In order to make an apple pie from scratch, you must first create the universe – Carl Sagan

It was Christmas Night and I was sitting in a girl’s apartment. The two of us were on her couch, one of her bare feet was in my hands, and we were talking about – among other things – the things we’d like to know. Languages we’d like to speak fluently, concepts we’d like to understand, disciplines we’d like to master. I listed off Spanish, photography, music – all of which remain on my mental list of ‘someday’.

I said I wished I knew more about physics, and she shook her head.

‘No,’ she said. ‘You’ve lost me there. Metaphysics, yeah. But why physics?’

What I said at the time was that physics is a field I wanted to know more about because everything that happens, large or small, seen or unseen, happens according to the laws of physics; that this invisible force, while it may not always be apparent, governs us nonetheless. It was a statement which was accurate, if hardly poetic.

And then, as conversations do, the conversation moved on to other subjects and different avenues, and the topic of my curiosity about the mechanics of the world was forgotten.

But what I should have said to her then – now that I’ve put some thought into it and found the words I think express it best – is that physics is the language of understanding and answers; it’s the how and the what of the world. It gives us the raw data of life and existence; add human perception to that and you can begin to see that what we all too often take for granted is truly amazing.

What I should have said is this.

You, sitting there, here with me – in chemical terms, you are 65% oxygen, 18% carbon, 10% hydrogen. 3% nitrogen, 1.5% calcium, 1.2% phosphorus. You are sulphur and chlorine and sodium, magnesium and cobalt, zinc and iodine and selenium and fluorine. You’re a woman, so you are, on average, 2.3 grams of iron (as a man, I’m 3.8).

Smaller than this, you are electrons, protons, and neutrons. Even those electrons, protons and neutrons can be further divided down, into leptons and quarks; the smallest building blocks of matter.  This is what you are made from, and you are gravity and electromagnetism and the strong and the weak nuclear force; the four fundamental forces that hold the universe together. And this is not always what you were.

13.73 billion years ago (give or take 0.12 billion years), all there was, everywhere, was a single point. There was nothing else. A singularity; of infinitesimal size, of infinite density and infinite heat. It’s hard to wrap the human mind around this concept; we rebel at trying to consider that everything, everywhere, and everywhen was contained in one indivisible space and time.

And then, in an instant… expansion, and the beginning of everything. Before this moment, there was nothing but this moment. After it, the Universe. And although we don’t know, because our skill doesn’t yet match our curiosity, it’s possible that in this, the moment when time started, those four fundamental forces that keep the Earth turning, that throw shadows behind us when we move through the world, that send quiet ripples across the face of lakes and deepen the sky from blue to black, were one.

This is where cosmic evolution began – the Big Bang kick-started everything that has come since then. With a staggering, omnipotent amount of energy like that released, you get particles being created; brought into existence by sheer force. When people talk about the light of creation, they don’t know just how literal they’re being. Photons, the elementary particle of light itself, flooded through the new-born Universe, a greater pyrotechnic show than any human is ever likely to see. Maybe it will end with a whimper, and maybe it will end with a bang, but it started with light.

Understanding this, how the smallest building blocks of existence inter-relate – this is particle physics, high-energy physics.

There are two laws that become important here. The Law of the Conservation of Energy, and the Law of the Conservation of Mass/Matter. In a closed, isolated system, the sum total of energy doesn’t change. The sum total of mass and matter doesn’t change. Basically speaking, nothing gets in or out – nothing can. Energy may change shape, sure – light a candle and its chemical potential becomes heat and light, clap your hands and kinetic energy becomes sound – but the sum total of energy in the Universe isn’t going anywhere, neither up nor down.

The upshot of this is that all of the matter and the energy in the Universe right now – up to and including the 6.7 x 10 to the power of 27 atoms that are you (that’s 6.7 billion billion billion atoms) were present – if in very different forms – right from the very beginning of everything.

A quick word about your brain.

The human brain is, bar nothing, the most complex and complicated object in human experience. Nothing else comes close. You have 86 billion neurons working away – and an estimated one hundred trillion synaptic connections – inside your head. That’s one hundred trillion connections that flicker on and off with electrochemical energy as you live your life from day to day, that make you who you are. While you study, while you work, while you eat, while you drink, while you sleep, while you wash the dishes or watch TV, these connections are flickering on and off, sending or blocking impulses of thought and reaction.

Now listen carefully.

What all of this means is that while your timelines are vastly different, you and the stars you see when you look up at the night sky were born out of the same instant in space and time. The pieces of you have traveled further distances than you will ever be able to imagine to be here, to be now; they have spun through blinding light and impossible darkness, through gravity and magnetism, riding out the shockwave of creation until this moment.

Your heart beats for the same reason that the ocean tides murmur in and out. You breathe for the same reason that the solar wind sweeps through the space between planets. Your dreams shared their infancy with the sky, and your thoughts are sisters to storms and the sea.

Everything that you are, everything that you’ve done, everything that you will ever be – all of this stems from the single instant in which the Universe began, in light. Whatever else may happen, there is no part of you that is untouched by the truth of this.

This is what physics teaches us, and this is something to be remembered.

Thank you to Laura Spitler at Cornell Astronomy, Sheldon Stone at Syracuse High Energy Physics, and Matthew Kirkcaldie at UTAS Neuroscience for making sure I got my facts straight.