What is the relative size of the universe?

The Universe: Seriously, How Big Are We Talking?

Okay, let’s wrap our heads around something truly mind-blowing: the size of the universe. It’s everything. I mean everything – from the atoms buzzing around inside you to the most distant galaxies we can detect. It’s a lot to take in, right? Trying to picture it all can feel like trying to empty the ocean with a teaspoon. While we can’t know the absolute size (and maybe it’s even infinite!), we can talk about what we call the observable universe. And trust me, that’s already plenty to keep us busy.

Think of the observable universe as a giant bubble with us smack-dab in the center. Since the Big Bang happened about 13.8 billion years ago, light from the farthest reaches has only just had time to reach us. That sets a limit on what we can see, like looking through a peephole in a door.

So, what’s the radius of this cosmic bubble? A cool 46.5 billion light-years. That means the whole thing is roughly 93 billion light-years across! Now, a light-year is already a crazy distance – almost 6 trillion miles. Try wrapping your head around that!

“Observable” doesn’t just mean what we can see with our best telescopes today, either. It’s a fundamental limit, like the ultimate cosmic speed limit signposted by the speed of light itself. Nothing can travel faster, so nothing from farther away could have reached us yet.

And here’s where it gets even weirder: the universe isn’t sitting still. It’s expanding, like a balloon being inflated. This expansion has been going on since the Big Bang, and it’s still happening now. This stretches the distances involved. So, those objects that emitted the light we’re seeing now, 13.8 billion years ago? They’re now a whopping 46 billion light-years away because the universe has been expanding the whole time!

Scientists use something called the Hubble constant to describe how fast the universe is expanding. It’s roughly 73 kilometers per second per megaparsec (a megaparsec is about 3.3 million light-years). Basically, the farther away something is, the faster it’s moving away from us. Fun, right? Actually, the exact value of the Hubble constant is a bit of a headache for cosmologists. Different ways of measuring it give slightly different answers, leading to what they call the “Hubble tension.” It’s like two different road crews using different measuring tapes!

What about beyond our observable bubble? Well, that’s where things get really speculative. The truth is, we simply don’t know. The universe could be much, much larger than what we can see, or even infinite. Some areas are just too far away for their light to have reached us yet.

There’s this idea called cosmic inflation, which suggests the universe went through a period of incredibly rapid expansion in its earliest moments. If that’s true, the entire universe could be mind-bogglingly huge – maybe 1.5 x 1034 light-years across. That’s like, 3 x 1023 times the radius of the observable universe. My brain hurts just thinking about it!

Okay, let’s try some comparisons to bring this down to Earth (pun intended!). Imagine the Earth as a tiny grain of sand. On that scale, our entire solar system would only be about the size of a quarter.

Now, picture the observable universe as a football field. On that scale, our entire Milky Way galaxy would be just a grain of rice. And our solar system? Forget about it – it would be way too small to even see.

One more: Think of the Burj Khalifa, the tallest building in the world. If the observable universe were as tall as that building, the Milky Way would only be 1 millimeter tall. And our solar system? A thousand times smaller than a grain of sand. It’s just bonkers!

The observable universe contains an estimated 2 trillion galaxies, and each of those galaxies contains billions or even trillions of stars. Some estimates put the total number of stars in the entire universe as high as 10100. That’s a 1 followed by 100 zeros. Seriously, numbers don’t even seem real at that point.

And let’s not forget the cosmic microwave background (CMB). This is basically the afterglow of the Big Bang, the oldest light in the universe. It was released about 380,000 years after the Big Bang when things had cooled down enough for atoms to form. It’s like a faint hum coming from every direction in space, and it gives us valuable clues about the early universe.

So, where does all this leave us? Well, the universe is unbelievably, mind-bendingly huge. The observable part alone is 93 billion light-years across, and the total universe could be much, much bigger, maybe even infinite. As we keep exploring with better technology, we’ll keep learning more. And who knows? Maybe one day we’ll finally get a handle on just how big “everything” really is. Until then, I’m happy to just stare up at the night sky and feel a little bit awestruck.