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Tuesday, April 7, 2015
Science ...

The other day I was listening to a lecture how philosophy and science relate to each other, and it make me think about string theory. String theory, even though far from being proven and adopted as an established scientific teaching, is nonetheless quite a successful paradigm. It accomplishes a lot (or at least has the potential to, should enough empirical evidence accrue that ensures its widespread acceptance). One of the biggest things that it does involves the unification of gravity with the Standard Particle Model and quantum physics; i.e. the quantization of gravity. This is currently a long-sought holy grail in modern physics, i.e. quantum gravity.

If a solid theory of quantum gravity were developed, the confounding infinities of Einstein’s relativity equations describing gravity would finally be banished; there would be no more worries about singularities and infinite-density black holes. There is a cost, however — the acceptance of super-symmetry (requiring the discovery of a whole family of new and presently never seen sub-atomic particles, although the Large Hadron Collider in Switzerland is busy looking); and of many extra spatial dimensions (which we don’t see in our daily lives because they are somehow rolled up in ways that are too small to affect us).

The charm of string theory is that one single mathematical paradigm can potentially relate and explain electromagnetism, the strong and weak nuclear forces, the Higgs field, and gravity. It would provide a ‘theory of everything’, or almost anyway. Aside from the need for supersymmetrical particle discovery and lots of extra dimensions, however, the big problem with string theory is that it is NOT simultaneously a ‘theory of nothing’. I.e. it doesn’t integrate space and time into the basic paradigm. It assumes space-time as a background constant, albeit governed by the rules of relativity (gravity being the force that enforces these rules).

So, there is a really big question that concerns both science and philosophical metaphysics — i.e. ARE STRINGS REAL??? Does every bit of matter and bosonic energy bundle (such as light and magnetism, but also the Higgs field interaction and weak force effects) come down to a one-dimensional line (i.e., a “string”) wiggling and dancing around in space and time? I never liked that idea. The present Standard Particle Model paradigm, that all particles are infinitesimal points in space, has many problems. Thus the on-going search for something better. But if 0-dimensional points don’t get down to the most fundamental level of things, why should 1-dimensional strings do any better? They seem too complicated and too elaborate to really be the basic building block of reality. They seem too contrived to base a “grand unification” of totally everything around.

Here once again is the big problem — a definition of “everything” has to include nothing. I.e., space. And if you mess with space, Einstein tells us that you are also messing with time. Is time more like something, or nothing? That’s a tough one. The point is, string theory does not directly take on space and time. Like Newtonian physics, it requires a space/time backdrop to dance around in. This dilemma is called the background independence problem. String theory is not fundamental enough to actually attack the bastion of spacetime itself. Einstein’s relativistic paradigms of gravity show that space, time, matter and energy are tightly and inherently linked.

So, it seems to me, from a very fuzzy / intuitive basis (the basis upon which I live most of my waking life), that a true quantum “theory of everything” is going to have to attack space-time itself. Thus far, string theory doesn’t do that, although string theorists are aware of the problem and are working on it, especially thru anti-deSitter spacetimes and conformal field theories. But personally, I doubt if a few additional equations will solve the problem . . . the whole theory will need its roots dug up and a new “fully and arbitrarily non-perturbative” foundation poured for it.

Given all of this, I assert my opinion that strings and string theory is more “instrumentalist” in nature than “realist”. I.e., it is a good intellectual “instrument” thru which insights can be gained about nature; but it is not reality itself. I believe that the string theory people have tripped upon a complex math paradigm that catches a lot about quantum reality. It drills down farther than relativity theories and quantum field theories under the Standard Particle Model have been able to do thus far. It is pretty remarkable what it can do. So it isn’t going away anytime soon.

But there’s something about gravity itself that hints that strings are NOT real. The classic Einstein insight is that gravity is not a force, but a bending of spacetime by energy (either mass or bosonic energy will do). Gravity itself is not a movement of something in spacetime — so how can you envision gravity as a string dancing on a spacetime stage, when the stage itself is continuously warping and bending because of its dance? How do you dance on the roiling waves of an angry sea? Especially when the faster you dance, the more exaggerated and unpredictable the waves become.

In sum, gravity is much more complex than the movement of a string in spacetime. It is a part of spacetime itself. It just is the rulebook on how spacetime reacts in the presence of energy, whether in the form of fermions or bosons or both. In a way, gravity is not really a new string, but a response to other strings. That response may indeed be quantum and not continuous (thus avoiding the infinities of Einstein’s equations). By looking at gravity as a string-based particle, you capture that insight. And yes, that is a REALLY BIG DEAL. But too much good conceptual stuff is otherwise lost when you see gravity that way.

Again, this relates to the background independence problem with string theory, i.e. the need for a fixed stage of space and time (or at least one that responds very predictably to string quantum interactions, and does not fade off into the fuzzy quantum randomness / probability distribution nature of most mass and energy quanta). A rival to string theory, called “loop quantum gravity“, tries to integrate space and time as part of the fundamental quantum system. It tries to climb a higher mountain than string theory does. Unfortunately, so far it hasn’t gotten very far from base camp. String theory is more than half way to the mountain top, but once they reach the top, they will probably see other mountains around them reaching higher into the clouds.

So sure, string theory can allow you tp picture gravitons (i.e., quantum gravity interactions) as strings dancing about in a given frame, doing the job of warping the frame’s background sheet or “manifold” of time and space in a quantum fashion (i.e., in defined mosaic-like chunks, not smoothly and continuously). But on a deeper level, the sheet / manifold of spacetime is more of an actor itself, not a passive responder or stage upon which the string is acting. It’s kind of like watching a play on a stage, and knowing that the actors are really illusions created by the stage and backdrop as they quickly warp themselves before your eyes.

Thus, string theory catches something that the current Standard Model and relativistic gravity theories do not. But they have not hit the bedrock of physical reality. Thus, they are useful instruments. The instrumentalist view is the better way to look at string theory.

Sidepoint — in a way this is also true for the familiar boson and fermion particles. At bottom, the field that supports each particle is the truer reality, more than the particle itself. The field is not an independent stage on which the light photon dances, but is the thing that warps itself to create the photon !!

And one final sidepoint: Seth Lloyd, in his book Programming The Universe, sets out a concept of reality based upon the interaction of information wires (something like electrical wires — a means of carrying an information signal) and information nodes (a point where information comes together and calculates something). His “quantum circuit model” seems pretty close to the loop quantum gravity paradigm of spin networks and spin foams, as the basis for space, time, energy and matter.

Both Lloyd’s circuit model and the loop quantum gravity spin networks seem like a more fundamental way of integrating mass and energy with spacetime. They are more basic and less instrumental. But too bad that they are much less developed than string theory. Bottom line, string theory is a big step in the search for what everything is ultimately composed of. But hey, some string theory people are starting to talk about sub-string “partons” or bits, akin to pearls in a necklace.

So, strings are a darn good “instrument”, a good and amazing way of looking at things. But they are not ultimately real, in my opinion (for whatever that is worth).

◊   posted by Jim G @ 3:38 pm      
 
 


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