Development of Science
“I don’t understand what I shall obtain by studying protons and neutrons,” wondered Sahil one day when I was conversing with him about the significance of studying physics.
“It is all scientists’ imagination,… there’s no logic behind it,” Sahil expressed his feelings.
I was taken aback, “How he could think of the science like this!” Then it occurred to me, that this might be Sahil’s justification for his misplaced perception of physics and chemistry as both of them involve the structure of atom and he believes that the structure of the atom is only the imagination of scientists and not true. I could not believe that he could be so mistaken in his comprehension of the structure of the atom, but there it was and now his belief had become so cogent that he was not ready to listen to any other reasoning. Then I realized why his teachers at coaching institute were unable to understand him, because he believes that the structure of the atom is not true. The reason for his conviction was that he had missed studying basic level science in the rush to study the higher level of science that the coaching institutes try to dump onto the students. Putting him in the coaching institute had burdened him physically and mentally and he was not able to cope. Although he was trying hard, his efforts were going in vain. I cursed myself for putting him under this stress. But this is what every student aspiring for IIT has to do these days, he himself also wanted it this way. I was helpless. Now it was too late to tell him to not to attend the coaching institute.
There was not enough time for me to explain this to him from basics as his examinations were approaching fast. Still, I guessed- it would be better to clear his misunderstanding on the subject as much as possible, and may be that would help him. Now I knew that no psychologist, no pundit could help him. And if his well-qualified teachers could not understand and help him, then it was going to be a challenging task for me. I had no other option but to go for it and try to talk to him.
I needed once again to perpetrate the role of a teacher which I had done long ago when I was teaching at a coaching institute. I was inured to tutoring science and mathematics to classes X, XI and XII.
So I started to brace myself again. I took a few notes from his text-books and from the internet. After few days when I reckoned I was ready, I went to Sahil’s room for talking to him on the subject. He was working on a problem in mathematics. I directed him to take an interlude from his mathematics and come with me to drawing room. He was hesitant yet followed me.
“I cannot answer your questions about not studying physics and chemistry,” he spoke up, as he anticipated my line of questioning.
I told him assuredly, “I am not going to ask you anything about your interest in physics and chemistry. I just want you to listen to what I have to say. If you deem it necessary, you can ask me any question, but from my side, no questioning.”
“Okay,” he said, as the deal seemed fair to him.
I told him that when we see around us, we find many substances such as water, earth, iron, aluminium, various gases and liquids. For centuries, the human race has been wondering, what these substances are made of? Whether these are made of the five basic elements air, earth, fire, water, and sky, or are there some other core constituents too?
“They are made of elements,” interrupted Sahil as the answer to this question seemed very undemanding to him, though I had not directly asked him to give answer to this question. While furnishing the answer, his face still showed that he was not interested in this talk at all… he wanted it to be over soon.
“Oh yes, you know that!” I appreciated him. “But do you know how difficult it was to ascertain that they are made of elements?” I tried to engage him in simple conversation.
“No, it’s easy. Everybody knows, they are made of elements,” he replied.
“Imagine about four hundred years ago when there was no knowledge of elements,” I continued. “People were only familiar with the objects they observed such as air, sand, iron, gold, copper, water, fire, and the sky. So they envisioned that only five elements constituted the whole universe namely air, water, fire, earth, and sky. And every other substance could be created from these five basic constituents.”
“Then how did the other elements came to be known?” Sahil asked, as he now seemed a little interested.
“In 1661, Robert Boyle proposed that matter was composed of various combinations of different “corpuscles”, and not the classical elements of air, earth, fire and water.”
“What is a corpuscle?” Sahil asked.
“A corpuscle is an indivisible part of a substance just like atom.”
“But did they know about atoms back then?”
“No, atom is a Greek word meaning an indivisible part. The word “atom” was in use at that time but not in the sense that we identify it today.”
“Yes, I am aware that atom is a Greek word. So, corpuscle and atom were one and same thing,” Sahil suggested.
“Quite similar but not exactly alike. Corpuscle was also used for light, whereas atom was used for matter only,” I informed him. “During the 1670s Issac Newton used corpuscularianism in his development of the corpuscular theory of light.”
“What is this theory?” asked Sahil.
“Newton visualized that light was made of some indivisible particles called “corpuscles”. He considered these corpuscles to behave like particles and travel at very high speed.”
“Then how did the atom come into existence?” Sahil asked.
“The atom came into existence when the science of chemistry began to develop,” I replied.
“Why chemistry, I thought we were doing physics now.”
“I am neither educating you on physics nor chemistry, just telling you the story of development of science. Do you want me to continue?” I asked, just to gauge whether he was becoming interested.
“Yes, we can go on, but I hate chemistry.”
“In 1789, French researcher Antoine Lavoisier discovered the law of conservation of mass and defined an element as a basic substance that could not be further broken down by the methods of chemistry.”
“Yes, I know what an element is; it is the purest form of a substance.”
“But until Lavoisier discovered this, nobody knew about element,” I told him. “All substances are either compounds or mixtures of these elements. Two or more elements when combined in a particular ratio, form compounds. But it was still not known how these elements combined?”
“It must have been very difficult time without awareness on the method of combination of elements; we now know all the rules of their combination, valance electron rule, covalent bonds etc.” Sahil was amused.
“Yes, you know all these rules, but you don’t know how these rules were unearthed?”
“In 1805, John Dalton explained why elements always react in ratios of small whole numbers and devised the law of multiple proportions. He proposed that each element consists of atoms of a single, unique type, and that these atoms join together to form chemical compounds.”
“So, the atom was proposed by scientists while working on chemical compounds and that was nearly 150 years after the corpuscles, but how did the atom became so complicated with all the protons, neutrons, electrons etc., and we have to remember so many rules about them?” asked Sahil.
“John Dalton proposed the existence of atom but at that time, nobody knew the size of the atom. In 1865 Johann Josef Loschmidt measured the size of the molecules that make up air, and this was considered a great discovery,” I informed Sahil.
“But how did this scientist measure the size of one molecule of air?” asked Sahil.
“You can check that yourself on the internet. For the time being we shall move ahead,” I told him as I did not know the answer to his question. “After establishing the existence of such a small particle, which was basic for all elements and hence for all substances, it was very difficult to study it further as it was not visible in microscopes,” I said moving on further.
“If you can’t see something then how can you study it further or even say that that thing exists. So protons and electrons are just imagination of scientists,” Sahil declared his doubts.
“There are many things in this universe that you can’t see but they exist. You cannot rule out their existence just because you can’t see them,” I told him.
“I don’t believe that,” objected Sahil.
“I’ll tell you one incident. Once a physics teacher was explaining to his students that there exist only those things that we can register by using our sense organs: eyes, ears, skin, nose; just as you are saying that things don’t exist if you can’t see, hear, feel or smell them,” I told Sahil.
“Then what happened?” he asked.
“Then one of the students got up and asked his class-mates whether anyone had seen, heard, touched or smelt the teacher’s brain?”
“No” everybody replied.
“Then it implies that our teacher does not have a brain,” the student reasoned and all his classmates laughed.
“That is interesting, but isn’t it different than a physical quantity?” Sahil was still not ready to accept the logic.
“I agree, this is not a physical quantity but many physical entities are not registered by our senses such as X-rays but they exist. Do you want to know who that student was?” I asked Sahil.
“You mean to say that this incident was true?” he asked in surprise.
“Yes, I think so. The student in this incident was Albert Einstein,” I told him.
“If Einstein believed that way then surely it must be,” said Sahil, accepting that there can be things that our senses cannot register. “But does that mean that protons and electrons really exist?” he asked.
“Yes, they exist and it took lot of hard work and imagination by great scientists to prove this fact,” I told him and continued how these particles could be found that were not visible under any microscope. In the early 19th century, British scientist Michael Faraday explored the phenomenon of electrolysis. Electrolysis involves passing an electric current through a substance, such as an ionic compound dissolved in a solution of water. The current separates the constituent elements of the compound—the positively charged ions collect at the (negative) cathode and the negatively charged ions collect at the (positive) anode. Faraday discovered that the amount of an element formed increased in proportion to the amount of electricity passed through the substance. This suggested that atoms, although themselves electrically neutral, are made up of smaller particles that carry electric charge.
Toward the end of the 19th century, physicists realized that if they applied a high voltage between two electrodes (a cathode and an anode) in a vacuum tube, the cathode would release a discharge. This discharge was called a cathode ray. In 1897 the British physicist Sir Joseph J. Thomson revealed that these rays were made up of tiny particles almost 2,000 times lighter than an atom of hydrogen. He also showed that electric and magnetic fields could move them around, thus proving they were electrically charged. These tiny, light, electrically charged particles were named electrons.
From his experiment J.J.Thompson concluded that electrons were a component of every atom. Thus he overturned the belief that atoms are the indivisible, ultimate particles of matter.
At that time, the structure of atom was not established because atom could not be seen even with powerful microscopes but since it had been found that electrons were a part of every atom and the atom as a whole was neutral, it was contemplated that there must also be a positive charge on an atom. Until that time protons were not known, so Thomson postulated that the low mass, negatively charged electrons were distributed throughout the atom, possibly rotating in rings, with their charge balanced by the presence of a uniform sea of positive charge. This was known as the Plum Pudding model. In this model, the presence of a uniform sea of positive charge was an assumption yet to be verified.
”Yes, I know about the Plum Pudding model, but I never knew why they needed this model when they already knew about the behaviour of electrons?” said Sahil. “Now, I see that this was the basic model when scientists did not know about protons and neutrons. But did they not wonder why the negative charged particles did not cancel out the positive charge in the Plum Pudding model?”
“Yes, there were shortcomings in that model, but at that time, that gave the best explanation,” I replied.
“How did the things change after that?”
In 1909, physicist Ernest Rutherford bombarded a sheet of gold foil with alpha rays, which were known as positively charged helium atoms at that time. He discovered that a small percentage of these particles were deflected through much larger angles than was predicted using Thomson’s proposal. Rutherford interpreted the gold foil experiment as suggesting that the positive charge of a heavy gold atom and most of its mass was concentrated in a nucleus at the centre of the atom. This was known as Rutherford’s model.
“Yes, now I’ve got it. Earlier I had read about Rutherford model, but had some difficulties in understanding it. Now things are falling in line,” said Sahil.
“Rutherford model led to the discovery of nucleus,” I told him.
“Before this, we never knew that the nucleus existed!” Sahil had a surprised look on his face.
“Yes, we did not know about the nucleus before Rutherford’s experiment,” I agreed. “Rutherford suggested that electrons revolved around the nucleus and that the attraction toward the nucleus due to the electrostatic force between the nucleus and electrons is balanced out by the centrifugal force on the electrons due to their circulatory motion.
So, it was Rutherford’s imagination that gave us nucleus, said Sahil and I realized that he was now trying to prove his point that protons and electrons are the imagination of scientists.
“Yes, but imagination supported with logic,” I corrected him.
“Daddy, I thought that protons and electrons etc. are in the imagination of scientists, but now I understand that they had some basis for imagining these particles,” Sahil said and this surprised me.
“Good,” I appreciated him, as I felt some relief on hearing that he had begun to see some logic in the existence of protons and electrons. “So, it became evident that the electrostatic force between the nucleus and electrons is balanced by the centrifugal force of electrons revolving around nucleus,” I added further.
“Yes I know that. But Daddy, where do the electrons get their negative charge?” asked Sahil.
I did not know what to say. I thought for some time and the best answer I could give was that they have the smallest negative charge. But why? I had no clue. I made it a point to think about this question and to do some research on it.
Next day, when I had some free time while sitting in my factory office, I thought of searching on the internet about Sahil’s question. I found that Benjamin Franklin had given the convention of negative charge on electrons when he gave his conjecture regarding the direction of charge flow (from the smooth wax to the rough wool) when wool and wax were rubbed together. He then set a precedent for electrical notation, which is prevalent today. It meant that the positive and negative charges are just a convention to differentiate between the two. But why does this difference exist? Until we know the reason for this difference, we cannot find the source of negative charge on electrons. What is negative charge? I was thinking, but I could only understand that where-ever there is negative charge, there is abundance of electrons. This meant that negative charge is due to presence of electrons but I was unable to find the source of negative charge on electron. It is true that negative charge is the basic property of electron but how the electron attained this basic property, I was not able to understand.
When I reached home after finishing work , Sahil came and told me that he had read about the structure of atom in his physics book and he could now understand it a little better, but he still had some doubts. Settling down into sofa in the drawing room, I asked him, ‘‘What are your doubts”?
“Rutherford model had some limitations… I don’t understand them.”
“Yesterday I told you that Rutherford suggested that electrons revolved around a nucleus in fixed orbits,” I reminded him.
“Yes,” he agreed.
“Then a discovery was made that when a charged particle has motion, it loses energy and hence the electrons revolving around nucleus will lose their energy continuously and eventually fall into the nucleus,” I supplied further information.
“Oh yes, I have read about this too but could not understand how this discovery was made?”
“Here’s your tea,” said Shalini, handing me a cup of tea.
“Do you want your milk now or later?” she asked Sahil.
“I’ll take later. Now I am busy. Daddy, tell me about this discovery,” said Sahil indicating me to go on.
“I don’t know how this discovery was made but it led to a number of changes to the atomic model. We won’t concern ourselves how this discovery was made, but will make use of it,” I suggested to Sahil.
“Due to this discovery, it was evident that the electron will slow down due to loss of energy. As it slows down, its centrifugal force will reduce and it will be attracted towards the nucleus and slowly it will fall into the nucleus.”
“It means that Rutherford’s model was not correct,” Sahil guessed.
“You cannot say that it was entirely wrong but things needed further explanation if we were to accept this model,” I advised him.
“In 1913, Niel Bohr suggested that the electrons were confined into clearly defined, quantized orbits, and could jump between these, but could not freely spiral inward or outward in intermediate states. An electron must absorb or emit specific amounts of energy to transition between these fixed orbits.
Bohr’s model of the hydrogen atom, showing an electron jumping between fixed orbits and emitting a photon of energy with a specific frequency
“Why do electrons behave like that and how did Bohr knew that electrons can only jump from one orbit to another and not have intermediate position?” queried Sahil.
“Bohr only suggested that electrons should behave like that, and then only they can stay surrounding the nucleus; otherwise, they will fall in nucleus as per the new discovery of losing energy when a charged particle has motion,” I responded.
“So it was Bohr’s imagination to give the electrons a reason to keep revolving around the nucleus and prevent them from falling in nucleus,” wondered Sahil, and indicated one more cause for his belief that subatomic particles are in the imagination of scientists.
“You are right; this was Niel Bohr’s imagination but he came up with a better model than Rutherford’s. Though this model was based on imagination, there was one more reason to accept his model,” I tried to defend.
“What was that?” countered Sahil.
When the light from a heated material was passed through a prism, it produced a multi-colored spectrum with some fixed lines. The appearance of these fixed lines in the spectrum was successfully explained by these orbital transitions.”
“This was the best model of atom then,” suggested Sahil.
“Yes, but Bohr’s model also had its limitations.”
“I have read about the limitations, but never understood them. Can you repeat them for me?” Sahil requested.
“I don’t remember all the limitations but the main one was that Bohr’s model violated the uncertainty principle because it considered electrons to have known orbits and angular momentum: two things that cannot be directly known at once,” I expressed.
“Daddy, the ‘uncertainty principle’ name itself is confusing. How can there be a principle of uncertainty?” questioned Sahil.
“You know that electron is very small.”
“You know that for seeing anything, light has to hit that object and then reflect from it back to our eyes.”
“Yes, we cannot see anything if light does not hit something and come back to our eyes.”
“You also know that light has a ‘photon’ as its smallest unit.”
“Yes, it is a packet of energy and can be considered to have dual nature of particle as well as wave. I have read about it.”
“When this photon hits the electron, it imparts some energy to the electron.”
“Due to that energy, the electron will start moving if it was at rest or it will change its direction of motion, if it was moving.”
“Then by the time photon reflects back to your eye, the electron must have already moved to some other position.”
“This is the uncertainty principle, that you cannot measure the position and velocity of particles like electrons at the same time. If you want to know the position, you cannot be certain about its velocity, and if you want to know the velocity of an electron, you cannot be certain about its position. In Bohr’s model, he suggested that electrons are moving in fixed orbits. When we assume fixed orbits, then we are fixing their position and since the angular momentum in a fixed orbit is fixed for electrons, it means their speed is fixed. This becomes contradictory to the uncertainty principle.”
“I understand it now. I just used to cram this, never knowing what it meant. Now, I think I’ll not forget it. I will read further in my book and ask you if I have any doubts,” Sahil seemed satisfied with my explanation.
I was happy that he had started showing some interest in physics. But I had his question still roaming around in my mind: where do the electrons get their negative charge? During my internet search, I had found that it is just a convention given by Benjamin Franklin: electrons are negative and protons are positive. Something must make them different; assuming them to be different and following a convention was not satisfying for me. Then a thought came to me: besides not knowing the reason of negative charge on electron, I also didn’t know how the electron was created. If I don’t know how the first electron was born then how could I know how the protons, neutrons, and other particles were born? It means we don’t know how the universe was born. I had read that the universe came into being due to the Big Bang. The Big Bang happened about 15 billion years ago and created the universe, but what kind of matter was present before the Big Bang? Did that material also contain the elementary particles like protons and electrons or was something different from our world? Sahil’s one simple question had started my chain of thoughts, which now moved on to the creation of the universe.