Richard Kenway Everything is a computer Richard Kenway

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, …



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


Standard Model

• matter, as we know it, is made

of quarks and leptons

• interacting through four forces

QCD


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


do protons decay?

• watch 50 kton of water 1km underground

(1 kton = 1033 protons)

• none observed

years103.2 lifetime 33 Kp


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


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,

‡


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


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



determination of Standard Model parameters

depressingly self-consistent

• only the Higgs

boson is missing


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%


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


reverse engineer our Universe today

visible matter →

dark matter →

Millennium simulation 10,077,696,000 particles

?


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


life, the Universe, everything…

• nuclei … neutron stars

• fusion … solar weather

• chemistry … designer

materials

• complex molecules …

living organisms

• brain … mind

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Richard Kenway Everything is a computer Richard Kenway