A Brief History of 20th Century Science

Over the last century, we’ve significantly evolved our understanding of the universe. Although I design software by day, by night I am a voracious reader and learner. And I’ve found that the best way to retain information is to explain it to others.

So this post aims to briefly summarize some of the most influential scientific ideas introduced in the last hundred years.

1. The idea of the “atom”.

When you hear the word atom, you might think of tiny building blocks that make up matter. But in the 19th century, the atomic view represented a much broader concept.

The idea was that all natural phenomena consisted of fundamental building blocks. That you could break down anything into smaller units. And configure those units to produce anything in nature.

A few examples of the atomic view include:

  • The chemical atom as a building block of matter.

  • The gene as a building block of inheritance. Proposed by Gregor Mendel in 1865, this led to our modern understanding of genetics, inherited traits, and DNA.

  • The germ as a building block of disease. Louis Pasteur and Robert Koch demonstrated convincing evidence for the “Germ Theory” of disease in the 1850s, which led to a golden era of bacteriology and the identification of the thousands of deadly organisms.

So when you think of atoms, it’s not just a matter of oxygen and nitrogen. It’s a matter of looking at natural phenomena as if they were composed of fundamental elements like Legos.

2. The idea of “energy.”

Until the mid-19th century, scientists agreed that all phenomena could be explained in terms of matter in motion.

This is called “Materialistic Determinism”.

Given the properties of atoms – and the rules for configuring them – you could put matter together. And when matter moved, it generated everything we know in nature.

At least, that used to be the core of modern science — until energy joined the party in the 19th century.

This new theory of energy was called “Thermodynamics”.

Thermodynamics recognized that energy was a real phenomenon in nature, parallel to matter. It doesn’t just exist in the abstract. It always takes a concrete form.

A few examples of energy in concrete form include:

  • Heat energy

  • Mechanical energy

  • Electrical energy

  • Chemical energy

  • Gravitational energy

Thermodynamics is the general theory that describes all those types of energies together. It was one of the most innovative ideas of 19th-century science, and remains one of the most successful theories of all time.

3. The idea of the “field.”

The word “field” in did not exist as we know it in the 19th century.

A field is an immaterial something capable of exercising forces on material objects. It’s almost… ghostly.

For example, an electrical field has no mass and extends throughout all of space. But a charged particle entering that field will experience a force – either propulsion or attraction.

Imagine an electrical field surrounding a negatively charged electron. Now bring another negatively charged electron into the field. What happens?

They will experience repulsive force. But if we bring in a proton instead, they will experience an attractive force.

How did that happen? There’s no physical contact between the electron and proton. It was the “field” that did it!

This notion that there might be physical realities that aren’t material that can be described accurately and exert forces on material objects was a huge shift in the 19th century.

4. The idea that structure matters.

For a long time, we presumed that understanding the building blocks of reality was all that mattered. Then a chemist in the 1830s discovered that changing the physical arrangement of atoms in three-dimensional space changed the actual properties of those molecules.

For example, consider crystals. They are simply a unique arrangement of atoms arranged in a symmetrical lattice. But their structure creates completely new properties, far above and beyond those of the individual atoms.

So simply knowing the number of atoms in a molecule isn’t enough to predict the properties of that molecule. But you can predict its properties if you know how they were configured in three-dimensional space.

5. The theory of light as a wave.

From the 17th to the 19th century scientists thought light was a stream of atoms, like tiny bullets. Newton called them corpuscles. But it became evident that this “corpuscular” theory could not fully explain light’s behavior.

To account for observational data, a new theory emerged: that light was a wave. Waves are distributed in space, with a frequency and length. In 1865, the Scottish physicist James Clark Maxwell published an electromagnetic theory of energy. He hypothesized that visible light is just one set of frequencies within the total spectrum of frequencies of electromagnetic energy.

Maxwell’s theory encompassed all frequencies of light within a spectrum:

  • Below visible light includes infrared, which we experience as heat.

  • Above visible light includes ultraviolet, which can cause sunburn.

  • Far above visible light is x-rays… etc.

Maxwell’s s electromagnetic theory of energy — which explained what it meant to say that light was a wave — was considered the most important theory in physics by the close of the 19th century.

6. Probability and statistics.

In order to explain the relationships among the pressure, volume and temperature of gases, Maxwell and an Austrian physicist introduced a new idea: that some natural processes require probabilities in order to describe them.

They suggested that probabilities weren’t caused by a lack of the information needed to give a total picture of nature. Instead, certain fundamental natural phenomena were by nature probabilistic.

This idea was suggested in their kinetic theory of gases. Later in the 20th century, it became an extremely important concept and a fundamental principle of quantum mechanics. (More on that in future posts.)

7. The idea of non-Euclidean geometry.

For about 2,300 years, Western science, philosophy and mathematics were based on the confident assumption that deductive reasoning was linked to truth. That if some set of ideas could be organized deductively, then those ideas were true.

For example, Euclidean geometry is a set of theorems that describe mathematical objects like triangles and circles. It’s based on axioms, definitions and postulates that are considered to be self-evident.

The Greeks and almost nobody challenged this for 2,300 years. These definitions didn’t need any proof, they were just obvious as soon as you understood the words.

The assumption was that because the theorems of Euclidean geometry were deduced in strict logical fashion from self evidently true axioms, that Euclidian geometry was true about space. It was considered the geometry of the space in which we live and move.

But in the middle of the 19th century, a handful of mathematicians independently discovered that you can have deductively perfect geometries that contradict Euclidean geometry.

So which of these geometries is true of real space?

That becomes an empirical question that can’t be answered deductivelyYou have to do it experimentally. But once it’s experimental, it loses the logical purity of beauty.

The discovery of non-Euclidean geometry was a blow to the connection between reasoning and reality.

Could we ever again be as confident as Descarte, Spinoza and Leibniz were in the 17th century, who worked out deductively what must be true?

All of a sudden the connection between reason and truth — reason and reality — came into question.

8. The idea of symbolic logic.

Another development in math was the invention of symbolic logic, which shows how notation can have a tremendous impact. Simply replacing words with symbols can lead to new kinds of insights.

The prevailing view of logic used to be that things were the ultimate reality, and relationships were a secondary consequence of the way things were organized. But symbolizing logical relationships suddenly called our attention to just that: relationships.

We found that relationships had properties of their own, independently of what they related.

For example, consider a parent-child relationship. It has consistent properties that a sibling relationship doesn’t have. And you don’t have to know the parent or child to know many of their properties. If A is the parent of B, B cannot be the parent of A… etc.

This recognition led to a hierarchy of abstract logics built on the properties of relationships, and relationships between relationships. This strengthened the conviction that relationships had a reality, and reality did not have to be reduced to just things.

Three Instruments That Led to These New Ideas

A few instruments invented in the 19th century are worth mentioning. They provided new ways to observe nature and led to many of the ideas above.

1. The Color Corrected Microscope.

The microscope had become largely useless by the beginning of the 19th century. The objects people wanted to look at required powers of magnification far beyond traditional microscopes.

The corrected microscope, which provided high-power magnification without blurring, was introduced in the 1930s. By the end of the century biologists could see not only cells, but the nucleus within the cells — and even structures called chromosomes within the nucleus.

This newfound ability to observe the world at significantly smaller scales was a huge leap forward in our quest to understand the nature of reality.

2. The Spectrometer.

It’s mind-boggling to consider that we know the chemical composition of stars and planets millions of light years away. This wasn’t always the case.

Spectrometers break a beam of light up into its component frequencies. This led to huge advances in determining the chemical composition of matter, stars, planets, and the origin of our universe.

And the spectrometer was a critical instrument in building the body of data that quantum theory explained for the very first time. But quantum mechanics, now considered the most powerful theory in all of physics, is a topic for another time.

3. The Interferometer.

Albert Michelson, the first American to win the Nobel prize, was obsessed with measuring the speed of light with excruciating precision.

To do so, he took light from a single source and split it into two beams traveling different paths. Then he combined them again to produce interference. Analyzing that interference pattern – whether it constructively strengthened the intensity (if arriving in phase) or destructively weakened the intensity (if arriving out of phase) — allowed him to measure extremelysmall distances.

The interferometer led to huge advances in astronomy, engineering, oceanography, nuclear physics, fiber optics and much more. It played a critical role in formulating quantum theory, and is now used in industry and research labs all over the world.

Six Themes That Cut Across the Disciplines of 20th Century

Narrow specialization in fields has led to incredible discoveries. But zooming in too far can prevent us from seeing the broader fundamental principles that underlie all domains of science. By surveying the last hundred years of progress, we have the opportunity to zoom out and connect the dots, highlighting some basic tenants that span all disciplines.

1. Relationships are real.

The idea that reality is ultimately describable in terms of relationships inverts thousands of years of Western intellectual history, which attributed reality to things. By the end of the 20th century, relationships have increasingly become what science has to pin down, not things.

2. Things exist as a part of larger systems.

We are now increasingly looking at natural phenomenon as full systems. Although our limited human senses have led many to believe otherwise, we are finding that nothing is truly separate from the larger whole. This has profound implications in understanding our place in the cosmos and how we choose to live our lives.

From the perspective of science, this means not just looking at how Lego blocks are built up from the bottom, but understanding the whole entire structure holistically – including the relationship of every individual part to the whole structure. This goes from the smallest scales to the largest scales: from quarks, atoms, molecules, cells, bodies, ecosystems, biospheres, solar systems, galaxies, all the way up to superclusters and beyond.

3. Dynamism: change is normal.

Dynamism means accepting change as normal, and not trying to reduce everything to stasis.

In the 19th century, scientists looked for equilibrium situations. How does a natural situation come back to equilibrium, back to peace and harmony within nature?

In the 20th century, we increasingly look at non-equilibrium situations, which can show how nature is capable of self-organization. That becomes critical when you try to understand life.

4. Complexity emerges out of simplicity.

It was a true discovery in the 19th century that you could get unlimited complexity from the combination of very simple things. You don’t have to have a complex foundation in order to have a complex superstructure. This led to modern branches of science like chaos theory.

5. Subjectivity vs. objectivity is not clear cut.

Over the course of the century, we began to recognize that the distinction between subjectivity and objectivity — between mind and world — is not very clear cut. This idea turns up in physics, philosophy and the social sciences.

6. Science becomes a group effort across all disciplines.

In the course of the 20th century, scientific research became increasingly cross-disciplinary and collaborative.

Modern breakthroughs come less and less from one individual hero scientist. The focus also seems to be tilting away from saying “I’m a physicist” and “I’m a chemist” and “I’m a biologist”, and toward cross-disciplinary research.

Moving Forward

This overview goes barely an inch deep on several fascinating topics. My hope is simply to provide a taste of some of the exciting things that have happened since the 19th century. In future posts, I may dive into specific topics in more detail.