If people actually dumped index funds for cash en masse it would be catastrophic. To attach some numbers, MSFT averages about 35M shares in daily volume, and that includes all the market makers, HFTs, etc. BlackRock (iShares) owns 593M shares of MSFT and Vanguard owns another 482M. Together, the amount of shares that index funds own is about a month and a half of total trading volumes. I'd bet that such a crash would unfold over about 2-3 days, which brings up the specter of stocks literally going "no bid", where there are not enough buyers for every seller to sell, at any price.

Likely the government would step in and inject cash directly into the markets to support them in such a scenario, because a broad-index stock market crash is the modern-day bank run. Retirees carry the bulk of their savings in the form of stocks; if it disappears, we'd likely face revolt.

Same old story of too big to fail. The government will "inject cash", that is borrowed, so that retirees 401k accounts don't go down. But who pays back the borrowed funds? The non-retirees. Everything is optimized for the boomer generation to be fine, who cares about anyone else?

If you're retired and that exposed to stocks then you deserve to lose the money you risked.

Pretty sure most people just sit in the default requirement 20XX year funds, which heavily weight away from equities once people are retirement age.

Market makers aren't included in those numbers, Vanguard, etc don't trade normally but on secondary markets most of the time.

If you hit sell on a vanguard ETF and it sells on the market, then Vanguard isn’t the buyer is it? So in that situation with everyone dumping ETFs there would be a lag on the time taken for the ETF to sell and Vanguard to then dump the stocks back out in the market. It’s never occurred to me the situation where huge numbers of people dump index funds and how Vanguard/Blackrock account for that without becoming bag holders of the underlying stocks themselves.

In any case, I’m not sure that large enough numbers of ETF holders are sitting close enough “to the button” to hit sell in the event of a sharp downturn occurring over the space of even a week or two. And a lot of them would see it as an opportunity to DCA into the dip anyway.

If it's an ETF it's a little complicated. The usual mechanism for selling an ETF is that there's a buyer on the other end who's buying shares in the ETF itself, not the constituent stocks. Arbitrage keeps the price in line with the index constituents; if the ETF diverges from its constituent assets, some HFT can buy the ETF and sell the constituents and that will force them to converge.

However, most ETFs are also setup such that they can create or destroy shares in response to large shifts in demand. In this case, if enough people hit sell, the ETF itself will buy back shares and use the proceeds to sell the underlying assets, in a transaction that mechanically should be market-neutral and just propagate the supply/demand of the fund down to the individual stocks.

With Vanguard specifically, it's even more complicated, because VTI is not a separate ETF. It's a share class of the Vanguard Total Stock Market Index Fund. But the mechanism is largely the same - it has the same Authorized Participant system to mint new shares in case of high demand and redeem shares if everybody sells, and then passes these requests on to the underlying mutual fund, which can then piggyback on some of the tax efficiency benefits of the ETF.

Right, got it. Thanks for the info.

Yeah I think it's more realistic to reallocate to ETFs which skip the frothy stuff. I wrote a comment about this in the other thread: https://news.ycombinator.com/item?id=48367563

These stocks crashing (not saying it will or won’t happen), means AI is crashing, and that will be a much broader selloff than these 3. Add Microsoft, Micron, Amazon, Oracle, Nvidia, Supermicro, Dell, etc, any company that has direct or indirect exposure to the massive AI boom (and possibly their lenders).

Just look at Corning’s lifetime chart

While unlikely to happen at scale, by way of anecdata I'll say that I and my extended family have almost all shifted money away from funds that are heavily coupled to the fate of GenAI.

The bottom is going to fall out of the market and it's going to take years to recover, I don't see any reason to suffer through that (and neither do my retirement-age relatives).

I'm after steady gains in an approximately efficient market, not a wildly unsustainable speculative boondoggle, thanks.

So you’re still hedging or you 100% fled AI? I presume you have gone to a broader portfolio. But if tech crashes doesn’t everything? And isn’t tech holding up the entire market so they won’t let it happen? And how can you even avoid GenAI if people are cramming it into everything and it’s constantly shocking sectors of the market?

If the bottom is falling out of the market in AI I think it's likely other things will fall too though.

What’s your portfolio? I don’t particularly have a wealth of investment options in my employer-provided 401k (ADP Workforce Now)

Not OP but I’m in a broad-based Euro index so I gain on the stocks and on the fact that the dollar is going to shit. I haven’t seen the enormous AI-juiced gains that have become commonplace but I’m also insulated from commodity hardware companies trading like rocket ship startups and whatever ends up coming out of that insanity.

Somebody is going to have to explain the business case for Micron trading like it’s Google. We all know that fabs are a low-margin capital intensive business, right?

example of a steady gain in an approximately efficient market if Big Tech crashes?