Chapter 1: The Magnitude of the Universe

When we consider how far galaxies can be, often stretching millions of light-years away, it's easy to feel overwhelmed. Let's delve into the true enormity of the Universe.

How often have you heard that the Universe's scale is astonishingly immense? Scientists continue to debate whether it might be infinite, but given light’s maximum speed, this speculation is somewhat moot. The portion we can observe, known as the 'visible Universe,' is so expansive that it challenges our ability to comprehend its billions of light-years width. It's time to step back from our immediate surroundings, view the broader cosmos, and appreciate how minuscule we are in comparison to this vast arena where we live our lives.

To start, let's focus on something familiar: Earth. This large, water-covered planet is home to a diverse array of life forms, with the notable exception of a select few astronauts orbiting it aboard the International Space Station (ISS), which is just 408 kilometers above the Earth's surface.

To better understand Earth's dimensions, consider this: the planet has a diameter of 12,742 kilometers (7,917.5 miles) and a circumference of 40,075 kilometers (24,901 miles). These figures can be hard to visualize, so let’s provide a relatable analogy. If the entire population of Australia, approximately 25.5 million people, lay down in a straight line, their combined height would circle the equator. In fact, we would have enough people for an extra million! If we performed the same exercise with the population of the USA, they would wrap around Earth more than 13 times.

Still struggling to grasp the scale of our beautiful planet? If you could drive around the Earth non-stop at a speed of 70 mph (112.7 kph), the journey would take you 14 days, 19 hours, and 35 minutes — and that’s without any breaks!

All of human and natural history has unfolded on this planet, which feels like an endless expanse of mountains, oceans, and coffee shops that we call home.

Next, as we continue to zoom out, we encounter the Solar System, which encompasses Earth, numerous other planets, a variety of asteroids, and many comets, all orbiting our fiery star.

The Solar System's boundaries are somewhat vague because any object orbiting our Sun could technically be considered part of it. We have yet to explore the farthest reaches to discover what distant objects might be there. Currently, the farthest confirmed object from the Sun is the dwarf planet Sedna. While the existence of the Oort Cloud is debated, it is thought to be further away.

Sedna follows a highly elongated orbit that takes 11,400 years to complete. At its closest, it is 73 times farther from the Sun than Earth (73 AU), and at its most distant, it could be as far as 900 AU from the Sun—an incredible 130 billion kilometers (80.77 billion miles) away. If we define the Solar System's edge at this distance, we confront a truly staggering scale.

If you were to travel from Earth to this boundary at the maximum speed ever attained by humans—24,791 mph (39,897 kph) achieved by Apollo 10 astronauts—it would take almost 385 years to reach the edge of the Solar System. To arrive there today, you would have needed to leave Earth in 1635 when Charles I was king of Britain and colonization of Connecticut was just beginning.

However, since few of us experience such speeds, let’s consider a more realistic scenario: traveling in a Boeing 747–8i at 659 mph (1,060.5 kph). This journey would take nearly 14,477 years. To arrive today, you would have had to depart Earth around the time agriculture was first developed. So, if you're planning a trip to Sedna, you might want to start saving your air miles!

Next in our cosmic journey is our galaxy, the Milky Way, which spans approximately 105,700 light-years across—a substantial leap from our Solar System.

Imagine lining up 372 million Solar Systems in a row; that’s equivalent to the width of the Milky Way. This number exceeds the total users on Twitter (330 million, at the time of writing).

If we apply the same analogy to Earth, we’d require 78 billion of them—roughly equal to the total number of garments purchased worldwide each year.

Clearly, the idea of traversing the Milky Way in a rocket ship is impractical, as it would take eons to accomplish. The only conceivable method for humans to cross it might involve wormholes, whose existence remains hypothetical.

The Milky Way is not just vast; it contains around 250 billion stars, nearly double the number of mammals on Earth (130 billion). These stars are all situated more than five light-years away from us, making our cosmic neighborhood feel spacious, but not overcrowded.

But this is merely our galaxy. In the observable Universe, it is estimated there are around 2 trillion galaxies, with an average distance of 9.9 million light-years between them. These figures can be overwhelming, so let’s seek some perspective.

This number of galaxies is comparable to the number of cells in a newborn baby, with human cells averaging about 100 micrometers in size. Unlike the cells in a newborn, however, these galaxies are notably spaced apart, with enough distance to fit 93 Milky Ways in a row with room to spare.

So, while the Universe is filled with galaxies, it is still far from being cramped. Now, let’s consider the most distant object we can observe. How far away is it?

The most distant known galaxy, GN-z11, lies 31.96 billion light-years from Earth. This might seem perplexing since the Universe is 13.8 billion years old, suggesting that light could only have traveled 13.8 billion light-years in that time. So how can we see an object 31.96 billion light-years away?

To clarify, we don’t actually see the galaxy from that distance. GN-z11 formed just 400 million years after the Big Bang, and the light we observe has been traveling for 13.4 billion years. Since then, the galaxy has moved away due to the expansion of space. Thus, what we see is an ancient image of the galaxy, which is now 31.96 billion light-years distant.

This galaxy is so far removed that we could fit 302,365 Milky Ways between us and it—an equivalent to the current population of wolves (wild and captive) or the number of grains of rice in a 5.5 kg bag.

What about the theoretical limit of the visible Universe? Given that the Universe is 13.8 billion years old, one might assume it would be 13.8 billion light-years wide. However, as GN-z11 illustrates, due to the expansion of space, the farther we look into the cosmos, the further back in time we perceive. Consequently, the theoretical size of the visible Universe is much greater than 13.8 billion years.

After crunching the numbers, the diameter of the visible Universe measures around 93 billion light-years. However, we cannot 'see' objects that far. To observe something 93 billion light-years away, its light must have been emitted at the time of the Big Bang, and unfortunately, nothing emitted light during that early epoch.

So how immense is 93 billion light-years? We could fit 880,000 Milky Ways side by side across the diameter of the visible Universe—similar to the population of Jacksonville, Florida, or the total number of African buffalo alive today.

If we replaced Milky Ways with Earths, we would need 68.6 quadrillion of them. To put that staggering number into perspective, that’s the equivalent of the number of molecules inhaled over a two-day period.

Thus, we’ve explored the staggering scale of the Universe. After our cosmic journey, I can't help but feel incredibly small. Yet, take comfort in the knowledge that this vast and diverse Universe still holds a unique place for each one of us.

This first video titled "How big is the universe ... compared with a grain of sand?" delves into the comparative scales of cosmic distances, helping to visualize just how vast the Universe truly is.

The second video "How Large is the Universe? Bigger than you can Imagine?" further explores the mind-boggling dimensions of the Universe, offering insights that stretch the limits of our imagination.