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A Depict from “The Quest for the Ultimate Theory of Science”

By: Binod Bhattarai (M.Sc. Physics, St. Xavier’s College, Kathmandu Nepal)

Sweet is by convention, bitter by convention, hot by convention, cold by convention, color by convention; in truth there are but atoms and the void.

– Democritus

Hello there. Yes you, let’s schmooze for a while. Seems like you’re having a rough day huh? Or having fun?? Whatever, let’s ponder on your last night….Sorry for a dark beginning but night is fun anyway ;). Here I’m taking you to a lonely night ride away from your home. You are reading a science article so without any delay let’s get scientific here. How about starting with a gentle thought experiment? Yes I said only gentle. Do you remember your bed you slept on last night? Yes your bed, hammock, truckle, trundle or whatever.

Oh yes I forgot we were about to conduct a thought experiment. Alright let’s focus now. Imagine you woke up suddenly in the middle of a night and you find darkness all around you. No it’s not the NEA doing power cuts. Here I mean serious darkness, nothing but only emptiness all around you. Yes even your bed is gone. You can’t even see where you are standing. Now if you tend to move, can you tell where you were moving and how far have you gone? Sounds eldritch? Nothing is creepy here so no worries. You moved your feet but still can you tell where you are going? Ok let’s make it easier now. How about adding the bed in our earlier thought experiment? Ok now start with the presence of bed and you but nothing else in our experiment, if you move you can always tell whether you moved away from the bed, towards left or towards right. Or even up and down if you had wings. See as soon as we add a reference point all the things start making sense at a sudden.

The world is made of tangible things that we can observe and recognize. These things exert forces, or bump into one another, and their motion change in response to those influences. If we could know all the positions and momentum of every particle in the universe, we could predict the future and the past with perfect accuracy. But unfortunately, there is something wrong with our world where uncertainties start counting and it creates a totally different world called the quantum world. According to quantum mechanics, what we can observe about the world is only a tiny subset of what actually exists. Newtonian mechanics is usually referred to as “classical” mechanics by physicists, who want to emphasize that it’s not just a set of particular rules laid down by Newton. Classical mechanics is a way of thinking about the deep structure of world. Einstein’s general relativity all fits into the classical framework. But now we know better: Classical Mechanics isn’t correct. In the early decades of the twentieth century, physicists trying to understand the behavior of matter on microscopic scales were gradually forced to the conclusion that the rules would have to be replaced with something else. That something else is Quantum Mechanics.

In quantum mechanics, there is no exact information of where a matter is located. In our earlier experiment when we saw nothing, there was still a probability that our bed was somewhere. The space of states in quantum mechanics are specified by something called a wave function. It may seem hard to imagine an experiment that could distinguish between the possibilities. The only way to know where it is would be to look for it but there is a crucially important phenomenon that drives the difference, known as quantum interference.

In classical mechanics, where the state of a particle is a specification of its position and its momentum, we can think of that state as specified by a collection of numbers. For one particle in ordinary 3-D space, there are six numbers: the position in each of the three directions, and the momentum in each of the three directions. In quantum mechanics the state is specified by a wave function, which can also be thought of as a collection of numbers. The job of these numbers is to tell us the probability of getting a certain result for any observation or measurement we could imagine doing.

A wave function oscillates through space and time just like a wave on a water surface. When we see a wave on a water surface, the level of the water isn’t uniformly higher than what it would be if the surface were undisturbed; sometimes the water goes up, and sometimes it goes down. If we were to describe the wave mathematically, to every point on the surface we would associate amplitude, the height by which the water was displaced and the amplitude would sometimes be positive and sometimes negative. Wave functions in quantum mechanics work the same way. To every possible outcome of an observation, the wave function assigns a number, which we call the amplitude and which can be positive or negative. The complete wave function consists of particular amplitude for every possible observational outcome; those are the numbers that specify the state in quantum mechanics, just as the positions and momenta specify the state in classical mechanics. Thus there is amplitude that your bed is somewhere and your whole house could be. So no worries you’ll get back there soon. And tonight be certain no matter what happens your bed is going to be there somewhere here or somewhere else.

It is not that modern physics has rediscovered ancient Buddhist wisdom or something but the quantum world is leading us to brilliant future possibilities and is arguably the greatest triumph of human intelligence and imagination in all of history.-Sean Carol