The beginning of everything, aka Big Bang!
An introduction to Big Bang Cosmology
Hello Universe!
I’m starting my Medium journey with this post which will talk about the very basics of how the Universe started:
The Big Bang.
First and foremost, I’m not a physicist (sadly) so I’ll explain what the theory says in layman’s words and if you need more info I’m glad to help with some references, just contact me with some comments here and I’ll help as much as possible. In fact, this will be the norm for all my posts.
So, the biggest question for some is “How it all began?”
Others will ask “Why it exists at all?”
These two are very, VERY, different concepts and we will keep focus from now on the HOW and not WHY.
That’s because, on physics, the WHY question about the beginning of the universe is kind of silly, if nothing existed there’s not a why behind it. This question is basically on the metaphysic realm.
“Yeah I understand that, so how has it began?”
Well, there’s a multitude of theories about that. The most accepted so far is the Big Bang Theory — not the series, although it is very good.
The picture below is a graphic on the expansion, temperature and states that our Universe had through the ages.
This is pretty much an image of the Big Bang, the very moment that TIME was created together with SPACE.
That’s why, for example, it is a bit silly to ask “what happened before” because time itself didn’t existed, so there’s no “before”.
Again we are using General Relativity as the basis, Quantum Theory can bring pretty strange and interesting ideas here but, but for now, we will stick with General Relativity.
And why this theory is the most accepted so far? Because we have plenty of evidence that it is correct!
First, it is a prediction of Einstein’s General Relativity, a theory that passed every single test thrown at it so far, so if it wasn’t true General Relativity itself would have problems.
Another big argument for it is the fact that Universe is expanding and with this fact, again with General Relativity as our basis, physicists calculated that the Universe must have been way smaller, an infinitesimal point that we call a Space-Time Singularity — on the moment of Big Bang both density and temperature were infinite.
Finally, we have the Cosmic Microwave Background — CMB for short — which are echoes of the big bang itself.
But what is this CMB and why it matters?
Well, short story is that CMB is a microwave static that permeates all the universe with the same pattern.
If you point a radio antenna to the sky to whatever direction, you will get this static in your signal. This means that the signal source comes from all parts of the Universe with the same intensity.
The graph below shows the CMB spectrum.
CMB source is the Universe itself!
This signal was first discovered by Arno Penzias and Robert Woodrow Wilson by accident when they measured the CMB to be about 3.5K. For this work, they received a Nobel prize in 1978.
Below, you can see an image from the CMB that permeates all the Universe:
The CMB is the echoes of the process that created the first atoms.
During about 300 thousand years after the Big Bang, give or take, the Universe was too hot for atoms to be created, we are talking several hundred thousand degrees here. This state of the universe occurred during the Recombination Epoch of the Universe.
At this epoch the Universe was basically a hot ionised plasma of photons, protons and electrons.
At about 400 thousand years after the Big Bang it started to get colder and when it reached about 3000 degrees, what was previously just a plasma started to become gas and gave the chance for the first Hydrogen atoms to be created.
The CMB is exactly the electromagnetic wave that was generated during this plasma-gas transition that was shifted to microwaves as the Universe got colder and bigger.
The fact that we see this microwave at this temperature and with this spectrum is one of the strongest evidences that gives us confidence that the Universe was smaller and hotter in the beginning and, because of it, that the Big Bang cosmology theory is right.
The actual temperature of the Universe as of now is 2.3 degrees, Kelvin. Yeah, less than 3 degrees above absolute zero!
“OK Diego, the universe is expanding and for that fact, it had to be smaller and that makes a case for a Singularity and Big Bang which is predicted by General Relativity, also CMB is one of the evidence for it. Cool, I get it!”
NICE! That was the very idea of this first post!
“But… what is General Relativity at all?”
Well, that’s our next post!
On that, I will try to explain a bit on what General Relativity is and what it does means and predicts. As this is a very, very bold topic we might need to slit it in parts, so stay tuned!
Please note that I haven’t gone through all the stages that Universe had, according to the Big Bang cosmology theory, as it would need a better understanding of General Relativity and some (a lot) Quantum Theory knowledge as well. I will cover this after some more introductory posts.
For now, just digest this info and stay up for more posts.
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