My own action adventure engine

[Xkeeper]

The solution to that physics problem is running physics multiple times in smaller timesteps, not not using dt.

The problem is, let's say Physics is taking too long.

Your game misses a frame update; easy enough, run Physics twice to catch up (since high dt = major errors or crashes).

But uh oh, you just nearly doubled the time it takes physics to update; so you skip more frames, and have to run it more often to catch up, until eventually it gets ridiculous.

Sure, you can get around it by doing a bunch of shit to limit dt-catchups to sensible values and all that other crap, but if you're mucking with dt that much you may as well just make it static.

[kikito]

The problem is, let's say Physics is taking too long.

Then your problem wouldn't be dt; the problem would be that, literally, physics take too long.

The right solution would be removing unused bodies, stopping simulations of non-critical stuff, etc.