Thread by @FamedCelebrity

The DOOMSDAY Argument -- Doomed.🧵

Also called the Carter Catastrophe, some researchers believed they discovered, through purely probabilistic reasoning, a formula which shows man has only ~700 years left.

Vdeo at end.

Poundstone calculated we have a 50-50 chance of surviving 760 years.

His argument:

1. Your birth is not special, so you had a 50% chance of being born in the middle of man's reign.

2. There were to date about n = 100 Billion of us.

3. There will be N total men.

4. From that it's easy to calculate a 50% chance that N ≤ 2 * n.

5. Since n = 100 B, N ≤ 200 B in total. Or 100 B yet to be born.

6. If 150 million are born each year, as stats show, then 100 billion / 150 million per year = 50% chance of 666 years left.

Yet this can’t be right.

Have you spotted the error?

Many don’t.

Think about it a moment before scrolling further.

Consider the first man born. Call him Adam. For him, n = 1. He looks at the math of the DA and calculates there is a 50% chance N ≤ 2 * 1. So he will not be surprised when he comes across Eve. Adam would, though, be shocked to learn that some 100 billion more were to arrive.

Maybe Adam could have used a tighter probability than 50%. Suppose he wanted to be 99% certain instead of just 50-50. Then our equation becomes N ≤ 100 * n.

That means Adam was 99% certain that the total number of people who ever live would be less than or equal to 100—not a hundred billion.

Then consider man number 200 billion, who, we calculated gave a 50% chance will be born 666 years from now. He, not knowing he is the last, would calculate the DA and conclude there is a 50% chance N ≤ 400 billion!

The Doomsday Argument shows things getting better!

Here's the full explanation: