Consider answering the following questions:
How much longer will humans
exist?
How long will a marriage last?
How much longer will that
building be standing?
William Poundstone explains a
simple approach to answering such questions in his book The Doomsday
Calculation: How a Formula That Predicts the Future Is Transforming Everything
We Know About Life and the Universe.
The Doomsday Calculation approach
uses the Copernican principal which states that we are not in a special place
(or time). Let’s take an example of you meet two couples for the first time at an
event. The first couple has been together for a year, second couple for ten
years. If you had no other knowledge of their relationships and you had to predict
which couple would more likely be still together in a year, most people who
probably pick the second couple. Your answer would be the same if you had to answer
the question for being still together in five years or more. The first couple
may be perfectly matched, but only given the evidence of the current length of
their relationships, the second couple has demonstrated more longevity.
The Copernican principal states our
observation of the couple is at no special time. In meeting the second couple
who has been together ten years, we could be meeting them near the beginning of
70+ year marriage or we could be meeting them a year from a breakup, Let’s
breakup the full (unknown) length of the relationship into quarters. We have a
25% chance of meeting them in the first quarter, a 50% chance of meeting them in the middle two
quarters, and a 25% chance of meeting them in the final quarter.
The middle 50% is the range we’re
interested in. If your meeting with them happens at the low end of this range, 25% of
the length of their relationship has been ten years and they have another 75%
or thirty years left. On the other hand, if ten years is the 75%, they only
have another 25% left, which in this case is three years and four months
remaining. With those two extremes evaluated, we can state we are 50% confident
the relationship will last between three years and four months to thirty
additional years.
Perhaps you want to state your
range with a higher confidence level. That will mean widening the interval.
Moving to 75% confidence, the interval becomes approximately a year and a half
to seventy more additional years.
Poundstone gave a brief summary
of the doomsday calculation with additional examples in: Doomsday
argument: the end of humanity, predicted by a math equation - Vox
William Poundstone is the author of 16 books,
including The Doomsday Calculation: How a Formula That
Predicts the Future Is Transforming Everything We Know About Life and the
Universe.
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