Ultimately, science is an eminently practical endeavor. If the claims that scientists make were false, we wouldn’t be able to confirm and apply those theories through technological innovations. Cellphones, computers, and other machines could not exist if our theories about electricity were wrong. There are still people who believe that the earth is flat. Flat-Earthers hold conferences every year, they (attempt) to get published in scholarly journals, and they hold public lectures on occasion and even write books on the subject. No one is stopping these individuals from exercising their first amendment rights; they are still free to express themselves in public. They are entitled to their own opinions. But they are not entitled to their own facts. The evidence does not support their hypothesis for a flat earth, so their research is not published along with other established facts because their claims cannot meet the burden of proof required of them. The evidence for each hypothesis is critiqued through the process of peer review. Conservatism in science means that the new theory will fit well within existing theories. Theories that overturn our conventional understanding of the world are not necessarily a dealbreaker; if they do cause the upheaval of scientific facts, however, they must also prove to provide a more fruitful, consistent and simplified way of looking at the world. (As well as explain why the debunked theory didn’t)
One example of this comes from the world of chemistry. For over a century, it was assumed that atoms were indivisible particles that made up all matter. At first there was the Dalton’s billiard model that suggested atoms were indivisible particles. This theory was completely discredited with the discovery of elementary particles like electrons. J.J. Thomsen, for example, discovered electrons in his classic cathode ray tube experiments; by running an electrical field through vacuum tube with a positive and negative-charged end, Thomsen found a stream of particles coming out of the negatively-charged cathode end of the tube. By applying a perpendicular magnetic field to an electrical field in the tube, Thomsen was able to calculate the mass-to-charge ratio of the particles coming from the cathode. He deduced that these negatively-charged particles we now call electrons were much smaller than hydrogen atoms. According to the so-called Thomsen Plum Pudding model of the atom, atoms had areas with a negative charge and these negative charges were suspended in a “soup”, “cloud”, or “vortex” of positive charges.
Furthermore, the Plum Pudding model proved to be a more consistent way of looking at the world, for a time. The Plum Pudding model suggested that atoms were solid and electrons distributed evenly throughout a positive goop. Along came Ernest Rutherford, who set up an experiment in 1909 to test the validity of this model. He fired alpha particles at gold foil. Rutherford expected, based off of what scientists had discerned so far, that the alpha particles would slice through the atoms in the gold foil and end up on the other side of the gold foil. And yet, he found that some of these alpha particles bounced off of the foil and went in the opposite direction, towards the spot from which they had been fired. According to Rutherford, it was like firing a cannonball on a tissue paper and seeing it bounce against the paper right back at him. Armed with observation, Rutherford devised a brand new way to conceive of the atom. He suggested that most of the matter of an atom was clumped in the center and that this nucleus of the atom had a positive charge. He surmised that because atoms have a net neutral charge, there had to be electrons with a negative charge, but that these electrons weren’t found in the nucleus, they had to be positioned outside the nucleus. Rutherford’s new way of looking at the atom was undoubtedly challenged by many, but it in part survives today because the theory can better explain our scientific observations than the Plum Pudding model. Especially because it overcame the contradictions of the Plum Pudding model; if the Plum Pudding model were likely true, alpha particles should not bounce off of atoms as Rutherford and others observed. The Rutherford model successfully explained the phenomenon without eliminating the positive and negative charges that scientists knew existed within the atom.
However, there was no way that the Rutherford model could explain the movement of electrons around the nucleus or precise wavelength patterns emitted by particular elements when heated. Rutherford envisioned that electrons moved outside the nucleus like planets orbiting a star. But it was discovered later that either the position or the velocity of an electron can be calculated, but not both at the same time. Given this uncertainty in the movement of electrons, electrons couldn’t be moving in such unpredictable ways as the Rutherford model led scientists to expect. So another model arose to amend the Rutherford model, called the Bohr model, which could better explain how the electrons moved by electrostatic forces rather than gravity. The Bohr model suggested that electrons floated around the nucleus in rings, based on work in spectroscopy that showed electrons have “levels” of energy and can hop from one level to another and back down again when excited by a photon. The Bohr model was highly successful in explaining the Rydberg formula used in atomic physics to describe the wavelengths of the spectral emission lines of atomic hydrogen. So Bohr predicted that these spectral lines were created when electrons are hit with a photon and get excited to a higher energy level. Each element has a different number of electrons, and therefore each element has different spectral emission lines.
The Bohr model could only explain how photons interact with the single electron on the simplest element hydrogen, though. Electrons only seemed to occupy certain energy levels and when photons struck electrons, an electron would jump from a low energy level to a high energy level, emitting light. This is recognizable when someone describes metal as “white hot” for instance. The Bohr model could not predict the spectral emission patterns of anything heavier, yet spectral emission lines can easily be observed in a lab by heating up a metal until it becomes white-hot. Finally, with the development of quantum mechanics, physicists found that the orbiting electrons around a nucleus didn’t really behave like particles, but rather they behaved like both waves and particles. So a new model was proposed to replace the Bohr model of the atom. The quantum mechanical model explains that the movement of electrons occur in atomic orbitals, vague areas outside the nucleus where electrons are most likely to be found. Electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves. Our detection methods necessitate physicists to strike electrons with a photon in order to measure their position. If scientists strike an electron with a high-energy gamma ray photon, though, they would know with startling accuracy the position of the electron at the time that it was observed (Because the wavelength of the gamma ray is so tiny, physicists would know within one gamma ray wavelength where the electron was when it was struck), but once the gamma ray strikes the electron, the electron would get an unpredictable change in speed and sprint off at an unknown velocity. If physicists tried to measure an electron with a lower-frequency light ray, they would run into another set of problems. A radio wave has a much longer wavelength, so when it strikes an electron, it delivers a much smaller change in velocity; scientists can estimate how fast an electron is travelling because striking an electron with a low-energy wave would only impart a negligible change in speed. But, the trade-off here is that scientists wouldn’t know the position of the electron very well because the wavelength of a radio wave, for instance, is so long that the electron could have been struck by a photon anywhere on that wave. So it is impossible to know both the momentum and position of an electron accurately. Yet, when electrons jump between atomic orbitals when excited by a photon, they behave like particles. The biggest conundrum, arguably, plaguing some physicists is the incompatibility of quantum mechanics and general relativity. The laws ascribed to gravity don’t seem to work in a quantum mechanical system and vice versa. Until this inconsistency is reconciled, the quantum mechanical model will remain incomplete, at best.
So if the quantum mechanical model is incomplete at best, why do scientists even use it? Scientists recognize the limitations of each new theory and the need for further refinement. Incomplete knowledge is better than no knowledge at all. And although the Bohr model is incomplete, the facts that we can glean from it have stood up to scrutiny and in the future the Bohr model can be improved upon or discarded as new discoveries are made. So science is both a body of knowledge and a means of acquiring new knowledge that is constantly updating and improving itself as new observations come to light. We end this blog post with one final thought; science is an ongoing process. We will never know everything with absolute certainty, but with each approach we gain a more nuanced understanding of reality. The limits to our knowledge cannot be used to disqualify the knowledge that we have gained or counted as evidence in favor of non-scientific thinking.