Three problems with the science of The Tomorrow War

Here are three problems I have with the science of The Tomorrow War:

1: On the proper use of time travel

Time travel requires the creation of a closed timelike curve (CTC): a closed loop in which spacetime returns to the starting point.

Let’s assume that a CTC is possible (an open question in physics), and it allows a single signal (yes=signal, no=no message) to be sent to a time machine that’s already operating, after which the connection ends. What can be done with this low bandwidth connection?

Say your goal is to win the lottery. You start your chrono-receiver and buy a lottery ticket. If you win, you send a yes. If you don’t get a signal, you increment the lottery number and try again. Even if your chance of winning is 1 in a billion, you will eventually get to the correct number.

What do you do after winning the lottery? Solve the next problem. Anything that is physically possible for you to becomes trivial given enough attempts. You just need to build an Ideal Solution Database (ISD) to keep track of successes and ensure each attempt is unique. You are using the CTC to perform computation on an infinitely powerful computer. You can’t go back to before the time machine was invented (that’s how a CTC works), but you can optimize your action post-creation to achieve any and all outcomes that are physically possible. (If this is confusing, watch the Rick and Morty episode “Edge of Tomorty: Rick Die Rickpeat”)

Where does the energy for this process come from? Where does the entropy go? From a thermodynamic perspective, time travel is problematic, whether you want one trip to make sure your parents have that first date, or a quintillion trips to become God-Emperor of Earth.

So this is the basic problem with all time travel in fiction. Even if you don’t set out to create the ISD, the temptation of optimizing any action leads toward the creation of an ISD. As each goal is achieved, the next goal is brought forward in time. The only limitation is the time to record each goal in the ISD, and the process can be used to optimize the ISD too. History compresses into a singularity and the flow of time as we know it ends.

While the time loops may be infinite, the ISD calculations and actions still generate entropy, so the ISD civilization has an expiration date. Assuming the civilization remains in a particular area of space (such as a solar system), it will perform all work possible until reaching heat death. From the perspective of an outside observer, the ISD civilization accelerates to a singularity, then vanishes.

If a CTC is impossible, what’s the point of this speculation? All intelligence tries to approximate a CTC+ISD. When you try to throw a basketball into a hoop, you first create a simple model universe in your mind that simulates the trajectory of the ball, then test the hypothesis by shooting the ball. You repeat the process, using simulation and testing to perfect the ISD in your mind. All intelligence works by running simulations, testing them, then creating a solutions database from the results. Unlike a CTC, each iteration has takes time and uses energy. To minimize this cost of simulation, civilizations are likely to trend to ever more efficient computing, bound only by Landauer limit, the theoretical lower bound on energy consumption.

Currently, we recognize a big difference between simulations (whether in our mind, computer software, or a physical system, such as a wind tunnel) and reality. However, a future civilization which exist entirely as software, and may convert the fabric of reality into computational substrate (aka comptutronium) may not recognize such a distinction. If the Landauer limit is somehow overcome, future civilizations will achieve what is effectively a CTC+ISD.

#2: On the threat of invasive species

Earth already experienced a great extinction from an invasive species 2.4 billion years ago that killed 99% of all life on earth. It produces a chemical that was highly toxic to nearly all other lifeforms. That phylum is still the most plentiful lifeform on earth. (That chemical is oxygen and the lifeform is cyanobacteria.)

Today, we are still dealing with lifeforms that are constantly trying to convert the entire biomass of the planet to copies of themselves.

Can you guess what that lifeform is? It’s every single living organism, from the smallest bacterium to us humans. Every organism has evolved over billions of years to optimize the conversion of inorganic matter and other living organisms into copies of itself. The introduction of a new, alien species that dramatically outcompetes other lifeforms in every ecosystem on a purely evolutionary basis would be a quite difficult problem.

To take a small flaw as an example: the “White Claw” invaders in the film can take down top predators – and they can also glide. But flight requires light, hollow bones, whereas brute power to take down large animals and throw military vehicles like matchsticks requires massively strong bones and bulky muscles. The laws of physics constrain all life to specific ecosystems because all life faces all sorts of compromises.

#3 On the proper use of intelligence

In The Tomorrow War, the invaders compete with humans by a non-intelligent (or at least low-intelligence), non-tool using species. Whatever consciousness they have, the White Claws presumably do not adapt strategy or technology to the human responses.

This summer, I’ve been trying to get rid of weeds in my backyard. At first, I tried pulling them by hand, but they grow back. Then I tried an edger, but it does not destroy the roots, so they grow back quickly. Then I tried 30% concentrated vinegar, and it works because it’s absorbed by the roots and kills the plant. While the weeds might eventually adapt to vinegar, the point is that I can change technology much faster than the weeds can evolve new defenses.

Humans have been dealing with invasive species for as long as agriculture has existed. Our key weapon in the fight is our technology. We determine which strategy works and then scale it up. We don’t keep using the same failed methods (small arms fire), like the protagonists of The Tomorrow War.

What should we have done to deal with the White Stripes? Well, wasting resources to firebomb them when they already dominate an ecosystem is stupid. Instead, all initial resources should have been spent to identify a viable defense method, then scale it up. Even within the movie, it only took a day to find a toxin — why did they only think of that in the last gasp of the war? If not a toxin, then what about armored vehicles? Here’s another problematic aspect of big dumb animal invader science fiction: living beings are still made of blood and guts. Physics puts upper limits on density and power so that a tank will always be able to take out a biological being — and do it beyond line of sight.

A small, hidden invader is much more difficult to defend against. A virus, bacterium, or even something mosquito-sized is a much scarier threat than a big dumb animal. Mosquitos have been around for over 200 million years, and their victims still haven’t been able to mount an effective defense.