Memory Lane Is a One Way Street

Some people think that college should happen later, when brains are less flighty and more able to bear the weight of their owners’ futures. I don’t know about that — the put-off-college people end to belong to the same camp as the “everyone should major in STEM fields” people — but I do know that my six- and seventeen year-old brain was too flighty to be entrusted with the weight of the universe. By which I mean physics.

If my high school experiences with math and english were formulative — the former handed me chips that I willingly stacked on my shoulders, the latter taught me how to see, through essays I still refer back to — my experiences with the sciences were very nearly a vacuum. On the subject of biology, I can say only that my teacher’s name was Earl King, and that an erkling is an evil goblin who snatches little babies, a fact I learned during a timely Boggle game. Regarding chemistry, I recall monotonous labs whose results I tried to narratively spice up, to the good-humored chagrin of my teacher. Also, the word stoichiometry, but not its meaning. And of physics, all I have is the formula for force, f=m*a. No, I’m lying — I thought it had an x and a v in there!

It’s ironic that I remember so very little of physics when it is memory that caused me to revisit the subject, all these years later. Specifically, I was interested in the effect time going backwards would have on memory. A central conceit of a story I’m working on is that time runs backwards for the human intruders of an aquatic world, causing them to grow younger, which, in turn, allows them to survive underwater1. It’s critical that the characters get physically younger, but I couldn’t figure out how this de-aging would impact their memories. Or, more accurately, I couldn’t figure out if I could justify keeping their memories at least partially intact, as I wanted to do. And so I turned to physics.

Of course, I didn’t know it was physics I was turning to until after I’d googled “if time went backwards memory.” And it wasn’t just physics, it was quantum physics! And so I passed a very enlightening morning learning (or, more likely, re-learning) about, among other things, entropy, the arrow of time, and a very smart and very depressed scientist named Ludwig Boltzmann.

First things first: the scientific explanation for time going forward hinges upon a hypothesis that has not yet been proven.

Let me, ah, try to explain.

At the turn of the 20th century, the aforementioned Boltzmann decided he’d had enough of his colleagues’ “it just is” mentality towards both heat and entropy. Boltzmann postulated that heat was generated by atoms moving around, and that entropy was the number of ways atoms and their energy can be arranged in a system, and that the reason entropy always increases is because there are more ways for systems to become more chaotic than than there are for it to become less chaotic. Eg, in my apartment, there is really only one place the sofa can go and not be in anyone’s way, but there are dozens of places it can go and be in everyone’s way2. Anyways, Boltzmann used the Second Law of Thermodynamics to explain why time only goes forwards: because entropy always increases, the past will always have lower entropy than the future.

If you’re thinking that sounds a bit circular — well, you aren’t alone. Indeed, the atoms whose probabilities of rearrangement compel them, per Boltzmann, from the tidiness of the past towards the future, are governed by laws entirely agnostic to time’s direction. That is to say, it is as equally unlikely for a broken egg (messy) to have ever been whole (tidy) as it is for the egg to unbreak (tidy again).

Boltzmann puzzled over this a lot, and eventually he hypothesized that the reason time goes forward instead of backward is because the universe started out in a state of low entropy. Only he couldn’t prove it — at that point, the universe was another one of those “it just is” existences, and the notion of it starting at all was considered ludicrous, to say nothing of it starting in a state of low entropy. Poor Boltzmann, who, as I mentioned, was not exactly mentally stable, wound up taking his own life because of the damn Past Hypothesis — without its proof, he thought his life’s work was for naught.

It wasn’t of course. History would show him to be right about atoms and entropy, and about the universe having a starting point. Today, most physicists also believe in the Big Bang Theory, which supports the Past Hypothesis: low energy hot dense speck moves to high energy vast, cooler universe (with massive objects, gravity causes wisps to have higher entropy than clumps). Where physicists today get hung up on is why the universe was a low entropy hot dense speck to begin with, as a high entropy hot expanding speck is a much more probable byproduct of a cosmic explosion.

One possible theory is that the low entropy speck that would become our universe was calved off a high entropy multiverse, and that perhaps the speck only looks low entropy because we don’t know what came before it. If this is true, if entropy moved from high to low to high again, then the arrow of time is really more like a circle, with the distant past butting heads with the distant future.3

Calving aside, the explanation for time going forward relies upon the universe being low-entropy at its incipience, and, at a more base level, upon the Second Law of Thermodynamics being unshakeable. In 2009, a physicist by the name of Lorenzo Maccone decided to shake it up.

Maccone figured out that if you apply the principles underlying quantum mechanics (lol not even going to go there) to larger systems, entropy can decrease for certain phenomena, however — and this is where things get very mind-bendy — the process of decreasing will erase any trail of the phenomena’s having happened. So basically, we could turn back time, but if we did, we wouldn’t remember having done so. And therein lies the answer to my initial question. Not the answer I was hoping for, but, I mean, damn! Physics, man.

I’d like to close this post with a shamefaced apology to my physics teacher. Mr. Chiklis, it wasn’t you, it was me. Also, your brother-in-law’s album is … not bad! The “Fame” cover, at least, is worthy of increased entropy.


  1. It’s v good for my current self that my high school self wasn’t able to read that sentence.
  2. This, by the way, is the Second Law of Thermodynamics, and I want to say I knew that when I selected it as the title of my first book. Perhaps I did.
  3. QQ: is philosophy part of advanced physics curricula, and vice-versa?

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