Heterogeneity and Convergence of Olfactory First-Order Neurons Account for the High Speed and Sensitivity of Second-Order Neurons
- Published: December 04, 2014
- DOI: 10.1371/journal.pcbi.1003975
Blog sobre a (minha) vida científica – "E toda banda larga será inútil se a mente for estreita"
Some while back, I found myself sitting next to an accomplished economics professor at a dinner event. Shortly after pleasantries, I said to him, “economic growth cannot continue indefinitely,” just to see where things would go. It was a lively and informative conversation. I was somewhat alarmed by the disconnect between economic theory and physical constraints—not for the first time, but here it was up-close and personal. Though my memory is not keen enough to recount our conversation verbatim, I thought I would at least try to capture the key points and convey the essence of the tennis match—with some entertainment value thrown in.
Cast of characters: Physicist, played by me; Economist, played by an established economics professor from a prestigious institution. Scene: banquet dinner, played in four acts (courses).
Note: because I have a better retention of my own thoughts than those of my conversational companion, this recreation is lopsided to represent my own points/words. So while it may look like a physicist-dominated conversation, this is more an artifact of my own recall capabilities. I also should say that the other people at our table were not paying attention to our conversation, so I don’t know what makes me think this will be interesting to readers if it wasn’t even interesting enough to others at the table! But here goes…
Physicist: Hi, I’m Tom. I’m a physicist.
Economist: Hi Tom, I’m [ahem..cough]. I’m an economist.
Physicist: Hey, that’s great. I’ve been thinking a bit about growth and want to run an idea by you. I claim that economic growth cannot continue indefinitely.
Economist: [chokes on bread crumb] Did I hear you right? Did you say that growth can not continue forever?
Physicist: That’s right. I think physical limits assert themselves.
Economist: Well sure, nothing truly lasts forever. The sun, for instance, will not burn forever. On the billions-of-years timescale, things come to an end.
Physicist: Granted, but I’m talking about a more immediate timescale, here on Earth. Earth’s physical resources—particularly energy—are limited and may prohibit continued growth within centuries, or possibly much shorter depending on the choices we make. There are thermodynamic issues as well.
Economist: I don’t think energy will ever be a limiting factor to economic growth. Sure, conventional fossil fuels are finite. But we can substitute non-conventional resources like tar sands, oil shale, shale gas, etc. By the time these run out, we’ll likely have built up a renewable infrastructure of wind, solar, and geothermal energy—plus next-generation nuclear fission and potentially nuclear fusion. And there are likely energy technologies we cannot yet fathom in the farther future.
Physicist: Sure, those things could happen, and I hope they do at some non-trivial scale. But let’s look at the physical implications of the energy scale expanding into the future. So what’s a typical rate of annual energy growth over the last few centuries?
Economist: I would guess a few percent. Less than 5%, but at least 2%, I should think.
Physicist: Right, if you plot the U.S. energy consumption in all forms from 1650 until now, you see a phenomenally faithful exponential at about 3% per year over that whole span. The situation for the whole world is similar. So how long do you think we might be able to continue this trend?
Economist: Well, let’s see. A 3% growth rate means a doubling time of something like 23 years. So each century might see something like a 15–20× increase. I see where you’re going. A few more centuries like that would perhaps be absurd. But don’t forget that population was increasing during centuries past—the period on which you base your growth rate. Population will stop growing before more centuries roll by.
Physicist: True enough. So we would likely agree that energy growth will not continue indefinitely. But two points before we continue: First, I’ll just mention that energy growth has far outstripped population growth, so that per-capita energy use has surged dramatically over time—our energy lives today are far richer than those of our great-great-grandparents a century ago [economist nods]. So even if population stabilizes, we are accustomed to per-capita energy growth: total energy would have to continue growing to maintain such a trend [another nod].
Second, thermodynamic limits impose a cap to energy growth lest we cook ourselves. I’m not talking about global warming, CO2 build-up, etc. I’m talking about radiating the spent energy into space. I assume you’re happy to confine our conversation to Earth, foregoing the spectre of an exodus to space, colonizing planets, living the Star Trek life, etc.
Economist: More than happy to keep our discussion grounded to Earth.
Physicist: [sigh of relief: not a space cadet] Alright, the Earth has only one mechanism for releasing heat to space, and that’s via (infrared) radiation. We understand the phenomenon perfectly well, and can predict the surface temperature of the planet as a function of how much energy the human race produces. The upshot is that at a 2.3% growth rate (conveniently chosen to represent a 10× increase every century), we would reach boiling temperature in about 400 years. [Pained expression from economist.] And this statement is independent of technology. Even if we don’t have a name for the energy source yet, as long as it obeys thermodynamics, we cook ourselves with perpetual energy increase.
Economist: That’s a striking result. Could not technology pipe or beam the heat elsewhere, rather than relying on thermal radiation?
Physicist: Well, we could (and do, somewhat) beam non-thermal radiation into space, like light, lasers, radio waves, etc. But the problem is that these “sources” are forms of high-grade, low-entropy energy. Instead, we’re talking about getting rid of the waste heat from all the processes by which we use energy. This energy is thermal in nature. We might be able to scoop up some of this to do useful “work,” but at very low thermodynamic efficiency. If you want to use high-grade energy in the first place, having high-entropy waste heat is pretty inescapable.
Economist: [furrowed brow] Okay, but I still think our path can easily accommodate at least a steady energy profile. We’ll use it more efficiently and for new pursuits that continue to support growth.
Physicist: Before we tackle that, we’re too close to an astounding point for me to leave it unspoken. At that 2.3% growth rate, we would be using energy at a rate corresponding to the total solar input striking Earth in a little over 400 years. We would consume something comparable to the entire sun in 1400 years from now. By 2500 years, we would use energy at the rate of the entire Milky Way galaxy—100 billion stars! I think you can see the absurdity of continued energy growth. 2500 years is not that long, from a historical perspective. We know what we were doing 2500 years ago. I think I know what we’re not going to be doing 2500 years hence.
Economist: That’s really remarkable—I appreciate the detour. You said about 1400 years to reach parity with solar output?
Physicist: Right. And you can see the thermodynamic point in this scenario as well. If we tried to generate energy at a rate commensurate with that of the Sun in 1400 years, and did this on Earth, physics demands that the surface of the Earth must be hotter than the (much larger) surface of the Sun. Just like 100 W from a light bulb results in a much hotter surface than the same 100 W you and I generate via metabolism, spread out across a much larger surface area.
Economist: I see. That does make sense.
Economist: So I’m as convinced as I need to be that growth in raw energy use is a limited proposition—that we must one day at the very least stabilize to a roughly constant yearly expenditure. At least I’m willing to accept that as a starting point for discussing the long term prospects for economic growth. But coming back to your first statement, I don’t see that this threatens the indefinite continuance of economic growth.
For one thing, we can keep energy use fixed and still do more with it in each passing year via efficiency improvements. Innovations bring new ideas to the market, spurring investment, market demand, etc. These are things that will not run dry. We have plenty of examples of fundamentally important resources in decline, only to be substituted or rendered obsolete by innovations in another direction.
Physicist: Yes, all these things happen, and will continue at some level. But I am not convinced that they represent limitless resources.
Economist: Do you think ingenuity has a limit—that the human mind itself is only so capable? That could be true, but we can’t credibly predict how close we might be to such a limit.
Physicist: That’s not really what I have in mind. Let’s take efficiency first. It is true that, over time, cars get better mileage, refrigerators use less energy, buildings are built more smartly to conserve energy, etc. The best examples tend to see factor-of-two improvements on a 35 year timeframe, translating to 2% per year. But many things are already as efficient as we can expect them to be. Electric motors are a good example, at 90% efficiency. It will always take 4184 Joules to heat a liter of water one degree Celsius. In the middle range, we have giant consumers of energy—like power plants—improving much more slowly, at 1% per year or less. And these middling things tend to be something like 30% efficient. How many more “doublings” are possible? If many of our devices were 0.01% efficient, I would be more enthusiastic about centuries of efficiency-based growth ahead of us. But we may only have one more doubling in us, taking less than a century to realize.
Economist: Okay, point taken. But there is more to efficiency than incremental improvement. There are also game-changers. Tele-conferencing instead of air travel. Laptop replaces desktop; iPhone replaces laptop, etc.—each far more energy frugal than the last. The internet is an example of an enabling innovation that changes the way we use energy.
Physicist: These are important examples, and I do expect some continuation along this line, but we still need to eat, and no activity can get away from energy use entirely. [semi-reluctant nod/bobble] Sure, there are lower-intensity activities, but nothing of economic value is completely free of energy.
Economist: Some things can get awfully close. Consider virtualization. Imagine that in the future, we could all own virtual mansions and have our every need satisfied: all by stimulative neurological trickery. We would stil need nutrition, but the energy required to experience a high-energy lifestyle would be relatively minor. This is an example of enabling technology that obviates the need to engage in energy-intensive activities. Want to spend the weekend in Paris? You can do it without getting out of your chair. [More like an IV-drip-equipped toilet than a chair, the physicist thinks.]
Physicist: I see. But this is still a finite expenditure of energy per person. Not only does it take energy to feed the person (today at a rate of 10 kilocalories of energy input per kilocalorie eaten, no less), but the virtual environment probably also requires a supercomputer—by today’s standards—for every virtual voyager. The supercomputer at UCSD consumes something like 5 MW of power. Granted, we can expect improvement on this end, but today’s supercomputer eats 50,000 times as much as a person does, so there is a big gulf to cross. I’ll take some convincing. Plus, not everyone will want to live this virtual existence.
Economist: Really? Who could refuse it? All your needs met and an extravagant lifestyle—what’s not to like? I hope I can live like that myself someday.
Physicist: Not me. I suspect many would prefer the smell of real flowers—complete with aphids and sneezing; the feel of real wind messing up their hair; even real rain, real bee-stings, and all the rest. You might be able to simulate all these things, but not everyone will want to live an artificial life. And as long as there are any holdouts, the plan of squeezing energy requirements to some arbitrarily low level fails. Not to mention meeting fixed bio-energy needs.
Physicist: But let’s leave the Matrix, and cut to the chase. Let’s imagine a world of steady population and steady energy use. I think we’ve both agreed on these physically-imposed parameters. If the flow of energy is fixed, but we posit continued economic growth, then GDP continues to grow while energy remains at a fixed scale. This means that energy—a physically-constrained resource, mind—must become arbitrarily cheap as GDP continues to grow and leave energy in the dust.
Economist: Yes, I think energy plays a diminishing role in the economy and becomes too cheap to worry about.
Physicist: Wow. Do you really believe that? A physically limited resource (read scarcity) that is fundamental to every economic activity becomes arbitrarily cheap? [turns attention to food on the plate, somewhat stunned]
Economist: [after pause to consider] Yes, I do believe that.
Physicist: Okay, so let’s be clear that we’re talking about the same thing. Energy today is roughly 10% of GDP. Let’s say we cap the physical amount available each year at some level, but allow GDP to keep growing. We need to ignore inflation as a nuisance in this case: if my 10 units of energy this year costs $10,000 out of my $100,000 income; then next year that same amount of energy costs $11,000 and I make $110,000—I want to ignore such an effect as “meaningless” inflation: the GDP “growth” in this sense is not real growth, but just a re-scaling of the value of money.
Physicist: Then in order to have real GDP growth on top of flat energy, the fractional cost of energy goes down relative to the GDP as a whole.
Physicist: How far do you imagine this can go? Will energy get to 1% of GDP? 0.1%? Is there a limit?
Economist: There does not need to be. Energy may become of secondary importance in the economy of the future—like in the virtual world I illustrated.
Physicist: But if energy became arbitrarily cheap, someone could buy all of it, and suddenly the activities that comprise the economy would grind to a halt. Food would stop arriving at the plate without energy for purchase, so people would pay attention to this. Someone would be willing to pay more for it. Everyone would. There will be a floor to how low energy prices can go as a fraction of GDP.
Economist: That floor may be very low: much lower than the 5–10% we pay today.
Physicist: But is there a floor? How low are you willing to take it? 5%? 2%? 1%?
Economist: Let’s say 1%.
Physicist: So once our fixed annual energy costs 1% of GDP, the 99% remaining will find itself stuck. If it tries to grow, energy prices must grow in proportion and we have monetary inflation, but no real growth.
Economist: Well, I wouldn’t go that far. You can still have growth without increasing GDP.
Physicist: But it seems that you are now sold on the notion that the cost of energy would not naturally sink to arbitrarily low levels.
Economist: Yes, I have to retract that statement. If energy is indeed capped at a steady annual amount, then it is important enough to other economic activities that it would not be allowed to slip into economic obscurity.
Physicist: Even early economists like Adam Smith foresaw economic growth as a temporary phase lasting maybe a few hundred years, ultimately limited by land (which is where energy was obtained in that day). If humans are successful in the long term, it is clear that a steady-state economic theory will far outlive the transient growth-based economic frameworks of today. Forget Smith, Keynes, Friedman, and that lot. The economists who devise a functioning steady-state economic system stand to be remembered for a longer eternity than the growth dudes. [Economist stares into the distance as he contemplates this alluring thought.]
Economist: But I have to object to the statement that growth must stop once energy amount/price saturates. There will always be innovations that people are willing to purchase that do not require additional energy.
Physicist: Things will certainly change. By “steady-state,” I don’t mean static. Fads and fashions will always be part of what we do—we’re not about to stop being human. But I’m thinking more of a zero-sum game here. Fads come and go. Some fraction of GDP will always go toward the fad/innovation/gizmo of the day, but while one fad grows, another fades and withers. Innovation therefore will maintain a certain flow in the economy, but not necessarily growth.
Economist: Ah, but the key question is whether life 400 years from now is undeniably of higher quality than life today. Even if energy is fixed, and GDP is fixed once the cost of energy saturates at the lower bound, will quality of life continue to improve in objectively agreed-upon ways?
Physicist: I don’t know how objective such an assessment can be. Many today yearn for days past. Maybe this is borne of ignorance or romanticism over the past (1950′s often comes up). It may be really exciting to imagine living in Renaissance Europe, until a bucket of nightsoil hurled from a window splatters off the cobblestone and onto your breeches. In any case, what kind of universal, objective improvements might you imagine?
Economist: Well, for instance, look at this dessert, with its decorative syrup swirls on the plate. It is marvelous to behold.
Physicist: And tasty.
Economist: We value such desserts more than plain, unadorned varieties. In fact, we can imagine an equivalent dessert with equivalent ingredients, but the decorative syrup unceremoniously pooled off to one side. We value the decorated version more. And the chefs will continue to innovate. Imagine a preparation/presentation 400 years from now that would blow your mind—you never thought dessert could be made to look so amazing and taste so delectably good. People would line the streets to get hold of such a creation. No more energy, no more ingredients, yet of increased value to society. That’s a form of quality of life improvement, requiring no additional resources, and perhaps costing the same fraction of GDP, or income.
Physicist: I’m smiling because this reminds me of a related story. I was observing at Palomar Observatory with an amazing instrumentation guru named Keith who taught me much. Keith’s night lunch—prepared in the evening by the observatory kitchen and placed in a brown bag—was a tuna-fish sandwich in two parts: bread slices in a plastic baggie, and the tuna salad in a small plastic container (so the tuna would not make the bread soggy after hours in the bag). Keith plopped the tuna onto the bread in an inverted container-shaped lump, then put the other piece of bread on top without first spreading the tuna. It looked like a snake had just eaten a rat. Perplexed, I asked if he intended to spread the tuna before eating it. He looked at me quizzically (like Morpheus in the Matrix: “You think that’s air you’re breathing? Hmm.”), and said—memorably, “It all goes in the same place.”
My point is that the stunning presentation of desserts will not have universal value to society. It all goes in the same place, after all. [I’ll share a little-known secret. It’s hard to beat a Hostess Ding Dong for dessert. At 5% the cost of fancy desserts, it’s not clear how much value the fancy things add.]
The evening’s after-dinner keynote speech began, so we had to shelve the conversation. Reflecting on it, I kept thinking, “This should not have happened. A prominent economist should not have to walk back statements about the fundamental nature of growth when talking to a scientist with no formal economics training.” But as the evening progressed, the original space in which the economist roamed got painted smaller and smaller.
First, he had to acknowledge that energy may see physical limits. I don’t think that was part of his initial virtual mansion.
Next, the efficiency argument had to shift away from straight-up improvements to transformational technologies. Virtual reality played a prominent role in this line of argument.
Finally, even having accepted the limits to energy growth, he initially believed this would prove to be of little consequence to the greater economy. But he had to ultimately admit to a floor on energy price and therefore an end to traditional growth in GDP—against a backdrop fixed energy.
I got the sense that this economist’s view on growth met some serious challenges during the course of the meal. Maybe he was not putting forth the most coherent arguments that he could have made. But he was very sharp and by all measures seemed to be at the top of his game. I choose to interpret the episode as illuminating a blind spot in traditional economic thinking. There is too little acknowledgement of physical limits, and even the non-compliant nature of humans, who may make choices we might think to be irrational—just to remain independent and unencumbered.
I recently was motivated to read a real economics textbook: one written by people who understand and respect physical limitations. The book, called Ecological Economics, by Herman Daly and Joshua Farley, states in its Note to Instructors:
…we do not share the view of many of our economics colleagues that growth will solve the economic problem, that narrow self-interest is the only dependable human motive, that technology will always find a substitute for any depleted resource, that the market can efficiently allocate all types of goods, that free markets always lead to an equilibrium balancing supply and demand, or that the laws of thermodynamics are irrelevant to economics.
This is a book for me!
The conversation recreated here did challenge my own understanding as well. I spent the rest of the evening pondering the question: “Under a model in which GDP is fixed—under conditions of stable energy, stable population, steady-state economy: if we accumulate knowledge, improve the quality of life, and thus create an unambiguously more desirable world within which to live, doesn’t this constitute a form of economic growth?”
I had to concede that yes—it does. This often falls under the title of “development” rather than “growth.” I ran into the economist the next day and we continued the conversation, wrapping up loose ends that were cut short by the keynote speech. I related to him my still-forming position that yes, we can continue tweaking quality of life under a steady regime. I don’t think I ever would have explicitly thought otherwise, but I did not consider this to be a form of economic growth. One way to frame it is by asking if future people living in a steady-state economy—yet separated by 400 years—would always make the same, obvious trades? Would the future life be objectively better, even for the same energy, same GDP, same income, etc.? If the answer is yes, then the far-future person gets more for their money: more for their energy outlay. Can this continue indefinitely (thousands of years)? Perhaps. Will it be at the 2% per year level (factor of ten better every 100 years)? I doubt that.
So I can twist my head into thinking of quality of life development in an otherwise steady-state as being a form of indefinite growth. But it’s not your father’s growth. It’s not growing GDP, growing energy use, interest on bank accounts, loans, fractional reserve money, investment. It’s a whole different ballgame, folks. Of that, I am convinced. Big changes await us. An unrecognizable economy. The main lesson for me is that growth is not a “good quantum number,” as physicists will say: it’s not an invariant of our world. Cling to it at your own peril.
Note: This conversation is my contribution to a series at www.growthbusters.org honoring the 40th anniversary of the Limits to Growth study. You can explore the series here. Also see my previous reflection on the Limits to Growth work. You may also be interested in checking out and signing the Pledge to Think Small and consider organizing an Earth Day weekend house party screening of the GrowthBusters movie.
Cinco anos atrás, quando estava dando uma palestra sobre física a estudantes do Ensino Médio no Massachusetts Institute of Technology, Randall Munroe percebeu que a plateia não estava muito interessada.
Ele estava tentando explicar o que são energia potencial e potência -conceitos que não são complexos, mas difíceis de entender.
Assim, no meio da palestra de três horas, Munroe, mais conhecido por ser o criador da HQ on-line xkcd, resolveu apelar para “Star Wars”.
“Pensei na cena de ‘O Império Contra-ataca’ em que Yoda tira a asa-X do pântano”, comentou.
“A ideia me ocorreu quando eu estava dando a aula.”
No lugar de definições abstratas (um objeto erguido ganha energia potencial porque vai se acelerar quando cair; a potência é o índice de mudança na energia), Munroe fez uma pergunta: quanta energia da Força seria Yoda capaz de produzir?
“Fiz uma versão aproximada do cálculo ali mesmo, na sala de aula, procurando as dimensões da nave na internet e medindo as coisas na cena no projetor, diante dos alunos”, contou. “Todos começaram a prestar atenção.”
Para a maioria das pessoas, a física não é interessante por si só. “As ferramentas só são divertidas quando a coisa com a qual você as utiliza é interessante.”
Os alunos começaram a fazer outras perguntas. “E o final de ‘O Senhor dos Anéis’, quando o olho de Sauron explode, quanta energia há nisso?”
A experiência inspirou Munroe a começar a pedir perguntas semelhantes dos leitores do xkcd.
Ele reuniu esse trabalho, incluindo uma versão dos cálculos que fez sobre Yoda e outros materiais novos, no livro “E se?”, lançado em setembro e que desde então está na lista dos livros de não ficção mais vendidos.
Como afirma sua capa, “E se?” é repleto de “respostas científicas sérias a perguntas hipotéticas absurdas”.
“O livro exercita a imaginação do leitor, e o humor espirituoso de Munroe é encantador”, comentou William Sanford Nye, mais conhecido como “Billy Nye, the Science Guy”. “Ele cria cenários que, por falta de um termo melhor, precisamos descrever como absurdos, mas que são muito instrutivos.”
O que aconteceria se você tentasse rebater uma bola de beisebol lançada a 90% da velocidade da luz? “A resposta é ‘muitas coisas’, e todas acontecem muito rapidamente. Não termina bem para o batedor (nem para o lançador).”
Se todo o mundo mirasse a Lua ao mesmo tempo com um ponteiro de laser, a Lua mudaria de cor? “Não se usássemos ponteiros de laser normais.”
Por quanto tempo um submarino nuclear poderia permanecer em órbita? “O submarino ficaria ótimo, mas seus tripulantes teriam problemas.”
As explicações são acompanhadas pelos mesmos desenhos e o mesmo humor nerd que garantiram a popularidade do xkcd. (O que significa xkcd? “É simplesmente uma palavra para a qual não existe pronúncia fonética”, explica o site do seriado on-line.)
Na época em que era estudante de física na Universidade Christopher Newport, na Virginia, Munroe começou a trabalhar como técnico independente em um projeto de robótica no Centro Langley de Pesquisas, da Nasa, e continuou depois de se formar.
Foi nessa época que ele começou a scanear seus desenhos rabiscados e colocá-los na web.
O contrato com a Nasa terminou em 2006, por decisão mútua das duas partes.
Munroe tornou-se cartunista em tempo integral e se mudou para a região de Boston porque, explicou, queria viver numa cidade maior, com mais coisas de geek para fazer. Em 2012 ele incluiu a parte de “E se?” no site.
Hoje ele recebe milhares de perguntas por semana. Muitas são evidentemente de estudantes à procura de ajuda com sua lição de casa. Outras podem ser respondidas com uma só palavra: “Não”.
“Uma das perguntas que recebi foi: ‘Existe algum equipamento comercial de mergulho que permita a sobrevivência debaixo de lava incandescente?'”, Munroe contou. “Não. Não existe.”
Munroe também gostava de fazer perguntas quando era criança. Na introdução do livro, ele conta que se perguntava se havia mais coisas duras ou moles no mundo. Essa conversa causou impressão tão forte à sua mãe que ela a anotou e guardou.
“Dizem que não existem perguntas estúpidas”, escreve Munroe, 30. “Isso não é verdade, obviamente. Acho que minha pergunta sobre as coisas duras e moles foi bastante estúpida. Mas tentar responder uma pergunta estúpida de modo completo pode levar você a alguns lugares muito interessantes.”
Neuronal networks can present activity described by power-law distributed avalanches presumed to be a signature of a critical state. Here we study a random-neighbor network of excitable (SIRS) cellular automata coupled by dynamical (depressing) synapses that exhibits bona ?de self-organized criticality (SOC) even with dissipative bulk dynamics. This occurs because in the stationary regime the model is conservative on average and in the thermodynamic limit the probability distribution for the global branching ratio converges to a delta-function centered at its critical value. Analytical results show perfect agreement with annealed simulations of the model and enable us to study the emergence of SOC as a function of the parametric derivatives of the stationary branching ratio.
Instituto de Estudos Avançados, USP, São Carlos.
September 10, 2013 by lukebarnes
I’ve spent a lot of time critiquing articles on the fine-tuning of the universe for intelligent life. I should really give the other side of the story. Below are some of the good ones, ranging from popular level books to technical articles. I’ve given my recommendations for popular cosmology books here.
I haven’t read Brian Greene’s book on the multiverse but I’ve read his other books and they’re excellent. Stephen Hawking discusses fine-tuning in A Brief History of Time and the Grand Design. As usual, read anything by Sean Carroll, Frank Wilczek, and Alex Vilenkin.
The field of fine-tuning grew out of the so-called “Large numbers hypothesis” of Paul Dirac, which is owes a lot to Weyl and is further discussed by Eddington, Gamow and others. These discussions evolve into fine-tuning when Dicke explains them using the anthropic principle. Dicke’s method is examined and expanded in these classic papers of the field:
A number of papers, while not discussing fine-tuning, are very relevant as they discuss how the macroscopic universe depends on the values of fundamental constants. Here are a few good examples.
Here are a few good review papers, arranged in order of increasing technical level.
Here are some of the papers that have performed detailed calculations of specific fine-tuning cases, in chronological order.
Particle Physics Parameters
Part of the reason why the fine-tuning of the universe for life is of such interest to philosophers is that it is often used as a premise in an argument for the existence of God. A lot of the literature on the fine-tuning argument, pro and con, misses the mark by a large margin, in my opinion. Here are three of the best expositions of this argument.
Unsurprisingly, such claims have not gone unchallenged. Here are some of the best responses.
By Clay Farris Naff | November 18, 2011 | 21
Scientific American Blog
“Does aught befall you? It is good. It is part of the destiny of the Universe ordained for you from the beginning.”
– Marcus Aurelius, Stoic Philosopher and Emperor of Rome, in Meditations, circa 170 CE
“’He said that, did he? … Well, you can tell him from me, he’s an ass!”
– Bertie Wooster, fictional P.G. Wodehouse character, in The Mating Season, 1949
People have been arguing about the fundamental nature of existence since, well, since people existed. Having lost exclusive claim to tools, culture, and self, one of the few remaining distinctions of our species is that we can argue about the fundamental nature of existence.
There are, however, two sets of people who want to shut the argument down. One is the drearily familiar set of religious fundamentalists. The other is the shiny new set of atheists who claim that science demonstrates beyond reasonable doubt that our existence is accidental, purposeless, and doomed. My intent is to show that both are wrong.
I do not mean to imply a false equivalence here. Concerning the fundamentalist position, my work is done. Claims of a six-day Creation, a 6,000-year-old Earth, a global flood, and so forth have been demolished by science. It has not only amassed evidence against particular claims but has discovered laws of nature that exclude whole classes of claims. To the extent we can be certain about anything, we can rest assured that all supernatural claims are false.
The “New Atheist” position, by contrast, demands serious consideration. It has every advantage that science can provide, yet it overreaches for its conclusion. The trouble with the “New Atheist” position, as defined above, is this: it commits the fallacy of the excluded middle. I will explain.
But first, if you’ll pardon a brief diversion, I feel the need to hoist my flag. You may have inferred that I am a liberal religionist, attempting to unite the scientific narrative with some metaphorical interpretation of my creed. That is not so.
I am a secular humanist who is agnostic about many things — string theory, Many Worlds, the Theo-logical chances of a World Series win for the Cubs – but the existence of a supernatural deity is not among them. What’s more, I am one of the lucky ones: I never struggled to let go of God. My parents put religion behind them before I was born.
I tell you this not to boast but in hopes that you’ll take in my argument through fresh eyes. The science-religion debate has bogged down in trench warfare, and anyone foolhardy enough to leap into the middle risks getting cut down with no questions asked. But here goes. Read more [+]
Received 23 August 2012; revised 29 May 2013; published 27 August 2013
Many different kinds of noise are experimentally observed in the brain. Among them, we study a model of noisy chemical synapse and obtain critical avalanches for the spatiotemporal activity of the neural network. Neurons and synapses are modeled by dynamical maps. We discuss the relevant neuronal and synaptic properties to achieve the critical state. We verify that networks of functionally excitable neurons with fast synapses present power-law avalanches, due to rebound spiking dynamics. We also discuss the measuring of neuronal avalanches by subsampling our data, shedding light on the experimental search for self-organized criticality in neural networks.
©2013 American Physical Society
IARA BIDERMANDE SÃO PAULO
A opção de ouvir toda e qualquer música nova está a um toque na tela. E você vai sempre escolher aquelas mesmas velhas canções.
Quem crava qual será a sua seleção são os autores de um estudo feito na Universidade de Washington sobre o poder da familiaridade na escolha musical.
A pesquisa foi feita com mais de 900 universitários, autodeclarados apreciadores de novos sons. Pelo menos foi isso o que disseram em questionários prévios. Curiosamente, o lado B dos participantes apareceu quando foram confrontados com escolhas reais entre pares de músicas. A maioria optou por aquelas que tinha ouvido mais vezes.
Ouvir sempre a mesma música não é falta de opção ou imaginação. Segundo o coordenador do laboratório de neuromarketing da Fundação Getulio Vargas de São Paulo, Carlos Augustos Costa, é coisa da sua cabeça.
“O cérebro não gosta de nada complicado. Se você ouve um som novo, tem de parar para entender, mas se a música tem padrões familiares, é sopa no mel: você decide imediatamente ouvi-la.”
Familiar é um padrão musical que a pessoa sabe reconhecer ou um estilo associado a memórias positivas.
“A música que você já conhece tem um valor emocional enorme. Cada vez que você a ouve, a associa a uma sensação de prazer e, quanto mais ouve, mais reforça essa associação”, diz a neurocientista e colunista da Folha Suzana Herculano-Houzel.
|Editoria de arte/Folhapress|
|As dez músicas mais lucrativas, nacionais e internacionais|
Em homenagem à minha mãe, falecida dia primeiro de agosto passado. Em duas versões, uma para meus amigos religiosos, e outra para meus amigos ateus. A figura se refere ao conceito de mãe da década de 1960-70, quando eu era criança. Acho que, hoje, eu incorporo para meus filhos algumas perguntas que eram da mãe. Ou não?
Por que Deus (o Acaso) permite
que as mães vão-se embora?
Mãe não tem limite,
é tempo sem hora,
luz que não apaga
quando sopra o vento
e chuva desaba,
na pele enrugada,
água pura, ar puro,
com o que é breve
e passa sem deixar vestígio.
Mãe, na sua graça, é eternidade.
Por que Deus (o Acaso) se lembra
– mistério profundo –
de tirá-la um dia?
Fosse eu Rei do Mundo,
baixava uma lei:
Mãe não morre nunca,
mãe ficará sempre
junto de seu filho
e ele, velho embora,
feito grão de milho.
Via Nestor Caticha:
Mi infancia son recuerdos de un patio de Sevilla,
y un huerto claro donde madura el limonero;
mi juventud, veinte años en tierras de Castilla;
mi historia, algunos casos de recordar no quiero.
Ni un seductor Mañara, ni un Bradomín he sido
-ya conocéis mi torpe aliño indumentario-,
mas recibí la flecha que me asignó Cupido,
y amé cuanto ellas puedan tener de hospitalario.
Hay en mis venas gotas de sangre jacobina,
pero mi verso brota de manantial sereno;
y más que un hombre al uso que sabe su doctrina
soy, en el buen sentido de la palabra, bueno.
Desdeño las romanzas de los tenores huecos
y el coro de los grillos que cantan a la luna.
A distinguir me paro las voces de los ecos,
y escucho solamente, entre las voces, una.
Converso con el hombre que siempre va conmigo
-quien habla solo espera hablar a Dios un día-
mi soliloquio es plática con este buen amigo
que me enseñó el secreto de la filantropía.
Y al cabo, nada os debo; me debéis cuanto escribo,
a mi trabajo acudo, con mi dinero pago
el traje que me cubre y la mansión que habito,
el pan que me alimenta y el lecho en donde yago.
Y cuando llegue el día del último viaje,
y esté al partir la nave que nunca ha de tornar
me encontraréis a bordo ligero de equipaje,
casi desnudo, como los hijos de la mar.
Lembranças de infância, um pátio em Sevilha,
Um pomar claro com um limoeiro a madurar;
Minha juventude, 20 anos na terra de Castilha;
Minha história, casos que já não quero lembrar.
Não sou um Manara, ou um grande sedutor
Estranhas roupas, não sei de onde vieram
Mas do Cupido a assinalada seta do amor,
Eu recebi, e amei, a quantas me acolheram.
O sangue em minhas veias procura certa rima
Mas, em meus versos, a primavera corre serena;
Mais que um homem que sabe sua doutrina,
Sinto, no bom sentido, o amor em quarentena.
Ocos tenores, cantando alto pelas videiras
O coro dos grilos se elevando para a Lua.
Distinguir os ecos das vozes verdadeiras,
Simplesmente ouvir a voz que é a sua.
Eu falo com aquele que sempre está comigo,
Quem fala sozinho quer falar com Deus um dia;
O solilóquio é minha conversação com esse amigo
Ele que me ensinou o segredo da filantropia.
Afinal de contas, nada devo enquanto escrevo,
Vou para meu trabalho e para meu salário,
A casa em que habito, a roupa que manejo,
O pão que me alimenta, a cama, o armário.
E quando chegar o dia último desta viagem,
A partir o navio do qual é impossível escapar;
Acho que a bordo, com bem pouca bagagem,
Estarei quase nu, como as crianças do mar.
Ohio State’s Christopher Hill joked he was showing scenes of an impending i-Product launch, and it was easy to believe him: young people were setting up mats in a hallway, ready to spend the night to secure a space in line for the big reveal. Except the date was July 3 and the location was CERN—where the discovery of the Higgs boson would be announced the next day.
It’s clear the LHC worked as intended and has definitively identified a Higgs-like particle. Hill put the chance of the ATLAS detector having registered a statistical fluke at less than 10-11, and he noted that wasn’t even considering the data generated by its partner, the CMS detector. But is it really the one-and-only Higgs and, if so, what does that mean? Hill was part of a panel that discussed those questions at the meeting of the American Association for the Advancement of Science.
As theorist Joe Lykken of Fermilab pointed out, the answers matter. If current results hold up, they indicate the Universe is currently inhabiting what’s called a false quantum vacuum. If it were ever to reach the real one, its existing structures (including us), would go away in what Lykken called “fireballs of doom.”
We’ll look at the less depressing stuff first, shall we?
Thanks to the Standard Model, we were able to make some very specific predictions about the Higgs. These include the frequency with which it will decay via different pathways: two gamma-rays, two Z bosons (which further decay to four muons), etc. We can also predict the frequency of similar looking events that would occur if there were no Higgs. We can then scan each of the decay pathways (called channels), looking for energies where there is an excess of events, or bump. Bumps have shown up in several channels in roughly the same place in both CMS and ATLAS, which is why we know there’s a new particle.
But we still don’t know precisely what particle it is. The Standard Model Higgs should have a couple of properties: it should be scalar and should have a spin of zero. According to Hill, the new particle is almost certainly scalar; he showed a graph where the alternative, pseudoscalar, was nearly ruled out. Right now, spin is less clearly defined. It’s likely to be zero, but we haven’t yet ruled out a spin of two. So far, so Higgs-like.
The Higgs is the particle form of a quantum field that pervades our Universe (it’s a single quantum of the field), providing other particles with mass. In order to do that, its interactions with other particles vary—particles are heavier if they have stronger interactions with the Higgs. So, teams at CERN are sifting through the LHC data, checking for the strengths of these interactions. So far, with a few exceptions, the new particle is acting like the Higgs, although the error bars on these measurements are rather large.
As we said above, the Higgs is detected in a number of channels and each of them produces an independent estimate of its mass (along with an estimated error). As of the data Hill showed, not all of these estimates had converged on the same value, although they were all consistent within the given errors. These can also be combined mathematically for a single estimate, with each of the two detectors producing a value. So far, these overall estimates are quite close: CMS has the particle at 125.8GeV, Atlas at 125.2GeV. Again, the error bars on these values overlap.
That specific mass may seem fairly trivial—if it were 130GeV, would you care? Lykken made the argument you probably should. But he took some time to build to that.
Lykken pointed out, as the measurements mentioned above get more precise, we may find the Higgs isn’t decaying at precisely the rates we expect it to. This may be because we have some details of the Standard Model wrong. Or, it could be a sign the Higgs is also decaying into some particles we don’t know about—particles that are dark matter candidates would be a prime choice. The behavior of the Higgs might also provide some indication of why there’s such a large excess of matter in the Universe.
But much of Lykken’s talk focused on the mass. As we mentioned above, the Higgs field pervades the entire Universe; the vacuum of space is filled with it. And, with a value for the Higgs mass, we can start looking into the properties of the Higgs filed and thus the vacuum itself. “When we do this calculation,” Lykken said, “we get a nasty surprise.”
It turns out we’re not living in a stable vacuum. Eventually, the Universe will reach a point where the contents of the vacuum are the lowest energy possible, which means it will reach the most stable state possible. The mass of the Higgs tells us we’re not there yet, but are stuck in a metastable state at a somewhat higher energy. That means the Universe will be looking for an excuse to undergo a phase transition and enter the lower state.
What would that transition look like? In Lykken’s words, again, “fireballs of doom will form spontaneously and destroy the Universe.” Since the change would alter the very fabric of the Universe, anything embedded in that fabric—galaxies, planets, us—would be trashed during the transition. When an audience member asked “Are the fireballs of doom like ice-9?” Lykken replied, “They’re even worse than that.”
Lykken offered a couple of reasons for hope. He noted the outcome of these calculations is extremely sensitive to the values involved. Simply shifting the top quark’s mass by two percent to a value that’s still within the error bars of most measurements, would make for a far more stable Universe.
And then there’s supersymmetry. The news for supersymmetry out of the LHC has generally been negative, as various models with low-mass particles have been ruled out by the existing data (we’ll have more on that shortly). But supersymmetry actually predicts five Higgs particles. (Lykken noted this by showing a slide with five different photos of Higgs taken at various points in his career, in which he was “differing in mass and other properties, as happens to all of us.”) So, when the LHC starts up at higher energies in a couple of years, we’ll actually be looking for additional, heavier versions of the Higgs.
If those are found, then the destruction of our Universe would be permanently put on hold. “If you don’t like that fate of the Universe,” Lykken said, “root for supersymmetry”
UPDATE: Para quem não entendeu, o texto é uma paródia…
a1 Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
Interstellar probes can carry out slingshot manoeuvres around the stars they visit, gaining a boost in velocity by extracting energy from the star’s motion around the Galactic Centre. These manoeuvres carry little to no extra energy cost, and in previous work it has been shown that a single Voyager-like probe exploring the Galaxy does so 100 times faster when carrying out these slingshots than when navigating purely by powered flight (Forgan et al.2012). We expand on these results by repeating the experiment with self-replicating probes. The probes explore a box of stars representative of the local Solar neighbourhood, to investigate how self-replication affects exploration timescales when compared with a single non-replicating probe. We explore three different scenarios of probe behaviour: (i) standard powered flight to the nearest unvisited star (no slingshot techniques used), (ii) flight to the nearest unvisited star using slingshot techniques and (iii) flight to the next unvisited star that will give the maximum velocity boost under a slingshot trajectory. In all three scenarios, we find that as expected, using self-replicating probes greatly reduces the exploration time, by up to three orders of magnitude for scenarios (i) and (iii) and two orders of magnitude for (ii). The second case (i.e. nearest-star slingshots) remains the most time effective way to explore a population of stars. As the decision-making algorithms for the fleet are simple, unanticipated ‘race conditions’ among probes are set up, causing the exploration time of the final stars to become much longer than necessary. From the scaling of the probes’ performance with star number, we conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time to warrant the existence of the Fermi Paradox.
(Received April 02 2013) (Accepted May 24 2013)
FERNANDO TADEU MORAES
DE SÃO PAULO
A neurocientista Suzana Herculano-Houzel, 40, dedicou-se nos últimos anos a entender como o cérebro humano se tornou o que é. Seu trabalho a levou a ser a primeira brasileira convidada a falar no TED Global, famoso evento anual de conferências de curta duração que reúne convidados de várias áreas do conhecimento.
Herculano apresentará em sua fala de 15 minutos, nesta quarta, os resultados de suas pesquisas sobre como o cérebro humano chegou ao número incrivelmente alto de 86 bilhões de neurônios: o consumo de alimentos cozidos. “Entre os primatas, temos o maior cérebro sem sermos os maiores. Grandes primatas, com a sua dieta de comida crua, não possuem energia suficiente para sustentar um corpo enorme e um cérebro grande.”
Na entrevista, concedida por telefone, a professora do Instituto de Ciências Biomédicas da UFRJ (Universidade Federal do Rio de Janeiro) dispara críticas à cultura brasileira de pesquisa científica, “que não incentiva a originalidade e a diversidade de pensamento”, à pós graduação nacional, “muito fraca”, e ao programa de bolsas Ciência Sem Fronteiras, “do jeito que está, parece demagogia” e defende a profissionalização da carreira de cientista.
|A neurocientista Suzana Herculano-Houzel, que irá falar no TED Global, em seu laboratório na UFRJ|
Foto: Meu filho Raphael Osame Kinouchi, loirinho descendente de japoneses…
Estava lendo os comentários internacionais de uma TED Talk quando me deparei com isso:
Nick Bikkal. Engraçado que tudo o que está assinalado em vermelho me parece extremamente familiar…
Eu sou um estrangeiro vivendo há 20 anos no Japão. Tenho 2 crianças no sistema escolar. No jardim de infância eu estava muito bem impressionado com os professores daqui. Eles passavam horas preparando as aulas do dia seguinte. Os professores realmente se importavam com seus alunos. Mais tarde, eu me tornei um pouco menos impressionado. Minha filha foi um dos poucos estudantes que ajudaram a obter que uma professora fosse expulsa porque ela mandava mensagens de texto enquanto dava aulas.
Crianças nessa idade começam a ir para os Juku, cursinhos. Eles são BIG BUSINESS aqui. Suspiro! Nos níveis HS JHS as crianças continuam indo aos Jukus, para que possam passar por um teste para que eles possam entrar em uma escola melhor na próxima nível
O objetivo é chegar a uma das universidades renomadas. O objetivo das universidades é produzir um servidor público ou um empregado de uma empresa de nome como a Sony ou Panasonic, etc. Lá você acaba trabalhando muitas horas extras … nem sempre pagas.
O sistema é muito politizado. Não há moral, educação espiritual. (O “Senso comum” japonês é algo que deve ser entendido aqui). Japoneses, como as pessoas têm visto especialmente nos esportes internacionais são muito nacionalistas. Eles não se preocupam tanto com os eventos. O que é importante é que se uma equipe representa seu país, eles devem ganhar. Suspiro.
Educação baseada em livro, regurgitando o que é dito pelo professor, memorização, etc, todos fazem parte da dieta de escolaridade. Conhecimento prático, pouco. O objetivo é o de ser um membro funcional da sociedade produtora de consumo. Depois de algumas gerações estudando Inglês, a língua internacional, relativamente poucos conseguiram domina-lo, e muito menos estão confiantes com o idioma. Ensinar é uma indústria de US $ 20 bilhões. É negócio. Eu quero vender meu livro e meu sistema de ensino a você.
É um país muito pacífico, que precisa de um novo paradigma. Eu gostaria que eles pudessem virar na direção do sistema finlandês. Tão popular aqui que o governo finlandês tem / tinha (?) Uma página de seu sistema de ensino em japonês. Qualquer que seja. É um trabalho em andamento, eu digo.