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04/12/07 Journal Club / Vibrating Turtles 1
Irrefutable Theory of Vibrating Turtles
Journal ClubApril 12, 2007
Peter Mendygral
04/12/07 Journal Club / Vibrating Turtles 2
Irrefutable Theory of Vibrating Turtles
• 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
04/12/07 Journal Club / Vibrating Turtles 3
Outline
• Brief History• Current Status• Predictions• What Is It?
04/12/07 Journal Club / Vibrating Turtles 4
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
04/12/07 Journal Club / Vibrating Turtles 5
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)
04/12/07 Journal Club / Vibrating Turtles 6
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)
04/12/07 Journal Club / Vibrating Turtles 7
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
04/12/07 Journal Club / Vibrating Turtles 8
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”
04/12/07 Journal Club / Vibrating Turtles 9
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
04/12/07 Journal Club / Vibrating Turtles 10
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
04/12/07 Journal Club / Vibrating Turtles 11
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
04/12/07 Journal Club / Vibrating Turtles 12
What Can String Theory Predict?
• 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
04/12/07 Journal Club / Vibrating Turtles 13
What Can String Theory Predict?
• 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
04/12/07 Journal Club / Vibrating Turtles 14
What Can String Theory Predict?
• Large Hadron Collider
– Perhaps we may see some black holes created with properties suggested by string theory
– Non-detection wouldn’t rule it out
04/12/07 Journal Club / Vibrating Turtles 15
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)
04/12/07 Journal Club / Vibrating Turtles 16
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
04/12/07 Journal Club / Vibrating Turtles 17
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
04/12/07 Journal Club / Vibrating Turtles 18
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.”
04/12/07 Journal Club / Vibrating Turtles 19
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.”
04/12/07 Journal Club / Vibrating Turtles 20
Irrefutable Theory of Vibrating Turtles
• 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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