The SIMPLEST Explanation of QUANTUM MECHANICS in the Universe!

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CHAPTERS:
0:00 Why do we need Quantum Mechanics?
2:23 What's "weird" about QM?
4:07 What is the Measurement Problem?
6:29 Uncertainty principle Explained
8:35 Why don't we see quantum behavior in macro?
9:31 Entanglement explained
10:25 What do atoms actually look like?

SUMMARY:
This video explains Quantum Mechanics intuitively. Classical mechanics failed to describe how an electron could orbit an atom. An accelerating charge always creates electromagnetic radiation. This means it would constantly lose energy and crash into the nucleus. Only quantum mechanics could explain why this does not happen by showing that electrons exist in quantized orbits proportional to Planck's constant.

Louis de Broglie showed that they must be waves. And Erwin Schrodinger developed an equation to explain this wavelike behavior. Max Born came up with the idea that the wave function in the Schrodinger equation should be interpreted as a probability. So quantum objects have only a probability of being found at any particular location in space, which can only be determined once we measure it, not in advance.

Quantum objects are not like little basketballs. They are like waves because they create interference patterns like we see in the double slit experiment. The problem is that we only observe particles, not waves.

So the concept of measurement was introduced to account for what we observe. The most common interpretation of quantum mechanics is that whenever a measurement is made, the wave collapses and becomes a localized wave, or particle.

What is a measurement? Measurement is an interaction, and interaction of the quantum object with some kind of measuring device, more specifically an irreversible exchange of energy.

But there is a huge problem. No one can explain how or why this “wave collapse” occurs through measurement. This is called the “measurement problem” in quantum mechanics.

And since all our information comes from a measurement of some kind, we can never directly see this quantum world. Everything we observe must go through this measuring process that seems to result in the conversion of quantum objects into particles.
#quantummechanics
#quantumphysics
So how this wave evolves according the Schrodinger equation, is never actually seen. This is a fundamental problem that we need to resolve. In Quantum mechanics, objects have wave-like behavior described by wave functions, which are abstract mathematical solutions to the Schrodinger equation. These waves aren't localized but instead take up all of space. It isn't until you look for a particle that it becomes what appears to be a particle; before that, the particle is a collection of probability waves that theoretically extend out to the entire universe.

This has profound consequences. One is called the Uncertainty Principle, which states that you can never simultaneously know exactly where something is, and how fast it is going. More precisely we cannot know the position and momentum at the same time. This is not a limitation of our measuring devices. The universe itself doesn’t know the answer.

Why don’t we see this wave behavior in macro objects like a basketball? Well, actually all objects actually do have wave-like behavior! But their wavelength is so small, that you don't notice it. For example, the wavelength of a tennis ball moving 10 meters/second, is 10^-33 m. This is less than the width of a proton.

A second consequence of wave-like behavior is nonlocality. A wave exists over multiple regions of space. This nonlocality explains interference, but it also means that waves can add together to give complex interference patterns. This gives rise to strange correlations between such particles, called “Entanglement.”

Einstein called this, “Spooky action at a distance” because it appears to indicate instant communication between distant objects at faster than the speed of light, which is forbidden by Relativity theory. But while two or more objects are correlated, no communication is actually happening.

The wave behavior of electrons also means that the concept of circular orbits of electrons around the nucleus of atoms, that you commonly see everywhere, is wrong. A better picture is that they exist in a well-defined probability cloud around the nucleus.

The main point is that the Universe is quantized. Familiar quantities such as energy, momentum, electric charge, mass – possibly even time and space – are not continuous. They occur in discrete quantum units.

[SabineHossenfelder]

The more of Arvin's videos you watch, the more intuitive you'll find it :)

[sol_mental]

This was indeed very clarifying. The quantization of the universe is like "pixels in a screen". There's never signal in-between two pixels, the light is either coming from one or the other. But put together enough pixels on a small enough area and you won't even notice it's pixelated, you'll start to form other patterns that your brain will use to understand what's going on. This is just FANTASTIC! Thanks a lot for the video!!

[deepghetto]

You're a credit to scientific community Arvin. As an intellectual not in this field, your explanations are an incredible resource.

[timothycwinn]

Thanks Arvin! This was one of the best and most succinct intuitive “explanations” of “quantum mechanics”. It helps understand what it is and what it isn’t. It seems like a mathematic equation(s) verses an intuitive understanding of reality. The intuitive answers remain hidden within the equations that are used for quantum mechanics. It was very helpful as I try to generate more intuitive theories of my own.

[jdbrinton]

You are extremely skilled at explaining concepts! Could I recommend a video on vector spaces? A lot of these explainers just glance over the vector space and I think it's key to understanding how "everything possibility happens at the same time" in QM.

[paulc]

Thanks Arvin, for another great video on QM. Since it is a subject you have covered many times, explaining many different aspects of QM, have you ever considered making a video including more about the Philosophy of QM ? Without getting too technical, I mean the difference between what is actually "Real" (Ontology) and what we think we "Know" (Epistemology), might make for a different and interesting video. Thanks again Arvin and Best Wishes from Wales.

[Tomas.Malina]

Nice explanation, now you can naturally continue to mention coherences and virtual particles, as there actually are intermediate steps when a particle changes states. And also, that the quantized states only apply to bound particles, not to free ones - a nice concept to illustrate is the Dirac sea (and maybe expand on its importance in some of the less known GUTs) 🙂

[anywallsocket]

Einstein did not think entanglement was spooky in of itself, he thought the instantaneous 'effect' of measuring one entangled pair on the other was spooky. And the measurement problem is still unresolved, so nature remains spooky.

[juggyfreak]

This is actually the first quantum mechanics video that I could follow until the end ... nice explanation !

[gwentchamp]

Perhaps the explanation for the Heisenberg uncertainty is that the amount of information in the universe is fixed. If more information is "extracted" in one part, it has to be "subtracted" somewhere else. Well, this is my way of thinking about it but it might be complete B.S. 😜

[Murtie]

Super video, I've watched lots of your videos and I'd been trying so hard to understand it better that I watched other channels and read some articles, I should have known you'd help me fill in the blanks eventually :)

[NoActuallyGo-KCUF-Yourself]

[Holds Arvin's beer]
[Watches video]
Sorry, your beer was in a superposition of full and empty.

[waqaraliabbasikalhoro]

Thanks sir, you're really doing tremendous sort of work .students like us are very thankful teacher like you .🙏

[shabzone]

Much respect to this channel because most other "educational" channels would make the first 2:23 minutes of this video into a 15 minute video full of fluff

[kapilshekhar]

If only you had been my teacher in school and college ! Profound Thanks Arvin

[Phoenixspin]

I told my math teacher once, "Just shut up and calculate." I was promptly escorted to the Principal's office.

[zeropain]

Nice video! I always like the basics. Funny, you show the electron orbit analogy is wrong, and then a minute later you show an electron orbiting a nucleus? I like videos like this, the basics are so important.

[Maltiez]

Not measurements make particle-like behaviors, but its wavy behavior itself that somewhat resembles (not quite, but still) standing waves. There is clear distinction between measurement part of QM and wave function part (just take unitary evolution operator and non-unitary measurement operators for example). Actually if we consider QM as methodology and actual models like Schrödinger equation like distinct theories or models, that it will make much more sense, and QM become just a methodology of measuring wave functions, with which we can build different models like Schrödinger equation, Pauli equation e.t.c.
"No one can explain how wave collapse occurs" - actually not, there is an explanation, and quite correct one: wave function (that representing all our knowledge about system, by definition) collapse is just a process of bayesian update of that knowledge, that results in collapse. Collapse is not a physical process, it is artifact of scientific method, and it appear in every developed enough field of science, but it so pronounced only in specific fields, like QM. The Measurement problem is actually, as it seems to me, more educational problem, and it is more deep that it seems, and it apllies to whole science including mathematics (where there is a debate about proper definition of probability as limit of consecutive measurements (classical one) or measure of our ignorance/knowledge (bayesian one)).

What can be deeper than equation? Model? May be model is deeper, but I think that author is not talking about whole model, but instead about not scientific but philosophical... things.

11:34 - Wrong, its wave function (or more precisely whole atom wave function) is evolved in smooth continuous way despite of discrete nature of its basis in given set of physical quantities. And then we take a measurement and collapse it in one of particular basis state. Actually nature of QM is continuous due continuity nature of wave function. Discreteness is emerged from continuity in specific cases (simplest one: just any potential well).

Otherwise this video is quite good. Not mathematical and correct enough for me, but I'm just some nerd and not target audience. And stuff mentioned above has not been fully settled down yet even in theoretical physics community.

[brothermine]

Detection does NOT necessarily imply "particle." (1:22) An alternative explanation is that the rest of the wave jumped to the detection point, even though some of the wave may have been far away a moment earlier. This behavior violates the Locality assumption, but not enough is known about the fundamental nature of spacetime to have confidence in Locality, particularly given other "spooky action at a distance" phenomena such as entanglement and wavefunction collapse. There's plenty of evidence to support the conclusion that matter travels as waves, not particles... interference in particular.

[steviejd]

Dear Arvin, your content and presentation are first class, thank you so much for taking your precious time and educating us, I feel so lucky to have found you.