For centuries, enquiring minds have been trying to understand the mysteries of the universe. With every new discovery and question answered, at least ten more arise. That has been constant in the field of physics. The twentieth century was exceptionally filled with exciting discoveries from physicists which was further supported by the advancements made in technology.

So, what difference does this make in your life? Well, the field of physics continues to uncover the mysteries of the universe and it is worth knowing how some of these major discoveries have changed our view of things. In addition, you will get to find out what still remains a mystery.

In this book summary readers will discover:

- The beginnings of modern science
- Isaac Newton versus Albert Einstein
- The Theory of Quantum mechanics
- The Theory of Quantum gravity

## Key lesson one: The beginnings of modern science

Prior to the scholars of ancient Greece, everyday occurrences were explained in terms of the supernatural and higher powers. The Greeks, however, used observation, reason and mathematics to delve deeper into the world that surrounded them. Anaximander for example used rational methods to describe how the rain came to be. It was not a god who made it rain but rather evaporation which led to an accumulation of water in the sky that fell back down.

Then there was Democritus who first introduced the concept of atoms. He believed that everything in the world is made up of atoms and that these atoms must have a finite size. This theory is the basis of spatial extension which states that matter must have size and occupy space. Physics continue to develop and Greek philosophers like Plato and Aristotle put forward the idea of using mathematics as a tool for understanding the universe. Ptolemy actually created formulas to calculate the movements of the planets. With his formulae, it became possible to predict a planetâ€™s future position.

It was almost a thousand years later that Renaissance scholars like Copernicus and Galileo took up these mathematical tools once again. Copernicus changed what everyone believed about astronomy and stated that the sun was the centre of the solar system and not the Earth like previously thought. Then Galileo used a new invention called the telescope to see the details of the planets in the universe. Galileo also tested his hypotheses multiple times and gave rise to proper scientific method. One hypothesis that Galileo tested was that all objects fall at a constant speed. His experiments revealed that it was not the speed of the object but rather the acceleration of the object that remained constant. This became the first mathematical law for earthly bodies – the speed of any falling object on Earth will increase by 9.8 meters per second.

These were the earliest instances of modern science and as time passed, the discoveries just kept on coming.

## Key lesson two: Isaac Newton versus Albert Einstein

In the seventeenth century, about a century after Galileoâ€™s calculations, Isaac Newton started contemplating his work. Newton had been looking at the behaviour of a theoretical little moon orbiting the earth. He realized that the force that affected the speed and curve of an orbiting body was most likely the same force described by Galileo previously when contemplating falling objects. This is how Newton began to develop the theory of universal gravitation. Newton proposed that all bodies in the universe are drawn toward each other by gravity.

Then in the nineteenth century, Michael Faraday and Clerk Maxwell discovered electromagnetism. Electromagnetism is defined as the force that binds together the electrons within atoms and what binds atoms together to make molecules. They also proposed that there is a field throughout space that allows electromagnetic forces to act. Then in 1905, Albert Einstein stepped in with his theory of special relativity. This theory stated that different observers could experience the laws of time and space differently depending on their unique conditions. At the time, the theory set the scientific world alight with contemplation. General relativity brought together matter and space being subjected to the same laws of gravitational field. Space was not empty – it was the gravitational field constantly affecting all matter.

This was in contrast to what Newton described as he considered space and time separately. Einstein, however, took what Newton had done and explained how mass could bend the space around it causing bodies to be pulled toward each other. Einstein didnâ€™t stop there though. He also considered the origins of the universe and came up with the theory of a big bang. If the universe were finite, all bodies within it would be pulled to the centre due to gravity. This would result in an inward collapse of all matter. Einstein concluded that since this has not occurred, the universe must be expanding outwards and if it is expanding outwards, it must stem from an event that started this motion. This is the basis of the big bang theory.

## Key lesson three: The Theory of Quantum mechanics

The twentieth century brought with it another revolutionary discovery that changed physics forever – quantum mechanics. In contrast to general relativity that looks at space and matter, quantum mechanics takes a look at the microcosmic level of atoms and particles. Although quantum mechanics has been around for a while, it still contains many mysteries that physicists continue to work with.

It all started with Max Planck. His original experiments involved the calculation of energy in electrical fields. He took a bit of a mathematical shortcut and assumed that the energy in the field was present in small packets that he called quanta. Planck was pleasantly surprised when he found his assumption and calculations to be true. This was followed by Einsteinâ€™s own discovery that light was also made up of these small packets. Einstein was closely followed by Niels Bohr who found that an atomâ€™s electrons can only have a certain amount of energy. What the three of them had actually discovered was one of the fundamental aspects of quantum mechanics – the universe is granular. This means that is it made up of finite packets

The next fundamental part in terms of quantum mechanics is that the world is relational. This was first discovered by Werner Heisenberg. Heisenberg found that electrons donâ€™t always have an exact location in space and their position can only be determined if it is interacting with something else. This meant that an electron can only exist because of its relation to another object. The third and final aspect of quantum mechanics is indeterminacy. What this refers to is that thereâ€™s only a probability that physical events can be predicted and never a certainty.

These make up the three fundamental aspects of our world according to quantum mechanics – granularity, relationality and indeterminacy. It continues to baffle physicists as they continue to further research the aspects of quantum mechanics.

## Key lesson four: The Theory of Quantum gravity

At this moment in time, the two main parts of physics – the theory of general relativity and quantum mechanics are basically contradicting each other. For starters, general relativity states that space is curved and everything is continuous. According to quantum mechanics, however, space is flat and everything is granular made up of quanta or tiny packets.

In an eager attempt by physicists to bring these two opposing theories together, the modern field of quantum gravity was proposed. Quantum gravity is based on two fundamental claims. One is that space is not continuous and is instead also granular. This has been stated multiple times going back to Democritus who stated that everything has a size and occupies space. Physicist Matvei Bronstein also stated that space is not infinitely divisible back in the 1930s and the research that has followed has supported this. The smallest size space can be divided to has been determined and named the Planck length. This means that space is more like matter and is now being referred to as atoms of space and quanta of space indicating its granular nature.

The second fundamental claim of quantum gravity concerns time. In some places, time passes faster or slower than in others. It is a simple fact, the higher up you are, for example, the faster time will pass. It is because of this that physicists disregard time in their equations. It is not a universal and reliable scientific measurement and is therefore not used in quantum gravity.

**The key takeaway from Reality is Not What it Seems is:**

Physics has fascinated many minds over the centuries. This area of study holds the key to the worldâ€™s mysteries along with the origins of the universe. From the very beginning, bright minds have sought answers through scientific research with the help of technological advancements. Isaac Newton stepped forward with his theory that time and space was absolute. However, this was quickly set aside by Einsteinâ€™s theory of special relativity along with the development of quantum mechanics. This just opened a new can of worms though and physicists have now branched out to answer the questions that these theories unlocked.

**How can I implement the lessons learned in Reality is Not What it Seems: **

At its core, physics and physicists never settle on believing that a theory is unshakeable. No matter what theories arise, they continue to question, experiment and build upon what they have learned. It is not because they do not believe but instead that they know that there is always more to be discovered. This is an admirable trait as they continue to strive for answers to the mysteries of the universe. This is something that you can also apply. Keep an open mind about people and your surroundings because there is no limit to what you may learn.