Question: 1 What is the universe made of?

Luke Humphrey answered on 22 Mar 2022:

Great question DerrekO!

I can answer this from a nucleosynthesis point of view…

The short answer is:
the universe is made of elements. The basic hydrogen & helium was created during the big bang, most light elements were formed by nuclear fusion in the cores of stars, and most heavy elements were formed during the supernovae at the end of star’s “lifecycle”. Some rare elements are formed by rarer processes, generally astrophysical in nature. A very small amount are created by humans in a lab.

This image shows the periodic table and uses colours to show the origins of the elements:

The long answer is:
The furthest back in time we know about is the Big Bang (aka “Cosmic Egg”). At this time, the universe was a singularity, a single point. We know that space-time expanded from this point and it’s still expanding today. The first moments were really complicated, with really strange concepts like the four fundamental forces (electromagnetism, gravity, and the strong and weak nuclear forces) coming into being. You’d have to ask a specialist about the details!

Just a few seconds after the big bang, the universe was composed entirely of hot plasma, like the stars are today. In this plasma, you had about 75% hydrogen and 25% helium. Hydrogen (1 proton) is the simplest element, which formed naturally as the universe cooled and expanded to allow elements to form. All other elements are made by nuclear reactions, the 25% helium (2 protons) was formed by fusion of hydrogen in the time where the universe was cool enough for elements to form, but hot enough for them to fuse.

At this part of the timeline, the universe was expanding and cooling down and fusion could no longer take place in outer space. As spacetime expanded, matter started to clump closer together due to gravity (the force that pulls all masses together, the same force that pulls us to the ground, and pulls the earth orbit to the sun).

Matter clumping together eventually formed stars, and more and more matter clumped onto these balls, the cores began to get compressed more and more until they once again became plasma, and hydrogen could fuse into helium. Stars generally fuse light elements into heavy ones, releasing energy in “hydrostatic equilibrium” which means they make enough energy to keep their shells from collapsing in on themselves due to gravity. Once they run out of hydrogen, they start fusing the helium they just made into even heavier elements, and so on up to iron (26 protons).

When a star dies, it releases all the elements it made out into space, which then mixes with matter from other exploding stars and clumps together again. The process repeats into generations of stars. Our sun is a 3rd generation star, so it’s grandparents were the first stars!

The matter that makes up the sun, the planets, earth and everything on it, including yourself, originally came from exploding stars.

If you want to push your question further, you could ask what elements are made of. This enters the realm of quantum physics. There’s no easy way to explain any of this, but I like to think of it this way: just as throwing a rock in a pond leads to ripples that die down into stillness. The big bang created ripples in spacetime which are the universe. Our ultimate fate is stillness, what scientists call the “heat death of the universe”: when all matter is in perfect equilibrium and nothing changes any more. In between is life, the universe, and everything.