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Hey Crazies.
Quantum mechanics is weird.
The concepts are so alien to us, which I think adds to their appeal.
If we're being honest though, I kind of hate Quantum.
But what I hate even more are the myths people develop about it.
I know people still have them because I keep getting comments like this.
So let’s set the record straight.
Myth #1: Sometimes electrons behave like particles.
Sometimes they behave like waves.
It’s called Wave-Particle Duality.
False!
Before you freak out, let me explain.
First, we have to be careful with the word "particle."
A particle is vaguely defined as a small portion of matter,
which is always true for things like electrons, protons, and neutrons.
No matter what their behavior, they are always small portions of matter,
so they’re always particles.
That’s why we can call all of these things elementary particles.
But the "particle" in wave-particle duality is saying much more than that.
It implies that those small portions of matter, those electrons, protons, and neutrons,
also exhibit exactly the same behavior as normal objects.
For clarity, let’s just call this an object instead of a particle from now on.
That means we’ll call it wave-object duality instead.
Second, the justification for this idea usually comes from the double-slit experiment,
which I’m really tired of hearing about and I’m sure you are too.
So here’s the quick version:
Say you’ve got two walls, but the one in front has two openings.
If you launch a bunch of paint balls at the first wall,
a pattern develops on the second wall.
We’ll call this pattern "object behavior."
If you do this same experiment with sound, you get a very different pattern.
We’ll call this "wave behavior."
It’s a way for us to know if a small thing is an object or a wave.
But it gets weird when we do the experiment with microscopic things like electrons.
If we only detect the electrons at the second wall, we see wave behavior.
If we detect the electrons at both walls, we see object behavior.
It would appear that what quantum particles are depends on the circumstances.
But that’s not actually the case.
Electrons, protons, and neutrons are always particles, but are never truly objects.
But didn’t the experiment just show that...
No. No, it didn’t.
Yes, we sometimes get patterns like this for particles,
but we have to be careful about what we think that means.
The double-slit experiment doesn’t tell us that particles behave two different ways.
It tells us that our ordinary notions of behavior are wrong.
Quantum particles do not have wave-object duality.
They are never objects.
They are always waves.
Quantum particles only behave one way.
Their way!
What are you going to do about, punk?
Myth #2: When particles are measured, they stop obeying quantum mechanics
and start obeying classical mechanics.
[Giggle] No.
While it is true that a quantum wave function collapses after a measurement,
you’re misinterpreting the word “collapse.”
You keep using that word.
I do not think it means what you think it means.
I can actually address this by expounding on something I said during the last myth.
Quantum particles are never objects.
They are always waves.
So they’re always governed by quantum mechanics.
Hmm, an example might be helpful.
Here’s the wave function for an electron in a very simple box.
You can see it could be just about anywhere in the box.
If we’d like the electron to have a more definite location, we need to measure it.
The easiest way to do that is with a photon.
The interaction with the photon changes the wave function.
That change is called a collapse.
Now the electron is here
ish.
We can’t forget the Heisenberg Uncertainty Principle.
It says we can’t ever know any property exactly.
Most people are familiar with the one relating position and momentum.
These are typically called uncertainties, but that’s a terrible name.
They’re actually standard deviations, because quantum is all about probability.
What’s a standard deviation?
OK OK OK.
Here’s a crash course in statistics.
For example, school exams are scored from 0 to 100%.
Traditionally, those scores are distributed something like this
with the mean average right in the middle.
The standard deviation tells us something about the spread of the scores.
Roughly 68% of them should be within one standard deviation of the average,
roughly 95% within two standard deviations, and so on.
If gives you an idea of the width of the curve.
The same kind of thing happens with a quantum wave function.
This position here is just an average.
It’s not exact.
The standard deviation is not zero and, just like with the exam scores,
it gives you an idea of the spread or width of this curve.
Can’t I narrow this down some more?
Yes, you can make the standard deviation smaller, but never zero.
The higher the energy of the photon, the more localized you can make the electron.
But these two standard deviations, position and momentum, multiplied
must be greater than this number, so neither one of them can be zero.
On top of that, the more definite you make the position,
the less definite you make the momentum.
In other words, the less wavy you make the position,
the more wavy you make the momentum.
And all properties of a particle are related like this in one way or another.
You can’t escape quantum mechanics.
Myth #3: Reality only exists because conscious observers exist.
Alright look, I understand how easy this misconception is to come to.
I had the same misconception a long time ago.
It’s also philosophically interesting, but it’s simply not true.
Reality would exist whether we exist or not.
The universe does not require human beings.
It does not require a conscious mind.
It does not require life.
This electron didn’t change from this wave into this wave,
because a person was looking.
It changed because it interacted with a photon.
The human experimenter was an unnecessary part of that event.
The same goes for the double-slit experiment.
The experimenter is unnecessary.
All that matters is the interaction.
Particles interacted with each other long before life evolved in this universe
and they will continue to do so long after life goes extinct.
So let’s recap.
One!
Quantum particles do not have wave-object duality.
They are never objects.
They are always waves.
Two!
Quantum particles always obey quantum mechanics.
And three!
Quantum mechanics does not require conscious observers.
Stop jumping to conclusions!
If you have any questions about quantum mechanics, please ask in the comments.
Thanks for liking and sharing this video.
Don’t forget to subscribe if you’d like to keep up with us.
And until next time, remember, it’s OK to be a little crazy.
So, I said “doobly doo” in the last video and some of you were like:
OMG! You stole that from so-and-so!
For the record, everyone stole that from Wheezy Waiter.
You know, this guy.
Anyway crazies, thanks for watching!