Prince Rahul's Key Ideas from What If? 2
by Randall Munroe

Would there be any danger from standing next to a large object that was 0 Kelvin?

• Cold objects can condense the air itself, causing liquid oxygen to collect on their surfaces like dew.
• It’s highly reactive and tends to cause flammable things to spontaneously ignite.
• A really cold object can set your house on fire.

I have a Nothing Grenade™. When detonated, it instantly replaces itself with a sphere of perfect vacuum 2 meters across. What would actually happen when it went off?

• The sphere of vacuum would collapse, colliding in the center with so much force that it would rapidly heat and might even turn briefly to plasma.
• Energy would radiate outward both in the form of a pulse of heat and a shock wave, capable of causing severe injury or death and of destroying small structures. In other words, what you have is a regular grenade.

Could a person eat a whole cloud?

• No, unless you’re allowed to squeeze the air out first.
• Clouds are made of water, which is edible. Or drinkable.
• If you try to eat a cloud, you’ll just burp out more cloud faster than you can eat it.
• A fluffy cloud the size of a house contains about a liter of liquid water, or 2 or 3 large glasses, which is about the volume a human stomach can hold at one time.

What if you were hanging on a helicopter blade by your hands and then someone turned it on?

• Helicopter rotors take a little while to get up to speed.
• Once the rotor starts moving, it might take 10 or 15 seconds for it to make its first full turn, so you’d have enough amount of time to make eye contact with the pilot before you rotated out of view.
• If you were hanging on, by that point you’d already be swinging noticeably outward and you’d feel an extra 10 or 20 pounds of weight from the centrifugal force.

If a T. rex were released in New York City, how many humans/day would it need to consume to get its needed calorie intake?

• About half of an adult, or one ten-year-old child.
• Tyrannosaurus rex weighed about as much as an elephant.
• T. rex ate seem to cluster around 40,000 calories per day.
• According to Ryan’s shirt, an 80-kg human contains about 110,000 calories of energy, so a T. rex would need to consume a human every two days or so.

As plastic is made from oil and oil is made from dead dinosaurs, how much actual real dinosaur is there in a plastic dinosaur?

• Coal and oil are called fossil fuels because they formed over millions of years from the remains of dead organisms buried underground.
• The standard answer to “What kind of dead stuff does the oil in the ground come from?” is “Marine plankton and algae.” In other words, there are no dinosaur fossils in those fossil fuels.
• Land life, on the other hand, is more likely to form peat and eventually coal.

Why don’t compasses point toward the nearest hospital because of the magnetic fields created by MRI machines?

• MRI medical scanners have powerful magnets in them. The scanners are shielded, so the strongest parts of the magnetic field are contained inside the scanner, but a weaker field extends out around it.
• While the magnetic fields from MRI machines aren’t strong enough to lure in compass-guided explorers from around the country.

What would be the most expensive way to fill a size 11 shoebox (e.g., with 64 GB Micro SD cards all full of legally purchased music)?

• If you really want to fill a shoebox with an arbitrarily large amount of money, you could get the US treasury to mint you a trillion-dollar platinum coin, something that—due to a loophole in a law around minting commemorative coins—it is technically authorized to do.

If I pulled out my eyeball and aimed it so that it was looking into my other eyeball, what would I see (assuming the nerves and veins remain undamaged)?

• Pointing an eyeball at an eyeball doesn’t create some kind of weird loop, like pointing a camera at its own video feed.
• Each eyeball just sees an eyeball.

I noticed recently that the number of people in a family tree increases exponentially with each generation: Which got me thinking—are most people descended from the majority of Homo sapiens who have ever lived? If not, what fraction of all the people that have ever lived am I descended from?

• A 2004 simulation by Douglas L. T. Rohde and colleagues estimates that the identical ancestors point is likely somewhere between 5000 and 2000 BCE.
• At that date, everyone who left descendants at all is an ancestor of everyone.