Quantum tunneling, as the name suggests, is a quantum phenomenon. Although tunneling has no counterpart in classical physics, it is an important consequence of quantum mechanics. It is basically a phenomenon in which particles move through a barrier that is otherwise forbidden according to classical physics laws. This barrier can be a physically obstructed medium, such as an insulator or a vacuum, or a region of high potential energy.

The mechanism of quantum tunneling

Let us suppose a situation where we have to ride our bicycles across a hilltop. Classically speaking, the bicycle will only climb the hilltop if it has enough energy to climb up to it. However, quantum mechanically, the cycle will move to the other side of the hilltop even if its energy is less than the required energy. (It’s just an analogy to understand the concept, a bicycle is definitely not a quantum object).

Quantum Tunnelling
Classical and Quantum approach for a particle to cross a barrier. Image Courtesy: normaals/Getty Images

According to the laws of quantum mechanics, a particle can behave both as a particle and wave. So, when it comes to the phenomenon of quantum tunneling, the wave nature of the particle comes into the picture. Now suppose, an electron has to cross a potential barrier that is much higher than the energy carried by its wave.

In regions where the potential energy is higher than the wave’s energy, the amplitude of the wave decays exponentially. If the region is narrow enough, the wave can have a non-zero amplitude on the other side. Hence, we have a non zero probability of finding the particle on the other side of the barrier, which was classically impossible.

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How does quantum tunneling sustain our Sun?

We all know that the Sun produces heat and light energy by fusing hydrogen nuclei. The hydrogen nuclei slam together to produce helium atoms. However, most hydrogen atoms in the Sun’s core don’t have enough energy to stick together. To fuse, they have to overcome the forces of repulsion of their positive charges, i.e., the Coulomb barrier. But generally, they don’t have enough energy to do so.

Then, how is our sun still fusing hydrogen nuclei and producing energy? This is where quantum tunneling comes to the rescue! With quantum tunneling, the hydrogen nuclei can cheat. They have enough energy to get relatively close to each other, and then they tunnel through the remaining barrier to stick together.

Hence, thanks to the tunneling phenomenon, the Sun’s nuclei can fuse even though they don’t have enough energy to fuse on their own. Remember, not all nuclei will tunnel; only some will. But, even this small probability is enough to keep our Sun alive. Quantum tunneling is thus an important component in supporting fusion reactions in stars, and ultimately, our life.

Some other applications :

Apart from being highly useful in the nuclear fusion of stars, quantum tunneling also plays an important role in radioactive decay. It is among the central non-trivial quantum effects in quantum biology. Proton tunneling is a key factor in the spontaneous mutation of DNA. Moreover, this phenomenon is of great importance in the working of semiconductor devices, tunnel diodes, and even in the working of superconducting junctions. Cutting short, quantum tunneling indirectly plays an important role in sustaining our everyday needs and hence, is a booming sector of research, development, and advancement these days.

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11 thoughts on “What Is Quantum Tunneling And How Is It The Reason behind Our Existence?”

  1. Brahmendra Bachi

    But why quantum tunneling should occur.
    In physics every phenomena has a reason which can explain any law from physics.
    What is the law related to occur quantum tunneling?

    1. You are right every phenomenon in physics has a specific reason . Butt here in quantum physics it is hard to understand a sentence itself it is in fact very confusing. If quantum tunnelling or quantum physics were not to be there then not even the big bang would be possible . If quantum physics didn’t come to our rescue not a single quark would have formed and complex bodies like us humans or bigger bodies like galaxies or universes(if multiverses exist ) would have formed
      So what I mean is that few things don’t have explanations or reasons. Quantum physics is very very very very very complex it need a years of experience to explain things in it .

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  3. Quantum Tunneling does exist in Classic Physics! They are called black-holes, in fact this tunneling reoccurs on every level of universe.

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  8. basudeba mishra

    A particle does not behave both as a particle and a wave – it moves in a wavy path due to bow-shock effect. There is no true void in the universe (). When a boat is pushed in still water, it faces resistance in front. This pushes the boat up only to come down due to its density difference. This traces a wavy path. The same thing happens in the quantum world also.
    There are no separate laws for the quantum world. The same laws of physics governs everything. The so-called quantum tunneling is not a quantum phenomenon, but a universal phenomenon. It is related to the scale. Think of a strainer straining tea. The liquid passes through the strainer, while the tea leaves cannot pass through it. The same thing happens in the micro world also.
    One example often given is as follows: Suppose an electron has to cross a potential barrier that is much higher than the energy carried by its wave. In regions where the potential energy is higher than the wave’s energy, the amplitude of the wave decays exponentially. If the region is narrow enough, the wave can have a non-zero amplitude on the other side. Hence, it is said that we have a non-zero probability of finding the particle on the other side of the barrier, which was classically impossible. Now, think of a boat trying to cross a channel. If it is narrow enough, the boat cannot cross. But if the boat is narrow enough, it can easily cross over. Again it is a matter of scale – not separate law for the quantum world.
    Or look at a fan regulator. It regulates the flow of electric energy. It can bring the fan to zero also. In that position, the fan will not move unless there is a lose contact and the electricity leaks.
    Another example often cited is fusion of hydrogen nuclei to form helium in Sun’s core. Most hydrogen atoms in the Sun’s core don’t have enough energy to overcome the Coulomb barrier – forces of repulsion of their positive charges. It is postulated that they tunnel through the remaining barrier to fuse together. However, not all nuclei will tunnel – only some will. Here the behavior is due to the strong force. Think of two positively charged up quarks sticking together inside a proton. They do not tunnel through.
    Quantum tunneling also is said to play an important role in radioactive decay. But this is a wrong notion. Two positive charges repel each other and explode in the absence of a confining strong force. There is no need to drag in tunneling unnecessarily.
    It is said to be among the central non-trivial quantum effects in quantum biology. Proton tunneling is a key factor in the spontaneous mutation of DNA. This is also the wrong explanation. It is like the proton neutron conversion chain that occurs spontaneously.
    Other phenomena can be explained similarly.

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