Phys 111 Final -Echlos
Explain with a picture and few words why the speed of light being a constant for all observers regardless of their state of constant velocity motion seems paradoxical?
*hoverboard drawing* c - 1/3c ≠ 2 x 10^8 m/s -The speed of light doesn't change because they're independent of each other and no objet with mass can come close to reaching the speed of light.
What string theory success led to the 1st string theory revolution?
-1984: Schwarz and Green showed theory was anomaly free and rich enough to describe the 4 forces. -String theory requires extra dimensions (makes anomalies go away, w/ 10D) -5 consistent string theories -forced to work with approximate equations which can only be solved using approximations
What string theory success led to the 2nd string theory revolution?
-1995: Ed Witten and others showed the 5 consistent theories are all related to each other which led to larger M-theory
Why do string theorists no longer have to worry about the tachyon particle traveling faster than the speed of light?
-5 new SUSY theories were discovered none of which had tachyons (needed 10D) -SUSY included both bosons and fermions, causing tachyons to disappear.
How are BPS states used to show the strong coupling limit of one string theory is dual to the weak coupling limit of another?
-BPS states, if they have the same BPS state then physics is the same so they are strong/weak dual -a supersymmetric string excitation with minimal mass for a given charge --special because properties don't depend on the strength of the string coupling constant
What must string theory assume about the compact space to create three families of particles as found in the standard model? Is this a unique answer? Explain
-Calabi Yau spaces fit the requirements -each calabi yau space has three hole which describe the 3 families are particles -not a unique answer because the calabi yau can be distorted an infinite amount of ways.
In what sense are BPS states non-perturbative?
-Doesn't depend on whether the string coupling constant is strong or weak -highly constrained -the BPS properties are the same at both strong or weak string coupling
Name three possible scenarios for which string theory could be validated
-Ed Witten says a string from early universe could get so large we can see it with a telescope -a fifth force is discovered -discovering a particle with an electric charge of 1/7
Name the superpartners of the particles in the standard model and their corresponding spin.
-Electron (spin 1/2) fermion, Selectron (spin 0) boson -Quark (spin 1/2) fermion, squark (spin = 0) boson -Photon (spin 1) boson, photino (spin 1/2) fermion -Gluon (spin 1) boson, gluino (spin 1/2) fermion
Which of the force particles in nature depend on the shape of the compact dimensions and which don't?
-Gluons, photons, weak gauge bosons, all depend on the shape -Gravitons don't depend on the shape of the compact space
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 shapes of the extra dimension that emerges?
-Heterotic E at strong coupling leads to M-theory by the string growing an extra dimension to become like a ribbon (the dimension technically was already there but couldn't see it) -Type II B theory very similar thing happens and the string grows to be like a donut
Explain the types of dualities depicted in fig 12.10 and give an example of each type.
-Heterotic O (R=10, Nw=2, Nuv=3) <--> Heterotic E (R=1/10, Nw=3, Nuv=2) -Type IIA (R=10, Nw=2, Nuv=3) <--> Type II B (R=1/10, Nw=3, Nuv=2)
What are the names of the 5 different consistent super string theories? In light of the second superstring revolution is five potential theories of everything a problem?
-Heterotic O, Heterotic E, Type I, Type II A, Type II B -5 super string theories appeared to need 10 total spacetime dimensions -can't have 5 versions of a theory of everything
What is the photoelectric effect?
-If the frequency is high enough, electrons emerge from metal -the electron is held to the metal by a certain energy -if photon frequency is too low there isn't enough energy to liberate the electron
Name some of the particles in the standard model of particle physics. In the quantum field theories describing the standard model, what is the structure of these fundamental particles?
-Matter/Force Particles: gluon, photon, weak gauge boson, electron, muon, muon neutrino. -they are point particles with no size or internal structure.
What physical properties stay the same and which ones change in a space-tearing flop transition?
-Only the masses of particles are altered or can change by space tearing -Other properties (charge, force, # of fams) stay the same.
Why do some people say the "M" in M-theory refers to membrane?
-Other objects besides strings--> ribbon --> membrane -M-theory contains membranes for the string becomes 2-brane
What are two consequences of quantum geometry?
-Smallest the dimension can be is planck size -there are two ways to measure distance
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.
-The properties (mass, charge, energy, force) we see are due to the vibrations of strings -These dimensions of the hidden/compact space influence how the strings vibrate and thus the masses, charges, and force interactions of everything
What point is Brian Greene trying to make by introducing the art competition between Slim and Jim? Explain.
-When using the electron accelerator smaller particles are more beneficial to understand the make up of the peach pit or in the art competition, the piece of art. -Useful probe particles can't be substantially larger than the physical features being examines, otherwise they will be insensitive to the structures of interest.
What parameters in the standard model might string theory be able to explain?
-Why the mass of different fundamental particles are what they are -How to make quantum foam smoother -Potentially explain the 3 families -ability to unify the 4 forces
Does the number of particle families depend on the number of even-dimensional holes or odd-dimensional holes? Explain
-Yes, the number of families depends on the number of holes in the dimension. -If there are 3 holes in an even dimensional space mirror symmetry/duality makes it so there are 3 holes in an odd dimensional space they will both yield the same physics
What is meant by the principle of relativity?
-You can't tell the difference of whether you're at rest or moving at constant velocity -all observers moving at constant velocities with respect to each other should find the same laws of nature operating in their frames of reference.
What does Witten mean when he says that string theory predicts gravity?
-not really a prediction because we already knew about gravity/graviton -even if we didn't already know about general relativity, string theory predicts gravity and you find it through string theory regardless of already having theories regarding it. -predicts gravity as the massless messenger particle
Where in the universe do physicists and astronomers have strong evidence to suggest the existence of black holes? What is this evidence?
-stellar remnants in binary star systems -super massive black holes can be determined by observing orbiting mass -gravitational waves due to black hole mergers
If the string coupling constant is small (less than 1) how many dimensions does string theory or M-theory have?
-string theory has 10D -Coupling causes 11D in M-theory
Name four characteristics of a wave
1. Amplitude: max displacement from equilibrium 2. Wavelength: distance from peak to peak 3. Frequency: Number of oscillations per second 4. Period: the time for one complete oscillation
Name 3 Consequences of a large string tension
1. Causes the strings to be small (planck length) 2. The natural energy scale is planck mass (very large) 3. You get many different string excitations with masses of integer multiples of the planck mass (Mpl)
In the past when physicists tried to make a quantum field theory of non-point particles what problems did they encounter? Who were some of these physicists?
1. Conservation of quantum mechanical probability 2. Impossibility of faster than light speed transmission of information -Heisenberg, Dirac, Feynman
Name two major difficulties Greene and collaborators encountered when comparing the after space-tearing flop transition Calabi-Yau manifold with it's mirror.
1. Determining the correct calabi-yau space 2. Difficult to calculate the masses of the particles in mirror symmetry
What are the four known fundamental forces of nature? Give an example of each
1. Gravity -falling apple 2. Electromagnetic force- light/anything electrical 3. Strong Nuclear force- holding together protons & neutrons 4. Weak Nuclear force -decays elements & fundamental particles: muon decays into electrons
Staring with the equivalence principle, explain the logical connections allowing Einstein to discover the general theory of relativity.
1. Gravity is indistinguishable from acceleration 2. Showed that acceleration warps spacetime 3. Seems to imply that gravity is warped spacetime
Name four primary characteristics of quantum mechanics
1. Quanta: all the fundamental particles (quark, photon, electron) 2. Duality: all fundamental quanta are simultaneously particle and wave 3. Probabilistic: only a chance that an experiment will have a particular outcome 4. Uncertainty:
Explain how you can understand the four big concepts in quantum mechanics using the double slit experiment.
1. Quanta: being projected through slits; photon or electron 2.Wave-particle Duality: manifests in one single spot on screen 3. Probability: we don't know position of electron, there is probability it will hit somewhere on the screen, QM doesn't know which slit it'll go through 4. Uncertainty: if you know which slit particles go through, you have reduced uncertainty in position
What are the goals of string theory?
1. Resolve the conflict between general relativity and quantum mechanics 2. Unify all the forces of nature 3. A theory of everything
Name 3 problems with figure 3.5
1. Space is only shown to bend along two dimensions not 3 of the spacial dimensions. 2. Not showing the warping of time 3. There is no external object pulling the center object down like the earth does or a ball on a trampoline.
Name two early confirmations of Einstein's general theory of relativity.
1. The precession of perihelion of mercury- 1/6th of a degree 2. Observed the bending of light by a gravitational field
What are the known symmetries of space, time and motion?
1. The principle of relativity 2. The equivalence principle
What two ideas (postulates) form the foundation for Einstein's special theory of relativity?
1. The speed of light is constant: it's the same regardless of how you move relative to the light. 2. Principle of relativity: constant velocity motion is relative/the laws of physics don't depend on the observers state of constant velocity motion.
Name 3 reasons why we might expect supersymmetry to be a symmetry of nature?
1. There are other symmetries that have been found to be obeyed in nature, why not SUSY 2.If nature obeys SUSY then standard model forces unify at short distance/high energy 3. Fine tuning problem
State three observations about space and time that can be made by observers moving relative to each other.
1. Time Dilation: moving clocks run slow relative to an identical clock at rest. 2. Lorentz Contraction: moving lengths contract in the direction of motion relative to an identical plank at rest 3. Relativity of simultaneity: events that are simultaneous to one observer are no longer simultaneous to an observer moving relative to the first
What are the two Heisenberg uncertainty relations we discussed in class?
1. Uncertainty in position x uncertainty in momentum is greater than or equal to plank's constant divided by 2. 2. Uncertainty in energy x uncertainty in time is greater than or equal to plank's constant divided by 2.
Name three reasons why we might expect supersymmetry to be a symmetry of nature.
1. Why wouldn't nature use this symmetry if it has used other symmetries before 2. Fine tuning problem, parameters in the standard model need to be fine tuned 3. At high energy or small distance, the 3 forces on the standard model unify SUSY
How many space and time dimensions are in the original string theory?
10 = 9 space + 1 time
How many space and time dimensions are in M-theory?
11 = 10 space +1 time
How many spatial dimensions are being represented in figs 8.4, 8.7, 8.8, 8.9, and 8.10?
8.4: 3 (circles) 8.7: 4 (spheres) 8.8: 4 (donuts) 8.9: 6 (single calabi yau) 8.10: 8 (calabi-yaus in space)
What happens to spacetime at small space and time scales? How small is small?
A planck length which is 10^-33, quantum mechanics and heisenberg uncertainty principle are all important; particles are created and destroyed, which is quantum foam and things are chaotic.
In what sense does string theory simplify our view of fundamental particles?
All fundamental particles are structurally the same, and only difference is their vibrational patterns. -Gives us the potential to predict masses, charges, and 3 families.
What pattern do you observe on the detection screen when a high intensity light source illuminates a double slit apparatus?
An interference pattern
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?
An interference pattern
What is blackbody radiation?
Anything with temperature radiates electromagnetic radiation. The frequency or wavelength depends on how hot the object is
Explain the result in question above, using quantum physics.
As the frequency of light is decreased there is a point where the speed of the emitted electrons drops t zero and they are no longer being ejected from off the surface of the metal, regardless of the possibly blinding intensity of the light source. Because energy is related to frequency no intensity.
In light of M-theory developments in what sense are strings still special?
At weak string coupling the strings are low mass objects (the lightest objects ever???) aka the foundation for a theory of everything
In the quantum cafe, why are the ice cubes rattling around in the glass?
Because it's part of the uncertainty principle. -rattle more vigorously in the smaller glass because they have a smaller position so there is greater momentum
Explain how two observers in relative motion can not agree on the interaction point of two strings?
Because of the relativity of simultaneity. -Fig 6.9 george see the strings interact closer to the bottom due to a different motion and the relativity of simultaneity.
Why does string tension need to be so large?
Because the force of gravity is super weak and the equation is: force of gravity = 1/string tensions -gravity to 10^24 times weaker than electromagnetic force -since gravity is so weak it requires string tensions to be very large to satisfy inverse relationship
How can we know that conclusions we reach about a light clock also apply to a Rolex watch?
Because they are both in sync and follow the same rules
Why can physicists not make precise calculations about the shape of compact dimensions?
Because they're hidden -too many solutions: use approximate equations finding approximate solutions
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.
Because when the clock is moving slower and at a fraction of the speed of light, the slowing of time is so small that it isn't visible.
Why can't you move past somebody if you are a being in lineland?
Because you can only go left and right, since it's only 1 dimension.
Give an example of the precision of QED
Being able to keep track of 1 penny out of a trillion dollars.
What types of particles did the first string theory explain?
Boson particles- theory by Veneziano and had 26 dimensions -was a problem because nature contains both bosons and fermions, it also had tachyons.
In what sense is quantum chromodynamics (QCD) like QED?
Both are quantum field theories for force fields (strong and electromagnetic)
Name a physicist who worked on orbifolding.
Brian Greene, apenwall
What is mirror symmetry in string theory? Why is it important to mathematicians and string theorists? Give an example
Calculations in dual space apply to Calabi-Yau spaces -if they both yield the same physics then when math is hard is one space the easier math in the other space gives you an answer for both. The three families of particles is the same in two distinct calabi yau spaces that are dual -all the physical properties (mass, charge etc) are the same = full duality
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 every be able to probe the Planck length?
Can only probe down to 10^-21 cm, while plank length is 10^-33cm -we would need an accelerator the size of the galaxy so no.
Why can't I measure the position of a particle to a high precision with long wavelength light?
Can't measure the position of a particle with a high precision with long wavelength light, because the long wavelength has low energy photons which provides poor resolution.
What is Einstein's biggest blunder?
Couldn't understand that the universe was always expanding so he added an extra term to his equation to make the earth static.
Explain using the equivalence principle and a picture why light bends in a gravitational field.
Deep space and strong gravitational field, the acceleration or gravity pulls the light down.
What is the difference between an electron and photon?
Different in how they vibrate -Photons are massless force particles, that make up light. -Electrons are massive matter particles
Who was the first person to properly explain the photoelectric effect?
Einstein
Why does Stephen Hawking say, "Einstein was confused, not quantum theory"?
Einstein didn't believe quantum theory because there was room for an element of chance, but experiment after experiment show that Einstein was wrong and quantum theory can be proven, while still leaving room for probability.
Give an example demonstrating the relativity of simultaneity.
Einsteins example of lightning and one person being on a train and the other watching from the embankment.
How does the force in quantum electrodynamics (QED) work?
Electromagnetic force -2 electrons interacting with each other repel each other so the force that is there when they are repelling (force mediating messenger particle) that electric charge creates a force of repulsion.
What forces are included in the standard model of particle physics?
Electromagnetic, strong nuclear force, and weak nuclear force
What do we mean by an even or odd- dimensional hole?
Even: a hole in an even dimension figure (2D even ex is hole in paper) Odd: hole in an odd dimensional figure (3D)
In class we discussed 3 ways of understanding the relative nature of simultaneity. Choose the one way you like best and explain what is meant by relativity of simultaneity.
Everything is relative and is based on the observers position and motion
In what sense did supersymmetry find its beginning in string theory?
First string theory includes bosons which were then found to have fermions as their super parters, this led to the discovery of the 5 different SUSY theories
Define supersymmetry
For every fermion, there is a super partner particle boson. For every boson there is a super partner particle fermion.
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?
Fundamental particles are strings, their internal structure is the vibrating strings, the different vibrational patterns give rise to different masses and charges.
What space(s) with compact dimension(s) are large and extended dimensions can we properly visualize with a drawing?
Garden hose
If a very small compact dimension were to grow in lineland and become visibly, what type of surface would you have?
Garden hose 2D
What is/are the conflicts between general relativity and quantum mechanics?
General relativity requires smooth spacetime, quantum mechanics suggests quantum foam. General relativity gives infinite answers for quantum theory of gravity.
How does Einstein's general theory of relativity resolve the conflict in #4? aka two above
General relativity says that there's spacetime and that matter (like the sun) bends spacetime, and matter (like the earth) moves in the warped/bent spacetime -this warping creates gravity, which travels at speed of light aka ripples
With the aid of a picture explain what Einstein means by our motion through spacetime is at the speed of light. Locate points of no motion through spacetime, and maximal motion through space and time on the diagram.
Graph with curve across it. x-axis: Motion through space y-axis: motion through time -all points on curve are possible -we are on y-axis towards the top with no motion through space but max through time -light is on x-axis with no motion through time but max motion through space.
What is the conflict between Newton's theory of gravity and Einstein's theory of special relativity?
Gravity acts instantaneously across space, Einstein said nothing can go faster than the speed of light aka nothing can happen instantaneously
Einstein spent his entire life trying to unify which forces of nature?
Gravity and the electromagnetic force
What is the equivalence principle? Explain with aid of picture.
Gravity is indistinguishable from acceleration.
What did Planck have to assume to properly predict blackbody radiation?
Had to assume quanta with proportional energy to frequency (not proportional to amplitude)
Starting with the equivalence principle, explain the logical connections allowing Einstein to discover the general theory of relativity.
He first found that gravity is indistinguishable from acceleration. He showed that accelerated motion warped spacetime. This implies that gravity seems to be warped spacetime.
What was Witten's insight into the space-tearing flop transition?
He showed the virtual string (pops out of vacuum) world sheet (tube) protects the world space from catastrophic consequences. -he yielded an insight into why the space tearing transition is allowed by showing that the world sheet of a string can protect the tearing space
Explain how a fundamental string can have mass
Heavier particles have internal strings that vibrate more energetically, while lighter particles have internal strings that vibrate less energetically
Where are the extra dimensions we don't see?
Hidden: they're compact and small and are planck size
Is the geometry you learned in high school obeyed on the tornado ride? Explain.
High school geometry: Euclidean geometry and isn't obeyed because it uses and explains the circumference of a circle on a flat sheet of paper. Now we're measuring the circumference of a warped circle, meaning the warped circle will have a greater circumference than that on the flat sheet of paper.
When Kaluza first postulated extra spatial dimensions in 1919 what was his motivation? How were his ideas received by Einstein? Why was his theory not accepted?
His idea was that you could unify electromagnetism and gravity, in the end his theory makes an incorrect prediction for the charge to mass ration of the electron -Einstein at first liked his idea but held up publication for 2 years.
Newton was embarrassed by what aspect of his theory of gravity?
His theory worked well but he didn't know how it worked
What was Einstein's happy thought and why did it make him happy?
If a person falls freely they won't feel their own weight
If supersymmetry is not discovered at the large hadron collider, will string theory be proven wrong?
If it's NOT discovered it won't be proven wrong and there are other ways to validate and verify super string theory
Using the tornado ride as an example, clearly explain how space is warped (or curved).
If you look at the ride from the outside, Jim measures the radius but his ruler doesn't change size the lorentz contraction only makes it's width skinnier. Slim is on the edge of the ride and his ruler is lorentz contracted and measures a larger circumference, C, compared to off the ride.
Explain how it's possible to understand the answer to question #1 aka above
In deep space they don't have a reference point to know who really is at rest, as long as no one accelerates they are both on equal footing to believe the other person's clock is running slow -other means such as messages/calls won't work since it takes time for them to transmit
What is the reductionist viewpoint?
Is that a theory of everything means that in principle everything can be explained by a formula, including emotions.
What is the physical significance of the string coupling constant?
It can be anything -weak coupling means the string coupling constant is <1 -strong coupling constant means the string coupling >1 it determines the strength of the interaction
Explain in words the key features of a quantum field theory (QFT)
It involves quantum mechanics, special relativity and force fields.
How is the spin of a particle determined?
It is associated with the pattern of vibration that the string executes
How does string theory force us to think differently about space?
It says there are multiple dimensions in the universe.
Is string theory accepted?
It's believed by some, those who don't believe it don't because it hasn't been proven experimentally and it requires acceptance of multiple dimensions.
For weak gravitational fields like the earth, is spatial curvature or time curvature easier to see?
It's easier to see time warping instead of space warping.
Why is the Heisenberg uncertainty relation not relevant for our everyday world?
It's not relevant for our everyday world because it requires h bar to be big so the uncertainty relations can apply to the macroscopic world
What happens when you repeat the experiments in questions 1-2 using electrons instead of photons?
It's showing that electrons also have duality and are particles and waves at the same time.
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?
Light clocks are a constant process and something we are able to visualize.
What do you have to assume to properly explain the photoelectric effect?
Light comes in packets of energy called photons
According to James Maxwell, what is light?
Light is oscillating electric and magnetic fields (electromagnetic waves)
How are wavelength and frequency related for light waves?
Light speed = the wavelength times the frequency
Why can we not see the wavelength of a baseball flying through the air?
Mass is inversely proportional to wavelength, the bigger the mass the smaller the wavelength m= 1/wavelength
Explain in one concise sentence the essence of Einstein's general theory of relativity.
Matter (like the sun) warps space and time and influences matter (like the earth) that moves in that warped spacetime.
What is a light clock?
Measures a photon moving between two mirrors, one tick is the photon moving back and forth between the mirrors. -Shows special relativity
Can two observers in relative motion agree on the interaction point for two point particles? Explain.
NO because of the relativity of simultaneity, the string is an extended object, ensuring that there is no unambiguous location in space or moment in time when the strings first interact. It depends on the state of motion of the observer.
Does string theory say it's impossible to have more than one time dimension?
NO, but one simplifies and makes it easier to explain and understand
Can space tear in Einstein's general theory of relativity? Explain
Nope, general relativity says that space can't tear -but there can be wormholes that already exist in the universe
Make a cartoon sketch showing the before, during, and after of a space-tearing flop transition using the mirror Calabi-Yau. Does anything dramatic happen to the mirror Calabi-yau space during the tear?
Nothing catastrophic or dramatic happens to/in the dual mirror space
Name two technological applications of Einstein's famous question, E = mc^2
Nuclear power: mass to energy Nuclear Weapons: mass to energy Particle Colliders: energy to mass
Why can a string not be probed sub-planck length distances?
Once we go past planck length, it makes the string larger. Because with strings as fundamental particles, we can't get to or below plank length. Using qm continually increasing the energy of a string doesn't continually increase its ability to probe finer structures.
What are two types of vibrational energies associated with a string? Briefly explain what each energy corresponds to
Ordinary Vibration: vibrational energy of the string itself -physical vibration of the string Uniform Vibration: quantum mechanical energy of motion -due to motion
In the analogy between blackbody radiation and the warehouse landlord, what physics concepts correspond?
People = Oscillators (electron and atoms Money = energy (quanta) Temperature = temperature Furnace setting = energy radiated
From whose perspective can one easily explain the twin paradox?
Perspective of twin on earth, because they're at rest and don't accelerate at all.
What is the tool used by physicists to understand the approximate equations of string theory?
Perturbation theory
What size is a string particle expected to be?
Planck length = 10^-33 cm
What is the natural mass scale for a string?
Planck scale, it's the mass-equivalent of a vibrating loop, being some whole number times the planck mass some 10 billion times that of a proton
What is the anti-particle of an electron called?
Positron
What is the more precise answer for how string theory allows for a consistent theory of quantum gravity?
Precise answer: string interactions are smooth due to relativity of simultaneity. The resolution is that strings not points smooth interactions of the quantum foam particle creation or destruction enough to allow for a quantum theory of gravity. -if particles are strings then for strings the exact interaction point depends on your state of motion and thus is not unique.
What is quantum electroweak theory and why is it important?
Quantum electroweak theory is a quantum theory for the weak force but it is when the weak force unifies with the magnetic force called the electroweak force.
Explain quantum tunneling
Quantum tunneling is passing through an energy barrier and it requires borrowing energy for a short amount of time. -Need a large h bar for us to borrow that amount of energy
What is the difference between Riemannian geometry and quantum geometry? For our universe at what length scales is each geometry important?
Riemannian Geometry: macro world geometry, requires smooth quantum space, uses point particles, general relativity Quantum Geometry: planck scale, occurs if fundamental objects are strings
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.
Rough answer: to see small sizes (high energy) we use small quantum mechanic wavelength which is inversely proportional to energy.
In 1974 what did Schwarz and collaborators show the massless messenger particle of string theory could describe?
Showed massless messenger particle could be the graviton -Problem w/ theory is anomalies and inconsistencies w/ the equation
What makes a black hole black?
Spacetime is so warped and the gravity is so strong that on the inside of the event horizon there is no light and it can't escape, making it black.
What property of a particle determines if it is a boson or fermion? Give examples of both types of particles.
Spin -particle- electron: fermion has a 1/2 spin -Superpartner- Selectron: boson spin = 0
When string theorists try to calculate the string coupling constant what do they find?
String coupling x 0 = 0 so string coupling could be anything
In regards to a compact dimension, how is string motion different from a point-particle?
String motion is similar to a point particle in that they can move around dimensions just like points, but they're different because strings can wind around dimensions.
Why are there an infinite number of massive expected string particles in integer multiples of the Planck mass?
Strings can execute an infinite # of vibrational patterns. Never ending sequence of possibilities characterized by an even greater number of peaks and troughs (3rd consequence of stiff strings)
In string theory what ARE fundamental particles such as electrons and photons?
Strings with different vibrations
What is the standard model of particle physics?
Strong, electromagnetic, and weak forces which are described by controllable quantum field theories.
What is Louis de Broglie's contribution to physics?
Suggested that the wave-particle duality applied to light and matter. -reasoned through e-mc^2. -if energy = mass, energy is inversely related to wavelength, and implies mass is inversely proportional to wavelength
What does the super in superstring theory refer to?
Super symmetry
What is supergravity and how is it related to M-theory?
Supergravity is a point particle theory of supersymmetric gravity in 11D -M theory al low energy is the same and dual to 11D symmetry
What point does Greene make by introducing the word syzygy?
Supersymmetry gets us to understand these BPS states which have 3 defining characteristics -supersymmetry = english dictionary -minimum mass = shortest word -given charge = 3 y's
What is orbifolding?
Taking a Calabi-Yau space and creating a new distinct Calabi-Yau shape
If the tornado ride were in deep space far from gravitating objects, in what sense would the ride mimic gravity experienced on earth?
The acceleration of the ride mimics gravity that is felt on earth that isn't presented in deep space. Einstein's general theory of relativity explains that gravity is indistinguishable from acceleration.
How does the flow of time on earth compare to an identical clock 6,000 miles above the surface? Ho do we know?
The clock that is 6,000 miles above doesn't run slower because it's experiencing the acceleration of the earth. The clock on the earth runs slower because it does experience more acceleration.
In the video we saw, what example was used to depict the conflict in question above?
The cosmic catastrophe, how earth moves and falls out of orbit if the sun disappears.
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 earth is traveling so quickly that there's a lorentz contraction, meaning the distance becomes shorter, allowing the earth to reach the muon before it decays.
What happens when calculations are made in a quantum field theory of gravity?
The infinities are uncontrollable because there is an infinite number of them.
As viewed from earth how does the lifetime of an approaching muon compare to a muon at rest?
The lifetime of an approaching muon is moving quickly and reaches earth before decaying, because a time dilation occurs, so time is slower for the muon and it experiences one tick for every 10 ticks on earth aka time slows down for muon so lifetime seems longer
Using the tornado ride as an example, explain how acceleration leads to warping of time.
The person on the edge is moving the fastest compared to the person towards the center of the ride. By special relativity the clock has the largest time dilation and runs the slowest relative to someone towards the center of the ride or someone who isn't on the ride.
How do you explain results in 2 above according to Feynman?
The quanta (electron/photon) takes all possible paths and goes through both slits simultaneously
Explain with a picture why the electromagnetic force gets stronger when probed at small distance or high energy.
The quantum foam shields the charge of the electron; the strength of the electric charge determines the strength of the electromagnetic force -at small distances there's less shielding which means a stronger charge/force
As Slim stands still on the outside edge of the tornado ride moving at constant speed, why is he accelerating?
The ride is moving at a constant speed, but he is accelerating because he is going in a circle, or constantly changing direction, and changing direction means he's accelerating.
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?
The rules of quantum mechanics and general relativity don't mesh and are incompatible. Black holes, early universe, hoverboards.
In what sense did Newton unify the heavens and earth with his theory of gravity?
The same force that makes apples fall on earth (gravity) is what also keeps the moon orbiting around the earth.
How does the string uniform motion energy depend on the radius of the compact space?
The smaller the radius becomes the bigger the Uniform Vibration energy gets because they have an inverse relationship -Euv=Nuv/R -similar to situation of ice cubes in the cup, the smaller r the more the strings move
Using a light clock clearly state the argument for why time slows for moving clocks relative to stationary observers
The speed of light is the same for both but the moving clock's photon has farther to move, making time slow down -the faster the clock the slower time is going
How does the string winding energy depend on the radius of the compact space?
The string winding energy is equal to the radius times the winding number or the number of times the string is wound. -Ew=NwR -as R increases Ew increases
How do you explain the results above according to Schrodinger?
The traveling photon is a probability wave that has equal probability to be at both slits. -single photon goes through both slits
What is the twin paradox?
The traveling twin who accelerates returns younger then the twin at rest on earth.
If the original string theory is correct (disregard M-theory) how many spatial compact dimensions are there? What shapes meet the stringent requirements of string theory?
There are 9 spatial dimensions and 1 time dimension -6 are compact and 3 are extended -Calabi Yau shape meets stringent requirements
Given the crazy ideas coming from quantum mechanics, why should we believe it?
There has never been an experiment that contradicts quantum mechanics
In the quantum mechanical explanation of blackbody radiation why can't very high-energy photons contribute to the radiated energy?
There isn't enough energy to excite the high energy photons to make them want to contribute
What needs to happen for a string to have a small or zero mass?
There needs to be a quantum cancellation. Ex: graviton has a mass = 0
In particle physics experiments how are probes of small wavelength created?
They are put into accelerators -particle accelerators use protons or electrons as probes since they're small and better suited for the task
How will two people (George and Gracie) moving away from each other view time passing on the other person's clock?
They will each think the other persons time is moving slower and think they themselves are stationary even though neither of them have a reference point that isn't the other person. -both their clocks are running slow
Under what conditions do the strong, electromagnetic, and weak forces unify?
Under short distances/high energy, when SUSY is true
What precedence is there in physics for unification of forces?
Unification of the electric and magnetic force and it's light
To conclude that the minimum size for a dimension is greater than 1 (Planck Size) what type of probe must be used? Why is this the natural choice of probe?
Use a low mass probe is used to get an R > 1. The natural choice is a low mass probe because this is available to us
When string was first discovered what was it used to explain?
Used to describe the strong nuclear force, but didn't work and turned out QCD did work to describe the strong force
Name some of the interesting phenomena found in the quantum cafe or in H-bar
Walking through walls, ice cubes rattling, ice cubes going through the glass, not necessarily getting an orange drink
In string theory what controls the number of dimensions which are large and extended instead of being small and compact?
We don't know
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?
We expect that high intensity light at low frequency should be enough to emit electrons.
For what values of string coupling constant does perturbation theory work? Explain why
Weak coupling when string coupling constant is <1 -each term has more interactions, when terms are added up the total number is more precise -BALL PARK
Into what particles does a muon decay? What force plays a role in muon decay?
Weak nuclear force, into an electron, muon neutrino, and electron antineutrino
What happens to the velocity (or momentum) of a particle when you use short wavelength light to detect its position?
When you use a short wavelength of light to detect the particles position the momentum is disrupted by the high energy photons.
When R is small what are the light probes and heavy probes?
Winding is light and uniform vibration is heavy
When R is large what are the heavy probes and light probes? Why?
Winding probe is massive/heavy and uniform vibration probe is light -it depends on whether R is greater than or less than 1, the winding probe is directly proportional to R and uniform vibration is inversely proportional to R
If I wanted to detect something with a size of 1cm what wavelength of light would I need to use? Explain.
Would need a wavelength of light that's 10^34J
Can large spatial dimensions tear?
Yes because space is space regardless of size
If supersymmetry is discovered at the Large Hadron Collider, will string theory be validated?
Yes it will be validated but no proven -there are other point particle SUSY theories but since strings require SUSY this would be a step in the right direction
Do we expect to be able to find super partner particles experimentally? If so when and where might they be discovered?
Yes people are expecting super partner particles to be discovered at large hadron collider, but none were found yet
Are infinities encountered in QED? Are they controllable? Why?
Yes there are infinities and they aren't controllable because of the uncertainty principle, and no smooth spacetime and the probability stuff.
Has something similar to the twin twin paradox been confirmed experimentally?
Yes, used jets to confirm this on earth but the difference is so small
Has string theory been able to predict the mass of a graviton? An electron?
Yes: the mass of a graviton is 0, which makes sense because gravitational force is transmitted at light speed & only massless particles travel at this max velocity Electron: 0.0005 GeV
What do we mean by duality in string theory? Give an example
You can't tell the difference between the two physics of the two different spaces -mirror symmetry -Type II B -Strong weak coupling
What happens when you try to explain blackbody radiation with classical physics?
You get an infinite energy contribution from high frequency electromagnetic energy.
When comparing an R=10 universe with an R=1/10 universe, what difficulties arise when a direct measurement of the radius is made?
You have to decide what probe to use -low energy probe will always measure a size larger than the plank length for radius -high energy probe will always measure a small radius that is a size smaller than plank size The natural choice is low energy probe
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?
You interchange the two, then you will get the same total energy, for r=10 and r = 1/10
If you wanted to create a wormhole to travel between your house and Cal Poly, what would you need to do to space?
You would need string theory to exist and have space tear
Why does string theory need extra dimensions to work?
to have an acceptable range of probabilities between 0 and 1
