# Strings, Gravity and Locality:

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Strings, Gravity andLocality:

AnOverview of Modern Cosmology

Physics at the Dawn of the 20th Century: The Clockwork UniverseNewtons Third Law of MotionF=mdx/dtUniversal Law of GravitationF=GMm/r2Maxwells EquationsE = /x E = B/tB = 0x B = J + E/t If one knew the positions of all objects occupying space, these laws would allow him to predict all events until the end of time : nothing could be uncertain; and the future just like the past would be present before his eyes.

Physics at the Dawn of the 20th Century: Newtons Absolute Space and TimeAbsolute, true, and mathematical TIME passes equably without relation to anything external, and thus without reference to any change or way of measuring of time. Absolute, true, and mathematical SPACE remains similar and immovable without relation to anything external.

Physics at the Dawn of the 20th Century: The End of Physics

"Everything that can be inventedhas been invented" U.S. Patent Office in 1899.

The end of science is at hand all that is left is working out details, refining the value of certain physical constants to a few more decimal places and mopping up of a few remaining but trivial questions.

The 20th Century Revolutions: General Relativity & Quantum Mechanics

General Relativity: A New Understandingof Gravity and SpacetimeGravity is the curvature of space and time.Equivalence of mass and energy (E=mc2).Spacetime Space and time no longer independent and absolute.Time dilation and length contraction.

General RelativityEinsteins Field EquationsCurvature Tensor - G Represents geometry of spacetime.

Stress-energy Tensor -T Distribution of matter and energy.

Cosmological Constant- - Property of space. - Needed for a static universe.The Field Equations

G = T

Static Universe

G + = TSpace tells matter how to move. Matter tells space how to curve.

Early Unified Field TheoriesEinstein spent last 30 years of life working on this vision without success.Kaluza Klein TheoryPostulated curled up 5th dimension.Offered hope of unifying electromagnetism and gravity.Later experiments ruled this out.No success.

Birth of Modern Cosmology

The expanding universe.Uniform expansion.v = H0r

Cosmic Microwave background.Cosmological principle2.7KFrom when Universe 300,000 yrs old.

The Big BangA Dynamic Universe - General Relativity. - Evolving from early homogenous state. - Decelerating expansion. - Possible beginning and end.Fate determined by amount of mass (critical mass).Finite/unbounded, infinite/bounded, etc?.~ 15 billion years old (~ /H0).

Quantum MechanicsThe Other RevolutionWave-particle duality.Heisenberg Uncertainty Principle.Complementarity.Causality, probability and clockwork. Non-locality. Copenhagen.

God does play dice!

Quantum Mechanics The FundamentalsUncertainty Relationships

xP = /2Et = /2AB = /2

Schrdinger's Equation

22(x,t)/2mx2 + U(x)(x,t) = i(x,t)/tBells Inequality

P(a,b) P(a,c) 1 + P(b,c)

Quantum Mechanics & CosmologyQuantum fluctuations: The Genesis engine?Quantum fluctuations: A vacuum alive with energy.Quantum fluctuations: A natural source for a cosmological constant.Quantum fluctuations: CMB anisotropies, the seeds of structure.Evaporating black holes.

Quantum Mechanics andThe Standard ModelForcesElectromagnetic (QED)Weak ForceStrong force (QCD)No gravity

Misc.Electroweak unification.Particle masses are added in not predicted.ParticlesFermions (matter)QuarksLeptonsMatter/Anti-matter pairs.Bosons (forces)GluonW and Z bosonPhoton

Dark Matter and NeutrinosDark MatterBaryonic.Massive Compact Halo Objects (MACHOS).Supermassive Black Holes.Non-Baryonic.Weakly Interacting Massive Particles (WIMPS).NeutrinosFundamental particle.Weakly interacting (Trillions pass through our bodies every second).Very small mass.Under ground tank detectors.

Cosmology in the Early 1990sBig BangGeneral RelativitySmooth & homogeneousCMB anisotropies (QM)Expanding universeDeceleratingFate dependant on massVacuum energyStandard ModelFundamental particlesElectroweak unificationUniverse seems flat.Something missing?QM GravityUnification of forcesHomogeneity of CMBFlatness of spaceMass questionDark matter

ExtensionsUnified Field TheoryGrand Unification Quantum Gravity (graviton)Higgs interactionHiggs bosonInflation10-35s A.BB10-32s duration1050x expansionSymmetry breaking/Vacuum energy/ cosmological constantHomogeneitySmooth curvatureSeed structureSupersymmetryfermions bosons bosons fermionsEvery particle has a super partnerPredicts Higgs boson

Superstring Theory:The Theory of Everything?HistoryString theory 70.Initially strong force.Fails, butPredicted massless spin 2 particle graviton?Quantum gravity?Supersymmetry + gravity = 11-D supergravity. Supersymmetry + strings = 10-D superstrings 80.Theory of everything. 5 versions.Duality and the relationship between theories 95.0-9-D P-branes.

Superstring Theory:What is it?1-dimensional strings 10-33cm.Particle - mode of vibration.MatterForce10-dimensional spacetime.QM and gravity.By doing away with dimensionless point.In fact, requires gravity!Spacetime not fundamental Emergent on a classical scale?

M-TheoryThe Real Theory of Everything?11- dimensional theory.Unites 5-string theories while including supergravity and p-branes.Duality - Simply different aspects of same theory.Ends of open strings confined to move within brane.Properties of branes revealed by examination of strings which endpoints it contains.Dimensionality may only emerge in semi-classical contexts as an artifact of particular solutions.Do not know the final form yet.

String/Brane CosmologyBig Bang modelNo singularity.Same mechanism as for QM/GR.Space may not be fundamental on these scales.Cosmic strings seeding structure

The Universe as a brane.3 dimensional space as a 3-brane.Open strings constrained to brain would not see outside. So large dimensions could be unnoticed.Gravity not constrained: measurable consequences.Measure extra dimensionsEkpyrotic UniverseUniverse as a 3-brane afloat in a higher dimensional space with other 3-branesInitially cold and flat3-branes collideEnergy results in matter and radiationFinite temperatureInflation

Cyclic ModelSelf dual pointContraction until dual to large scale

Cosmic Acceleration!1998 studies - Rate of expansion increasing!Dark Energy Cosmological constantQuantum vacuum energyToo much thoughGeneral relativity negative pressureG + = TG = + TProperty of space form of energy

M-Theory Leaked GravityGravity not confined to braneLeaks puts tension on braneinherent warp Einsteins Measurable large distances

Cosmic Composition95% Universe mystery.30% Dark matter.Non-baryonic.65% Dark energy.5% normal stuff..3% Neutrinos.

MultiverseLevel I Cosmic HorizonSame physics.Different Initial conditions.infinite space - Infinite regionsLevel II Bubble InflationSame equationsPossibly different constants, particles and dimensionality.Chaotic inflation bubble regionsLevel III QM Many WorldsLevel IV MathematicalAny mathematical model.Any laws of physics.

9 Questions for21st Century PhysicsAre there undiscovered principles of nature: new symmetries, new physical laws? (M-Theory, etc)How can we solve the mystery of dark energy? Are there extra dimensions? Are all forces simply one aspect of a single force? Why so many kinds of particles? What is dark matter and how can we make it in the laboratory? What are neutrinos telling us? How did the universe come to be? What happened to all the antimatter?

How Do We Know What We KnowNature shows us only the tail of the lion. But I do not doubt that the lion belongs to it even though he cannot at once reveal himself Einstein.

Scientific knowledge is a body of statements of varying degrees of certainty Feynman

It is 'Scientific' only to say what's more likely and less likely Feynman

It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we say about Nature. - Niels Bohr

All of us live with the knowledge that there is an ultimate truth and our mistakes will be discovered. - Persis Drell

The Landscape of Cosmology

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