Cal Poly Physics 111 Final
Unified electric and magnetic fields to come up with a theory of light. Electromagnetic radiation as vibrating and magnetic fields
According to James Clerk Maxwell, what is light?
Q.E.D. does have infinities in the probability calculations, but the infinities are controllable.
Are infinities encountered in Q.E.D.? Are they controllable? Why?
His velocity keeps changing direction, so he feels as though direction change is constant change in acceleration or speed
As Slim stands still on the outside edge of the tornado ride moving at constant speed, why is he accelerating?
Yes, the muon would make it to earth. The muon lives 10x longer when falling to earth
As viewed from earth how does the lifetime of an approaching muon compare to a muon at rest? How does this change in a muon's lifetime affect how far the muon travels as viewed from earth?
The properties we see are due to the vibrations of the strings which occur by stretch and compact -strings vibrate which determines mass, charge, energy, force, or interactions
Being as precise as possible, according to string theory what determines properties of particles we see in our large extended dimensions? You may use the electron mass as an example.
Rough: to see small sizes (high energy), we use a small QM wavelength which is inversely proportional to the energy. At LHC, the particle energy is about 14 Tev (tera electron volt) which can probe ~10^-21 cm or 10^-19m
Brian Greene discusses two answers for how string theory resolves the conflict between general relativity and quantum mechanics. Explain the rough answer and why we shouldn't be satisfied with this answer.
Yes, because size does not matter, space is space!
Can large spatial dimensions tear? Explain why we believe this to be true or not.
In GR, space cannot tear, needs to remain smooth
Can space tear in Einstein's general theory of relativity? Explain.
-Observers in relative motion agree when 2 point particles interact with each other -Yes, there is a single point
Can two observers in relative motion agree on the interaction point for two point particles? Explain.
bosons and fermions come in pairs. for every fermion particle (ex: electron) in the standard model, there is a super partner boson (ex: selectron, spin 0)
Define supersymmetry.
yes, people were expecting superpartners to be discovered at the larger hadron collider (LHC) but unfortunately, none yet (within a year)
Do we expect to be able to find superpartner particles experimentally? If so, when and where might they be discovered?
NO, not necessarily, but 1 is much easier
Does string theory say it is impossible to have more than one time dimension?
-Number of families depend on the number of holes -If there are 3 holes in an even OR odd dimensional space, they are dual to each other therefore yield the same physics
Does the number of particle families depend on the number of even-dimensional holes or odd-dimensional holes? Explain.
Electromagnetism and gravity
Einstein spent his life trying to unify which forces of nature?
-mass is proportional to energy, string energy is related to frequency so frequency is related to string vibrations -Mass is proportional to energy & String energy is related to string vibration or frequency and amplitude
Explain how a fundamental string can have mass
light does not travel instantaneously, so it takes time to Gracie to get the signal of what time it actually is. Time slows down when one moves relative to the speed of light
Explain how it is possible to understand the answer to question above
figure 6.9: George see the strings interact closer to the "bottom" (in a different place) due to a different motion and the relativity of simultaneity
Explain how two observers in relative motion can not agree on the interaction point of two strings?
-Quanta: being projected thru slits -Wave/particle duality: manifests in one single spot on the screen -Probability: Don't know position of electron, there is probability that it will hit somewhere on the screen QM does not know what slit it will go through -Uncertainty: If you know which slit particle goes through you have reduced uncertainty in position increased velocity
Explain how you can understand the four big concepts in quantum mechanics using the double slit experiment?
matter warps space time and space time influences the movement of matter
Explain in one concise sentence the essence of Einstein's general theory of relativity.
-quantum-because all of the probabilistic and uncertainty issues -field theory-because it merges the quantum principles into the previous classical notion of a force field -relativistic-because special relativity is also incorporated.
Explain in words the key features of a quantum field theory (Q.F.T.)
-Borrowing energy for a short period of time to go through a physical barrier -To tunnel through an energy barrier that classically can't be penetrated, a particle borrows energy from nothingness for a short amount of time, consistent with the energy time uncertainty. Once through the barrier, energy is returned.
Explain quantum tunneling.
In 1907 before General Relativity, Einstein realized that light should be bent in a gravitational field using the Equivalence Principle
Explain using the equivalence principle and a picture why light bends in a gravitational field.
Might think person and light it moving, but you actually only see person moving, so you see 670c less than you had imagined
Explain with a picture and a few words why the speed of light being a constant for all observers regardless of their state of constant velocity motion seems paradoxical?
-Farther apart the force gets weaker -At a large distance, energy fluctuations shield the bare charge of the electron. -The charge strength is less. -At a small distance, there is less shielding, stronger charge and stronger force.
Explain with a picture why the electromagnetic force gets stronger when probed at small distance or high energy?
You need to switch the uniform vibration number and winding number
For a universe of size R to be dual to a universe of size 1/R, what must happen to the winding mode number and uniform vibration number?
time curvature is easier to detect, therefore making it more important
For weak gravitational fields like the earth, is spatial curvature or time curvature more important?
-Weak coupling, when the string coupling constant<1 -Each term has interaction, when they terms are added up the more interactions the more precise it becomes
For what values of the string coupling constant does perturbation theory work? Explain why.
1. Muon is at rest 2. Earth and its people are moving towards the muon 3. Lorentz Contraction shortens the distance to only 600m
From the point of view of the muon at rest, how do we explain the fact that the earth reaches the muon before it decays?
The non-traveling twin, Gracie, has a much easier perspective to understand. For every 10 years for her, it is 1 year for her twin
From whose perspective can one easily explain the twin paradox? Explain.
UN Train Example -light reaches forward-land and backward land simultaneity -Light is moving at the same speed but has a shorter distance, so off the train the light travels a shorter distance to forward land, reaching forward land first and then backward land.
Give an example demonstrating the relativity of simultaneity.
-The agreement between experiment and theory is 1 part in about 10^11 -A billionaire has a billion dollars or 10^9 dollars or 10^11 pennies -1 part in 10^11 says you know about all of your pennies as a billionaire and thats pretty precise!
Give an example of the precision of Q.E.D.
there has never been an experiment that contradicts quantum mechanics
Given the crazy ideas coming from quantum mechanics why should we believe it?
Yes, it has been proven by atomic clocks and jet planes capable of measuring small distances -atomic clocks can measure nanoseconds
Has something similar to the twin paradox been confirmed experimentally? Explain.
-string theory easily predicts massless particles but has difficulty predicting small mass particles like electrons, neutrinos, quarks, etc (all matter particles in the standard model) -gravitron=0; string theory predicts mass of graviton to be 0 -Not an electron because they have small, unpredictable finite mass
Has string theory been able to predict the mass of a graviton? An electron?
BPS states, if they have the same BPS state then physics is the same so they are strong-weak dual
How are B.P.S. states used to show the strong coupling limit of one string theory is dual to the weak coupling limit of another?
-larger wavelengths requires a smaller frequency or a small wavelength requires a bigger frequency because the product -must equal the speed of light wavelength x frequency=speed=C -inversely related
How are wavelength and frequency related for light waves?
Principle of relativity
How can we know conclusions we reach about light clock also conclude to rolex watch
the photon takes all paths simultaneously; goes through both slits/knows both slits are open
How do you explain the results in questions 2. above according to Feynman?
1. Schodiner: the photon has a probability to go through both slits equally 2. Feynman: photon takes all paths simultaneously
How do you explain the results in questions 2. above according to Schrodinger?
Theory of GR warping or bending of space time by matter creates gravity -ripples in space time called gravity waves travel at the speed of light
How does Einstein's general theory of relativity resolve the conflict
Adds 7 more dimensions giving us 11 total -largest things are made of tiny vibrations
How does string theory force us to think differently about space?
-The clock on earth ran 4 nanoseconds slower when done in 1976 by NASA -Time goes faster for the clock 6,000mi in the air. The accelerated clock slows down, which means that the time goes slower for the clock on earth. Less gravity = less acceleration = time runs faster
How does the flow of time on earth compare to an identical clock 6,000 miles above the surface? How do we know?
-quantum electrodynamics is the QFT describing electromagnetism. Therefore, because we know that the fundamental particles involved in the electromagnetic force are photons we can use the Feynman Diagram to visualize how the force works. When two electrons come together, they repel each other, which is the "shooting" of photons back and forth between themselves.
How does the force in quantum electrodynamics (Q.E.D.) work?
-E of uniform vibration = Nuv/R -inverse relationship
How does the string uniform motion energy depend on the radius of the compact space?
-The winding number is the number of times the string wraps around -Ewn = (Nwn)(R)
How does the string winding energy depend on the radius of the compact space?
-spin: intrinsic spin of the particle itself which creates a magnetic field -Spin is the particles(StringS) are spinning in a circle. -To determine the spin you can use a magnetic field
How is the spin of a particle determined?
11 dimensions - extra dimensions are needed to give acceptable 0-1 range of probabilities
How many space and time dimensions are in M-theory?
10 dimensions: 4 familiar, 6 hidden
How many space and time dimensions are in the original string theory?
Both clocks run slow relative to another, they see each other as time has slowed. Gracie the non-traveling twin sees George, slow down, stop, and speed back up again
How will two people (such as Gracie and George in the text) moving away from each view time passing on the other person's clock?
smaller than 1cm, wavelengths bend around small object, so then you cannot see with high precision
If I wanted to detect something with a size of 1cm what wavelength of light would I need to use? Explain.
A garden hose, draw both large and compact dimensions -only case you can properly visualize with a drawing of both large and small dimensions
If a very small compact dimension were to grow in lineland and become visible, what type of surface would you have?
-large amplitude of low frequency light, might think the electrons would come off because it's high energy but this doesn't happen! because the individual photons don't have enough energy
If low intensity light is shining on a metal and no electrons are emitted, using classical physics what do we expect to happen as the intensity is increased?
There are other point particle SUSY theories, but since strings require SUSY this would be a step in the right direction
If supersymmetry is discovered at the Large Hadron Collider, will string theory be validated? Explain.
Not necessarily, super gravity is a SUSY point particle theory in 11 dimensions
If supersymmetry is not discovered at the Large Hadron Collider, will string theory be proven wrong? Explain.
9 spatial dimensions, 1 time (10 total) Calabi yau shapes meet the stringent requirements
If the original string theory is correct (disregard M-theory for the moment), how many spatial compact dimensions are there? What shapes meet the stringent requirements of string theory?
-string theory 10 dimensions -coupling causes 11 in M-Theory
If the string coupling constant is small (less than 1), how many dimensions does string theory or M-theory have?
On the ride you are constantly accelerating, A=G, therefore you are being pulled by gravity
If the tornado ride were in deep space far from gravitating objects, in what sense would the ride mimic gravity experienced on earth?
tearing space would be the first step, can be done in string theory
If you wanted to create a wormhole to travel between your house and Cal Poly what would you need to do to space?
John Schwarz showed that the massless messenger particle could describe gravity if the strings were planck length 10^-31m
In 1974 what did Schwarz and collaborators show the massless messenger particle of string theory could describe?
They are put into accelerators
In particle physics experiments how are probes of small wavelength created?
Strings can wind and translate across space points can only translate across space
In regards to a compact dimension, how is string motion different from a point-particle?
Quarks and electrons strings that vibrate
In string theory what ARE fundamental particles such as electrons and photons?
The way the strings vibrate controls all of the properties of particles and forces
In string theory what controls the number dimensions which are large and extended instead of being small and compact?
-Previously physicist (Dwac, Feynman, -Heisenberg, Pauli) did try to make non-point particle theories work but they failed failures: 1.faster than light particles (Tacyons) 2. probabilities didn't add up (to one→ acceptable range of probabilities 0-1)
In the past when physicists tried make a quantum field theory of non-point particles what problems did they encounter? Who were some of these physicists?
when in the quantum cafe, the value of Planck's constant is large, allowing us to more easily see the ice cubes uncertainty in position and uncertainty in momentum
In the quantum cafe, why are the ice cubes rattling around in the glasses?
If the minimum energy a particular wave can carry exceeds the energy it is supposed to contribute, it can't contribute and instead lies dormant
In the quantum mechanical explanation of blackbody radiation why can't very high-energy photons contribute to the radiated energy?
-do not depend on whether the string coupling is strong or weak -highly constrained
In what sense are B.P.S. states non-perturbative?
Success: 1. predict orbits of planets extremely precisely 2. mass creates gravitational field and force, unified forces of gravity on earth to be same with forces in heaven
In what sense did Newton unify the heavens and earth with his theory of gravity?
Superstring theory predicts supersymmetry. Turns out string theorists discovered 5 constant theories
In what sense did supersymmetry find its beginning in string theory?
explains that there is one fundamental entity- the string
In what sense does string theory simplify our view of fundamental particles?
An electron, electron neutrino, muon neutrino and all via the weak force
Into what particles does a muon decay? What force plays a role in muon decay?
Yes and no, not proven by experiment, but solves some compelling in physics
Is string theory accepted?
No, we learned in flat space where C=2pieR, curved spaces that the curved spaces circumferences does not hold true
Is the geometry you learned in high school obeyed on the tornado ride? Explain.
Greene
Name a physicist who worked on orbifolding.
1. frequency 2. wavelength 3. amplitude 4. period
Name four characteristics of a wave?
1. Quanta: packet or bundle of energy 2. Particle/wave duality: all fundamental particles are both wave and particles 3. Probabilistic Theory: if multiple outcomes of an experiment are possible, you can only determine the probability of a particular outcome 4. Uncertainty in theory: called Heisenberg uncertainty relations. Experiments that demand the idea of quanta
Name four primary characteristics of quantum mechanics
1. Disappearing cigarette 2. Ice cubes left his glass 3. Walk through walls
Name some of the interesting phenomena found in the quantum cafe (video) or in H-bar (text)
electron (½) fermion - selectron (0) boson photon (1) boson - photino (½) fermion non standard model particles graviton (2) boson - gravitino (3/2) fermion Quark, spin ½, Fermion - Squark, spin 0, Boson
Name the superpartners of the particles in the standard model and their corresponding spin.
1.makes the strings small (planck length) 2.natural mass scale is large (planck mass) 3.masses tend to be integer multiples of the planck mass
Name three consequences of a large string tension.
Telescope 5th force discovered might find an electric charge of 1/7
Name three possible scenarios for which string theory could be validated.
1. why wouldn't nature use this symmetry, nature has used all the other symmetries of space, time and motion 2. fine tuning problem: (pg 174 bottom) parameters in the standard model need to be fine tuned to one part in 10^15 the fine tuning is not needed if nature obeys supersymmetry 3. at high energy or small distances the 3 forces on the standard model (EM, weak, strong) unify SUSY is true
Name three reasons why we might expect supersymmetry to be a symmetry of nature?
1. Precession of perihelion of mercury's orbit 2. Need to wait until 1919 for a total lunar eclipse to be able to see light from a distant star being bent by the sun's gravitational field
Name two early confirmations of Einstein's general theory of relativity.
Determining the correct Calabi Yau space Difficult to calculate masses of particles in mirror symmetry
Name two major difficulties Greene and collaborators encountered when comparing the after space-tearing flop transition Calabi-Yau manifold with it's mirror.
1. Nuclear weapons 2. Nuclear power, diablo canyon 3. Particle accelerators make particles -at LHC 2 protons collide to make Higgs Boson
Name two technological applications of Einstein's famous equation, E=mc2
Newton did not understand how gravity worked
Newton was embarrassed by what aspect of his theory of gravity?
-Happy thought: equivalence principle which says if gravity = acceleration, and acceleration is warped in spacetime then gravity is warped in spacetime as well -Theory of general relativity: matter warps space time which affects how matter moves -Equivalence principle, gravity is indistinguishable from acceleration. Acceleration is equivalent to curved spacetime. Therefore, gravity is equivalent to curved spacetime.
Starting with the equivalence principle, explain the logical connections allowing Einstein to discovery the general theory of relativity.
1. Terrorist on bomb scale 2. Elevator rise
Starting with the equivalence principle, explain the logical connections allowing Einstein to discovery the general theory of relativity.
1. Time Dilation 2. Lorentz Contraction 3. Relativity of Simultaneity
State three observations about space and time that can be made by observers moving relative to each other.
-Low mass, low energy probe must be used for large distances -Natural choice because this is the easy way to do it
To conclude that the minimum size for a dimension is greater than 1 (the Planck size), what type of probe must be used? Why is this the natural choice of probe?
-When all standard model force and matter particles have superpartners. -High energy or small distances and all partners have subpartners
Under what conditions do the strong, electromagnetic, and weak forces unify?
Because it is has a further distance to travel
Using a light clock, clearly state the argument for why time slows for moving clocks relative to stationary observers.
We can easily see the time slowing down because we can see the distance changes. The speed of light is constant, if the distance is bigger the time takes longer
Using a light clock, explain why we can only easily see time slowing for moving clocks relative to stationary observers when the clock moves close to the speed of light.
-Slim is on the outside and measures a larger distance, therefore a larger circumference than off the ride -Slim's ruler is Lorentz Contracted
Using the tornado ride as an example, clearly explain how space is warped (or curved).
From off the ride perspective, only using special relativity the motion through space, is the greatest on the shorter edge, therefore the motion through time must be the slowest
Using the tornado ride as an example, explain how acceleration leads to warping of time.
we would need an accelerator the size of the galaxy. -the LHC can bring us to 10^-21 but we need to get to 10^-33 cm
Using today's particle accelerators what length scale can be probed? How does this length compare with the Planck length? Will a manmade particle accelerator ever be able to probe the Planck length?
1. Gravitational - apple falling to earth 2. Electromagnetic Force - hold atoms together, friction force 3. Strong (nuclear) force - holds quarks together 4. Weak (nuclear) force - decay of neutron or muon
What are the four known fundamental forces of nature? Give an example of each
1. Resolution of Conflict between GR and QM 2. Explain theory of everything 3. Unification of the 4 fundamental forces
What are the goals of string theory?
-space translations: experiments performed in different locations give same results rotations: experiments in different -orientations give the same results time: same experiments results today and tomorrow motion: -principle of relativity the equivalence principle
What are the known symmetries of space, time, and motion?
-Heterotic 0, Heterotic -E, Type I, Type II A, Type II B -the five superstring theories appeared to need 10 total space + time dimensions -M theory relates the five superstring theories to each other and M theory in 11 spacetime dimensions
What are the names of the five different consistent superstring theories? In light of the second superstring revolution is five potential theories of everything a problem?
1. (uncertainty in position) x (uncertainty in momentum) greater or equal to hbar/2 (very small number) 2. (uncertainty in time) x (uncertainty in energy) greater or equal to hbar/2
What are the two Heisenberg uncertainty relations we discussed in class?
-Ordinary vibration: the wiggling of the string -Uniform Vibration: quantum mechanical wavelength or vibration associated with motion and energy due to point particles
What are the two types of vibrational energies associated with a string? Briefly explain what each energy corresponds to?
-Smallest a dimension can be is Planck Size -There are only two ways to measure distance
What are two consequences of quantum geometry?
If energy is quantized comes in clumps of energy (called photons) with the energy (E) proportional (∝) to frequency (f)
What did Planck have to assume to properly predict blackbody radiation?
Even dimension hole: hole 2, 4, or 6 dimensions - example: hole in a piece of paper Odd dimensional hole: hole in 1, 3, or 5 dimensions - example: human or sphere with hole through them
What do we mean by an even or odd-dimensional hole?
You can't tell the difference between the two physics in the two different spaces -Mirror Symmetry -Type IIB -Strong Weak Coupling
What do we mean by duality in string theory? Give an example.
energy is "lumpy" (photons that are little bundles or quanta of light); the energy of each photon is proportional to the frequency of the light wave
What do you have to assume to properly explain the photoelectric effect?
-The graviton does not depend on the shape of the compact dimensions, "Robust Features" -But the electromagnetic, weak, and strong forces do depend on structure of the compact space
What does Witten mean when he says that string theory predicts gravity?
supersymmetry
What does the super in superstring theory refer to?
The quantum foam shows particles being created out of nothing for a short amount of time
What happens to space time at small space and time scales? How small is small?
you alter it, ,higher energy photons with smaller wavelengths
What happens to the velocity (or momentum) of a particle when you use short wavelength light to detect its position?
They don't work they give infinite answers
What happens when calculations are made in a quantum field theory of gravity?
-electrons also create an interference pattern the the double slit experiment -electrons behave the same as photons and produce the same interference pattern; therefore, display the same double slit results
What happens when you repeat the experiments in questions 1. and 2. using electrons instead of photons?
-using classical physics the energy emitted from a blackbody is infinite but the energy is finite so, the theory is wrong -it is actually infinite because classical physics says energy in a wave only depends on amplitude all oscillators which create the light are excited and there are an infinite number leading to infinite energy -Planck solves blackbody radiation problem
What happens when you try to explain blackbody radiation with classical physics?
-General relativity requires smooth spacetime. QM suggests quantum foam 1) QM uses quantum foam & GR requires space to be smooth 2) GR gives infinite answers for Quantum theory of gravity
What is (are) the conflict(s) between general relativity and quantum mechanics?
His equations suggested that the universe is static when in fact it is expanding.
What is Einstein's biggest blunder?
-Discovered matter waves -this is way an electron is a wave
What is Louis de Broglie's contribution to physics?
Measures a photon moving between two mirrors, one tick is the photon moving back and forth once between mirrors
What is a light clock?
anything with temperature (light bulb filament, you, me, straightener, earth, sun) radiates photons/electromagnetic energy or light energy. The hotter anything is, the more it radiates
What is blackbody radiation?
You can't tell the difference of whether you're at rest or moving at constant velocity
What is meant by the principle of relativity?
Attachment of points in one Calabi-Yau using precise mathematical rules to create a new distinct Calabi-Yau space
What is orbifolding?
-Quantum electroweak theory unites the weak and electromagnetic force -It's important because the unification of these two forces is possible
What is quantum electroweak theory and why is it important?
-Supergravity is a point particle theory of supersymmetric gravity in 11 dimensions -M-theory at low energy is the same and dual to 11 D symmetry
What is supergravity and how is it related to M-theory?
selectron
What is the anti-particle of an electron called?
Finding the resolution between GR and QM -if you allow fundamental particles to be strings, conflict can be resolved
What is the biggest conflict in modern day physics that string theory hopes to resolve? What problems in physics require resolution of this conflict in order to be more fully understood?
1. Gravity acts instantaneously across space -Einstein's theory said nothing can go faster than the speed of light--things don't happen simultaneously 2. Did not know how it works -GR solved
What is the conflict between Newton's theory of gravity and Einstein's theory of special relativity?
-Riemannian geometry is based on the idea of points as the fundamental entity, Einstein's theory of gravity is based on smooth, curved spacetime uses the math of Riemann geometry -Quantum geometry is used for Planck's lengths, fundamental entity is being a string
What is the difference between Riemannian geometry and Quantum geometry? For our universe, at what length scales is each geometry important?
We cannot tell the difference between gravity and acceleration
What is the equivalence principle? Explain with the aid of a picture.
at SLAC (stanford linear accelerator) collide electrons and positrons (antimatter of an electron) -photons come out when they collide -if these particles are strings, then for strings (not points) the exact interaction point depends on your state of motion and thus is not unique
What is the more precise answer for how string theory allows for a consistent theory of quantum gravity?
-Mpl=10^-19 Gev -natural mass scale is large (planck mass)
What is the natural mass scale for a string?
-if a photon has sufficient energy (high enough frequency) electrons are emitted -when the energy (threshold) of the photon matches the energy holding the electron to the metal (work function), the electron can be emitted
What is the photoelectric effect?
The strength of the interaction between strings
What is the physical significance of the string coupling constant?
if we have a theory of everything, then we know all particles and there interaction, then we know everything including emotion
What is the reductionist viewpoint?
the theory of the three non gravitational forces (strong, weak, electromagnetic, NOT gravitational) and the three families of matter particles
What is the standard model of particle physics?
strings, tension accounts for differences in energy
What is the structure of the fundamental particles in string theory? How does string theory account for the differences between fundamental particle properties like the mass and charge of electrons and quarks?
Perturbation theory
What is the tool used by physicists to understand the approximate equations of string theory?
Two identical twins, one stays on earth, one travels, traveling twin ages slower. -This can only been seen if you travel fast
What is the twin paradox?
The spacetime is so warped (or gravity) is so strong, that no even light can escape observed in the center of galaxies and as stellar remnants. So small with heavy mass, light cannot escape it
What makes a black hole black?
-That the Calabi Yau spaces have 3 holes which explains the 3 families of particles -Unfortunately, this is not a unique prediction of string theory, there are many possibilities with 3 holes -Not unique because it can be distorted and there are about 10,000 of them
What must string theorists assume about the compact space to create three families of particles as found in the standard model? Is this a unique answer? Explain.
QM cancellations between oscillations
What needs to happen for a string to have a small or zero mass?
-Standard model has many unexplained parameters, such as the mass of fundamental particles. Particles in the standard model are points with no size. -particles in the standard model are points with no size -SM doesn't include gravity
What parameters in the standard model might string theory be able to explain?
-we see interference pattern -if light was a particle, you might expect two bright spots, but you actually see an interference patterns lots of light (constructive)and dark spots (destructive) because light is acting like a wave
What pattern do you observe on the detection screen when a high intensity light source illuminates a double slit apparatus?
-individual photons hit the screen in different apparent random locations, but after a long time an interference pattern emerges
What pattern do you observe on the detection screen when one photon at a time illuminates a double slit apparatus over a long period of time?
-Types of particles -Families
What physical properties stay the same and which ones change in a space-tearing flop transition?
Supersymmetry gets us to understand which have 3 defining characteristics -shortest word represents minimal mass -3 Y's which represent a charge of 3 -supersymmetry represents English dictionary
What point does Greene make by introducing the word syzygy?
when using the electron accelerator, smaller particles are more beneficial to understand the makeup of the 'peach pit' or in the art competition- a piece of art
What point is Brian Greene trying to make by introducing the art competition between Slim and Jim? Explain.
Unification of the electric and magnetic force and its light
What precedence is there in physics for unification of forces?
spin determines if its a boson (even integer spin 3/2, 1/2) or fermion (one half integer spin 0,1,2) boson examples: Higgs particle (0) graviton (2) strong gluon (1) photon (1) force particles in standard model (table 1.2) fermion examples: gravitino (3/2) photino (½) all matter particles (table 1.1)
What property of a particle determines if it is a boson or fermion? Give examples of both types of particles.
strings are expected to be very, very small, the planck length 10^31m or 10^33 cm
What size is a string particle expected to be?
-1984 the first superstring revolution -Michael Green and John Schwartz showed: the theory was anomaly free AND had a rich enough structure to describe the four fundamental forces
What string theory success led to the 1st string theory revolution?
-1995: second superstring revolution -Ed Written used non-approximate methods to show the 5 string theories are related by "dualities" All 5 string theories are related to the M theory
What string theory success led to the 2nd string theory revolution?
1. The constancy of the speed of light 2. The principle of relativity
What two ideas (postulates) form the foundation for Einstein's special theory of relativity?
-Original string theories by Veneziano, described Bosons (strong force) and 26 total dimensions -The early string theory discovered by Venrizno only described boson (strong force). This is a problem because nature contains fermions and bosons. On closer inspection string physicist found that for every Bosonic string exciton (particle) there was a corresponding fermion.
What type of particles did the first string theory explain?
-Happy Thought: if a person falls freely he will not feel his own weight; shows the relationship between acceleration and gravity -This made him happy because gravity is abstract but accelerated motion is tangible and understandable
What was Einstein's happy thought and why did it make him happy?
-showing the string was to show that virtual strings (quantum foam) protect the space tearing from cataclysmic consequences
What was Witten's insight into the space-tearing flop transition?
Introduced the idea of a small compact hidden dimension to understand electromagnetic and unify this force with gravity -This idea made a wrong prediction for the charge to mass ratio for an electron
When Kalluza first postulated extra spatial dimensions in 1919 what was his motivation? How were his ideas received by Einstein? Why was his theory not accepted?
-Winding number is heavy to measure small distances -Uniform vibration is light to measure large distances
When R is large what are the heavy probes and light probes? Why?
-Winding number is light, inversely proportional, to measure large distances -Uniform vibration number is heavy, to measure small distances
When R is small what are the light probes and heavy probes? Why?
-you have to decide what probe to use if you use the low energy probe, you'll -always measure a size larger than planck's length -if you use high energy probe, you'd only be able to measure the small radius- a size less than the planck's size
When comparing an R=10 universe with an R=1/10 universe, what difficulties arise when a direct measurement of the radius is made?
string coupling constant x 0 = 0; constant can be anything
When string theorists try to calculate the string coupling constant what do they find?
1968: Veneziano "accidentally" discovered string theory -early string theory was used to try and describe the strong nuclear force (correct theory is quantum chromodynamics (QDC)
When string theory was first discovered what was it used to explain?
small, too compact, so they are hidden and we can't see them
Where are the extra dimensions we don't see?
-Black holes in the center of galaxies at a late stage in life. -Light has been observed bending around seemingly empty patches of space between Earth and distant stars(black holes)
Where in the universe do physicists and astronomers have strong evidence to suggest the existence of black holes? What is the evidence?
Everything (electromagnetic, weak, strong) but gravity depends on shape
Which of the force particles in nature depend on the shape of the compact dimensions and which don't?
Einstein and nobel prize for it
Who was the first person to properly explain the photoelectric effect?
High tension, It can keep increasing as long as far as energy can increase
Why are there an infinite number of massive expected string particles in integer multiples of the Planck mass?
-once we go past Planck length, it makes the string larger -Because with strings as fundamental entity, we can't get to or below planck's scale, so it turns out that quantum foam is not as rough as we thought with particles as the fundamental entity.) Strings smooth the roughness of the quantum foam.
Why can a string not be used to probe sub-planck-length distances?
they cannot because they are hidden
Why can physicists not make precise calculations about the shape of compact dimensions?
It's too big, greater mass of an object the smaller the wave length, can't see
Why can we not see the wavelength of a baseball flying through the air?
Larger wavelengths bend around the small object, therefore you cannot detect it with high precision
Why can't I measure the position of a particle to high precision with long wavelength light?
1-D universe, you can only go back and forth - cannot pass through each other
Why can't you move past somebody if you are a being in lineland?
It includes both bosons and fermions in supersymmetry causing the tachyon to disappear
Why do string theorists no longer have to worry about the tachyon particle traveling faster than the speed of light?
Rolex would not be fast enough, must move at speed of light to be able to see the differences
Why do we use a light clock instead of a Rolex watch when we discuss how time slows for moving clocks relative to stationary observers?
there has never been an experiment that contradicts QM
Why does Stephen Hawking say, Einstein was confused, not the quantum theory?
String theory demands extra dimensions to make probabilities within a reasonable range (0-1)
Why does string theory need extra dimensions to work?
strings have super high strong tension because it needs to be small-inverse relationship between tension and gravity
Why does the string tension need to be so large?
hbar is too small
Why is the Heisenberg uncertainty relation not relevant for our everyday world?
Heterotic-E at strong coupling leads to M-theory by the string growing an extra dimension to become like a ribbon. A similar thing happens to type-2 theory. The string grows to become like an inner tube.
Witten discovered two paths to M-theory from the previously known five distinct string theories. Explain how an extra dimension emerges for the two paths to M-theory Witten discovered. What is (are) the shape(s) of the extra dimension that emerges?
stooop end of midterm focus questions
stop, end of midterm focus questions
