Drives politics leftwards: This is confusing to me because I'm sitting leftward. This insidious set of incentives is shifting society's values towards mine. I want this to happen. Am I supposed to be rubbing my hands together and cackling gleefully as Cthulhu does my bidding?

Today? Absolutely.

But Cthulhu doesn't stop swimming. The Whigs (both parties on both sides of the Atlantic applied), the Republicans (in the "First French Republic" sense), the Democrats (in the Jacksonian populist sense) and even most recently the Social Liberals all learned that lesson the hard way when they ended up taking their turns on the right side of the Overton Window.

You are not an exception; eventually, there will be a point at which today's intellectuals become tomorrow's targets. Given the ferocity of the anti-science postmodernism of Europe and California today, I don't think it's that far off. Look up the word "biotruth" or do some research into the anti-GMO movement and you'll see your leftist buddies are on the front line right now fighting against the very science which might someday make transhumanism possible.

Governmental entropy: So, the way you phrased that makes me assume that this doesn't mean "overturning of social order via revolution". But what does that mean, then? How is it measured? What's a real-world correlate?

Entropy is an apt metaphor here actually;

Your metaphorical solid block of hydrogen at 0K is something like the thousand year Fnarg. Authority is absolute, atomic and universally acknowledged. Of course, in reality absolute zero is impossible but the principle remains that a more ordered state is one of greater regularity and lower volatility. We've all heard the proverb about how a woman could carry a pot of gold from one end of the silk road to the other under the Mongol Empire's rule, and while certainly an exaggeration it's clear that terrorism and organized crime in the modern sense would have been virtually impossible there.

On the other hand our metaphorical ideal gas might be something like the state of affairs during the Congolese or Somalian Civil Wars; or in other words, most of Post-Colonial Africa. The governments of these nations are actually rather large, in the sense that they employ a lot of people and pay them pretty well, and when you factor in the various NGOs and foreign governments propping them up their bureaucracies are extraordinarily complex while providing no actual governance or exercising any actual sovereignty. Those abdicated functions are carried out, if at all, by short-lived local warlords or tribal chiefs who are so insecure in their positions that constant terrorism of the people is the only way to survive.

There's a lot of room in between those extremes, for example I'd say the US today is an uncomfortably warm liquid, but that doesn't change the nature of the spectrum. Order is a state where unambiguous leadership creates a simple structure of government to incentivize productive behavior, whereas Chaos is a state where a leadership vacuum creates political complexity / volatility that incentivizes counterproductive behavior.

I would thereby not make the inference that Moldbug is scientifically illiterate, but that Moldbug mistrusts the validity of scientific consensus itself.

I don't see a distinction; if you think science is that institutionally corrupt, on a scale greater than even Lysenko could have aspired to, you're not functionally different from a postmodernist and have just as little credibility when talking about institutional science.