I’m assuming the pressure somehow forces the heat to penetrate everything quicker to heat from the inside.
In: Physics
So the fact that the steam has nowhere to escape plays a big part also?
Steam have a lot more heat capacity then dry air. Normally if you put a cold roast into the oven it cools down the air around it so it takes a long time to heat up. However it is not able to cool down the steam around it so it will experience much higher temperatures. You can experience some of the same yourself as dry heat or cold weather is not as bad as humid heat or cold weather. And in a sauna the difference is extreme. But another reason your pressure cooker is better is the pressure part. By containing the pressure it allows the temperature to get much higher then it normally would. This not only allow the heat to rise to temperatures similar to those in your oven but also allows the air in the pressure cooker to absorb even more steam so it takes even more to cool it down.
Once water is boiling, it stays at a constant temperature as the liquid converts into a gas (steam). Increased pressure also increases the temperature at which water boils so things cook faster.
Related fact: that’s also why you have to cook things a bit longer at higher altitudes. A city in the mountains has less air pressure than a city at sea level so you have to adjust recipes.
The answer is twofold. The pressure increases the boiling temperature of the water that is doing the cooking (higher temp means faster heat transfer). Water is also far (by a lot) more conductive than air (case in point, boiling water hurts immediately and hot air from an oven doesn’t).
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