Basic question: if every stock, bond, and government debt investor started actually believing the obvious advice and buying index funds and holding for the long term, where would the stock prices themselves come from?

Yes, but don't forget to put the expected costs of home repair in the spreadsheet (repair costs are implicit in rent).

An excellent list, agreed on all points.

On homes: yes, assuming you buy with a mortgage, these are short-term risky, but they are also long-term safe. This also means they are short-term high-expected return and long-term lower return. On average home prices rise at just slightly above the inflation rate (in my area a little faster right now, about 3%). So when I bought a $335k house with 5% down (<4% interest, 30 yr mortgage), that means my equity (initially ~17k) rose by close to 80% in the first year. Factor in closing (read: transaction) costs and it's still an expected 50% return. But that will fall to 3% over 30 years once my equity rises to 100%. And in my case, the mortgage payment + taxes was already hundreds of dollars less than my previous rent (and the mortgage payment will never go up), interest and property taxes are tax deductible, and my state has programs to significantly reduce the costs of PMI. I stared at a lot of spreadsheets before pulling money out of my brokerage account to buy a house.

Sure, the problems with the physics are right in there with bothersome things that Harry says that you could still justify, starting with the non sequiturs about conservation of energy when McGonogall turns into a cat.

I disagree with su3su2u1 (the tumblr author) about levitation; that doesn't violate conservation of energy if it's mediated by a force, and why shouldn't it be? On the other hand, turning into a cat violates conservation of mass (or would appear to, and that should be easy to check with a bathroom scale), which (via E = mc²) translates into a huge energy violation. But bringing up the quantum Hamiltonian? FTL signalling? Su3su2u1's analysis is correct.

The justification for this is that Harry is 11 and has only a vague idea about how physics actually works. But then it's hard to tell what we should learn from Harry and what we should ignore. (For that matter, I don't even know if Eliezer knows better than Harry or not.)

As a point of interest, wasn't it Merlin's original intent that, at minimum, everyone mentioned in a prophecy should have access to it? It was only centuries later that the Unspeakables sealed the prophecy records away, so why does the Line of Merlin Unbroken have a function for bypassing that seal, how does anyone know this, and why is using it forbidden?

Harry has to some extent undone the work of Merlin. Merlin's interdict ensures that the most powerful magics slowly die out of the world as wizards and witches die with their secrets. Harry's scheme for immortality in the magical world puts a stop to the losses, and allows magical knowledge to be kept as it is re-discovered, however slowly. Previously the loss rate exceeded the discovery rate. I think that is about to be reversed. And the Interdict of Merlin was put in place to avoid a prophesied destruction of the world.

Ch. 80

And when (the legend continues) the Seers continued to foretell that not enough had yet been done to prevent the end of the world and its magic, then (the story goes) Merlin sacrificed his life, and his wizardry, and his time, to lay in force the Interdict of Merlin.

My guess is that he ignores this site completely these days, except for the Main posts, so better post what you want him to see there. Also, he replied to this particular point in r/hpmor.

As further evidence that the vow blocks killing all the people consider this.

The vow blocks Harry from telling muggels about magic and starting mass healing. At the time it blocks him the ideas he thought of were transfiguring nuclear weapons and plagues that could replicate before the transfiguration wore off. Neither of those poses any danger to "the world" but they pose great danger to the worlds people. Harry doesn't think of up quarks until after he has already been blocked. So the vow seems to be interpreted as killing everyone being the end of the world. Which is quite possibly how Harry understood it.

So I've been thinking about the feasibility of cutting stuff with a thin wire. As the thickness of the wire goes to zero, and the tensile strength goes correspondingly up, does the effort required for cutting actually go to zero?

It seems to me that it can't go to exactly zero, because you still need to counteract whatever forces were holding the material together. But does it go to a small value or a large value, in the case of cutting a strong material like bone? Say, if we tried using a thin wire to decapitate a person standing up, would they actually get decapitated, or would they just fall over?

This might be a dumb question, but is the specific lesson of the Something To Protect article reflected in these last chapters? If so, in what way?