A Dimensional Guide to the Universe

The Universe is big. Very big. Most of us are aware of the mesmerizingly large world that cradles us in its star dusted arms. All it takes is to look up at the night’s sky to realize what a small speck of existence we are, amidst our mysterious cosmos.

The observable universe is so large that traversing it at the speed of light would take 93 billion years, and by then it might have doubled in size, due to its expanding momentum.

But that’s not the full picture.

The truth is, magnitudes of space entirely incomprehensible to our senses exist right under our noses, and strangely enough, they are more alien to us than our most ambitious astronomical pursuit to the stars.

Before we delve into the intricacies of our reality and its relationship to spatial scale, we must first learn about the four fundamental forces that govern all the interactions around us.

Gravity is the force of attraction between particles of matter.
First modelled by Sir Isaac Newton with this simple description, its approximations were later smoothened out by Albert Einstein’s theory of relativity.
Our current understanding of gravity describes the fabric of the universe as space-time, a 4-dimensional framework constructed of the three spatial dimensions, connected with a time dimension. Space-time is curved by matter, causing the orbit of the celestial bodies, the formation of galaxies, stars and planets.

Gravity is intuitive and satisfying. It dominates at large scales and acts through immensely large distances of space.

Strong Nuclear Force

This interaction is responsible for keeping the fundamental particles: protons and neutrons intact. Through this force, there can exist such a thing as a proton and a neutron, which can be described as the building blocks of matter, along with the electron. Without it, particles would not interact with each other, like a jigsaw puzzle made of incongruent pieces.

Weak Nuclear Force

Constituting the second nuclear force, the weak force describes the mechanism of interactions between particles that causes the radioactive decay of atoms.

Electromagnetic Force

The electromagnetic force is the force of attraction between oppositely charged particles and functions similarly to the gravitational force. The greater the charge, the greater the force; which can be felt throughout an infinite distance in space.
As the name suggests, there are two components to the force: the electric- and magnetic force.
Stationary particles exert the electric component of this force, creating an electric field; but once the particles are set in motion, a magnetic field is generated as well.
This explains why electric wires become magnetic when an electric current flows through them.

Now that we are familiar with the fundamental governing forces, let’s compare their relative effects at different scales.

The Planck Scale (10exp(-35) meters)*

The Planck scale is the smallest possible observable scale in the universe. Below this scale, according to Quantum Mechanics, you wouldn’t be able to predict with any meaningful certainty where any given particle is located.
Here, classical ideas about space and time cease to be valid, and quantum effects dominate. At this scale, the zoomed-out, smoothened view of space-time gives away, and we can observe the granular nature of its fabric. This reality is truly uninhabited, microscopic even in the scope of the building blocks of the universe: fermions and bosons.
This scale is so mind-bogglingly small that we humans are comparatively closer to the size of the observable universe than that of the Planck scale. We might not be as small as we feel after all.

The nuclear scale (10exp(-15) meters)*

At scales the size of a proton, by no surprise, the strong nuclear force dominates. All other forces pail in comparison to the influence of the strong interaction. The relative strength of the fundamental forces are represented below:

The nuclear forces are so insurmountably powerful only at these tiny scales, which makes sense given the size of the particles subject to their influence. In this dimension, reality can only be properly represented with quantum mechanics. Particles don’t interact in the ways we intuit, behaving as packets of energy exchanging their momentum and energy in discrete ways, rather than our fluid and continuous understanding of the world.

The Pico, Nano and Micro Scale (10exp(-12) ➞ 10exp(-6) meters)*

If we zoom out 1000 times, we start to see molecules and the first signs of life: viruses, bacteria and cells. Here, the dominant force is electromagnetic, most commonly manifesting as surface tension molecule attraction. Particles in this scale don’t “fall down” or orbit each other’s nuclei; the presence and exchange of ions drive most of the movement around. Quantum mechanics is still strongly relevant.

The Milli Scale (10exp(-3) meters)*

Here, things start to become familiar to us. From tiny complex life forms such as tardigrades to insects and the smallest vertebrates, this scale is controlled by an equilibrium between gravity and the electromagnetic force.
A ladybug will certainly fall to the ground if swept off a surface but could get trapped inside a water droplet, hanging on the underside of a table.
Here, we can start to picture life as we know it, even if it truly isn’t possible.
A human body at this size would overheat and violently explode in a matter of seconds. This is because our bodies and metabolisms are finely tuned to our size; shrinking us down would decrease our volume more than our surface area, and so would produce too much energy and heat for our cells to bear.

The Astronomical Scale (10exp(3) meters ➞ infinity)*

At the scale regarding celestial bodies, as expected, gravity is at its strongest. Electromagnetic phenomena can be observed, but are all due to gravity itself, such as the radiation of stars. This process is caused by the immense gravitational pressure that hydrogen molecules are subject to in the nucleus of starts, that fuse together and release particles into the cosmos.

The human scale (10(-1) ➞ 10exp(2) meters)*

Finally, we come full circle. This is the spatial scale of reality we inhabit, where kinetics and mechanics obey our intuitions. Where the winning point is scored by an eager and ambitious player, throwing the ball in a perfect parabolic trajectory clean through the net of the hoop. The scale where a ballerina gracefully balances her entire body on the tips of her toes as the audience watches in awe, and where children giggle as they feel the adrenaline-fueled weightlessness of rocking on a swing.
It’s easy to think that our experience is all that the universe has to offer, but taking a closer look at how reality works at different spatial scales can help us broaden our idea of what it means to exist.

*Note on scale dimensions: “exp” refers to exponent. For example, 10exp(-3)= 0.01, 10exp(3)=1000

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