i-1fda9b237bb6ca3857a5866b3c1279b9-string_theory.jpgThe Complete Idiot’s Guide to String Theory is one way for you to attempt to understand String Theory. While any such effort will probably not work, you will probably learn some things along the way as long as you are not a theoretical physicist. If you are a theoretical physicist, this book will just make you mad, so don’t even go there.


String theory describes the universe much like Newtonian Physics describes the universe … in a way that explains what we observe and what we think is possible. Newtonian Physics falls short of explaining some basic observations, and has been replaced by Einsteinian Physics. However, Einstein did not conceptualize his theories of relativity because he saw things in nature that Newton could not explain. Instead, there were certain ‘knowns’ that had been well demonstrated regarding the physical universe, and certain PGT’s (pretty good theories) about how the universe worked, which, when you thought about them enough, caused a theoretical conflict with the “knowns.” Einstein re-described the universe more accurately than Newton prior to the invention of tools that would allow observations to be made that contradicted Newton and required Einstein. In other words, Einstein thought us to the next level of thinking.

This is not quite so with the other major theory of the Universe, which I’ll call the Standard Model but you may know of as Particle Physics or even Quantum Physics or Quantum Mechanics. In this case, the initial formulation of the model, which came in several stages, included coming up with theory to explain unexpected observations, as well as theory based on simple measurement and observation. Eventually, the Standard Model congealed enough that it started popping out its own predictions (much like Einstein’s models did), which mostly take the form of as yet observed particles. In other words, the Standard Model is a combination of thinking ahead of observation and thinking about observation.

String theory is pure thinking.

There is no observation that one can make using an instrument that gives some goofy result that can best be explained by String Theory. String Theory is a very high level mathematical formulation that gains its prowess not from making natural question marks turn into explanation points (as the other theories of physics tend to do) but rather, from the dubious distinction of making mathematicians get all Squeeeeee over the fact that several once-thought-to-be utterly different complex formulas are really all the same, simultaneously deep and overarching single one-formula-to-rule-them-all formula.

The essence of string theory is actually very simple. String theory links together certain key feature of particle physics with certain key features of dimensions to extend both concepts in a way that describes, and thus kinda explains, all forces including subatomic forces and gravity. Any detail beyond that is almost incomprehensible so don’t even try.

But what about this book? Does it explain string theory in a way that makes sense and is convincing?

Certainly not. String theory makes no sense and is not even close to convincing. So if the theory does not manage those tasks, then some dumb book certainly is not going to be able to do them.

String theory is essentially intractable from a human perspective. We are physically and psychologically incapable of understanding string theory. I think I have a good metaphor for this dilemma.

Imagine that for some reason you had to believe that any behaving multi-celled organism … a frog, a dog, a nematode, another human … had a human like mind and human like senses and sensibilities. You do not have the option of having any other form of belief. If that was true, you would never be able to really get what was going on in the natural world, but you would have explanations for everything. You would explain the nectar foraging behavior of bees, the drumming of the prairie chicken on the lek, the sounding of whales, and the schooling of fish in purely human terms. If someone came along with an alternative theory that said that different types of organisms have a) different types of brains and b) different sets of senses, that would be hard to believe as it would conflict with your view of everything. Furthermore, a theory that explains the behaivor of an earthworm, a duck, a monkey, and a grasshopper needs to operate not at the level of the mind, not at the level of the brain, not at the level of the five sense, visually oriented world of humans. Rather, it would operate at the level of the neuron. It would be “Neuron Theory.” You would have to grasp what a neuron was, how it worked, how there could be certain different kinds of neurons. Then you would be asked to accept how a bunch of these neurons linked together, and even communicating with each other across space using senses, can produce the diversity of behaviors that you were previously assuming all had a very different explanation. The gap between this “neuron” thing and the diverse complex world “neuron theory” purported to explain would be so huge that you would have a hard time accepting it.

String theory is like that but much harder.

Like so many other things in the physical sciences (even basic engineering) there is a gap between the typical human understanding of a phenomenon and the mathematical model that fits the phenomenon. The human understanding may lead to a set of predictions or descriptions that are just plain wrong, while the mathematical formulation leads to predictions or descriptions that are just plain right, and that actually tell us about things we cannot really otherwise guess at. In some cases, the math forces us (through the proximate mechanism of curiosity) to find a way to make an observation that we would never otherwise make …. to make detectable a particle normally hidden from our human senses, for instance.

String theory has yet to produce a description that outlines a gap in physical (observed) knowledge that can be filled with a doable experiment. If the large hadron collider manages certain amazing tricks, a couple of predictions of String Theory may be tested, but first they’ve got to get that machine to run for more than a few days.

If you don’t know much about String Theory and you are not a physicist, I do recommend this book. The other book that is good for this sort of thing is The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory
. Either way, you won’t get String Theory, but you’ll have fun getting there, until near the end when you realize that the driver of this particular bus is as lost as you are.

Comments

  1. #1 DuWayne
    April 30, 2009

    Either way, you won’t get String Theory, but you’ll have fun getting there, until near the end when you realize that the driver of this particular bus is as lost as you are.

    When gas was much cheaper and I had more time on my hands, I became enamored by Douglas Adams explanation of how Dirk Gently navigated – by following someone who looked like they knew where they were going. On two separate occasions, I nearly got my ass kicked, on another, the police were called. However, on three occasions I ended up at parties (though there was some unnatural selection going on) and one time, I followed a guy out to the boonies about half way between Kalamazoo and Grand Rapids. When he pulled over I decided to stop as well.

    It turned out that he had gotten lost and hadn’t the foggiest idea where he was. When I asked him where he was trying to go, it was no longer a case of the blind leading the blind – I pulled in front and guided him directly where he was going. I was then invited in and we did lines of coke with his “friend” for several hours.

    The moral of the story being, sometimes you have a lot of fun getting most of the way, turns out the bus driver hasn’t the foggiest fucking clue – but it works out that you do…

  2. #2 Nathan Myers
    April 30, 2009

    I see this and the “Elegant Universe” as, primarily, religious texts, and secondarily, mathematics texts. They tell us next to nothing about physics, physicists, or the physical universe. (What they do tell us of those things is better got from a book on, you know, actual physics.) Instead, they tell us about the beliefs of stringists. Stringists may be unique among religious adherents in (a) being supported primarily by federal grants and (b) testing their doctrines against mathematical formalisms — albeit, formalisms of their own devising. Conjectures they all prefer to agree on, of course, are not tested, nor any that cannot actually be solved within the formalism.

    Practitioners of “string physics” are not physicists at all, in any practical sense. The older ones studied, and even practiced, physics, years ago. What they’re actually doing nowadays (in their observance) is pure mathematics. Mathematicians have never been obliged to pay attention to reality — except during the war — but they have not lately had the budgets that physics departments enjoy. Pure mathematics is a fine endeavor, but it’s not really honest to pretend you’re doing physics, and to displace actual physicists from physics departments. I gather it’s punishingly hard for a non-stringist to get on at a physics faculty these days.

  3. #3 Greg Laden
    April 30, 2009

    So, Nathan, you don’t by string theory? Can you tell us why in terms a layperson would understand?

  4. #4 Jason Thibeault
    April 30, 2009

    DuWayne: they called that Zen Driving when I was still in high school, just learning to drive. I hadn’t even heard of Douglas Adams at that point in my geek life.

    Nathan: What? String theory isn’t a theory about some very fuzzy areas of physics that we can’t observe directly, it’s actually religious dogma?? Okay, now I gotta get myself this book ASAP. I wonder, if I learn it well enough, then make up some extra stuff on top, if I could be a prophet of a sub-sect of the Church of String Theory.

    http://xkcd.com/171/

  5. #5 Nathan Myers
    May 1, 2009

    Greg: I’m a layperson too. I’m just going by first principles; a scientist is somebody who tests theories against experiment. They don’t, so what are they? What they actually do all day is mathematics, so that’s a clue, but they’re not true mathematicians, since they insist that their work has something to do with reality. (The Babylonians and Mayans did too.) In the absence of any evidence whatsoever, this insistence can only arise from belief. To believe you have a line on the fundamental nature of the universe in the absence of any possible evidence is a good working definition of religiosity (or megalomaniacal delusion, but I repeat myself). But it might just be a big scam. (Or do I repeat myself again?)

    I just feel sorry for all the good physics students suckered into it.

  6. #6 Dunc
    May 1, 2009

    There is no observation that one can make using an instrument that gives some goofy result that can best be explained by String Theory.

    Well, no single observation, perhaps. But you can observe the relativistic universe and the quantum universe, derive theories which explain their behaviour, and notice that they’re completely incompatible. This is goofy and inexplicable, and therefore requires new physics. String theory is the best we’ve got so far. It may turn out to be as baseless as phlogiston or the aether, but clearly something is required to put physics back together again.

  7. #7 NewEnglandBob
    May 1, 2009

    As a layperson I have read the following books on string theory and QM and physics in the last year:

    The Elegant Universe: Superstrings, Hidden Dimensions, & the Quest for the Ultimate Theory By Brian Greene

    The Fabric of the Cosmos: Space, Time, and the Texture of Reality By Brian Greene

    Just Six Numbers: The Deep Forces that Shape the Universe By Martin Rees

    Quantum Gods: Creation, Chaos, and the Search for Cosmic Consciousness By Victor J. Stenger (reading now)

    Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law By Peter Woit

    Six Easy Pieces: Essentials of Physics, Explained by its Most Brilliant Teacher By Richard P. Feynman

    Six Not-So-Easy Pieces: Einstein’s Relativity, Symmetry, and Space-Time By Richard P. Feynman

    Hiding In The Mirror: The Mysterious Allure of Extra Dimensions, from Plato to String Theory and Beyond By Lawrence M. Krauss

    Atom: An Odyssey From the Big Bang to Life on Earth … and Beyond By Lawrence M. Krauss

    Quantum Enigma: Physics Encounters Consciousness By Bruce Rosenblum & Fred Kuttner

    The Trouble with Physics:The Rise of String Theory, The Fall of a Science, and What Comes Next By Lee Smolin

    Three Roads to Quantum Gravity By Lee Smolin

    The Cosmic Landscape: String Theory and the Illusion of Intelligent Design By Leonard Susskind

    The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics By Leonard Susskind

    …and I have little confidence that string theory explains anything about the universe on a Plank level or on a cosmological level.

    I feel it is not even a theory and it makes no predictions. The standard model is a workable current theory and I expect the LHC will enhance it further.

  8. #8 hmd
    May 1, 2009

    As a former physicist who has worked in published in areas relating to string theory (albeit 15 years ago) I can say a few things here:

    Most string theorists understand that they are working with very highly abstract mathematical theories that lack direct predictive power at energies that are even remotely accessible. They almost all wish it were otherwise.

    The Standard Model – that is, quantum field theory with SU(2) x U(1) x SU(3) gauge symmetry and three generations of quarks and leptons – is very good at describing and predicting high energy physics. For example, it predicted the need for a top quark well before it was actually observed. It can calculate some things like the magnetic dipole moment of the electron and this can be measured accurately to many many decimal places with complete agreement. It also predicts that there should be some kind of Higgs boson(s) and a rough range of probable masses for this, but there are a lot of possible variations on this.

    General Relativity is very good at describing the large scale structure and behavior of the universe. At these scales, all those electromagnetic and nuclear forces either don’t operate or cancel out, and gravity is the primary driver. GR is the theory of gravity, and it is very good. It makes many interesting predictions (such as existence of black holes, perihelion shift of Mercury, time dilation, etc.) that have been verified experimentally.

    Quantum field theory and general relativity don’t mix. They can’t coexist. So one or the other has to be modified, and this modification will probably only be visible at Planck scale energies. String theory is one of the few options currently on offer for a theory that looks like QFT and GR at larger distances and lower energies.

    At first, there was some hope that there would only be a one or a few string theories that were consistent with the specific low energy particle content of the Standard Model. In this case, one might have hoped for some interesting and unique predictions about, say, the nature of the Higgs sector or particles with masses above our current limits of observation but still low enough to be feasibly observed. But this hope turned out to be false – there are lots of different string theory variants.

    So we are left with the unsatisfying situation that string theory needs to be more developed mathematically. We hope (again) that a more developed theory would either (a) lead to some interesting predictions, or (b) lead to greater understanding of what options exist besides string theory for unifying QFT and GR.

  9. #9 MartinB
    May 1, 2009

    Actually, as Feynman once pointed out, string theory *does* make one clear prediction, unfortunately, it is wrong: Our universe has to be 10 (or 11 or 26?, depending on you personal variant) dimensional.

  10. #10 hmd
    May 1, 2009

    Yes, it does predict that there are other dimensions. Or at least other degrees of freedom in the case of fermionic or heterotic string theories.

    But it doesn’t predict what those other dimensions will be like. It doesn’t require that they be large, flattish and easily traversed. So it isn’t really quite accurate to say that this prediction is falsified. All in all, though, it would be fair to say that this is a strike against string theory. Or would be, if there were any alternative theory to compare it against that didn’t suffer the same problem.

  11. #11 Notagod
    May 1, 2009

    String theory is the study of the statement “Oh, I don’t know” expressed mathematically. Oh, I don’t know but I think it has a valid purpose of really opening the mind to all possibilities. That is probably good when investigating things as flighty as subatomic particles. But, like the christian religion should not be used as a basis for real life.

    Nathan wrote:

    Stringists may be unique among religious adherents in (a) being supported primarily by federal grants and (b) testing their doctrines against mathematical formalisms

    I don’t disagree with the statement but would add that religions in the United States are supported by the federal government through tax exemption. That is very real support considering the taxes the churches should be paying.

  12. #12 Nathan Myers
    May 1, 2009

    Cosmology and astronomy are in as much trouble as fundamental physics these days. Their problem is different in that they have a positive abundance of relevant data, but is similar in that they have taken a religious approach to their subject.

    Astronomers are in the position of the police detective who is convinced your grandmother murdered everyone in her village, loaded each into her trunk, and disposed of them somewhere unknown. Reminded that she couldn’t lift the bodies, couldn’t move fast enough to have done the job in the time allotted, or drive, he posits an army of invisible zombie accomplices. Solid-state physicists don’t get to invent invisible zombie armies. Neither do biologists.

  13. #13 Glenn
    May 1, 2009

    Why bother to try to understand something that has no scientific data to back it up? String theory is more of a mathematical fantasy than a theory, its not even a hypotheses.

  14. #14 José
    May 2, 2009

    Reminded that she couldn’t lift the bodies, couldn’t move fast enough to have done the job in the time allotted, or drive, he posits an army of invisible zombie accomplices.

    A better analogy would be to call Plasma Theory all invisible zombies with no grandma.

  15. #15 Nathan Myers
    May 3, 2009

    What?

  16. #16 José
    May 3, 2009

    You accuse conventional physics of having to fudge some things in order to describe the universe, but you support plasma theory, which is almost entirely fudge.

  17. #17 Nathan Myers
    May 3, 2009

    Nobody mentioned “plasma theory” (whatever that may be). There’s nothing exotic about plasma — it’s just electrons and nuclei — but the mathematics is intractable. Evidently that’s enough to motivate some people to tie themselves in knots to avoid thinking about it.

    Anyway that has nothing to do with inflation, dark matter, or dark energy, which are the astronomers’ present problem. It’s one thing not to understand the universe, but it’s worse to find yourself believing in ghosts more massive than the universe. Solid state physicists don’t seem tempted to make up such stuff.

  18. #18 José
    May 4, 2009

    Nobody mentioned “plasma theory” (whatever that may be).

    Oh, don’t play dumb. Call it whatever you want.

    There’s nothing exotic about plasma

    No one said plasma was exotic. But using it to describe how the universe works on a large scale is still all fudge.

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