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Physics & Cosmology Flashcards

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1
Q

How does quantum entanglement work?

A

two quantum particles can interact since that they are described by a single wave function

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2
Q

How have we tested quantum entanglement?

A

The EPR paradox: if we fire off 2 particles in opposite directions, we can measure either position OR momentum and know the details for the other, but since these are all uncertain properties, then it is tantamount to nonlocal coordination between the 2 particles.

Bell’s Inequality followed this

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3
Q

What is a neutron star?

A

Small, white collapsed star not massive enough to turn into a black hole

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4
Q

How is Hawking radiation generated?

A

Quantum fluctuations around the event horizon allow particles to leave and antiparticles to fly into the black hole, eventually evaporating it.

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5
Q

What is the no boundary case for the universe?

A

There was no time before the universe: it expanded out of nothing, like walking out of the North Pole

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6
Q

Why do time dilation and length contraction happen together in special relativity?

A
  • A Lorentz Transformation transforms a block of space time (as represented by a flip book) to maintain constant speed of light from all perspectives. This distortion causes both time and space to change together
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7
Q

In the Twin Paradox, who is older at the end? How do we resolve the paradox?

A

The one who stayed in place is older. They are different because the one on the ship isn’t not in a constant inertial frame

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8
Q

How does String Theory’s additional dimensions provide a path to a Unified Theory?

A

Just as gravity bends the dimensions of space, EM could bend another dimension

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9
Q

How does E=MC^2 make sense as mass being the same as energy?

A

Mass isn’t a measure of stuff; it’s a measure of energy (even potential) in the stuff

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10
Q

Why isn’t Schrodinger’s Cat really alive and dead?

A

When the particle hits the poison, the superposition of wave functions collapse through decoherence as there are complex real world impacts to the wave function

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11
Q

What is Einstein’s theory of special relativity?

A

Because the speed of light is absolute, time and size must change for the observer.

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12
Q

According to Hawking, how might wormholes exist, and why would they allow for time travel?

A

With extreme warping of spacetime (such as near a black hole), it may be possible to find “shortcuts” through space. Due to special relativity, there is no absolute sense of time, so events may not have happened in the same order depending on your location

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13
Q

How did black body radiation lead to the idea of energy quanta?

A

Since black body radiation is equal at all wavelengths, and shorter wavelengths have higher energy, the output goes to infinity. Planck determined that if radiation was emitted in quanta at fixed intervals, this avoided the problem.

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14
Q

What is Schrodinger’s equation?

A

It describes how a wave function changes over time

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15
Q

What does a wave function describe?

A

It is a probability distribution of space (or other property) for the location of.a particle, but not really because the particle isn’t actually in one unknown place: it’s actually uncertain

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16
Q

what is a superposition?

A

A combination of multiple wave functions (that may each represent different states of the same particle)

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17
Q

What is Bell’s Theorem?

A

there’s a correlation of hidden properties that puts a limit on what can be coordinated between 2 particles. The only way to get past this limit is with nonlocal quantum effects, which have been observed

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18
Q

What is a quantum measurement and how does it relate to decoherence?

A

When you measure a superposition, you effectively entangle it to a much broader and more complex superposition. It doesn’t tell us how a certain result is picked but clearly draws a line about how measurement matters

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19
Q

What is the de Broglie-Bohm interpretation?

A

There is a localized, real particle, but it is influenced by the entire wavefunction

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20
Q

What is the Copenhagen interpretation?

A

Since we can’t know what happens, it is a waste of time to think about it, so focus on what we can observe

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21
Q

What is the many world interpretation?

A

All paths are taken in different universes, and they affect each other

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22
Q

What is quantum tunneling, and how does it happen?

A

The wave function may spread out past barriers given the uncertainty between energy and time and allow particles to appear in surprising places. It is essential to much technology today.

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23
Q

What is quantum teleportation?

A

Clone and know the state of a quantum particle given some classically communicated information

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24
Q

What was the first black hole discovered and how?

A

Cynus X-1. In 1971, they spotted. Binary system where the other star wasn’t visible; they guessed it was a black hole

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25
Q

Why do all of the planets spin in the same direction?

A

Planets were formed by an accretion of the dust spinning together, and they continued in the same direction

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26
Q

What is gravitational lensing?

A

gravity bends the light from the back side and distorts it: this create a sphere around the event horizon

27
Q

What is a quasar?

A

Quasi-stellar radio source: far away super-massive black holes with an accretion disk to form galaxies

28
Q

Why are events before the Big Bang irrelevant?

A

Because all laws of science (and predictability) break down, prior events cannot have any impact on subsequent events, so they cannot be “earlier”

29
Q

What is a light cone?

A

The set of past events that could reach a given event or the set of future events that could be reached from a given event.

30
Q

Why does time run appear to run slower near massive bodies?

A

As light travels out from the body, it loses energy, so it’s frequency goes down, so the length of time between wave crests increases.

31
Q

How did Hubble calculate the distance to other galaxies?

A

Certain types of stars had known luminosity and distance in our own galaxy, so calculating the apparent brightness of those stars gave a distance

32
Q

How and when did we determine that the universe is expanding?

A

In the 1920s, astronomers noticed the spectrum of stars were shifted red, corresponding to the speed they were moving away from us. Also, the shift was proportional to their distance from us.

33
Q

How does Hawking argue that time must appear to flow with increasing entropy?

A

Memory is constructed through structuring the mind, which is a local decrease in entropy, so if entropy ran backwards, our memory would need to follow

34
Q

In particle physics, what does it mean to have a spin of 1/2?

A

The particle must complete 2 revolutions to return to their original state

35
Q

What would be the consequence of Pauli’s exclusion principle not being true?

A

Two matter particles with the same position and velocity within the limits of the uncertainty principle would collapse due to force particles into a high density soup

36
Q

What is the spin of all matter particles?

A

1/2

37
Q

What is the spin of force carrying particles?

A

0, 1, or 2

38
Q

What are the four fundamental forces?

A

Gravity, EM, strong and weak nuclear forces

39
Q

What does the strong nuclear force do?

A

Keeps protons and neutrons together. It is the spin 1 particle gluon

40
Q

What does the weak nuclear force do?

A

Responsible for radioactive decay of atoms

41
Q

How does electromagnetic induction work?

A

circuit with an alternating current flowing through it generates current in another circuit simply by being placed nearby. The alternating current generates fluctuating magnetic fields, affecting conductors in the field

42
Q

How does a battery work?

A

Two electrodes have a buildup of electrons between them. When you connect the two terminals in a circuit, then there’s a flow of electrons (current) through the circuit and also flow of ions through the electrolyte.

43
Q

How does a capacitor work? How do they compare to batteries?

A

Buildup of charge on 2 plates separated by a dielectric (rather than chemical), generating an electrostatic field. They charge and discharge quickly and are relatively large

44
Q

What is the difference between wet and dry batteries? What are the advantages?

A

Dry batteries have a dry electrolyte. The wet batteries have higher capacity but need to be in specific orientations

45
Q

Why are there jets at the top and bottom of a black hole?

A

The spinning disk of matter around the black hole creates a magnetic field, and anything else shoots off the top and bottom

46
Q

Why do bigger stars burn out faster than smaller stars?

A

To counteract gravity, they must generate more energy through fusion and burn out their fuel.

47
Q

What is an event horizon?

A

The boundary at which light cannot escape the gravity of a black hole

48
Q

What is the weak anthropic principle?

A

We see the universe the way it is because we exist. Intelligent beings see that the universe can create life because we luckily were here

49
Q

What is the strong anthropic principle?

A

Given the wide number of configurations for our universe, they all exist and we happen to see this one because we exist. Less useful because we can’t access those worlds

50
Q

Where did the matter of the universe come from?

A

As the universe expanded, it generated negative gravitational energy, which is canceled by the positive matter of the universe.

51
Q

What does it mean for the universe to be finite with no edge?

A

You could keep going in one direction and eventually end up where you started (like going around the Earth). In practice, you could not go fast enough to make this happen

52
Q

Why does faster than light travel suggest the possibility of time travel?

A

Depending on your perspective and speed, then the ordering of events changes. If faster than light travel makes one ordering possible, then the opposite may exist from another perspective.

53
Q

Why do wormholes also allow for time travel?

A

If you can travel forwards to carry news of events, then you can also travel in the opposite direction to effectively go backwards in time to when it happened.

54
Q

Why can’t you time travel before the time machine was made?

A

The closed timeline curve needs to pass through the point in space time to get back to there. If a Time Machine existed, it would need to exist there.

This wormhole spacetime warping hasn’t existed yet, but perhaps it could in the future created by the technology.

55
Q

Why in string theory do we have 3 accessible dimensions? Why not more or less?

A

As an anthropic principle, 2 dimensions would be insufficient (we would be cut in half by digestive tracts) and more than three would results in unstable gravity

56
Q

How do LEDs work? How do incandescent lightbulbs work?

A

LEDs pass electricity through a semiconducting material (diode) that emits light through electroluminescence. Electrons jump across a p-n junction.

Incandescent lightbulbs pass electricity through a filament that heat up and glow through resistance.

57
Q

What is an astronomical unit?

A

Distance from the earth to the sun. About 150 million kilometers or 8 light minutes

58
Q

What is the Kuiper Belt?

A

Circumstellar disc (like the asteroid belt) beyond Neptune. It includes Pluto

59
Q

What is the Oort Cloud?

A

Cloud of stuff in interstellar space around the sun.

60
Q

How long ago was the Big Bang?

A

About 14 billion years ago

61
Q

When did life first emerge on earth?

A

About 4 billion years ago

62
Q

When did the sun and solar system first form?

A

4.5 billion years ago

63
Q

When did the Earth first form? Who figured this out? How and when?

A

4.5 billion years ago. In the 1950s, Clair Cameron Patterson used radiometric dating to measure the age of a meteorite

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