Physics Written Exam
What is the basic "why" of the universe? How does the book suggest we find out?
"Why" it all works. We must begin by figuring out what the matter is like at its deepest, most fundamental level (break it down as far as it will go; right now that level is particles).
What are two possible explanations (or hypotheses) for the enormous inequality between matter and antimatter?
#1: During the Big Bang, more matter was formed than antimatter meaning that the vast majority of matter and antimatter annihilated itself, and the bits leftover were matter #2 During the Big Bang, the same amount of matter and antimatter was created, but over time, something about the particles themselves caused there to be more matter than antimatter
How might the shape of space-time allow us to visit other stars? (The book lists two ways.)
(1) A Warped Idea: Squeeze space between us and a distant location (2) A Worm Hole: It connects two places in the universe that are far apart from each other.
. Explain the three ways we know that there is dark matter? Which is the most convincing piece to physicists? [Spinning galaxies, Gravitational lensing, Colliding galaxies (most convincing)]
1) Spinning Galaxies 2)Gravitational Lensing 3)Colliding Galaxies The most convincing is the Colliding Galaxies.
what are the three problems with string theory?
1) While it can describe the whole universe, it hasn't done so yet. 2) still only a descriptive theory, and can't yet make any predictions that we can test 3) the dynamic predicted by string theory are determined by the number and shape of spaced-time dimensions, and there are a ton of ways one could choose these dimensions
What kind of energy makes up most of our total mass? What percentage of the mass is from stuff and what percentage is from energy? Is it the energy that binds atoms to each other (to make molecules)? Is it the energy that binds protons, neutrons, and electrons together (to form atoms)? Is it the energy that binds quarks together (to form protons and neutrons)?
1. Binding energy. 2. 99% energy and 1% 3. stuff 4. no 5. no 6. Yes
What are three ways that physicists can try to detect dark matter (other than via the three lines of evidence above)?
1. Detectors that go off when an atom gets touched by dark matter 2. Use a high-energy particle collider 3. Use Telescopes
What are emergent phenomena? Why do they make the world easier to study? Will the ultimate theory of everything describe emergent phenomena? Explain.
1. Emergent phenomena are essentially Lego pieces that are composed of smaller pieces 2. They make studying the world easier because of the Organization principle (complex objects composed of smaller, simpler objects) 3. The ultimate theory will not describe some emergent phenomena of the true building blocks of the universe; it will be about the true building blocks of the universe and how they fit together
What are the three possibilities for the size of the entire universe? Which one of these is true?
1. Finite universe/matter in infinite space 2. Finite universe in finite space 3. Infinite universe 4. We have no idea which of these is true
What is gravitational mass? How is it different from inertial mass? Why do we think that they are actually the same thing?
1. Gravitational mass more of like a gravitational charge: when two particles have mass they feel a gravitational attraction proportional to their mass. 2. Gravitational mass determines the force of gravity on an object. And we measure it using a scale. 3. We think they are the same because we can measure the mass both ways and don't notice a difference between gravitational and inertial masses of an object.
What two kinds of competing effects are responsible for the structure of rocks, asteroids, planets, stars, and galaxies? On a cosmological scale, which is winning? Which is having "little local victories"?
1. Gravity and pressure 2. pressure is winning 3. Gravity is winning little victories
What instrument do physicists use to "see" down to 10-20 meters? How many orders of magnitude larger is this than the Planck length? What is the analogy that the authors use to explain how much of a difference this is?
1. High-energy collisions in particle colliders 2. 15 3. It is as though the smallest ruler you have or the smallest object you could see was 1,000,000,000,000,000 meters long (10^15)
Describe how quantum mechanics (QM) treats gravity differently from the other three forces. Why does quantum mechanics fail to describe gravity? How would quantum mechanics treat gravity if it could? How does general relativity (GR) describe gravity?
1. It treats the other three forces as small particles, but they haven't discovered a gravity particle 2. It fails for two reasons: 1) fitting gravity into the standard model requires a particle that transmits the force of gravity. 2) we already have a great theory for gravity. 3. Graviton theory: Little quantum balls flying between particles? 4. GR looks at gravity as a distortion of space itself.
What are some possible answers to the question, What happened before the Big Bang?
1. Maybe the answer is that there is no answer (like asking the question, what is north of the north pole?) 2. Maybe it's black holes all the way down 3. Maybe there is a cycle (crung, bang, crunch, bang...) 4. Maybe there are lots of universes
Do we know what inertia is? And so do we know what mass is? If mass = stuff + energy then what is "stuff"? Is there such a thing as "stuff"?
1. No we don't 2, We can measure it but we don't know what it is. 3. "Stuff" doesn't exist in our formulation of Physics. 4. No there is no such thing as stuff
Does "fundamental force" mean "smallest force"? Explain. How many fundamental forces are there? What are they?
1. No. It is about finding out which of the forces we know about are actually parts of the same thing. 2. Three. Electroweak, Strong Force, and Gravity
How might a collision of two black holes help us determine whether there is a quantum theory of gravity (that is, to see whether QM or GR is correct)? What are some difficulties with this suggestion? What is another possible way to test which theory is correct? What currently makes this kind of test unlikely.
1. Observing two masses exchanging a graviton would determine that gravity is a quantum phenomenon. This could potentially be done by two cosmically massive objects (black holes) slamming into each other. 2. This is not something we could possibly build or operate; the natural event does not happen regularly, and it is not repeatable; even if we did witness a collision sending out gravitons, they would be very hard to spot 3. Find a physical situation where the two theories differ in their predictions. We could do this by exploring a black hole. 4. Seems unlikely that we could visit a black hole, survive it, do experiments, escape the inescapable gravitational field, and return to earth with the results
We can't measure dark energy or dark matter directly. How then can we know the total percentages of each so precisely? That is, how can we have this "precision ignorance"? (There are three ways.)
1. One way is the Cosmic Microwave Background— a baby picture of the universe. 2. The rate of the expansion of the universe. 3. The structure of the universe today
What does it mean to "see something"? How does this relate time to how far you can see?
1. Seeing means that you are catching photons that started their journey at the thing you are trying to see and then made their way to your eye (or telescope). 2. Everything you can see has to be inside a sphere centered in your head whose radius is the distance light can travel since the universe was born.
What is string theory? Why is it appealing?
1. Suggests that the universe has ten or eleven dimensions of space-time if not more. We can't see most of these because they are rolled up or very small, and they are filled with tiny little strings. These strings vibrate and can look like any of the particles we have discovered, depending on how they vibrate 2. It is mathematically beautiful and theoretically fascinating
What three things do we know about dark matter? [that there is something there, how much it is, and where it is]
1. That exists 2. How much it is 3. Where it is
What does it mean to say that reality is pixelated? How is this related to the Planck length?
1. That is to say that there could be some smallest, meaningful distance to the universe, a quantization of distance to the universe 2. It is possible that Planck length could give us a rough estimate of the general size of the universe's pixels of space
What is the "testable universe"? Why is it growing? What discipline shrinks as a result?
1. The fraction of the universe that we can confirm and know about using science 2. We are developing new technologies and new tools 3. Philosophy
What is the highest energy that the LHC has accelerated a particle to? What is the highest energy that we've ever measured a particle? What produced such a high- energy particle?
1. The highest energy that the LHC has accelerated a particle to was ten teraelectron volt (10^13 eV). 2. The highest energy we've ever measured a particle was at 10^20 eV. 3. We have no idea what created this.
. What is it about the Standard Model that suggests that the particles it describes aren't genuinely fundamental particles? How might we tell if there are more fundamental particles?
1. The neat arrangement and patterns seem to suggest that something more is going on 2. Keep smashing things together at higher and higher speeds or find new particles that fit into the table
According to the authors, what is a theory of everything? What do "simplest" and "deepest" mean?
1. The simplest possible mathematical description of space and time and all the matter and forces in the universe at its deepest level." 2. Simplest = nonreducible, bare bones 3. Deepest = describes the universe at the smallest possible level
Explain how different theories can all be correct at different levels at the same time. Why does this make physics possible for us?
1. There are things like the motion of a bouncing ball that could be derived using both Newtonian physics and quantum field theory (although it would be ridiculously difficult to use this) 2. In theory, you could derive the formation of galaxies or fluid mechanics or organic chemistry from a correct theory of the lowest level of reality, but that would be extremely difficult. The fact that the universe is describable and understandable at multiple levels makes physics possible for us
What are the four possible fates of the universe? Which is the only one that actually fits the observable data? How soon will any of these scenarios happen?
1. There is so much stuff force of Gravity will slow down the expansion and reverse everything. The Big Crunch. 2. There is not enough stuff so the universe will keep expanding forever. 3. There is just enough stuff for Gravity to slow down expansion but not enough to shrink it. Thus the universe approaches zero. 4. Some incredibly powerful and mysterious force is expanding space itself so the universe is growing faster and faster.(This is the only one that fits the observable Data). 5. But all of this will happen Billions and billions of years from now.
What are all the basic elements of the universe—even forces—according to quantum mechanics? How is this different from how the more modern and powerful description of quantum mechanics describes the basic elements? (See footnote 118.)
1. They are all quantum particles 2. More modern description: basic elements are all quantum fields that exist everywhere and particles are places where the fields get excited
What do we ordinarily think of mass as? Why is this wrong? What is mass? What is inertia? What is inertial mass? How do we measure inertial mass?
1. Think of mass as how much stuff an object has. 2. Wrong because mass also includes the energy. 3. Mass is the property of objects that makes them resist changes in velocity. 4. Inertia is resisting acceleration 5. Inertial mass gives the inertial resistance to acceleration 6. WE measure inertial mass by applying a known force and measuring the acceleration
How can we detect planets outside our solar system even though they are orbiting much brighter stars?
1. We can look for a small wiggle in a star's position 2. we can also look for periodic dips in the light from the star
Does antimatter feel gravity? What about the other forces?
1. We don't have enough evidence to say whether or not they do. 2. Yes, antiparticles feel the other forces in reverse
Why must the total electric charge of two particles be conserved when they collide? What is another property that must be conserved? How does this explain why an electron and proton don't annihilate each other even though they have opposite charges?
1. We have no idea why, 2. "Electroness" and "muoness" have to conserved. Annihilation only works with somethings antiparticle 3. Because they are not antiparticles. the electrons antiparticle is a positron.
Why do the charges of the quarks and electrons perfectly balance?
1. We have no idea. According to our best theory, these numbers could have been anything. 2. It could indicate that there are deeper components or the two types of particles are really two sides of the same coin.
What is dark matter made of? What kind of options are there? [new particle(s)+new force(s)]
1. We really don't know a lot about what it is made up of yet. A simple answer is that Dark Matter is made of a new kind of particle that uses a new kind of force to interact very, very weakly with normal matter. It also could be made up of several kinds of particles.Another possibility is that dark matter is made up of WIMP. and it has a hypothetical force to interact with our normal matter, or MACHO (massive astrophysical compact halo object)
What would a distance anti-star or anti-galaxy look like to us? Why do we think that antimatter isn't somewhere else, far from us?
1. We would see the boundary where matter and antimatter met light up from annihilation of particles. 2. Because it seems likely that if the observable universe is made up of normal matter, so would the rest of the universe. If the universe is organized into clusters of matter and antimatter then the early universe would have needed to be widely separated.
What are some of the current ideas about the nature of dark energy?
1. comes from empty space 2. new forces or special fields that permeate space just as the electromagnetic field does,
Why does the fact that the universe has any structure at all require an explanation? Briefly, what is this explanation?
1. we would think that if the universe was infinite and smooth the the universe would be frozen because none of the particles could be compelled to move. If it were finite and smooth all the particle would be attracted to the center. We don't see either of these. 2. Small quantum fluctuations in the early universe were stretched by the rapid expansion of space-time (i.e inflation) into huge enormous wrinkles that seeded the formation of stars and galaxies by gravity, which was aided by dark matter at some point, and dark energy began stretching space out even farther
What are the four ways that matter interacts?
1.) Gravity 2.) Electromagnetism 3.) Weak Nuclear Force 4.) Strong Nuclear Force
How many neutrinos from the Sun pass through your fingernail each second? Why isn't this dangerous?
100 billion neutrinos pass through your fingernail each second. This is not dangerous because only 1 out of all 100 billion will recognize you are there and will bounce off of you
How many matter particles? Are these really fundamental?
12 matter particles We don't really know whether or not they are fundamental. They could be made out of smaller components which would account for some of the patterns we see, but we have not discovered those smaller components yet.
How many total elementary particles are there?
17 elementary particles
What year did astronomers discovered that the universe is expanding?
1931
What is the universe's speed limit? What is its value?
300 million meters per second
What percentage of the universe's mass/energy do all our current theories account for?
5% (normal matter)
Explain how a particle accelerator could detect extra dimensions.
A Particle Accelerator measures particles, if a particle is moving in other dimensions, we wouldn't see them moving in ours but it would have more energy and thus have more mass.
What gives a particle its electric charge? What is an electric charge?
A charge, actually, is something a particle has, it is a label. An electric charge just means a particle can feel electrical forces
What does "dimension" mean in science and math?
A possible direction of motion
If there were an extra (fourth) spatial dimension that is just like our normal three, how would the world appear to us? Why are we pretty sure there isn't an extra spatial dimension like this?
A.) You would see your *3-D* world changing around you. B.) Because we would notice things appearing and disappearing if they move toward and away from is in this other dimension.
"We don't know yet at a fundamental level the reason all the pieces in the universe fit together." What kind of answer would be appropriate for this question?
Again, we don't know why it works, we just know it works.
What is the observational phenomenon discovered in the early twentieth century that provided evidence for a Big Bang? How did the theory of general relativity help lead to this conclusion?
All the galaxies we can see are moving away from us, meaning that the universe is expanding If you project the expansion backward in time as far as possible, the equations predict that the entire universe was contained in a single point with enormous mass, zero volume, and infinite density.
Why might knowing about dark matter be important?
And it also highlights the fact that we still don't know about our universe and there is a lot left to learn. We can't claim to understand our universe without understanding a huge part of it.
If gravity is so weak, how can it also be so strong that it controls galaxies and planets?
Because gravity's force is proportional to the mass of the objects involved and it can only have positive mass.
If more than three dimensions are possible, why can't we detect them like the other three?
Because it could be different than the other three so we can't sense it.
Why do solid objects feel solid?
Because the molecules inside objects hold tightly to one another with electromagnetic bonds and repel the molecules in our hand.
How would measuring gravity at small distances help us detect extra dimensions? What makes this kind of experiment difficult?
Because they found at a smaller distance— one millimeter— gravity reacts differently than it does on the larger scale. If extra dimensions do exist they are one millimeter or smaller.
Why do physicists care that gravity is different from the other forces?
Because they want to fit things into patterns in order to understand. And gravity can't fit into the pattern of all the other forces.
Why do we think there must be space everywhere?
Because we don't think there can be parts of the universe which lack space.
Life is either common or rare in the universe. How do both possibilities match our experience? That is, what evidence supports the first? What evidence is there for the second?
Both possibilities match our experience through our various forms of life on earth. There are things that vary widely among organisms on earth and yet there are also things that are fundamental to all life forms.
How is the actual value of c both very fast and very slow?
C is slow compared to distances you have to travel to move between the stars or galaxies and fast compared to human experience.
What subdiscipline of mathematics is the language of physics. Why?
Calculus Because it is able to convert many tiny little slices into one smooth variation.
Has the speed of light changed over the universe's history? Will it change in the future? Explain.
Changed in the Past: Pre-Big Bang, Big Bang inflation current era of expansion. It will change in the future because to say it won't is to be overconfident.
What are cosmic rays? What are some sources of cosmic rays?
Cosmic rays are simply particles from space Cosmic rays come from stars, the sun, and other space objects.
Dark energy is causing the universe's expansion rate to increase. Why is dark energy called "dark"? Why is it called "energy"?
Dark because we can't see it. Energy because it's pushing everything apart.
Describe how quantum gravity is a problem for our standard view of the Big Bang.
In the early stages of the Big Bang, quantum gravity effects dominate, but we have no idea how to describe them
What is interesting about the fact that either there is (or was or will be) life on other planets or there isn't?
Either answer is mind-blowing and we know that one of them must be true
What other physical property is time associated with? In what ways?
Entropy Entropy has a strong preference for one direction in time; it always increases with time (second law of thermodynamics)
What is the heat death of the universe?
Entropy increased to the maximum level which causes the universe to have its maximum disorder.
According the authors, how have physicists observed quantum fluctuations?
In the baby picture of the universe from the CMB, we can see that the universe was not perfectly smooth. It had tiny ripples that represent quantum fluctuations of the early universe
Why is time so difficult to define? Is it an objective, human-independent thing or is our concept of time just something we need in order to describe our subjective experience?
Even plausible definitions of time raise even more questions about what it is; Partly why time is so hard to explain because it is so ingrained in our experience and our way of thinking.(119); hard to imagine human experience apart from time Even if time is an objective, human - independent thing, we wouldn't know anything about it as that because our subjective experience of it would prevent us from studying it.
What is one possible (and strange) explanation for why gravity is so weak?
Extra dimensions that gravity is diluted into
Imagine that each instant is a snapshot. In what two ways do these snapshots relate to each other in terms of time?
First: Time links the snapshots together in a chain, putting them in a particular order. Second: It requires the snapshots be causally connected to one another.
What is the common understanding of the Big Bang? Is it the actual moment of birth of our universe?
Generally thought of as an explosion. Everything was crammed into a very small volume and all that matter flew out through space, leading to the things we see today. It is thought to be the origin of our universe, but it fails to explain what caused it
There are hundreds of millions of the highest-energy cosmic rays hitting the Earth each year. Why are they so difficult to detect?
Given the size of the earth, it is not likely that it will get hit by a cosmic ray. The earth is a very large target compared to these tiny particles. This is why the chances to detect are so slim.
What are gravitational waves? Why was their detection so important? How might they be useful in helping us find a quantum theory of gravity?
Gravitational waves are the ripples in space caused by accelerating masses. It confirmed what Einstein thought that gravity bends space itself. It doesn't help us with a quantum theory.
What is counteracting or working against the universe's expansion?
Gravity
In addition to its difference in strength, how else is gravity different from the other forces?
Gravity doesn't have "negative" mass. It doesn't repel particles with mass. This means it can't be canceled out. It also only works in one direction.
Why is it important to understand gravity?
Gravity is basically the only force that works on grand scales, which means that it's one of the main forces that's determining the shape and eventual fate of the universe; it may also open the door to visiting another star system
How does general relativity differ from quantum mechanics with respect to how they view space and gravity? What problems does this cause for uniting the two theories?
Gravity is not a force that two things with mass feel towards each other but a bending of space 1) in order to make quantum mechanics work, scientists have to apply renormalization. When you try and apply renormalization to quantum gravity theory in bendy space, however, it doesn't work because as soon as you get rid of one infinity, another one pops up. 2) if we were to incorporate gravity as a quantum mechanical force, then there has to be a quantum particle to transmit it which nobody has ever seen.
As far as we know, what is the only force that applies to dark matter? How do we know?
Gravity is the only force that applies to dark matter. Because if dark matter as mass then that means it feels gravity.
Which of the two photons hits its target first according to the Earth-bound hamster? Which of the two photons hits its target first according to the floating astronaut? Which of the two photons hits its target first according to the rocket kitty? Which photon actually hits its target first—or do they both hit their respective targets simultaneously? Explain.
Hamster: They hit at the same time Astronaut: The left photon hits the target before the other. Kitty: The right proton hits the target first. All of the answers are right relative to where you are. We have to gubr up the idea events happen at the same time for everyone everywhere.
Describe how the size of the universe is a problem for our standard view of the Big Bang.
If all things are expanding away from the Big Bang, then our horizon should be expanding faster than everything else, giving us a view that is larger than the entire universe
Explain what it means for the overall structure of space to be flat or curved. What is the overall structure of space? How do we know? (There are two ways.) Why is this overall structure surprising?
If space were flat then it would be possible to travel in one direction forever. But if it were curved then we would have the ability to appear in the same spot from the opposite direction. We could "loop" back around. There is a "positive curvature" and a "negative curvature." The overall structure of space is flat. There are two ways we know 1) measuring triangles. This measurement works because triangles don't follow the same rules in a curved space as they do in a flat space and 2) measuring energy in the universe. This is so surprising because if we had just a little bit more mass or energy the universe would be curved or different but we seem to have the perfect amount.
Using 2D slices explain how a 2D creature might think about a 3D world. Using 3D "blocks" explain how a 3D creature might think about a 4D world in which there are three spatial dimensions and the fourth dimension is time.
In 2d you can only think in slices, if you moved 3D-ly you wouldn't be able to sense motion in a new direction, but if the slices were different you would notice the difference between slices.The same would be true for 3D - you wouldn't notice a new direction of movement but you would see different blocks. This might work with time - the world changes around you with time and then you stitch together the blocks to create a 4d world
What is inflation and how does it account for the size of the universe and the extreme uniform temperature of the universe? Why doesn't this violate the law of relativity?
Inflation = a nearly instantaneous twenty-five order of magnitude faster-than-light expansion of the fabric of space-time Faster-than-light here means the growth of new space, adding distance faster than light could cross it, not literal faster-than-light motion in space which is impossible according to the law of relativity
What does dark energy do?
It causes the universe to expand.
How could there be life on Earth if it didn't originate here?
It could have traveled to earth via meteorites
Explain some of the issues surrounding the question why time only moves forward
It doesn't make logical sense for it to move back (ex: ice cubes form in drink on a hot day); we never "remember" future events in the way we remember past events.
How is the electron "copied" in two different ways?
It has its heavier cousins(because of different dimensions) and it has an antiparticle
Is space continuous and smooth or "pixelated"? What reasons are there for thinking that it might be pixelated?
It is pixelated. One reason is because everything is quantized: matter, energy, forces etc. So it would make sense for space to be quantized as well.
When was dark matter first predicted? When was it first taken seriously?
It was first proposed in the 1920s. It was first taken seriously in the 1960s.
Why is general relativity called a "classical theory"?
It was invented before quantum mechanics
If the rate of expansion of the universe continues to increase, what will the night sky eventually look like? Explain.
It will look starless. Because all the stars would have moved away.
Why is dark matter called "dark"? Why is it called "matter"?
It's called "dark" because we can't see it. We know it has mass that is why it is called "Matter."
What is locality? Explain how altering the value of c would change locality.
Locality: the number of things that can affect you is limited to the number of things that are close to you. If you alter c that things that happen anywhere could have instant effects on the earth.
Did the universe begin at its highest or lowest level of entropy? Explain.
Lowest. Entropy only increases. Hence the universe had to start at its lowest
If mass is what gives a particle its inertia [or is it the same thing?] then what gives a particle mass? That is, why does a particle have mass?
Mass in a particle is more like a label we apply to an infinitesimal quantum object.
What is our theory of matter? How many kinds of particles make up ordinary matter? [3, (But what about energy, photons,?]
Matter as we know it is composed of atoms of the elements listed in the periodic table. Each atom has a nucleus surrounded by a cloud of electrons. The nucleus contains protons and neutrons, each of which is built from up quarks and down quarks. 3
What makes up molecules? What do molecules make?
Molecules are made from atoms(made up of up quarks, down quarks, and electrons). Molecules form all the complex objects in the known 5%
Why is traveling back in time probably impossible?
Moving backward in time can break causality. Without causality nothing makes sense. It would be hard to have a consistent universe
Light in a vacuum cannot travel faster than c. Can it travel slower than c? Explain.
No massless particles e.g. photons always travel at the maximum speed and never slow down
. What is the Drake equation?
Number of intelligent species we could potentially talk to (N) = number of stars in the galaxy + number of planets per star + fraction of livable planets + fraction of livable planets that actually develop life + fraction of planets with life that develop intelligent life + the fraction of intelligent species that develop technological civilization and can send messages or spaceships into space. + the probability that they are around at the same time as we are
We know that the hundred or so elements are composed of only a handful of smaller components and that these smaller components are composed of only a few even smaller ones. What do we call this process of explaining many things in terms of fewer things? Do you think this process leads to greater understanding? Why or why not?
Organization principle Much like a Lego universe (trying to find the smallest Lego pieces) Yes, because if you discover what that smallest Lego piece is then you would know the basic system for how everything locks with everything else. The downside to this is that it could potentially continue ad infinitum.
Is our observable universe getting larger, smaller, or staying the same? Explain.
Our observable universe is getting larger at least one light-year every year. The volume of the observable universe grows even faster because the slice of space that is added every year has a larger volume than the previous year's slice.
If the Earth's surface is protected from the super-high-energy particles by the atmosphere, how do we detect these particles?
Particles are detected by large plots of land with smaller particle detectors. This only means that you will see a few every year.
With both the periodic table and the Standard Model table there are two features of the tables that have led us to a deeper understanding of the universe. What are these two features?
Patterns and missing pieces
Why do we think that these super-high-energy particles are coming from a source relatively close to the Earth?
Photonic fog in the universe slows down particles which means that these high-energy particles must be coming from somewhere close.
How many matter particles are there? How many other particles are there that transmit forces?
Physicists have discovered nine more particles than the 3 we have had. They also discovered 5 more particles that transmit forces.
How do QM and GR view space differently?
QM look at gravity as a force between two objects. GR looks at gravity as a distortion of space itself.
What two possibilities does the book present for the size of the observable universe? Which one is the correct one?
Since nothing can travel faster than the speed of light, the observable universe must be the age of the universe times the speed of light , or 13.8 billion light-years in every direction. Since space itself is a thing that can expand faster than the speed of light (and has), we can see things that use to be inside our horizon but are now past it, up to about 46.5 billion light-years in every direction.(correct one)
Why isn't "normal" matter really normal?
Since our "normal" matter is actually the minority(5%) and the dark matter is the majority(68%). It isn't fair to call it "normal" because it is rare, comparatively.
How fast is the observable universe expanding?
Slower than the speed of light (according to general relativity)
Does space go on forever or is it "closed" Somehow? Explain.
Space could have an edge. Just because space is flat doesn't mean it can't have a boundary. An example of this is wormholes where two points of space that are far apart are connected to each other.
Explain the three things that space can do that aren't compatible with either view. What does this imply about what space is?
Space doesn't fit these two view because space can bend, ripple, and expand. This implies space is a physical thing.
What is loop quantum gravity?
Space is built out of tiny invisible units called loops that are the size of the Plank length or 10^-15 meters. If you weave enough of theses loops together, it might be possible to derive all of space and matter
How fast does the Earth-bound hamster see each of the two photons moving? How fast does the floating astronaut see each of the two photons moving? How fast does the rocket kitty see each of the two photons moving? How fast are the two photons moving? That is, what are their absolute (not merely relative) speeds? Explain.
Speed=At the speed of light.
What is plasma?
Strands sent out by solar flares that carry extra dangerous particles
What does string theory say about the building blocks of the universe and the universe's dimensions?
String Theory says that our universe is made up of tiny one-dimensional strings. Instead of zero-dimensional particles. String theory suggest that our universe has a lot of dimensions!
What are two possible theories of quantum gravity that physicists are currently working on?
String theory and loop quantum gravity
What force keeps protons and neutrons stuck together?
Strong Nuclear Force
What is supersymmetry? Has it been empirically verified?
Supersymmetry claims that every particle has yet another kind of mirror or superparticle(a particle that has a different quantum spin) It has not been verified
How might the LCH make black holes? Would this be dangerous? Explain.
The LHC smashes protons together since gravity is super strong in small distances. No. Because these black holes evaporate very quickly.
Explain how we might answer the question "What is the universe made of?" What are some of the fundamental issues involved in answering this question? [Simplicity, organizing principle, complexity, observability, periodic table of the elements, Legos,]
The Periodic Table is an example of this "simplification" we are after. It also reveals how organized the world is. This tool— the periodic table— allows us to construct other things in our universe(stars, rocks, dust). This is called the Organizing Principle, which is our understanding that the universe is made up of complex things which in turn are made up of simple things.
The most basic parts of matter that can be organized into a table. What other table is this similar to?
The Periodic Table of Elements
Has the Standard Model been experimentally verified? Is the Standard Model complete? [aside: particle accelerators]
The Standard Model is based on real observations As far as we know it is complete, but there is always a possibility of finding a new particles (especially when it comes to studying dark matter)
Why think that the organizing principle of simplification is possible? What would be the alternative? [each thing has its own kind of particle, goop or smooth stuff]
The alternative could have been each thing as it's own particle. Another alternative is that things are not made of tiny particles at all.
Were the closer stars moving faster than the distant ones or were the more distant ones moving faster? Which were redder? What did the astronomers expect and why did they expect it?
The distant stars are moving slower. The closer stars are moving faster. The closer stars were redder. The scientists expected the opposite because in their minds two things had happened: a universe that exploded a long time ago and gravity trying to put it back together.
Events can occur in different orders for different observers. Is there a limit to this reordering? Explain.
The limit is causality. We cannot violate causality, because without causality water would boil without you ever turning on the stove. Chaos.
Why aren't supermassive black holes at the center of galaxies likely candidates for the source of very high-energy cosmic rays? What are some other candidates, according to the authors?
The location of active galactic nuclei don't match the very high-energy cosmic rays. Other candidates are alien scientists, the matrix, a new force, and physics.
How does the Higgs theory explain mass? What year was the Higgs particle discovered?
The more a field interacts with a particle, the more inertia (or mass) it seems to have. Inertia generated by a particle interacting with this field is the particle's mass. 2012
Physicists tend to think that simpler theories are better than more complex ones. What is an important criterion for what makes one theory simpler than another?
The number of numbers in it.
What do we know about what dark energy is?
The only thing we know is that something is causing an increase in expansion rate.
What percentage of the stuff (matter/energy) of the universe does ordinary matter make up? What makes up the remaining stuff of the universe and in what amounts (percentages)?
The percentage we know is 5%. The remaining 95% is dark energy(68%) and dark matter(27%)
According to the authors, what is the "biggest topic known to mankind"?
The size and structure of the universe
What is one important tool we have for studying space? How might we take advantage of this?
The tool: space is distorted by mass and energy. To take advantage of this we should examine and study black holes. Black holes are cosmically huge masses that are squeezing and straining.
. If theories of emergent phenomena (i.e., non-fundamental theories) are useful and effective, why search for a ToE?
These theories miss the satisfaction of revealing how the universe really works. Knowing the deepest truth helps us understand our place in the universe.
As far as we know, what do all particles with antimatter partners have in common?
They all have electric charge
Elementary particles aren't "little balls of stuff." What are they?
They are little fluctuations that permeate the entire universe.
Where are nearly all the objects in the night sky located, cosmically speaking? The best answer is not "Part of the night sky."
They are part of our own galaxy (because they are the brightest and closest objects)
How do astronomers tell whether a star is a bright one far away or a close one that it dim?
They can tell because they discovered a type of star (Ia Supernovae) that predictably did the same thing everywhere in the universe : when they reach a certain size the implode.
How do astronomers know the speed at which the galaxies around us are moving? In what direction are they moving?
They did this by looking at the stars, whose lights very far away thus old and comparing that to the present. Thus they see faraway objects moving at one speed and then closer objects moving at another speed, they can deduce the speed of things has changed over time. The can measure the directions by using the Doppler Effect.
Explain how lead is "transparent" to neutrinos.
They don't bounce off the particles in lead. Lead is transparent to them.
According to the authors, what is the key to making a scientific theory scientific? How would it be possible for theories about the Big Bang to be scientific?
They have to make testable predictions that can be validated in experiments We can test theories about the Big Bang as long as they make predictions about things we can find in the rubble
How can astronomers actually observe the past right now? How can this tell them whether the expansion of the universe has changed?
They look at stars far away because their light is "old." They compare this to the stars now. Because farther away objects are moving at a different speed than the ones close to us(recent).
What evidence caused astronomers to infer that the universe expanding? If the universe is expanding now what can we reasonably conclude about its past?
They measured the light from our surrounding stars and galaxies and concluded that everything was moving out. 2. That it's bigger than it used to be and it used to be very small
How might science be ready for another revolution?
We are at a point where we know very little, but have powerful new tools to discover things. Things we accept now, such as GR and QM might be shattered and replaced with min-blowing new ideas.
What are the twelve matter particles? How many (and which) are needed to make up every kind of atom? How many are left? What are they for?
Up, down, charm, strange, top, and bottom (quarks) Electron, muon, tau, νelectron, νtau, νmuon (leptons) Only up and down quarks and electrons are needed to make up every kind of atom Nine particles are left, and we have no idea what they are for
Describe the two initial views of space that the chapter considered (and then rejected)?
View One: Space is an infinite void. Rather it is the lack of stuff. View Two: Space exist in the context of matter. It is the relationship between matter.
What are some necessary ingredients for life as we know it?
Water, carbon, nitrogen, phosphorus, and sulfur
Everyone experiences time the same way. Explain
We all experience time one-second-per-second-rate. ????
How is the universe like a loaf of raisin bread?
We are the raisins and the universe is the loaf. As the bread bakes and rises all the raisins move away from each other but they stay the same size.
Why are the particles of the Standard Model called "fundamental"?
We can't yet see if they are made of smaller particles
Why are things put together the way they are and not some other way? What kind of answer would be appropriate for this question?
We do not know the answer to this question (as a christian it's because God ordained it)
Why does the universe have a speed limit? Why is this speed limit c? Could it have been other values?
We don't know - it could be that it reveals something deeper about the universe -e.g. A theory of space-time.Or it could be that it could be that it could've been anything
Why are there matter particles other than the three that make up ordinary matter?
We don't know.
What is a possible candidate for the cause of inflation?
We have no idea, but physicists have theorized about a new kind of substance with negative pressure that causes the rapid expansion of the universe and eventually transformed into more familiar matter
Why are there three generations of particles?
We have no idea, but we there cannot be a fourth because of the discovery of the Higgs boson
What do we know about dark matter? How close is the nearest dark matter (probably)? Can it hurt you?
We know: it has mass, it's invisible, it's around galaxies, regular matter can't touch it, and other dark matter can't touch it. Dark Matter is most likely surrounding us. It can't hurt us.
How will we know when we've reached the ToE?
We may never know with 100% certainty
How many possible elementary particles are there?
We really don't know.
Why think that space might need to be inside some additional thing?
We think space might be inside something because the concept of "space goo" makes it sound like it would be inside of something.
Describe how the uniformity of temperature of the universe is a problem for our standard view of the Big Bang
We would expect the temperature on one side of the earth to be colder than the other if everything did originate from a single point, but they are the same temperature. This is a problem, assuming that we are not at the exact center of the universe since that would be very unlikely.
Should we expect there to be more matter than antimatter?
We would expect there to be the same amount(and if there was the same amount we would have expected all the particles and antiP. to have met and turned into photons).
What force do neutrinos use to interact with each other particles?
Weak Nuclear Force
How do electrons repel each other?
When two electrons repel each other they are exchanging a photon. They do it by "shooting a photon" at each other.
According to the authors, what question is sometimes called "the Ultimate Mystery"? What kind of answer do they say we are looking for? What other questions does this lead to?
Why does the universe exist and why is it the way that it is? Looking for an explanation based on some fundamental law or fact about the universe that shows the universe had to exist and that it couldn't have been made any other way (and still be consistent) Why is the universe this way and not that way? Why do fundamental laws exist? And why does the universe follow them?
What does Wiki say that physics is? What is the basic job of physics?
Wiki defines time as "the study of matter and its motion through space and time. The basic job of physics is to use the past to understand what futures are possible and how we could affect them.
Are electrons, protons, and neutrons like tiny billiard balls? Explain.
Yes and no. They are not really tiny, hard spheres. They are fuzzy quantum particles defined by waves and ungoverned by uncertainty and probability. However, the picture of atoms as tiny billiard balls works to describe how gas atoms bounce around inside a container. They are like spheres to a certain degree.
Can different people measure the speed of the same event differently?
Yes. In space, clocks measure the passing of time slower compared to on earth. Our clocks disagree if we are moving at high speeds relative to each other.
Is it possible for anything to travel faster than the speed of light? Explain.
Yes— technically. It is technical because it depends on some mediums For example, a muon can pass through blocks of ice faster than light passes through ice. So technically this is faster than light You still can't travel faster than light in a vaccum.
Sometimes mathematics tells us seemingly impossible things about the physical world and so we often reject these counterintuitive proclamations of math. But sometimes we don't. How do we know when to reject/accept a mathematical result?
You can't? Generally, go with the result that equates with reality and agrees with physical constraints.
What two areas of physics did Paul Dirac combine to get the "Dirac equation"? Explain how Dirac used this equation to predict antimatter.
a. He combined quantum mechanics and relativity. b. The equation does a great job at describing the particles at high speeds, but the equation worked with both the negatively charged electrons and the positively charged electrons (antielectrons
Explain (without referring to bodily functions) how extra spatial dimensions would explain the ridiculous weakness of gravity. How does the size of the dimension factor into this explanation? What do we think we know now about the size of any extra spatial dimensions?
a. It would help because forces get weaker the more dimensions there are as they are diluted throughout all the dimensions B. The smallness of the dimensions would explain why gravity feels so weak - it's actually strong at tiny distances (<cm) but by the time it gets over that size it has been dissipated C. That if they exist they're smaller than a millimeter
How are antimatter particles different from their ordinary matter partners? How are they similar? How is the concept of symmetry related to antimatter?
a. They are different in electric charge, and in charges for the weak and strong nuclear forces. B. Same mass and described by the same quantum properties. C. antiparticles/antimatter are an example of symmetry. Particles/antiparticles are like two sides of the same coin.
The redder a star is the _____________________ it is moving away?
faster
Is the sun's power source fission or fusion?
fusion
Why think that time is a "fourth" dimension? Why think that it's not? That is, how are space and time different?
hinking about it as 4th dimension is mathematically convenient to our theories. Time is not a set of interconnected locations. Rather, we think of time as linking together of causally connected static snapshots of the universe.
Do supernovae explode or implode? Explain
implode. The create a corresponding big explosion.
Do our scientific theories tell us what caused the birth or what came before the universe was born?
no
Has the universe's expansion always been increasing?
no, just the last 5 billion years
. The book says that, Time is the ________ and ____________ of the snapshots
ordering and spacing
How many force-carrying particles are there? Name them.
photon, w bosons, z bosons, gluon, and Higgs boson
What distinguishes quarks from leptons?
quarks feel strong force (and have fractional electric charges)
What makes it difficult to observe an Ia supernovae?
short lived explosions
What exactly is expanding?
space
Complete the sentence: "Things are moving through space away from us, and at the same time
space itself is expanding
What is the only pattern to the masses of the elementary particles?
this is the pattern in the periodic table, the only pattern we've found in the standard model is that every generation is more massive than the last
Explain what happens when a particle and its antiparticle partner meet? How is this similar to what happens when two particles collide in the LHC? How is it different?
when they meet, they destroy each other completely: the particles disappear and their masses are completely converted into a high-energy force-carrying particle. The particles are annihilated and a huge amount of stored energy is released and other kinds of particles can emerge b. In both situations, the particle interaction result in annihilation of the original particles into new particles c. it's different because particles and antiparticles have opposite charges which makes them more likely to smoosh together, and also because they perfectly complement each other, they can annihilate into something neutral
How much mass does a photon have?
zero
