It does. But light pressure is the Poynting vector divided by c. What that means is the thrust in Newtons is basically the power of the laser divided by c. That means that a megawatt laser can produce less than 0.001 Newtons of thrust, which applied to a mere 1000 kg payload gives you less than a millionth of a meter per second squared acceleration. One can grow old and die before building up a reasonable delta V, at 30 million seconds per year, assuming your 1000 payload could sustain a MW output for a lifetime.
Take that same MW, run it for one second, and turn it into a 1 kg reaction mass with a million joules of energy and it gives you a momentum change of order 1000 Newtons (per second), or accelerates your 1000 kg payload at 1 m/sec^2. But then you only have 999 kg left.
It's all the brutal arithmetic of moving around in space. Light is easy to generate with an energy source but it produces irrelevant thrust until you start to talk about gigawatts of power, sustained. Throwing reaction mass makes far more thrust per unit of energy, but you LOSE the reaction mass you throw. No free lunches, sorry. The arithmetic is sustained almost independent of what kind of mass you throw or what you use as an energy supply.
A light sail using free sunlight MIGHT be marginally productive, provided that you can build kilometer-square shrouded lightsails with (substantially) less than a metric ton of mass. That's a million square meters, which means in turn that if it is a mere 1 mm thick it has a volume of 1000 m^3. Any reasonable density means that it is already up there in the general ballpark of your desired payload, and very order of magnitude difference adds a LOT to transit times. And then there is the shroud.
Is the material science problem for building a light sail solvable? Perhaps, but it isn't going to be easy, and we can't do ones capable of substantially shifting orbits at this point, although NASA is testing them for being able to fix the decaying orbits of near-Earth satellites, where one has only to compensate for micronewtons of drag with micronewtons of light sail force. Even 1 N/1000 kg is enough acceleration to be very useful, but 0.001N/1000 kg is nearly useless.
Lasers aren't ever going to lift a ship up from the surface of the earth via a light sail. It is not entirely impossible that ground-bound lasers cannot be directed into an ablative material in the base of a ship that then vaporizes, superheats, and emerges as a plasma drive, but even that is highly speculative and requires extremely precise alignment of thrust vectors and the ship's vertical axis in the presence of both turbulence and coriolis effects during liftoff.
The place light sails become arguably useful is in orbit (however you get there). At that point, IF one can generate a light sail shroud on the order of 1 km^2, one can start to get some nontrivial acceleration for a not completely absurd payload not from lasers, but from the sun. At that point, one can get order of 10 N of thrust, which for 1000 kg of payload yields an acceleration of 0.01 m/sec. This doesn't sound like much, but every two to five minutes one can add a meter/second to a selected vector. Every day one can add hundreds of meters/second. Sunlight is free, and for certain payloads (not humans) you don't care how long it takes.
A light sail is perfectly capable of promoting metric ton scale payloads from Earth orbit to Mars orbit, even if it takes a year or more to get there. By filling a queue of such payloads -- firing one off per day, for example -- one could transport substantial physical resources from Earth orbit to Mars over the course of a year or two and use them to build an orbital platform and/or drop them down to a targeted site on Mars. The only cost is the standard 32 MJ/kg net energy required to get to near-Earth orbit.
So the real question is: Can we use lasers plus ablation (not light sails) to reach near Earth orbit with less than the 1000 or so to 1 energy/fuel penalty associated with rocket launches? And that is not at all clear. It will have to compete with alternative solutions, as well, such as fusion drives (assuming we get fusion at some point) or electromagnetic cannon mass launchers.
The problem with reaching Mars, or Jupiter, or the stars themselves, isn't getting there from Earth orbit. It is getting TO Earth orbit. That's half of escape energy right there, and once you are in orbit and away from atmospheric drag, even low thrust solutions become efficient provided one can maintain them for long periods of time, and light sails or (maybe) high efficiency ion drives are both candidates for moving non-living mass around on timescales uncomfortable for humans but just fine for human food, or water, or other resources required for the colonization of space or at least the nearer planets or their moons.
This is all very expensive, to be sure, but it isn't infeasible from the physics point of view and as always, economies of scale or technical improvements may lower the costs over time. Grabbing a nickle-iron asteroid as it passes near the Earth and attaching one of the in-system drives might let us use resources already at the top of the orbital gravity well and avoid the cost of lifting all of that mass up entirely.
So far temperature rises are still within the 95% confidence interval of multimodel ensembles so they must be getting close to getting it right.
You do know that this is utterly meaningless from a statistical point of view, right? There is no such thing as an "ensemble of models" or a "probability distribution of models" in any sense that makes sense according to the axioms of statistics, and there isn't the slightest theoretical foundation for a statement of "confidence" based on averaging over multiple models, especially models of chaotic nonlinear dynamical systems. There isn't even a theorem for making statements of "confidence" for single chaotic nonlinear dynamical systems.
You should really read AR5's section on statistics where they openly acknowledge all of these points -- deep in a section no politician will ever read.
How about this: Suppose we apply a hypothesis test to each model, one at a time (which is at least semi-justifiable) and reject all of the models altogether whose envelope of predictions deviates from reality by some reasonable threshold. Then we can look at the predictions of the survivors. That would, of course, eliminate maybe 2/3 of the models from the "ensemble" right there, and the remaining models would have a much lower ECS. Where ECS itself has been in "free fall" for the last few years because the planet simply hasn't warmed as fast as the model ensemble average was predicting and it was becoming an embarrassment.
As I said above, the basic problem isn't the honesty of any given computation or group. It is in the writing of the summary for policy makers in a way that asserts a statistically indefensible "confidence" as if there is some justification for the number they pull out of their ass, and deliberate obfuscate the uncertainties to maintain the illusion of "settled science". The climate scientists and earth scientists I know are a lot less certain than the SPM is, and all scientists know better than to claim that the science in their discipline is "settled", even when it isn't based on solving Navier-Stokes equations without any believable empirical validation.
So you have complete confidence in the estimates of total climate sensitivity from, say a decade ago? Or five years? We understand all feedbacks? Hansen's assertions for sea level rise were all absolutely true?
Nobody sane is arguing that the climate hasn't warmed. Nobody sane is arguing that CO_2 is irrelevant to that warming. But quantitatively, there is substantial disagreement both with different models and with reality. There are also statistical abominations in abundance, such as presenting the multimodel ensemble mean and SD as if it is a normal predictor of the climate.
Quantity matters. If CO_2 drives only zero-feedback warming of around 1 to 1.5 C per doubling, it is by no means clear that we should be taking the measures we are taking at their current cost.
Historically you may be correct, but what is "the long term"? It isn't weeks, or years, it is at least decades. I didn't come close to citing all of the cases where science in entire countries has been corrupted by a political agenda -- Lysenkoism, "Nazi Science", etc, or by a religious agenda (the entire world, basically, prior to the Enlightenment) -- or bodies of work that were sheer fantasy produced by an appalling failure to understand the rules of probability and statistics (such as early ESP research). Duke has had its share of the latter, with the Rhine institute on campus right up to a couple of years before I arrived to go to school here, and with the recent scandal wherein a medical researcher systematically faked results in the medical center for almost a decade. As I said, nobody makes a career out of null results, and the pressure to obtain non-null results WHEN YOU REALLY BELIEVE WHAT YOU ARE TRYING TO PROVE tests the honesty and integrity of many humans to the breaking point. Wal Mart greeter or respected scientist is determined by getting non-null results, period because we have utterly corrupted science itself by introducing an enormous reward bias in favor of discovery of new results of economic value and literally punishing the equally important work that cuts away all the pieces that have no economic value.
In the end, research is controlled by human beings who have beliefs and who are plugged into a social and economic network wherein they derive status, power, and money attendant on the general acceptance of a particular narrative, scientific or not. There are without doubt selfless scientists and scientists who manage to remain objective and properly skeptical of their own beliefs and their own contributions within this narrative, just as there are plenty who are greedy, power oriented, and who will defend their own contributions by means fair and foul to preserve their status and prerogatives. And on the best of days, our brains are flawed -- we make errors that we are blind to because they are our own errors, we see fluffy sheep and great white sharks in the clouds, we see the image of Jesus burned onto a piece of toast and consider it to be a miraculous communication from God.
There is a lot of appreciation of this out there, although to some extent it is voices crying in the wilderness because the system we have, while flawed, may be as good as it gets and as you say in time will probably get things right and crawl forward instead of backwards (at some substantial human cost). Statistics Done Wrong is worth a read, as is The Black Swan -- both detail ways that the human tendency to extrapolate the "normal", to cherrypick, to data dredge, to indulge confirmation bias or use statistics badly and then claim "proof" in the literature corrupts the developing narrative, often for decades. There are a bunch of meta-studies that demonstrate how pervasive confirmation bias is in the studies published in certain fields, notably social sciences, psychology, economics, and medicine.
In my own reasonably well-informed opinion Climate Science in particular absolutely belongs in this category, as it is so strongly intertwined with political and economic activism, so strongly linked to vested interests in both directions, that objectivity is almost impossible. There are, after all, trillions of dollars on the table, all "loot" available to special interests depending on which narrative is accepted as "true". I also know more than a bit about the difficulty of the problem itself -- solving a coupled Navier-Stokes system at a granularity 10^30 times larger than the Kolmogorov scale decades into the future on a spinning, tipped, oblate spheriodal ball that is 70% ocean and otherwise covered with fractal land surfaces of varying and variable surface properties illuminated by a somewhat variable and equally unpredictable star has to count as the most difficult computational physic problem ever attempted, and yet people bandy around terms like 93% certa
Hmmm, so by the same token, we must conclude that e.g. the NSF can be called into question as to whether or not they have influence of the publications of the scientists they support, the NIH over the ones THEY support, the DOE over the projects they support, etc etc. Because the only funding that is clean is the funding you earned yourself doing unrelated work.
Once upon a time, the "ideal" ivory tower model of the University was that you banded together with a bunch of other academics, taught classes, and used the resulting income stream to support your life and your research. The whole concept of tenure was built on the notion that once you passed through a review process designed to first and foremost guarantee that you could teach classes at the University level and not be an embarrassment or drive off students, you ought to be free to pursue whatever research you liked and publish whatever you found without fear of political or economic repercussions in the event that your results were not politically correct or disagreed with the conclusions of some Famous Filosopher who preceded you.
To some extent, this model existed and persisted in both the United States and Europe up through the end of World War II. Then Big Science was born along with the nuclear bomb, and Big Medicine followed in Big Science's footsteps almost immediately. The government started funding more and more research at the University level, initially in nuclear physics (which simply required a lot of money to do at all), then in general physics, chemistry, medicine, all at an ever increasing pace. It rapidly got to the point where one simply could not get a tenured position at any University in the US without demonstrating an ability not to teach, not to "do research", but to obtain grants through a cycle of application and renewal through at least a couple of three to five year grant cycles. And this in turn, absolutely relied on doing research that had No Null Results. Null results meant No Tenure For You, it meant being put out onto the street and falling back on a small position at a teaching college or selling cars -- if you were in any sort of science department at first, then increasingly in other departments or areas of knowledge.
It also meant that your academic career was completely at the mercy of the granting agencies even AFTER getting tenure. Sure, supersymmetry or string theory or whatever the fad of the day is are popular this year, but after a decade of results null or otherwise, the funding dries up as new directives from on high arrive as to what we the people "need" to stimulate. Even tenured professors have to shift disciplines into whatever the latest rage is or risk being marginalized, given a broom closet for an office, being gently asked to leave (pretty please) to make room for an aggressive young researcher more willing to be blown by the winds of Popular science.
So speak to me not about clean, pure money, at least not with the implication that government money is somehow "good" but corporate money is "bad" because the corporations influence the direction of your work but the government (agencies) do no not. The current system of funding absolutely guarantees that a truly substantial fraction of University research is just confirmation bias at work, getting non-null results in precisely the sweet spot of what the granting agencies want to fund in order to perpetuate one's funding. It is also a mistake to imply that just because a large, august body of "objective" scientists whose work is clearly disconnected from any politically or economically sensitive conclusion all agree on a consensus view of some "truth" that that truth is actually true. Counterexamples exist in abundance, the latest one being that dietary cholesterol, instead of being (as the consensus view held it in countless publications all supposedly supported by objective research) Satan Himself attempting to destroy your heart and soul with plaque, is mostly irrelevant to heart disea
...as one can easily see. This is a crater in the middle of a paddy field. The regular array of tufts of greener is planted rice. The crater is order of a meter across or maybe a bit less (scale from the array of rice plants) and is formed in soft paddy mud that has had all of the rocks and solid material removed over as many as hundreds of years. This strike didn't kill anyone.
From the article, the second strike was near a tank -- which is basically a large open well sometimes surrounded by or even formed out of stone or masonry, typically NOT located in the middle of a muddy, flooded rice paddy -- injured several people and killed one, which means that it had more energy than the rice paddy strike and likely hit ground solid enough to cause significant shrapnel. A rice paddy is pretty close to a perfect environment to NOT cause a lot of shrapnel.
Just sayin'. I'm guessing the newspaper had a stock photo of the first hit and figured most people would be too ignorant to detect the "error" and wanted to be first to press to get wider reading and didn't wait on somebody going to photograph the actual crater.
No worries. With the Great Global Warming Conspiracy in place, power companies have already been raising rates and gouging people for years and anticipated being able to do so for decades. Solar simply bites into that with net metering.
But it is nothing like the bite that is going to happen if any of the three or four companies or major projects that claim to be on the verge of fusion energy turn out to be correct within the allotted timeframe. Or, better yet, if two or three companies solve it slightly differently at once, so there isn't even a window of real patent-monopoly free from competition.
Of course that is also going to more or less kill solar in its tracks unless/until they can get prices down to order of $0.10/watt/decade of operation. That will break even with fusion, maybe, possibly -- the difference between free but unreliable "fuel" in the case of solar vs almost free and reliable fuel in the case of fusion, with both of them costing order of $100 million/GW for the generation facility, a quantity that is recoverable at current retail rates in a matter of days of operating at capacity (power companies charge order of a billion dollars for ten hours of the electricity produced by a gigawatt plant).
If Lockheed-Martin's semi-sized megawatt plant works, we might even see the real demise of the electrical grid and giant regulated monopolies, over time. Communities could buy off-the-shelf generation in a modular way and plug it into a municipal grid and pay for it on a co-op basis.
In the meantime, all measures taken to combat carbon dioxide raise the cost of electricity. All things that raise the cost of electricity increase the profits of the government regulated monopolies that sell it, that are usually permitted only a more or less fixed marginal profit. They'll make electricity using squirrels in cages if that's what the public mandates, as long as they get a fixed MARGINAL profit on the final retail price.
Proposition A) We should never let crazy or stupid people own or carry firearms, just like we shouldn't let them reproduce, vote, operate power tools, drive, teach, preach, or work in government.
Proposition B) It is crazy and stupid to own a firearm! Studies show that you are more likely to shoot a relative than a criminal (even if that relative DID "need killin'"). They are expensive. They serve no useful purpose except to enable an individual to hurt someone or punch meaningless holes in things from a distance. Criminals have a higher probability of carrying firearms than the general population, which means that it is a provable fact that firearm owners are more likely to be criminals. So crazy, stupid and you're probably a criminal as well you gun owners you.
Conclusion) If you want to own a firearm, you shouldn't be allowed to. Only people who have no interest in owning firearms should be allowed to own or carry them. And only then if they aren't, by a definition that I (being sane and smart) would be happy to write down as a standard to be fairly applied to the entire populace, crazy or stupid or both.
Carry on the good work, brother! We can work on the reproduction, voting, etc later!
... we could all just fly naked. Think of the advantages! No more worries about concealed weapons that are any larger than will comfortably fit in an orifice. An opportunity to really get to know your neighbor. Necessarily improved climate control -- no more flights that are too cold or too warm. And a complete lack of literalist religious folk on the aircraft, because for most of them appearing naked in public is an even bigger sin than allowing infidels to spread lies about the one true faith or failing to bring on the apocalypse so Jesus can return to usher in the Kingdom of Heaven.
The merely prudish would, of course, take the train, which would be a welcome burst of new business for alternative transportation. Throw in a little alcohol and a whole new meaning of "in-flight entertainment" could emerge as a new cultural norm. The increased happiness among fliers could lead us to world peace!
It's the perfect solution. At least as long as they have one of those boxes that say "your body must fit inside of this box in order to take this flight" -- for humans...
Again, do you have the slightest bit of actual evidence to support this? I know for a fact that students at Duke who's families have donated millions of dollars to the University have been given F's and expelled for cheating. Also, I do not understand these words: "take back a failing grade". No, professors never have to "take back a grade" that was correctly assigned. Duke has a written policy that grades CANNOT be changed once assigned. Most faculty have no idea who the family of any given student is and whether or not they are big donors -- names mean nothing and nobody comes around and says "Suzy Q comes from the powerful Q family, don't give her a failing grade".
This is all fantasy. It's all the stuff of bad novels, or Animal House quality movies, not reality. Neither I nor anyone I've ever taught with or heard of teaching in other courses has ever, ever, been questioned about a failure. Nor, for the record, are we pressured concerning athletes famous or otherwise that we teach. I won't say there is no sexism or racism at all, but it is a per-individual-teacher thing and is strongly opposed, in writing and in active practice, on pretty much every University community and, by the way, in law.
Saying we now need statistical hullabaloo is laughable. Not even close. We need to get Universities to actually teach people instead of coddle them, and we need professors and Deans willing to do the same. College has become a joke on the public in order to grow government and make a few people rich. Even if you want to teach as a professor, the Deans will not defend you because they fear a student's opinion more than care for the Universities reputation. Yes, that's right. A history teacher can't teach history if it "offends" a student because feelings" now trump facts in college. That's fucking scary!
Not that I want to interrupt a lovely rant, and I don't disagree with everything you say, but this paragraph does make me pause and do it anyway. Most of the faculty I know (and I know quite a lot of faculty, being a member of the faculty and preparing to teach several courses for the spring semester starting next Wednesday:-) do sincerely want to teach and do their best to teach. Coddling is not even an issue, with a very few exceptions. I also am very curious as to why you would say that Deans won't defend professors who teach (against who, Evil Students? Parents? An angry mob?) because they "fear a student's opinion more than they care for the University's reputation". That doesn't even make complete sense and is completely contradicted by all of my experience with many, many deans over 39 year of teaching at one level or another in college. I would therefore argue that you need to support this statement with more than just an assertion that this happens. Sure, maybe, probably, somewhere, sometime. But is it the rule rather than the exception? I think not.
It doesn't even make sense. First of all, as far as I know once you are given a course to teach, you are God with a capital G for that course. Sure, there are guidelines for what should be taught and some (reasonable) expectations for how you will teach it, but the whole "Ivory Tower" thing and "tenure" ensures that there isn't a whole lot they can do about it if you choose to be a maverick but give you crappy courses to teach, a broom closet for an office, and as few promotions as they can get away with. Oh, sure, maybe stern talkings to as well. This is assuming that you don't actually break one of the few rules that ARE written down, such as Thou Shalt Not Fondle thy Students. Not even a Dean can go in and override grades I give in a course, for example, at least to the best of my knowledge.
Second, to MY experience the Deans mostly work the exact opposite of the way you assert. They are the court of last resort for the student, not to "force" the instructor to change but to mediate any honest disputes and, usually, to enforce the University's less pleasant rules on the student, not the faculty. Who deals with cheats? A student is LUCKY if it is only their professor -- then they only get an F and thrown out of the course. Once deans get involved, it is more likely to be suspension or expulsion. Who tracks the problem students as they wend through the system? Deans. Who has to deal with deaths in the students' families, with mono mid-semester, with learning disabilities, and sure, sometimes with faculty who really are assholes or asshats or both? Deans.
I cherish the deans I interact with, and I interact with deans a lot because I am lead professor in large courses rather frequently, so I have a large student population with a higher probability of students with problems in there I cannot solve. Deans are invaluable -- they are not only much needed lubrication in a system with lots of rough edges and a lot of stress, they are the final level of human judgment on top of a system of impersonal and sometimes overly harsh rules. Deans have the power to do great good for both students and faculty, and almost without exception do an exemplary job. Animal House really was just a funny movie, not reality.
That's a beautiful, passionate, almost poetic response. Sadly, it is completely wrong. None of that stuff ever happens at any significant rate outside of your fantasy life. In fact, I can't recall having heard of any student who ever made any of those claims, although I'm sure that there must be some, somewhere, that have (personality disorders being as prevalent as they are in the general population).
Actually, students have a pretty finely honed sense of fair play. If you flunk them and they deserve to flunk, you rarely get more than whimpering and sometimes begging. Ditto for most other grades, and grade boundaries. If you flunk them on a technicality, of course, they will be resentful -- and with some reason. But no, students do not in general argue over grades claiming that the professor is biased against them due to race, creed, color, etc, except possibly in the very rare cases where there is some reason to make the argument.
As for learning analytics -- I have to say that it is (also sadly) mostly bullshit. I don't know about soft subjects, but in things like math and physics:
a) It is painfully, oppressively difficult to find a good object instrument to measure "learning" at the college level. And I say this as somebody that has used what there is for upwards of a decade. The instruments themselves are badly flawed and it is impossible to prevent an instructor from teaching to the test if they so desire (indeed, it is difficult NOT to teach to the test if you know what is on it and what weight will be assigned to outcomes in terms of "ranking" teaching/learning performance in the course.
b) There is nothing like standardization of the courses at the level required to build a uniform instrument that might be of some use. In Europe they have such a thing, supposedly, and too bad for them! If Joe gives a wussy, "physics lite" algebraic physics course but Suzie gives a tough, full calculus course covering exactly the same chapters, how do you even compare them. Now imagine comparing them and developing performance analytics when they don't even cover the same chapters from the same book in the same order and with the same basic understanding of the material they are teaching...
Here's a single example of the problems we really do face. I give all of my entering physics students an assessment to determine how much they remember of basic math. A page of algebra. A page of simultaneous equations. A page of differential calculus. A page of integral calculus. A bit of vectors and trig. Nothing difficult as far as calculus goes -- one can manage a typical intro physics course with five -- that's right, only five -- integral/derivative rules on board, plus the chain rule/u-substitution, plus the product rule/integration by parts.
Every student entering the class is supposed to have passed two full semester college calculus courses. Yet the mean score on the assessment is around 50%, with plenty of students scoring as low as 15 to 25%. And these are bright students at a very good university.
Forget "analytics". The problem is deep, not shallow. It isn't going to be solved by improved statistics on more tests.
Are you trying to tell me that the burned patch on my toast isn't a divinely placed image of Jesus, part of a message intended for Me Alone to help me Believe?
Next you will tell me that the clouds aren't really full of fluffy little sheep being eaten by equally fluffy sharks.
Sometimes even AC deserves a positive mod point for sheer irony. Ironically enough, I have none to give you, and besides, I don't want to be perceived of as supporting someone on a government watch list, especially someone that mumbles back and forth to him/her anonymous self almost as if they were multiple personalities.
Sorry, I let a reference to Bishop Berkeley, who made all of these arguments long ago back in the heyday of the materialism vs idealism wars. The idealism argument lost to everybody who wasn't religious a couple of centuries ago:
I just didn't have the patience to walk through the entire tired argumentation associated with Berkeley and his tree falling in the quad and god and David Hume's empiricism that ultimately won the argument and ended the era of bullshit philosophy. But I can, if you like.
Several posts in the thread do a perfectly fine job of it, though. Solipsism cannot be refuted, but neither is there any good reason to think it is true. The same is the case for Berkeley's arguments. Scientific materialism, OTOH, is supported empirically to the extent that nobody seriously doubts it compared to the alternatives simply because there is no evidence to oppose it and every minute of our existences constitutes experience that tends to support it.
Rather, you should have said, "the one thing *I* have irrefutable evidence for is just my own experience -- I don't know that anything outside of my own thoughts exists, and I could be participating in a pseudo-masturbatory exercise of pretending that there is an external world and other people out there and this imaginary place called Slashdot where I pretend to communicate with these figments of my imagination."...
...in which case you should be wondering, "Why am I bothering to pretend to argue with myself about this?" and return to pretending that if you jump out of a tall building over hard pavement that those illusory "laws of physics" won't erase your brain function and self very much like a squashed bug.
Or that a stroke or simple old age won't do the trick, like it or not, over time.
No arguments. Although "terraforming" to the extent of seeding a water ocean to transform a marginally unfavorable atmosphere biologically doesn't seem impossible or unreasonableI didn't recognize the reference to SF -- just as a matter of curiousity, what's the story? I thought I'd read nearly all of the old SF, but obviously I'm mistaken.
Easy for which particular value of easy? The one equating to "the most expensive and ambitious project ever undertaken by humans?" Or did you mean to send a probe that arrives after the human species has either evolved into something else or is extinct?
So far, we have managed less than 20 km/sec at the outer reaches of the solar system, achieved with multiple gravity assists along the way. Estimates of the time required to reach the nearest start, which AFAIK has no candidates for the project, range from 81,000 years for ion drive to 85 years for Orion drive that so far does not really exist anywhere but in science fiction novels and which would cost a fabulous amount of money to build in orbit, fuel, and launch.
If we DID go to the trouble of converting asteroids into Orion-drive craft to go to stars, don't you think we could find some better use for them then to send nukes that would give us information about their atmospheres 3 or 4 centuries from whenever we sent them? Perhaps super-AI and genetic factories and terraforming equipment, perhaps something else? Or do you really think that it is reasonable to assume that humans can have an attention span and political civilization at this point that lasts the 400 to 1000 years necessary for projects like this? How is it even possible to justify the expense, given that there are only a few dozen more important issues confronting us that we need to resolve before this becomes conceptually feasible.
Of course you might reply that in ten or twenty years technology may have changed entirely. And I agree! But at the point is that then there will be additional, probably better options than dropping in a nuke. Like just (I dunno) sampling the atmosphere and transmitting back a message as to what it is (and a whole lot more).
Slashdot Mirror
Sigh. Newton lived in vain, I see.
Pardon me, I have to grab myself by the scruff of my neck and lift myself up out of my chair and go teach physics.
rgb
It does. But light pressure is the Poynting vector divided by c. What that means is the thrust in Newtons is basically the power of the laser divided by c. That means that a megawatt laser can produce less than 0.001 Newtons of thrust, which applied to a mere 1000 kg payload gives you less than a millionth of a meter per second squared acceleration. One can grow old and die before building up a reasonable delta V, at 30 million seconds per year, assuming your 1000 payload could sustain a MW output for a lifetime.
Take that same MW, run it for one second, and turn it into a 1 kg reaction mass with a million joules of energy and it gives you a momentum change of order 1000 Newtons (per second), or accelerates your 1000 kg payload at 1 m/sec^2. But then you only have 999 kg left.
It's all the brutal arithmetic of moving around in space. Light is easy to generate with an energy source but it produces irrelevant thrust until you start to talk about gigawatts of power, sustained. Throwing reaction mass makes far more thrust per unit of energy, but you LOSE the reaction mass you throw. No free lunches, sorry. The arithmetic is sustained almost independent of what kind of mass you throw or what you use as an energy supply.
A light sail using free sunlight MIGHT be marginally productive, provided that you can build kilometer-square shrouded lightsails with (substantially) less than a metric ton of mass. That's a million square meters, which means in turn that if it is a mere 1 mm thick it has a volume of 1000 m^3. Any reasonable density means that it is already up there in the general ballpark of your desired payload, and very order of magnitude difference adds a LOT to transit times. And then there is the shroud.
Is the material science problem for building a light sail solvable? Perhaps, but it isn't going to be easy, and we can't do ones capable of substantially shifting orbits at this point, although NASA is testing them for being able to fix the decaying orbits of near-Earth satellites, where one has only to compensate for micronewtons of drag with micronewtons of light sail force. Even 1 N/1000 kg is enough acceleration to be very useful, but 0.001N/1000 kg is nearly useless.
rgb
Lasers aren't ever going to lift a ship up from the surface of the earth via a light sail. It is not entirely impossible that ground-bound lasers cannot be directed into an ablative material in the base of a ship that then vaporizes, superheats, and emerges as a plasma drive, but even that is highly speculative and requires extremely precise alignment of thrust vectors and the ship's vertical axis in the presence of both turbulence and coriolis effects during liftoff.
The place light sails become arguably useful is in orbit (however you get there). At that point, IF one can generate a light sail shroud on the order of 1 km^2, one can start to get some nontrivial acceleration for a not completely absurd payload not from lasers, but from the sun. At that point, one can get order of 10 N of thrust, which for 1000 kg of payload yields an acceleration of 0.01 m/sec. This doesn't sound like much, but every two to five minutes one can add a meter/second to a selected vector. Every day one can add hundreds of meters/second. Sunlight is free, and for certain payloads (not humans) you don't care how long it takes.
A light sail is perfectly capable of promoting metric ton scale payloads from Earth orbit to Mars orbit, even if it takes a year or more to get there. By filling a queue of such payloads -- firing one off per day, for example -- one could transport substantial physical resources from Earth orbit to Mars over the course of a year or two and use them to build an orbital platform and/or drop them down to a targeted site on Mars. The only cost is the standard 32 MJ/kg net energy required to get to near-Earth orbit.
So the real question is: Can we use lasers plus ablation (not light sails) to reach near Earth orbit with less than the 1000 or so to 1 energy/fuel penalty associated with rocket launches? And that is not at all clear. It will have to compete with alternative solutions, as well, such as fusion drives (assuming we get fusion at some point) or electromagnetic cannon mass launchers.
The problem with reaching Mars, or Jupiter, or the stars themselves, isn't getting there from Earth orbit. It is getting TO Earth orbit. That's half of escape energy right there, and once you are in orbit and away from atmospheric drag, even low thrust solutions become efficient provided one can maintain them for long periods of time, and light sails or (maybe) high efficiency ion drives are both candidates for moving non-living mass around on timescales uncomfortable for humans but just fine for human food, or water, or other resources required for the colonization of space or at least the nearer planets or their moons.
This is all very expensive, to be sure, but it isn't infeasible from the physics point of view and as always, economies of scale or technical improvements may lower the costs over time. Grabbing a nickle-iron asteroid as it passes near the Earth and attaching one of the in-system drives might let us use resources already at the top of the orbital gravity well and avoid the cost of lifting all of that mass up entirely.
rgb
So far temperature rises are still within the 95% confidence interval of multimodel ensembles so they must be getting close to getting it right.
You do know that this is utterly meaningless from a statistical point of view, right? There is no such thing as an "ensemble of models" or a "probability distribution of models" in any sense that makes sense according to the axioms of statistics, and there isn't the slightest theoretical foundation for a statement of "confidence" based on averaging over multiple models, especially models of chaotic nonlinear dynamical systems. There isn't even a theorem for making statements of "confidence" for single chaotic nonlinear dynamical systems.
You should really read AR5's section on statistics where they openly acknowledge all of these points -- deep in a section no politician will ever read.
How about this: Suppose we apply a hypothesis test to each model, one at a time (which is at least semi-justifiable) and reject all of the models altogether whose envelope of predictions deviates from reality by some reasonable threshold. Then we can look at the predictions of the survivors. That would, of course, eliminate maybe 2/3 of the models from the "ensemble" right there, and the remaining models would have a much lower ECS. Where ECS itself has been in "free fall" for the last few years because the planet simply hasn't warmed as fast as the model ensemble average was predicting and it was becoming an embarrassment.
As I said above, the basic problem isn't the honesty of any given computation or group. It is in the writing of the summary for policy makers in a way that asserts a statistically indefensible "confidence" as if there is some justification for the number they pull out of their ass, and deliberate obfuscate the uncertainties to maintain the illusion of "settled science". The climate scientists and earth scientists I know are a lot less certain than the SPM is, and all scientists know better than to claim that the science in their discipline is "settled", even when it isn't based on solving Navier-Stokes equations without any believable empirical validation.
rgb
So you have complete confidence in the estimates of total climate sensitivity from, say a decade ago? Or five years? We understand all feedbacks? Hansen's assertions for sea level rise were all absolutely true?
Nobody sane is arguing that the climate hasn't warmed. Nobody sane is arguing that CO_2 is irrelevant to that warming. But quantitatively, there is substantial disagreement both with different models and with reality. There are also statistical abominations in abundance, such as presenting the multimodel ensemble mean and SD as if it is a normal predictor of the climate.
Quantity matters. If CO_2 drives only zero-feedback warming of around 1 to 1.5 C per doubling, it is by no means clear that we should be taking the measures we are taking at their current cost.
rgb
Historically you may be correct, but what is "the long term"? It isn't weeks, or years, it is at least decades. I didn't come close to citing all of the cases where science in entire countries has been corrupted by a political agenda -- Lysenkoism, "Nazi Science", etc, or by a religious agenda (the entire world, basically, prior to the Enlightenment) -- or bodies of work that were sheer fantasy produced by an appalling failure to understand the rules of probability and statistics (such as early ESP research). Duke has had its share of the latter, with the Rhine institute on campus right up to a couple of years before I arrived to go to school here, and with the recent scandal wherein a medical researcher systematically faked results in the medical center for almost a decade. As I said, nobody makes a career out of null results, and the pressure to obtain non-null results WHEN YOU REALLY BELIEVE WHAT YOU ARE TRYING TO PROVE tests the honesty and integrity of many humans to the breaking point. Wal Mart greeter or respected scientist is determined by getting non-null results, period because we have utterly corrupted science itself by introducing an enormous reward bias in favor of discovery of new results of economic value and literally punishing the equally important work that cuts away all the pieces that have no economic value.
In the end, research is controlled by human beings who have beliefs and who are plugged into a social and economic network wherein they derive status, power, and money attendant on the general acceptance of a particular narrative, scientific or not. There are without doubt selfless scientists and scientists who manage to remain objective and properly skeptical of their own beliefs and their own contributions within this narrative, just as there are plenty who are greedy, power oriented, and who will defend their own contributions by means fair and foul to preserve their status and prerogatives. And on the best of days, our brains are flawed -- we make errors that we are blind to because they are our own errors, we see fluffy sheep and great white sharks in the clouds, we see the image of Jesus burned onto a piece of toast and consider it to be a miraculous communication from God.
There is a lot of appreciation of this out there, although to some extent it is voices crying in the wilderness because the system we have, while flawed, may be as good as it gets and as you say in time will probably get things right and crawl forward instead of backwards (at some substantial human cost). Statistics Done Wrong is worth a read, as is The Black Swan -- both detail ways that the human tendency to extrapolate the "normal", to cherrypick, to data dredge, to indulge confirmation bias or use statistics badly and then claim "proof" in the literature corrupts the developing narrative, often for decades. There are a bunch of meta-studies that demonstrate how pervasive confirmation bias is in the studies published in certain fields, notably social sciences, psychology, economics, and medicine.
In my own reasonably well-informed opinion Climate Science in particular absolutely belongs in this category, as it is so strongly intertwined with political and economic activism, so strongly linked to vested interests in both directions, that objectivity is almost impossible. There are, after all, trillions of dollars on the table, all "loot" available to special interests depending on which narrative is accepted as "true". I also know more than a bit about the difficulty of the problem itself -- solving a coupled Navier-Stokes system at a granularity 10^30 times larger than the Kolmogorov scale decades into the future on a spinning, tipped, oblate spheriodal ball that is 70% ocean and otherwise covered with fractal land surfaces of varying and variable surface properties illuminated by a somewhat variable and equally unpredictable star has to count as the most difficult computational physic problem ever attempted, and yet people bandy around terms like 93% certa
Hmmm, so by the same token, we must conclude that e.g. the NSF can be called into question as to whether or not they have influence of the publications of the scientists they support, the NIH over the ones THEY support, the DOE over the projects they support, etc etc. Because the only funding that is clean is the funding you earned yourself doing unrelated work.
Once upon a time, the "ideal" ivory tower model of the University was that you banded together with a bunch of other academics, taught classes, and used the resulting income stream to support your life and your research. The whole concept of tenure was built on the notion that once you passed through a review process designed to first and foremost guarantee that you could teach classes at the University level and not be an embarrassment or drive off students, you ought to be free to pursue whatever research you liked and publish whatever you found without fear of political or economic repercussions in the event that your results were not politically correct or disagreed with the conclusions of some Famous Filosopher who preceded you.
To some extent, this model existed and persisted in both the United States and Europe up through the end of World War II. Then Big Science was born along with the nuclear bomb, and Big Medicine followed in Big Science's footsteps almost immediately. The government started funding more and more research at the University level, initially in nuclear physics (which simply required a lot of money to do at all), then in general physics, chemistry, medicine, all at an ever increasing pace. It rapidly got to the point where one simply could not get a tenured position at any University in the US without demonstrating an ability not to teach, not to "do research", but to obtain grants through a cycle of application and renewal through at least a couple of three to five year grant cycles. And this in turn, absolutely relied on doing research that had No Null Results. Null results meant No Tenure For You, it meant being put out onto the street and falling back on a small position at a teaching college or selling cars -- if you were in any sort of science department at first, then increasingly in other departments or areas of knowledge.
It also meant that your academic career was completely at the mercy of the granting agencies even AFTER getting tenure. Sure, supersymmetry or string theory or whatever the fad of the day is are popular this year, but after a decade of results null or otherwise, the funding dries up as new directives from on high arrive as to what we the people "need" to stimulate. Even tenured professors have to shift disciplines into whatever the latest rage is or risk being marginalized, given a broom closet for an office, being gently asked to leave (pretty please) to make room for an aggressive young researcher more willing to be blown by the winds of Popular science.
So speak to me not about clean, pure money, at least not with the implication that government money is somehow "good" but corporate money is "bad" because the corporations influence the direction of your work but the government (agencies) do no not. The current system of funding absolutely guarantees that a truly substantial fraction of University research is just confirmation bias at work, getting non-null results in precisely the sweet spot of what the granting agencies want to fund in order to perpetuate one's funding. It is also a mistake to imply that just because a large, august body of "objective" scientists whose work is clearly disconnected from any politically or economically sensitive conclusion all agree on a consensus view of some "truth" that that truth is actually true. Counterexamples exist in abundance, the latest one being that dietary cholesterol, instead of being (as the consensus view held it in countless publications all supposedly supported by objective research) Satan Himself attempting to destroy your heart and soul with plaque, is mostly irrelevant to heart disea
...as one can easily see. This is a crater in the middle of a paddy field. The regular array of tufts of greener is planted rice. The crater is order of a meter across or maybe a bit less (scale from the array of rice plants) and is formed in soft paddy mud that has had all of the rocks and solid material removed over as many as hundreds of years. This strike didn't kill anyone.
From the article, the second strike was near a tank -- which is basically a large open well sometimes surrounded by or even formed out of stone or masonry, typically NOT located in the middle of a muddy, flooded rice paddy -- injured several people and killed one, which means that it had more energy than the rice paddy strike and likely hit ground solid enough to cause significant shrapnel. A rice paddy is pretty close to a perfect environment to NOT cause a lot of shrapnel.
Just sayin'. I'm guessing the newspaper had a stock photo of the first hit and figured most people would be too ignorant to detect the "error" and wanted to be first to press to get wider reading and didn't wait on somebody going to photograph the actual crater.
rgb
Oops? Forgot the "kilo"...
Never mind.
rgb
No worries. With the Great Global Warming Conspiracy in place, power companies have already been raising rates and gouging people for years and anticipated being able to do so for decades. Solar simply bites into that with net metering.
But it is nothing like the bite that is going to happen if any of the three or four companies or major projects that claim to be on the verge of fusion energy turn out to be correct within the allotted timeframe. Or, better yet, if two or three companies solve it slightly differently at once, so there isn't even a window of real patent-monopoly free from competition.
Of course that is also going to more or less kill solar in its tracks unless/until they can get prices down to order of $0.10/watt/decade of operation. That will break even with fusion, maybe, possibly -- the difference between free but unreliable "fuel" in the case of solar vs almost free and reliable fuel in the case of fusion, with both of them costing order of $100 million/GW for the generation facility, a quantity that is recoverable at current retail rates in a matter of days of operating at capacity (power companies charge order of a billion dollars for ten hours of the electricity produced by a gigawatt plant).
If Lockheed-Martin's semi-sized megawatt plant works, we might even see the real demise of the electrical grid and giant regulated monopolies, over time. Communities could buy off-the-shelf generation in a modular way and plug it into a municipal grid and pay for it on a co-op basis.
In the meantime, all measures taken to combat carbon dioxide raise the cost of electricity. All things that raise the cost of electricity increase the profits of the government regulated monopolies that sell it, that are usually permitted only a more or less fixed marginal profit. They'll make electricity using squirrels in cages if that's what the public mandates, as long as they get a fixed MARGINAL profit on the final retail price.
rgb
Ah, I see what you are doing there...
Proposition A) We should never let crazy or stupid people own or carry firearms, just like we shouldn't let them reproduce, vote, operate power tools, drive, teach, preach, or work in government.
Proposition B) It is crazy and stupid to own a firearm! Studies show that you are more likely to shoot a relative than a criminal (even if that relative DID "need killin'"). They are expensive. They serve no useful purpose except to enable an individual to hurt someone or punch meaningless holes in things from a distance. Criminals have a higher probability of carrying firearms than the general population, which means that it is a provable fact that firearm owners are more likely to be criminals. So crazy, stupid and you're probably a criminal as well you gun owners you.
Conclusion) If you want to own a firearm, you shouldn't be allowed to. Only people who have no interest in owning firearms should be allowed to own or carry them. And only then if they aren't, by a definition that I (being sane and smart) would be happy to write down as a standard to be fairly applied to the entire populace, crazy or stupid or both.
Carry on the good work, brother! We can work on the reproduction, voting, etc later!
rgb
... we could all just fly naked. Think of the advantages! No more worries about concealed weapons that are any larger than will comfortably fit in an orifice. An opportunity to really get to know your neighbor. Necessarily improved climate control -- no more flights that are too cold or too warm. And a complete lack of literalist religious folk on the aircraft, because for most of them appearing naked in public is an even bigger sin than allowing infidels to spread lies about the one true faith or failing to bring on the apocalypse so Jesus can return to usher in the Kingdom of Heaven.
The merely prudish would, of course, take the train, which would be a welcome burst of new business for alternative transportation. Throw in a little alcohol and a whole new meaning of "in-flight entertainment" could emerge as a new cultural norm. The increased happiness among fliers could lead us to world peace!
It's the perfect solution. At least as long as they have one of those boxes that say "your body must fit inside of this box in order to take this flight" -- for humans...
rgb
And he would have made a great Elrond...
I'm sure his capsule knows the way to go.
Again, do you have the slightest bit of actual evidence to support this? I know for a fact that students at Duke who's families have donated millions of dollars to the University have been given F's and expelled for cheating. Also, I do not understand these words: "take back a failing grade". No, professors never have to "take back a grade" that was correctly assigned. Duke has a written policy that grades CANNOT be changed once assigned. Most faculty have no idea who the family of any given student is and whether or not they are big donors -- names mean nothing and nobody comes around and says "Suzy Q comes from the powerful Q family, don't give her a failing grade".
This is all fantasy. It's all the stuff of bad novels, or Animal House quality movies, not reality. Neither I nor anyone I've ever taught with or heard of teaching in other courses has ever, ever, been questioned about a failure. Nor, for the record, are we pressured concerning athletes famous or otherwise that we teach. I won't say there is no sexism or racism at all, but it is a per-individual-teacher thing and is strongly opposed, in writing and in active practice, on pretty much every University community and, by the way, in law.
rgb
Saying we now need statistical hullabaloo is laughable. Not even close. We need to get Universities to actually teach people instead of coddle them, and we need professors and Deans willing to do the same. College has become a joke on the public in order to grow government and make a few people rich. Even if you want to teach as a professor, the Deans will not defend you because they fear a student's opinion more than care for the Universities reputation. Yes, that's right. A history teacher can't teach history if it "offends" a student because feelings" now trump facts in college. That's fucking scary!
Not that I want to interrupt a lovely rant, and I don't disagree with everything you say, but this paragraph does make me pause and do it anyway. Most of the faculty I know (and I know quite a lot of faculty, being a member of the faculty and preparing to teach several courses for the spring semester starting next Wednesday:-) do sincerely want to teach and do their best to teach. Coddling is not even an issue, with a very few exceptions. I also am very curious as to why you would say that Deans won't defend professors who teach (against who, Evil Students? Parents? An angry mob?) because they "fear a student's opinion more than they care for the University's reputation". That doesn't even make complete sense and is completely contradicted by all of my experience with many, many deans over 39 year of teaching at one level or another in college. I would therefore argue that you need to support this statement with more than just an assertion that this happens. Sure, maybe, probably, somewhere, sometime. But is it the rule rather than the exception? I think not.
It doesn't even make sense. First of all, as far as I know once you are given a course to teach, you are God with a capital G for that course. Sure, there are guidelines for what should be taught and some (reasonable) expectations for how you will teach it, but the whole "Ivory Tower" thing and "tenure" ensures that there isn't a whole lot they can do about it if you choose to be a maverick but give you crappy courses to teach, a broom closet for an office, and as few promotions as they can get away with. Oh, sure, maybe stern talkings to as well. This is assuming that you don't actually break one of the few rules that ARE written down, such as Thou Shalt Not Fondle thy Students. Not even a Dean can go in and override grades I give in a course, for example, at least to the best of my knowledge.
Second, to MY experience the Deans mostly work the exact opposite of the way you assert. They are the court of last resort for the student, not to "force" the instructor to change but to mediate any honest disputes and, usually, to enforce the University's less pleasant rules on the student, not the faculty. Who deals with cheats? A student is LUCKY if it is only their professor -- then they only get an F and thrown out of the course. Once deans get involved, it is more likely to be suspension or expulsion. Who tracks the problem students as they wend through the system? Deans. Who has to deal with deaths in the students' families, with mono mid-semester, with learning disabilities, and sure, sometimes with faculty who really are assholes or asshats or both? Deans.
I cherish the deans I interact with, and I interact with deans a lot because I am lead professor in large courses rather frequently, so I have a large student population with a higher probability of students with problems in there I cannot solve. Deans are invaluable -- they are not only much needed lubrication in a system with lots of rough edges and a lot of stress, they are the final level of human judgment on top of a system of impersonal and sometimes overly harsh rules. Deans have the power to do great good for both students and faculty, and almost without exception do an exemplary job. Animal House really was just a funny movie, not reality.
rgb
That's a beautiful, passionate, almost poetic response. Sadly, it is completely wrong. None of that stuff ever happens at any significant rate outside of your fantasy life. In fact, I can't recall having heard of any student who ever made any of those claims, although I'm sure that there must be some, somewhere, that have (personality disorders being as prevalent as they are in the general population).
Actually, students have a pretty finely honed sense of fair play. If you flunk them and they deserve to flunk, you rarely get more than whimpering and sometimes begging. Ditto for most other grades, and grade boundaries. If you flunk them on a technicality, of course, they will be resentful -- and with some reason. But no, students do not in general argue over grades claiming that the professor is biased against them due to race, creed, color, etc, except possibly in the very rare cases where there is some reason to make the argument.
As for learning analytics -- I have to say that it is (also sadly) mostly bullshit. I don't know about soft subjects, but in things like math and physics:
a) It is painfully, oppressively difficult to find a good object instrument to measure "learning" at the college level. And I say this as somebody that has used what there is for upwards of a decade. The instruments themselves are badly flawed and it is impossible to prevent an instructor from teaching to the test if they so desire (indeed, it is difficult NOT to teach to the test if you know what is on it and what weight will be assigned to outcomes in terms of "ranking" teaching/learning performance in the course.
b) There is nothing like standardization of the courses at the level required to build a uniform instrument that might be of some use. In Europe they have such a thing, supposedly, and too bad for them! If Joe gives a wussy, "physics lite" algebraic physics course but Suzie gives a tough, full calculus course covering exactly the same chapters, how do you even compare them. Now imagine comparing them and developing performance analytics when they don't even cover the same chapters from the same book in the same order and with the same basic understanding of the material they are teaching...
Here's a single example of the problems we really do face. I give all of my entering physics students an assessment to determine how much they remember of basic math. A page of algebra. A page of simultaneous equations. A page of differential calculus. A page of integral calculus. A bit of vectors and trig. Nothing difficult as far as calculus goes -- one can manage a typical intro physics course with five -- that's right, only five -- integral/derivative rules on board, plus the chain rule/u-substitution, plus the product rule/integration by parts.
Every student entering the class is supposed to have passed two full semester college calculus courses. Yet the mean score on the assessment is around 50%, with plenty of students scoring as low as 15 to 25%. And these are bright students at a very good university.
Forget "analytics". The problem is deep, not shallow. It isn't going to be solved by improved statistics on more tests.
rgb
Are you trying to tell me that the burned patch on my toast isn't a divinely placed image of Jesus, part of a message intended for Me Alone to help me Believe?
Next you will tell me that the clouds aren't really full of fluffy little sheep being eaten by equally fluffy sharks.
You brute.
rgb
Sometimes even AC deserves a positive mod point for sheer irony. Ironically enough, I have none to give you, and besides, I don't want to be perceived of as supporting someone on a government watch list, especially someone that mumbles back and forth to him/her anonymous self almost as if they were multiple personalities.
Sorry, I let a reference to Bishop Berkeley, who made all of these arguments long ago back in the heyday of the materialism vs idealism wars. The idealism argument lost to everybody who wasn't religious a couple of centuries ago:
http://www.iep.utm.edu/berkele...
I just didn't have the patience to walk through the entire tired argumentation associated with Berkeley and his tree falling in the quad and god and David Hume's empiricism that ultimately won the argument and ended the era of bullshit philosophy. But I can, if you like.
Several posts in the thread do a perfectly fine job of it, though. Solipsism cannot be refuted, but neither is there any good reason to think it is true. The same is the case for Berkeley's arguments. Scientific materialism, OTOH, is supported empirically to the extent that nobody seriously doubts it compared to the alternatives simply because there is no evidence to oppose it and every minute of our existences constitutes experience that tends to support it.
rgb
Rather, you should have said, "the one thing *I* have irrefutable evidence for is just my own experience -- I don't know that anything outside of my own thoughts exists, and I could be participating in a pseudo-masturbatory exercise of pretending that there is an external world and other people out there and this imaginary place called Slashdot where I pretend to communicate with these figments of my imagination."...
Or that a stroke or simple old age won't do the trick, like it or not, over time.
rgb
Let me see, religious much?
Berkeley rides again. Seriously.
I now cease giving you your subjective existence by no longer thinking about you. Sorry about that.
rgb
This really bugs me.
No arguments. Although "terraforming" to the extent of seeding a water ocean to transform a marginally unfavorable atmosphere biologically doesn't seem impossible or unreasonableI didn't recognize the reference to SF -- just as a matter of curiousity, what's the story? I thought I'd read nearly all of the old SF, but obviously I'm mistaken.
rgb
Easy for which particular value of easy? The one equating to "the most expensive and ambitious project ever undertaken by humans?" Or did you mean to send a probe that arrives after the human species has either evolved into something else or is extinct?
So far, we have managed less than 20 km/sec at the outer reaches of the solar system, achieved with multiple gravity assists along the way. Estimates of the time required to reach the nearest start, which AFAIK has no candidates for the project, range from 81,000 years for ion drive to 85 years for Orion drive that so far does not really exist anywhere but in science fiction novels and which would cost a fabulous amount of money to build in orbit, fuel, and launch.
If we DID go to the trouble of converting asteroids into Orion-drive craft to go to stars, don't you think we could find some better use for them then to send nukes that would give us information about their atmospheres 3 or 4 centuries from whenever we sent them? Perhaps super-AI and genetic factories and terraforming equipment, perhaps something else? Or do you really think that it is reasonable to assume that humans can have an attention span and political civilization at this point that lasts the 400 to 1000 years necessary for projects like this? How is it even possible to justify the expense, given that there are only a few dozen more important issues confronting us that we need to resolve before this becomes conceptually feasible.
Of course you might reply that in ten or twenty years technology may have changed entirely. And I agree! But at the point is that then there will be additional, probably better options than dropping in a nuke. Like just (I dunno) sampling the atmosphere and transmitting back a message as to what it is (and a whole lot more).