The Big Picture
So, the story of everything begins with what we call the Big Bang. It’s this idea that the universe didn’t just always exist forever, but that it was suddenly born.
Back up to the middle of the 20th century, most scientists actually thought the universe was infinite and ageless. But then, things started changing.
- Einstein’s theory of relativity came along and gave us a much better handle on gravity.
- Then, Edwin Hubble made a huge discovery: he found that galaxies are moving away from each other in a way that lined up with predictions made earlier.
- Later, in 1964, and get this, totally by accident, cosmic background radiation was found. Think of it as an echo, a relic from the very early universe.
This radiation, plus other things we’ve seen, really made the Big Bang the theory that science accepted.
Since then, better tools, like the Hubble telescope, have helped us get a pretty good look at the Big Bang and how the cosmos is put together. What’s wild is that recent observations even seem to hint that the universe isn’t just expanding, it’s accelerating its expansion!
But how did this whole Big Bang thing even happen? How could something possibly come from nothing? Let’s dive into what we actually know about it. We can leave that absolute “beginning part” aside for a moment.
What Was the Big Bang?
First off, let’s clear something up: the Big Bang was not an explosion like a bomb going off.
Instead, it was all of space stretching everywhere all at once.
The universe started out incredibly, incredibly tiny, and then very quickly ballooned up to about the size of a football.
Here’s a mind-bender: the universe didn’t expand into anything. Space was just expanding into itself. The universe can’t expand into something else because, by definition, the universe has no borders. There’s simply no “outside” the universe. The universe is everything there is.
The Universe’s First Seconds
In this early, super hot, and super dense environment, energy wasn’t just sitting around. It was so intense that energy actually showed up as particles, but these particles only existed for the absolute shortest moments of time.
- Gluons would create pairs of quarks.
- These quarks would immediately destroy each other, maybe spitting out more gluons as they did.
- These gluons and maybe other quarks would then find other short-lived quarks to bump into, forming new quark pairs and gluons all over again.
It was so hot that matter and energy weren’t just theoretically linked, they were practically the same stuff.
Somewhere around this chaotic time, something crucial happened: matter won out over antimatter. Today, that’s why we’re left with almost all matter and hardly any antimatter at all. It worked out so that for every one billion particles of antimatter, somehow one billion and one matter particles were formed.
Also, instead of one big, ultimate force running the show in the universe, there were now several slightly different versions of it, each acting under its own set of rules.
By now, the universe had stretched out to about a billion kilometers across. This spreading out caused the temperature to drop. And because it cooled down, that cycle of quarks being born and then turning back into energy suddenly stopped. From this point on, the universe pretty much had to work with the particles it had.
Quarks then started joining up to form new types of particles called hadrons, things like protons and neutrons. There are actually tons and tons of ways quarks can combine to make all sorts of hadrons, but only a very small number of them are stable enough to stick around for any real length of time.
Seriously, just take a moment to appreciate this: by this point, only one second has passed since the very beginning of everything.
From Soup to Atoms
Fast forward a little bit. The universe has now grown to a massive one hundred billion kilometers across. It’s also gotten cool enough – down to about ten billion degrees Celsius – that most of the neutrons decay into protons, and the very first atom can form: hydrogen.
Picture the universe at this stage like an incredibly hot soup, absolutely packed with countless particles and energy zipping everywhere.
Over the next few minutes, things cooled down and settled really, really fast. Atoms started to form out of hadrons (like protons and neutrons) and electrons. This created an environment that was much more stable and didn’t have an electrical charge overall.
Some folks call this period the Dark Age. Why dark? Because there weren’t any stars yet, and that neutral hydrogen gas floating around didn’t let visible light travel freely. But really, what would visible light even mean back then anyway, when there wasn’t anything alive with eyes to see it?
Finally, There Was Light
After millions of years, that hydrogen gas started to clump together. Gravity pulled it tighter and tighter, putting it under immense pressure. Eventually, stars and galaxies began to form inside these clumps.
The intense radiation coming from these newly formed stars then did something important: it dissolved the stable hydrogen gas back into a charged state called plasma. This plasma is what still fills the universe today, and crucially, it allows visible light to pass through.
So, finally, after the Dark Age… there was light!
The Part We Don’t Understand
Okay, but what about that part right at the very, very beginning? The bit we skipped over for a minute? The part that could technically be defined as the Big Bang itself?
Here’s the honest truth: we don’t know at all what happened right then.
At this point, the tools we have – our current understanding of physics – completely break down. The natural laws that we’re used to just stop making sense. Time itself gets, well, a bit wibbly-wobbly.
To truly understand what went on in that initial moment, we desperately need a theory that can successfully combine Einstein’s theory of relativity (which handles the big stuff like gravity) with quantum mechanics (which handles the tiny stuff like particles). Countless scientists are working hard on this right now.
But this leaves us with a bunch of really big questions we can’t answer yet:
- Were there universes before ours?
- Is this the very first and only universe?
- What actually kicked off the Big Bang? Or did it just happen naturally, based on laws we haven’t even figured out yet?
We just don’t know. And maybe, just maybe, we never will.
Where We Fit In
But here’s what we do know for sure: the universe as we recognize it started here. And from that beginning, it went on to create particles, then galaxies, then stars, then planets like Earth, and eventually… you.
Think about it: we ourselves are made of stuff that was forged inside dead stars. So, we’re not really separate from the universe at all; we’re actually a part of it. You could even look at it this way: we are the universe’s way of getting to experience itself.
So, let’s keep experiencing it, and keep asking those questions, maybe until there are no more left to ask.
More Information
This explanation came from the video at this link: Video URL: https://www.youtube.com/watch?v=wNDGgL73ihY
The subtitles were created by the Amara.org community.