swansont

The earth is not a small bunch of people, isolated from resupply. We know that we can make do with a whole planet, near a star. Or even an island of sufficient size, which has access to resources outside of the island. But we're talking about systems that are smaller and more isolated than that. I'm looking for more than a hand-waving dismissal of the problem, which is all that I've gotten so far. It's been tried, and the attempt failed (Biosphere II), so it's not like we can say we have a great handle on how to get to a solution.

You were asked for supporting evidence. Saying, in effect, "Go dig it up yourself" isn't really an acceptable response, especially in light of it being in the context of things that nobody has ever done.

You were the one who said full (pace is full of the stuff we need to live), so you need to define it and provide a reference, and we are talking about interstellar trips. My objection is that we have not yet gone to Mars, and undtil we have, there is no hard data that longer trips are possible. And therein lies the problem. You cannot have slow expansion. You have to have something at each destination. It's like going into the desert — your endpoint of the trip has to be an oasis. Or on the ocean — the endpoint has to be land. You can't go 1 km a year into the ocean to get across it. McKendree cylinder represents an unproven technology, and we have never, ever demonstrated a small number of people surviving on their own, in isolation, for any length of time anywhere near to what is required, regardless of the size of their cupboard. Biosphere-2 failed pretty quickly, and the ISS gets resupply on a fairly short interval. Submarines aren't an apt analogy, because they can easily make water and air, but even then, they will run out of food. In space, any mass you want to bring with you has a fuel cost, which, in turn, increases the fuel cost.

I checked my math on this calculation. I think I improperly convertied the mass into consistent units (kg to g) so the number is wrong. There was a factor of 1000 in the numerator, rather than the denominator. It's milli-g. Still small, but not nearly as small as I had stated.

Citation needed

Full? No, it most decidedly is not. On an interstellar scale, the stuff we need is localized and those oases are far apart.

I've seen arguments that take a distance and argue that there is this very small speed that expansion requires, but the problem with that is it ignores the discrete nature of the travel. There is no place to stop and resupply in the middle of nowhere. It's not a matter of only going some speed. It's a matter of surviving until you get to the next habitable planet. You can argue it took 10,000 years to expand across the ocean to the new world, and that's 10,000 km (just for sake of argument), so the speed was just 1 km/year, but you don't just go 1 km out into the ocean that first year. At the very minimum you have to go to the next island. Again, I'm not convinced this is true. It's just an assertion. Not an actual argument.

What is the longest any group of humans have lived in an isolated environment, as one might experience in space travel?

That's "easy"? The ability to survive for a period of time in space with no umbilical for resupply would be one relevant (and I would have thought obvious) connection.

That's not apparent to me. Arguments I've seen in support of this seem flawed.

! Moderator Note That's really for the OP to define. It will do no good to have competing definitions in play in this thread.

! Moderator Note Dependent and independent variables seems to be another thing to discuss, in addition to limits that Strange has mentioned.

Conservation of momentum? No. Energy and momentum are not the same thing; the behavior of a system will depend on the details of the energy input and output. You can have a situation where you exert no net force on the system, in which case momentum is conserved. You can also have a net force, in which case momentum would not be conserved. Note, however, that not conserving momentum in such a case is not a violation of the law — it's the expected result. Momentum conservation does not get violated.

These two sentiments are in direct conflict. Citing Newton's laws is showing you in no uncertain terms you are wrong. Pointing to your own ignorance of physics isn't an effective counterargument.

You can use emission or absorption spectroscopy if the source is emitting light (e.g. a star, which is incandescent), but for a cold, dark object that's a much harder proposition.

No. Getting some photons in a photodiode — or your eye — is an observation which can be a measurement. Looking through a microscope is an observation. What is different about that if the device happens to have a scale visible through the viewpiece? Until you clearly define the distinction here, there can be no discussion.

No, not my area of expertise. AFAIK quantum computing is leveraging purely quantum behavior that has no classical analogue. There is no quantum state superposition involved in the interference in the double-slit. I disagree. These are not calculations.

Interstellar? Not so much. They are overselling the concept. The paper mentions manipulating cubesats, not powering interstellar craft. https://www.researchgate.net/publication/323390665_Demonstration_of_a_mN-Class_Photonic_Laser_Thruster Yes, you can get more propulsion by "recycling" the photons. But even at 3.5 mN, if you are accelerating a 350 kg payload (a human in a tiny pod, no food or supplies), that's 10^-5 m/s^2. Want to go 300 m/s? It'll take you a year before you're going that fast. That tiny acceleration is not sustainable, because the laser is getting further and further away from the payload, and the beam spreads out, lowering the intensity. The cubesat experiment used a smaller mass and was at a distance of only a few meters. (3.5 kg would be an acceleration of 10^-3 m/s^2, meaning it would move a meter in less than a minute, which is basically what their lab demo was)

You offered up 2 + 2 = 4 as well. As the double-slit has a classical solution, I am not sure that it solves any quantum computation problem.

Did you miss the panel that says "We only know how to do that for a few special problems"?

Measurement might be a subset of observation. Someone needs to provides a definition of what they mean by each

If it's part of the craft it's an internal force.

I don't know what this means. Thus far you have not ruled out "I combined a bunch of constants such that the units worked" which isn't science.

Observation. Not observer.

Momentum is conserved as long as there is not net external force on the system. As long as you have only internal forces, momentum stays the same. Rockets move because mass is ejected with some velocity. We define the exhaust to be outside the system. Symmetric ejection gives no net force, because these are vectors and they add to zero. If it's not part of the craft, then you need two systems, repelling each other. One could speed up while the other slows down. If it's traveling with the craft, you can't analyze it this way. It's not exerting an external force.