If there are multiple points of view on a particular issue - especially in politics - a good rule of thumb is: they are all wrong. Nowhere is this more obvious than in the application of politics to the science of climate change.

One thing that sets scientific theories apart from other kinds of knowledge is the capacity of scientific theories to make predictions about the physical world. A prediction is a logical consequence that one can derive from a scientific theory. For example, one can predict the times when and places where solar eclipses will occur on the Earth. One can predict the outcome of administering penicillin to a person suffering bacterial meningitis. While predictions are never certain (though nothing is because our knowledge is never complete) they are nonetheless possible. And they follow. That is to say there are logical reasons why they should be the case (or not be the case, as the case may be).

On the other hand, if you don’t have a scientific theory to explain some phenomena you cannot predict the outcome of your experiment. The only way of describing future states of affairs then is to guess wildly. In that case what you are doing is not predicting - in any scientific sense - you are prophesying. This distinction between scientific predictions and irrational prophesy was one made by Karl Popper and it leads to an important difference in the way people who lack knowledge view the world. In politics, attempts to describe future states of affairs are often nothing but prophesies devoid of any genuine predictions. In politics the decisions people make can always change the outcomes some person or group expects. In particular, discoveries in science can affect the decisions people make and the policies they enact. And the content of scientific theories are unpredictable before we discover them.

We cannot know what the future content of our better theories will be. Knowledge improves. In science this progress comes about by the gradual, incremental improvement of existing theories. Older theories are eventually shown false by criticism through experiment and replaced by better, deeper - closer to truth - theories. But our best theories can never predict the content of their successors.

Where this becomes critically important is in the realm of social policy. People, unlike electrons obeying the laws of physics, make choices. And those choices affect outcomes. This might seem so obvious as to not be worth stating - but the problem is many people - seemingly many scientists and many with an interest in science - forget this simple truth. The fact people make choices which affect outcomes makes them unpredictable in the strict scientific sense. Psychology, it is true, makes claims about the predictability of people at least to some extent. But that is merely a misconception. Physical systems - including people - are explained by good scientific theories or they are not. If they are - then those systems are predictable in the scientific sense.  But we do not have a scientific theory that can predict the behavior of people. Instead, the best we have is prophesy: attempts to foretell the future in the absence of explanatory theories.

This is not only a problem for psychology, but also sociology and politics. In those fields there is a tendency  to make more-or-less confident statements about the future by appealing to scientific theories while ignoring the choices that people might make which would affect the outcome of those very predictions. Let us make this more concrete: it is common today to debate the effects of global warming on things like sea level rise and the various economic impacts while ignoring what people in the future might do and what knowledge they might discover which would affect global warming.

So, for example - we hear that economic sanctions (like an increase in the cost of carbon dioxide producing industries) are needed in order to help curb the use of fossil fuels. This, it is said, could help to reduce the amount of carbon dioxide in the atmosphere. In Australia the target is somewhere between a reduction of 5% if you are on the right of politics (Labor and the Coalition) and 40% for the left side of politics (the Australian Greens). If you are on the far green left you might even hope that there is a 100% reduction in carbon dioxide emissions by anthropogenic sources and you might be hoping for a quick cessation of all fossil fuel combustion.

But what we know is that the the Human Induced Climate Change Greenhouse Effect seems to be approaching a tipping point and may already have passed a number of points of no return.  A 5% reduction is not going to stop, let alone reverse global warming. It will barely slow it. A 40% reduction will also have little impact - even if this was global. Even if we cut emissions in half by 2050 the planet will still warm by 2 degrees Celsius. This is more than enough to cause massive melting of the polar ice caps.  And it is possible a 100% reduction will not occur fast enough (even if it was to occur tomorrow) because the amount of carbon dioxide in the atmosphere is already too much to be removed by natural processes (namely rain) to stop global warming being accelerated by feedback mechanisms like melting permafrost and methane venting. So it looks, from all angles as though if nothing drastic is done, significant amounts of the ices in Greenland and Antarctica will melt leading to sea level rises. If nothing drastic is done. What we need is not a way to slow global warming or even a way to stop global warming. These are not solutions to the problem: the problem being the ice is already melting, the sea levels are rising and the climate is changing. If we agree all of that is a problem, we have only two options as Physicist David Deutsch points out: to devise ways of surviving at the higher temperature or ways of reversing climate change (that is to say - ways of actively cooling the globe).

Economic "solutions" like taxes do not even pretend to do anything like this. They are only proposed to slow the inevitable - not solve the problem. Nor, indeed, do alternative energy targets. While alternative energy sources like solar and wind should be pursued and more money put into research in this and other areas generally (for reasons I will come to) none of this will cool the globe, if that is what your aim is: to solve the problem of climate change.

The left and right have always been divided on taxation - at least in principle if not in practice. But because the problem is that the world is already too warm and sea levels rises have already begun - merely reducing the amount of carbon dioxide by the very cumbersome and slow technique of increasing the price of fossil fuels which (some people hope) somehow persuades people to use less energy will not solve the problem. As far as climate change is concerned all that taxation is purported to achieve is to merely delay the warming, not reverse it (which is what is needed). If we want global warming to stop, and reverse, we need to cool the globe. Actively reduce the amount of carbon dioxide in the atmosphere - not merely slow its rate of increase. Increasing taxes cannot do that. Merely reducing fossil fuel combustion - or even eliminating it altogether - cannot seem to be able to do that now either. It's already too late. Take note of what Eric Rignot and other NASA climate scientists are saying about the fact glacial melting in the Antarctic is now unstoppable. Of course that is pessimistic - glacial melting is just another problem and problems are soluble. It's just that it is unstoppable if the only thing you do is stop using fossil fuels. 

So stopping fossil fuel combustion cannot reverse global warming. We seem to have reached a tipping point and natural global warming is likely to continue anyway. Even if those climate scientists are wrong, they may not be far from wrong. If the tipping point has not already past, as they claim, it may be just around the corner. Given the growth of civilization, and the amount of carbon dioxide being put into the atmosphere and that which is and will continue to be put into the atmosphere, it is likely that global warming was already too late to stop decades ago. The seas were already warming, the ice already melting. The sea levels were always going to rise - no matter how quickly we stopped burning fossil fuels.

This sounds all very pessimistic. But it is not. Problems are not pessimistic - but proposed solutions can be. The idea that ineffective solutions we know cannot work should be tried anyway - at great expense and at great cost to individuals, industries, economies and societies is pessimistic. The idea we should search for better solutions and implement ones that just might work is optimistic. And the principle of optimism: that whatever the problem is we can* solve it - should be motivating us. [The complete version is, of course: whatever the problem is we can solve it - so long as we have the knowledge of how to do so...and this does not require us to break any laws of physics].

And so this is why the left and right of politics are both completely wrong on this issue as they are on so many others. The left is wrong because they think economic sanctions can work and fossil fuels are evil. And the right is wrong because they will not take this issue seriously enough - unwilling to acknowledge  that the danger is to large parts of civilization itself. If the sea level rises - millions will be displaced and weather patterns can become dangerously unstable as the atmosphere is loaded up with additional energy. Climate change will cause death and destruction on a scale that is almost unimaginable - if nothing effective is done. But that’s also the problem with the left. They are not suggesting anything seriously effective.

It’s possible (indeed common) for all sides of an important debate in politics to be completely wrong. The strange thing is - even if global warming wasn't man made - it would still be a serious problem. But, again - the left and the right typically do not see it that way. The right seems to want to argue "well because it's natural there is nothing we can do to stop it" and the left would seem to want to say "Well that's nature and we shouldn't interfere with nature".  Again - both misconceptions argue for inaction and are about problem denial, not problem solving.

So what should be done? We should prepare for the growing problem as we would for any natural or man-made disaster. We should look for solutions. We should admit that the problem is already here and we must either devise ways of living at a higher temperature, or think of ways of cooling the globe.

So we need to invest - heavily - in scientific solutions. This means pure science - across the board. Not just in fields directly related to global warming (like climate science) but more broadly. Solutions come from places we typically cannot even guess at. The solution of how to get your email and Facebook wirelessly from the server to your computer did not come from technology companies trying to build ever better modems. No. WiFi came (in no small part) from astronomy - in particular from pure research into black holes.  The solution of how to scan the body for tumors at super high resolution before they became dangerous did not come from investing directly in cancer research. No. MRI technology came from pure research in quantum physics and rested in large part upon the curiosity of a “lazy” Austrian physicist interested in how silver atoms behaved in a magnetic field.

But pure research requires money. And the more urgent the problem, the more brains we need working on it directly as well as on the periphery. We need science. And that costs. Equipment costs. Salaries cost. Education costs. We need to make lots of money - and fast - to pay for the research that will solve our problems. We need to believe that there are solutions or we won’t try. Or we will try non-scientific things that simply make us feel good without actually achieving anything. We might, for example, complain that profits are evil and wealth is evil and taxation is great and so decide that slowing or reducing private investment in solutions that just might solve the problems taxation never can. This is not to say public funding has no place: for now it must as that system of science funding is so entrenched and better to spend taxes on science than waste them elsewhere. But change must come incrementally. With science it would be good to increase both at once. Not one at the expense of the other. When it comes to public funding of pure science, the words of astrophysicist Neil deGrasse Tyson ring true here: "...it's not that you don't have enough money, it's that the distribution of money that you're spending is warped in some way that you are removing the only thing that gives people something to dream about tomorrow." (Note from 2018: Tyson was categorically wrong in a related message when he argued that people were deluded thinking that private companies like Elon Musk's "SpaceX" could lead space exploration as recorded here: https://www.theverge.com/2015/11/24/9792854/neil-degrasse-tyson-interview-delusions-of-space-enthusiasts But for this argument to be had in full it is important to note the significant amount of tax money that goes to SpaceX: http://www.latimes.com/business/la-fi-hy-musk-subsidies-20150531-story.html ) So it's not like we need more taxation we just need to think of better ways to spend the money that governments already have. And as nations become more wealthy and more educated, we can rely less on the few (those in power in governments) and more on the many (the individuals) to decide where to invest. That way politicians do not need to be in control of as much money (that is to say: they do not need to collect as much tax) and individuals can become better off, and better at helping to solve both their own problems and the problems of their society more broadly.

There will always be problems. That is the circumstance we find ourselves in. But for any problem there are solutions out there not yet found. So how do we find them?

Only with the most curious minds working on as many problems as possible all at once. For any solution in science, there is a scientist who was never interested in exactly that particular problem who made a crucial discovery without which the problem would never have been solved. This is to say pure science is always the key.

In the case of global warming this means the eventual solution - the means by which we cool the globe - will depend in part at least on what people not working on that problem will discover. Knowledge is a web of interconnected and interdependent ideas. A discovery in one discipline is never completely isolated from another. But this does not mean we should not also fund applied science - the more narrow application of what we already know to problems we have already discovered (in the case of global warming this would mean applying the knowledge we already have to formulate better engineering solutions we have already imagined). Of course we should put as much money into that as we can too. Not at any cost of course - but the minimum cost that will be effective and will solve the problem at a cost less than it would cost us if the problem went unsolved. We cannot, after all, ignore all the other pressing problems. We must always do more than one thing at a time. One problem cannot be at the expense of all others. The most important reason for this is that the biggest dangers come from problems we have not even encountered yet and so have no possible knowledge about. Take any huge problem facing civilisation today: global warming, genetically engineered bioweapons, the possibility of war or terrorism utilizing nuclear weapons, how to avoid an asteroid impact. None of these "problems" were dreamed of just a century ago. Again - this is why we need pure science. To uncover those problems before we fail to discover the means of averting them. The problems that lurk in our complete ignorance are the ones we need to be most urgently searching for.

But to return to the pressing problem at hand; global warming. Applied science here could mean working on how to put mirrors in space to reflect some of the Sun (an engineering effort that might cost trillions - or maybe substantially less if some industrialist or scientist stumbles upon a much cheaper technology while trying to build a better computer/car/aircraft/power station). It might mean looking at genetic engineering solutions on how to encourage algae in the sea to consume more carbon dioxide. It might mean looking at geological solutions like geosequestration.

But my guess is that it will most likely mean a solution we simply cannot foresee. Because that is how science works. That is what the history of science teaches us: that science is crucial in solving problems and the solutions come from unexpected places. In science this idea comes under the rather twee heading of “serendipity”.

But to fund all this important research we need money. As individuals, corporations and society. We need profits - that is to say additional money over and above that needed to survive. More money across all sectors and this requires growth. And lots of it. We need as much money as we can get to fund these scientists, their laboratories, their technicians and students. We need to encourage kids to enter a lucrative career in the sciences and not always rely just upon their charitable natures.

Increasing taxation on people and industries typically does the opposite. Extra taxation takes money away from the economy - it discourages investment and spending (because it simply leaves less money for investment and spending by companies and shareholders). It reduces productivity because less is being created because less wealth is available to create it. In general, politicians do not have the expertise to decide how best to spend money and they seem more and more unwilling to rely upon those who might have better ideas to advise them. Those who desire higher taxes - which takes money from industry and individuals - strangely have far too much confidence in politicians. It is a strange thing in politics that those on the right and left often claim a distrust of politicians and yet the left is willing to hand them more money to make bad decisions with and the right is willing to hand them more power to make more bad laws with.

Taxation is sometimes seen as a means by which we can punish so-called “evil” industries like coal and oil companies. But this is short sighted. Of course these industries create big problems. But all industries create problems. The size of the problem you create scales with the size of the problem you solve. In the case of the fossil fuel industry the big problem created is air pollution - but the problem solved is that of cheap energy and bringing electricity to those who otherwise would not be able to afford it. The oil and coal industries are solutions even if they are seen by some as nothing more than a source of problems. There are problems with solar too. And wind. And nuclear. It may be the case that with fossil fuels the problems are well known and large but the solutions they bring are sometimes ignored or downplayed. They, and not other energy sources, are the solution to how to bring cheap energy most quickly to people who need electricity most now. Namely - the people without it and who have never had it. The people in Africa and Asia and South America - the developing world. Where - in those places we can light up (literally and figuratively) the lives of children who might be able to plug in a cheap computer to a cheap power source and be provided with cheap internet because the coal is cheap and the power station is cheap. And yes, it’s putting out carbon dioxide. But that kid just might learn enough physics and chemistry and biology to find a solution that has eluded everyone else. They might discover the key to reversing climate change.

We hope some person, now being delivered the internet in a warm home for the first time by cheap energy might discover a truly cheap, extra efficient solar cell (because at the moment they are neither) and then we can move away from fossil fuels (this is modulo taxation. Of course if you tax fossil fuels much more then their cost will artificially be more than that of renewables. But I have already argued why I think that is a mistake).

If it truly were the case that there were cheap, efficient and effective options for the developing world to power their factories, industries, cities and societies in a way which could bring them up to the standard of living that people in places like the USA and Australia expect then those countries would already be using those sources. But they use what their people want and need most. They use the best sources. And by best we mean: the source of energy people can most afford, which are most reliable and which, on a cost-benefit analysis will allow them to have the kind of cities and technologies and societies we demand.

The solutions come faster when we can pay for people to find those solutions - (or when people have sufficient free time to work on solutions - as both Google and Apple grant their employees). And that happens when there is more money in the economy. Where development and growth happens faster.

So next time you hear someone argue that global warming is not a serious problem - you can argue they are being unscientific because the science tells us it is. But if someone says that the sea levels will rise if we don't start taxing the big polluters - they are making a prophesy, not a prediction. They are assuming that no new discovery will be made that makes that extra taxation an unnecessary impost. And those who think we need to slow growth and development through things like ceasing the use of fossil fuels altogether are being pessimistic. So be an optimist: have a stance that problems are always soluble. And people can find those solutions. Perhaps people like you or me. But also perhaps people who don’t yet have access to all the knowledge that needs improving so the big problems of our time can be solved. Optimism entails understanding that the only thing which stands in our way of finding solutions is lack of knowledge. Not lack of resources. Because the universe is infinite - resources are infinite too. But that is the topic of another post.

This post has been largely informed and inspired by the work of physicist and philosopher David Deutsch. In particular his book "The Beginning of Infinity". You can find I have used some of the ideas he articulated here, in this TED talk.

We can consider certain attributes of organisms a “niche” - a way life responds given environmental circumstances. So for example, grazing is a niche that is filled in Africa by zebra, gazelle and countless other large animals, the same niche is filled in Australia by Kangaroos and in North America by Buffalo. So grazing really is something that seems to crop up again and again. Or consider burrowing - that too appears to be something life seems to do again and again: Meercats in Africa, Tasmanian Devils in Australia and Hedgehogs in North America. Independently, in different places, separated widely by geography and time - grazing and burrowing, flight and eyesight evolved again and again. So what about intelligence? Is it a niche? 

50 million years ago, the continents looked roughly as they do now. We know they were separated from one another by the same oceans we are familiar with on the planet today. If you wanted to see how life would evolve in slightly different environments, the 50 millions years ago you effectively had separate continents, effectively isolated from one another on which to conduct your experiments in biology. Let's say you wanted to see if human-like intelligence would be inevitable in the same way, say: flight seems to be (flight evolved in insects, fish, birds and mammals to name just some).

So here's what you do: in Africa, set the experiment running for some 5 million years after the common ancestor of Humans and Gorillas split into those two families and observe that homo sapiens eventually evolve. Left alone, for well over 50 million years (it can be argued that the continents were essentially separate up to 200 million years ago) we find that unlike in Africa where you get human-level intelligence in another otherwise similar continent Australia, the most complex organisms that evolve are koalas and kangaroos, while on Madagascar we have Lemurs, in South America and India we have Monkeys and in the Oceans we have dolphins. A person watching this grand experiment unfold from a god-like perspective might well ask: “how much longer should we wait for human-like intelligence to evolve in Australia and South America? We've waited 200 million years. Those humans in Africa are going to start migrating to all the other continents soon now too.”

To put it more plainly: if human beings did not evolve in Africa, how long would one need to leave all the life on Australia alone, for any of the species currently inhabiting that continent to evolve something akin to human-like intelligence? What is the likelihood that kangaroos would, eventually, evolve the capacity to do what humans can do and build a radio telescope? The question is not meant to be rhetorical. We know that out of the millions of species extant and extinct only one of them ever developed human-like intelligence. Namely - humans. Perhaps there were people besides homo sapiens (like the Neanderthal) that evolved intelligence as well - but they too evolved in Africa from a very closely related - likely intelligent - common ancestor. This surely is an indication that human-like intelligence is anything but a convergent feature of evolution. Given the experiments of the separate continents here on Earth, we find that life seems not to find the characteristic of intelligence as useful an attribute for survival as, say, wings or bipedalism which again and again evolved independently. Features that genuinely are convergent.

Philosopher Peter Slezak from UNSW makes an important point about the number of independent, but necessary, mutations that were selected for in the chain of evolution that led from simple bacteria to human-like intelligence. It seems that if there were many evolutionary paths to human-like intelligence (such as there are with wings) then the odds would be lower – but as far as we can tell, there seems to be a single (or at least a very small number of) evolutionary path(s) that works – namely the path that has led to us. Such a path contains millions, maybe billions of steps. But let us be ridiculously conservative and assume that only 100 such steps are required. Now further, each of those independent, but necessary steps had a certain probability of occurring. Possibly the probability of each step was far far less than 1/100. Let us be conservative once more and assume each step had a ½ chance of occurring (Slezak actually uses the figure of 1/10 – but I am being even more conservative than he). Now if each step has a ½ chance of actually happening and there are 100 such steps, this means that the probability of replicating that chain of events required to reach an organism with our intelligence is going to be (1/2)^100 = 7.9 x 10^-31. This number is difficult to appreciate - far more difficult to appreciate than the number of stars in the universe – it essentially suggests that even if all the Earth like planets in the universe were covered in bacteria, the chance of finding another sample of intelligent life would still be essentially zero. In other words, no matter how astronomical the number of stars and planets in the universe may be, the biological odds of recreating some evolutionary pathway to intelligence is so small as to blow the astronomical number out of the water.

Carl Sagan however believed that the number of independent pathways towards intelligence are likely to be not simply more than just one, but numerous. It would seem however, that unless the number of pathways to intelligence is absolutely staggering then it is unlikely to make much of a dent in the number calculated above which it must be emphasized is ridiculously conservative – and, given the evidence we have been looking at life on Earth and in the fossil record, is the best model we have for the probability of life arising. In other words, as far as we can tell, given the best evidence on hand, intelligence has only one way of evolving: namely that leading to homo sapiens. If the number of pathways were large as Sagan thought and others think: what reasons are there for believing this? No evidence on Earth suggests that there is anything other than a very small number of pathways to intelligence.

Astrobiologist Charley Lineweaver recalls iconoclast Frank Drake of the Drake Equation stating that the reason he, like many people believe that the Search for Extra Terrestrial Intelligence t is a worthwhile venture likely to yield results is that if you look at the fossil record, what you find is evidence of increasing complexity. Importantly, what you find is that the relative size of the brain over time increases.

But Lineweaver has what I would consider a complete knockdown argument against that idea and he has gone to some length to explain why it is that arguing there is a trend towards increasing “complexity” or “intelligence” in the fossil record is flawed. He points out that starting from any sufficiently extreme feature and working back will always seem to indicate a trend towards that feature. A common asserted phenomena here is what is referred to as “increasing encephalisation quotient or EQ”.   EQ is a measurement of the size of the brain cavity compared to body mass. It appears that looking back through the fossil record, EQ increases. So it seems that evolution is selecting for greater and greater relative brain sizes and therefore intelligence. However Lineweaver asks us to consider what would happen if we were not humans but elephants in which case we would be more interested in what he calls the the “nasalation quotient” (NQ) which the fossil record shows there has been a gradual trend of increase in as well. All of the ancestors of modern elephants had shorter trunks, showing a trend in evolution towards towards long trunks. The point is that the trend towards longer noses is not a trend at all. Incrased NQ is an illusion. We can see that easily for our trunks are no longer than those of our ancestors and it seems there is no reason why trunks of modern elephants should continue to get longer, or shorter or remain the same. That is the point of random mutations and natural selection. The “trend” of long noses in elephants is not a general trend that occurs across species and certainly cannot be regarded as a convergent feature of evolution. Similarly human like intelligence cannot be convergent despite the insistence that there seems to be a trend.

So although there might be a lot of planets out there - and habitable ones - the question of whether there is intelligent life out there isn't so much a question of planets and astronomy. It's a question of evolution and here the biological numbers just swamp the astronomical ones.

This post is just an edited part of a much larger article on life elsewhere in the universe you can find here.

Nutrition and exercise struggle to be sciences. This is not to say that rationality and experiment cannot, or are not, applied to these fields - but rather that the conclusions so far reached are difficult to help inform a person interested in the “best” way to eat healthy and exercise efficiently. That is to say: sports science has so far been unable to make testable predictions of the sort that are repeatable or informative for the population generally. But this is not to say sports science is not worth pursuing. It is. There always exists an infinite frontier of ignorance before us in all subjects - so more investigation is always called for. But the problem with proclamations in the sciences of nutrition and exercise is that they are always so full of confidence and so devoid of carefully checked content. These fields are complex. Huge numbers -literally incalculable numbers of variables require computation in order for us to approach anything deserving of the word precision. So we must be skeptical of anyone claiming to be in possession of very specific recommendations for what foods you should or should not eat - how you should or should not exercise. Think stuff like: the top 10 list of most healthy foods. Yes, even when it's from a medical website. That link in particular is a catalog of poorly controlled studies. Modulo allergies, more or less: eat what you like.

So first, nutrition. The chemicals we refer to as “nutrients” number in the dozens.  And we simply do not know what all the nutrients that a human person requires happen to be let alone how much precisely is required. It is true we have some very general  guesses - but that's all they can ever be, because we know that different people will require different amounts and we simply haven't quantified much at all - even with questions apparently as simple as that. For example it happens to be the case that even with the nutrients we are most familiar with - multiple studies disagree about how much we "need". Indeed it seems quite major changes are made periodically when it comes to what amount of (say) sugar we need (if any). What, for example, constitutes a "deficiency" in something at familiar as Vitamin C? This is not a trivial question. Is merely not having scurvy enough to say one has had enough? Apparently not.

Anyone who takes even a passing interest in what is "healthy" versus "unhealthy" food will (or perhaps should) appreciate how misunderstood a nutrient like fat is. Some chemistry is needed to appreciate nutrition - fat, like the other macronutrients is not a single chemical but a word describing an entire class of compounds. Some people might be less interested in the question of what fat actually is to asking: How much do we actually need? What is a "healthy" amount? This question has no answer for different people will have different requirements - one of which is what they want. If the greater part of someone's day is devoted to the sport of sumo wrestling, they might require more because of what they want. And this is what takes nutrition away from being an entirely objective science like chemistry to something with a very personal, subjective, moral element. Desire becomes a factor, nutrition ceases to be a pure science in the same way chemistry is because what is “nutritious” for you is different to what is "nutritious" for me.

Is 100g of fat a day unhealthy? The question itself is meaningless and admits of no rational answer. Is the 100g for me or you or someone else? Is the fat mono-, poly- or un-saturated? If a person is literally starving - and 100g of fat is all that is available - that 100g is more than merely 'healthy' - it could be the difference between life and death. If a person is a marathon runner, they will burn up the equivalent of the energy contained within that fat before the race is over. Is the fat in question saturated or not? Is it eaten with sugar, or not? Does the person already have clogged arteries?  Is the person about to die from fatty acid deficiency?

So whether fat is “good for you” or not is not a question like “is cobalt a metal?” and indeed it never well be that sort of question. Because it is a question not simply of science (what is the case) but also of morality  - it is about what should be the case.

Of course this analysis does not apply only to fat. It applies to all nutrients - and every food more broadly. What amount is healthy? The answer will always depend upon a multitude of factors. The range of possible dosages of any nutrient will be vast and currently there is no known general purpose answer - no mathematical formula into which you can enter your height, weight, caloric intake per day, metabolic rate, etc, etc - that will be enable you to prescribe for yourself what amount of whatever nutrient you will need to achieve your goal, or what amount - for you - might be harmful. Until that day comes - what amount is "healthy" versus "unhealthy" will reduce to a very rough guess. And those scare quotes around the words "healthy" and "unhealthy" are no accident. There is no good definition that sharpens the meaning of those terms into something that can be useful beyond "not sick" and "sick" (and even there we have circularity). So, it seems a food is "healthy" if it does not make you sick. But, poison and bacteria aside, we do not know which foods, or how much of them, are required to make an otherwise healthy person ill. Or if indeed the same foods make the same people sick. Those with apple allergies can rightly say apples are extremely unhealthy.

Is alcohol a nutrient? Some studies at least seem to suggest it's better to drink heavy than not at all (while moderate daily drinking seems to be best). Yet, perversely in the state of New South Wales in Australia alcohol is taxed more highly than other commodities because of the supposed detriments to health and venues that serve alcohol must suffer severe restrictions on opening and closing times. Bad ideas about nutrition can lead to bad policies and jumping to one conclusion over another only ever leads to irrationality. At every turn it seems someone with not enough knowledge and too little skepticism has more than enough confidence to tell you what to do when it comes to what you should eat or drink. And they might even punish you with fines and prison if you deviate from their ideas about nutrition. This is no small thing.

Next: exercise. There is a mantra that often goes something like this among health gurus: Exercise is more important than diet. Or diet is more important than exercise. Or diet and exercise are equally important.

But important for what? For getting good at exercise? For getting as massive as a sumo wrestler? For the nebulous concept of "health"? Typically, it about weight loss. And often getting "fit".

Let’s say we deal with weight loss because that seems to be the most common reason people become atypically obsessed with how much activity they are doing and what they are consuming. But even when it comes to a well defined goal like "I want to lose 10 kg of my body mass" - no answer can be given as to what is more important - diet or exercise. A person who eats little but high fat hamburgers can still be very thin. Think a person who runs regular marathons. Anyone who runs 3 or 4 marathons (or more) a week will not be fat. There has never been a person who has run regular marathons who is also fat. You simply cannot consume enough kilojoules per day to put on weight if you are expending some tens of thousands per day in exercise. It just will not add up mathematically. This is proof positive that diet is not more important than exercise for keeping fat off your hips. Moreover, we all know of the glutton who seems to be able to eat hamburgers and chocolates and never get fat despite never exercising. From what we know, these people are burning a lot of energy just by resting - and why this is we just do not seem to know. We hand-wave the mystery away by saying "they have a fast metabolism" (in sports science and medicine it's called "Basal Metabolic Rate" or BAL and they have altogether unreliable formulae to help predict what one's energy expenditure might be given certain constrains. But giving a mystery a label, and coming up with an empirical formula doesn't actually provide any answers). Indeed all this simply begs the question: How can two otherwise extremely similar people respond so differently to identical food intake and exercise? This is a good scientific question we do not yet have good answers to. No doubt the answer in large part lurks within the genes - but where exactly, we do not know. These questions are the "dark matter" and "dark energy" of sports science. Merely statements of our collective and scientific ignorance.

One place where people have approached something like a scientific approach to nutrition and exercise is in the sport of bodybuilding. Here we can actually see, before our eyes, the effect of different theories. We can test the theory that eating 1000g of protein per day, 500g of carbohydrates and 200g of fat has upon the body of a 25 year old, 90kg male who follows a very strict, particular exercise regime where, within the best measurements available, burns some number of calories per day.

But even here the error bars are beyond the realms that any other quantitative scientist would regard as acceptable in order to establish trends. Some people will simply put on more muscle and burn more fat, even though they do the same amount of weight lifting and eat the same meals - and so this means general advice is typically not going to apply to - well anyone. Because there is no "general person". When at rest it is difficult to know how many calories John burns compared to Joe. And even if we do get an estimate, we do not know whether 10 minutes later, after the test is done, if John’s caloric burn will increase or decrease due to an almost infinite number of factors. We simply do not know enough about human exercise physiology to make such judgements. And even if we had a perfect experimental specimen - say John who we have studied for some years and in the process minimised those error bars - we know it is a very unreliable thing to extrapolate from this single data point to others - like Joe - let alone someone who is not 25...and a male...and a bodybuilder.

So for all we know about nutrition, using this very general knowledge to make specific predictions (like what should *I* eat to maximise *my* weight loss/muscle gain?) is not yet possible without further experimentation.

Of course what we do know is worth knowing. We know water is essential. We know protein is needed to build muscles. But whether broccoli or blueberries really do contain anti-cancer properties simply is not known. And anyone who asserts they do, is being dishonest. Worse than that - they are actually hurting people by giving false hope. Cancer, for example, we know is not a single disease - but many. And potential treatments, or preventatives, are going to be as broad as the disease itself. If someone tells you "Wheatgrass is going to prevent cancer" ask: which cancer? If they say "All of them" ask the best question of all: "How do you know?" If the best they have to offer is one of the thousands of "natural living" websites you know they don't know. No one does. If something really did prevent cancer, we would know about it. In the same way we all know aspirin works for mild headaches. We all know what works - and we use it. That's a good rule of thumb. Common knowledge when it comes to "health" is often superior to that from some purported expert. This is because "health" is so wooly and nebulous a term that broad general knowledge actually works better than narrow specific stuff.

All this is to say: be extremely skeptical. Almost all the nutrition and exercise advice you will be given is false. Almost all of the posts of facebook, most of the tweets on twitter - most of the stuff on supposed "health" websites - are replete with misconceptions. It would typically take very high level expertise - like degree level knowledge in nutrition, or a PhD in biochemistry - to sift the "discovered through the application of good scientific research carefully checked and repeated by multiple peers" from the "just a rumour" stuff. Most of the time what already passes for general knowledge is pretty robust. It's best to get a bit of protein, fat and carbohydrate each day. Drink when you're thirsty. Have some veggies to keep your vitamins up. It doesn't get much harder than this - and even those very general rules might be too strict.

Most of the time, in a rich country, you can eat most of what you want and do as much or as little exercise as you like.  You will be able to tell just by looking in the mirror if you like what you see. In a rich country you would actually have to do more work to suffer some deficiency, or risk cancer from some food you eat, or risk any bad disease by the amount of exercise you do not do. Of course, if you are a fat 200kg and thinking about buying one of those scooters to get you to McDonalds - it should be obvious to you that you're at higher risk of disease. It's common sense. You can see it in the mirror.

We do not know to what extent this or that chemical in food causes diseases like the many cancers that plague the population (remember when I use the word “chemical” I use it in the scientific sense - so I include things like “water” and “oxygen” and “protein” as well as “potassium benzoate” as chemicals). Likely none, on their own really do cause cancer. Almost all "this thing causes cancer" scare articles are complete lies. One of the best lies is the one about artificial sweeteners. The fact is: artificial sweeteners are great. They are not unhealthy - not in the slightest under any definition of "unhealthy". There is nothing wrong with them in moderation.

If it's what the reasonable person would say is "edible" and you're not allergic - and fits the definition of "food" as a starving person might understand the word - you can relax about it. Food is going to be considerably less of a cancer risk than, say, the granite and basalt rock beneath your feet at this very instance that is mildly -and entirely naturally -  radioactive. And which it is impossible to escape (and if you think living at higher altitudes away from bedrock might help - think again - there's even more radiation coming from the sky - also entirely naturally).  Radiation, like light - just is. Right now, the walls around your house, the sky above your head and the ground beneath your feet contains radioactive materials - that are there naturally. And we live with that. Are they harmful? Not really. Are they harmless? Well no - not really. But they are a fact and we have no means to guard against this background of relatively harmless but nonetheless damaging fact of life. And it doesn't matter in the long run if you live above slightly more granite than your neighbor because they just might get a little more cosmic radiation. So if you are concerned about stuff in your food potentially causing disease - you should be far more concerned about the rocks on which your house is built is the point. The latter we know can, according to our best physical theories, damage the DNA. The former, we are still guessing at the relevant mechanisms.

So eat what you like and just remember you cannot get around the laws of physics. In this case the first law of thermodynamics: energy cannot be created or destroyed - only changed from one form into another.

When applied to nutrition this simply means: if you want to lose weight: the amount of energy you take in must be less than the amount of energy you expend. If you want to gain weight, the amount of energy needs to be more.

So you can eat all the hamburgers and chocolates you like. But if you want to lose weight, you better burn more calories throughout the day so as to not store that stuff as fat. Because - in a healthy person at least - most excess calories will get stored as fat. That really is all there is to it, until - years from now - we have a precise, predictive science of nutrition and exercise. We just aren't there...yet.