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Flashcards in Physics & Cosmology Deck (56)
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How does quantum entanglement work?

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


How have we tested quantum entanglement?

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


What is a neutron star?

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


How is Hawking radiation generated?

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


What is the no boundary case for the universe?

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


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

* 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


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

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


How does a Unified Theory lead to String Theory?

Just as gravity bends the dimensions of space, what if EM bends another dimension?


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

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


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

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


What is Einstein's theory of special relativity?

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


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

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


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

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.


What is Schrodinger's equation?

It describes how a wave function changes over time


What does a wave function describe?

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


what is a superposition?

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


What is Bell's Theorem?

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


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

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


What is the de Broglie-Bohm interpretation?

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


What is the Copenhagen interpretation?

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


What is the many world interpretation?

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


What is quantum tunneling, and how does it happen?

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.


What is quantum teleportation?

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


What was the first black hole discovered and how?

Cynus X-1. Binary system where the other star wasn't visible; they guessed it was a black hole


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

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


What is gravitational lensing?

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


What is a quasar?

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


Why are events before the Big Bang irrelevant?

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


What is a light cone?

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.


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

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.