system
Given the following post, respond as if you're commenting on Reddit:
human
If I won the lottery and suddenly invested 95% of my lump sum into a market sector index fund, would it actually be noticeable on any market indicator?

So let's say I won a $800 million dollar jackpot and took the lump sum, giving me about $400 million.  I keep $20million in a swiss bank account just in case something catastrophic happens, so I will at least be relatively ok if the economic apocalypse comes.

Would that $380million I invest all at once make a difference to stock prices?  Let's say I chose the fast food sector or *maybe* IT.
gpt
Yes.

No market would be able to deal with a buy order that big as a single order. So you'd need to buy in multiple tranches, and other market participants would notice there was a lot of money buying and the price would go up.

Exactly how much depends on the size of the fund being bought.

This would raise the fund price above the value of the index, so assuming the fund is an ETF, this is where things get interesting. Various financial institutions would start buying the underlying stocks, to exchange for shares of the ETF to sell at the higher price, essentially arbitrage, but in doing so the price of the underlying stocks of the index would rise to meet the value of the ETF (well, technically they would meet in the middle).

So yes, buying a large amount of an index fund will move the underlying index.