensional reconstruction of the object. If a hologram is illuminated with the same coherent light with which it was produced, then the optical effect is as if the original object were being observed. When the observer moves his/her head around, different perspectives of the object can be seen. A remarkable property of holograms is that even if only a portion of the plate is illuminated the whole of the object is reconstructed, although the resolution of the reconstruction is not as great as when the complete plate is illuminated. One may say that the reconstructed object is embedded in any arbitrary segment of the plate.
Now, the physics of holograms is well understood. The point here is that the hologram serves as a simple analogy for Bohm’s concept of undivided wholeness. The universe is like a hologram, in which the whole image is contained within every segment. In other words, the whole is enfolded within each segment. By shining laser light on a part of the hologram, an unfolding occurs in which the form and structure of the whole become apparent. Similarly, processes of unfolding occur continually in the universe, yielding the patterns and structures which we can see and measure.
E8-based Theory of Everything: “Our universe is this beautiful shape”
On November 6, 2007, Antony Garrett Lisi, an American-born theoretical physicist, published the paper called “An Exceptionally Simple Theory of Everything”, describing a new unified field theory that connects the theories of quantum physics and gravitation using the mathematical shape E8.
Lisi’s inspiration lies in this elegant and intricate shape known to mathematics, called E8 – a complex, eight-dimensional mathematical pattern with 248 points first found in 1887, but only fully understood by mathematicians this year after workings, that, if written out in tiny print, would cover an area the size of Manhattan. E8 encapsulates the symmetries of a geometric object that is 57-dimensional and is itself is 248-dimensional. Lisi says “I think our universe is this beautiful shape.”
What makes E8 so exciting is that Nature also seems to have embedded it at the heart of many bits of physics. One interpretation of why we have such a quirky list of fundamental particles is because they all result from different facets of the strange symmetries of E8. Lisi’s breakthrough came when he noticed that some of the equations describing E8’s structure matched his own.
What Lisi had realised was that he could find a way to place the various elementary particles and forces on E8’s 248 points. What remained was 20 gaps which he filled with notional particles, for example those that some physicists predict to be associated with gravity. Physicists have long puzzled over why elementary particles appear to belong to families, but this arises naturally from the geometry of E8, he says. So far, all the interactions predicted by the complex geometrical relationships inside E8 match with observations in the real world.
The crucial test of Lisi’s work will come only when he has made testable predictions. Lisi is now calculating the masses that the 20 new particles should have, in the hope that they may be spotted when the Large Hadron Collider starts up.
“The theory is very young, and still in development,” he says. “Right now, I’d assign a low (but not tiny) likelyhood to this prediction. For comparison, I think the chances are higher that LHC will see some of these particles than it is that the LHC will see superparticles, extra dimensions, or micro black holes as predicted by string theory. I hope to get more (and different) predictions, with more confidence, out of this E8 Theory over the next year, before the LHC comes online.”
- Integral theory is a term often used to describe the teachings and work of the American writer Ken Wilber, referring either to the synthesis of different perspectives and methodologies, or to his own “AQAL” theory. More recently, the term has been adopted Hungarian systems theorist Ervin László in a scientific context.A key idea in Wilber’s philosophical approach is the holon, which came from the writings of Arthur Koestler. In considering what might be the basic building blocks of existence, he observed that it seems every entity and concept shares a dual nature: as a whole in itself, and as a part of some other whole. For example, although you are made of parts (your nervous system, your skeletal system, etc.), you are also a part of your society, and of your nation-state. A letter is a self-existing entity and simultaneously an integral part of a word. Everything from quarks to matter to energy to ideas can be looked at in this way — everything in creation except perhaps creation itself is a holon.
AQAL (pronounced aqual or ah-qwul) represents the core of Wilber’s recent work. AQAL stands for “all quadrants all levels”, but equally connotes ‘all lines’, ‘all states’ and ‘all types’. These are the five irreducible categories of Wilber’s model of manifest existence. In order for an account of the Kosmos to be complete, Wilber believes that it must include each of these five categories. All of Wilber’s AQAL categories — quadrants, lines, levels, states, and types—relate to relative truth in the two truths doctrine of Buddhism, to which he subscribes. According to Wilber, none of them are true in an absolute sense: only formless awareness, “the simple feeling of being,” exists absolutely.
Each holon, or unit of reality that is both a whole and a part of a larger whole, has an interior and an exterior. It also exists as an individual and (assuming more than one of these entities exists) as a collective. Observing the holon from the outside constitutes an exterior perspective on that holon. Observing it from the inside is the interior perspective, and so forth. If you map these four perspectives into quadrants, you have four quadrants, or dimensions (these are unrelated to the three spatial dimensions)
To give an example of how this works, consider four schools of social science. Freudian psychoanalysis, which [interprets people’s interior experiences, is an account of the interior individual (or, in the diagram, the upper-left) quadrant. B. F. Skinner’s behaviorism, which limits itself to the observation of the behavior of organisms, is an exterior individual (upper-right) account. Gadamer’s philosophical hermeneutics interprets the collective consciousness of a society, and is thus an interior plural (lower-left) perspective. Marxist economic theory examines the external behavior of a society (lower-right).
Thus all four pursuits – psychoanalysis, behaviorism, philosophical hermeneutics and Marxism – offer complementary, rather than contradictory, perspectives. It is possible for all to be correct and necessary for a complete account of human existence. Wilber has integrated these four areas of knowledge through an acknowledgement of the four fundamental dimensions of existence. Further, these four perspectives are equally valid at all levels of existence.