In our everyday conversations, we often throw around the word 'theory' to mean a hunch or an educated guess. However, among the scientific community, the word 'theory' carries a very different meaning. For clarity, a more fitting term for our everyday use of the word 'theory' is 'hypothesis' (i.e., an untested explanation). The word 'hypothesis' conveys an accurate representation of what someone truly means when they say, "there's this theory that aliens built the pyramids." What they are saying is that there have been speculations that aliens built the pyramids, but that explanation has not been confirmed—worth noting, abundant evidence supports the fact that ancient Egyptians (i.e., humans) erected these structures as tombs, while the evidence for the existence of aliens is equivalent to the evidence of my ability to read your mind—zero. It never fails to puzzle me that many today look at the pyramids and try to imagine themselves building it. Upon failing to do so, their flawed logic is that, "since I can't do it, they probably couldn't too ! Therefore... ALIENS DID IT !" Wouldn't a simpler explanation be that ancient civilisations were as resourceful and smart as we currently are? Afterall, more than 2,300 years ago, Eratosthenes achieved a feat that many today would deem to have been impossible without modern technology. Not only did Eratosthenes figured out that the Earth was round and not flat, but more impressively, he also calculated the circumference of the Earth to be 250,000 stadia (i.e., 39,250 km), astonishingly close to the actual figure as we know it today, 40,075 km (Walisiewicz & Celtel, 2023). I would love to share how he managed to achieve that remarkable feat but for now, I must get back on track to what I was saying. Since the claim, that aliens built the pyramids, is based on speculations, the accurate version of the statement would be, "there's this hypothesis (not 'theory') that aliens built the pyramids."
The disparity in the meaning of 'theory' between the scientific community and the public often leads to great confusion. Take the theory of evolution by natural selection, for instance. When people hear it, they frequently dismiss it as 'just a theory.' This, however, is a grave misconception, and the commonality of such statements clearly highlight a major issue—the widespread misinterpretation of what a 'scientific theory' truly entails. However, not to worry because by the end of this blog post, you would be able to define what is a 'scientific theory,' and also correct your everyday misapplication of the word 'theory'.
This image was created with the assistance of DALL·E 3.
Definition of a Scientific Theory
A 'scientific theory' is defined as an explanation of why or how something happens in the world, that has been verified through repeated testing and experimentation (i.e., scientific method) (Fives & Dinsmore, 2018).
(Read my blog post on What is the Scientific Method?)
Additionally, a 'scientific theory' should:
(1) exhibit strong explanatory capabilities
(2) generate specific and testable predictions
(3) be based on existing empirical research and evidence rather than speculative and untestable ideas
(4) be vulnerable to falsification
In epistemology—the study of knowledge—a 'scientific theory' is fromulated based on the process of IBE—Inference to the Best Explanation—which is "the procedure of choosing the hypothesis or theory that best explains the available data" (Vogel, 2016). The Spherical Earth Model (round Earth) is a 'scientific theory,' and the best explanation for why we have winters and summers. The best explanations from inferences is also called, a word which you might be familiar with, facts! As such, unbeknownst to many, 'scientific theory' is exactly the same as a fact!
Also, if you've been following along, you might have picked up that not every idea, explanation, or hypothesis gets the prestigious title of a 'scientific theory.' Only the ideas that have been seriously put through the wringer—tested, experimented on, and challenged continuously, and yet not been falsified (i.e., proven to be wrong)—earn that status. Think of it like a champion theory that has survived every single experiment and test that was set out to prove it wrong. The champion theories that are left standing, out of the thousands of other possible explanations that have been falsified, are then called a 'scientific theory.'
Now, one such champion in the scientific arena is Charles Darwin's theory of evolution by natural selection. It's like the heavyweight champion that has been in the ring for literally almost two centuries and still hasn't been knocked out. Notably, this is in spite of numerous attempts by millions of challengers across the world—millions are still trying. (Due to the prevalence of evolution-denial, I'm planning to dive deep into the wealth of evidence supporting this theory in an upcoming blog post, so subscribe and stay tuned!)
As it is one of the heavyweight champion theories, it is fitting for me to use Darwin's theory of evolution to exemplify the 4 characteristics I've highlighted, that a 'scientific theory' should possess.
Image of Charles Darwin. This image was created with the assistance of DALL·E 3.
Evolution Exemplifying the Characteristics of a Scientific Theory
(1) Exhibit strong explanatory capabilities:
Evolution provides a robust explanation for the diversity of life on Earth. It elucidates how different species have developed over time from common ancestors, addressing the question of how life has evolved into its present forms. Just to name a few others that are more relevant to us humans, evolution also explains antibiotics resistance, differences in our skin tones, existence of our wisdom teeth, our vestigial appendix, our tailbones, our nearly identical DNA with chimpanzees (98.5% similarity), and many others.
(2) Generate specific and testable predictions:
Evolutionary theory predicts that if species share a common ancestry, we should find evidence in their genetic code (i.e., DNA). Scientists have tested this prediction by comparing the DNA of different species, and the results consistently support the idea of a shared evolutionary history. Evolutionary theory also predicts that the DNA of humans should exhibit greater similarity to that of chimpanzees than baboons. This is attributed to the more recent common ancestor shared by humans and chimpanzees who lived 5-7 million years ago, indicating a closer evolutionary relationship compared to humans and baboons (common ancestor lived around 25 million years ago during the Miocene epoch). Evolutionary theory also predicts that the fossils of mammals should only appear after the emergence of reptile fossils in the fossil record. This prediction is constantly being tested and verified till today as when anyone—not just scientists—digs through the layers of the Earth today, they will discover mammal fossils appearing later than reptile fossils, just as predicted by evolutionary theory. Specific predictions are what make 'scientific theories' useful. If a theory can't make useful predictions, what's the point of it? The power of predictions by evolutionary theory is exemplified in the following example. The search for the transitional fossil of the intermediary species between swimming fishes to four-legged vertebrates, was specifically carried out at on Ellesmere Island in Canada. Why? Because from prior research and evidence, evolutionary theory predicts that the intermediary species would have appeared between 360 and 390 million years ago, and it would have lived in freshwater. Excavating the rock layer that belongs to an age that was in between the range of 360 and 390 million years old at Ellesmere Island ultimately yielded the fossil of Tiktaalik, a species that have both fish and tetrapod characteristics.
(3) Be based on existing empirical research and evidence rather than speculative and untestable ideas:
Evolution is grounded in a wealth of empirical evidence, including fossil records, comparative anatomy, and molecular biology. For instance, the discovery of transitional fossils like Tiktaalik (Amphibian-like fish) and Archaeopteryx (bird-like reptile) reinforces the idea of species gradually changing over time. Another example would be the order in which animals and organisms are found in the fossil records—the older rock stratas contain simpler organisms which gradually become more complex as time passes—and this is evidenced by more compex life forms in the younger rock stratas. Embryology evidence also shows that all mammalian embryos, including humans, possess tails and gills in their early stages, indicating a shared common ancestry with fishes.
I shall not go into detail about the evidence for evolution as that deserves a blog post on its own, but evolution is supported by evidences from a wide range of scientific disciplines, including paleontology (study of fossils), geology, biogeography, biochemistry, microbiology, molecular biology, botany, ecology, genetics, embryology, and comparative anatomy. The convergence of independent evidence from these different fields illustrates the robustness and credibility of evolutionary theory.
(4) Be vulnerable to falsification:
Evolutionary theory is open to falsification. If, for example, fossils were discovered in the wrong geological layers or if DNA evidence contradicted the expected patterns, it would challenge the theory. For example, evidence that will falsify evolution would be reptile fossils in the cambrian period (540 million to 480 million years ago), because evolution theory states that reptiles only came into existence only around the late carboniferous period (320 million years ago). To falsify evolution, one simply have present evidence that contradicts this, thereby falsifying evolution.
While many have tried—especially evolution-denialists, there have been zero evidence that falsify the examples that I have mentioned, let alone every other line of evidence that supports evolution. The consistent support from evidences in various scientific disciplines tells any rational being that the chances of future contradictory evidence arising, that destabilises the foundation of the theory, remains stupendously improbable. Let's put it this way, the chances of falsifying evolution is as likely as falsifying the Spherical Earth model.
Even if evidence were to challenge a certain aspect of evolutionary theory for example, whether species A evolved from species D or E, the central concept of evolution—that all living things share a common ancestor—would remain steadfast. Consider Einstein's breakthrough with the general theory of relativity. It didn't debunk Newton's Laws of Motion; instead, Newton's laws still hold for everyday objects like buildings or trucks. Einstein's theory, on the other hand, builds on Newton's Laws, and takes the reins when it comes to explaining the movements of massive objects like the Earth and the Sun. I admit that I've gone on for a little too long about this point, but the main takeaway is that evolution, just like every other 'scientific theory,' is vulnerable to falsification. This means that it can be proven to be wrong. We simply have to falsify any of the supporting evidence from the 11 scientific disciplines which I have mentioned previously. If a useful theory that is open to falsification have not been falsified after multitudinous experimentation and testing, it can then attain the title of a 'scientific theory'. As highlighted by Karl Popper's quote below, anything unfalsfiable cannot be a 'scientific theory'.
"A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice." -Karl Popper
List of Scientific Theories
Now that you understand what qualifies as a 'scientific theory,' here are a list of some 'scientific theories' from the physical and life sciences that have withheld all tests and experimentation till date. So if anyone says evolution is 'just a theory,' kindly explain to them what a 'theory' actually means in science, and that all of these below are 'just theories' of science as well.
Special Theory of Relativity (Albert Einstein): Deals with objects moving at constant speeds.
Theory of General Relativity (Albert Einstein): Describes gravity as a curvature of spacetime.
Newton's Laws of motion: Describes the relationship between motion of an object and forces acting on it.
Theory of Evolution by Natural Selection (Charles Darwin): Explains the diversity of life on Earth.
Theory of Electromagnetism (Maxwell's Equations): Unifies electricity and magnetism.
Quantum Mechanics: Describes the behavior of matter and energy at the smallest scales.
Big Bang Theory: Describes the origin of the universe from a hot, dense state.
Germ Theory of Diseases: Explains that microorganisms can cause infectious diseases.
Theory of Plate Tectonics: Describes the movement of Earth's lithospheric plates; explains earthquakes and tsunamis.
Atomic Theory: Describes the nature of matter at the atomic level.
DNA Double Helix Structure (Watson and Crick): Describes the structure of the DNA molecule.
Genetics (Mendel): Describes how traits are passed from parents to offspring due to changes in DNA.
Kinetic theory of gases: Describes the thermodynamic behaviour of gases.
Theory of Optics (Wave-Particle Duality): Describes the dual nature of light.
Heliocentrism: Sun at the center of the solar system.
Spherical Earth model: Describes the Earth as spherical, rather than flat.
Visualisation of an atom. This image was created with the assistance of DALL·E 3.
List of Superseded Theories
However, there is something else which I must highlight. Throughout history, there have been many 'scientific theories' that tried to explain our world and they were based on evidence from their time. However as technology and science itself progressess, some of these theories have been superseded by new theories based on new evidence. However, we still call some of these superseded theories as 'theories' today as they were used to be based on the best scientific evidence at that time. Therefore, please bear in mind that everytime you identify a 'scientific theory,' you should dig a little further to see if its an outdated theory that have been succeeded.
Here are a few examples of superseded theories:
Caloric theory–superseded by mechanical theory of heat.
Geocentrism–superseded by Heliocentrism (Sun-centered model).
Phlogiston theory–superseded by Oxygen theory of combustion.
Lamarckian Evolution–superseded by Darwinian Evolution (Natural selection).
Flat Earth Theory–superseded by Spherical Earth model.
Vitalism–superseded by mechanics of physics and chemistry (Biology).
Miasmatic Theory of Disease–superseded by Germ Theory of Disease.
Aristotelian physics–superseded by Newtonian physics.
Steady state theory–superseded by Big Bang Theory.
John Dalton's atomic model–superseded by Thomson's model.
Thomson's atomic model–superseded by Rutherford's model.
Rutherford's atomic model–superseded by Bohr's model.
Bohr's atomic model–superseded by Quantum Mechanical model (The atomic model that is accepted today).
Pseudoscientific Theories
Oh, there's one more and this is important! I would like to caution you that there are many pseudoscientific claims that masquerade themselves as 'scientific theories'. Pseudoscience, according to Oxford english dictionary, refers to “a collection of beliefs or practices mistakenly regarded as being based on [the] scientific method” (Glanzberg, 2006). These pseudoscience claims and theories would appear to sound scientific, giving the impression that they are a result of applications of the scientific method and that they are based on evidence. When in reality, they are not. A few examples of pseudoscience are astrology, law of attraction, MBTI, intelligent design, meridian point theory, traditional chinese medicine, crystal healing, creation biology, creation cosmology, reiki (energy healing), fengshui, and countless others. Hence, it is crucial that you do abit of research to see if the theories you identify are are indeed 'scientific theories,' and not pseudoscience—remember that not everything with the word 'theory' in it makes it a well tested'scientific theory'. (I'll be writing a blog on commonly believed pseudosciences in the future as well.)
Conclusion
There you have it! I hope you have come to a better understanding of what a 'scientific theory' is, and the stringent criteria it must satisfy before achieving its status. To any reasonable being, it becomes obvious that current 'scientific theories' that have not been falsified are the best explanations of the natural world for now. Furthermore, an important point to emphasise is that 'scientific theories' do not require belief to be true as they are formulated based on empirical evidence, which are not subjected to opinions. Whether you believe in Einstein's general theory of relativity or not, the theory works because of the evidence yielded through expermimentation, not because scientists believe in it! Additionally, technological systems that we use today are also evidence of its validity. Without general theory of relativity, there would be no GPS technology. This is one such example of the numerous 'scientific theories' that have garnered scientific consensus, not because of belief but because of evidence. Darwin's theory of evolution is one that stands beside Einstein's general theory of relativity, alongside with numerous others. If there's one thing you must takeaway, it's that 'scientific theories' are well tested and are grounded solely on empirical evidence, and this differs from the meaning of our everyday usage of the word 'theory'. Lastly, you should also be cautious when reading about superseded theories and especially more so, for pseudoscientific theories that masquerades as science.
But if 'scientific theories' are grounded on evidence, that means we must also evaluate the evidences that the 'theory' is built on. Junk evidence is not evidence. What constitutes as evidence and what does not? If a billion people said that they saw a horse speaking english, does it count as evidence? Some may say that a 'billion' people saw the horse speaking, not a million but a BILLION! Of course it counts as evidence! Is it? Well, not quite... What if you yourself saw the horse speaking, it has to be evidence right? Since you yourself saw it. Not quite either... (hint: personal recounts are junk evidence) Stay tune as I'll be writing a blog about the hallmarks of science which will enable you to indentify what qualifies as scientific evidence, and what does not.
References
Fives, H., & Dinsmore, D. L. (Eds.). (2018). The model of domain learning: Understanding the development of expertise. Routledge, Taylor & Francis Group.
Glanzberg, M. (2006). Truth. https://plato.stanford.edu/archives/fall2023/entries/truth/
Vogel, J. (2016). Inference to the best explanation. In Routledge Encyclopedia of Philosophy (1st ed.). Routledge. https://doi.org/10.4324/9780415249126-P025-1
Walisiewicz, M., & Celtel, K. (Eds.). (2023). Timelines of science. DK.
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