What is Quantum Mechanics Really Trying to Tell us about Reality? Featuring @SabineHossenfelder

FURTHER READING:

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 Youtuber 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.

[SabineHossenfelder]

Thanks so much for the collab Arvin, quantum mechanics is eternally fascinating to me!

[yashen]

WOW i genuinely didnt think id walk out of this video learning something new since iv spent years binging quantum mechanics videos but u just taught me about penrose gravitational collapse ! this is why i keep coming back to your channel. its not just regurgitated talking points. u take it a step futher

[justchecking]

The clearest, most sensible explanation of alternative views of QM wave functions I have ever seen. Thank you Arvin!! - J. D. German, Retired Physicist

[psiphisapiens]

There’s been a refreshing turn around in science communication lately. Videos about physics have evolved from entertainment to education, finally. Thank you.

[doloreslehmann]

I'll use an analogy to try to get my thoughts across: Imagine you throw a die in the air. Which number does it show? Well, all of them simultanously, right? It is undefined.
Now, a collapse of the wave function would be comparable to the die landing on a table surface, with just one side, and therefore one number, facing upwards. A many-worlds-situation would mean the die hits six different tables in six different worlds at the same time, showing a different side up on each of them. Superdeterminism would mean that, for some mechanism we haven't quite understood yet, only one of the six sides could possibly face upwards.
But what if the measurent wasn't like the die hitting any surface at all? What if it was more like us taking a photo of the die when it passes? The photo would show just one of the sides, giving us a measurement result, but the die would continue flying through the air. So, we would have one definite result that would define our subjective reality, as we would interact only with this, but the objective reality would remain undefined. Is there a model for this situation?

[rwarren]

This is right up there with the speed of quantum entanglement or freezing a photon to absolute zero and watching reality refuse to allow precise measurements. It’s just plain spooky! Thanks for graphic showing the wave function collapse. It really cleared things up. And a special thanks for bringing Sabine as well. I never miss her channel.

[AB-etnj]

"Shut up and calculate" isn't how Einstein revolutionized the field. Physicists need to think about these outcomes. If physics was just about calculating then we wouldn't even need physicists, we'd just use computers for that which are much better at shutting up and calculating

[velocirapper]

This is my favorite science channel. You explain things just perfectly for me to understand and you go further in depth than most other people and still explain it better.

[phalsgun]

Hi Arvin, really love your videos. It may seem like you are talking about same concepts repetitively in your videos, but you do explain it in different ways every time. That really helps me in understanding these concepts as a science enthusiast. I always watch and enjoy both of your videos.

[Arsenic]

Oh wow, two of my favourite physics Youtubers collaborating, absolutely fascinating! Thank you very much to both of you!

[kidzbopisstraightfire]

Two of my fave physics channels in one! Great job Arvin and Sabine

[SIASLbyRAH]

I really needed this. Thanks for making it! And for including Sabine too!!

[quantumdecoherence]

Beautiful presentation Arvin. Your channel is the clearest and easiest to follow and the graphics/visuals are second to none in helping to understand these complex topics.

[laurendoe]

From what I understand, Einstein also favored Super-determinism. As I understand it, he believed there were factors that we have yet to discover which would remove the probability aspect of quantum mechanics.

[byamboy]

Congratulations on this amazing achievement! I have been taught many things I thought I knew and could finally visualize and understand the quantum world in a systemic fashion.

[DarkMatter]

It's amazing how far we've come to understanding the rules of the universe... It seems like there's even more amazing times and discoveries ahead of us.

[robbxander]

Love to see Sabine on other channels. And Arvin, your videos are always on point. Mad props, my dude.

[mrtransmogrify]

Exciting & informative to see 2 of my fav physics content creators in collab... this is really one plus one = more than 2

[NNiSYS]

As always dear Arvin, your CLARITY is beautiful. Thanks for sharing it!

[xXYourShadowDaniXx]

Loved the physical interpretations of wave collapse, it would be cool to get a longer video on these with 3d examples!

Would also be cool to see a video specifically about the barrier between physical/quantum world, the size, why its hard to find/describe, etc.