richard kenway everything is a computer richard kenway
TRANSCRIPT
Richard Kenway
Everything is a
computer
Richard Kenway
May 2006 Richard Kenway 2
Theory of Everything
• TOE is unique: no free parameters– one Universe (God is a mathematician)
• TOE is not unique: various parameter values are allowed– a Multiverse (anthropic), or– one Universe is chosen (intelligent design)
conjecture 1: our Universe is completelydescribed by a mathematical model†
† includes quantum mechanics and so does not obviously exclude consciousness, free will, time travel, …
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objective of physics
• guided by mathematical beauty/symmetry
• falsification by experiment/observation …reverse engineering
the TOE
TOE today: General Relativity + Standard Model
reality = TOE today
• 25 free parameters … unlikely to be fundamental constants– our existence is very sensitive to their values
• not fully quantum … gravity
• weird enough
• discrepancies with experiment → new physics = progress
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Standard Model
• matter, as we know it, is made
of quarks and leptons
• interacting through four forces
QCD
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s
uu u
d
unified theory … consequences
• all particles are manifestations of one
fundamental entity
→ quarks can change into leptons
… protons decay
u u
d
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do protons decay?
• watch 50 kton of water 1km underground
(1 kton = 1033 protons)
• none observed
years103.2 lifetime 33 Kp
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calculating the proton lifetime
• if we compute the ‘QCD factor’, the experimental lifetime
bound constrains theories of new physics
• this requires simulating how quarks and gluons make a
proton
u
?
u GeV 10at physics newfactor QCDyears103.2 lifetime 1633 Kp
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simulation
• for imaginary time ~ a probability
→ Monte Carlo generation of quantum fields
• works for QCD
• other theories have a sign problem
→ the motivation for quantum computers
conjecture 2: the TOE may be simulatedto arbitrary precision on a computer†
† may need a quantum computer …‡ many worlds and their consequences enter here …
Si
Si
OO
eD
eD
S
Si
it
ee,
‡
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simulation of QCD
solverequation linear sparse
0,
Carlo Monte (hybrid)
lattice spacetimeEuclidean finite
1
,,det1
mUDUS eUOemUDDU
ZO G
• integral over anti-commuting quarks and SU(3) gluons
• we cannot measure experimentally quark masses or mixings,
only hadron masses and decays … reverse engineer
quark masses (& mixings) +
gauge coupling
properties
of hadrons
Lattice QCD
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computational cost and parallel computing5.35.2
PS
5.80.70.55.4 11
operations #
MaL
a
L
• lattice spacing must be
extrapolated to zero
keeping box large enough– halving lattice spacing
500 computing speed
• performance number of processors
Moore’s law: microprocessor speeds double every 18-24 months
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determination of Standard Model parameters
depressingly self-consistent
• only the Higgs
boson is missing
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but most of our Universe is also missing!
dark
ene
rgy
→
atoms + dark matter →
• atoms 4%
• dark matter 23%– inflaton, neutralino, axion, …
• dark energy 73%
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effective theories
• simulation bridges between short (L) and long scale (L')
• computational cost of virtual reality is bounded but very large
conjecture 3: reality is described by a finite set of effective theories each of which can be simulated†
† beginning with the TOE
1,D,e,De TTLx
S
LLx
S
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reverse engineer our Universe today
visible matter →
dark matter →
Millennium simulation 10,077,696,000 particles
?
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the challenge for computing
• Higgs boson or new physics
must be found at LHC– the next layer in the onion– QCD is an effective theory
• will classical digital
computers be sufficient?
conjecture 4: everything can be simulated†
† everything is a simulation?
QCDOC … the last pre-LHC machine
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life, the Universe, everything…
• nuclei … neutron stars
• fusion … solar weather
• chemistry … designer
materials
• complex molecules …
living organisms
• brain … mind