In this issue:
- post-privacy: musings as we hear more about Mythos and quantum computing
- N² – n: why shorting is mathematically cursed
- math shortcuts traders know by heart
- almost famous
Friends,
Post-Privacy
About 15 years ago, I read Drew Magary’s sci-fi novel The Postmortal. The book imagines a society that has created a pill of immortality. Your aging stops at the moment in time when you take the pill although it’s still possible to get hit by a car and die.
Civilization reorganizes around this new technology. Marriage contracts have a shelf life of 20 years. This reminded me of Larry David and Cheryl’s tiff, where Larry gets yet another self-induced cold shoulder from his wife, pressing his case that “til death do us part” means he’s free to see other people in the afterlife.
I went to the internet for a reminder of other outputs from the Postmortal world:
- The Rise of “End Specialists”: Due to severe overpopulation and the lack of natural deaths, the government creates specialized roles to handle population control, with characters like the protagonist, John Farrell, working as “End Specialists”.
- Widespread Violence and Dystopia: Society breaks down as “Greenie” environmental terrorists and pro-death protesters target those who have taken the cure.
- The “Cycle” Trend: People adopt hedonistic lifestyles, traveling excessively or changing careers, as they anticipate centuries of life ahead.
- International Reaction: Countries like China ban the cure and tattoo citizens with their birthdates, while others, such as Russia, militarize their “postmortal” population.
- The “Correction”: The novel, told through diary entries, news reports, and blog posts, follows the decline of civilization into a “pre-apocalyptic” state, culminating in the “Correction”.
I’m not a regular sci-fi reader, but I should be since I find this recipe of change one major assumption about how the world works and then see how it propagates quite fun. (I am about to re-read Brave New World!)
In the vein of that recipe, there’s a short story I’ve had swirling in the back of my head for a decade. It’s never gonna see the light of day because
a) it’s not a priority and
b) its premise is probably going to happen, spoiling the story
It’s the story of everyone’s private info being leaked on the web. Tax returns, bloodwork, nude photos, Nest footage, emails, DMs, location history. The real Y2K event.
The Postmortal model strongly influenced how I thought about it. There would be a minority of people, like the pro-death protesters who opted out of taking the pill, who were viewed as some anti-progress hippie. It would be the group of people who opted out of looking at other’s private data.
Think of it as a voluntary non-proliferation of grievance. I value whatever privacy remained as of 2026, I assume you do too. We are all adults. We agree to just not look. And society cleaves between the lookers and the ostriches. There’s a whole sci-fi book to be written about every aspect of this.
One of my favorite movies did a skit that would resemble dating in such a world. I love the moment when it “hits” Steve Guttenberg, “It says all that?”
The idea of a non-looker might have been remotely possible when there was friction to sorting and searching through petabytes of files.
But when it’s all leaked, that friction will be gone.
“Hey Claude, have any good friends talked shit about me?”
About a year ago, my family went on a CA gold rush tour at Marshall Gold Discovery Park in Coloma. Strong recommend by the way. The guide is an absolute treasure of historical knowledge. Anyway, you see how the indigenous lived in those lands before the settlers arrived. Touring the site, I was viscerally struck by the lack of privacy that their way of life entailed. Large families coexist in tight tent-like structures. I had to be the one who asked, not quite in these words but with a mix of diplomacy and subtle gestures, “Where did they screw?” As you might guess, tribes didn’t need to do a birds and bees talk. It’s more of a show without the tell.
As tech zooms forward, do social norms loop back to prehistory?
I made this joke a couple weeks ago. Except for it wasn’t a joke. I really multiplied 25×35 this way while sitting at my desk.
To spell out the link to investing math:
What did we notice?
a * b = Mean² − MAD² (where MAD = mean absolute deviation)
As soon as numbers deviate from the mean, their product is dragged down, even if the mean is unchanged. More deviation, more drag. And what is deviation? Volatility.
Bridging middle school math to investing math
In investing, we compound, or multiply returns. So even if the mean of two returns is identical, the dispersion between them matters. Not just matters. It matters quadratically.
No dispersion: The arithmetic mean of (8, 8) is 8. The geometric mean of (8, 8) is √(8×8) = 8.
With dispersion: The arithmetic mean of (5, 11) is still 8. But the geometric mean of (5, 11) is √(5×11) = ~7.4.
If you earn 10% on an investment and then lose 10%, your mean return is 0, but your actual compounded (geometric) return is 1 − √(1.1 × 0.9) = −0.50%.
Now increase the volatility: earn 40%, lose 40%. Mean return is still 0. Compounded return? 1 − √(1.4 × 0.6) = −8.3%.
The drag on your returns is a function of squared deviation. Put simply:
Compounded Return = Average Return − σ²/2
Nice intuition for nC2 combinations being (n²-n)/2 It’s also the number of pairwise correlations for n assets and why a correlation matrix looks like a triangle (or half a rectangle)
3:44 PM · Apr 3, 2026 · 6.88K Views
3 Replies · 4 Reposts · 38 Likes
N² – n shows up in investing as well!
Recall the levered silver flows post where we see the quick math of levered ETFs. For a fund to maintain its mandated exposure, the amount of $$ worth of reference asset they need to trade at the close of the business day is:
x(x - 1) * percent change in the reference asset * prior day AUM
where x = leverage factor
examples of x:
x=2 double long
x=-1 inverse ETF
x= 3 triple long
x= -2 double inverse
This isn’t just a levered ETF thing. The -1 leverage factor is exactly the same as just a vanilla short position. It’s a sneaky reason why the shorting is mathematically challenged.
The easiest way to think of this as an individual investor is to imagine you have an account value of $100. The account is holding $100 in cash, but it’s the proceeds from shorting a $100 stock (assume you don’t need any excess margin to maintain the short). If the stock falls to $50, your account value is now $150 (your cash + $50 mark-to-market profit on the short). You earned a 50% return on a 50% drop in the stock.
Now what?
If the stock falls another 50%, you make $25.
$25/$150 = 16.7%
If you want to maintain the same exposure so that you make 50% on your account on that second 50% drop, you would have needed to short more shares at $50.
How many more dollars’ worth of stock?
-1 (-1 -1) x -50% x $100 = -$100
You needed to sell an additional $100 worth of stock or 2 more shares at $50. Then on that last leg down, you would have made $25 on 3 shares total or $75.
$75 profit /$150 account value = 50% return
Learn more:
🔗 The difficulty with shorting and inverse positions.
People like little tricks. I published this article on X and it got over a thousand likes which is 3 standard dev engagement for me (probably. I’m going off feel.)
🧠Math Shortcuts Traders Know By Heart
A random smattering from it:
Straddle to Vol
Implied Correlation
Implied correlation ~ index variance / weighted average stock variance
Using implied vols instead:
Implied correlation ~ (index volatility / weighted average stock volatility)²
Example:
If the SPX is 15% vol and a typical stock in the index is 30% vol, implied correlation is (.15/.30)² = .25
The Moontower Rule of 70
This is related to the Rule of 72 but allows you to solve for the CAGR if you know how much your money has grown in X years.
CAGR = 70% * (doublings/years)
Example:
Your home is up 8x in 50 years.
What’s the CAGR?
8 is 3 doublings
70% * (3/50) = 4.2%
Doublings might sound like a complicated measure, but you should get up to 2¹⁰ as quickly as you know your multiplication table for 12s.
If something is up 50x, that’s somewhere between 2⁵ and 2⁶ or about 5.5 doublings.
And just like that, you can estimate log base-2 fairly quickly for any number up to 1024!
Finally I published this tool on the website to estimate slippage:
📱Square Root Impact Calculator
Last week, we talked about trading as a business. This week, we talk about options market making.
Some of the topics here were covered in further depth in Thursday’s half rant/half insider look: market maker privilege
I was at the Collective meet-up in Menlo Park this week (this was the 3rd time I’ve attended and it’s always a great way to connect with investors and just amazingly bright people. I always feel like an ape in this group, but that’s better than the opposite). Shannon, faciliator extraodinaire, gives guest prompts beforehand so they are prepared, including some fun ones like this icebreaker:
share a song that lifted their spirits and why
My answer is Hungry Eyes.
The backstory:
My friend Matt’s bachelor party was in Costa Rica in the early 2010s. We rented a dope house right on the beach. About 15 guys flew in for it. On arrival day, the first fellas claim the best rooms and all that. There’s that dynamic y’all know. Mixing your childhood friends with your college friends, work friends and so on. We’re pregaming before going out for the night and it just feels kinda tense.
Everone down’s the parting shot, the van’s here. We file out, take our seats. It’s quiet as we pull onto a bumpy road. Matt connects his phone to the van’s sound system and throws on a playlist.
That unmistakable sound of 80s kitsch.
Hungry Eyes. Vocals kick in, mood starts to change.
By the time we get to the hook, it’s a full-blown Almost Famous bus scene.
All was copacetic from that point. One of my favorite memories period.
Such a great prompt Shannon!
Stay groovy
☮️
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