# In a population of 30 million, how many people would a 3,000-year-old know?

In my universe, everyone is a few thousand years old (ranging from about 1,500 to 4,000 years) and the population is capped at around 30 million people. People live pretty spread out across a planet roughly the size of earth. Travel from any one location to another is quick, convenient and extremely common. There are some areas that are more urban, and others that are more rural.

So, how many people would an average 3000 year old know?

I know that some people are more social than others, and therefore would know a lot more or a lot less people but I want to look at the most average person rather than the outliers.

I also want to clarify that knowing someone would be classified as immediately recognizing someone in a crowd and having enough history with them to strike up a conversation, or recognizing someone on the news and being able to remember a conversation you had with that person. One-off interactions that a normal person wouldn't remember don't count as knowing someone for my purposes.

A quick google search told me that the average american knows about 600 people, but theoretically, you would get to know a lot more people if you lived a lot longer. I also know that as people grow older, they sometimes grasp to the people they've known the longest, and don't put as much effort into to meeting new people, so I'm curious to know what thoughts others may have on this.

• How would the memory of 3000-year old person would be working? Does it have unlimited capacity, the capacity of a 20-year old or he/she would be suffering from dementia? Nov 22, 2019 at 17:31
• @Alexander the people in this scenario have a technology that keeps them at a physical age of 20-25, so they would have around the same mental capacity with maybe some aid from external technological devices (similar to computers or smart phones). Like if you recognized someone but couldn't remember where they worked or if they were married, you could do a quick search. Nov 22, 2019 at 18:42
• How about people you used to know, but haven't seen in a long time? I can certainly remember many people from my childhood - classmates, teachers, neighbors, shopkeepers &c - even though I've had no contact with them for decades. Likewise with people I've worked with over the years. Given a lack of aging or other changes in appearance, I would probably recognize them and be able to take up acquaintanceship where we left off. Nov 25, 2019 at 5:58
• What is the level of technology? Nov 25, 2019 at 21:47

As per the work of Robin Dunbar, 150 people seems to be the maximum number of acquaintances you can maintain without forgetting important details, and it'd be pretty dull having to deal with forgetting someone's birthday the 200th time, so I'd say people would probably organize into 100-150 person groups.

• But that's true for people who live roughly 80-90 years or thereabout. Somebody who lives a thousand years would, by necessity remember more. It just doesn't do to forget something you could do in your early hundreds when you're in your six hundreds.
– VLAZ
Nov 22, 2019 at 17:14
• @VLAZ Doesn't matter. You can swap out social circles in a few months, and we already live much longer than that. Nov 22, 2019 at 17:18
• And why would it be considered important to remember someone's birthday, especially after they've passed their first century or so? I certainly don't remember any of my acquaintances' birthdays (adults, anyway - I do keep some track of kids), and generally take no notice of my own. Nov 22, 2019 at 17:59
• @jamesqf That's really not the point at all here. Nov 22, 2019 at 18:10
• @Matthew Wells: How not? You yourself gave remembering (or even knowing) someone's birthday as an important detail in knowing people. I simply pointed out that knowing birthdays is not necessarily part of knowing a person. Nov 23, 2019 at 2:59

I Agree with @Mathew Wells Answer, about 150 People. The question isn't about how long a person has lived it is about memory. People tend forget people, it starts with names, and eventually faces.

The statement average American knows about 600 people, or H. Russell Bernard and Peter Killworth, estimated from an earlier survey that the average American knew 290 people are very deceptive statements, as the way the survey is conducted is by asking, "How many people do you know named Kevin? How many named Karen? How many named Shawn or Sean, Brenda, Keith or Rachel?"

I can think a lot of people who share my name, would I recognize them on the street, perhaps not. I would most definitely wouldn't remember enough about our history to strike up a conversation. Either because my Interactions with them was very limited or it has been sometime.

We humans have evolved to keep roughly 150 people in mind, know how they are related. As it was an ideal number for our progenitor's body to be useful without expending too much energy on it.

Is there are a reason for people in your world to be any different ? Any Evolutionary pressure ?

Can you expand on travel is extremely common and convenient. People Traveling nomadic-ally, every few hundred years to a new city might know a lot more people, than people who travel frequently but restrict the travel between their city and another.

I agree with the 150 people answer, but I wanted to point out an additional fact:

The character will have known more people over the course of their lifetime, but most of those people will be dead by the time of your story. The number of people you "know" at any given moment is bound by the number of people you can interact with in the slice of time that constitutes the Venn diagram overlap of your lifetime and theirs.

Roughly zero, unless there were other 3000-year-olds with similar outlook, interests and values. Young people get increasingly irritating as grumpy old man syndrome strikes.

I mean, would they even speak the same language as anyone else alive?

To clarify — the terms of the question may have changed since I read it, but language changes and people would not necessarily communicate easily with folk from other centuries. I would expect a lot of fragmentation. Looking at the old but mentally capable people I know, a lot have had very limited social circles. Churches or similar groups can expand this, but without work or families people have far fewer contacts.

Obviously the rules of immortality and this society can be written as you like — but there is more to aging than physical factors. World weariness is a real thing and I suspect will strike most after the first few centuries.

• Everyone in this setting is a few thousand years old, so this doesn't seem to apply. Nov 22, 2019 at 20:33
• There is a society established and it's from people who are all millenia old. Saying every single one cannot hold a social relations at all seems to be counter to having a society.
– VLAZ
Nov 22, 2019 at 20:45
• You know what old people are like and how isolated they get, how bad they can be about forming new relationships, how they fall out with neighbors, family and friends and break off contact? Now multiply that by 40... Nov 22, 2019 at 21:08
• @NuclearWang, People born only 30 years apart can grow up in very different cultures which we often define as Generations. Instead of 3-4 Generations, this world would have hundreads Nov 25, 2019 at 21:42
• @Nosajimiki Right, but the number of subsequent generations has no bearing whatsoever on how many people in your generation you know. My point is that there will be plenty of other like-minded 3000-year olds to socialize with. Old folks in this world might feel even more removed from the youths (100 generations or more, instead of 3), but that won't make them any more removed from one another. Nov 25, 2019 at 22:10