Why is anything here?

The meaning of life, physically speaking

The remnants of a supernova. All that we are is because of these.

If you ever took a philosophy class in your educational journey, or have stared at the night sky, wondering why we are here, tiny motes in an incomprehensible universe, boundless with stars that seem endless, I am here to tell you why this is.

It is not because of God. But it is also not not because of God¹. Just that there is no evidence to support this universe being the brainchild of some supreme all powerful being who plays dice with us.

That said, what we do know, and what is supported by evidence, is that at some point in the past, about 13.8 billion years ago, there was nothing except a singularity.

Then this singularity “blew up²”. This is the “big bang” that you probably have heard of³. From that moment, the universe filled with a very hot plasma⁴ that was basically protons and electrons.

This “gas” or plasma expanded as it was literally millions of degrees in temperature⁵.

Now, as a physics geek, I can assure you that we would like to be able to estimate this expanding gas or plasma to be perfectly uniform (or homogeneous). That means that if you take a cubic meter of it and determine where every particle (proton or electron) is, the distribution would be perfectly uniform. And if you took a second cubic meter of this gas, it would also be the same density (number of particles) and uniformly distributed.

But if that was the case, the universe would be 13.8 billion light-years across, and it would be just this plasma of uniform density.

In short, it would be pretty boring stuff. Since we are here, we know that this assumption is not valid.

So, what did happen?

The inhomogeneity

I am not going to hold back and keep you in suspense. Because the expanding plasma/gas wasn’t uniform and homogeneous, there were local variations. That means that some protons were closer to each other than others. And this is where I get to talk about the miracle of Gravity.

Surely, you have heard of Gravity. It is what Sir Isaac Newton sussed out when one of his daydream sessions under an apple tree was interrupted by an apple falling on his head⁶. We as a species had known about gravity, but Newton was the first to put together a cohesive theory regarding it.

In short, the gravity equation that is the reason why we are here is simply:

\(F = \frac{G m_1 m_2}{r^2}\)

F is the force due to gravity
G is the gravitational constant 6.6743 x 10^-11 m^3/Kg*s^2
m1, m2 are the masses of the two particles
r is the distance between the two particles

It is a really simple equation, but what it tells us is that if two particles are closer together than other particles, they will be more attracted to each other and will begin to move closer together.

Over time, this will lead them to attract more particles, and more particles, creating localized regions where the local density increases. That will lead to ever more increasing in density⁷.

Now over a long time period, this will lead to the agglomeration of huge masses of protons. As they get closer together, and as they get larger, this leads to a second force, the Van der Waals force. As you get these protons closer together, they try to resist getting too close. But gravity will win, and overcome the VdW forces, and at some point, the density will become large enough to ignite a fusion reaction.

Note that at this point, the gas is just protons and electrons. There are no neutrons. They didn’t form until about 380,000 years post big bang when the first stars began to ignite.

Fusion reactions are relatively simple; it takes two protons (at this stage) and combines them into a single atom of Helium. That will be where the neutrons are created, it is proton+proton+proton+electron = Proton-proton-Neutron or Helium. Helium is the second most abundant element in the universe. And it was all created by the fusion of the hydrogen into helium, giving off a bucketload of energy.

Thus, you are seeing how the early stars were formed, and that they produced a lot of helium.

But as a star burns, it exhausts the hydrogen, and once that happens, the gravitational forces continue to mash the atoms closer together. This leads to a cascade of fusion reactions that continue to balance the forces of gravity with the energy output of fusion. Ultimately, this is how we get all the elements up to and including iron (Fe, atomic number 26, atomic weight 55). This is where the energy output of fusing lighter elements to produce heavier elements is less than the energy required to fuse the elements.

Image from the Hubble telescope. In any direction you look, with enough light gathering, you see stars, LOTS and LOTS of stars.

If you surf the literature, you might see references to stars burning oxygen, or calcium. We can see that in their spectrum (that is the light that we see) from the stars. But there will never be any stars burning any heavier elements than iron.

Once a star burns all its iron, it will go nova if it is large enough (our sun is) and expand before cooling off, or it will just begin to cool off and become a cinder.

The universe is littered with these.

But, what about all the heavier elements? Where the heck did they come from?

Well, if a star is large enough, has enough mass, it will not just nova, but will supernova. That is like a super atomic bomb. In this, the energy is large enough to force the fusion to create all the heavier elements. Lead, gold, yttrium, uranium, name it, and it was created in these stars that go supernova.

Literally, all the constituent elements in your body, in your car, in your house, all of it passed through a star.

And that star is the result of the inhomogeneity of the early universe post big-bang.

We are made of star stuff. And that one equation at the top of this is why we are here at all.

Pretty cool, huh?

Got questions? Ask away in the comments.

1. I do not pretend to know beyond what the evidence says, there may be a supreme being, or maybe there isn’t, but if there is, we can’t see it because it was there before the big bang.

2. For want of a better term, “blow up” works here. We weren’t there, but we do no that before that instant, we can’t see. This is why we build ever larger particle colliders in an effort to recreate the energies that existed after the singularity “happened”

3. No, not that shitty TV show.

4. Plasma is just a fancy word for a highly energetic (aka “hot”) gas

5. Fun fact: heat or temperature is a quantification of the motion of the atoms. It is why we can never get to absolute zero, as there is always some wiggling of the subatomic particles, but we can get damn close.

6. Like George Washington and his I can Never Tell A Lie fable, this is also a tall tale, but it is fun, so I will allow it

7. I am eliding on the simplicity of this. It requires some complicated mathematics, lots of 3 dimensional integrals, and nearly infinite calculations. But we physicists are good at scaffolding up to the complex and being able to get close enough to give accurate (enough) results. And explaining stellar formation is one of the great moments of physics.