Imagine that you’re cruising along at a decent speed on the freeway, enjoying the
ride and your sunny view of the beautiful countryside.
Suddenly, you see red and blue lights flashing in the rear-view mirror—a police car is
following you!
You pull to the side of the road and the officer approaches, then informs you that you were, in fact, speeding.
How does the officer know that you were going faster than the speed limit allowed?
Well, quite simply, he has a “speed gun”, which, when pointed at a moving object, gives an
accurate estimate of its speed.
In the real, physical world around us, it’s very easy to look at a moving object and estimate
where it’s going to be in the next few seconds.
This happens because the uncertainties in the speed and position of the object are so
small that we can’t detect them.
We just assume that the path or trajectory of the object will not change markedly in
the next few moments.
This is true in the world of automobiles, machines and other macroscopic objects that
surround us in everyday life.
However, the same methodology for estimating an object’s position or speed doesn’t
apply to particles as small as atoms—or even smaller.
In the world of atomic-sized particles, if you measure the position of a particle, say,
an electron, as it moves along its trajectory, you may INCORRECTLY assume that you can estimate
its position in the next few moments, just as you would for a macroscopic object, like
a moving car.
Consider this—you are able to watch this video because packets of light, called photons,
bounce off your screen and reach your eyes.
Those photons of light are what enable you to see this video.
On the contrary, seeing something as tiny as an electron is not so straightforward.
If you bounce a photon off it and try to detect that photon through an instrument, it's likely
that the photon will impart some amount of momentum to the electron.
As a result, the electron’s path will no longer be the same as it was earlier.
This is why your observation of either the position or the momentum of the electron will
be inaccurate.
This is the idea upon which the Heisenberg Uncertainty principle is based.
Werner Karl Heisenberg was a German theoretical physicist, a Nobel laureate and one of the
key pioneers of quantum mechanics.
He is known for many breakthrough discoveries over the course of his career, and the Heisenberg
Uncertainty principle is one of them, which he first published in 1927.
According to the principle, if we know everything about where a particle is located, we know
nothing about its momentum.
Conversely, if we know everything about its momentum, then we know nothing about where
the particle is located.
In other words, this principle means that we cannot measure the position and momentum
of a particle with absolute precision or certainty.
Mathematically, the uncertainty principle is represented like this, where `x' is position
and `p' is momentum This subject is closely linked with the concept
of wave particle duality.
When our understanding of quantum mechanics was in its early stages, a new discovery proposed
that light acts as both a particle and a wave.
Albert Einstein demonstrated that light, which had previously been considered an electromagnetic
wave, must also act as a particle, localized in packets of energy called photons.
Then, famous American physicist Arthur Compton conducted a historic experiment, the observations
of which could be explained ONLY if light had a wave-particle duality.
This is how it was first established that light can act as both a particle and a wave.
As physicists explored this discovery further, they found it wasn’t just light that behaved
this way, but that all matter, up to a certain limit, behaved both like a wave and a particle.
When we think of a given particle, we inherently “know” that it exists in a single place
at any instant in time.
We can show this in a graph representing the highest probability of finding that particle
in that specific place as a spike.
The spike would mean that the probability of finding the particle at that specific place
is 100 percent, while the probability of finding it anywhere else is 0.
That spike, therefore, will tell us the position of the particle with high precision.
But waves, as you know, don’t exist in one specific place, but are instead “spread
out”.
You can’t pinpoint a single spot and say, “Hey, look, that’s exactly where the wave
is”, because a wave has a high probability of being in several different places.
However, you can certainly identify and measure specific characteristics of a wave pattern
as a whole, most notably, its wavelength, which is the distance between two consecutive
crests or troughs.
We don’t see waves around objects in our everyday life because objects around us are
way too big to have a noticeable wavelength.
Consider this—the wavelength of a 0.1 kg ball moving at a velocity of 10 meters per
second is 6.626x10^-34 meter.
It’s THAT small!
That's why it’s impossible to see visible waves around everyday objects, even though
they do exist everywhere!
Particles that are as small or even smaller than atoms have large enough wavelengths to
be detected, and can therefore be measured in experiments.
Thus, if we have a wave whose wavelength and momentum can be measured accurately, then
it’s impossible to measure its specific position.
Conversely, if we know the position of a particle with high certainty, then we cannot accurately
determine its momentum.
This is what Heisenberg’s uncertainty principle is all about.
In a nutshell, the uncertainty principle states that you cannot accurately measure both the
location and momentum of a particle at the same time.
So, next time you try to measure the exact momentum and position of an electron with
absolute certainty in your laboratory, remember that you’re chasing a physical impossibility!