There is probably nothing in all of science that's as jaw-dropping and
confusing as the discipline of quantum mechanics. This is a set of physics
theories that describes a behavior of subatomic particles. There's so much
misleading information that has been written on this subject, that for most
people is very difficult to separate science facts from pseudoscience
speculation. And given how important quantum mechanics is, for example it's
the basis of all modern microelectronics from your cell phone, to your
GPS, to your computer, to your solar cell, I think it's extremely important for you
to be able to separate quantum physics facts from fiction. Let me give you a few
examples of facts that you will read about, view, or be told.
Quantum mechanics justifies free will because everything is random.
Consciousness is fundamental component of physics and the universe. None of
these statements are supported by quantum mechanics. So what is quantum
mechanics? And how does it actually work? And can it be explained simply in ten
minutes? The answer to that last question, I'm hoping you will agree, is yes. And the
other answers are coming out right now... I hope to dispelled the profound
misunderstandings and misconceptions about quantum mechanics by explaining, as
simply as possible, how quantum mechanics actually works, so you can judge for
yourself when you're being told misleading information. I ask you to
watch this video all the way through, because if you go straight to the
conclusions, I'm afraid you may still get the wrong ideas, and be misinformed by
people who would take advantage. So let's start with how quantum mechanics evolved.
In 1801 British physicist Thomas Young performed a simple double slit
experiment which showed that light was a wave, because it formed an interference
pattern, as a wave would. So for most of the 19th century, light was considered a
wave. However, in 1887 German physicist
Heinrich Hertz discovered something called the photoelectric effect. This is
a phenomenon where light can knock off electrons from atoms. But it was found
this phenomenon was not triggered by certain colors, regardless of the
intensity of the light, but only by higher frequencies of the light. So
ultraviolet rays resulted in this effect, but light at the red end of the spectrum
did not, no matter how bright you made it. this was not the way a classical wave
was supposed to behave. This mystery was solved by none other than Albert
Einstein, who proposed that light was not a wave, but came in packets of energy or
particles. You know them as photons. These were packets of waves, he said. And the
energy of these particles was proportional to the frequency of the
wave. So higher frequency light, corresponding to the blue and violet end
of the visible scale, carried more energy than lower frequency light, corresponding
to the red end of the spectrum. By the way, Einstein won the Nobel Prize for
this. He did not win it for Relativity. So Young's and Einstein's results seemed to be
in conflict. Was light a wave or a particle? But then, in 1909, G. I. Taylor
performed a double slit experiment such that only one photon was emitted through
the double slits at a time. So what was seen on the
screen? Well, if you shine a single photon through a double-slit, you will see a
single point on the other side. No mystery there. But then, as more and more
photons are shot one at a time through the slits, and if you do this millions of
times, a pattern emerges that looks like the same interference pattern that Young
had demonstrated more than a hundred years earlier. So individual photons look
like particles, but a bunch of photons behave together like a wave.
So photons appear to be both a wave and a particle. This was confusing. This
experiment was later performed with electrons, which also showed the same
pattern. But people were perplexed as to what a wave of an electron actually
means. We can understand water waves because we can see them.
They oscillate up and down. But what is actually happening with an electron? This
was a mystery. In classical mechanics, Newton's second law, force equals mass
times acceleration, makes a mathematical prediction regarding the path a physical
object will take. If you know its initial conditions, you can always figure out
where the object will be. Something that showed a similar mathematical
description, of the wave of electrons was needed, something that showed the
location of the electron, or the shape of its wave function. In 1925 ,Austrian
physicist Erwin Schrodinger invented the Nobel prize-winning equation that
revealed the shape of this wave function. It was the quantum mechanical equivalent
of Newton's law, and it's probably the most important equation in quantum
mechanics. We're not going to derive this formula, but I just want you to
understand one thing about it. Unlike Newton's equation, it is not
deterministic. It is not straightforward like Newton's equations. It evolves over
time. The Psi in the equation, which looks like a trident, is a wave function.
psi gives us the shape of the wave as a function of X. Schrodinger himself
struggled with the interpretation of this wave function. That is, what does it
actually mean? His interpretation was that it was the charge density of the
electron over space. But this was actually not correct and it
did not work. In 1926, German physicist Max Born, worked out that the psi
function was related to probability. He said it represented the probability of
finding the electron in any one point in space. So for example, this equation
describes the behavior of electrons in an atom. It shows how the electrons
occupy certain orbitals and what their shapes are. These shapes are really the
probability densities of finding the electron in any particular spot. And
unless you measure it, you can only come up with the probability of finding the
electron at any particular radius. The most accepted interpretation of the wave
function, called the Copenhagen interpretation, was pioneered by two of
the founders of quantum mechanics, Werner Heisenberg, and Niels Bohr. This
interpretation says that until a measurement is made, this equation tells
us that the electron is in ALL the potential positions at once!
This interpretation basically says that the wave function is not a real thing.
It only describes mathematical probabilities. The only thing that
matters is the measurement. That is the only time when the position, energy or
other property of the particle can be known. So when the measurement takes
place, that's when we say that its wave function has "collapsed," because only
at that point, can we ascertain where the electron is, and what his properties are.
When it's measured, its probability becomes a 100% where you
measured it, and 0% everywhere else. So, for example, if the wave function
for a particular system looks like this, the probability of finding the electron
at this location, and this location, would be the highest. And here and here would
be the lowest. But you won't really know where to find it, until it's measured. And
you're unlikely to find the electron in the same spot if you repeat the test. And
this so-called "collapse of the wave function" is where the main confusion
comes from when it comes to quantum mechanics. There is no equation that
outlines exactly how this collapse occurs after
measurement. This has been called the measurement problem of quantum mechanics.
I've been careful to use the word "measurement" instead of "observation," which
many textbooks and physicists use interchangeably. The problem with the
word observation is that it implies looking with your eyes, which requires an
observer, and a consciousness. But an observation in quantum mechanics does
not require eyes. It is simply a measurement. So what is a measurement?
Doesn't it require a measurer?...No, a measurement is an interaction of two
physical systems. What does this mean? When an electron bounces off an atom,
that's a measurement. An observation in physics does not mean a conscious
observer. Just about anything can be an observation. If an atom in superposition
interacts or bumps into another atom, it's an observation. And a wave function
will collapse. When any two systems interact, that can collapse probability
waves. There are no eyes, humans, or consciousness necessary. So let's get
back to the double slit experiment and figure out what it means. When a single
photon hits the screen, it collapses the probability wave of the photon. It shows
up as a particle. That same photon is acting as a wave prior to hitting the
screen because it hasn't been measured yet. The screen measures it. So as a wave,
it has a nonzero probability to show up anywhere on the screen, where the wave
would strike the screen. So as we shoot thousands and millions of photons, one at
a time, on the screen, the probability distribution becomes apparent in the
pattern shown. If enough photons are fired, you get a distribution exactly as
predicted by the wave function. Now you saw in an earlier video I made about how
the pattern changes to a double line pattern of photons, instead of waves, if
we make the measurement of the photon, before it strikes the screen. So, knowing
what I just told you about wave collapse, it should be obvious now why this double
line pattern shows up. We are collapsing the wave by measuring it before it hits
the screen. So now this photon is no longer in superposition. It is no longer
a probability, and not subject to the Born probability.
So the photon is a distinct particle before it strikes the screen. When it's
measured, it no longer behaves like a wave. So naturally, it's going to strike
the screen and show a pattern like a particle would. The measurement made was
a purely physical measurement. It would not matter if anyone, or any animal
looked at the measurement, or if someone took a photo of the measurement. All of
that makes no difference in the collapse of the wave. Overall what we can see is
that the fundamental underpinnings of nature are probabilistic, not
deterministic. Now many have used this phenomenon to justify free will. Well, we
have to be careful not to extrapolate what happens at the quantum level, to the
deterministic world of our everyday experience. Just because free will
implies that your decisions are not deterministic, and quantum mechanics also
implies that the properties of small particles are not deterministic, the two
are not related. There is no science linking the two. We may or may not have
free will, but quantum mechanics does not tell us anything about that. And
consciousness is not required to collapse the wave function. The universe
will exist, and will continue to exist, whether we are here to observe it or not.
Now I have not covered everything in quantum mechanics like quantum tunneling
or entanglement. These are big subjects that I'll tackle
in future videos. For now, I just wanted to convey the basics of how quantum
mechanics works and dispel some of the common misunderstandings. And if you like this video, then please share it with your friends and give us a
like also if you have a question posted below because I try to answer every one
of them I'll see you in the next video my friends!
