The faster he runs, the more preposterous his carbon footprint gets.
The Flash is a superhero in the DC Universe. According to the TV show (yes, I’m team Grant Gustin), The Flash is the alter ego of “ordinary forensic scientist” Barry Allen. I thought the phrase “ordinary forensic scientist” was funny, so I asked a friend who worked in the field what she thought. She told me, “I worked as a forensic scientist for three years and no one I met there was ordinary.”
Anyway, back to the Flash. His primary superpower is the ability to run at ridiculously fast speeds. In order to run, the Flash still needs to eat a massive amount of food to get the necessary calories. All of our food has its own carbon footprint, so this is what we’re going to focus on.
There are a few things that we need to know about the Flash to calculate his carbon footprint (which, again, is really just the carbon footprint of his food): 1) what is he eating, 2) how fast does he run on average, 3) how far does he run per year, and 4) what is the needed caloric intake to run that fast and that long? Let’s tackle these in reverse order.
Calories Burned
Olympic- and world-record sprinter Usain Bolt burns roughly 3.6 calories in 9.72 seconds when he runs at his top speed of 23 mph. Olympic marathon runner Meb Keflezighi burns around 2,600 calories in 2 hours, 9 minutes, and 25 seconds at an average speed of 12.16 mph. Using these two data points, we can extrapolate out to near the speed of light (Note: I did not say it’s okay to do this in real science).
That’s assuming a linear relationship between energy and velocity. But thanks to Einstein, we know that it takes exponentially more energy to increase your velocity when moving at relativistic speeds (more than 10% the speed of light, or 67,061,663 mph).
So we’ll use a linear relationship when the Flash is running slower than 10% the speed of light, and we’ll use a new exponential relationship when the Flash is running faster than 10% the speed of light.
Distance Run
The Flash’s hometown is Central City, population 750,000. That’s a fairly big city. And the Flash has to run around for most of his adventures. Let’s say he runs approximately 140 miles per adventure, plus additional longer runs when he has to get to Gotham or Metropolis to talk to his Justice League buddies. This makes a total of 10,200 miles per year spent running (over 8,500 miles more per year than a high-end marathon runner, training consistently).
Average Speed
Next, we need to figure out how fast the Flash usually runs. Rhett Allain at WIRED calculated that The Flash runs around 706 mph. While I trust his analysis, this sounds slow to me. This isn’t even as fast as a speeding bullet (3,409 mph), and we already know that the Flash is faster than Superman. This isn’t even open for discussion.
Believe it or not, 3,409 mph isn’t even close to the fastest a human has ever traveled. For that, we have to look at the Apollo 10 astronauts who reached 24,791 mph while inside their spacecraft. Now we’re talking! That’s fast! Let’s assume that the Flash would want to claim the fastest speed attained by a human by a pretty healthy margin. So let’s say his average speed is around 10 times the Apollo 10 astronauts, or 247,910 mph. Even at this speed, he’s still over 66,000,000 miles per hour short of relativistic speeds. So we use our linear relationship to give us the Flash’s calorie efficiency:
Efficiency = 942.3 cal/s
For comparison, assuming a 2,000 calorie per day diet, the average person’s calorie efficiency is 0.02 cal/s.
Ok, let’s assume that the Flash is able to run at relativistic speeds, and that he’s somewhat conservative and only runs at 15% the speed of light. Then his calorie efficiency becomes:
Efficiency = 665,527 cal/s
This number is preposterously big. It means that the Flash nearly burns in a second the number of calories an average person eats in a year.
Ok, let’s go full tilt and assume that the Flash can run at the speed of light. This is going to cause all sorts of problems, most of them involving exotic particles resulting from a catastrophic nuclear explosion. Another problem is that the Flash would have a terrible calorie efficiency:
Efficiency = 59,863,610,416 cal/s
Aaand… that’s it. I’m out of analogies. This number is too big to reasonably comprehend. It means that the Flash burns the same number of calories per second as 30,000,000 people burn per day.
What is he eating
All types of food have their own carbon footprint that comes from a combination of water use, fertilizer, transportation, storage, waste, and even cooking. To optimize his carbon footprint, the Flash would want to eat something that is calorically dense, but has a low carbon emissions coefficient (lb CO2 released per lb of food produced). Here is a chart of some familiar foods:
According to this chart, the best food for the Flash to be eating is peanut butter — he gets a lot of calories for the amount of carbon released into the atmosphere to make the food. But it’s probably safe to assume that he’s not only eating peanut butter, so we’ll see how much he has to eat (and what the carbon footprint is) for all of these foods.
First, let’s assume he’s running at 10x the Apollo 10 astronauts’ velocity.
|
10x APOLLO 10 VELOCITY |
|
| Amount of Food per ADVENTURE | Carbon Footprint per YEAR |
| ~4 hamburgers | 3,811 lb CO2e |
| ~half a deep dish pizza | 575 |
| ~2 cups of peanut butter | 131 |
| ~29 boiled eggs | 953 |
| ~75 tomatoes | 1,880 |
| A piece of tofu the size of a loaf of bread | 810 |
These numbers are… actually pretty reasonable. Good, even. They’re generally smaller than the average American’s food carbon footprint of 5,000 lbs per year. If the Flash is running at 15% the speed of light, these numbers get bigger:
|
15% SPEED OF LIGHT |
|
| Amount of Food per ADVENTURE | Carbon Footprint per YEAR |
| ~7 hamburgers | 6,630 lb CO2e |
| ~1 deep dish pizza | 1,000 |
| ~3 cups of peanut butter | 228 |
| ~50 eggs | 1,658 |
| ~130 tomatoes | 3,271 |
| ~tofu block the size of a bowling ball | 1,409 |
These are still pretty good and generally close to the average American’s food carbon footprint per year. Granted, the Flash is burning these calories in a minuscule fraction of the time, but still!
If the Flash is running at the speed of light, these numbers get ridiculous:
|
SPEED OF LIGHT |
|
| Amount of Food per ADVENTURE | Carbon Footprint per YEAR |
| ~a hamburger 10 feet long, 10 feet wide, and 12 feet deep | 89,450,791 lb CO2e |
| ~a deep dish pizza 165 feet across and 20 feet thick | 13,490,268 |
| ~enough peanut butter to fill a cement truck | 3,070,716 |
| ~all of the eggs | 22,365,904 |
| ~a tomato 25 feet across | 44,136,419 |
| ~enough tofu to fill 3.5 olympic swimming pools | 19,006,113 |
The Final Analysis
As the Flash runs faster and faster, his carbon footprint grows from a meager 131 lb CO2e to a monstrous 89,450,791 lb CO2e. Because he is the Flash, I think it’s safe to assume that he’s running really fast. Like, near the speed of light fast. If he mostly avoids meats (which typically have higher carbon footprints than other foods), his carbon footprint would be around:
The Flash = 25,000,000 lb CO2e
While the Flash might be able to move at superhuman speeds, he can’t exactly make food cook at superhuman speeds. So this begs the truly important question: if the Flash is a big fan of pizza, just how long would he have to wait for it to bake all the way through before running out on one of his adventures?