For example, compare these two options:
Option 1: Take 10 or 20 bus routes. Each being 5 to 10 miles long. Convert all buses to electric power.
Option 2: Take the same routes. Rip-up 200 miles of sidewalk (yeah, they'll be some overlap, this is just a quick mental exercise). Develop new technology. Install 400 miles of it (you need two directions of travel). Staff for installation, support, etc.
The first passes "physics" in that asking "does it make sense given all we know?" test results in a pretty quick "yes!". The second is such an obscene deviation from what would make sense from almost any perspective that it is surprising anyone would consider discussing it at all.
Take, for example, having 400 miles of active sidewalks. You just replaced a few buses with 400 miles of sidewalk moving most of the time. Why would anyone wait if the sidewalk is right there. Whereas before people would wait a few minutes for a ride now you are going to have dozens of miles of expensive power-consuming active sidewalks moving all the time simply to carry a single person 100 meters to then have them cross the street and get on the next active sidewalk. And, if it snows, now you are carrying tons of snow until you devote a small army of trucks to go clean the snow. I mean, the more you think about the reality of this utopic concept the stupider it sounds.
It'd probably make far more sense to have a small fleet of electric scooters available for rent and use only along a predetermined route. If you get off that route they turn off. So now, you'd have small one or two person clean scooters distributed along a 5 to 10 mile route for anyone to hop on and off as needed. At most you might have to walk a block or two to get one. This isn't an idea that I thought through. I'm just pulling it out of a hat to illustrate that the "physics" of this off-the-cuff concept would make far more sense than ripping-up hundreds of miles of sidewalk to install a monster of a system that makes less than zero sense.
The "does it pass physics" test refers to stuff that just doesn't make sense. Like a miracle, or the earth being 6,000 years old, or buying a supercomputer to do basic math or commuting in a Humvee. In other words, there are things that defy reasonable reality to such an extent that they simply don't make sense.
