As I anticipated my birthday this year, the math nerd in me realized that my age will be the same as my birth year (’63) – a once in a lifetime phenomenon. I wondered if there is a name for this birthday. I found out that there is a name for it. It was coined almost 20 years ago.
From a November 2007 article in The New Yorker:
“Named after New York City firefighter Bobby Beddia, it is a fun coincidence that only occurs during even-numbered years.
The concept was born when Beddia discussed the milestone with visitor and mathematician Rhonda Roland Shearer at his fire station in 2006. Tragically, he passed away in the line of duty later that day. Afterward, mathematician Barry Cipra coined the term “Beddian Birthday” in his honor.”
I had many minutes of fun thinking about what I prefer to call doubling birthdays. I’ve thought about when each of my seven siblings had or will have their Beddian birthday. For example, my youngest sister, Annie, will be 70 in 2040. (That’s easy math. 70 Γ 2 = 40). She’s seven years younger; double the difference in our ages is 14 years from now.
I thought about how some people will have to be really old, not just kind of old like me, to celebrate their Beddian birthday. A person born in the year 2000 will have to live to be 100!
Then I read that the aforementioned mathematician, Barry Cipra, came up with what he called the Beddia Theorem. He determined that at any given time, you can calculate the number of ages that are pre- or post-Beddian. Cipra said that the ages will fall into two separate time spans, except for years ending in ’98, ’99, or ’00.
- In odd-numbered years: There are exactly 50 pre-Beddian ages.
- In even-numbered years: There are exactly 49 pre-Beddian ages.
I spent a few minutes confused, then several minutes more figuring out the time spans to prove his theorem. I got it wrong the first time. (I initially started with 1927 and ended with 2026.)
1926-1963 Post-Beddian; 38 ages
1964-2000 Pre-Beddian; 37 ages
2001-2013 Post-Beddian; 13 ages
2014-2025 Pre-Beddian; 12 ages
It works. This year, there are 49 ages of people who have not yet celebrated a Beddian birthday. 37+12=49
Cathy’s theorem says that in even-numbered years, there will be two years of birth, 50 years apart, celebrating Beddian birthdays. This year, that’s 1963 and 2013. A child born in 2013 will turn 13 in 2026.
I plan to celebrate my childish enthusiasm for this silly milestone with two scoops of ice-cream!
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