Nikolai

No, it's not the stuff generated by hype while waiting for another version of KSP to drop. Apparently, scientists have just discovered a form of matter that was only hypothetical for fifty years. From what I've been able to gather, here's the basic idea: When electrons leave valence shells, they leave "holes". The "holes" are considered to be positively charged(*). "Holes" and electrons even attract each other; they act exactly as if they're positively charged particles. Excitonium is matter made up purely of electrons and "holes", held together by their mutual charge. There are no atomic nuclei. An "exciton" is an atom without a nucleus; excitonium is made up of excitons. --- (*) Just ask an electrical engineer. "Holes" are considered to be the charge carriers in semiconductors, which are electronic components of everything from diodes to transistors to microchips. The math works out the same as it would if we tracked electrons instead (the "real" charge carriers in circuits); the only difference is a change in sign.

Well, right, and you can see that if you take the time to simplify the expression of force on the ball into a constant times the distance of the ball from the center -- which is a spring equation. Springs follow sinusoidal motion. (The "spring constant" is equal to m*g/r, where m is the mass of the ball, g is the acceleration felt by the ball at the height from which you drop it, and r is the radius at which you drop the ball.)

Not only that, but the time it takes to get to the other side is exactly the same as it would take for the ball to orbit to that point at that altitude. Either way, the time to get to the other side is pi*sqrt(r/g), where r is the radius you drop it from and g is the acceleration due to gravity at that radius. I can do the math if you like.

Yes, possibly, but not because the Sun is going to go supernova; it's not massive enough for that. Some five billion years or so hence, the Sun will turn into a red giant. Its radius may grow large enough to swallow Earth. https://www.universetoday.com/18847/life-of-the-sun/

Sorry to be a troublemaker, but as usual, it's not that simple -- especially if we're talking about selecting a species' tendency to be social. That involves both natural and artificial selection, especially if we're talking about a tendency towards altruism.

Oh, I don't contest that the distinction is useful. It often is. It's just not the case that the boundary between the two is always clear. Well, there, again, we have a gray area. The modifications themselves are not selected, but the genes of the one who received the modifications (as a result of her own will or not) are selected for reproduction over someone else's. There's still selection going on, even if it's not selection of genes that would directly give rise to certain traits deemed attractive. I don't think it's that clear. The attraction I mentioned included neither posture nor body chemistry; you read those into my description somehow. I explicitly mentioned the attraction came as a result of modification to an individual's appearance.

Yes. (In all seriousness, the boundary between natural and artificial selection is far from sharp. For example, if you find an attractive female in appearance, mate with her for that reason and produce offspring, is that natural or artificial selection? What if her appearance has been altered -- she's preened her feathers, for example, as part of a strategy to attract mates? What if that alteration is done by a third party? Does it matter whether that third party performed that alteration on purpose or not, or what the specific goal of that alteration was -- whether attractiveness was the intent or the by-product of some other process? And so on.)

If you're close enough to the center of the disk to encounter gravity normal (perpendicular) to the surface, you're bound to find a surprise as you fly away. The gravitational force of a sphere falls away as 1/r2 from the center of the sphere; the gravitational force from an infinite disk (and the disk is "close enough" to infinite to act pretty infinite before you put some appreciable distance between you and it(*)) falls off as 1/r. In other words, you'd find it harder to get away from a disc than to get away from the surface of a sphere. I can do the math if you're interested. --- (*) This is a pretty common trick in physics. Sometimes, the math is easier if you pretend a surface is infinite. The electric field of a capacitor can usually be modeled by an infinitely-large plate where the charges on it are distributed uniformly; the math is much easier, and the results you get are "close enough" to real life.

Assuming that it was a close encounter of the third kind (face-to-whatever contact), and assuming that I had the wherewithal to think clearly, I'd ask for evidence that I could take with me that he/she/it/they was an interstellar visitor. It wouldn't have to be any kind of super-technological artifact, even -- I'd be content with a rock with no evidence of meteoric heating that unambiguously dated to eight billion years old, for example. I have to admit that it would be relatively easy for me to dismiss close encounters of the first and second kinds as tricks played on me by my senses.

Every five hours, actually. But still, very cute, Mr. Clarke.

This interloper has been dubbed Oumuamua, which means "first messenger" in Hawaiian. We also think we know roughly where it came from (the Carina and Columba Associations), meaning that we have some idea of how long it's spent in interstellar space (40 million years) and can constrain the mass of the planet that flung it our way in the first place (from a "super-Earth" to a gas giant 20 or 30 times the mass of Earth). It is expected that when we finish the Large Synoptic Survey Telescope in Chile, we will discover objects like this at a rate of one per year or so. https://arxiv.org/abs/1711.01300 https://arxiv.org/abs/1711.01344

We live in the largest supervoid known to science (the KBC Void), a region about two billion light-years in diameter. The Milky Way is within a few hundred million light-years of the center. EDITED TO ADD A SOURCE, SINCE IT'S ALWAYS A GOOD IDEA TO HAVE THEM: https://www.space.com/37191-we-live-in-a-cosmic-void.html

Last week, an asteroid was discovered with the provisional designation A/2017 U1. It's about 400 meters wide. What makes this exceptional is that it's an asteroid from another star. There are plans to measure its composition as it goes by. (It's moving too fast to be bound to the Sun.) We don't know which star it came from, exactly, but its angle of approach shows it coming from the galactic plane -- where most of the stars in the area are located. It probably spent millions or even billions of years in the interstellar dark before coming close to us, and after swinging by, will be consigned to interstellar space for millions of years more. http://www.ifa.hawaii.edu/info/press-releases/interstellar/

I've already thanked you guys for making such an awesome game and for getting my kids to understand and enjoy some of the nuts and bolts of space exploration. I'd also like to thank you for the insights you've provided into software design, and for even designing your widgets and editing tools such that my foray into 3D editing and animation software has enjoyed a much shallower initial learning curve. Your little project has improved my quality of life, and it's not often that a game gets credit for doing that.

This is a bit of an unusual request: I have an online friend who says that her father (who passed decades ago) might have been one of the divers from the USS Hoist when she served in the recovery flotilla for Gemini 4 in 1965. Does anyone know of any civilian-accessible resources that might be able to confirm or deny? She'd really like to be able to come by some video footage of the event, if any exists.

Steins;Gate, followed closely by Planetes, followed closely by Cowboy Bebop.

Whippersnapper. I remember when Pluto was just a point, before it even had a moon.

Truth. A nuclear explosion detonating near an asteroid's surface doesn't "push" the asteroid with a shockwave so much as emit enough X-rays to boil off a decent amount of asteroid material, and the reaction to the mass boiling away "pushes" the asteroid in the opposite direction. Also true. Rock is surprisingly resistant to being vaporized. And nukes are powerful, but not magically powerful. You need somewhere on the order of ten gigajoules delivered to a cubic meter of rock to vaporize it. http://www.madsci.org/posts/archives/mar2002/1015040902.Es.r.html

Yup, yup. And without engineering, science is just another kind of philosophy. Like I said, ongoing debate. =shrug= I guess this is all tangential to the point anyway, which is that space exploration is done to eventually put people in space, and we kind of seem to agree on that. Where people fall on this particular point doesn't really matter with respect to that. That particular point wasn't unclear. My question is why you felt the need to point out specifically that it was circular, not what your point was. But that seems kind of academic, really -- I genuinely think we agree about much more than we disagree about.

I'd have to go with The Avengers (the Diana Rigg years, specifically), Star Trek (the original series), Leverage, and Steins;Gate. And Sledge Hammer! was indeed awesome.

To be fair, this seems to be a topic of some controversy. Some see "science" as an endeavor that sprawls from technicians to the forefront of research. Others see it as more restrictive. The debate seems to follow many of the same "tyranny of the small" principles as those who care about whether that thing in the back of a rocket that provides propulsion should rightly be called an "engine" or a "motor". With that in mind, the way to convince people of your stance is not merely to repeat your assertion. Okay. What was your point in mentioning the circularity, then?

The primary definition of "engineering", as found in the 2017 Random House dictionary, is as follows: the art or science of making practical application of the knowledge of pure sciences, as physics or chemistry, as in the construction of engines, bridges, buildings, mines, ships, and chemical plants. Sure, it uses science in its methodologies, but practical application of science is itself a form of experimentation, and thus a form of science. They're not synonymous, but that's not a requirement. I never said it wasn't circular. You're erecting a straw man. But circular does not imply pointlessness, and it does not imply insignificance, and it does not imply meaninglessness. Most of what humans do is circular. We play sports to find out who's the best at playing sports. We have kids who may very well, in turn, have more kids. We work in order to eat in order to get the energy to work. We answer questions in order to ask more questions. All of these things, and more, are circular, but observing that tells us nothing about whether or not the endeavor is worthwhile. I believe that the more options humans have, the better off we can potentially be. It follows from that that pursuing greater capability and greater human presence is generally a good thing. A human race with the option to live places other than Earth are, it seems to me, better off than a human race that is stuck here.

Right. But my point was that it is not only planetary science that requires being on a planet. (Or are you of the opinion that engineering is not science?) My objective was to expand the discussion beyond things like geology as a reason to send humans to Mars (eventually). The only place we can test all the different components of a Martian environment simultaneously against our engineering cleverness is Mars. This kind of testing will be necessary if we seek to establish a permanent human presence on Mars. Again, I'll try to be plain: If geology, or things that operate on geological time scales, are your sole reason for going, then robots make a lot of sense now, and will make even more sense in the future. But I don't think that fact means that we have no scientific reason to be there with people at all, ever. If we want to use "Science!" as a reason to send people, we have to expand the conversation beyond geology into the sorts of science we can't do with robots. (Then we can discuss how well we're doing those other sciences -- if we're honest, kind of in a half-assed way, it seems to me -- but sticking with geology only presents part of the picture, and we can't really treat the "Science!" claims with any merit if we stick to only particular kinds of science.) Yes. And while we're there, we'll have to pit our scientific wherewithal against the challenges the planet presents. We do that already, in a smaller sense, because humans can't rump naked and eat berries from the local wildlife everywhere we live on Earth; we depend on a certain technological prowess in order to make certain locations livable year-round. But that's just a difference in the scale of technological ability. At the moment, yes, aside from infrequent bits of science and engineering that test our understanding of what happens to humans there, or tests our cleverness at coming up with solutions to keeping humans alive in a hazardous environment. But I don't begrudge it that.

Why are we necessarily concerned about sciences that primarily exist to return data (presumably, to people on Earth)? I would argue, for example, that a valuable component of manned exploration is as a prelude to manned habitation. There are engineering disciplines that would need to be done on Mars, for example, because they'd be the final test bed for implementation. I admit that many sciences could be more comfortably, conveniently, and economically explored right here and now -- especially if we're talking about ones attempting to boil natural phenomena down to overarching theories that should apply every bit as well here as there. But science is about much more than reduction to theory -- and ultimately, in applied sciences, there's no substitute for being there. Note that this does not mean that I think that Apollo was doing it right, nor that the proposed mission using multiple SLS launches to get us to Mars was doing it right. I concede that geology is more comprehensively performed with rocks. I don't want to pretend, however, that that's the only reason we go places in space, with robots or with humans. Let me be plain. It's not my desire to create a metric that would justify Apollo with this. My point was that asking for Mars papers written over the last three decades that used manned versus unmanned expeditions seemed like a rather pronounced exercise of motivated reasoning.

"From a science perspective"? That's a weird modifier, and kind of debatable. Perhaps from the point of those specific sciences that can be done in situ and that require maintaining a certain level of controlled experimentation and abstraction, but that's not the only kind of science that can be done. That's okay. It's not what I'm addressing, though. If I thought that only geology needed to be done, or only things that take place on geological time scales, then yeah, I think a robots-only stance makes sense. I'm also not opining that uncrewed missions are pointless, or even second-best. They have an absolutely critical role to play. I know that. That's why I suggested that one should measure the return per dollar spent.