See, now you're thinking ahead! Here's just 2 ETFs (passively managed index funds) that track the S&P 500:
Vanguard 500 Index Fund Investor Shares
NYSEARCA: VOO $130.17B Market Cap
Vanguard 500 Index Fund has total net assets of $520.3B
SPDR S&P 500 ETF Trust
NYSEARCA: SPY
Market Cap: $305.17B
So if TSLA was added to the S&P 500 index at its current SP of $430, just these 2 Index Funds (and there are many such Index Funds) would need to purchase approx. $1.5B in shares. You recall what the Saudi PIF purchase of $2B did to the TSLA SP in Spring 2018, and that buying was spread out over a number of months.
Further, if TSLA's SP is around $580 when its added to the S&P 500, then the 2 Index Funds mentioned above would need to buy about $2B worth of TSLA shares.
Obviously, if Longs are reluctant to sell, and Shorts head for the exit in a panick, then the SP goes up exponentially, rather than the linear $2B/$175B = 1.2% caused in a neutral redistribution of shares. I'd expect a 10-20x as a multiplier for that redistribution, which then implies between a 12-25% rise in SP caused by Index Funds purchasing $2B of TSLA stock.
But there will be other buyers besides these 2 large funds. Many other buyers.
Cheers!
It has been mentioned here that there will be investors that will front-run the addition to S&P 500, causing buying pressure BEFORE the date of addition. Which will increase the stocj price, which will increase the weight factor, which will increase the number of billions of dollars worth of TSLA which will have to be bought by index funds, which will increase the attractiveness of the front-running, which will increase the pressure on the shorts, which will increase short covering, which will increase the stock price, which will...
I’m stopping here, let’s just conclude that the addition to S&P500 may be the virtuous circle we’re waiting for (a vicious circle for the shorts).