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@SabineHossenfelder Channel: t.ly/kh9q
FURTHER READING:
Feynman lectures: t.ly/skft4
David Tong lectures: t.ly/FRnC
Textbook: t.ly/AksQ
CHAPTERS:
0:00 The "language" gap of quantum mechanics
3:07 What the math of quantum mechanics says
4:55 What is a wave function?
8:10 What is physical meaning of the wave function?
9:55 The Double Slit experiment explained
13:13 Sabine's physical interpretations of wave collapse
14:55 Why we can't "see" the wave function
15:42 Measurement problem
16:38 Many Worlds Interpretation
18:01 The "Answer"
SUMMARY:
What is the meaning of quantum physics? What does quantum mechanics mean? What is it telling us about the true nature of reality?
Are particles at the quantum level fuzzy and spread out, two places at once, or two different states at once, or affect each other instantly over any distance? Not really. There is no consensus on quantum reality.
The most important quantum equation is the Schrodinger equation. It includes a mathematical function - the wave function, which encapsulates all that can be known about a quantum object.
The object’s wave function has a value at all points in space. And this value depends on the state of that quantum object. If you know the wave function, Schrödinger’s equation lets you figure out where you’ll find the particle in space, or how fast it is traveling, or how much energy it has.
But what is the wave function? What is the wave made of? A water wave is made of water molecules. But a wave function for a quantum object isn’t really made of any substance other than information about the object. Also, the amplitude of a quantum wave function is generally a complex number which means that it has no physical meaning.
German physicist Max Born said that the square of the wave function is a probability that we’ll find the particle at a point in space - if we look. This makes knowing the particle ambiguous.
The wave function doesn't tell us where the particle probably is at any point in time. It tells us only the chance of finding it there if we look. The particle is not everywhere until measured. Born’s rule is only about the probabilities of the outcomes of measurements.
But this also doesn’t mean that nothing exists until we look. A quantum world exists whether we look or not. It says nothing obvious about what quantum reality itself is like.
Richard Feynman called the double slit experiment the central mystery of quantum mechanics. It shows that individual particles behave like waves in aggregate. But we don't see this because when we measure the particle at the screen, it takes a point-like position.
Is the wave function just math that lets us predict what we’ll see in a quantum experiment? Or is it a real, physical object like an ocean wave?
Some theories attempt to define the collapse as a real physical process.
To give you a fuller perspective, I invited fellow UKpostsr and friend Sabine Hossenfelder to tell you about these, Penrose’s gravitationally induced collapse, the GRW model and Superdeterminism. Sabine thinks Superdeterminism is correct.
We can’t really just see the wavefunction of a single particle, only the collapse. Standard quantum theory doesn’t actually provide any description of the measurement process.
Our own conscious awareness of the measurement result does not influence it. But it happens, and what causes it to happen is called “the measurement problem.”
Some researchers say that we can’t deduce anything much about that “underlying reality”. If all quantum mechanics gives us is probabilities about measurements, we just have to accept that that’s all we can know.
Physicists like David Mermin said “Shut up and calculate.” - they don’t want to bother about questions that lie beyond what we can measure and observe, because that doesn’t seem like science.
Others say that the most fundamental level, reality really is a wave function. This is the Many Worlds interpretation of quantum mechanics, or the Everettian view because it was first proposed by the physicist Hugh Everett in the 1950s.
We experience just one world because the measurement itself causes the universal wavefunction to split into separate universes, where a copy of you measures something else. These worlds are isolated from each other.
There is no good way to test which interpretation is correct. Quantum mechanics doesn’t appear to show that there is a set reality out there, independent of how we choose to look at it.
But this doesn’t mean that an objective reality doesn’t exist. But we are not completely independent of this reality.