|Jodutt Basrawi – University ID #: 004161598|
For Dr. Eric Scerri
It should be common knowledge by know – atoms do not behave in a normal manner. Atoms – and anything as big or as small as the atom – seemingly obey different sets of rules that change the typical face of reality. Quantum Mechanics – the mechanics of the motions and interactions of subatomic particles – has influenced the progress of our world. Quantum mechanics has also breached much of our imaginations. Just imagine if typical, regular sized objects behaved like atoms: individuals would be in two places at once; we’d be able to see the wavelengths made by moving projectiles with the naked eye; and we’d travel across distances without covering space. Niels Bohr, the man credited for the foundations of quantum mechanics, revolutionized our sights when he crafted and presented his model of the atom. Physicists, intellectuals, and even average citizens were stunned by the possibilities opened by Bohr’s model of the atom.
Bohr was around to save the day when scientists were pondering about the light reflected by heated gas samples (such as hydrogen gas). Why do heated gas samples reflect sharp lines of color? How come heated gas samples do not reflect a continuous set of colors? What determines the sharp spectral lines that atoms reflect and absorb? Niels Bohr believed that the answer to such questions lied in the structure of the atom.
Bohr’s model of the atom (the diagram above) explained why the spectral lines occurred from heated gas samples. Electrons of an atom could only orbit the nucleus in strict, circular paths. As you go farther away from the nucleus, the circular paths increase in radius. Furthermore, the paths are separated by plain space. Think of it like the solar system, where the planets orbit around the sun within their own paths. When the atom is excited (by heat or other form of energy), the electron jumps from a circular path closer to the nucleus to a circular path farther from the nucleus. As the electron “leaps” through these orbits, whenever it leaps closer to the nucleus, it emits energy in the form of specific wavelengths. These specific wavelengths are the sharp, spectral, colored lines we see in heated gas samples.
The big questions arose when Bohr explained how the electrons leaped from one orbit to another. The electrons seemingly move to other orbits without moving through the spaces in between the orbits (it’s like Mars suddenly teleporting to the Jupiter’s orbiting path). To account for this bizarre phenomenon, Bohr states that the electrons receive their energy in discrete, minimum chunks called quanta. These “quanta” also account for the discrete orbits of the electron around the nucleus. Literally, physicists were astounded by Bohr’s arguments. His model of the atom was counter-intuitive; it was not physically logical. The electron could go nowhere in between its discrete orbits, and its energy could only come in minimum quantity chunks. Our daily lives do not function like that, yet all matter of all things function with quantum-like behavior. Furthermore, physicists gained further skepticism when they at first could not measure or predict the “quanta” behavior of electrons. Bohr had a lot of smart people to convince.
Evidence soon mounted and supported Bohr’s model. Ultimately, electrons behave differently from large and even larger objects, such as baseballs and planets. The famous feud generated from such arguments was the indirect debates between Niels Bohr and Albert Einstein. Einstein disliked how Bohr was painting an ambiguous picture of physics and science in general through his arguments and his model of the atom. Bohr’s view of matter was contradictory to the hallmarks of classical physics, a science of prediction and certainty. Bohr believed that nature behaved in forms of possibilities and probability; making certain predictions was just a display of one of many scientific possibilities. Einstein was appalled by such a viewpoint of science. “God does not play with dice” and “I like to think the moon is there, even when I’m not looking at it” are two of many of his quotes he directed to Bohr while arguing against the values of quantum mechanics. Unfortunately for Einstein, many physicists liked what Bohr was saying, since probability still allowed predictions. Furthermore, with physicists like Schrodinger and Heisenberg painting clearer pictures and equations for quantum mechanics, it seemed like Niels Bohr had most of the support behind his works.
Another one of Bohr’s points behind the legitimacy of his works involved the act of measurement of electrons as “waves” (waves of possibility). When you measure a particle, the act of measurement forces the particle to rid all of its possible places it could have placed itself, consequently causing it to select one definite location where you end up finding it. In other words, the act of measurement forces the particle to choose one location out of all possible locations. This point further advocates the wave-particle duality of subatomic particles. Furthermore, it also suggested that the nature of reality is inherently fuzzy.
The aforementioned point by Bohr was vigorously applied when Einstein spoke against a seemingly illogical phenomenon in quantum mechanics called “entanglement”. Entanglement occurs when two particles end up in close proximities to each other and start to share a relationship. For example, if two electrons are entangled and one of their spins is measured, no matter the distance or circumstance, the other entangled electron would have an opposite spin. How can this be? Even when the electrons are light years away, they both seemingly have some form of communication. Einstein tried to rid the “fuzzy” nature of this phenomenon by stating that the entangled pattern of the electrons was determined from the moment they were separated by distance. Scientific evidence, however, points out that the fuzzy nature of the electrons does not allow a pre-determined, measured piece of data. In other words, in supporting Bohr’s point, the electrons are forced to decide one spin over other possible spins due to the act of measuring that electron’s spin (the act of measuring puts one definite spin on that certain electron).
Other challenges to quantum mechanics arrived after Bohr’s prime. John Bell, an Irish physicist and mathematician, attempted to mathematically disprove the “spooky” communication between entangled electrons. Disproving this “spooky” communication, Bell argued, would render quantum mechanics as a completely false science. Unfortunately for Bell, he died before performing his own, already written experiment procedures to follow up his argument. John Clauser, an American theoretical and experimental physicist, succeeded Bell as an opponent to quantum mechanics and obtained Bell’s experiment in a college library as a college student. Clauser himself found quantum mechanics to make no sense, and was a fervent supporter of Einstein’s views of physics. However, Clauser and Bell were proven wrong. When Clauser performed the experiment, he repeatedly tested thousands of entanglement particles to see if the signal between entangles particles travelled faster than the speed of light. According to the experimental results, the signals did indeed travel faster than the speed of light, justifying the “spooking action” communication that two entangled particles possess.
Bohr’s model of the atom mastered the works and patterns of one electron systems (hydrogen, helium (+1) ion, lithium (+2) ion, etc.). Bohr’s works particularly paid off when it was synergized with Balmer’s formula:
|n = 3, 4…|
Through a series of related equations and theories, Bohr was able to determine the angular momentum of an electron in a one electron system by stating that an emitted photon’s energy was the same as the difference between the upper and lower energy levels involved within his model. In other words, he had a relationship between the energy levels and the frequencies of the photons.
Bohr’s work, despite the good amount of evidence and calculations, drew skepticism from England, adjacent nations, and even Rutherford himself. Furthermore, the skepticism amplified when Alfred Fowler, an English astronomer who was an expert with spectroscopy, discovered new spectral lines in the Balmer series by using half-integers for “n” instead of whole numbers. These half integers were achieved by Fowler using a discharge tube that had a mixture of hydrogen and helium (the helium ion caused these new spectral lines to appear). In response to this apparent challenge by Fowler, Bohr adjusts Rydberg’s constant to account for the double charged nucleus of helium with assumption that it is a helium ion (+1 charge). With such an adjustment, Bohr still justified his model of the atom.
Bohr was still on stable ground after he saved his model through the adjustment of Rydberg’s constant. Bohr calculated that the ratio of the Rydberg constant for helium to hydrogen was 4. Fowler, however, in response to the calculation, continued the feud by calculating the ratio to five significant figures through his experimental expertise. Fowler found the ratio value to be 4.0016.
Bohr responds quickly to the more accurate Fowler calculation. He states that his adjustment to the Rydberg constant did not account for the finite mass of the nucleus. Once Bohr took the mass of the nucleus into account, the ratio worked out; it got closer to 4.0016. Bohr was seemingly the winner in this battle.
Bohr still received skepticism after his victory against Fowler. Fowler’s challenge brought questions as to whether Bohr was still working on the ambiguities within his model. To prove the skeptics of the scientific community wrong (and to simply discover more about the atom), Bohr worked alongside Henry Moseley, the physicist credited for arranging the periodic table by atomic number, with X-ray diffraction, in which Moseley utilized Bohr’s model to compile data.
Overall, Bohr’s model of the atom is considered an ad-hoc model. It only had one purpose: to tie together seemingly unrelated phenomena (such as the Balmer formula, Planck’s constant, the nuclear atom, and quantized angular momentum). Bohr’s model only explains one electron systems, and fails to go beyond in explaining neutral helium and its chemical successors. However, despite such restrictions, Bohr’s model characterized unique x-ray diffraction patterns (within the inner electrons of elements) and predicted the new spectral lines for ionized helium.
Niels Bohr, despite his evidence and passion, offered no explanation as to why quantum characteristics vanish for big, everyday objects. Some physicists propose that the explanation for the vanishing “quantum” characteristics of everyday objects is that the possibilities of our actions and everyday objects (our wave-like properties, like electrons) are played out in parallel universes. Furthermore, since we “measure” or “observe” everyday objects and other living things, our act of observation/measurement forces the matter to select one possibility/location to play out, and today, whenever I see an object, I am observing it in one of its possible states/locations. Overall, since we are made of atoms, and since Bohr proposed that the heart of matter explains all sorts of weird subatomic properties, it must be that we are exhibiting such weird patterns in some way.
Niels Bohr received the Nobel Prize in Physics in 1922 for his model of the atom. Besides his model, Bohr established a top tier physics institute (Institute of Theoretical Physics) in Copenhagen, where he and other scientists worked together to discover the mysteries of quantum mechanics. Heisenberg, for example, was at Bohr’s institution when he proposed the uncertainty principle. Furthermore, Bohr himself conceived the principle of complementarity, in which items such as subatomic particles should be analyzed separately, for they possess contradictory properties (electrons can be both particles or waves, depending on the experimental framework).
Bohr further amplified his fame when he was invited by the British and American governments to work on the Manhattan project in the secret Los Alamos laboratory in New Mexico. His primary goal was to further apply and therefore learn more about quantum theory. He also expressed that the Manhattan Project should be shared in the international community, including Russia, in hopes that it will catalyze scientific discoveries. Bohr’s expression was disapproved by then British Prime Minister Winston Churchill, who viewed sharing the secrets of the Manhattan Project as a “mortal crime”.
Aaserud, Finn. “Niels Bohr (Danish physicist) — Britannica Online Encyclopedia.” Britannica Online Encyclopedia. Britannica, n.d. Web. 22 Dec. 2012. <http://www.britannica.com/EBchecked/topic/71670/Niels-Bohr>.
Fowler, Michael. “From Bohr’s Atom to Electron Waves.” Galileo. University of Virginia, n.d. Web. 22 Dec. 2012. <http://galileo.phys.virginia.edu/classes/252/Bohr_to_Waves/Bohr_to_Waves.html>.
The Fabric in the Cosmos: Quantum Leap. Dir. Josh Rosen. Perf. Brian Greene. NOVA, 2012. Film.
“The Nobel Prize in Physics 1922.” Nobelprize.org. The Nobel Prize, n.d. Web. 22 Dec. 2012. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/>.