[ArGee]

So, wealth shuffled around but didn’t change in the aggregate? Some won and some lost?

[Alberta's Child]

Think of it like buying and selling your home.

If you bought it for $100,000 and it's now worth $300,000 just a few years later, then you can make a lot of money on the deal. But that $200,000 gain only happens if you sell it now.

If the value of the home goes back down to $200,000 you didn't lose any money even though it was worth $300,000 at some point. You're still $100,000 ahead.

[Pelham]

Index traders can make money during swings like that if they guess the correct direction.

But I doubt that there is a way to determine whether there has been an increase in aggregate wealth from that trading. What they do would be a small blip compared to pricing the entire stock market.