What is Heisenberg’s Uncertainty Principle?

Do you know What is Heisenberg’s Uncertainty Principle? Read further, to know!


Uncertainty is omnipresent in our daily lives. Who will win today’s football match, whether the price of the stock will increase or fall, whether you will live or die tomorrow?  The notion of “uncertainty” occurs in several different meanings in the physical literature. It may refer to a lack of knowledge of a quantity by an observer, or to the experimental inaccuracy with which a quantity is measured, or to some ambiguity in the definition of a quantity. One of the most famous theories about uncertainty in the world of quantum mechanics is Heisenberg’s uncertainty principle.

To explain this principle, let us take a simple example. Imagine your friend Charlie is a fitness enthusiast. You observe that he goes for a run on Tuesday. At this point can you conclude that Charlie will go for a run on next Tuesday as well? Well, at this point it is tough to say for sure because you have seen him do it just once. However, if you observe him for a month and he still goes for a run every Tuesday, then can you say he will go for a run next Tuesday as well? Still, there is an uncertainty as you cannot say for sure that he will go for a run next Tuesday. He might opt to stay in instead or he might decide to go for a vacation.

So you can never accurately measure his frequency of going for a run unless you spend infinite time observing him do so.

Similarly, Werner Heisenberg, a German theoretical physicist, proposed the theory of Heisenberg’s uncertainty principle in 1927 which says that you can never simultaneously know the exact position and the exact momentum of an object. In this case, the conjugate variables are the location and the momentum of the object.


To understand the notion of this principle, let us delve a bit into the implications of quantum mechanics.

According to quantum mechanics, everything in the universe behaves like a particle and a wave simultaneously. If we look at how particles behave, then they can be located at a single place at some point in time while a wave is spread out and its location cannot be pinpointed at a certain instant of time. To locate these small particles, they are struck with light and the reflected wavelength is observed. As light can also be considered as a wave and a particle, we can say that a photon is striking the particle which has a specific wavelength. A shorter wavelength will obviously ensure more accuracy in locating the object.

However, a shorter wavelength also means that the energy of that photon will be more, as energy is inversely proportional to the wavelength given by E=hc/ lambda. Where E is the energy and lambda is the wavelength of the photon. So if we use a photon of a shorter wavelength to strike the particle we want to locate, due to its high energy, the particle bounces off. We compromise the calculation of the location of the object and vice versa. This showcases that the more we know about one quantity in this principle, the less we know about the other.

Mathematically, this principle it is expressed as:    

Where delta x represents the uncertainty in position and the delta p represents uncertainty in momentum. Multiplying together the errors in the measurements of these values has to give a number greater than or equal to half of a constant called “h-bar”. This is equal to Planck’s constant (usually written as h) divided by 2π. Planck’s constant is an important number in quantum theory. It is a way to measure the granularity of the world at its smallest scales. It has a value of 6.626 x 310-34 joule seconds. In a broader sense, the inequality suggests that the product of the uncertainties can never be equal to zero. It is always greater than or equal to a positive constant.


Leaving aside all of this technical mumbo-jumbo, this principle can be oversimplified by this next example. If a cop catches you for over speeding and says that you were traveling at a speed of 100 km/h in a zone with a speed limit of 80 km/h. Then you can hypothetically argue with the cop saying he cannot accurately measure your position and speed simultaneously. If you are sure about my speed, you cannot possibly know where my car is! Though the argument is not logical, it encapsulates the essence of Heisenberg’s uncertainty principle. This means, though the principle applies to all objects, it is not relevant to objects we encounter in daily life.

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Heisenberg’s uncertainty principle finds its application in quantum communication. It allows the sending of encoded messages that cannot be hacked by any computer. If an eavesdropper attempts to read out the message in transit. They will be discovered by the disturbance their measurement causes the particles as a consequence of the principle. It is also useful in explaining concepts like alpha decay. It is a revolutionary principle that provoked thought experiments like “Schrodinger’s Cat“. This was a big step in quantum mechanics.

It says that the closer we focus on one aspect of a thing in life, the more we lose access to other relevant aspects. This applies to our thoughts, emotions, feelings, and life in general. There is always a trade-off in accuracy and precision between means and ends. It is a limiting factor in our scientific abilities, but in some sense, it is quite liberating.

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