No, the box is an essential part of the system. In the thought experiment neither the box nor the photon has mass but both possess momentum since the photon can bounce off the walls of the box. The photon and the box, together, form a system that has mass.

You can see how systems can have mass by rearraning the mass-energy equivalence equation to solve for mass:

m = sqrt(E^2 - (pc)^2) / c

The energy and momentum of a fundamental particle are related so you can't manipulate them independently. But if you have more than one particle it's pretty easy to manipulate the momentum of the system without changing the energy, and thus make m non-zero.

Many teachers, including the pop science variety, like to appeal to your intuition. Sometimes that's okay, sometimes it just stunt's your understanding. Your idea of mass is rooted in pre-20th century physics. The end of the 19th and beginning of the 20th century changed how we think about a lot of things, mass included. You're trying to take your idea of mass as an axiom and make everything else fit. It doesn't. Photons are massless. If they weren't, they would either not travel at the speed of light or have infinite energy. The "thing" that gravitates is energy and various types of energy flux, including momentum. That explains, consistently, how photons can travel at the speed of light, massless particles can interact via gravity, and adding energy to a system can increase its mass.

Energy density, yes.

https://en.wikipedia.org/wiki/...

People used to say "relativistic mass." We've realized that was a bad idea.

The UK has a head of state (a king) they've spent a thousand years learning should stand around a look pretty with medals and things but that's about it. The US has a head of state (a president) they've spent at least the last hundred years turning into a cult of personality and giving more and more power to.

France has spent a few hundred years violently oscillating back and forth between the two. They've demonstrated it doesn't really matter whether you call it a king or a president, it's how much power you give them.

The first fission reactor in space, the American SNAP-10A had an experimental ion thruster.

Yes, but it didn't go to Mars. That's why I said we didn't have good ion thrusters. The one on SNAP lasted a whole hour and apparently had quite a few problems even then. Getting the things to last long enough and produce enough thrust to be useful even for station keeping is a fairly recent thing.

Yes you can. You have to boot into recovery mode and then change the security level. This is already something you have to do to load third-part (even signed) kexts, which are sometimes required for certain types of presumably poorly written (or not Apple-blessed) hardware drivers.

Apparently this is even still possible on the iPhone chipped MacBook Neo.

If speed limits were enforced, they would be abolished tomorrow. They only continue to exist because most people can break the speed limit for years without getting a ticket.

If drivers received a fine every time they broke the speed limit, politicians houses would be burning down the next day and the law would be abolished the day after.

You know why encryption is legal despite Bush and Clinton's best attempts to prevent it?

Because Gen-X kids risked a decade in jail for breaking Federal law to ensure the code got out there and everyone had it. It simply became impossible to regulate because anyone anywhere in the world could download the code and run it.

Today programmers won't even say 'no' when governments demand they ID all their users.

Because it's not about age. It's about eliminating anonymity online.

There were laws requiring that escaped slaves were returned to their owners. I presume you would have obeyed those laws, even though they were immoral.

> You live in a country with laws.

A country with laws, yes. A country with law, no.

It's ludicrous to tell people they should obey the law when none of Epstein's clients have been arrested and probably at least half of the business owners in the country would be in jail if the laws on employing illegal aliens were enforced.

If an escaped slave had turned up at your house in the 1800s asking for help, would you have followed the law and sent him back to his owner? From your post, I'm guessing you would have.

I know a few Christian Nationalists. None of them are pushing for "Age Versification" and most are against it because it's clearly just another step toward The Mark of the Beast where people won't be allowed on the Internet unless they bend the knee to Satan.

This push is coming from the communists and WEF-bozos who want to eliminate anonymity on the Internet. Literally everyone who's been following this for long knows that.

Which is why you see support for it from both "left-wing" and "right-wing" governments. They both have the same hands shoved up their behinds.

I even wonder why they haven't done it much sooner.

We didn't have good ion thrusters back in the 50s, 60s and 70s and after that launching nuclear reactors into space was considered a bad idea, not without reason. A nuke plus ion engines isn't a slam dunk either, ion engines produce very little thrust and reactors are heavy even if you don't have to bother shielding them much, so there's an efficiency threshold you need to hit before it's worthwhile.

NASA has realized that beating, or at least competing with, the Chinese to a moon base is probably going to require a reactor, so why not demonstrate it as part of a drive too?

the original formulation of relativity and physics in general did not distinguish between rest mass creating gravitation and light speed particles generating gravitation

Maybe you have access to some early draft notes of Einstein's, but in his actual papers on relativity mass does not "create gravitation." Energy, momentum and some off-diagonal terms like stress and pressure gravitate. There is no mass term in the stress-energy tensor, nor anywhere else in the Einstein Field Equation. Mass is not fundamental in relativity, it's a property of a system. That property is the product of energy and momentum (and the other stuff) in particular configurations within the system so in many situations it can be used as a surrogate for the underlying energy, momentum and other stuff.

Physics prior to relativity did indeed say a lot of different, confusing things about mass, gravitation and light speed particles.

"Creating fusion" isn't hard. Kids do it for science fair projects. Here's a guy on Youtube making a fusion reactor.

Making a fusion reactor that produces more electricity than it uses is hard. That's what you're thinking of. Rocket engines famously do not usually produce electricity, and if they do they do it extremely inefficiently, so it's a completely different problem.

we don’t have massless drives

Reactionless drives. A massless drive would be an engine that didn't have any mass, I guess. We have lots of drives that don't involve throwing mass out the back, including solar sails, magnetotorquers, electrodynamic tethers, flashlights, etc. Hard drives have a few. Your car has at least one big one and a bunch of others besides, as does your body. None of them are reactionless though.

Reactionless drives are called that because they violate Newton's third law, which is really a statement about the conservation of momentum.