Taz asks

 Can you do a rundown of Halo from a scientific perspective? I’ve really enjoyed your writing about Armageddon and would like to hear your thoughts on the game that has (since its début in 2002) become a phenomenon. Tanks in advance!

My answer to this one isn’t particularly scientific in any rigorous sense of the word, nor does it have much to do with the Halo universe itself, but I’m going to do it anyway because it’s still kind of fun. Or at least I think so, anyway.

Most elements of the Halo universe are conventionally sci-fi – magic spaceships, magic faster than light travel, magic anti-gravity, all the stuff you really need to hand-wave away in order to make possible the intergalactic space war that forms the background for the Halo story. I can’t quibble with any of that, in the same way that I don’t quibble with the existence of wizards and undead in the Myth series: it’s necessary for the setting. However, what I can quibble with is the thing they put front and centre of the Halo games: the Halos themselves.

The Halos are ring-shaped megastructures with a diameter of 10,000km and what looks like a width of around 300-400km. On the inner surface of the ring is a fully-functioning biosphere with a breathable atmosphere, water, plant life and weather regions. The ring is spun to provide enough faux-gravity in the form of centrifugal force to keep all this stuff stuck to the inside of the ring. This kind of space habitat is not a new idea; it was first popularised in Larry Niven’s Ringworld and became a common part of the late Iain M. Banks’ Culture novels, with the Culture Orbitals being truly vast structures on the scale of millions of kilometres which dwarfed the comparatively titchy specimens on offer in Halo. If you’re trying to build somewhere for people to live in space and have access to ridiculously advanced levels of engineering technology, then a ring-shaped structure is not the worst idea in the world. While I can think of a lot of better ways to do it I can’t think of any reason why a ring wouldn’t work.

On the face of it setting Halo on a ringworld isn’t so terribly unscientific, then. They’d work as space habitats. But there are two problems with the implementation of ringworlds as seen in Halo. The first is rather prosaic: even the backwards human race is shown to have some form of artificial gravity system functioning on all of its spaceships. If you have artificial gravity then the primary – indeed the only – reason you would build your space habitat in the shape of a ring is negated; access to artificial gravity technology means that you no longer need to spin something to get the things on its inside surface to stay on, and so the question arises of why the hell you did that in the first place.

The second problem partially deals with the first, in that we discover during the course of the first game that the Halos aren’t actually intended to be space habitats at all. Instead the Halos are ancient superweapons designed to wipe out all sentient life within a large radius (I think a range of tens of thousands of light years is mentioned in the first game, with a network of seven Halos being enough to wipe clean the entire galaxy). Now, maybe the Halos weren’t built in a ring shape because the builders wanted people to live there. Maybe they have to be ring-shaped in order to carry out their function of galaxy-wide genocide. Who knows how these things work. Unfortunately this theory is somewhat sabotaged by the fact that there is a working biosphere on the inside surface of the Halo that is capable of supporting life, which would require the builders of Halo to go to a not inconsiderable amount of extra effort to get it all to work. If Halo is not supposed to be a space habitat then why the hell does it resemble one so exactly?

Of course the answer is that a ringworld is a pretty striking setting for an FPS which certainly seems to have done Halo no harm whatsoever; nobody who played it is going to forget booting it up for the first time and seeing the world curving up over their heads. That’s fine. The plot of Halo isn’t especially coherent anyway, so some inconsistency over what exactly the Halos are for versus how they’re designed is to be expected. However, the question did get me thinking as to what other useful things could you do with a ring-shaped megastructure. The resulting list was a fairly short one, consisting as it did of a single item: energy gathering via Dyson structures.

If you read or watch sci-fi at all you’ve probably heard of the Dyson sphere concept, at least in passing. A Dyson sphere is a shell of matter constructed around a star in order to maximise the amount of energy you can harvest from that star. Make the shell dense enough and there’d be practically no wastage; you’d  be able to gather 100% of the star’s energy output, which is a truly ludicrous amount of power. After the shell harvests all this power it would then be transmitted elsewhere so that the civilization that built the shell could do something useful with it.

Some misconceptions about the Dyson “sphere”: that it is a solid object, and that it has to take the shape of a sphere. A lot of sci-fi writers made the mistake of having their Dyson spheres be solid shells of matter enclosing their parent star. This is stupid for several reasons; if we’re considering structures on this scale we have to assume that the technology would exist to make the shell solid,  but a solid shell would be gravitationally neutral in relation to its parent star since it would envelope it uniformly at a constant distance. Each part of the shell would cancel out another part of the shell, which raises the interesting hazard of having the parent star drift into the side of the shell (or vice versa) since neither of them is gravitationally stable compared to the other. There’s also the minor niggle that there might not actually be enough construction material present within the star’s solar system in order to actually make a solid shell.

So solid Dyson spheres truly are science fiction, with no possibility that even a hyper-advanced race would be able to make one without circumventing a fair number of the laws of physics. Happily for us they are just a corruption of Freeman Dyson’s original idea, which was to have an orbiting array of satellites gobbling up a star’s energy output. While it would still be a massive engineering project this is much more plausible, and while not having a solid structure means the shell is going to be less than 100% efficient it does have the advantage that you can start the shell simple and work up from there. The simplest form of the shell is – you guessed it – a ring-shaped array of satellites all orbiting the parent star on the same plane. Scaling up would result in multiple interconnecting rings with very complex orbital characteristics, but if somebody could sit down and work out the maths there’s no real reason why it couldn’t be done.

Which does rather beg the question: why would you want to?

The answer to this is somewhat speculative and has to do with another commonly-referenced sci-fi concept called the Kardashev scale. The Kardashev scale isn’t any kind of absolute measure, but instead functions kind of like the Drake equation in that it’s supposed to jog us out of our stolid, Earth-based ways of thinking: assuming most technological barriers could eventually be overcome, then what would be the major limiting factor on a civilization’s progress? The answer is energy, and the Kardashev scale attempts to class a given civilization’s level of technological advancement by the quantity of energy it can harness/has access to. The scale as originally formulated by Kardashev goes like this:

• Type I Civilizations have the capability to utilise the entirety of the energy resources provided by their home planet.

• Type II Civilizations have progressed further and are capable of tapping into all or most of the energy generated by their parent star.

• Type III Civilizations have progressed furthest, and have found a way to harness the energy output of an entire galaxy.

Now, clearly that’s not remotely scientific in the least, and the concept of a Type III civilization in particular boggles the mind; we’re talking about completely utilising the energy of at least a hundred billion stars simply to service the needs of your civilization. Our own civilization can only make use of a fraction of the energy provided by the Earth – it doesn’t even rank as a Type I on the Kardashev scale — and from there it’s very difficult to imagine what the hell you’d need so much energy for. But that’s the point in the scale. It’s supposed to get us thinking about how large a civilization could grow if it were unconstrained by 20^th – now 21^st – century technology and modes of thinking.

It’s a fair bet humanity will make it to Type I status eventually, since this roughly corresponds to fusion power, nanotechnological capability and all that other World of Tomorrow stuff that never quite seems to turn up. We can just about envisage a Type II civilization, as while the idea of building rings of energy-gathering satellites around the Sun is quite outlandish it isn’t that infeasible either; we probably will be able to do that at some point if we don’t kill ourselves off through some kind of horrible climate catastrophe/Malthusian apocalypse. The sort of things a Type III civilization would get up to, on the other hand, are very firmly beyond our technological horizon, and the Kardashev scale is the only thing that’s really punched through that barrier to give us some idea of the scale and capability that a true far future civilization might eventually possess. It’s also acted as an enabler for dozens of hack sci-fi writers to produce oodles and oodles of poorly-formatted bollocks¹, but then no good idea ever went unsullied by that particular fraternity.

Anyway, Kardashev is one of those abstract things that’s supposed to drive other more scientific ideas, and this is something that it most certainly has succeeded in doing. You go to the Wikipedia page on the subject and you’ll find a dozen ways of reclassifying, improving on or extending the scale to incorporate this case or that case, but the sole warning on how seriously it should be taken is the line towards the end which states

It has been argued that, because we cannot understand advanced civilizations, we cannot predict their behavior. Thus the Kardashev scale may not be relevant or useful for classifying extraterrestrial civilizations.

I’d go farther than that, in that the Kardashev scale may not be that useful for classifying advanced human ones either. Most attempts to predict the future even fifty years down the line end up being laughable in hindsight, and it only gets worse as you get further and further away from our modern technological touchstones, so all this stuff I just said about ringworlds and Dyson spheres will probably end up being a load of old balls as well. Even scientists like to dream sometimes, though, and since using structures like these to gather practically unlimited quantities of power that are free for the taking would probably lead to post-scarcity societies like those seen in Star Trek and the Culture novels I’d say it’s a dream worth holding on to.

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gnomishlich asks

Armageddon, terrible movie about oil drillers on an asteroid how would a space shuttle or other space traveling vehicle fare for persons odds of arrival, survival, and departure from an asteroid?

Oh god, what have you done. WHAT HAVE YOU DONE.

You may think Armageddon is a terrible movie, and you would hardly be wrong to do so. Michael Bay’s job is to make blockbuster movies that make extensive use of special effects and loud action scenes to cover up the fact that they have no logical plot or consistent characterisation to speak of, and are designed to cater to people whose brains are operating on the mental level of a twelve year-old boy. Literally every single one of his films has been offensively bad. Like, not just the regular kind of bad, where you sit through it and it’s bad and at the end of it you think “Well, that was bad, I won’t be watching that again.” No, that would be too easy for Bay, and in fact if he ever made a film that was simply bad I’d think he was slipping somehow. What sets Bay’s films apart from the rest of the lowing, braying herd of CGI summer blockbusters is that they seem to be designed to piss the audience off. I honestly don’t know how you can watch a Transformers film and be anything other than utterly and completely ashamed and insulted – ashamed because you spent two-plus hours of your life watching this crap and you don’t want anyone else to know, and insulted because Michael Bay thinks you are stupid enough to enjoy something pitched at the level of a Transformers movie. It’s only a Michael Bay film that can make me feel soiled somehow after I’m done watching it, like I need a day-long shower to wash off all of the dumb that has built up on my skin. It’s hard to accurately recall just how horrible I felt after watching Transformers 3, but thanks to the internet my immediate reaction has been preserved for posterity:

Transformers 3 should be submitted to a peer-reviewed scientific journal because it conclusively proves many things that otherwise would have taken decades if not centuries of study and observation. The intellectual bankruptcy of Western civilization and culture. The non-existence of God. The ultimate futility of living in a world where the laws of physics allow such crimes to be perpetrated against the very nature of the universe. Like some sort of Lovecraftian horror that has slithered forth from an unholy nether dimension, Transformers 3 is so utterly and fundamentally at odds with everything good and sane that the mind atavistically recoils and refuses to comprehend it.  And even if I manage to purge the experience of having watched it from my memory it will still leave signs of its passage; a broad swath of tainted brain matter that cannot be reused for any other purpose but which instead grows and expands, subverting healthy tissue and corrupting my mind to its vile purpose until I am a twisted ur-man no longer capable of rational thought. Ia! Ia! Baythulu fhtagn!

Right. Yes. Anyway. Michael Bay films. Very bad. Very bad. Armageddon is a bad film, and it is no less bad for having been made during Bay’s early period (it was his third film or something), but by the standards of Michael Bay it is unremarkably bad. There’s nothing to make it stand out in terms of badness from the likes of Pearl Harbor or The Island – yes, it’s stupid, and shot with Bay’s trademark oversaturation of American flags fluttering in the breeze, and the scene with the minigun makes no logical or rational sense, but neither do any of his other films so there’s nothing here to mark it out as different in any way.

That is, unless you happen to have a PhD in solar system impact physics, at which point Armageddon becomes tied with Mission to Mars for the Worst Cinematic Atrocity Perpetrated Against Science award. You’ve got an unrealistically sized asteroid heading towards Earth which is stated to be “the size of Texas”, so about 700 miles across, except there’s only one asteroid (now dwarf planet) in the belt anywhere near that big and we’d notice if anything happened to it. The asteroid has been knocked out of its orbit by a comet; this is a chunk of ice which is typically Not Very Big and has sod all mass thanks to being made of spongey ice, and would have little impact on the orbital trajectory of a an asteroid 700 miles on a side¹. The asteroid itself looks nothing like an asteroid that’s just been walloped by a comet; there’s a few chunks of rock and clouds of debris orbiting with it like you’d expect, but I don’t think any asteroid would look quite as spiky as the one in Armageddon does. It should look just like a big rock, or like a big pile of agglomerated rubble compressed down into a sphere by its own self-gravity. Instead it looks all gothic and nightmarish and there’s lots of weird green and blue hues used in the lighting (again, trademarks of Bay) because that shit looks cooler, I guess.

Then you’ve got the actual asteroid impacts on Earth, which are also awful. The one at the start creates a moving wall of fire that eventually consumes the entire planet, and I don’t even know how this would work. Asteroid impacts tend not to be about fire so much as they are massive earthquakes and huge blast waves. Oh, anything caught nearby is going to be a crispy critter (read the first statement from a witness of the Tunguska event) thanks to the immense heat of the asteroid’s entry into the atmosphere and sheer quantity of energy liberated when it either hits the ground or explodes in an airburst, but we’re talking something about the size of a big nuclear fireball here, and not some all-encompassing global catastrophe. While the shock waves would devastate an area hundreds or thousands or miles around the impact site, truly global damage would be done through dust clouds/climate change for the smaller asteroids, and the physical disruption of the Earth’s crust for the larger ones.

The second thing this – and all other Hollywood films about asteroids, including Deep Impact – gets wrong is the speed of the asteroid. Asteroids in films move slowly, almost leisurely, like an out-of-control jet airliner rather than a piece of space rock moving at 20-30 kilometres per second. People on the ground have plenty of time to see them coming and make futile attempts to escape. In reality, unless the asteroid comes in at an incredibly oblique angle the time lag between an asteroid entering the Earth’s atmosphere and hitting the ground is about one second. Try snapping your fingers once; that’s how fast an asteroid impact would seem to a watching human. If they’re standing close enough to see it happen they’re screwed, and even people who are safely over the horizon will be killed by a blast wave pushing a wall of moving rock and debris towards them faster than the speed of sound. Even smaller asteroids (and we’re talking the metres-scale stuff that makes it to the ground here) would pack enough punch to explode with the force of a moderately-sized stack of TNT. You see the Barringer Crater? The thing in North America that’s over a kilometre wide and 200 metres deep? We think the rock that created it was about fifty metres in diameter. Fifty. Metres. Just one of the “tiny” rocks featured at the start of Armageddon would devastate a significant area of New York if it managed to score a direct hit, rather than just chopping the top off of the Chrysler building. Movies dramatically understate how lethal and destructive asteroid impacts are. It’s one of the many cases where the reality is actually far more terrifying than what’s on film, but it’s deliberately understated so as not to scare the living daylights out of the audience.

And then we get to your question, which is: could we fly a spacecraft up to an asteroid and land on it? The answer is, yes we can. In fact we have, and they even managed to get the spacecraft back to Earth orbit afterwards. Armageddon’s rendition of military space shuttles that handle like jet fighters in outer space is completely ludicrous, of course, but we’ve managed it with a robot probe so there’s absolutely no reason why we couldn’t do with an appropriately-designed manned spacecraft. Before the Orion program was gutted by the US administration one of the proposed missions was a trip out to a Near Earth Object – in other words an asteroid orbiting relatively close-by to the Earth (out past the orbit of the Moon, but not too far out) – so it’s something that is seriously considered by space agencies today, and it’d actually be considerably safer than a trip to Mars thanks to the shorter mission duration and the fact that “landing” on an asteroid doesn’t mean marooning yourself at the bottom of a gravity well.

This is what happens when somebody mentions Armageddon to me; I spend 1500 words ranting and then finally get around to actually answering their question in a single paragraph. The movie’s science was deconstructed years ago by somebody with far more patience than me², and it used to be shown to new management hires at NASA as a training exercise to see how many inaccuracies they could spot. It is quite literally the textbook case of How Not To Do It. Please, nobody ever bring it up on here again.

(Incidentally if you want to know if we could use Armageddon as a blueprint for saving the world from a real rogue asteroid, I already covered it in a previous post.)

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Joshwah asks

All fields of science have their mavericks: people who are prepared to run against the grain of consensus to deliver a startling insight that changes the paradigms about how we think about stuff. To what extent have mavericks shaped astrophysics, and to what extent to you think that astrophysics has benefited from anti-orthodoxy when compared to other disciplines?

Depends on what you mean by “maverick”, really. If you’re talking about people who bravely pushed a theory in the face of the entire scientific establishment telling them they were wrong and then, after several years of toil, being dramatically proven right by some hitherto unsuspected physical phenomenon, then I have to say I don’t think that’s ever really happened – at least not while we’ve had the modern scientific method around, anyway.

To what degree this is down to observer bias I do not know. I have a nagging feeling that histories of science tend to whitewash things with the benefit of hindsight and do not paint an accurate picture of the debates that might have raged over things like relativity and quantum mechanics. In general, though, scientific paradigm shifts happen in one of two ways:

1)     It becomes obvious that an existing paradigm is incorrect or incomplete in some way. Some scientists actively go looking for a new one, and when it is found it assumes the place of the old paradigm with reasonably little fuss because everyone knew there was something up it. This is more or less what happened with relativity – despite the theory making great waves in the press, it gained a certain level of acceptance by the scientific establishment astonishingly quickly because it was self-evidently better thanNewton’s theory of the universe. There was plenty of debate over it, of course, but once it had been tested on actual real-world things like gravitational lensing the opposition to general relativity more-or-less vanished. This is how science is supposed to work, and so we’ll call this the ideal case.

2)     It is not immediately obvious that an existing paradigm is flawed. Evidence to the contrary may mount up over the years, but in the absence of a single incontrovertible result that proves otherwise defenders of the old paradigm will always find some way to explain away the discrepancies in their world view. This is the non-ideal version of the paradigm shift, because the eventual acceptance of the new theory has absolutely sod-all to do with science. What happens here is that young scientists who are coming into the field with very few pre-formed opinions will favour the new theory, which is more correct. Older scientists who have lived with the existing paradigm for years – and, more importantly, who may have reputations built on it – will naturally favour what they know over any upstart theories attempting to knock it off of its perch. Eventually the old scientists die, and the young ones finally get to rewrite all the textbooks and switch out the old theory for the new one.

The best example of the second one¹ is the Alvarez father and son team (and others) who found a whole bunch of iridium in sedimentary rock laid down during the Cretaceous-Paleogene period that indicated an asteroid impact had given the Earth a bloody good thump at around about this time, which would explain why so many species happened to vanish from the fossil record more-or-less simultaneously.  This was back in 1980. It was a theory that captured the popular imagination and gained widespread public acceptance very quickly, but you would not believe the scientific rows over the Alvarez hypothesis that went on in the background. Geologists were pissed because Luis Alvarez was a Nobel prize-winning physicist who had worked on the Manhattan project, and not a fellow geologist – and now here he was solving one of the great geologic questions of the age. Meanwhile physicists were up in arms over the idea that a single asteroid impact could cause so much devastation on a global scale. It wasn’t until the Shoemaker-Levy impacts on Jupiter in 1994 that the dissenting physicists finally shut up, and it was only three years ago – March 2010 – that a scientific panel did a comprehensive literature review and finally agreed that an asteroid impact was the most likely culprit behind the K-T extinction event. The scientists on that panel were just starting their careers when the theory was originally proposed, and it took them thirty years to declare competing theories like massive volcanism dead and buried.²

So the problem behind this question is that given the way science tends to work, the scenario you’re envisaging rarely – if ever – happens. If an existing paradigm proves resistant to change then it’s only time and a gradually-mounting weight of evidence that will eventually cause it to collapse, and not the efforts of any single scientist or group of scientists, no matter how energetic they are. That being said, I do think mavericks have existed in the field of astrophysics, although not quite in the way you might think. If you go back to the first type of paradigm shift – the one where it all goes relatively smoothly – there’s always a group of die-hards who will continue to challenge it even after the new theory has become prevailing scientific orthodoxy. Much of the time these people are publicity-hungry quacks or have otherwise vested interests in speaking out against the new status quo, but there’s a notable few who have had particularly well thought-out problems with the new paradigm and spent a considerable amount of time picking holes in it.

These people are rare – off the top of my head I can only think of Fred Hoyle’s resistance to the Big Bang theory and Einstein’s assault on quantum mechanics, although I’m sure there are others who are substantially less famous and whose work went largely unremarked upon in the history books – but their dissent is genuinely useful. By asking awkward questions they poked holes in areas where the new paradigm was particularly weak. This prompted the next generation of scientists to spend a decade or two running around trying to patch said holes up, and the theories are stronger for it. Blind resistance in the face of overwhelming evidence is stupid, but blind acceptance of a theory is just as bad and somebody has to play devil’s advocate.

You might think there’s little difference between advancing a new paradigm that nobody thinks is true and resisting one that everyone thinks is true. Either case sets you at odds with the rest of the scientific establishment, but there is a crucial difference: the former potentially has a great payoff in that you probably get your name stuck to the theory for the rest of human history, and failing to get it adopted isn’t the end of the world since posterity will eventually prove you right. The latter carries the danger that even though your criticism might eventually be constructive and even necessary, future generations view you as something of a backwards-thinking luddite – which is pretty much what happened to Hoyle and even Einstein in his later years. In a field where reputation is everything this is something that matters, and while it can be hard to tell the difference between one of the mavericks prepared to criticise the current sacred cow of science and a curmudgeonly old stick-in-the-mud (and I’m not saying there isn’t a significant overlap between the groups) it’s nevertheless something that only a few scientists have the guts or the pull to do in a conspicuous manner.

As to your question of to what degree mavericks have shaped the development of astrophysics in particular, my answer would have to be: no more than any other field, and probably less than most of them. Astrophysics is a discipline based on extreme cunning and a lot of what-ifs, and even then it’s not a hundred percent clear that what you’re looking at is even real. As a field it’s very fuzzy around the edges, and not the sort of thing much given over to decisive swings in the way we look at the universe because there’s always room to argue around the shortcomings of a particular theory. It’s had its fair share of personalities and visionaries, true, but it’s been the case for the last century or so that astrophysics is a consensus science. One scientist can argue his or her pet theory, but they’d have to shout pretty loudly to be heard over all the other scientists doing the same thing. Astrophysics is a very democratic branch of science, in the purest sense of the word, and it’s rather difficult for a single individual to alter the status quo one way or the other unless they’re armed with some very conclusive experimental results.

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Darren asks

I recently played Killzone 2, and the only thing that particularly stood out to me was the gun that shoots lightning. Besides being the only unusual weapon in the KZ2 arsenal, it was extremely well-realized, and actually looked like it would be functional. Would a gun that shoots lightning actually be possible? And would lightning in general make an effective weapon?

Possible? Maybe. Effective? Well, you could probably get it to maim/kill people. Practical? Absolutely not.

There’s nothing particularly exotic about lightning. Air within a cloud circulates through electric fields, causing the water within it to pick up electric charge and thus causing electric charge to build up within the cloud. The cloud is separated from the ground by a body of air with a given dielectric strength (read: resistance to having electrical shit travel through it). Once the electrical charge of the cloud is great enough to overcome the dielectric strength of the air beneath it an interesting thing happens: the insulating properties of the air not only fail, they break down entirely, resulting in the formation of an electrically conductive path of ionised air between the ground and the cloud called a leader. Through this leader there can either be an electrical discharge from the ground (which is also highly charged at this point) to the cloud, or the cloud to the ground – either way you get lightning strokes.

This is a really simplified version since the exact mechanisms behind lightning generation in clouds aren’t really understood that well, but in general you need two things to make lightning: a relatively large quantity of charge and a path of least resistance for it to travel through to whatever you want to hit with that charge. The basic mechanism can be reproduced by using a van de Graff accelerator to build up a large static charge and then allowing it to discharge through something moved close to the sphere – a negatively charged rod, your finger etc. etc. It’s the same principle, except the amount of charge you’d need to kill somebody is fairly large, and having to trick somebody into moving close enough to your charge source for it to discharge naturally wouldn’t make it a very good weapon.

So really what’s needed here is a way of creating a path of least resistance between you and your target, and at this point you say something along the lines of “Well, lightning looks pretty but if I wasn’t too bothered with having the actual lightning effect why the hell wouldn’t I just use a pair of wires?” And lo, you have invented the taser. Sure, you could try and gin up some way of creating an ionised stream of air like a lightning cloud does, but the problem here is that you can’t control where that stream goes – the lightning bolt could hit the target, it could hit somebody standing next to the target, it could decide to try and earth itself through your shoes, the list is endless. If your objective is to pass a current through somebody to hurt or kill them then the taser setup is infinitely more practical; if your objective is simply to hurt or kill somebody I recommend using a regular bullet-firing gun, since this would be much more effective even if you could tell the lightning where to go. Lightning is an unpredictable natural phenomenon that can only be induced, not controlled, and this makes it a very poor weapon.

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Maxx asks

Mars One – this seems rather ambitious for the timeframe they are proposing. Do you think they will get there? Is our technology at the state that this is actually possible?

Oh god, where to even start with this one.

Okay, this is dumb for a vast, vast number of reasons, but they won’t necessarily be the ones you think. First, yes, technically the technology exists – or will exist – for the private sector to get payloads to Mars by 2023; the upcoming Falcon heavy lifter from SpaceX is designed to do just that, and there’s even a collaboration with NASA on the drawing board to send it and a modified Dragon capsule to Mars around 2018-ish for unmanned sample return purposes¹. We have also carried out a significant quantity of research into isolated living environments and closed-circuit life support systems both on the ground and in orbit, to the point that while we have never sent anyone to live off-world in the long-term we could probably do it if we ever set our minds to it. However, when I use the term “we” here I’m referring to nation states and multi-national spaceflight agencies, not a six person internet startup company in the Netherlands, and this is because just sending an unmanned probe to and operating it on Mars is ludicrously expensive at $2.5 billion dollars for the Mars Science Laboratory mission (you know it as the Curiosity rover). The amount of material required for a permanent inhabited colony would be many, many times that cost, which puts a Mars colony far beyond the ability of private enterprise right now.

That’s the simple “Whuh?” smackdown I’d give to any private company that was planning to send people to Mars, no matter how well-thought out their concept was. Mars One is a special brand of crazy, though. Mars One, in no particular order:

• Wants to have the entire colony built by robots before the astronauts arrive.²
• Wants to power the colony on solar panels instead of using a nuclear reactor.³
• Wants to fund basically the entire thing through selling reality TV rights.
• Wants to make the trip one-way for the astronauts.

These are all really stupid things to be doing, but I want to talk about this last point because it shows a staggering, staggering ignorance of history. The reasoning behind it is this:

However, there are individuals for whom traveling to Mars has been a dream for their entire life. They relish the challenge. Not unlike the ancient Chinese, Micronesians, and untold Africans, the Vikings and famed explorers of Old World Europe who left everything behind to spend the majority of their lives at sea—for people like these, it is about exploring a new world and the opportunity to conduct the most revolutionary research ever conceived, to build a new home for humans on another planet.

Mars One will offer everyone who dreams the way the ancient explorers dreamed the opportunity to apply for a position in a Mars One Mission. Are you one for whom this is a dream?

Right. Right. I wonder if these people are in touch with the real world, like, at all? I don’t know about the Chinese, Micronesians or Africans but the Vikings and the “famed explorers” of Old World Europe didn’t go exploring just for shits and giggles. Like all colonisation efforts the Viking expeditions to Iceland and Greenland were driven through a desire for new farmland and exploitable natural resources. The first expeditions to the New World were driven by a desire to find a new route to the fabulously wealthy Spice Islands in the East Indies.  The first colonies in the New World weren’t filled with romantic adventurers, they were populated by those seeking certain opportunities that weren’t available to them in the Old World. ⁴ People didn’t endure a miserable, months-long sea voyage for the love of the thing, they did it because they thought they could build a better life for themselves that they couldn’t by staying at home – preferably a life that involved making lots of money. The Americas of a few centuries ago were a land of stupefying bounty, but the first colonies either failed or came within inches of extinction via starvation before the natives helpfully delivered food, pointed out which crops were likely to be edible, and – more importantly – introduced the colonists to cash crops like tobacco.

The thing here is that in order to entice people to endure significant hardship in the name of founding a new settlement, that new settlement needs to offer something the old one did not. Often this was because conditions in the old settlement had become so intolerable that packing up and moving across an ocean to an unknown land did suddenly start to seem quite attractive. However, unless you are living in unimaginable poverty in a Third World nation somewhere your life on Earth is infinitely more comfortable than a life in the first Martian colony would be (remember, you can’t even talk to anyone back home in real-time from Mars, since it takes seven minutes for communications signals to travel each way). I mean, on the reduced timescale these jokers are proposing a trip to Mars would likely be a death sentence anyway, but making it one-way means that you’re asking people to give up lives of comfort and plenty on Earth to spend the rest of their years in a miserable and inhospitable limbo. And the only way they’d get years would be if they remembered to pack enough anti-radiation shielding, since Mars has no magnetosphere and the atmosphere won’t stop much solar radiation before it gets down to the surface. The chances of death – especially on this plan – are overwhelmingly likely. Remember that the one-way thing exists to obviate the need for the planners to include a return vehicle in their mission budget, so if something goes wrong the colonists will be well and truly screwed.

I don’t doubt they can find somebody to sign up for this, but whoever they get is unlikely to be the best and the brightest and even then they’ll have plenty of time to get cold feet during the decade of training they’ve mandated.  You can’t get people to make a one-way trip to Mars by appealing to the romantic spirit of adventure and you can’t do it by appealing to capitalistic instincts by paying them lots of money. In todays’ world you’d have to do it by appealing to nationalistic ones instead and you’d have to back it up with an actual rational mission plan and a hell of a lot of money, but that’s not an option open to Mars One because they’re private enterprise. And let’s remember, by the way, that the primary purpose of private enterprise is to make money. Not coincidentally I might have written all of these words based on the assumption that Mars One is a real idea that somebody has had, but to me it looks like the umpteenth attempt to part fools from their money via the internet. The only thing that surprises me is that there isn’t a Kickstarter for it.

Yet.

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I don’t know, you go two months without a single question and then three come along at once. Anyway, Glory Be To Smurf, For He Is Awesome asks

So I was watching a program that said we’d dammed so many rivers that it had altered the spin of the earth by a fraction of a second. That got me thinking, firstly on how the hell that made a difference and secondly if there was anything humanity could do to really alter the spin of the earth?

I’d be interested in knowing if this program went into detail at all rather than just blurting that out as a known fact, but: yes, damming rivers will alter the speed of rotation of the Earth. This is down to a curious quantity known as moment of inertia, which I think has been mentioned on here once or twice but which I’ve never gone into in detail.

Wikipedia’s summary of moment of inertia is that it is “a property of a distribution of mass in space that measures its resistance to rotational acceleration about an axis”. What that means, shorn of science-speak, is that while the acceleration you derive from applying a given amount of force to an object will be dependent on that object’s mass (as from F = ma), if you’re trying to rotate it then the shape of the object will also become a determining factor. Some shapes are easier to set spinning than others because they have lower moments of inertia. Amongst other things, this is why acrobats or divers tuck their legs in close to their body when they perform a somersault; that compact shape is easier to spin – and so will spin faster – than if their limbs were splayed out every which way.

As a demonstration we’ll use the very simple example of the moment of inertia of a pendulum, largely because it’s the only one where I can still follow the maths. If you have a simple weight on the end of a massless line, then the moment of inertia of the pendulum will be

where m is the mass of the weight and r is the distance separating that mass from the pendulum pivot point. That dependence on r is key; it is not just mass that affects the moment of inertia of the pendulum, but also where that mass is in relation to the pivot point.

Now, if you’re applying a turning force to an object, that turning force will be known as torque. Torque for the pendulum is calculated by

where α is the pendulum’s angular acceleration. Note here that this equation is equivalent to F = ma for a rotating body, with the moment of inertia I standing in for the mass m. Finally, the angular momentum of the pendulum can be found by

where ω is the angular velocity of the pendulum. Once again, this is equivalent to the equation p = mv for a non-rotating body, with moment of inertia once again standing in for mass.

This moment of inertia/mass equivalence makes it somewhat easier to understand why the MoI makes rotating bodies harder/easier to spin faster/slower, but it’s not a perfect comparison. For one thing a closed system tends not to be able to alter its mass on the fly, whereas it can change its moment of inertia just by changing its shape. And this is where we come back to the Earth and all those dammed rivers; the Earth is a closed system, and by damming the rivers we have changed the distribution of the Earth’s mass to a very small – yet measurable – degree. There are now billions of tons of water flowing at a level a couple of hundred metres above where they would be if the river had remained undammed. This means the Earth’s moment of inertia has increased. But since the Earth is a closed system¹ , it’s still rotating with the same angular momentum that it did before we dammed the rivers. Looking back at that angular momentum equation above: L stays the same. I has gone up. This means that the angular velocity ω – the speed of rotation — must decrease, and that the Earth is spinning more slowly as a result of the dams.

How large a shift in rotation are we talking about? Not that large; your typical dam would produce a change of just a few hundredths of a microsecond in the time it takes for the Earth to complete a full rotation. And remember, damming a river is just about the easiest way to shift that much mass around the Earth’s surface that humans can manage since water flows rather than having to be dug up and transported. Even something ridiculous like draining the Mediterraneanwouldn’t do much to the rotation since all that water would get spread out over the rest of the seas and oceans, resulting in only a small shift in the overall distribution of mass around the Earth’s surface. So no, barring magic future science there’s nothing humans can do to seriously shift the Earth’s rotation. There’s just too much mass involved.

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Alex asks

Hi Hentzau, I know that the conservation of energy is an immutable thing, but what happens with capillary action in liquids? Where does the energy for that come from, and how does it work?

For those not in the know, capillary action has little if nothing to do with the flow of blood around the body. “Capillary” is a term used to refer to any small tube, and the capillary action Alex is talking about is shown in the headline image. When you stick one of these small tubes into a body of liquid such as water the liquid will rise up a little way inside the tube before stopping, apparently in defiance of mundane forces such as gravity. The raised surface level of the water inside the capillary means the water molecules have effectively gained gravitational potential energy, and the energy required to do this has to come from somewhere.

That somewhere is the water molecules themselves. A liquid is a somewhat more ordered form of matter than a gas, and one of the ways this increased degree of order manifests itself is through something called cohesion. Each water molecule inside a glass of water has a preferred alignment with the surrounding water molecules thanks to interactions between the electrons in their outer shells chemically bonding to one another¹ If it is moved out of this alignment it will always try to return to it if it can, and this makes water molecules strongly cohesive. The cohesion of water can be observed simply by looking at raindrops on a leaf – the water in the drops will not be spread out over the surface of the leaf but will instead be clustered together into several large clumps, like this:

Those drops are being held together by the natural cohesive forces between the water molecules inside them. Every molecule of water has a balanced set of cohesive forces acting on it from all sides from surrounding molecules – except the ones at the surface. The surface molecules are pushed up by the molecules underneath them but they have no counterbalancing force from above, resulting in the phenomena known as surface tension: the surface of water will actually deform slightly under very light loads – like paperclips or insects – rather than breaking apart and sinking the object on top of it, and this is thanks to the slight upwards force provided by cohesion.

You should be starting to see how cohesion can lead to capillary action, but there’s a missing piece of the puzzle: adhesion. Where cohesion is the attraction between similar molecules, adhesion is an attraction between molecules that are dissimilar. A high level of adhesion between the fluid and the walls of the capillary will overcome the surface tension of the fluid and cause it to form a concave meniscus (read: top of the fluid) with the fluid molecules touching the sides of the capillary being dragged up higher than the fluid molecules in the centre by adhesion. Cohesion forces attempt to compensate and push the fluid up to match the fluid levels at the sides, and then the fluid levels at the sides move up again thanks to adhesion, and this process repeats and the fluid continues to rise until the capillary action is finally counterbalanced by gravity.

(If the level of adhesion between fluid and capillary is too low to overcome surface tension – say between mercury and glass – then the level of the fluid in the capillary will actually be lower than the fluid outside it. This is because the mercury forms a convex meniscus with the fluid at the side of the capillary at a lower level than the fluid in the centre, which means the molecules inside the fluid are already in their ideal configuration and there’s no compensating cohesive forces dragging the fluid upwards in the face of gravity)

Finally there’s the question of why thinner capillary diameters draw fluid to a higher level than thick ones. This is because the amount of capillary action you get out of a given capillary is going to be proportional to the contact length (the top edge of the liquid) between the fluid and the capillary that’s drawing up the fluid through adhesion, which is in turn proportional to the diameter of the capillary. On the other hand the weight of the fluid in the capillary is proportional to the square of the diameter, so while a bigger capillary diameter means more contact length it also means a larger quantity of fluid to be raised against gravity, and the latter increases exponentially compared to the former as you increase the sizeof the capillary. Ergo, smaller capillary diameters go higher. QED.

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Note: last post for a little while thanks to real life concerns making a nuisance of themselves. Will post again this time next week. Probably.

Sultana Josh asks

Jetpacs. How would they work?

This should be phrased “Jetpacks. How do they work?” Because jetpacks aren’t sci-fi. They’re a real, working thing. You know that bit in Bond flick Thunderball where Sean Connery straps on a jetpack to escape some angry pursuers? That sequence is real. The flight is real. What the stuntman is using there is something called the Bell Rocket Belt developed for the US Army in the early 1960s, and it works using the fundamental principle of any rocket or jet engine: shoot reaction mass out the back to provide thrust. The Bell version used a mix of nitrogen and hydrogen peroxide which decomposed to superheated steam¹ and oxygen when exposed to a catalyst which was then blasted out of a pair of curved nozzles. On the front of the belt was a pair of joysticks which the wearer could use to change the facing of the nozzles, the direction of the thrust, and the direction of his travel.

So we’ve had functioning rocket packs since the 1960s. Why haven’t they caught on in a big way? The Wikipedia article mentions two factors, one of which was obvious to me and the other which you don’t often think about but is actually kind of important: not only do jetpacks only have room for extremely limited quantities of fuel (the Bell could fly for 20 seconds, meaning that short hop in Thunderball was actually all it was capable of) but they operate at altitudes too low for parachutes to function. This means that if something goes wrong the person wearing it is super-dead. While they are spectacular they are also impractical, expensive and dangerous compared to other forms of transport; the US Army concluded that helicopters would be far more useful and discontinued the Bell contract in the mid 60s, and that’s pretty much been the end of serious jetpack research. Enthusiasts and speciality equipment manufacturers still make and sell their own models but they are not significantly better than the fifty year-old Bell design, and they are unlikely to ever become so.

Jetpacks – or more accurately, rocket packs – in space are more effective. Since they are operating in a more or less Newtonian environment and do not have to constantly act against the Earth’s gravity the fuel expenditure involved is much less gratuitous. You may be familiar with this picture of astronaut Bruce McCandless in freefall around the Earth. Strapped to his back is something called the Manned Manuevering Unit, which actually functions more like the reaction control systems found on most spacecraft than it does a classical jetpack: it used small squirts of reaction mass to set the astronaut in motion and gave him a great deal of fine control over where he was going. The MMU was used on three missions in 1984 reasonably successful, but after the Challenger disaster in 1986 it was viewed as too much of an unnecessary risk to the astronaut when the tasks it was used to carry out could be accomplished more safely by robotic arms and tethered spacewalks. So even in space they’re viewed as too impractical compared to more boring forms of doing the job, which is pretty much the concept of jetpacks in a nutshell.

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Lord Smurf asks

I can just about get my head around a planet orbiting two suns, but this: http://www.bbc.co.uk/news/science-environment-19950923 confuses me. I notice that it says two of the suns are ‘circling’ the planet, rather than ‘orbiting’. Is there a difference? I always think of suns as the giants of solar system so I don’t understand how they can orbit a planet, rather than the other way round. How does this system actually work because all the articles are telling me how amazing this is but none of them actually say how the damn thing works.

That news article is rather spectacularly contentless. Fortunately – and unsually for the BBC – they included a link to the paper in the article (do this more often, journalists) which does explain what is going on pretty well. It’s written in the usual scientific hieroglyphics, but then that’s what you have me around for, isn’t it?

The title of the paper is a big clue as to what is going on: it’s called “Planet Hunters: A Transiting Circumbinary Planet in a Quadruple Star System”. There’s two stars orbiting a common barycentre in a classic binary setup, and this is what the planet they’ve found is orbiting, as seen below:

What you’re looking at here are the various dips in the overall intensity of the light observed from this binary system as the objects within it pass in front of each other; when they do this they block some of the light from reaching the Earth just like an eclipse. The primary and secondary eclipses labelled on the graph are caused by each of the binary star pair eclipsing the other. I’m going to take a wild guess and say the primary is bigger than the secondary, which is why it blocks more light and results in a bigger dip in the light graph when it eclipses. However, there’s also a couple of tiny, tiny dips not associated with either member of the binary system, and this is caused by the planet they’ve found.

Planets orbiting binary systems aren’t hugely unusual, and they can orbit one or both stars in the binary without any apparent ill-effects. The surprising thing about this particular discovery is what happened when the astronomers zoomed out a little bit.

The second point of light in the bottom left hand corner – catchily termed the 0.7” contaminator – is a second binary star system orbiting the first at a distance of greater than 1000 AU, effectively making it a quadruple star system. This second pair of stars is rather small and dim in comparison to the first, orbiting at a distance of about 40 AU from each other, and since both of them are so far away there’s nothing that says a planet can’t exist perfectly happily in an orbit close in to the primary binary system (the paper mentions that something called “eccentricity pumping” happens in models where the second binary system is closer than that, which I imagine refers to repeated gravitational perturbations from the second binary gradually stretching out the orbit of a planet into an increasingly elliptical shape until it finally breaks free and is ejected from the star system entirely).

And that’s it, really. That BBC news article is awfully written and mixes up what is orbiting what, when it’s actually a fairly simple thing to understand: the primary binary system has most of the gravitational pull in this system and it’s this the planet orbits. The secondary binary is weakly bound to the primary in a circular orbit and is both smaller and much further away from the planet than the primary, which is what allows the planet to survive.

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Rear Admiraless Josh asks

In The Empire Strikes Back, there’s a bit where the Falcon goes into an asteroid field pursued by a bunch of TIE fighters, and they have to avoid a load of rocks flying around very fast in close proximity. It’s what a lot of people think of asteroid fields as being like, but logically that’s can’t be right, as the rocks would just bash each other into sand over the course of a couple of centuries. So what is the inside of an asteroid field really like? What is the largest thing you can swing around while reasonably expecting not to hit anything?

Ooooh, “rocks just bash each other into sand over the course of a couple of centuries” is so close, and yet so far.

I actually have mentioned collisional evolution before on here but it was rather in passing so you can be forgiven for missing it; in short, the long-term evolution of any belt-type collection of objects is going to be primarily driven by two things:

1)     The average velocity (and hence kinetic energy) of an impacting body in the belt.

2)     The critical energy density required to blow a body in the belt to smithereens without it eventually reforming under its own gravity.

So basically you have to be going fast enough to cause some real damage, and the thing you’re hitting has to be weak enough that that damage will be lasting. As ever, the hardest part about blowing massive objects up in space is that in addition to actually physically destroying the target you have to give most of the resulting fragments enough energy so that they’re accelerated up above the object’s escape velocity. I mostly dealt with the larger type of object in my Ph.D research – dwarf planets and the like – so gravity was Kind Of A Big Deal for them, but… *rummages through paper archive*

This is the result of some computer modelling done in a paper by Durda et al. (1999, Icarus, 135, 431-440.) which attempts to figure out how the strength of asteroids increases with their size. There’s actually a whole bunch of models there but they all follow the same basic behaviour of an initial decrease in the material strength of an asteroid as its size increases (this is because it is easier for cracks to propagate through big bodies than it is through small ones) and then a sudden upswing at around the 1km diameter mark. This is the point at which the object is large enough that its gravitational strength becomes the primary factor working against its destruction, and material strength becomes more or less irrelevant. In other words it doesn’t matter if you’re hitting an object made out of rock or taffeta; if it’s 10km on a side it’s the gravity of the object you’re going to have to overcome, not its material strength.

So how big are the asteroids in the asteroid belt? Obviously their sizes vary, and the overall size distribution looks something like this.

(Taken from this great American novel via a second-hand source because obviously I don’t have sixty-five quid what are you crazy.)

This is the expected power law distribution of any large collection of objects driven by collisional evolution, with the only aberrations being those two small bumps. The interesting thing about the asteroid belt, though, is that this size distribution has remained static over time. That is, if you were to go back in time a couple of million years (this being the timescale over which collisional evolution operates) and take a similar survey of the asteroid belt, the size distribution graph would look much the same, implying that whatever is going on in the asteroid belt has produced a population of bodies which is stable over solar-system timescales.

It was not always thus, of course. The asteroid belt originally had far more mass in it (about one Earth) than it does today (about 0.01 Earth masses), so the population we see in the asteroid belt right now are the stable one percent survivors of whatever happened to eject the other ninety-nine percent. “Whatever happened” is overwhelmingly likely to be the chaotic gravitational interactions, peturbations and resonances of the solar system’s early years. For example, there’s lots of very large, very conspicuous gaps in the asteroid belt at certain orbital radii which are down to resonances with Jupiter amplifying the planet’s gravity and shooting anything unfortunate enough to be found in those gaps out of the solar system. So it’s not just asteroids colliding with each other that can “destroy” them, it’s outside influences as well.

Anyway, that was something of a tangent. The thing to take away from this is that while collisional evolution was a big factor in the initial makeup of the belt, the current population is — more or less — stable and unchanging. With that in mind, what would flying through it in a spacecraft be like? Immensely boring, I suspect; the average distance separating asteroids in the belt is about one million kilometres, although that is a number based on the volume of the belt and the number of asteroids rather than any hard and fast measurements of actual distance separations. Certainly it’s sparsely populated enough that every single interplanetary probe we have sent to explore the outer solar system – Jupiter, Saturn, Uranus, Neptune and Pluto – has made it through without even the faintest glimmering of an incident. A million kilometre gap is quite a large target to aim for, after all, especially when it has more million kilometre gaps on either side. You’d be lucky to see an asteroid at all, let alone the swarms of them seen in Empire Strikes Back.

(Speaking of, I’m fairly confident saying that an asteroid field of the type seen in Empire could never actually happen. The only way you could get so much debris so densely packed is by destroying a planet – which isn’t completely out of the question given the Empire’s Death Star – but if the fragments were produced by that kind of process then they’d all be flying away from a central point at some ridiculous velocity, not just sitting there chilling and occasionally bumping up against their buddies.)

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