Did the universe start with a Big Bang?
No. This is one of the most misleading scientific terms out there. It wasn't Big (at the start) and it wasn't a Bang.
But the Big Bang Theory is the leading explanation for how our universe began.
What is the Big Bang Theory?
Under Big Bang Theory, the universe began around 14 billion years ago. At that time, the entire universe was squashed inside a single point called a singularity. This singularity was infinitely small and infinitely dense.
Then the singularity inflated. It inflated with such incredible speed that the universe went from existing as a singularity to creating particles such as protons and neutrons in just one second.
Over the next 14 billion years this singularity expanded to form the universe as we see it today.
Explaining this expansion is tricky. It's like the galaxies are currants in a lump of dough. When you bake the dough, the currants move further apart as the dough (space) expands.
Let's look at a Lego example. Ironman is baking Batman a birthday cake with yellow currants and black dough. This expansion would look a little something like this:
As a side note, Ironman sucks at baking.
How do we know the Big Bang theory is right?
We don't. But there are several key pieces of evidence that the Big Bang theory is correct.
First, there's something called the Cosmic Microwave Background Radiation. This is the afterglow of the expansion of the early universe where microwaves are coming from every direction in space. The Big Bang Theory is the only theory to explain its presence.
Second, the further away a galaxy is from us, the faster it is moving away from us. Everything is moving away from everything else. If we went back in time everything would eventually be squashed together into one incredibly dense point - or a singularity. This is one of the key concepts of the Big Bang Theory.
Also, the more distant a galaxy is, the longer its light takes to reach us (because the speed of light is finite). When we look at these distant (seemingly younger) galaxies, they look very different from closer (seemingly older) galaxies. This suggests the universe is evolving - which does not match one of the leading contenders to Big Bang Theory (Steady State Theory). But this evolution of galaxies does match the Big Bang Theory.
Finally, the observed proportions of elements such as hydrogen, helium and lithium in the universe match the predictions of the Big Bang Theory.
So, there we go. The Big Bang is less of a cosmic explosion, and more of an "Everywhere Stretch". But I suppose that's not as catchy a name, is it?
Extra reading and watching
Professor Stephen Hawking's 1996 lecture "The Beginning of Time" describes the Big Bang in more detail, as does this article from CERN and here's another more summary of the Big Bang from Space.com. If you're interested in the Big Bang alternatives out there, click here.
Finally, here's a video explaining the basis of the Big Bang:
What is Sunday Science?
Hello. I’m the freelance writer who gets tech. I have two degrees in Physics and, during my studies, I became increasingly frustrated with the complicated language used to describe some outstanding scientific principles. Language should aid our understanding — in science, it often feels like a barrier.
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