We all have these thoughts that come to us in the early hours of the night. Who am I? Why are we here? What if my phone was powered by vacuum tubes instead? Randall Munroe has the answer to, well, just one of those questions, but also the answers to a whole host of others that have been collated What happened if? 2: Additional reputable scientific answers to absurd hypothetical questions. Yes, that’s a T-Rex eating a plane. In the excerpt below, Munroe examines what it would take to pull an average-sized person in a chair across Australia’s tallest skyscraper using only the power of pigeons. Many and many of pigeons.
excerpt from What happened if? 2 by Randall Munroe. Copyright © 2022 by Randall Munroe. Excerpted with permission from Riverhead, an imprint and a division of Penguin Random House LLC, New York. All rights reserved. No part of this excerpt may be reproduced or reprinted without the written permission of the publisher.
How many pigeons would it take to lift an average person and a starting chair to the height of Australia’s Q1 skyscraper?
In a 2013 study, researchers at Nanjing University of Aeronautics and Astronautics led by Ting Ting Liu trained pigeons to fly to a perch using a weighted harness. They found that the average pigeon in their study could take off and fly up while carrying 124 grams, about 25 percent of their body weight.
The researchers found that the pigeons could fly better if the weights were slung under their bodies rather than on their backs, so you’ll likely want pigeons to lift your chair from the top rather than supporting it from the bottom.
Let’s say your chair and straps weigh 5kg and you weigh 65kg. If you used the pigeons from the 2013 study, it would take a flock of about 600 of them to lift your chair and fly it up.
Unfortunately, flying with a load is a lot of work. The pigeons in the 2013 study could carry a load 1.4 meters up to a perch, but they probably couldn’t have flown much higher. Even unencumbered pigeons can only keep up the strenuous vertical flight for a few seconds. A 1965 study measured a climb rate of 2.5 m/s for unencumbered pigeons.* So even if we are optimistic, it seems unlikely that pigeons can lift their chair more than 5 meters.†
No problem you might think. If 600 pigeons can lift you the first 5 meters, then you only need to take another 600 like the second stage of a rocket to carry you the next 5 meters when the first flock gets tired. You can bring another 600 for the 5 meters after that and so on. The Q1 is 322 meters high so around 40,000 pigeons should be able to take you to the top right?
no There’s a problem with this idea.
Since a pigeon can only carry a quarter of its body weight, it takes four flying pigeons to carry one resting pigeon. This means that each “level” requires at least four times as many pigeons as the one above it. Lifting one person is only allowed to take 600 pigeons, but lifting one person and 600 resting pigeons would take another 3,000 pigeons.
This exponential growth means that a 9-step vehicle that can lift you 45 meters would require nearly 300 million pigeons, roughly the entire world population. Reaching halftime would require 1.6×1025 pigeons, which would weigh about 8×1024 kilograms – more than Earth itself. At this point, the pigeons would not be pulled down by Earth’s gravity – Earth would be pulled by pulled up by the gravity of the pigeons.
The full 65 step vehicle to reach the top of the Q1 would weigh 3.5×1046 kilograms. Not only is that more doves than there is on Earth, it’s more mass than there is in the galaxy.
You could make things more efficient by reusing pigeons. In the 2013 study, the researchers gave the pigeons 30 seconds to rest on the perch before bringing them down for another try. If each “stage” lasted two seconds, and the pigeons refreshed after 30 seconds, you could fly a 15-stage plane arbitrarily high – but that would still require trillions of pigeons.
A better approach might be not to carry the pigeons with you. After all, pigeons can get to the top of the skyscraper themselves, so you might as well send them ahead to wait for you instead of letting their friends carry them up. If you could train them well enough, you could slide them along at the appropriate height, then grab them and pull them up for a few seconds when you reach their height. Keep in mind that pigeons cannot grab and carry things with their feet, so they would need small harnesses with aircraft carrier-style hooks to catch you.
With this arrangement it is possible for you to fly to the top of the tower yourself with just a few tens of thousands of well-trained pigeons. You should probably make sure you have a security system in place to keep you from falling to your death every time a hawk flies by and startles the doves.
Not only would the vehicle be more dangerous than an elevator, it would also be a lot more difficult to choose your target. You could to plan to get to the top of the Q1, but once you take off… you will be completely under the control of anyone with a bag of seeds.