04/12/07Journal Club / Vibrating Turtles1 Irrefutable Theory of Vibrating Turtles Journal Club April 12, 2007 Peter Mendygral

04/12/07 Journal Club / Vibrating Turtles 1

Irrefutable Theory of Vibrating Turtles

Journal ClubApril 12, 2007

Peter Mendygral



• Greene, B., 1999, The Elegant Universe• Hedrich, R., 2006, “String Theory – From

Physics to Metaphysics”, arXiv:physics/0604171

• Woit, Peter., 2006, Not Even Wrong• Schwarz, J., 2007, “String Theory –

Progress and Problems”, arXiv:hep-th/0702219v2


Outline

• Brief History• Current Status• Predictions• What Is It?


Twisted History

• 1921: Kaluza-Klein Theory– E&M can be combined with gravity if a 4th spatial

dimension is added

• 1968-1974: Dual Resonance Model– Simultaneously developed by Y. Nambo, H.

Nielsen, and L. Susskind as an interpretation of the strong interactions of scattering particles

– Uses Euler β-function to give scattering amplitudes

– Solutions resemble modes of an oscillating string


Twisted History

• 1971: Supersymmetry Introduced– Symmetry between fermions and bosons– Proposed in particle physics to solve fine tuning

issues– Also proposed in string theory when fermions

were added

• 1970s: Gravity “Discovered” in String Theory– Accidental production of massless, spin-2 graviton– Combining gravity and supersymmetry =>

supergravity = (something I fear, like Jackson)


Twisted History

• 1984: The “Big Year”– Normalizations and cancellation of a few

infinities rids string theory of “anomalies”• Now incorporates parity violations• Symmetry is restored in small symmetry

breaking limit

– String theory now considered candidate to describe all elementary particles

– Requirement that 6 extra spatial dimensions exist (for symmetry reasons)


Twisted History

• Calabi-Yau Manifolds– Needed to get extra 6

dimensions, keeping 3 we know of, and enable non-zero fluxes of fields (e.g. magnetic) through space

– Fold extra dimensions onto generalized Calabi-Yau Manifolds of 6 dimensions

– Part of the problem with the theory today, there’s thousands and likely more of these


M-Theory(a.k.a. “Magic-Theory”)

• 1995 Edward Witten unveiled conjectures that 5 existing string theories were all descriptions of one theory– Side note, Witten briefly attended

UW-Madison as graduate student in economics and had aspirations of being a political writer

• He proposed they were all manifestations of one theory, “M-Theory”


M-Theory(a.k.a. “Magic-Theory”)

• M-Theory is not well defined as a theory• Supposedly non-perturbative version of

superstring theory• Theorists would like it to:

– Be unique (avoid the 10500 potential vacua)• Pick a specific Calabi-Yau shape• Get rid of the landscape problem

– Calculate from first principles the 105 extra parameters in supersymmetric standard model

– Save the environment and end the War

• No evidence that any of this is will happen


M-TheoryBranes Of All Types

• This new version requires higher dimensional entities than 1D strings

• Strings with open ends need a boundary on which to vibrate– p-branes, p is some number of dimensions– D-branes, membranes derived from Dirichlet

boundary conditions for open strings– Observable universe defined by 3D

D-brane evolving in time in 10 dimensional space

• This is purely speculative


What Can String Theory Predict?

• Cosmological Constant– Each realized universe in string theory

produces a new cosmological constant– Values more or less random– 1/10120 produce nearly the expected

value– With ≥10500 realizations there’s still a

little too many to pick from– Not much predictive power there



• Inflation– Mechanism would be D3-brane and

anti-D3-brane colliding and annihilating– One scalar mode of an open string

connecting the branes is the inflaton– Tension released in branes heats up the

Universe and many new strings are produced

– Cosmic superstrings• Tension so small they have avoided detection• Discovery of linear lensing may reveal them



• Hawking Radiation– The absence of a real theory of

quantum gravity prevents checking how this would work in a consistent theory

– For certain specially chosen backgrounds, string theory can predict the occurrence of Hawking radiation

– Of course not for physical black holes in 4 visible dimensions



• Large Hadron Collider

– Perhaps we may see some black holes created with properties suggested by string theory

– Non-detection wouldn’t rule it out


Current Status

• Over 30 years of effort– Lots of papers (7404 found on SPIRES

alone as of 04/11/07)– ~23 graduate programs– Hundreds of active theorists– Books, NOVA & Science Channel

programs, plenty of popular articles• The “only game in town” (except

Loop Quantum Gravity)


Current Status

•Not one testable experimental prediction– Only can describe phenomena already

described by other theories– Anthropic principle often invoked to

avoid landscape issue• Problem is not with the theory, it’s how

nature is• Leonard Susskind


Is It Even Science?

• Is it mathematics?– Peter Woit would say,

“Certainly not!”• Math requires rigorous proofs

of theorems via well defined constructs

• Is it physics?– Theorists not active in

string theory would say it’s more like math

– Lacks experimental/physical motivation


Is It Even Science?

• Is it faith?– Harvard PhD John Hagelin would

say yes• Distinguished physicist with

plenty of well cited papers• Now identifies unified superstring

theory with that of the Maharishi’s “unified field of consciousness”

– Michio Kaku• “The mind of God is music

resonating in 11-dimensional hyperspace.”

– String theory often defended with the phrase: “…you can’t falsify string theory, not yet.”


Is It Even Science?

• The theory is a “set of hopes that a theory exists”

• Can it be falsified?– Philosopher Karl Popper proposed

science is:• An explanation that can be used to make a

falsifiable prediction

• “It’s turtles all of the way down.”



• From Not Even Wrong :“…what if I decide to speculate that at

sufficiently short distance scales, physics is to be described not in terms of particles, strings, etc., but in terms of turtles? …most people would say that I was not doing science. …if after a few months work I did manage to derive the parameters of the standard model from the turtle assumption, then people would have to change their minds…”


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04/12/07Journal Club / Vibrating Turtles1 Irrefutable Theory of Vibrating Turtles Journal Club April 12, 2007 Peter Mendygral