About the universe

It's wonderful to have you here! The universe is an incredibly vast and beautiful playground to explore.

To help me tailor our journey through the cosmos, could you tell me a little bit about what interests you most about the universe, and if you have any background in science or astronomy?

I'm interested in how it all started and how big everything actually is.

It is so exciting to explore those exact two questions, because they stretch the human mind to its absolute limits. To kick off our journey, we will follow a simple learning path designed to unpack how the universe is put together, how incredibly massive it is, and where it all came from.

Your path

Our Solar System and Neighbors

Stellar Life Cycles and Galaxies

Cosmology and the Big Bang

What is the Universe

When we talk about the , we are quite literally talking about everything. It is not just the empty space between the stars; it is the entire cosmic tapestry of all space, time, matter, and energy. Every single thing that has ever existed, exists right now, or will exist in the future is a part of it. This includes the tiniest subatomic particles, the phone or computer you are using to read this, all the planets, the , and even the flow of time itself.

Continue to the scale of the universe

The Scale of the Universe

To understand how big everything is, we have to talk about the . This is the portion of the entire universe that we can actually see from Earth today, because light from those distant regions has had enough time to travel to us since the beginning of time itself. The size of this observable bubble is mind-boggling: it is roughly 93 billion light-years across. Because a is the distance light travels in one year (about 5.88 trillion miles), trying to measure the cosmos in miles or kilometers is like trying to measure the distance across the United States in fractions of an inch.

To help us visualize just how much stuff is packed inside this 93-billion-light-year bubble, let's look at how the universe is structured on a giant scale.

Nested concentric circular boundaries representing the cosmic scale of the universe from a human to the observable universe.

I've started setting up a visual tool above to help us compare these scales. Inside this massive space, astronomers estimate there are as many as 2 trillion individual galaxies. Each of those galaxies, like our own Milky Way, contains billions or even trillions of stars. If you multiplied them all out, there are more stars in the observable universe than there are individual grains of sand on every single beach on Earth.

Continue to how the universe started (the Big Bang)

The Origin of Everything

It is so exciting to transition from how big the universe is to how it all actually began! About 13.8 billion years ago, everything that exists today—every speck of matter, every drop of energy, and even space and time themselves—was crushed into an unimaginably tiny, hot, and dense point called a . Then, in an instant, this point began to expand rapidly outward in an event we call the Big Bang. It wasn't an explosion of something into an empty room; rather, it was the rapid stretching of space itself.

Wait, what was there before the Big Bang?

That is easily one of the most profound, mind-bending questions anyone can ask, and it is a topic of intense scientific debate. The short, honest answer from modern physics is: we don't know, and the question itself might not even make sense in the way we think it does. Because the Big Bang wasn't an explosion of matter into existing space, but rather the creation of space and , asking what came "before" the Big Bang might be like asking what is "north of the North Pole." There is simply no direction or dimension there to point to.

At that exact starting moment—the singularity—our current mathematical equations and laws of physics completely break down, leaving us with a beautiful mystery.

Now that we have explored the definition, scale, and origin of the universe, are you ready to continue to our next subtopic and take a closer look at our own cosmic neighborhood, the solar system?