Four Fundamental Forces of Nature

The Four Fundamental Forces of Nature

As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you. A force is defined as a push or pull that changes an object’s state of motion or causes the object to deform. Newton defined a force as anything that caused an object to accelerate — F = ma, where F is force, m is mass and a is acceleration.

The familiar force of gravity pulls you down into your seat, toward the Earth’s center. You feel it as your weight. Why don’t you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat. Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen.

Gravity and electromagnetism are just two of the four fundamental forces of nature, specifically two that you can observe every day. What are the other two, and how do they affect you if you can’t see them?

The remaining two forces work at the atomic level, which we never feel, despite being made of atoms. The strong force holds the nucleus together. Lastly, the weak force is responsible for radioactive decay, specifically, beta decay where a neutron within the nucleus changes into a proton and an electron, which is ejected from the nucleus.

Without these fundamental forces, you and all the other matter in the universe would fall apart and float away. Let’s look at each fundamental force, what each does, how it was discovered and how it relates to the others.

Gravity

The first force that you ever became aware of was probably gravity. As a toddler, you had to learn to rise up against it and walk. When you stumbled, you immediately felt gravity bring you back down to the floor. Besides giving toddlers trouble, gravity holds the moon, planets, sun, stars and galaxies together in the universe in their respective orbits. It can work over immense distances and has an infinite range.

Isaac Newton envisioned gravity as a pull between any two objects that was directly related to their masses and inversely related to the square of the distance separating them. His law of gravitation enabled mankind to send astronauts to the moon and robotic probes to the outer reaches of our solar system. From 1687 until the early 20th century, Newton’s idea of gravity as a “tug-of-war” between any two objects dominated physics.

In his general theory of relativity, Albert Einstein envisioned gravity as a distortion of space caused by mass. Imagine that you place a bowling ball in the middle of a rubber sheet. The ball makes a depression in the sheet (a gravity well or gravity field). If you roll a marble toward the ball, it will fall into the depression (be attracted to the ball) and may even circle the ball (orbit) before it hits. Depending upon the speed of the marble, it may escape the depression and pass the ball, but the depression might alter the marble’s path. Gravity fields around massive objects like the sun do the same. Einstein derived Newton’s law of gravity from his own theory of relativity and showed that Newton’s ideas were a special case of relativity, specifically one applying to weak gravity and low speeds.

When considering massive objects (Earth, stars, galaxies), gravity appears to be the most powerful force. However, when you apply gravity to the atomic level, it has little effect because the masses of subatomic particles are so small. On this level, it’s actually downgraded to the weakest force. Let’s look at electromagnetism, the next fundamental force.

Electromagnetism

If you brush your hair several times, your hair may stand on end and be attracted to the brush. Why? The movement of the brush imparts electrical charges to each hair and the identically charged individual hairs repel each other. Similarly, if you place identical poles of two bar magnets together, they will repel each other. But set the opposite poles of the magnets near one another, and the magnets will attract each other. These are familiar examples of electromagnetic force; opposite charges attract, while like charges repel.

When scientists worked out the structure of the atom in the early 20th century, they learned that subatomic particles exerted electromagnetic forces on each other. For example, positively charged protons could hold negatively charged electrons in orbit around the nucleus. Furthermore, electrons of one atom attracted protons of neighboring atoms to form a residual electromagnetic force, which prevents you from falling through your chair.

But how does electromagnetism work at an infinite range in the large world and a short range at the atomic level? Physicists thought that photons transmitted electromagnetic force over large distances. But they had to devise theories to reconcile electromagnetism at the atomic level, and this led to the field of quantum electrodynamics (QED). According to QED, photons transmit electromagnetic force both macroscopically and microscopically; however, subatomic particles constantly exchange virtual photons during their electromagnetic interactions. But electromagnetism can’t explain how the nucleus holds together. That’s where nuclear forces come into play.

The Strong Nuclear Force

The nucleus of any atom is made of positively charged protons and neutral neutrons. Electromagnetism tells us that protons should repel each other and the nucleus should fly apart. We also know that gravity doesn’t play a role on a subatomic scale, so some other force must exist within the nucleus that is stronger than gravity and electromagnetism. In addition, since we don’t perceive this force every day as we do with gravity and electromagnetism, then it must operate over very short distances, say, on the scale of the atom.

The force holding the nucleus together is called the strong force, alternately called the strong nuclear force or strong nuclear interaction. In 1935, Hideki Yukawa modeled this force and proposed that protons interacting with each other and with neutrons exchanged a particle called a meson — later called a pion — to transmit the strong force.

In the 1950s, physicists built particle accelerators to explore the structure of the nucleus. When they crashed atoms together at high speeds, they found the pions predicted by Yukawa. They also found that protons and neutrons were made of smaller particles called quarks. So, the strong force held the quarks together, which in turn held the nucleus together.

The Weak Nuclear Force

One other nuclear phenomenon had to be explained: radioactive decay. In beta emission, a neutron decays into a proton, anti-neutrino and electron (beta particle). The electron and anti-neutrino are ejected from the nucleus. The force responsible for this decay and emission must be different and weaker than the strong force, thus it’s unfortunate name — the weak force or the weak nuclear force or weak nuclear interaction.

With the discovery of quarks, the weak force was shown to be responsible for changing one type of quark into another through the exchange of particles called W and Z bosons, which were discovered in 1983. Ultimately, the weak force makes nuclear fusion in the sun and stars possible because it allows the hydrogen isotope deuterium to form and fuse.

So those are the four forces — gravity, electromagnetism, the weak force and the strong force. Science continues to work toward understanding how these forces related, and to strive to assemble a “grand unified theory of everything”. But let’s first ask where did these four forces come from and when. Is the Theory of Evolution any help? Absolutely not. It doesn’t even get a chance to apply until life has already started and gotten to the stage where it can successfully reproduce using DNA.

Did these four forces come about after the origin of the universe? Nope. Most scientists accept the “Big Bang” as the starting point of the universe. But without the four forces, there could be no universe. Therefore, the four forces had to exist before the universe when there was nothing. We could try to say they came about at the same instant as the universe exploded into being, but we still have to conclude that the four forces were “there” somehow BEFORE the explosion.

Watch and listen to Gerald Schroeder, doctorate in physics from MIT, points out these facts in a video:

Consider the Characteristics of the Four Forces:

They are “omnipresent”, meaning that the effect of the forces can be felt everywhere. In America, Africa, Europe, and the world over. At the top of the tallest building, and at the lowest point of the earth. They present everywhere in the universe, and although they are not physical, they operate ON the physical
The forces are also “invisible”. We experience the effects of the forces, but cannot see the forces themselves. They are outside the domain of time, space and matter, which we all live in. We are contingent on these laws – they are NOT contingent on us.