This site is based in the US. Therefore, the convention it follows should be that of the US. Any use of a comma as a decimal delimiter here is simply wrong.

Besides that, the use of six digits when only two or maybe three are actually significant is just clumsy.

Except those things mostly have real airfoils, and don't need such a high TWR to plow through the air like the flat plate in the article.

No body is fully elastic. You will have infinitesimally small energy losses due to changing internal stresses in the two bodies. You get very very close to 100% recovery, but not 100% recovery. The energy is still there. It hasn't escaped your hypothetical closed system. It is simply not recoverable in a useful form. It is disordered. Reversible processes are those "special cases".

Of course doing so has the side effect that no one will give you loans because your currency is too unstable to be of any international value.

Those numbers already take into account the difference in traffic volume. An individual loaded tractor trailer causes several thousand times the damage as a single sedan. In other words, there would have to be 80x the volume of passenger traffic on the road to cause the same amount of damage as present truck traffic.

So what? You're artificially buoying up industries that perhaps shouldn't be. Nearly all of our shipping is done over the road, due to cost and convenience. Make roadway shipping pay to repair its fair share of damage done to the roadway. Initially, shipping costs will rise. Costs for all products would rise across the board as those increased operating costs trickle down to consumers. Over time, those companies will find new ways to reduce costs. Money would be pumped into the rail system, expanding and modernizing it to improve speed and throughput. Manufacturing would become more regionally diverse so less has to be shipped across the country. Fewer vehicles on the road means lower traffic congestion. Less roadway maintenance further means lower traffic congestion. Locomotives are more efficient per unit of shipped material are more easily managed in terms of emissions. Fixed, limited access railways can be more easily converted to electric.

The trucking industry would suffer, unquestionably, but it's a much more complicated issue than you give it credit for, and perhaps the advantages in other areas outweigh those effects.

Is that taking into account traffic volume, as a typical loaded tractor trailer is going to cause several thousand times the damage as a typical sedan.

You would need a nuclear reactor to provide enough power to land on the Moon using an arcjet.

By that, you actually mean everything has to do with thermodynamics. You're adding energy to disassociate a molecule. Thermodynamics dictates that you cannot recover that same amount of energy by letting the constituent elements recombine. Tyr07's uncertain belief coincides with one of the fundamental principles at play in any real world system.

No it doesn't. The only way you could hope to achieve anywhere near that is through some combined cycle process that scavenges waste heat from the fuel cell. You might find some experimental units pushing 70%, but anything commercially available is going to be under 60%.

Assuming realistic values for electrolysis and fuel cells, you're already well under 40%. Depending on your compression ratio, you're only likely to recover 50-60% of the energy spent compressing the hydrogen for storage, so that's either higher losses, or higher capital costs for storage volume. Tack on a couple percent for leakage, and 25% is very reasonable.

The energy required to compress and cool the hydrogen into a liquid in the first place, as opposed to just larger, less insulated, high pressure gas tanks, would more than offset any gains made by using the boiloff to cool your data center.

Yes. Electrolysis does not violate the laws of thermodynamics. What I assume you were getting at, electrolysis usually runs around 50-60% efficiency and fuel cells range from 30-70% depending on the chemistry, and in practice since you have to store it, you also have to factor in compression losses, hydrogen leakage, and burners to bring your decompressed gas back up to the operating temperature of your fuel cell. Total cycle efficiency is going to be under 25%.

That makes the assumption that your daily average production and consumption is anywhere close to your yearly average, or that you have an absolutely massive energy storage system capable of storing hundreds of petajoules to last the winter months.

I'll admit, I don't understand why the arbitrary reference time we use currently is any less valuable now that we have surface clocks whose real time is measurably changing due to relativistic effects.

Why can't we compute what the relativistic slew rate between two different locations will be and compensate?

So someone who straps a couple homemade AP motors to the side of an ultralight qualifies as well? (One could argue doing such a thing would preclude them classification as an ultralight...)

They're daring, sure, but they're not pioneering new territory, as we did this over 50 years ago; they're just making it cheaper. Even when they do get there and make it cheaper, there's no way to expand upon its capabilities without a complete from-scratch redesign. They're not enabling anything further. Unless they directly expand science, industry, or medicine, or indirectly provide the tools for others to do so, they're not benefiting society, just themselves personally. Being a hero implies acting for the benefit of someone other than one's self.