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If an average human in build and intelligence were to gain immortality for whatever reason what is the limit to what they could learn and remember?
This human is for all intents and purposes a normal human, except they stop aging after reaching the age of 30.

Would it matter what year this person was born? Such as the difference between someone born in the stone ages vs. someone born in the 21st century?

Would they have to come up with special tricks to remember more things like a memory palace or something?

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    $\begingroup$ Discovery Channel had a show several years ago where Adam Savage discussed and portrayed a series of ideas that would lead to vastly expanded human lifespans. At one point it was mentioned the brain would be "full" after 1000 years, although there was no clear explanation given. I have also seen this figure in some SF stories as well. This article does not directly answer the question, but might provide a starting point: scientificamerican.com/article/what-is-the-memory-capacity $\endgroup$
    – Thucydides
    Apr 23, 2016 at 4:02
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    $\begingroup$ Your human could always keep a diary/journal. $\endgroup$
    – alexw
    Apr 23, 2016 at 5:41
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    $\begingroup$ A related question could be: Is there a duration after which you can say that you are not the same person as before? With time, there will be less and less correlation between the way you think and what you remember now compared to a long time ago. $\endgroup$
    – Tony
    Apr 23, 2016 at 10:22
  • $\begingroup$ I suppose you are talking about a perfect memory, which works like a harddrive. Normal memory erases a lot of things, and we probably remember less than 1% of the stuff we experience in the day, usually as simple facts rather than pictures. Normal brains would never run out of capacity since it saves almost nothing long term, and forgets most of that eventually. $\endgroup$
    – Ryan
    Aug 24, 2016 at 20:03
  • $\begingroup$ I don't think it works exactly like how many mb you have. Instead, as I understand it, concepts are built up in a hierarchy. So instead of clearing a section of your hard drive you just move that into different concepts at different levels of the hierarchy. So maybe you never run out of space, you just see things in different ways. $\endgroup$
    – user875234
    Mar 16, 2018 at 17:47

3 Answers 3

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According to How to Create a Mind by Ray Kurzweil, the human neocortex contains around 300 million pattern processor modules, and "that a human master in a particular field has mastered about 100,000 chunks of knowledge." The primitive modules are assigned redundantly, with some things having many thosands of copies and others just a few. You can trade off overall capacity with integration/cross-corelation (e.g. the "fragmented hard drive" effect Jim mentions is predicted, and is more akin to reduced indexing). See also this answer for more background.

Experts already use the whole capacity of their brains. So an immortal won't continue to learn more and more, though maybe he will refine his ability in more subtle ways, optimizing his expertise and being able to try different methods by trial and error over the span of centuries.

The amount of storage for autobiographical information is also the same, so as he lives longer the amount he remembers will be a smaller and smaller proportion to the whole. But, so much is the same so what's lost, really? More interesting and unique experiences will continue to occur over time, so these will crowd out the mundane until that's all he ever remembers of the past. Talking to him, it would seem that he has had a very exciting life! But actually, the normal lifespan worth of excitement is spread out over thousands of years, with most of the time being mundane.

His own mind may perceive the past as exciting, while recent decades are boring. But it's always the case, as day to day memories fade except for the exciting parts.

December 2017: I came across a graphic story expressing a similar idea: Schlock Mercenary, Book 9: The Body Politic — Part II: Royal Flush.

As we grew older, less and less of short-term memory was deemed 'new' or 'different' enough to be committed to long-term storage. Entire years, and eventually decades would fly by unremembered. Sanity fled, and life became a cheap commodity again. Civilization itself began to die.

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  • $\begingroup$ Nice, I like the idea of the person forgetting mundane things and having what appears to be an exciting life. $\endgroup$
    – TaylorAllred
    Apr 23, 2016 at 3:00
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    $\begingroup$ Hmmm, I think I heard this song about 200 years ago... $\endgroup$
    – Scott Downey
    Apr 25, 2016 at 14:04
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    $\begingroup$ Smells might cause psychological effects due to recall of something that's been almost completely lost or overwritten: like a dangling pointer. $\endgroup$
    – JDługosz
    Apr 25, 2016 at 14:26
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    $\begingroup$ In National Geographic's Breakthrough (natgeotv.com/uk/page/breakthrough), they have talked about memory and how unreliable it is. Some scientists recorded people talking about what they were doing and what they felt during the 9-11 event. Then they reviewd the same people after a year, then again after another a few more years. The people interviewed greatly contradicted themselves. $\endgroup$
    – KC Wong
    Jun 29, 2017 at 1:04
  • $\begingroup$ @JDługosz But even that will degrade over time. I have never heard of using a dangling pointer as a metaphor for that though, but it makes perfect sense! $\endgroup$
    – forest
    Mar 16, 2018 at 8:38
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Prologue

Despite some of the answers claiming to know perfectly how memory works, the reality of modern science is that we do not understand the brain. At all. Like literally, popular science always acts like real science understands everything, but that's not how it is whatsoever. Just to give an indication of this: when I had my introductory (so not even some deep level) course on Human Physiology in university about 5 years ago every second or third paragraph on the brain ended with some note that we don't really understand it yet and a whole lot more research is needed. Our professor illustrated this by showing the scientific model of the circulatory system throughout the last 1000 years and pointed out that our understanding of the brain is comparable to when they thought blood was created in the kidneys and then moved to the rest of the body.

There are a lot of theories about the workings of the brain and if you look up the sources of the other answers you will find a whole lot of 'may's and 'might's. Or you end up with doctors in Psychology making claims about how the brain works (such as with the 'Slow Thinking Processes'-theory). Right now the brain is one of the biggest mysteries out there and what we know is a lot of little pieces and we have no idea how to put those pieces together (imagine a jigsaw puzzle with a few million pieces where you have a couple of thousand)

Answer

So to directly answer your question there are two different approaches you can take:

  • Option 1: The brain is a complex deterministic set of particles interacting. Free will does not exist and is just a human illusion.

    Result: The brain can only store a finite amount of stuff. How much? We have no idea yet and you can pick anything you like for world building purposes. The big question being especially whether normal old age memory problems are a result of brain degradation (solved by immortality) or a result of the amount of memories (worsened by immortality).

  • Option 2: The brain and human intelligence is something that falls outside the natural as it is understood by modern science. Free will actually exists.

    (Important note: There is nothing unscientific about this, although it's an unpopular line of thought in traditional secular science. Science is only descriptive, so applying the label 'unscientific' to things that are not understood by modern science is incredibly misleading.)

    Result: Realistically you end up with even more world building freedom here, as you can both justify an infinite memory, or any arbitrary limit you want. In-universe explanations would be along the lines of a scientifically described soul/spirit which would be unique to intelligent beings, although - just like with everything else - science could never understand it (which wouldn't stop the scientific method from building some amazing models describing it).

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    $\begingroup$ I think you under - appreciate how much has been learned about the brain lately. We've gone from "presumably some kind of neural network because form follows function" to details of firing processes within a cell and details of how cortical columns work and details of layers of neurons that do image processing in the optic nerve and visual cortex, etc. Look at projects like Blue Brain and the SpiNNaker chip. Your textbook may have been out of date even when you used it, and it may be cautious in the authors knowing that they know nothing in this rapidly-moving field. $\endgroup$
    – JDługosz
    Apr 25, 2016 at 14:36
  • $\begingroup$ A better analogy with the circulatory system would be knowing about supply and return and 4 chambers and valves, but not how fluid dynamics allows the heart to not damage red cells when it pumps, and not know how the blood-brain barrier manages to work physically. So it would not be wrong to toss out facts on the mitrol valve or capilaries under the fear "we don't know everything". $\endgroup$
    – JDługosz
    Apr 25, 2016 at 14:42
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    $\begingroup$ @JDługosz But that's exactly the thing, we're at the level where we know random details (the couple of thousand jigsaw pieces I mentioned), but the act of thinking, acting and memory are things we just hypothesize about. Not too long I spoke with a researcher on the cutting edge of Deep Brain Stimulation, and even he more or less literally said 'we have no idea really what we're doing and why it works, but using trial & error we somehow are able to help people'. And even if that textbook might've been out of date, the professor's comparison was quite recent. $\endgroup$
    – David Mulder
    Apr 25, 2016 at 16:22
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Yes, there is a limit to what a human can learn and remember

But I haven't found any quantitative value for this maximum. It also probably varies depending upon the person and environment.

Lost Memories

However, the human brain is adaptive and has a mechanism for throwing away extraneous information but retaining the important stuff. Dreams play an important role in this function. Dreams reinforce the strength of certain memories and this keeps those important memories above the magic threshold of being forgotten.

As humans forget things, it frees up neurons for storing other information. Even at young ages, the brain works on freeing up memory.

Slow Thinking Processes

If you have been around the elderly, you may have noticed that they seem to think slowly.

For decades it was thought that this slowness of thought was an indicator of mental decline in the elderly. Lately however, scientists have found evidence that the slow-down more closely resembles a "full hard drive" - meaning the elderly take longer because they have to look through more memories to get to the one they want.

Older people do not decline mentally with age, it just takes them longer to recall facts because they have more information in their brains, scientists believe.

Much like a computer struggles as the hard drive gets full up, so to do humans take longer to access information, it has been suggested.

So a very old person will both have forgotten much of what they used to know (especially that information that isn't still frequently used) and their ability to recall important bits of information or make decisions based upon their knowledge should continue to decline with age (somewhat like a fragmented harddrive).

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  • $\begingroup$ I like the analogy you used with computers, gives me another idea for a question. $\endgroup$
    – TaylorAllred
    Apr 23, 2016 at 2:58
  • $\begingroup$ In my answer I noted quantities. $\endgroup$
    – JDługosz
    Apr 23, 2016 at 2:59
  • $\begingroup$ Your link re dreams has one relevant sentence, near the end: "It may even be critical for the integration of newly acquired memories with more remote ones (see chapter 8)." The bulk of it just shows that the content of deams comes from memories. And, interesting, "There is little evidence that people actually learn during their dreams." $\endgroup$
    – JDługosz
    Apr 23, 2016 at 3:12
  • $\begingroup$ I heard another report on this that said part of the role of dreams is reinforcing important memories. I haven't found the reference to that yet. But I hope to find and link that into this too. $\endgroup$
    – Jim2B
    Apr 23, 2016 at 3:35
  • $\begingroup$ The new link doesn't cover this directly but is interesting. $\endgroup$
    – Jim2B
    Apr 23, 2016 at 3:39

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