Using electrolysis to extract hydrogen from water is, to use your phrase "a known quantity and doesn't need to be repeated for every new study in the field". In other words, that process is real and "passes physics".
If, on the other hand, we propose to use electrolysis to generate liquid hydrogen to use as fuel, the ENTIRE PROCESS has to pass physics.
It does not.
Why?
Well, it takes approximately 55 kWh of electrical energy to extract 1 kg of gaseous hydrogen from water.
Great.
However, 1 kg of gaseous hydrogen contains 40 kWh of energy.
In other words, you have to use MORE energy to extract the hydrogen than the energy it contains. This idea, at the most basic level, does not pass the physics test. It's a fantasy.
If the creation of hydrogen fuel via water electrolysis is an example of something that "doesn't pass physics" then the idiom "doesn't pass physics" obscures more than it clarifies. There is nothing physically implausible about water electrolysis. Despite the energy losses, water electrolysis to produce hydrogen fuel may be better than the alternatives; for example, you can launch a rocket to orbit with hydrogen fuel but you can't do that with electricity. If "doesn't pass physics" is supposed to be shorthand for economic implausibility relative to alternatives, just make the economic argument instead of referring to physics.
> There is nothing physically implausible about water electrolysis.
You are getting lost in the semantics and an example I grabbed as an illustration and ignoring the message, which is simple:
Anyone can propose anything. And that's fantastic. No problem. However, at some point, it has to make sense. And it has to make sense while looking at the entire process, not just a small element of it.
There are a lot of things in life that sound fantastic, until you run a full analysis and understand that they don't really make sense, particularly at scale. This has to be the first step.
Beyond that, after that step, the project has to be compared to other proposals that can deliver similar or better results. This, again, can usually be done before launching into these projects. It's about that list of dependencies I posted in my other comment.
Why?
Because we are wasting valuable time and money on fantasies, that's why.
Making a business comparison to try to further illustrate the point. In business you have to run through top level before jumping head-first into anything at scale. You also have to run competitive analysis and decide if your proposal is actually realizable and competitive.
In my work in aerospace I have to do this all the time. We are used to conducting what's usually called "Trades Analysis". This is a document where you present and analyze, to a sufficient level, all reasonable options to solve the problem you are trying to address. This is the starting point for a discussion that usually leads to choosing the solution or approach that makes the most sense within the stated objectives and constraints.
> If "doesn't pass physics" is supposed to be shorthand for economic implausibility relative to alternatives
No. That's not it. It really is about everything else first and foremost. Before you consider economics you have to consider science. Again, for the entire process, not a small portion of it. Of course, there are cases where the economics is so obviously ridiculous that scientific analysis quickly becomes irrelevant. A ridiculous example would be something like mining materials from the moon to make common concrete on earth. We don't need to look at science to know that would be economically and ecologically ridiculous.
> for example, you can launch a rocket to orbit with hydrogen fuel
If you change the problem, you change the required analysis methodologies. Still, you have to look at the process in its entirety and in the context of comparisons to other ideas. That's why nobody launches rockets into orbit using hydrogen. It doesn't make sense when looked at from a macro perspective.
My advice:
Always take a very large step back. Try to understand and quantify the entire picture. Things have to make sense at the macro level.
If, on the other hand, we propose to use electrolysis to generate liquid hydrogen to use as fuel, the ENTIRE PROCESS has to pass physics.
It does not.
Why?
Well, it takes approximately 55 kWh of electrical energy to extract 1 kg of gaseous hydrogen from water.
Great.
However, 1 kg of gaseous hydrogen contains 40 kWh of energy.
In other words, you have to use MORE energy to extract the hydrogen than the energy it contains. This idea, at the most basic level, does not pass the physics test. It's a fantasy.
If the creation of hydrogen fuel via water electrolysis is an example of something that "doesn't pass physics" then the idiom "doesn't pass physics" obscures more than it clarifies. There is nothing physically implausible about water electrolysis. Despite the energy losses, water electrolysis to produce hydrogen fuel may be better than the alternatives; for example, you can launch a rocket to orbit with hydrogen fuel but you can't do that with electricity. If "doesn't pass physics" is supposed to be shorthand for economic implausibility relative to alternatives, just make the economic argument instead of referring to physics.