Spaced repetition is particularly effective when it comes to memorizing a large volume of information quickly and retaining it for the long term. This is applicable to a wide range of subjects, including history (facts and dates), physics (formulas and laws), mathematics (formulas and laws), and many others.

There is often a misconception that subjects like physics are solely about understanding and reasoning, but at the school level, it is necessary to have a solid grasp of the laws and formulas. Without this foundation, it is like attempting to write a program in a programming language without knowing the syntax. You have to stop and look up the syntax for each line of code, slowing down the entire process. Some things simply need to be memorized to achieve a certain level of proficiency.

People are already doing this though. If you are a historian, you are already having spaced repetition on your subject of interest, since every book you pick up from the field will cite the seminal information everyone knows in the field. You are constantly being refreshed on it. Likewise in physics or math, if you specialize in some niche, you are constantly reviewing the groundwork and in all likelihood reading a good deal of review articles as well. That being said, there's no point in the professor of history reviewing their calculus from undergrad, and there's no point in the physics researcher to review all the central dates and names of world history every few years. If you strive to have the breadth of an ocean you won't have time for much depth. There's just a finite amount of information one can intake a day.

> Without this foundation, it is like attempting to write a program in a programming language without knowing the syntax. You have to stop and look up the syntax for each line of code, slowing down the entire process. Some things simply need to be memorized to achieve a certain level of proficiency.

This is pretty much the opposite of my experience. I have learned many programming languages and never found it useful to memorize any syntax. I read the book/docs/tutorial once, and then reference it (or code I previously wrote) just-in-time whenever I need a reminder, and find that whatever I use repeatedly is quickly committed to memory. I don't see how memorization could make this faster.

This is definitely not my experience with space repetition. I really wanted it to work for me but I found it didn't help at all with retaining anything. I was using anki.

The more cards I created/added made it worse.

Curious: How many cards did you create? And how often do you test yourself? You really need to do it daily with few gaps for it to be very effective.

I would recommend not giving up but instead altering your approach. I tried spaced repetition multiple times in grad school and completely failed at it. I then tried again over 10 years later (and much older!) and it was really like attaining a super power. The success is even more remarkable because compared to my university days, I am much less actively using the material in the cards.

In my case, the difference between the two attempts was sticking to the daily schedule[1] and getting better at creating relevant cards.

And keep in mind: SR aids in recall, not in understanding. There have been times where I look at the cards on a certain topic and do very poorly (consistently). I then realize it's partly because some key understanding has been lost. I then need to do a proper study session (get the book out, read for understanding, perhaps do some problems). After that study session, I get good on the cards and stay good for a long time. In the last 4 years, I've needed to do this perhaps twice.

[1] Yes, I do stop from time to time, but those are the exceptions, not the rule.

I created cards as I was learning the topic. And I was doing it daily or twice daily.

I certainly wanted it to work, when I first learned about it I thought it was the answer. But I seemed to get worse and more stressed out because I wasn't learning anything.

I'm not too fussed about it not working for me. I don't think there is a one size style of learning.

This has been my experience as well (especially with Anki), though I've always felt like my ability to memorize information to be poor in general. In my experience, I find it easier to memorize things rather through brute force/frequent repetition. To use memorizing foreign language vocabulary as an example; repeating words to myself, listening, or writing them out for 30-60 minutes everyday or every few days (as opposed to spreading out fewer terms over, say, two weeks). The conjecture I have is that my brain commits to memory more heavily based on frequency/intensity during short intervals of time rather than long intervals of time, but it's just a guess.

Not sure if I'm just an outlier, but I think you're right that many learning heuristics aren't one-size-fits-all. Hope you can find something that's effective (and enjoyable) for you. :)

100% this.

Once I realized that understand is different from recall, it made a world of difference.

In all of my physics classes (high school, undergrad, grad), we were allowed to have a formula sheet with whatever we wanted written on it. Furthermore, important equations would just be given to us on the test, in case you forgot to write it. Even so, test scores were usually below 50% (corrected by curving after). Memorizing formulas to study would have been a laughable waste of time, the better approach is to practice a wide variety of problems.

If one has to look up a formula, can we say that they have a good understanding of it? If one had to look up a multiplication table each time they calculated something, how far would they have gone in learning?

I think you have it backward. All that time/energy wasted memorizing multiplications could have been used to understand more complicated topics. It's a cool party trick but it won't make you better at solving problems past high school level. I would prefer to work with someone who understand the concepts well and how to apply them than someone who can recall 32x9 or 10 digits of pi from memory.

When people complain about the difficulty of their college math courses or the math problems they solve at work, I can assure that it's not because they had a hard time remembering the answer to a multiplication. In a lot of cases, the equations they are trying to solve don't even have numbers in them. And when there are numbers, you won't be able to calculate them mentally because they won't simplify like they do in a no-calculator math exam.

You might not have realized, but a lot of the work when designing a no-calculator exam is to make sure people can compute the numbers mentally. When you step out in the real world, 32x9 becomes into 32.091x9.1^1.1. It turns ugly real fast when you have to deal with real numbers instead of a carefully crafted exam question.

I would have to look up Maxwell's equations right now if I needed them. Nevertheless, I am confident I have a good understanding of them. What I have in my head are important relationships (conservation laws, symmetries, wave solutions, etc.), not the exact mathematical formulas.

to add to this, I think spaced repetition is to learning, the way typing speed is to programming. It's good at solving for the minor frustrations and slowdowns that stand in between you & the complex reasoning to get to a solution.

When I can edit code via vim keybindings quickly, I can move things, sketch ideas, swap entire blocks, and so on, easily. That lets me check and look at things, and allow my whole brain to be spent on higher level things like looking at the control flow, applying aesthetic considerations to simplify, or whatever.

I failed Calc 3 as a college freshman because I had taken high school calc as a junior, leaving a full year between. I understood the ideas of calc 3, but couldn't remember the basic stuff like integrating tan() or whatever. (and I also didn't have any study discipline at the time to actually solve for my situation). So I couldn't answer the questions on a test even though I knew the steps I would need to take past a roadblock. Solvable with study, which would have been effective in the form of spaced repetition flash cards.

You could call the way the curriculum is organised "spaced repetition", but this isn't personalised and thus missing the feedback part of spaced repetition. Generally, children aren't taught the method of spaced repetition itself. "Learning how to learn" should be its own subject early on.