If you could know one asset price twenty years out

Dennis Shiraev emails me:

You are an investor with $10 million planning to cash out in 20 years. A genie appears and offers to send you the price of one but only one asset 20 years from now to inform your investment decisions (a stock, currency pair, commodity, equity index, etc.). What do you want to know? The genie also gives you 20 year cumulative inflation (or exchange rate change for non USD assets) so you won’t need to worry about price/value disentangling.

I said the price of Bitcoin but also considered the IBOVESPA or Shanghai composite index prices.

This isn’t as simple as it might seem at first.  You might look for the most volatile price among the liquid assets whose trading you can access.  But knowing the price only twenty years out then tells you little about what is happening in the meantime.  Which price twenty years out gives you the most information about the global path of prices along the way?  That may suggest looking for a price with some persistence, and which contains lots of information about other prices too.

For purposes of tractability, let’s assume that prices are not rescaled in the meantime, through say major changes in currency names or index definitions, and that knowing the future price of a variable is in some way commensurable with the current understanding of that same variable.

Then I would opt for the Shanghai composite.  I don’t see Bitcoin prices as correlated with enough other facts about the future state of the world.  Plus, if it turned out that price would fall to zero or undefined, you might find it hard to short significant quantities of Bitcoin in the meantime.