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.
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my friends!