Five important scientific theories that have changed the world - science articleSince the beginning of the civilization, scientific thinking and scientific theories evolved constantly. Scientific progress has taken the humanity a long way, paving the progress of our society. We cannot ignore the contribution of science and research to the comfort of our lives. You are likely reading this article on a computer, a mobile phone or a tablet. Well, thank science for that! We live now on average 30 years more than one century ago. Guess what, science is responsible for this!

All the advances of science begin with a scientific theory. Such a theory is an explanation of some aspect of the world that can be tested repeatedly using experiments, in conformity with the scientific method. There are many scientific theories that greatly contributed to our progress and helped us understand the world around us. It is difficult to say which one is the most important. Here, I am faced with the difficult task of choosing and explaining only five theories and this is going to be unfair to many other scientific concepts, maybe equally important. Therefore, in this article, I will (subjectively) present what I believe to be some important scientific theories, together with a short description and why they are important. Here we go!

The quantum theory

Few scientific concepts are as weird as the quantum theory. It is the theory that allows a cat to be both dead and alive until you check on it. It predicts that future events could influence the past. And, it states that particles that might be found anywhere have a zero probability of existing in one particular place!

The quantum theory was developed to compensate for the shortcomings of the classical theories in physics. They could not explain well some parts of reality. For example, the classical Newtonian physics fails when applied to very fast moving objects; under strong gravity conditions, or at the level of very small systems (like atoms). The quantum theory explains how very small particles of matter (electrons, protons, neutrons, etc.) behave. It is the theory that best explains the behavior of these components. Moreover, it allows matter to be perceived as a form of energy, as it is the case for light, which is seen both as particles (photons) and energy (light waves).

The development

The first quantum theory was developed by Max Plank in 1900. He built on ideas of previous scientists, including Ludwing Boltzman that suggested in 1877 that the energy levels of a physical system, such as a molecule, could be discrete. Plank’s theory stated that energy is quantized (is made of small “packets” of energy). Later, the quantum theory was applied to electrons by two other scientists Stefan Procopiu and Niels Bohr. In 1905, Albert Einstein came with some critical developments to the quantum theory and published the light-quantum hypothesis. Einstein is, in fact, one of the most important figures in the history of quantum physics, although he didn’t accept most of his own quantum findings, considering them to be too “spooky”. In 1926, physicist Erwin Schrödinger formulated the wave equation, developing further the quantum mechanics. Schrödinger is known for his famous Schrödinger’s cat experiment. Later in the 20th century, the quantum theory evolved and started to be applied in various scientific fields, from chemistry to biology.

Applications of the quantum theory

The science behind the quantum theory has many practical applications. Atomic clocks, the most precise clocks in the world, are measuring time using the principles of quantum physics. Instead of measuring the oscillations of a physical object (such a pendulum or a quartz crystal), like regular watches do, they measure the radiation frequency that makes electrons switch between energy levels.

Quantum principles are also used in encrypting messages. This is achieved by randomly polarizing photons in order to store a message. This type of code is virtually unbreakable unless one has the exact quantum key used for the initial encryption. Other applications of the quantum theory include the development of quantum computers and high-resolution microscopy based on photon entanglement.

The stem cells

Virtually every week we hear about some new groundbreaking study involving stem cells and how it promises to revolutionize medicine. Stem cells hold the promise for regenerating body parts, healing incurable diseases and even delaying aging. But, what are these famous stem cells? And what can they truly offer us?

Stem cells are undifferentiated (juvenile) cells that have an amazing ability: they can transform into any type of cell from a living organism! Theoretically, they are permanent sources of new cells that could replace damaged or aged tissues to keep the body healthy and functional. Stem cells are considered a medical miracle, with potentially unlimited applications in health, medicine, and research.


The discovery and history of stem cells

The history of stem cells is not a very long one. In 1981, Sir Martin Evens from Cardiff University was the first to discover embryonic stem cells in mice, and he won a Nobel Prize for it in 2007. On July 5, 1996, at the Roslin Institute in Edinburgh, Dolly was born. Who, you ask? Dolly the sheep, the first mammal ever cloned from an adult cell! She greatly advanced the field of stem cells. The technique that was used to clone Dolly was later applied by scientists to produce induced pluripotent stem cells (iPS cells). These are stem cells obtained from adult skin cells (instead of embryos). This discovery was awarded another Nobel prize in 2012. They have the same ability to differentiate into any cell type, but, they are ethical-safe since there is no need to extract stem cells from embryos anymore. The first medical use of stem cells occurred in 2010 when a person with spinal cord injury received embryonic stem cells therapy. Two years later, stem cells were used to treat blindness. Further advances occurred in 2013-2014 with successful therapeutic cloning (creating stem cells genetically matched to specific people) and in 2014 with the beginning of human clinical trials for induced pluripotent stem cells.

Applications of stem cells

The most obvious possible application of stem cells is tissue regeneration. Every cell in the body has its origin in a stem cell. In theory, correct instructions provided to stem cells could produce new cell types to regenerate damaged or diseased tissues.

Stem cells could be used to specifically cure certain diseases. For example, they could be used to regenerate brain tissue affected by neurodegenerative disorders like Parkinson’s and Alzheimer’s diseases. They could replace deficient cell types in the body, like for example, insulin-producing cells that are lost in diabetes. In 2013, a group of scientists reported creating new blood vessels from stem cells in mice, thus opening the gates for cardiovascular disease applications. Curing diseases with stem cells is still in the research phase for the moment, so we still need to wait a little bit before this approach becomes common practice.

One of the most important practical uses of stem cells is scientific research. Scientists routinely use them to understand how an organism is formed during development, how to cure cancer, or how genetic traits are passed on. Moreover, researchers are constantly trying to discover new methods to control the transformation of stem cells into desired tissues, with potential direct clinical applications.

In practice, today stem cells are already used to treat medical conditions such as leukemia or heart disease. However, there is still a long way to go until science will be able to completely control the differentiation of the stem cells. When that moment comes, the applications will be limitless.

Watch this video explaining the concept of stem cells:

The evolution of species

On 27 December 1831, when he embarked on the ship HMS Beagle, Charles Darwin was unaware that this voyage will shake the scientific world and forever change his life. It was the beginning of an intense scientific journey that ultimately led to the theory of the natural evolution of species. The concept of evolution was first formulated by Darwin in his book “On the origin of species”. Almost at the same time, another biologist, Alfred Russel Wallace, developed a similar theory of natural selection and his contribution to this concept is now widely accepted.

The theory of evolution by natural selection states that the changes that affect organisms in time are driven by modifications in the physical and behavioral traits that can be passed from a generation to another. The heritable traits that allow an organism to better adapt to an often-dynamic environment will help the species survive. Moreover, they will spread faster because these organisms will reproduce more efficiently. Although some may beg to differ, the evolution of species is one of the most well-supported theories in science with evidence from a large variety of disciplines: genetics, biology, geology, paleontology, etc.   


History of the theory of evolution

The theory was first described by Darwin in 1859, in his book “On the Origin of Species”, although some ideas about evolution were already present before this. French zoologist Jean-Baptiste Lamarck (1744 – 1829) proposed a mechanism for evolution, the first consistent theory of this type. He anticipated that a changing environment could force organisms to develop new traits. His concepts were well accepted until Darwin’s theory came on stage. In 1858, an English naturalist, Alfred Russel Wallace, developed a theory of evolution very similar to Darwin’s. Wallace corresponded on the subject with Darwin and they decide to present their theories at the same time to the scientific community in London. The very next year, “On the Origin of Species”, was published.  

Initially, the evolution through natural selection was a radical idea, and it was not very well received by everyone. The thought that a land animal could gradually evolve into a marine mammal (as in the case of whales) was a bit too erethic for those times. Darwin had no expertise in genetics, but he observed a pattern in the living world which was later confirmed by genetic discoveries. He speculated that traits are passed from one generation to another. This process can sometimes introduce new physical or behavioral features that can be beneficial and thus are preserved. Gradually, this process may lead to the generation of an entirely new species. We now know that mutations can occur randomly and that these mutations are the tools of evolution. The physical and behavioral changes that underlie the natural selection occur at the level of genes and DNA.

Importance and practical applications of the theory of evolution

Many areas of science and biology rely on the theory of evolution. Its principles are regularly applied by breeders trying to obtain new variations of plants or animals. This is called artificial selection and it is widely used in agriculture and for selection of a specific trait in animals or other organisms.

It is applied as well in ecology, conservation biology and epidemiology. For example, we know now that flu viruses change every year through mutations, in agreement with the evolutionary mechanisms described by Darwin. This is why we need to get a new flu vaccine every year.

The theory is even applied in computer science. It has been used to develop evolutionary algorithms and evolution strategies that are applied to solve complex problems, for example in engineering. Evolutionary algorithms are innovative software that can solve multi-dimensional problems better than other computer programs.


We all have heard about radiation, but few really know what it is. Radiation is all over us and it comes in many shapes and forms. It can be natural or artificial. Natural radiations include the radiation from the sun, but also the one emanated by the radioactive minerals in the soil and underground chemicals. Artificial radiation is produced by mobile phones, televisions, microwaves, to name only a few sources. Some radiation is good; another is bad, so let’s see how it is works!


The discovery of radioactivity

The story begins in 1895 when physicist Wilhelm Röntgen discovered the X-rays. One year later, Henri Becquerel was using naturally fluorescent minerals, such as potassium uranyl sulfate, to study the properties of the X-rays and he discovered radioactivity in the process. However, the most important contribution came from Marie Curie who, working together with her husband, greatly expanded our understanding of radioactivity. She was the first woman to receive a Nobel prize for her discoveries. She discovered the radioactive element radium in 1898.

But what is radioactivity? It is the spontaneous emission of energy (radiation) from atomic nuclei that are “unstable”. The emission of radiation helps the nucleus shift to a more stable energy state. There are several types of radiation: alpha, beta, gamma, etc., but discussing them is beyond the point of this article. If interested, you can read more about them here: types of radiation.

Radioactivity is measured using special devices that can count the number of atoms decaying over time. The unit of measurement is called curie (Ci), named after the Curie family. One Ci is the equivalent of 37,000,000,000 disintegrations per second!

Radiation Infographics: types of radiation and example sources
types of radiation infographics

Why is radioactivity important?

Understanding radioactivity has allowed us to learn how to protect ourselves from radiation and how to harness the energy of atoms and use it for our benefit.

There are many practical uses of radioactivity and radiation. Radioactive elements called tracers are used in medicine to assess how organs function. They are commonly used in medical diagnosis and investigations, but also in biological research. Radiation is often employed to sterilize medical instruments and food. This works because microorganisms are killed by intense radiation. The process has been refined to such an extent that there is no risk of contamination with residual radiation.

Radioactive energy is collected in nuclear reactors and used to power our society. Nuclear power stations regularly use uranium to produce energy. There are also other industrial applications of radioactivity: analysis of materials, industrial radiography and many more.

Some consider radiation to be dangerous, which is true in many cases. However, remember that some forms of radiation are good for us. For example, ultraviolet radiation (UV), a form of natural energy originating in the sun, stimulates the production of vitamin D. Thus, exposing yourself to a little bit of sunlight is beneficial, but remember to use sunblock products for prolonged exposure. When too much radiation from the sun reaches our skin, it becomes dangerous.

The theory of relativity

You are very familiar with this theory already, even if you don’t know it yet. Think about this: time flies when you are having fun, but it passes by very slowly when experiencing something unpleasant. Of course, the theory of relativity is a bit more complicated than that. In fact, we should talk about two theories: the theory of special relativity and the theory of general relativity. These theories predict some very strange phenomenon, that contradicts common sense like space travelers aging slower than people on the home planet; clocks that measure time differently, as a function of the speed at which they travel; light bending by massive objects, and so on.


Origins of the theory of relativity

In 1905, Albert Einstein published a paper arguing that the speed of light in vacuum is the same for everyone, independent of the speed at which the observers are traveling. Moreover, the laws of physics are the same for these observers (unless they are in accelerated motion). This was the first time the theory of special relativity was introduced. Before Einstein, it was believed that the speed of light changes based on the position of an observer.

One of the aims of this theory was to solve several problems in electromagnetism. However, it had profound and weird implication for both space and time. Space and time could not be kept constant if the speed of light was absolute. The consequence of this is that time and space must be interconnected, forming a single structure, the space-time continuum. Several consequences arise from this theory. Time passes slower when the observer moves very fast, a phenomenon called time dilatation. At the same time, objects reduce their size since any length measured in the fast-moving environment is shorter (length contraction). Finally, the mass of a fast-moving object would be measured by a stationary observer as a larger mass. This is the idea that eventually led Einstein to what is now probably the most famous equation in history: E=mc2.

Later, in 1915, Einstein included acceleration in his previous theory and came up with the theory of general relativity. One of the main implications of the new theory was that very massive objects are able to distort the fabric of space-time. To imagine this, think about a soft, flexible surface on which a heavy object is placed. The surface will be deformed by the weight of the object.

How does space-time stretch? Watch this short video explaining the effect of massive objects on the gabric of the Universe:

Practical applications of the theory of relativity

Electromagnets use some of the principles of the relativity theory. It is the working basis behind transformers and electrical generators. Another application is the GPS (Global Positioning System). In order to provide accurate location, the GPS satellites must correct for the effect of relativity. The satellites move very fast around Earth so they must consider the relativity in order to time signals precisely.

Extremely massive structures, such as clusters of galaxies, can bend light waves due to their huge gravitational force. This phenomenon is called gravitational lens and it is used by astronomers to see very distant stars. It was experimentally confirmed in 1979. It works similar to the lens in a magnifying glass, except the image is not focused in one single point, but in several, creating multiple images of the same object.  


The above-discussed theories are only five out of many that have made history and changed the way we live. It is impossible to cover all of them, but I am happy to provide some links to follow if you are interested in reading about other important scientific theories and concepts. Here it is:

The Fibonacci series (mathematics)

The game theory (economy)

The Freudian Theory of Personality (psychology)

Oxygen theory of combustion (chemistry)

Heliocentrism (astronomy)