According to my girlfriend, mathematically the “20s” have only begun since the start of this year as of 01/01/2021.
I’m open to the concept, as I googled it and it seems to be some kind of “school of thought” but I think she was doing a really bad example of explaining it to me, using examples such as the 1st floor of a building is the ground floor, technically. But that isn’t really mathematical, because in maths you begin with 0 then, for example, 0.1, 0.2, 0.3 etc, but I’m not that confident of my maths skills as I’ve never particularly been that good.
She also said because you go from 1BC to 1AD, there was no “Zero Before Christ” or “0 Anno Domini”, but I argued that that is just where we decided the consecutive years begin from with the Gregorian Calendar, and isn’t mathematical.
Am I fundamentally mistaking what she means by mathematical? It was kind of starting to make my head hurt as according to that math, somebody isn’t 10 years old until they’ve been alive for 11 years, which is what I said to her, and she said yes, then seemed confused herself. which is why I’m requesting an from you guys, as from googling the subject, I’ve found myself quite interested in this concept but I’m massively struggling to wrap my head around it.
Thanks 🙂
In: Mathematics
She is wrong. If for no other reason than that it is commonly accepted that 2020 was the start of the decade and being the time scale is purely arbitrary, whatever the majority say is in fact the truth. If she wants to be technical than just say the the first decade only went from 1-9 and the second from 10-19 then Continued in that pattern.
think about it what was the first decade? well the very first 10 years. year 1,2,3,4,5,6,7,8,9 and 10.
Now what is the second decade?? the years 11,12,13,14,15,16,17,18,19 and 20.
But do you see that? the second decade started in the year 11, the 3rd decade will start on the year 21. and sooo on until the decade we are in today that started in the year 2021 and not 2020.
I do not understand people like you. A decade is defined as a time period of ten years so why would you go about inventing theories based on mathematical concepts of when a decade begins. My IQ is 119 as of an officially administered IQ test online so I hope that you will understand my logic of this reply.
Your girlfriend is only correct in the most old fashions of terms.
The 3rd decade, of the 21st century began in 2021.
But the 20’s started in 2020.
They use different convention.
The first one uses the 1 to 0 convention.
The second one uses the 0 to 9 convention.
Nobody really uses the 1 to 0 convention for decades, only for centuries.
This only really came back into living memory because there was controversy on when the 3rd millennium started in 2000 or 2001.
And a lot of people were wrong in thinking it was the start of the 2nd millennium.
There are 10 years in a decade, and if this is the first year, then the last year of the twenty-twenties will be 2030.
Back in 1999 we called it the twentieth century. She seems to have got this concept mixed up and gone in the wrong direction.
Your girlfriend is correct. You don’t start counting at zero. If you put an apple on a table would you say you have zero apples? No. You have 1.
Same goes for years.
You’re not alone in this! There are actually huge divides in all kinds of different fields related to engineering and programming and math, about whether it makes more sense to start counting things from 0 or from 1 in this context or that. You’re quite right in saying that it’s a ‘school of thought’ thing, there often is no consensus on what these conventions should be, or which is more ‘mathematical’.
But if any of these conventions really are non-mathematical, I think the Gregorian convention is a pretty good candidate. Lots of places in math, we use the natural numbers starting from 1, and lost starting from zero, and some places we use the whole number line of integers… but I can’t think of anywhere in “real” math that we’d ever use a number line which has negative integers and positive integers but skips 0, which seems to be what the B.C./A.D. year numbering system does.
You might be amused to learn that these kinds of misunderstandings are broadly known as “fencepost errors”. They’re called this, because of a classic puzzle that goes something like “If you build a 30 meter fence with posts spaced 3 meters apart, how many posts do you need?” We often miss the answer to questions like this by 1, because we lost track of whether we count 0 or not.
Our calender starts with 1AD, before that was 1BC. (This is the stupid mistake that causes all the issues…)
This means that the first Century AD is years 1-100. Second Century is 101-200. The first decade of a century will then start with years 1-10.
However, when someone talks about the “20s”, they don’t mean the third decade of the current century, which would start in 2021, they mean the 10 years 2020-2029. A decade just means as set of 10 years, they can start whenever you like. If you are referring to your own second decade, that stars when you are 10 years old. Since you are born at 0 years old, your first decade is years 0-9.
>But that isn’t really mathematical, because in maths you begin with 0 then, for example, 0.1, 0.2, 0.3 etc, but I’m not that confident of my maths skills as I’ve never particularly been that good.
This is untrue. Where you “begin” in math depends on what you’re doing. There are many different sets of numbers. The set of positive integers begins with 1. The set of non-negative integers starts at 0. The set of real numbers is unbounded on both ends, which means that it doesn’t start anywhere.
Which set of numbers you use depends on the application. If you need to count how many toes you have, you don’t start at 0 and end with saying you have 9 toes.
The calendar *could* have started at 0, but there’s no mathematical rule dictating that it had to. And- historically speaking- the idea of “0” as an actual number is somewhat recent. This should be taken to the silly extreme that some people take it and say that ancient cultures “had no concept of zero” (They still would have understood what it meant to have no arrows left in their quiver), but people who don’t spend a lot of time doing advanced mathematics (which, by ancient standards, was multiply/dividing large numbers) are going to much more naturally think of 1 as the first number, not 0, because why would you start counting something until you have at least one of them?
So, given how long ago our current calendar was established, making the first year “1AD” would have seemed more intuitive.
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