I recently spent over a week in full research-promotion mode, and I’m finding it tough to switch back into research-doing mode. Coincidentally, I don’t think I’ve actually written a blog about my graduate research yet, though I’ve put descriptions of it on both my personal web site and Cornell group web site. So, I’m going to try and get it all out of my system…
Suppose you ask: Hey, Joe! What’s your research about?
Well, it’s about building Transformers in space out of Legos connected by tractor beams. Seriously. Okay, fine, they’re not “tractor beams,” more like…”tractor fields.” But other than that, not a bad description. Here’s an old-ish video version:
I demonstrate flux pinning
First: Why?!
There are a lot of possible reasons why we ought to be thinking about building large-scale structures in space. Imagine assembling a huge space telescope out of hundreds of mirror segments, giving the telescope an effective light-gathering area of hundreds of meters and letting us peer into the dimmest corners of the Universe – from the most distant objects to extrasolar planets. Or, if we’re interested in space-based solar power (putting solar power collectors in space, where they could gather sunlight 24 hours a day without atmospheric filtering, and then beaming that power down to Earth) we would want to make the biggest collector area we can. Proponents of geoengineering approaches to climate change mitigation have been seriously considering constructing a giant sunshade to reduce solar incidence on the Earth, a short-term solution that could stave off environmental impacts while we work up longer-term fixes. And finally, if we want to maintain a long-term human presence in space – from Mars explorers to microgravity research and manufacturing technicians to paying space tourists – we will need vehicles and stations with enough room to accommodate many people, hold life support and other supplies, and provide equipment to stave off the detrimental effects of microgravity on human physiology.
All of these possible applications – any one of which would have tremendous implications for our lives on Earth – demand that we build a large structure in orbit out of smaller components. The reason for this is simple: launch vehicles can only carry so much mass and volume into orbit. Those limits are on the “stowed” size of spacecraft, so we do have the option to build craft that deploy, or unfold, out of their tightly-packed, mostly cylindrical launch configuration and into some more spindly and useful shape. For example, most Earth-orbiting satellites get their power from large solar panel “wings” that would not fit into a launch vehicle fairing unless rolled up in some clever way. There’s a lot of research these days on inflatable spacecraft, that could expand to many times their stowed size and get structural support from their internal pressure, but even those balloon-like craft cannot get indefinitely bigger than their launch envelope. Deployments and inflatables only make the volume or length of the spacecraft larger – so, for the same mass, you end up with spindlier structures, which might be fine for some applications but not others. So, in order to get the really big spacecraft, we must assemble smaller pieces to make the final system. Think of the International Space Station assembly process. Continue reading Hey, Joe! What’s your research about?→
I’ve been getting a lot of my subject matter from Ryan lately, it seems…
Well, in any case, he put a link on Twitter to Sam Harris’ TED talk about science and morality, and how science could feed into morality. It’s well worth looking at and thinking about a little.
Morality has to do with distinguishing “right” from “wrong,” and Harris has a very good point that scientific methodology could be applied to help make that distinction. However, while I listened to his talk, a very important point came to mind. Let me set this up with the statement that many concepts or measures in this universe don’t come out to binary extremes. (Quantum states of spin-1/2 particles, for instance, are an exception.) In most cases, it’s not a question of just being on one side or the other; it’s a question of how far towards one side or the other your measurement comes out. I think the same is true of morality: how right is one thing compared to another? How wrong are the alternatives?
In answering such questions with scientific processes – not an idea I disagree with, in principle – we would likely end up at some kind of optimization problem. Given all the scientific data about the possible reactions and effects of a particular decision, how can we make the most “right” decision? That’s a pretty straightforward problem to approach scientifically. However, we must be careful about how we define “most!”
As an example, if you drive you have probably had the experience of getting stuck at a stoplight somewhere, getting frustrated, and saying to your passenger or yourself, “Wow, these lights are stupid. I’d love to meet the guy who designed them, they could be a lot better than they are.”
The operative word there is “better,” and the question is, how do you tell which stoplight timings are better than others? Probably, the guy who designed them actually chose the best timings. But what he considered “the best” is maybe not what you consider “the best.” Maybe he maximized the traffic flow on the main street instead of the cross street. Maybe he minimized the average number of red lights cars encounter along a certain route. Maybe he found the timing that gave the least amount of wait time at certain intersections, while also giving the highest possible rate of cars through the intersection, during rush hour on average Thursday mornings. Which one of these definitions of “best” is best? And why is it so? There is an assumption underlying the process here, and it can have a dramatic effect on the results.
I think we have to keep that point in mind while considering Harris’ points. We have a lot of data on actions and consequences. We can use scientific processes such as optimization to try and synthesize that data into a decision about what is right and what is wrong. But we have to bear in mind the assumptions that underlie that process, be up front about them, and be willing to entertain other possibilities.
My blog had been trucking along with a reliable readership of perhaps a dozen people, when, suddenly, after a slightly stream-of-consciousness post about the physics of space combat, Gizmodo asked to reprint the material from my blog. It was never my intention to get so much attention – but apparently that article turned into the most-commented content on Gizmodo that week! I got lots of questions and comments and emails after that and noticed lots more pingbacks on my blog entries afterward.
I couldn’t help but think, “Wow, if only my research activities would generate this sort of interest! I’m trying to build tractor beams and wrote up my experiences from Vomit Comet flights. How is that not cool enough?!” At least I got to abuse my 15 seconds of Internet fame to plug NASA a bunch!
Well, just a couple weeks ago, Karl Haro von Mogel from the University of Wisconsin, Madison, contacted me to interview me for his radio show, “The Inoculated Mind,” which airs on the student radio station in Madison. This was my first on-air interview, and I had a lot of fun with Karl! You can listen to a podcast of the show on his web site. It sounds from the beginning of his show that Karl and I would get along nicely, and then a little before halfway through he plays the interview. If I sound excited, it’s for good reason!
Many thanks to Karl for having me on his show, and for chatting with me about my research as well as the sci-fi stuff! (Oh, what the heck, my research is practically about science fiction, too!) And great use of Battlestar Galactica music and lead-in with the science of Avatar’s unobtainium!
And, of course, a link to the short story Karl brought up: High Orbit. Enjoy!
Just as a freebie, after the jump I am going to list several common questions and comments I got after Gizmodo picked up my initial blog, and respond to them a little bit. I am falling for exactly the issue that Phil Plait identified in his comment on my post – this could go on ad infinitum! So I’m done with this post now, but if you want even more about space battle physics, click here: Continue reading revenge of space combat physics→
Phil Plait of Bad Astronomy posted a few days ago about caved-in lava tubes on the Moon. This isn’t really new news, but it’s still pretty darned cool news. He posted some images of the cave. However, I found a major, glaring error in the LROC image data.
I fixed it.
Lava cave - fixed!
Seriously, though…those sites are perfect premade Moon base locations. Imagine a team of astronauts putting an inflatable dome over the hole in the roof, belaying down there, putting inflatable endcaps a few tens of meters down the lava tube in each direction, spraying expandable foam sealant into all the crevasses, and using some ISRU atmosphere generators to pump the tube full of oxygen.
I know I am not at my blogging best when I just write, “hey, look at these spectacular images!” But…look at these spectacular images!
An image-of-the-day gadget on my iGoogle home page showed me this picture, which I subsequently spent about a half hour trying to locate at a primary-source web site. It is wicked cool.
Possible Cyclic Bedding in Arabia Terra (HiRISE/MRO)
Click to go to this image’s description page on the University of Arizona HiRISE site. (Be sure to bookmark the 2560×1600 wallpaper version!!!)
I really want to know how these terraced buttes got to be the way they are…it looks like they must have been eroded in stages, with each layer from the top getting peeled back successively, but somehow the individual layers hold together – those are some pretty steep walls. I can see in the southwestern portion of this image that some of the terrace walls are eroding away in chunks; there are a couple good fallen boulders over there. The layers might be some kind of sandstone, because they haven’t eroded away in lots of rocks and boulders, so they don’t seem very friable, but there’s obviously a lot of source material for dunes in this area so the butte walls might be getting ground down into very small grains. I’m not sure what the fluvial history of Arabia Terra is – on Earth, that would be bound to play an important role in creating landforms like this.
I also really love the expression of the more recent aeolian features in this area. Looks like there are prevailing north-south winds on the east side of this image (I’m going to say the wind blows to the north because the north sides of the dunes look more like slip faces to me), but from the east-moving dunes in the terraced valley-like feature at center bottom and the east-west oriented ripples on the larger dune field, the winds are apparently going in rather circuitous routes around these buttes. There are also some confusingly-oriented dunes and ripples in the southwest portion of this image, probably from the wind winding around all the rocky towers. (In my mind, I can hear it whistling.)
Looks like the valley from which the east-going dunes have traveled is an exposed outcrop of one of the terrace layers. This image can resolve objects less than a meter in size, so the various crisscrossing dark lines in the light-toned outcrop might be joints or something.
Anyway, this is not a new image and I haven’t studied or researched this stuff…I just saw it today and wrote a little stream of consciousness of geological ideas. I just think this image looks beautiful and I want to send some rovers/people there. Any planetary science guys want to comment?
Last, and just for grins, here are some goodies I turned up in my search for that image on the UA HiRISE site. Here we have some dramatic contrast between dunes and some lighter, rockier topographically high areas:
Pitted Layers Northeast of Hellas Region
Here’s some great layer exposures around some hills – and if you zoom into the large version of this one, you can find some wild and interesting ripple patterns:
Pre-State of the Union buzz is that NASA’s Constellation program is dead.
Now, I haven’t really seen the White House rationale for this, but I suspect it goes something like this: “This country is in a pretty crappy economy right now. We’re bogged down with health care policy in Congress. And global climate change will be a more pressing problem in the future. We don’t have the time, money, or resources to devote to something like space exploration that doesn’t return any direct benefits.”
If you’ve been reading my blog since my time at NASA last summer, you know that I am a big fan of manned space exploration, but not necessarily a fan of the current Constellation architecture. I’m fine with seeing Constellation go, but only if we replace it with something gutsier. So I am not okay with axing Constellation and flatlining NASA’s budget. (Though Constellation was pretty much crippled in the first place by the “do it on the existing budget!” directive in 2004.)
The argument against NASA will likely be one of limited resources and the perception that space exploration doesn’t return anything for the average US citizen. As a counter, let’s start writing the White House and our legislators in the Senate and House, and ask them which terrestrial problems can NASA solve for us? The answer is a laundry list – and a compelling one, just off the top of my head!
Want to grow the US economy and create jobs?
— Give NASA a strong mandate and plenty of resources!
Funding NASA is one of the very few sure-fire ways for this country to glean direct economic benefits. For every $1 that the United States government puts into NASA, the US economy grows by as much as $8. (One source here). This makes it one of – if not the – most effective ways for the federal government to have a positive effect on the economy. That’s a gain of 800%. Compare that to the ambiguous and uncertain economic growth from bailouts, tax cuts for the richest 2%, two wars, unspent stimulus funds, or Congressional shenanigans. NASA creates high-tech jobs, administrative jobs, IT jobs, engineering jobs, research jobs, custodial jobs, manufacturing jobs, analysis jobs. NASA creates technologies, hardware, and software, and puts out contracts for the development of more technologies, hardware, and software. Money going to NASA boosts the economy of every state in the union, some by hundreds of millions – or even billions – of dollars.
Economic growth by state from federal NASA funding (click for full size)
NASA can best provide these economic benefits if it has an ambitious, driving goal – pushing it to turn out as much of a return on the investment as it can – and sufficient resources to pull it off. If it’s the economy we’re worried about, we should be afraid of not funding NASA enough!
Want to keep this country competitive in technological development and scientific progress?
— Fund NASA!
The White House web site recognizes that “the United States is losing its scientific dominance.” Are iPod apps and Twitter really going to carry the tech sector of the US economy in the future? Especially when we are exporting a lot of tech jobs and highly educated workers to other countries? If we want to secure our national future, we need to make sure that we produce plenty of high-powered brains in our own country, and that we work on the latest in science and technology in the research labs and R&D centers available to us. Down the line, if Americans stop caring about science and technology, we are going to be producing smaller quantities and lower quality goods and services. Our development will stagnate when compared to other countries. We will have to look abroad for solutions. Even if that’s not a bad thing outright, why wouldn’t we want high-tech developments and cutting-edge science produced close to home?
We can only derive so much benefit from all the MBAs and lawyers we churn out. But technological and scientific fields develop whole new markets and whole new disciplines that we can use to create better products, better services, better knowledge, and a better society. Remember that when President Kennedy directed NASA to land on the Moon, we had a grand total of 15 minutes of human spaceflight experience. New industries, spun off by fields from specialized materials science to computer technology, that had not even been conceived yet had to be invented. The very foundations of the US manufacturing industry had to be advanced forward a decade to meet the tolerances required for the Apollo vehicles. Imagine what could come out of a similar program today!
NASA is a leading agency in funding both basic science research and technological development. The conclusions from this research percolate into the biotech, electronics, computer, aviation, communications, materials, chemical, defense, and medical industries – just to name a few! The science funding goes to universities and research labs all over America. Technologies developed in the course of pursuing the space program find their way into cars, airplanes, traffic control systems, manufacturing, construction, the food services industry, and even the average American home. If that money keeps flowing, those industries keep growing – and new industries sprout up!
Want to keep the next generation interested in science and technology, so we – and they – invest in their education?
— Give NASA an exciting mission and the money to pull it off!
President Obama has made appreciative statements in the past about the role NASA plays in inspiring American youth to pursue higher education, especially in challenging scientific and technical fields. This must continue. We cannot let children think of science and engineering as the sole domain of nerds and geeks, unpopular kids or unrelatable kids. For the US to be competitive in science and engineering, we need scientists and engineers. That means we must have children who develop and maintain an interest in science and engineering. So we need to make science and engineering, and education in those fields, popular. Fun. Invigorating. Sexy.
But NASA can’t simply “inspire the youth” just by its mere existence. It needs to be in the news. In the news, doing cool things. In the news, doing cool things, constantly. For that, NASA needs a really high-profile, risky-yet-achievable, demanding, sense-of-surmounting-the-impossible mission. As if this nation had dedicated itself to a goal, before this decade is out, of something on par with landing a man on the Moon and returning him safely to the Earth. Something that captivates a youth with an Internet-induced, ever-shrinking attention span. I propose establishing a permanently crewed base on Mars within the next 15 years, by 2025. Such a mission will not only keep the young scientists and engineers of our nation rooting for the space program, and interested in the space program, while they are learning – it will also give them something productive to work on when they finish! NASA is both a means and an end, but only if it has sufficient resources and a mission far more ambitious than the 2004 Vision for Space Exploration.
Want to find ways to feed the hungry?
— Tell NASA to put a permanently crewed base on Mars!
If we try to establish a self-sustaining colony on the Moon or Mars, we need to feed the crew. And if we go for Mars, a self-sustaining base is pretty much a requirement to make the launches feasible. The astronauts would not be able to rely on regular resupply missions.
This means taking what we know about how things live and grow, and finding a way to develop food sources in a space outpost. We would have to leverage everything we know about hydroponics, algae growth, genetic engineering of bacteria, nutrition – the alchemy of turning raw materials into nutritious, palatable food for humans. And since launches to Mars would have severe mass limits, all this will have to be packed into as lightweight and small a package as possible.
Once developed, those technologies would be perfect for taking to the Third World, to the deserts, to impoverished nations and soup kitchens on Earth. We could solve global hunger once and for all, by finding ways to provide families with self-sufficient food-generating equipment. The kind of equipment that comes from NASA ingenuity and NASA money – but it will only do so if the government directs NASA to tackle the problem!
Want to get medical care to as many people as possible in poor, remote countries with little infrastructure?
— Send NASA astronauts to Mars!
If we send astronauts to Mars, they are going to be completely out of reach of medical care. The nearest emergency room will be – at minimum – 45 million miles and half a year away. The Mars base crew are going to have to take care of themselves. This means that, not only is at least one of them going to have to be an ER surgeon or something, but they are going to need medical equipment. Not just any medical equipment, either; ultra-rugged equipment that functions on little to no power with near 100% reliability. Equipment that gives fast, comprehensive test results. Equipment that is easy to use and understand. Equipment that is, or folds up to be, very small and ultraportable. You know – tricorders.
The Mars base is also going to need treatments. Treatments that are easy to administer. Patches, drugs, capsules, ultra-miniaturized subcutaneous infusion pumps, and the like. But again, getting things to Mars requires that they be small and low-mass – five years’ supply of daily vitamins for a dozen or so astronauts would hardly fit the bill! So, they are going to need rugged, reliable equipment to manufacture those drugs on Mars with super-limited resources.
Imagine if Doctors Without Borders could get their hands on all that. Or the Red Cross. Or the Peace Corps. They could…but only if we tell NASA to go to Mars and give it the means to do so!
Want to solve global climate change?
— Tell NASA to keep people permanently in space!
Yeah, that’s right – I didn’t say “mitigate” or “delay.” I said solve.
NASA drives innovation in batteries, photovoltaic cells, Stirling converters, fuel cells, and nuclear power. NASA has to squeeze every last drop of electrical power out of every battery on every spacecraft. NASA has to build their electronics to take meager power supplies.
Crewed spacecraft are closed environments that must support human life. They have to recycle, to reuse, to be careful what they bring in and out. They have limited supplies, limited fuel, limited electrical power, and they must accomplish ambitious science and exploration goals.
Send astronauts to Mars, and they will have to make more use of the scarce resources of the Red Planet than even Space Station astronauts do on ISS, because they will be so far from assistance. They are going to have to maximize what they can do for any input of solar power or raw material. Everything that comes from Earth is going to be incredibly precious, and will have to stretch out its useful lifetime for months or years. The astronauts are going to have to recycle their air. And they’re not going to be able to rely on taking their equipment to the shop every few months or replacing it every few years – it’s all got to work reliably for decades.
Those high-efficiency solar cells, low-power electronics, extreme-reliability equipment, 100% recyclable materials, CO2 scrubbers and chemical recyclers are sure going to come in handy for replacing coal and oil here on Earth.
So let’s solve some problems here on the ground. Let’s go out into space!
Before “Avatar,” I’d seen a couple of movies in 3D and had not really been impressed with what the extra five bucks got me. Up until that point there was really only a single scene in a single movie in which I thought the 3D effect actually added anything to my experience. (It’s the shot in Pixar’s “Up” in which the house floats in front of the sunset…all the colors of the sunset shine through all the colors of the balloons, each balloon is a nice round object, and the whole collection of balloons looks three-dimensional. Beautiful.) For the most part, though, I tend not even to notice that a movie is 3D unless I’m specifically looking for the three-dimensionality – if it’s a good movie, the story and characters ought to hold my attention more than that – or if the filmmakers try some cheesy, gimmicky, amusement-park-style 3D “popping” effects, a la “Beowulf.”
“Avatar” changed my mind a little, in that many more of the scenes looked so damn cool in 3D. But the more I thought about it, the more I became convinced that while the 3D experience was pretty neat, if I go see “Avatar” any more it will be in 2D, because it really didn’t add that much to the movie. The forest creatures and sweeping panoramas will look just as good projected in 2D. The only aspects of that movie that would miss out are the holographic computer displays, and those aren’t really that important.
In fact, I think that Hollywood ought to just abandon this 3D movie kick. It’s not that I get a headache or think that cool things can’t possibly be done in 3D. It’s that even when filmmakers do the cool things, it adds so little to a movie that I’m definitely not inclined to shell out for a 50% surcharge on a ticket. Here’s why…
First: great movie, literally awesome visuals, stunning effects, good acting and execution, fun alien creatures, who cares if it’s a retelling of Pocahontas.
What I absolutely did not expect when I finally got to see James Cameron’s ‘Avatar’ yesterday afternoon was to see my own research appear in the movie. Granted, it doesn’t take a front-row seat and it doesn’t play any major plot roles. As I was driving home with my girlfriend (a fellow aerospace engineer), we got into a discussion about how this was a reasonably hard sci-fi movie. None of the technologies seem particularly farfetched: ducted-fan helicopters exist on Earth at a low technology readiness level (TRL), as do exoskeleton power suits. 3D glassy computer displays aren’t a stretch, nor are hovering VTOL aircraft on a low-gravity world. The flight to Alpha Centauri takes 6 years, meaning some reasonable sort of sublight propulsion. The ship Sully arrives on even has rotating segments, big radiators, and solar collectors. The avatars themselves don’t even seem too crazy, since we keep hearing about advanced prostheses that can be controlled by a user’s thoughts. (I’ll reserve judgment on mixing alien and human DNA until we have real alien DNA on hand.) Nor does a planetwide neural interface – though I have to wonder what selective pressures would cause such a thing to evolve – given that we have bacterial, fungal, and other life forms on Earth that can split and recombine, blurring the distinction between organisms.
But surely, I thought, those floating mountains are ridiculous. Visually stunning, yes, and great for those 3D flying scenes. But physically ludicrous.
Pandora's Hallelujah mountains
We are led to believe, in the movie, that these mountains float against the force of (albeit reduced) gravity because there is an exceptionally strong magnetic field generated on Pandora. Cameron even gives us direct evidence of that field: you know how iron filings align themselves with a magnetic field, like that of a bar magnet?
Iron filings aligning themselves with magnetic field lines
Well, the magnetic field on Pandora is so strong that geologic formations align themselves with the magnetic field. The field is so outrageously strong that whatever iron content is in Pandoran minerals – most likely not 100%, even if those rocks are pure hematite or magnetite or something like that – is sufficient to make rocks suspend themselves against gravity in the shape of the magnetic field lines:
A field that bends rock to its will!
I know for experience that this might not necessarily be impossible, for a sufficiently strong magnetic field. After all, in my lab is a whopping-big NdFeB rare-Earth magnet about the size of a margarine tub, and even when it’s contained within its sarcophagal wooden box, I can get six-inch steel bolts to suspend themselves, against gravity, at a 45° angle in its field. So, for a sufficiently strong magnetic field, this flux-line rock formation is not at all out of the question, believe it or not!
How about the mountains themselves? Couldn’t the magnetic field strong enough to make these “flux arches” also levitate mountain-sized chunks of rock?
Well, I thought, surely not if it is solely the repulsion of like magnetic poles that is responsible. After all, Earnshaw’s theorem says that the familiar field sources that drop off with distance, like gravity, electrostatic attraction, and magnetostatic attraction, cannot be arranged in a passively stable configuration. If you don’t believe me, then I set for you a challenge: get some ordinary bar magnets, and lay them out on a table. Try to arrange them in such a way that they are within a few centimeters of each other, but the attraction of opposite poles and repulsion of similar poles cancel out so that the entire arrangement sits on the table without moving. (For safety’s sake, do not do this with the rare-earth magnets I mentioned above, because when you fail at the challenge, the magnets will jump towards each other with substantial force. Rare-earth magnets are brittle and will shatter if that happens, sending neodymium shrapnel flying around – if they didn’t pinch your fingers when they impacted.) You will find that no matter how hard you try, no matter how many friends you get to hold the magnets in position and simultaneously release them, no matter how you angle them and tweak them, you won’t ever be able to prevent at least one of the magnets from attracting or repelling some other magnet. The whole arrangement will either fly apart or collapse together. You might think that in 3D you’d be able to come up with some super-clever configuration that is stable, but, in fact, if you move beyond the two dimensions (and three degrees of freedom) of the table top the situation gets far worse, because all the bar magnets try to align themselves with one another in 3D. So, a combination of purely magnetic and gravitational forces cannot result in a stable configuration of those mountains.
“But, ha!” you say. “You must be wrong! You said that a combination of gravitational field sources can’t be in a stable arrangement, and clearly, the planets of our solar system have been stably orbiting each other for four billion years! And I’ve even seen those Levitron tops – magnetic tops that stably levitate against gravity, just like those mountains!“
The Levitron: just two magnets, one inside a spinning top
The key difference between a Levitron or an orbit and the bar magnets on a table top are that they are dynamically stable. They requiremotion to preserve stability. Stop the planets from orbiting, and they will fall into each other and the Sun. Stop the Levitron from spinning, and it flops over – aligning itself with the magnet in the base – and drops to the ground. So, for Pandora’s mountains to levitate like that, they must be spinning or moving in some way. It might be the case that, if they were at Pandora’s equator, the repulsive magnetic force actually “cancels out” the low gravity of the moon enough that the mountains are actually in circular orbits about Pandora’s equator. But that situation is dynamically tricky, requiring exquisite balances of forces – and I would estimate from the different sizes of floating mountains that they have different magnetic mineral contents, so the balance between gravity and magnetism would be different for each mountain and each would have a different orbit. Doesn’t work.
So what’s the answer? Well, it’s all in those little gray crystals the imperialist human colonists of RDA are after. Unobtainium.
An unobtainium crystal, unobtrusively levitating. Wait, what?
Above is a picture of an unobtainium crystal from the movie. It’s levitating above some crazy sci-fi antigravity contraption, that holds it stably up in the air where people can poke at it, spin it, pluck it out of midair and play with it before putting it back in exactly the same spot again. Now, wait a minute – where have I seen this behavior before? Oh, right. My research lab.
A rare-earth magnet levitating over a high-temperature superconductor
That is a picture I took of a NdFeB magnet, stably levitating over the high-temperature superconductor yttrium barium copper oxide, or YBCO. (For scale, the magnet is 3/4″ across.) You can do everything with that magnet that they do with the sample of unobtainium in ‘Avatar.’ Leave it alone, and it happily floats in midair. Poke it, and it rocks a little before going back to its equilibrium position. Give it a twirl, and it’ll spin over the YBCO – and if the magnet isn’t cylindrically symmetric, it’ll eventually stop spinning and settle down again. Pull it away from the YBCO, and you can put it back later and watch it float in exactly the same midair spot as when it started. You can even pin different sizes and shapes of magnets – all stable against gravity. This whole setup would work perfectly if the magnet was on the table and the YBCO was doing all the floating, too. It’s all because the magnet induces currents in the YBCO that are not opposed by any resistance – “supercurrents” – which generate their own magnetic fields that then interact with the magnet.
“Wait,” you ask, “that magnet is just a magnet. The supercurrents make magnetic fields. I thought you said that magnetic field sources couldn’t be arranged in a stable configuration! It’s Earnshaw’s Theorem again.”
That would be an astute question. The answer is that, in this case, the superconductor doesn’t have a fixed magnetic field. As the magnet moves around – let’s say it starts to fall from its equilibrium position, because gravity is pulling on it – then its motion causes the supercurrents in the YBCO to move around. The new distribution of supercurrents gets superimposed on top of the previous distribution of supercurrents, with the net result that the magnetic field from the YBCO tends to push back on the magnet, keeping it in its original position. It’s as if the field lines of the magnet get stuck, or trapped, in the volume of the superconductor. The effect is called “magnetic flux pinning” for that very reason, and it happens with Type II, or “high-temperature” superconductors. (If you know about Meissner repulsion, flux pinning is related but not the same.) So, that blue-glowing antigravity generator in the RDA command center, with the levitating sample of unobtainium, is very likely just a magnet. And the Hallelujah Mountains are just a scaled-up version of the magnet and YBCO in my lab.
But, you probably noticed from that photo, the YBCO has to be below liquid nitrogen temperature in order to superconduct and exhibit flux pinning. Clearly, Pandora is not at cryogenic temperatures, which pretty much pegs “unobtainium” as a room-temperature superconductor – a type of material that is highly sought-after in research labs today, and would indeed be extremely valuable. That means that the Hallelujah Mountains on Pandora likely consist of large deposits of unobtainium, which are flux-pinned to the stupendously powerful magnetic field lines coming from that field sources on the planet. This explains the value of unobtainium, how the mountains levitate the way they do, and why the floating mountains are so close to the flux arch structures.
There’s another interesting link between ‘Avatar’ and flux pinning. Remember how I said that the effect of flux pinning is as if a magnet’s field lines get stuck within the superconductor? Well, if you had a good electricity and magnetism course, that notion might sit uncomfortably with you, because you were probably taught that “field lines” or “flux lines” are not physically real, but are a good visualization tool for magnetic fields, which exist everywhere around a magnet and not just in neat little looping lines. Well, you’d be right, but things tend to get kind of weird inside superconductors. Magnetic fields are quantized just like everything else, and it is these magnetic flux quanta that get “stuck” inside the YBCO. In fact, they actually get trapped on impurities within the YBCO’s crystal structure. You might think that these quanta of magnetic flux would be called “fluxons,” but because they correspond pretty well to magnetic field lines, papers on superconductivity and flux pinning tend to throw around several names for them – like “flux lines,” “field lines,” and “flux vortices.” That last name likely comes from the fact that, in the superconductor, each of the magnetic field lines induces a little loop of electric current that races in a circle around the flux line, like a little vortex. The sum total of all these little currents adds up to the distribution of supercurrents that gives us flux pinning.
In ‘Avatar,’ every time they fly near the flux-arch structure, they talk about a “flux vortex.” It sounds like your classic sci-fi trope of combining sciency-sounding words. (“Invert the phase capacitors!”) But, hmm…maybe, just maybe, that’s not mere technobulshytt after all!
I’m pretty convinced that all this isn’t accidental. The filmmakers had every intention of unobtainium being a room-temperature supercondcutor and the floating mountains being flux-pinned to the field source within the planet. Because I know that this is not the first article on the web about it! But the fact that it’s my own research in this movie: now that is cool! (For the uninitiated, I’m working on using flux pinning to assemble and reconfigure modular spacecraft. More info on my web site and my research group web site. You can also check out Youtube videos of me demonstrating flux pinning and our microgravity experiments with flux-pinned spacecraft mockups from last summer.)
Of course, ‘Avatar’ doesn’t get it all right. And they shouldn’t be expected to. I know from my research that flux pinning is a very short-range effect; getting those mountains to levitate would require a (probably literally) mind-bogglingly powerful magnetic field. Not something I’d expect to see from a planetary dynamo. Nor would a dipolar magnetic field within Pandora explain the flux arches: those are clearly centered on a magnetic field source at the surface of the world. And if the field source is powerful enough to get the rocks to bend around and follow field lines – all the aircraft, armor suits, guns, mobile lab trailers, and equipment carried by the human scientists and soldiers probably has more than enough ferromagnetic metal content to be ripped towards the field source. And that doesn’t even account for this happening:
Oh, well. But, speaking as someone who hopes that our future space program will involve spacecraft build out of components that “levitate” near each other without touching, but still acting as if they are mechanically connected, I would sure love to see some room-temperature superconductors and floating mountains!
What are a long car trip and hosting boring virtual office hours good for? Thinking about how our science and society would be different if the Earth had rings. Science fiction writers, take note.
As I was writing that earlier post, my officemates and I got into a discussion about some of the implications to (at least Western) science and philosophy of such a ring system. One of them suggested that the rings, which would be mostly aligned with the Earth’s equator but would precess with the Moon, would be quite obviously separate from both the purported “celestial spheres” and the Earth, so maybe the ancient Greeks could have dispensed with that destructive Platonic notion much earlier in the history of Western science.
I got thinking and realized that, in addition to their own dynamics, the rings would have a few other obvious effects on the science of those cultures at high enough latitudes to get a good view of the ring system, without seeing them edge-on.
First, the shadows of the Earth and Moon would be visible on the rings. These shadows would be shaped like portions of circles, and would vary in size and shape with time of day, month, and year. From observations of these shadows, easily possible with the naked eye, the Greeks, Egyptians, and Chinese ought to have been able to show without any doubt that the Earth and Moon are spherical. They may have been able to deduce the position of the Earth’s spin axis and axial tilt by comparing the shape of the rings and the shadows on them to the time to year. (These experiments could be quite simple: make a stiff, lightweight circle or hoop, hold it at arm’s length at night, move the circle in and out and tilt it back and forth until its edges line up with the shadow on the ring. Add a little simple geometry, and BAM: I would have just found the axial tilt of the Earth.) They should also have provided some kind of estimate of the distance to the Moon, as observers could compare the size of the Moon with the size of its shadow. And comparing the Earth’s shadow on the rings to the positions of the background stars would have given the ancients an incredibly accurate nighttime clock.
Second, and perhaps most importantly of all, the rings would vary radially in opacity. This would make them beautiful to behold, yes, but it would also give naked-eye astronomers an absolute scale for photometry. Annuli of the rings would block out the light from some stars, but not others. The thicker rings would block more stars than thinner rings, giving a gradation of occultation scales. By comparing which rings block out which stars, observers would have been able to make statements about the relative brightness of the stars with a degree of precision unknown until Christian Huygens arrived on the scene – even surpassing the precision of that experiment. Still more exciting, if the ring was able to occult the Sun, that same method could have been used to measure the light output of the Sun. Now, coupled with the insight that the Sun is a star and a crude estimate of the Earth-Sun distance, an observer should have been able to deduce from naked-eye observations approximate distances to the stars.
I’ll say that again: If the Earth had rings, the ancient Greeks, Chinese, and Egyptians might have had a sense of the scale of the Cosmos. The Romans and Indians might have known what a parsec is.
Furthermore, this photometry could have been used on the visible planets as well as stars. That would have told the ancient astronomers that Mercury, Venus, Mars, Jupiter, and Saturn were a lot closer to the Earth than the stars. In fact, if the ancient photometers tracked the brightness (and, therefore, distance from the Earth) of each planet over time, they would have noticed something interesting: the planets move in circles about a point that is not located within the body of the Earth, but is rather in the Sun. The heliocentric model for the Solar System would have been adopted in ancient times.
Now, knowing that the planets go around the Sun, and the stars are all rather a long way away from the Sun and from each other, ancient astronomers might have realized that other stars could have planets just like the Sun does. Think about what that idea might have done to Western philosophy and religion in their formative years: other Earths? In the sky?! Going around other Suns?
Here’s a possibility I’m not sure about: if the ring was thick enough, it’s possible that it might dim the Sun enough that an observer could safely look at our star with their naked eyes. If so, then sunspots might have been visible to the ancient civilizations. In that case, they might have known that the Sun is not a perfect glowing sphere, and that it rotates. They might have known about the 11-year solar cycle.
And then, imagine what could have happened once Galileo stormed onto the scene with his telescope. When he looked at Saturn, he would have known exactly what he was looking at. “Ears” indeed! By watching Saturn’s rings wax and wane with each Saturnian year, he would have identified the orientation of Saturn’s ringplane to the ecliptic. Knowing that Saturn has rings would have told scientists that Earth’s features are not unique to our own planet.
Early telescopes might have been powerful enough to identify some of the larger rocky chunks making up the Terrestrial rings. Observing their orbits at different radii within the ring could have lent a lot more data to scientists like Kepler and Newton, who were trying to figure out what forces kept the planets in orbit. Armed with data on the orbits of ring particles and Kepler’s Laws, early scientists might have been able to get a pretty good estimate for the mass of the Earth and fix the Earth-Sun and Earth-Moon distances pretty accurately.
I’m thinking that, given how great a dynamical laboratory the Saturnian ring system is, rings around the Earth would have allowed the progress of science to advance much more rapidly, as the rings would provide a precise tool for measurements of position, time, and distance of celestial bodies. If the laws governing those bodies had been puzzled out, say, before Christianity dominated Europe, imagine what society would have resulted….
