There are two great theories of physics: Relativity Theory (the macro Universe) and Quantum Mechanics (the micro Universe). Unlike Relativity Theory, Quantum Mechanics does not contain the concept of gravity. String Theory started out 40 years ago as an attempt to develop a Quantum Theory of gravity. Or in other words, it was an attempt to develop a common single theory which would unify Relativity Theory and Quantum Mechanics.
[It does not bother me that there are two competing models of reality which do not fit together seamlessly. Do you remember the limit theorem in Calculus–the
e which kept getting smaller and smaller but never reached the limit of zero? I see gravity much like
e. Gravity is the weakest but the longest-ranged force. As the scale of reality keeps getting smaller and smaller, gravity approaches zero. Quantum Mechanics deals with reality at the sub-atomic level. Gravity exists in Quantum Mechanics–but it is so small that, for all practical purposes, it can just be ignored.]
In its attempt to unify Relativity Theory and Quantum Mechanics, String Theory becomes an all-encompassing theory of everything. It has so much complexity that it can address any physics issue. If some bit of reality is discovered which does not fit String Theory, no problem. Just add a little addendum to String Theory in order to handle this new inconvenient truth.
[This expansion of the model to incorporate all reality (rather than finding another model which fits basic reality better) reminds me of an abuse of regression analysis which I occasionally saw in my business career. One such mis-application remains etched quite clearly in my brain–a study of the relationship between the weather and the consumption of (fast-food) hamburgers in Indianapolis. (I will try to keep this short and non-technical.)
Statistically, a stronger model has less variables (e.g., precipitation, temperature, humidity) and more observations (number of stores, length of study–years vs. months, detail of observations–hours vs. days). The results of this study were satisfactory, but not spectacular–except for two
outliers–two pieces of data which did not fit the model at all and completely destroyed statistical measures of
goodness of fit and
Rather than going back and recasting the model anew (expanding the data, changing the variables, or examining the outliers), a short-cut was taken. One honest short-cut would have been to completely omit the outliers and admit the model did not include all the data; but that would undermine the credibility of the study. Instead, the outliers were
papered over by adding two
dummy variables, each of which completely explained away one of the outliers. Although the strength of the model (t test, F ratio) was weak, (a technical detail which did not catch the attention of the non-statistical client), the results were accepted on face value.]
So, String Theory is by definition the ultimate theory of physics and strings are the ultimate sub-atomic particle. (This is reminiscent of atoms, which were also defined as the smallest particle of reality–for a time.) Although
particle is not the right word–
entity is better.
end-lessstrings form loops or holes, depending on the perspective, like a doughnut or torus. A one-loop/hole string is like the number
0; a two-loop/hole is like the number
8; and so on. Eventually strings with up to an incredible 480 loops or holes were created.
It is hard to contemplate all this complexity without coming to the conclusion that there must be one or more additional levels of reality below or beyond strings. But the true believers still find it impossible to consider the possibility that strings are not the final entity.
There are more than five different string theories, which contradict one another. However, all are considered to be true! Then there is M-theory (or Super String Theory) which attempts to unify the competing string theories into one consistent structure. Most of these theories have ten dimensions (9 space and 1 time); but M-theory has eleven dimensions. Nine spacial dimensions!? Yes. What happened to the other six? Theoretically, at the time of the Big Bang, all nine dimensions expanded and contracted randomly, until the three dimensions, which we now know, expanded together simultaneously, trapping the other six and forcing them to remain at Planck length (miniscule). Or so the fairy tale goes.
[Why do we have three dimensions? As a young man, I tried to define physical space with more than or less than three dimensions. First, I tried to define physical space in which each dimension was 60º from all the other dimensions, rather than the conventional 90º. I was not able to do it in my head or on paper. I tried other angles–120º, 72º, 45º, 40º. No luck. Next, I tried to imagine three-dimensional space with just two polar coordinates–a vector distance coordinate located along a spiral coordinate, which curved from the origin point so as to pass through all points in physical space. It was a brilliant concept which would have made Escher's optical illusions look like kindergarten scribbles. But I knew in an instant that the concept was not feasible.
Then, I had my epiphany–based in part on my second effort above. We have three dimensions because we need three numbers to locate an object in physical space.
ground–(2 distances and 1 angle).
Dimensions have no distinct physical reality–they are just a convenient way to locate a point in physical space relative to another point.]
String Theory is one of the few theories of physics which is NOT
falsifiable (not able to prove untrue). The high priests of String Theory take pride in asserting that it is impossible to prove or disprove String Theory. The rationale is that we are dealing with reality at the Planck level, beyond the reach of our current instrumentation. So, String Theory exists as no more than theoretical mathematical equations written on university black-boards. In addition to
moi, String Theory has a number of prominent critics. Perhaps a majority of physicists are skeptics–no one has ever taken a poll.
[Compare String Theory with Relativity Theory or with Newtonian Mechanics:
The score is 4 to 0.]
OK, String Theory is a crock; but what does this have to do with Cosmology? String Theory buttresses concepts such as: gravitons, the Big Bang, and Inflation Theory. On the other hand, it is the theoretical expansion of the Universe which most undermines String Theory. There are three traditional models of an expanding Universe–all based on the density of matter in the Universe:
Big Bang, Big Crunch)–Universe expands and then contracts; it has a maximum size.
This fourth alternative has been added in recent years, based on empirical observation.
String theory is compatible only with model #1, because the Universe has a maximum size in this model; it is contra-indicated by models #2, #3, and #4, because they are open ended and have no maximum size.
String Theory does contain at least one concept I find useful. (This also ties into the preceding paragraph.) The useful concept is the
Reciprocal Universe of String Theory–the Universe is simultaneously both a large, expanding universe and a small, contracting universe. The expanding universe starts at zero size and goes to a maximum; while a contracting universe starts at a maximum and goes to zero size. For this to work, the Universe needs to have a maximum size. (Which is why only model #1 above is compatible with String Theory.) These different
views of the Universe depend on measurement technique and affect all things, not just the Universe. For example, a massless photon is no different than a massive black hole, according to String Theory.
In my essay on the
Center of the Universe, I write:
The size and expansion of the Universe depend on a point of view. It is valid to think of every thing in the Universe as fixed in size and the Universe as expanding. But is also equally valid to think of the Universe as fixed in size and everything in it (including the laws of physics) as contracting.
This is not the same thing as the Reciprocal Universe concept, but String Theory makes my idea seem at least plausible, if not outright reasonable. [READ MORE: Center of the Universe]
String Theory has no overall organizing principle (e.g. equivalence of gravity and acceleration or of mass and energy in General Relativity). Rather it is an agglomeration of mathematical constructs built one on top of another–much like a coral reef. It is theory by committee–many great minds have labored over String Theory for more than four decades. There have been many interesting tangents; but still there is no gravitational theory for Quantum Mechanics.
That about summarizes my view of String Theory. It may contain some useful ideas, but overall it is just a giant, theoretical sand castle. It is a concept developed as the consensus of dozens of theoreticians. It is always coming, but never arrives. It is always
on the verge of some giant breakthrough. It lacks the coherence of a single creative genius who understands the really big picture.