By Brandon Gage

Author’s note: these concepts are incredibly complex, and are generalized for the sake of promoting basic understanding and spurring curiosity.

Number 1: Its origin.

The Universe as we know it began 13.8 billion years ago in an event scientists refer to as the Big Bang. The name, however, is a bit of a misnomer. It was neither big, nor was it a bang, since no space or time existed in which a bang could have taken place. Rather, it was a near-instantaneous expansion of both time and space. The traditional Big Bang theory states that everything, all time, all space, all matter, burst into existence from an infinitely small, infinitely dense point known as a singularity (more on singularities later). But that’s not the whole story.

The true birth of the Universe took place In the first billionth of a billionth of a billionth of a billionth of a second (that’s 0.00000000000000000000000000000000000001 seconds) in what cosmologists call Cosmic Inflation. This “inflationary epoch” lasted until the Universe was 10^-32 seconds old. The primordial Universe was dense and had temperatures of trillions of degrees. In the fractions of fractions of seconds to come, the Universe cooled enough to form quarks, the tiny point-like building blocks of protons. Like quarks, electrons are fundamental. They have no smaller parts. So, that means, that all matter is nothing more than the interactions of 3 quarks and an electron.

As the Universe continued to cool, matter and its mirror-opposite, antimatter, were able to coalesce. After they formed, they immediately began annihilating each other. When the two converge, they convert into pure energy. The reaction is 100 percent efficient.

The Universe went through more changes in its first second of existence than in any other second, and all time, since the Big Bang.

So then why are we here? Because, for reasons that are still unknown, there was an asymmetry in the amount of matter and antimatter that formed in those first few seconds after the Big Bang. For every billion antimatter particles, there was a billion and 1 matter particles. The Universe we know and love is the result of a one-in-a-billion imbalance between matter and antimatter in the first seconds of the cosmos. The result was a hot, dense soup of hydrogen and helium that through gravity, and over time, formed the first stars and galaxies.

Number 2: Its size.

The Universe is huge. Really huge. Like, incomprehensibly huge. Our visible Universe has a radius of 13.7 billion light years. We will never be able to see beyond it, because there hasn’t been enough time for the light from distant galaxies to reach us. Distant galaxies have their own cosmic horizons too. And since the Universe’s expansion is accelerating, our night sky will grow darker and darker, eventually appearing empty in a few billion years. The farther away a galaxy is, the faster it’s moving away from us. This is because dark energy is stretching the fabric of space faster than the speed of light at the edge of the visible Universe.

Consider: a civilization 5 billion years or so into the future looking out into the Universe would have no idea that anything but their own galaxy exists. This was humanity’s assumption less than a century ago before astronomer Edwin Hubble discovered that the Universe was filled with other galaxies. What a lonely place the Universe will be, and what a time it is for us to be alive. We evolved at the perfect time in history for the Universe to figure itself out… and that is exactly what science does. Humans, having evolved from the elements created in supernova explosions of giant stars, are literally the Universe’s way of figuring itself out. And yet, the Universe itself doesn’t know nor care whether we exist or not. We are just the result of complex chemistry and natural selection. Take a moment to consider how profound this truly is.

Because of the effects of inflation, however, the actual radius of the Universe is estimated to be 45-50 billion light years. Which means the diameter is between 90 and 100 billion light years from end to end, in every direction, from every point in the Universe. There is no center, yet anywhere could be considered the center by any observer.

But wait, there’s more (albeit hypothetical but I love huge numbers so bear with me). If the Universe is 100,000,000,000 light years across from every possible point, then we could factor in those extra distances in calculating its true size. So what’s a hundred billion times a hundred billion times a hundred billion (three dimensions, y’all)? A Universe of 10^33 (10,000,000,000,000,000,000,000,000,000,000,000) cubic light years. This number is known as a decillion.

On the smallest scale, however, the Universe consists of a smallest possible length, known as the Planck length. It’s 10^-35 meters, which is 100 billion billion times smaller than a proton. There are more Planck lengths in one meter than there are meters in the entire diameter of the 100,000,000,000 light-year-wide Universe.

Number 3: The Universe is mostly empty space.

It may seem counterintuitive to our everyday experience, but despite the countless stars and the hundreds of billions of galaxies we observe, the density of the Universe is only 5 hydrogen atoms per cubic meter. And at the atomic level, it gets even stranger. Subatomic particles, such as protons, neutrons, and electrons, aren’t solid. They are tiny bundles of energy, that take the form of either particles or waves, depending on if they are observed (more on this later). But the reason you aren’t falling through your chair is due to the repelling electromagnetic force of electrons. They have negative charge, and since negative charges repel each other, it is this effect that gives us the perception of solidity.

Even atoms themselves are mostly empty space. The nucleus, made up of protons and neutrons, is 100,000 times smaller than the atom as a whole; this is like placing a pea in the middle of a Nascar stadium, except as previously mentioned, subatomic particles aren’t solid as we think of it. They are arrangements of spinning bundles of energy, bound together by various forces; the strong force which holds atomic nuclei together, the weak force which is responsible for radioactive decay, electromagnetism, and gravity.

Number 4: We don’t understand what makes up 95 percent of the Universe.

Crazy, right? The matter and energy from which everything we see and experience is comprised accounts for only 5 percent of what’s out there. The rest of it, dark energy and dark matter, account for 70 and 25 percent of everything, respectively. And we don’t yet understand either of them. But we know they are there. Dark matter can be inferred due to its gravitational influence; it’s what holds galaxy clusters together. But it doesn’t interact with light or ordinary matter, hence the name. There are theories as to what it is, but until a testable hypothesis is derived, it’s quite possible it could forever remain a mystery.

Dark energy is what is driving the acceleration of the Universe. Around 5 billion years ago, the Universe’s rate of expansion started speeding up. Why? How? We have no idea. We just know that it is. We can observe this phenomenon in the Universe’s largest structures: cosmic voids between superclusters of galaxies that are expanding, pushing clusters of galaxies farther and farther apart. In fact, figuring out just what exactly dark energy is makes it the biggest mystery in all of cosmology. Oh, and new observations by the Hubble Space Telescope indicate that the Universe is expanding faster than previously thought. Why? Dark energy, maybe. Or possibly a new type of yet-to-be discovered particle.

Number 5: Quantum entanglement.

Quantum entanglement is, perhaps, the strangest property of reality, and one of the least understood. The basics aren’t too hard to understand (just don’t ask “why,” for your own sanity), so here we go.

Basically, quantum entanglement involves two subatomic particles linked in such a way so that when the state, or spin, of one particle is observed or changed, the state or spin of the other changes in the opposite direction. So if one particle is spinning up, the other is spinning down, and if one is changed, the other changes too. Ok, sounds kinda reasonable. Things come in pairs. Cool. Unfortunately, quantum mechanics isn’t friendly to intuition, and no property of nature demonstrates this better than quantum entanglement.

I should note that particles aren’t “spinning” in the traditional sense, but it’s the term that’s used. Until a spin is determined, a particle exists in a “superposition of uncertainty,” meaning it exists in all possible states simultaneously, until it’s measured or observed, at which point its spin just… happens.

Entangled particles will always have opposite spins, no matter what, no matter how far apart they are; even if they are at opposite ends of the Universe. That’s what makes quantum entanglement so difficult to understand. Entangled particles seem to share information faster than the speed of light. And not just a little bit faster in a margin-of-error kind of way. We’re talking quadrillions of times faster. Infinitely fast. Instantaneously, in fact. No matter how far apart entangled particles are, if you change one, the other does the opposite. Always. 100 percent of the time.

This “spooky action at a distance” as Albert Einstein called it has baffled physicists for over a century. Einstein believed that information between particles can never travel faster than light, so somehow, observing a particle and inferring its partner’s spin is merely recognizing information that was already there. Neils Bohr, that other early 20th century genius who gave us the model for the atom, however, disagreed. He believed that the act of observation determined the spin of one particle, thus changing the spin of the other. In other words, the spin of a particle is NOT predetermined; meaning a particle won’t spin up, down, left, right, etc until it’s observed.

Well, in 1964 Irish physicist John Bell performed an experiment that proved that Bohr was right, but only about half-way. It turns out, a particle’s spin is not only determined by observation, but that the spin is apparently chosen, at random, by the particle. Which means that its partner, which could be at the opposite end of the Universe, somehow knows which way to spin even though it has no idea which way its partner will spin in the first place. And again, this information is somehow shared instantaneously.

Let’s break this down into an everyday kinda situation. Pretend you’re sitting in Central Park and with you is a marble in a closed box, whose color is uncertain. Could be red, could be green. You best friend is in Trafalgar Square in London, also with a marble with two potential colors in a closed box. Neither of you have any idea, nor any way of predicting, which color your marble will be when you open the box. And of course, the marbles are entangled for the sake of this thought experiment.

The Central Park marble’s box is opened and the marble appears red. This means that the marble in London will absolutely, positively be green. And vice versa. But there is no way to know which color either will be, until one of them is observed, at which point the color of the other is determined before the box is even opened.

...and this was the simplified version.

Yeah. Weird. Why? Physicists are still struggling with this. We just know that this is what it is. There are many theories as to why particles behave this way, from connections via wormholes, to there being an infinite number of parallel Universes, to the Universe being a computer simulation where time and space are mere illusions (which totally solves this problem, incidentally).

What’s really cool, though, is that quantum entanglement has practical applications, primarily in quantum computers, cyber-security and communication encryption. Using quantum entanglement for security means that system is unhackable, accessible only with a special quantum key, specifically programmed for a particular pair of particles.

Spooky action indeed.

Number 6: Black holes.

Black holes are the remains of giant stars that die in supernova explosions that have so much mass, their cores collapse into an infinitely dense point known as a singularity. Nothing can escape the pull of a black hole, not even light. Black holes are where the known laws of physics break down.

Black holes are everywhere and dominate the Universe. Most black holes have masses from 3 to a few dozen Suns. These are known as stellar mass black holes. There are millions of them in our own galaxy. But the really big ones, known as supermassive black holes, are what holds galaxies together and what may be responsible for the existence of galaxies in the first place.

Supermassive black holes of millions to billions of times the mass of the Sun lurk at the center of every large galaxy. The Milky Way’s central supermassive black hole, Sagittarius A*, has a mass of 4 million Suns. And that’s small compared to some of the real monsters out there. In 2012, the biggest black hole yet discovered weighs in at a gargantuan 17 billion solar masses. Ironically, it sits at the center of a small galaxy, roughly 250 million light years away.

Supermassive black holes at the centers of galaxies that are actively feeding on matter are known as Quasars, and they are the most powerful objects in the Universe. They emit as much energy as a trillion Suns and outshine whole galaxies, and are visible across the entire visible Universe. Their defining characteristics are massive, concentrated jets of energy and charged particles reaching tens of thousands of light years into space.You don’t want to be in the pathway of one of these things.

Since gravity is infinite in the center of a black hole, the closer you get to its edge, known as the event horizon (the point past which nothing can escape), the more time slows down, relative to the observer. So if you and a friend were in space and your friend decided he wanted to jump in, time for him would pass normally as gravity pulls him apart atom by atom in a process known as spaghettification. YOU, on the other hand, would see him approaching the black hole, slower, and slower, and slower, until eventually, it would appear as though he stopped falling in as he approached the event horizon. Time and space are warped so much that it would take an infinite amount of time for you to see him actually fall into the black hole.

Pretty cool right? This time dilation has some serious implications for potential time travel. In theory, like in the movie Interstellar, a spacecraft could use the gravity and angular momentum around a black hole to shoot forward into time, since time would pass slower the closer a traveler is to a black hole (relative to the outside world, of course). Going backwards in time, however, is probably impossible, since you’d have to travel faster than light, and it opens up all sorts of nasty paradoxes that no one would really enjoy dealing with.

Anyway, black holes pose some problems for classical physics, if not solely for the mystery of where stuff goes once it falls inside. Matter, energy, nor information can be destroyed, so they must take some other form, or go somewhere else entirely.

There are a number of theories surrounding what happens to material that falls into a black hole. The holographic principle suggests that the information is encoded on the 2-dimensional surface of the event horizon. Some have theorized that matter that goes down the cosmic drain buds off into a new Universe, creating a new Big Bang. This theory, however, hints at the possibility that our Universe itself exists inside a black hole, which means that all of everything is just an infinitely deep rabbit hole of Universes inside of black holes. I… yeah. But hey, why not.

Since black holes absorb light, we cannot see them directly, but we can infer their existence by what orbits them and the glowing clouds of gas and dust swirling around their event horizons, known as accretion discs. This matter is moving at millions of miles per hour and can reach temperatures of billions of degrees. But like the stars that collapsed to form them, black holes too will one day evaporate due to Hawking radiation (more on this in the final section).

Number 7: Time.

Everyone's an expert on time even though no one knows what the hell it is. Seriously, think about it. What is it? Is it the passage of events? Is it you passing through predetermined sets of events? Is it a countdown to the end of the Universe? Let’s assess.

Time began, we think, at the moment of the Big Bang. We perceive ourselves to be moving through time in a forward direction, known as the arrow of time. But time is a lot stranger that we ever imagined, thanks to Einstein’s theory of special relativity. And, the laws of physics operate independently of time, meaning they can run forwards or backwards. E=MC^2 and the other equations of classical physics do not involve time at all.

First, time ticks at different rates everywhere in the Universe, relative to the observer. The closer you are to massive objects with strong gravitational fields, the slower time appears to pass to the observer. So, technically speaking, your time passes more slowly for your feet than for your head, since they are closer to the Earth. Anything with mass has gravity; galaxies, stars, planets, people, cats, even atoms have gravity.

Second, the faster you travel, the slower time appears to pass to you, rather than an outside observer. Light, having the maximum possible speed in the Universe, experiences no time at all. Time stops when you reach the speed of light.

These are all pretty well-known principles, but what if it’s all wrong? What if time is, in fact, counting down rather than moving forward? This is what the Second Law of Thermodynamics, known as entropy, may suggest. This fundamental law of nature, represented by the equation

S = k. Log W, is immortalized on its discoverer Ludwig Bolzmann’s tombstone.

Entropy states that order will always trend toward disorder. The Universe began as a unified, orderly state, which, over time, becomes more complex and less… orderly. The equation works like this. Entropy is the product of Bolzmann’s constant and the maximum number of possible arrangements of all atoms, over all of time. Yeah, it hurts my head too, but it is what it is. The implications, however, are enormous.

Bolzmann’s equation shows that anything that can happen, given enough time, will eventually happen. Which means that there may be an infinite number of parallel universes in which all possibilities occur, at some point, somewhere.

So how does this relate to time counting down? Well, if the Universe started as a uniform, orderly state, then increasing entropy suggests that time itself is subject to entropy until there is no usable matter, energy or time left in the Universe; meaning the most possible time existed at the moment of the Big Bang, and has been decreasing ever since. So, eventually, there may be no usable time left, because there will eventually be no usable matter or energy. As conscious beings, we may perceive time as moving forward simply because we are observing entropy happen, like watching ice melt. We see it as an event occurring forward in time, but in an objective sense, it’s just disorder increasing.

But wait, there is yet another possibility: that time doesn’t move, we just move through time. In this sense, time is a physical construct, which does sort of make sense considering space and time are interlinked (hence why we refer to it as spacetime).

This implies that all time exists all the time; past, present, and future, all exist simultaneously. We just experience unique individual moments that already exist, and over which we have no control. Think of it as watching a movie. Slow a film down, and each frame is a single moment, contained within it everything in the Universe at that specific point in time. Speed it up, and we see what appears to be events unfolding. Time could be the same thing, in principle… an infinite number of moments, subject to observation.

Oh, and in case you were wondering, there is a minimum length of time, just as there is a minimum length of space. Known as a Planck time, it’s 10^-44 seconds. There are more Planck times in one second than there have been seconds since the Big Bang; by about 20 orders of magnitude. The Universe is approximately 10^22-10^24 seconds old.

Tick tock tick tock tick tock tick tock.

Number 8: The inevitable heat death of the Universe and the end of everything as we know it.

My favorite cosmological topic, mainly because of the incomprehensibly large time scales involved. To understand how the Universe will end, we must go back to the beginning.

The Big Bang occured 13.8 billion years ago and the era in which we live, known as the stelliferous era, in which galaxies, stars, planets and life can form, will last for another 100 trillion years. So in a sense, we exist in what is still the Universe’s infancy (which raises questions about whether or not we are alone in the Universe).

After the last stars die out, the Universe will consist of black holes, black dwarfs, and neutron stars. This is known as the degenerate era. It will last for roughly 10^30-10^60 years, during which all protons and matter will decay into low energy photons of colossal wavelengths. Beyond this point, we enter the black hole era, where all that’s left in the Universe are black holes, slowly evaporating via Hawking radiation. The black hole era extends 10^100, or a googol years into the future, when even the most massive black holes will have evaporated away. The Universe then enters the dark era, where photons gradually lose the last of their remaining energy into the void, leading up to the official end of everything: the heat death of the Universe. The Universe will be 10^1000, or ten trecendotrigintillion (that’s a 10 followed by a thousand zeros) years old. For all intents and purposes, the Universe will be dead. Nothing but the bubbling quantum fluctuations of the vacuum will remain, and even the vacuum itself eventually will fizzle away into nothingness.

The end.