The Line We Can't Cross | Mike Green on the Passive Investing Endgame

Key Concepts

• Inelastic Markets & Passive Investing: The growth of passive investing is creating increasingly inelastic markets, potentially leading to volatility and even market closures.
• Energy Transition & Grid Strain: A major shift from fossil fuels to electricity is underway, placing significant strain on the US electrical grid and driving up energy costs.
• LLM Impact & Productivity Paradox: Large Language Models (LLMs) are powerful analytical tools, but their benefits are not universally translating into productivity gains, and their energy demands are contributing to grid issues.
• Housing Market Misallocation: The US housing market suffers from a misallocation of housing stock, not a true shortage, requiring regulatory reform and adaptive reuse of existing structures.

Part 1: The Inelastic Market Hypothesis & Passive Investing’s Impact

The discussion began with an exploration of the “inelastic market hypothesis” (Gabay & Koyen, 2020), challenging the conventional efficient market hypothesis. Mike Green argues that markets are becoming less able to absorb supply and demand shocks due to the increasing dominance of passive investing, currently estimated at 54% with a 4% annual increase. He reframes passive management not as a buy-and-hold strategy, but as a systematic algorithm driven by inflows and outflows. This constant trading, including during index reconstitutions, fundamentally alters the assumptions of Bill Sharp’s original model of passive investing, which defined it as never transacting.

The impact of these passive flows is disproportionately felt by individual securities, particularly those with lower liquidity. A formula (derived from JP Bush’s work) illustrates this, demonstrating the relationship between a security’s volatility, trading volume, and the price impact of an order. Index arbitrage has become a significant hedge fund strategy exploiting the predictable trading patterns of passive funds, exemplified by the run-up in Tesla’s price prior to its inclusion in the S&P 500 in December 2020. Green criticizes Vanguard’s fee cuts (a 30% reduction from 3 to 2 basis points) as a strategic move to attract more inflows, exacerbating the problem.

He estimates a critical passive ownership threshold of around 83%, beyond which market closures become likely, based on modeling work replicating Andrew Low’s research. Active manager elasticity has also declined, from 75-80 to below 50, partly due to pressure to mimic index performance. Green expressed a pessimistic outlook regarding regulatory intervention, believing the trend towards passive dominance will continue.

Part 2: Macroeconomic Shifts, LLMs, and the Future of Energy & Housing

The conversation then shifted to the macroeconomic implications of transitioning away from fossil fuels, anticipating a complete flip to an electricity-based energy system within the next 20-30 years (from 75-80% fossil fuels to 75-80% electricity). This transition is described as a significant logistical challenge – a “pig in the python” – requiring “extraordinary investment and innovation.” Currently, only 15% of energy reaches the electrical grid due to losses during generation, while fossil fuels are allocated roughly equally between energy for human consumption and as raw materials for fertilizer and animal feed.

Green detailed his extensive use of LLMs – Claude, ChatGPT, Gemini, and Grock – as analytical tools, viewing Gemini as equivalent to a second-year financial analyst and Claude as superior for writing. He emphasized the importance of “domain specific knowledge” for effective LLM utilization, noting a “33-year accelerated learning curve” associated with their application to financial markets. He believes LLMs have effectively “subtracted 10 years” from his cognitive decline, but also acknowledged the current “extraordinary hype” surrounding them.

This hype is contributing to strain on the US electrical grid, driving up the cost of power generation. Installation costs for natural gas combined cycle turbines have doubled in the last 5 years, and nuclear energy faces uncertain upfront costs, even with Small Modular Reactors (SMRs). These increased electricity costs are not offset by productivity gains from LLMs for most people, creating a potential “sociological phenomenon” and becoming a political issue, as evidenced by Donald Trump’s commentary. Microsoft’s potential need to become a utility to power its data centers was presented as an example of the challenges ahead, highlighting the lower profitability of utility businesses.

The discussion briefly touched on the Netflix film The Rips as a potential commentary on corruption.

Finally, the conversation turned to the housing market. Green argued that the US doesn’t have a shortage of housing, but rather a misallocation of existing stock, driven by Baby Boomers aging in place. He predicted a future government building program would likely result in building the “wrong type of housing in the wrong places,” advocating instead for deregulation of residential construction, conversion of commercial real estate, and a focus on making cities more energy-efficient and safe. He dismissed Trump’s plan to have agencies buy back MBS as ineffective, characterizing it as “ineffective tribal government.”

Conclusion

The conversation presented a complex and interconnected view of current economic challenges. The rise of passive investing is altering market dynamics, while the energy transition and the adoption of LLMs are creating new pressures on the electrical grid and raising questions about productivity gains. Addressing these challenges requires a fundamental rethinking of market structure, energy policy, and housing regulations, moving beyond conventional wisdom and embracing innovative solutions. The underlying theme is a sense of urgency, with Green suggesting that inaction could lead to significant economic consequences.