10 Essential Scientific Laws and Theories Everyone Should Know

Scientists rely on a variety of tools to explain the workings of nature and the universe, with laws and theories being among the most fundamental. A scientific law is typically a concise mathematical expression, like E = mc², derived from empirical data and applicable under specific conditions. For instance, in E = mc², c denotes the speed of light in a vacuum.

A scientific theory aims to consolidate a collection of evidence or observations about specific phenomena. It often provides a broader, testable explanation of natural processes. While not always reducible to a simple equation, a scientific theory captures a fundamental aspect of how the universe functions.

Both scientific laws and theories rely on fundamental aspects of the scientific method, including formulating a hypothesis, testing it, gathering (or failing to gather) empirical evidence, and drawing conclusions. For an experiment to form the foundation of a widely accepted law or theory, its results must be replicable by other scientists.

In this article, we’ll explore 10 scientific laws and theories worth revisiting, even if you’re not frequently using tools like a scanning electron microscope. We’ll begin with a cosmic explosion, delve into the fundamental laws governing the universe, touch on evolution, and then venture into the complex world of quantum physics.

10: Big Bang Theory

If there's one scientific theory you should understand, it's the one that describes how the universe reached its current state. Rooted in the work of Edwin Hubble, Georges Lemaitre, and Albert Einstein, the big bang theory suggests that the universe began nearly 14 billion years ago with an enormous expansion. At that time, all matter in the universe was concentrated in a single point, and the expansion initiated then continues to this day.

The big bang theory gained significant scientific credibility after Arno Penzias and Robert Wilson identified cosmic microwave background radiation in 1965. Using radio telescopes, they detected persistent cosmic noise or static. Working with Princeton scientist Robert Dicke, they validated Dicke's theory that the big bang left behind faint radiation detectable across the universe.

9: Hubble's Law of Cosmic Expansion

Let’s focus on Edwin Hubble for a moment. During the roaring 1920s and the challenging years of the Great Depression, Hubble was making revolutionary strides in astronomy. He not only confirmed the existence of galaxies beyond the Milky Way, but he also observed that these galaxies were rapidly moving away from ours, a phenomenon he termed recession.

To measure the speed of this galactic motion, Hubble introduced Hubble's Law of Cosmic Expansion, also known as Hubble's law, expressed by the equation: velocity = H × distance. Here, velocity refers to the galaxy's recessional speed; H is the Hubble constant, representing the universe's expansion rate; and distance is the galaxy's distance from the one being compared.

The value of Hubble's constant has been revised over time, with the current accepted figure being 70 kilometers/second per megaparsec, a unit used to measure vast intergalactic distances [source: White]. For our discussion, the exact number isn’t crucial. What’s significant is that Hubble's law offers a straightforward way to calculate a galaxy's speed relative to ours. Most importantly, it confirmed that the universe is composed of numerous galaxies, all moving in ways that trace back to the big bang.

8: Kepler's Laws of Planetary Motion

For centuries, scientists and religious leaders debated the nature of planetary orbits, particularly whether they revolved around the sun or Earth. In the 16th century, Copernicus introduced his contentious heliocentric model, proposing that planets orbit the sun. However, it was Johannes Kepler, building on the work of Tyco Brahe and others, who provided a clear scientific framework for understanding planetary motion.

Kepler's three laws of planetary motion, developed in the early 17th century, explain how planets move around the sun. The first law, known as the law of orbits, states that planets follow elliptical paths around the sun. The second law, the law of areas, asserts that a line connecting a planet to the sun sweeps out equal areas in equal time intervals. For example, if you measure the area traced by Earth's orbit over 30 days, it remains constant regardless of Earth's position in its orbit.

The third law, the law of periods, establishes a direct relationship between a planet's orbital period and its distance from the sun. This law explains why a planet like Venus, which is closer to the sun, has a much shorter orbital period than a distant planet like Neptune.

7: Universal Law of Gravitation

While it may seem commonplace today, over 300 years ago, Sir Isaac Newton introduced a groundbreaking concept: any two objects, regardless of their mass, exert a gravitational force on each other. This principle is expressed through an equation familiar to many high school physics students:

F = G × [(m₁m₂)/r]

F represents the gravitational force between the two objects, measured in Newtons. M₁ and m₂ denote the masses of the objects, while r is the distance separating them. G is the gravitational constant, currently calculated as 6.672 × 10 N m kg [source: Weisstein].

The universal law of gravitation is invaluable because it enables us to determine the gravitational attraction between any two objects. This capability is particularly crucial for tasks like placing a satellite into orbit or mapping the trajectory of the moon.

6: Newton's Laws of Motion

While discussing one of history's greatest scientists, let’s turn to Newton's other renowned principles. His three laws of motion are fundamental to modern physics, admired for their simplicity and elegance.

The first of Newton's three laws asserts that an object in motion will remain in motion unless an external force acts upon it. For instance, a ball rolling on the floor might be stopped by friction or redirected by a child kicking it.

The second law links an object's mass (m) to its acceleration (a) through the equation F = m × a. Here, F stands for force, measured in Newtons, and is a vector, meaning it has both magnitude and direction. The rolling ball, for example, has a specific vector indicating its direction of movement, which is factored into force calculations.

The third law is concise and widely recognized: For every action, there is an equal and opposite reaction. This means that any force applied to an object or surface is met with an equal force in the opposite direction.

5: Laws of Thermodynamics

C.P. Snow, the British physicist and novelist, once remarked that a nonscientist unfamiliar with the second law of thermodynamics is akin to a scientist who has never read Shakespeare [source: Lambert]. Snow's famous analogy underscores the significance of thermodynamics and the importance of its understanding for everyone, not just scientists.

Thermodynamics explores how energy functions within systems, whether in an engine or Earth's core. It can be distilled into fundamental laws, which Snow succinctly summarized as [source: Physics Planet]:

Let’s break this down. When Snow said you can't win, he meant that since matter and energy are conserved, gaining one requires sacrificing the other (as in E=mc²). Additionally, for an engine to perform work, heat must be supplied. However, in any system that isn’t perfectly closed, some heat is inevitably lost to the environment, leading us to the second law.

The second principle — you can't break even — highlights that due to the constant rise in entropy, returning to the same energy state is impossible. Energy concentrated in one area will inevitably disperse to areas with lower energy levels.

The third principle — you can't quit the game — refers to absolute zero, the lowest theoretical temperature, measured at zero Kelvin (or minus 273.15 degrees Celsius and minus 459.67 degrees Fahrenheit). At absolute zero, molecular motion ceases entirely, eliminating kinetic energy and minimizing entropy. However, achieving absolute zero is impossible in reality, even in the depths of space; one can only approach it.

4: Archimedes' Buoyancy Principle

Upon uncovering his buoyancy principle, the legendary Greek thinker Archimedes is said to have exclaimed "Eureka!" and dashed unclothed through Syracuse. This momentous find occurred when he observed the water level rise as he entered his bath [source: Quake].

Archimedes' principle of buoyancy states that the upward force on an object submerged or partly submerged in fluid is equivalent to the weight of the fluid displaced. This principle is crucial for density calculations and is fundamental in the design of submarines and various marine vessels.

3: Evolution and Natural Selection

Having explored the foundational ideas about the universe's origins and the role of physics in everyday life, we now shift our focus to the human body and its evolutionary journey. Scientists widely agree that all life on Earth shares a single ancestor. However, to achieve the vast diversity seen in living organisms, some had to evolve into unique species over time.

At its core, this diversification happened through evolution, characterized by descent with modification [source: UCMP]. Organisms developed varied traits via processes like mutation. Traits that enhanced survival, such as a frog's brown coloration enabling it to blend into a swamp, were naturally favored, giving rise to the concept of natural selection.

While these theories can be explored in much greater depth, the essence of Darwin's revolutionary 19th-century discovery remains: evolution driven by natural selection explains the extraordinary variety of life on our planet.

2: Theory of General Relativity

Albert Einstein's theory of general relativity is a pivotal discovery that transformed our perception of the universe. Einstein proposed that space and time are not fixed entities and that gravity is more than just a force acting on objects. Instead, the gravity of a mass warps the surrounding space-time fabric.

To visualize this, picture yourself moving eastward in a straight line across the Earth from a point in the Northern Hemisphere. Over time, your location on a map would show you both east and significantly south of your starting point due to Earth's curvature. Traveling directly east requires adjusting for Earth's shape, much like the difference between a flat map and a globe.

Space operates similarly. For instance, astronauts in a shuttle orbiting Earth might perceive their path as a straight line. In reality, Earth's gravity curves the space-time around them, causing their trajectory to appear as an orbit around the planet. This effect is also seen around massive objects like planets or black holes.

Einstein's theory had profound implications for astrophysics and cosmology. It resolved a small irregularity in Mercury's orbit, demonstrated how starlight bends, and provided the theoretical groundwork for understanding black holes.

1: Heisenberg's Uncertainty Principle

Einstein's expansive theory of relativity provided deeper insights into the universe's mechanics and set the stage for quantum physics. However, it also added complexity to theoretical science. In 1927, this notion of the universe's laws being somewhat flexible led German scientist Werner Heisenberg to a revolutionary breakthrough.

With his Uncertainty Principle, Heisenberg concluded that it's impossible to precisely determine two properties of a particle at the same time. For instance, you can accurately know an electron's position but not its momentum, and vice versa.

Niels Bohr later uncovered a principle that clarifies Heisenberg's findings. He demonstrated that electrons exhibit both particle and wave characteristics, a phenomenon termed wave-particle duality. This concept has become fundamental to quantum physics. When determining an electron's position, it is treated as a particle at a precise location, making its wavelength uncertain. Conversely, when measuring its momentum, it is viewed as a wave, allowing us to determine the amplitude of its wavelength but not its exact position.

Continue reading for more fascinating science content you might enjoy.