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Strings, Geometry, and the Ultimate Reality: The Debate

The views expressed are those of the author and are not necessarily those of Scientific American.

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musser and horgan

Can strings be the ultimate constituents of the universe–more fundamental than matter or energy, and even than space or time? If they’re not made of matter or energy, what are they, then?

If you look for some light fare for your placid Saturday afternoon, here’s an idea: ponder these ultimate questions–on life, nature, the universe and everything–with my fellow SciAm network bloggers George Musser and John Horgan, by watching the debate they had last night at

George and John make an especially compelling duo to watch because their personas are almost diametrically opposed. George’s is that of an unabashed optimist, and toward the end he states his belief that science will eventually discover the ultimate simple laws of everything that will make everyone smack their forehead and go, “why didn’t I think of it?”

John on the other hand has for decades fashioned himself as the curmudgeon of science journalism, poking fun at the cultural idiosyncrasies of science and essentially declaring game over in his 1997 book The End Of Science: Facing The Limits Of Knowledge In The Twilight Of The Scientific Age (as well as in numerous articles for Scientific American, where he used to be a senior writer).

Both of them however reason with much more nuance and subtlety than those simplistic descriptions would have you think, as they demonstrate in more than an hour of discussion intertwining the grand themes of fundamental physics: string theory, the multiverse, cosmic inflation and the anthropic principle–and even the issue of what science itself is.

The part I found most intriguing is toward the beginning, when John takes issue with the idea that strings, those infinitesimally thin and frustratingly enigmatic loops that many of our readers either hate to love or love to hate, aren’t made of matter or energy.

Instead, some physicists say, strings would somehow occupy a deeper layer of reality. It is matter and energy that are made of strings, not the other way around. Similarly, John laments, some physicists contend that strings do not exist in space or time, but instead that space and time themselves may be made of strings.

“My question was,” John says, “What is a string then? If it’s not something that can be situated in space and time and if it’s not constituted of matter or energy, what the hell is it? Is it some kind of pure mathematical form?”

(Mathematical? Now you’re talking, I said to myself.)

George’s answer: let’s not get ahead of ourselves. “It is perhaps premature to talk about what a string might be made of since it’s already a big jump to talk about strings.”

I suspect however that John’s objection is more of a philosophical nature. It strikes at heart the same dispute between realism and phenomenology that has divided physicists ever since Albert Einstein and Niels Bohr were arguing over the implications of quantum mechanics. Simplifying, one could trace that tension all the way back to the philosophers of ancient Greece, starting with Parmenides and Heraclitus.

Immanuel Kant on the other hand observed that science cannot access the ultimate nature of reality–the noumenon (or “thing in itself”). Our eyes and ears, or our finest scientific instruments for that matter, only detect phenomena, not noumena.

In that view, a scientific theory cannot say what the ultimate constituents are: only that they behave according to the predictions of certain mathematical rules. Thus, the question of what the string is made of is not relevant as long as we can experimentally verify that it acts the way that a theoretical string does.

And theoretical strings are geometrical objects; in modern geometry–and by modern I mean ever since Carl Friedrich Gauss, 1777-1855, and Georg Bernhard Riemann, 1826-1866–geometrical objects can be defined intrinsically, that is, it is not necessary to think of them as occupying a larger “space.”

But strings may forever be beyond the scope of science, as John points out. His objection is that strings are too small to detect with any conceivable experiment.

George (who is the author of The Complete Idiot’s Guide to String Theory) had a great answer: that smallness is not specific to strings.  Any theory that unifies all forces of nature will have to include gravity. But gravity is extremely weak compared to the other forces, which implies that detecting its quantum behavior requires experimenting with energies that are completely outside of our reach. Any test of a quantum theory of gravity “will have to be indirect and none of them is going to be decisive.”

One thing that fascinates me about the focus on phenomena versus noumena is that in my view, on a very different philosophical level, it is beautifully paralleled in the formal structure of mathematics. Modern math is entirely rooted in the theory of sets, in the sense that any mathematical object and construction can be defined starting from sets. But in any description of set theory that I’ve seen, you never say anything about what the sets ultimately are made of. There’s never a set that contains anything except other sets.






About the Author: Davide Castelvecchi is a freelance science writer based in Rome and a contributing editor for Scientific American magazine. Follow on Twitter @dcastelvecchi.

The views expressed are those of the author and are not necessarily those of Scientific American.

Comments 8 Comments

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  1. 1. schlafly 3:32 pm 07/30/2011

    A set theorist would say that the number three is defined as a set with 3 elements, and each element is another set. Other definitions are possible, and the laws of arithmetic are the same. So string theory is like that? The strings satisfy some philosophical need to define the foundations, but they have no relevance to any real-world observation or computation? If so, then string theory is more philosophy than science.

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  2. 2. @dcastelvecchi 4:51 pm 07/30/2011

    I meant my comparison only in the vaguest of terms. If string theory is true, strings would the foundation for of all of the real world, so they would be _very_ relevant to it.

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  3. 3. Uncle.Al 4:57 pm 07/30/2011

    The only predictive and testable gravitation theories are geometries. The only spacetime test physics has *never* run is a massed geometric test. Atomic mass configuraton in space is chemistry not physics.

    All quantum gravitations, plus the Higgs and SUSY in the Standard Model, are empirical disasters. One and all postulate mirror-symmetric vacuum toward massed fermions, then manually add symmetry breakings. The vacuum is observably chiral toward mass all the way down: biological homochirality, the Weak interaction, chiral beta-decay rate variation with season (inert achiral alpha-decay rate), and neutrino-antineutrino reaction channel divergence. Massless boson photons are inert (arxiv:0912.5057, 0905.1929, 0706.2031, 1106.1068). General relativity handles massed fermions because massed spin sense substantively sums to zero. (The mass fraction of electron net polarized angular momenta in magnets cannot exceed 0.00005 – and that for elemental Mn-55 100% aligned undecatiplets, which is impossible)

    A substantive volume of filled space can add perfectly in-phase for all its mass. A trace vacuum chiral background active only toward fermionic mass is easily detected: Opposite shoes violate the Equivalence Principle.

    Crystallography builds mathematically perfect opposite shoes, emergent at atomic scale and self-similar to kilogram size, as 11 pairs of enantiomorphic space groups in 230 space groups total. Three of those pairs have no opposite sense or racemic screw axes within a single space group. Chemically and macroscopically identical, opposite geometric parity atomic mass distributions (left shoes versus right shoes on a vacuum left foot) will falsify the Equivalence Principle in existing apparatus, in a 90-day experiment.
    Two geometric parity Eotvos experiments, 5×10(-14) divergence sensitivity. The loaded rotor is fist-sized.

    GR becomes its superset teleparallel gravitation, string theory loses BRST invariance, and SUSY is dead because a shared founding postulate was defective. Stop whining, start looking. The worst it can do is succeed.

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  4. 4. Torbjörn Larsson, OM 5:52 pm 07/30/2011

    Horgan’s speaks for platonism as a dualism, when he claims that energy isn’t a deep property of physics. It is nuts, or rather Noether, as it is simply an expression of a global symmetry over time.

    Realism has been a testable part of science since its beginnings. It can be defined as constrained reactions on constrained actions and is the most basic part of any mechanics. (Action-reaction in classical mechanics, observation-observable in quantum mechanics.)

    So reversely Kant was wrong too. There is nothing in principle that keeps us from constraining observations onto more general theories by way of predictivity. In fact that is what is observed.

    In that context Horgan makes another boo-boo. String theory is by its construction testable latest at the planck scale. Recent observations, starting with photon timing on supernovas and now polarities of same photons, seems to reach into this scale. [It is eminently googeable.]

    The later result is arguable, to probe planck scale currently it needs supersymmetry else it is shy 2 orders of magnitude. Supersymmetry isn’t very compelling in naive physics, as it is not the base case relation between symmetries (Coleman-Mandula theorem).

    But all this points to the trend that we are starting to probe planck scale physics.

    @ Uncle.Al:

    “The only predictive and testable gravitation theories are geometries.”

    This shows that any claim, however false, is used by crackpots as a reason to spout inanities. (Eötvös effects are already looked at and constrained, much as far as we can reasonably get today.)

    Currently geometrical “quantum gravity” theories fail, as they have no mass gap, not even a lower energy so neither obey relativity nor have a dynamics. As much as they are testable, they fail gregariously.

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  5. 5. jhorgan 8:40 am 07/31/2011

    David, thanks a lot for your kind words. I had fun, and I think (hope) George did too. Your comments remind me of the quip–not sure who said it–that modern physics, in its reductionist drive to explain things in terms of more fundamental things, has become “about” less and less, until finally it is about nothing at all.

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  6. 6. Wilhelmus de Wilde 10:39 am 08/5/2011

    Reductionism is one of our ways of trying to solve problems.

    The problem that I have with string theory is “Who the Hell is playing the Violin ?” and that in an area below the Planck length, an area that we cannot control untill now.

    My reductionism asks me also the origin of these different type of vibrations of the strings, the music may be exellent but I like to know the artist and the composer (if you know the artist the next question is the composer isn’t it?)

    If you use the energy of the vacuum as the origin of these vibrations, (the coming out of particles and antiparticles in the absolute vacuum), the problem is staying the same, this energy of creation out of zero is coming from somewhere, it is so easy accepted as the explanation of radiation of black holes, but if it is arriving in the whole universe the factor is a 10^120 to great for our reality.

    Sorry that I brought up to problems at once here but the energy from the vacuum was used as an explanation on my question once by a string theorist.

    keep on thinking free


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  7. 7. kebil 6:33 pm 08/11/2011

    Wilhelmus, why would strings need an artist or composer. That is the same as saying that the universe needs a creator. And, as I understand it, the universe is created out of nothing, but that makes sense because the sum total of all the energy, forces, matter, and antimatter, dark energy, and dark matter, as well as the vacuum energy, sums up to zero

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  8. 8. jnanivn 12:55 pm 02/17/2012

    One needs to evolve new concepts to understand Prime functions-strings lead to Cosmic Dance of Lord SIVA.
    Cosmology vedas Interlinks help in this direction-Reflectors,3-Tier Consciousness, Source, Fields and Flows
    that form part of protective Index.Now Search Prime Cosmological Index.

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