The Fundamental Forces of Nature

A lot of people think that physics is simply a visible way to understand math; that math is the clockwork of the universe and is capable of predicting future events, explaining past events, and making students contemplate dropping out to become influencers.

Yes, this is partly true - like how the weather forecast said today should be ‘partly’ cloudy. However, if physics were just applied math, some lonely soul could theoretically deduce the entire universe from their basement without ever experiencing it. The problem is, pure math spawns multiple valid versions of reality, yet we’re stuck with just one mysteriously specific universe. It’s simultaneously fine tuned such that tweaking one constant could vaporize us all, yet appears held together by duct tape and academic hubris.

Think of the universe as that ancient TV set from your grandparents’ basement - you know, the one that survived the Cold War and refuses to die. Physicists’ methods are the bizarre ritual required to make it work: three precise slaps to its left side, one whispered curse word, and the remote held at exactly 37 degrees while balancing on one foot during a waxing moon. We accept these absurdities because the alternative - having to unplug and reboot the entire universe - would really ruin everyone’s day.

What I mean by all these absurdities, is that depending on where you look, different rules apply, different numbers pop up, and different characteristics of the universe can be known. As it turns out, I cannot fully describe black holes using only Newtonian dynamics, and I cannot reasonably describe medieval catapults using quantum mechanics.

There are four fundamental forces of nature, and depending on the size of the physical object you are studying, a different force will dominate the regime and demand a particular kind of math. At first glance, the math behind each force appears unique - but that’s just another cosmic prank. Many ‘groundbreaking’

mathematical discoveries were actually hiding inside classical equations all along, like a Trojan horse filled not with Greeks, but with more equations.

But before we look this mathematical gift horse in the mouth and watch in horror as infinite series and tensor calculus spill out, let’s meet our four horsemen of physical reality.

The Four Forces

A force is an interaction that can cause an object to change its motion. Frequently, we think of this as a push or pull, similar to how I might push my freezer door closed after pulling out an unacceptably large quantity of ice cream.

Some familiar forces may be frictional, centripetal, tension, or air resistance. The interesting thing is, all of the forces I listed are different manifestations of the fundamental forces. Similar to how a baker can make bread, cake, or cookies from flour, forces like friction, air resistance, and tension are actually fundamentally just the electromagnetic force. Centripetal force is often gravity, and I’m not sure how many of us think about the nuclear strong and weak forces, but they’re also fundamental ingredients in there too.

Let’s start big.

The Very Big and Very Heavy

If you’ve ever been on a trampoline, then perhaps you remember how differently the fabric sinks when an adult steps onto the trampoline as compared to a small baby. If I were to step onto a trampoline, the fabric would dramatically sag, especially right where I was standing. A baby, however, would barely make a dimple in the fabric. If this baby happened to be finely dressed in a slick leather suit, he would slide right into me, wherever I stood on the trampoline - not that I’ve been conducting such experiments myself, officer.

We see all of this because, as it turns out, I am more massive than a baby. It also turns out that this is a good way to visualize a gravitational field.

All objects with mass “bend” spacetime similar to how I caused the trampoline to bend. For small objects, however, this little bend is such a tiny ‘dimple’ that it can hardly be noticed. When we talk about atoms or electrons, or even something as large as my tub of ice cream from the freezer, it would take an incredibly (perhaps even insanely) precise experiment to measure the gravitational pull that these objects produce.

However, when we scale up to planets, stars, black holes, and galaxies, their gravitational force becomes harder to ignore than that evolutionary experiment growing in your roommate’s mini-fridge.

It is on this large scale that we use Einstein’s theory of general relativity to explain how gravity alters spacetime (the trampoline of the universe).

The Medium Big and Medium Heavy

If we look at protons, electrons, and neutrons, we see that the universe has a mildly divided grocery list. There are positively charged ingredients (protons), negatively charged ingredients (electrons), and the Switzerland of ingredients (neutrons, which carry no charge). This is the realm of the electromagnetic force.

Like a disastrous Thanksgiving dinner, the universe has strict seating arrangements. Protons next to other protons explode apart faster than celebrity marriages, electrons flee from other electrons like nervous teenagers at a dance, and neutrons silently document the drama in their forthcoming ‘tell-all’ memoirs. Positive protons are attracted to negative electrons, which is solid proof that the universe runs on toxic relationships. Neutrons maintain all the social awareness of a goldfish at a NASCAR race.

Electromagnetic forces may be seen plainly or in a more obscured fashion. On a large scale, we can see the electromagnetic force as it runs Earth’s bouncer service (its magnetic field) which keeps out unwanted cosmic radiation while helping lost hikers find their way home.

Yet we also find that the sum of microscopic particle dramas result in what scientists politely call ‘contact’ forces.

Some contact forces, such as the normal force, are like your personal space bubble made physical; charged particles repel one another so you don’t fall through floorboards or walk through walls.

Other contact forces, like friction, are the particle world’s version of that prom date who thinks letting go of your hand voids the laws of physics. In the case of friction, charged particles on two surfaces attract each other and resist an object sliding.

The electromagnetic force, similar to the gravitational force, is present on all scales. The electromagnetic force dominates for interactions that occur on a scale between atoms and planets, but when you reach astronomical distances, gravitational forces become the true powerhouse of the universe.

The Quite Small and Quite Light

Like protons, my mother and I are cursed with an excess of similarities. Some are lovely, while others (including our volcanic tempers, titanium-grade stubbornness, and an arsenal of perfectly flawed arguing techniques) turned my teenage years into a prolonged version of the Spider-Man meme.

In the same way that age and maturity allowed us to overcome the mutual repulsion, the nuclear strong force match-makes similarly charged particles. For instance, though there is electromagnetic hostility between protons, the nuclear force brings the particles together to form stable bonds within atomic nuclei [2]. Without this microscopic peacekeeper, atoms wouldn’t just divorce - they’d shatter into subatomic shrapnel.

The Ridiculously Small and Ridiculously Light

The nuclear weak force acts on an even smaller scale; a range of about 10−17 meters, which is so tiny that even a proton looks like a giant [3]. The weak force is like the universe’s greatest cosmetologist, giving sub-atomic particles extreme makeovers. Through extremely heavy force-carrier particles, the nuclear weak force can completely alter the nature of a particle.

Imagine the nuclear weak force as orchestrating a game of hot potato except the potato has been switched with an adult African elephant. If this elephant were to land in your arms, I think it is safe to say that your physical state of being would undergo a rather extreme and permanent makeover. This is what the nuclear weak force does. For example, a neutron could receive a positively charged W boson (which is about 80 times the weight of a neutron [1]) from a neutrino through the nuclear weak force. This would turn the neutron into a proton and the neutrino into an electron.

It is also the nuclear weak force which enables fusion, which is the process by which stars produce energy and heavier elements [3]. So once again, we must thank the little guy for allowing us to exist and live happy, sun-filled days eating home-grown tomatoes.

References

[1] Improved atlas result weighs in on the w boson. Cern Accelerating Science, Mar 2023. URL: https://home.cern/news/press-release/physics/improved-atlas-result-weighs-w-boson.

[2] Christine Sutton. Strong force. Encyclopedia Britannica, Sep 2024. URL: https://www.britannica.com/science/strong-force.

[3] Christine Sutton. Weak interaction. Encyclopedia Britannica, Sep 2024. URL: https://www.britannica.com/science/weak-force.