Season 2
EP03 - What Quant Traders Do For The Economy
How quantitative trading provides economic value. Learn about liquidity provision, price discovery, market making, bid-ask spreads, and how quants make markets more efficient.
It makes me sick, Kurumi.
What's making you sick? The latency?
The waste! This bank capital could build houses! It could build bakeries! Hospitals! Science!
Instead, it's lent to math nerds to play a zero-sum game of 'Guess the Number' in microseconds.
They re-engineered the internet just to act faster than everyone else. It's pointless.
Nothing is created. No bread is baked. No cars are built. It's just money moving in a circle.
You think it's a circle?
It's a Refinery.
Imagine a world without Quants.
'I have $1 Billion in Apple Stock! I need to sell it to pay retirees!'
This is a market without Liquidity.
He wants to sell. But the buyer (The Bakery) isn't here right now. The buyer comes next Tuesday.
'I'll buy your gold. But since I have to wait until Tuesday to sell it... I'll pay you 50% of the value.'
'That's robbery!'
'That's the Risk Premium. Take it or leave it.'
Okay, that sucks. But we talked about it. We don't need that much liquidity.
(fufufu) Do we not?
The Quant says: 'I will buy your Apple stock right now for $149.99.'
'And I will sell it to the Bakery next Tuesday for $150.01.'
The Quant made $0.02.
And the Pension Fund saved millions.
Instead of losing 50% to the Pawn Broker, they lost 0.01% to the Quant.
This 'Minigame' you hate? It is a war to reduce the cost of doing business.
Quants fight each other to offer the best price.
But they borrowed money from the bank to do it!
They borrowed money to be the Inventory.
You can't run a supermarket with empty shelves. Quants borrow cash to fill the shelves with stock so you can buy whenever you want.
So they provide... service?
They provide Price Discovery.
The world is messy. People panic. Prices fluctuate wildly based on rumors.
The Quant takes the noise—the panic, the rumors, the glitches—and mathematically filters it.
By betting against the panic (Arbitrage), they force the price to stabilize.
They stabilize the cost of bread for your bakery. They stabilize the exchange rate for your vacation.
But the leverage, Kurumi! They borrow 10x their money!
If they are just 'stabilizing,' why do they need so much cash? It feels like gambling.
Gambling is betting on a coin flip (50/50).
Quants bet on Inefficiencies.
The profit margin for 'stabilizing' the market is tiny. Maybe 0.001%.
To make a living off 0.001%, you need massive volume. You need leverage.
Banks lend to them because they are Market Neutral.
They don't care if the market crashes or booms. They profit from the volume of the trade.
It is safer than lending to your bakery, which goes bust if people stop eating gluten.
Okay. They are efficient.
But do they have to ruin the internet? They lay private cables just to be 1ms faster!
Do you pay to trade stocks on Robinhood?
No. It's free.
Why do you think it's free?
Because... they are nice?
Because the Quants pay the broker for the privilege of trading with you.
It's called Payment for Order Flow.
Their 'Minigame' subsidizes your access to the market.
Fine, I get why they exist. But how is their business model possible?
It feels like magic. They borrow billions, trade instantly, and somehow print money. It has to be a scam.
It's not a scam. It's Stochastic Control Theory.
We process raw data into profit using four engineering pillars.
1. Inventory Control (Liquidity).
2. Cointegration (Arbitrage).
3. Covariance Matrices (Leverage).
4. Flow Segmentation (PFOF).
That sounds like a Physics textbook.
It is. Money is treated like a fluid. And fluids have rules.
So you bought a lot of Apple. Isn't that good?
Every share we hold is exposure. Double the inventory, double what a move costs us.
We're way over on Apple!
That means we bought too much. If the price drops now, we lose millions.
That's Inventory Risk.
So we cut our price until someone takes it off our hands.
The bigger the position, the cheaper we have to make it. That's the whole mechanism.
A holding company wants to accumulate Apple. They're paid to hold it.
We aren't. We have a weight limit. They end the year heavy; we end the day flat.
By lowering the price, we discourage sellers (don't give us more!) and encourage buyers (please take it!).
It's a Negative Feedback Loop.
So... the price change isn't random?
No. The price moves because the Market Maker needs to get back to flat.
Okay, Inventory is defense. How do they attack?
One idea is to use Cointegration.
Most stocks are Random Walks (Non-Stationary). You can't predict them.
But the difference between two related stocks is often Stationary.
See this sine wave? It always returns to zero.
We don't predict the price of Coke. We predict the tension in the spring.
The price spread is stretched! Coke is too high!
So the algorithm executes a Pair Trade.
Short Coke -100. Long Pepsi +100.
We are Market Neutral. We don't care if the market crashes. We only care that the spring snaps back.
But the spring only snaps back a tiny bit! Pennies!
How does that pay for the servers?
That's where the Banks come in.
Banks lend to us because we engineer away the risk using Diversification.
If I bet on one coin flip, it's risky.
If I bet on 1,000 coin flips that are uncorrelated, the variance drops to near zero.
The Law of Large Numbers protects the bank.
So you borrow 10x your money...
Because my mathematical risk is 1/10th of a normal investor.
I am not gambling. The edge on each trade is tiny, and I take it ten thousand times a day.
Leverage is what turns a rounding error into a salary.
Payment for Order Flow. Isn't this the controversial one people complain about?
Engineering-wise, it's just Signal Separation.
So you look at an order and see it's toxic?
No. They look identical. You can't tell from the order.
You tell from what the price does in the second after you fill it.
So you just wait and see if you got robbed?
If it sits still, they had no idea where it was going. That order was uninformed.
But if the price keeps sliding after you bought from them, they probably weren't done selling.
...and you're the one holding it now.
Every fill from that one is a loss I haven't written down yet. We call that pattern Informed Flow.
So we pay brokers to send us the dentist's orders instead of his.
You’re paying money to NOT trade with the smart guy??
I am paying to know which one I am trading with. That is cheaper than finding out afterwards.
Inventory Control handles the risk. Cointegration finds the profit.
You're learning pretty fast.
So it's not a slot machine. It's a casino operation!
It is four boring systems that each refuse to lose money in a different way.
Banks lend more to just 'Business Ideas'
They also lend to Engineering Architectures that can prove their failure rate is statistically impossible.
'It does feel like a great thing to build, after all.'
EP02 - What High-Frequency Trading Does
How high-frequency trading works. Learn about latency arbitrage, order book dynamics, FPGAs, colocation, and how HFT firms profit from microsecond speed advantages in markets.
EP04 - Why Backtests Lie
Why trading strategies decay over time. Learn about backtesting mistakes, overfitting, look-ahead bias, reverse engineering, and why alpha strategies become obsolete.
