Mozaik.

Čas branja: 5-10 minut, z videom 15-20 minut

Lani je minilo 50 let od prvega eksperimenta v okviru programa SETI (Search for Extraterrestrial Intelligence oz. iskanje zunajzemeljske inteligence). 50 let poslušanja radijskih signalov iz vesolja in ducat let njihovega analiziranja s pionirskim programom distribuiranega računanja, SETI@home, pa nič. Nobenega odkritja, nobenega vesoljca. Kaj to pomeni?

Pravkar sem končal s knjigo Paula Daviesa, The Eerie Silence. Davies je bil kar nekaj let aktivno udeležen pri programu SETI in je kot tak v edinstveni poziciji, da postavi nekaj ključnih vprašanj in poskuša nanje odgovoriti. Oz., kot pravi, čas je, da kritično pogledamo kaj počnemo: praktično od odkritja radijskih valov naprej že iščemo ozkopasovni radijski signal iz vesolja. Tako smo si predstavljali inteligenco — in tako je inteligenca tudi izgledala — leta 1950.

Že na Zemlji pa se je v zadnjih 50 letih zgodilo ogromno sprememb. Če pogledamo že področje komunikacij — vse od odkritja laserja naprej do zavedanja, da je oddajanje radijskih in TV programov v vesolje zelo neučinkovito, zato jih danes raje pošiljamo po žicah in optičnih vlaknih. Posledično je danes Zemlja radijsko precej temna, tako da od daleč najbrž sploh nihče ne bi opazil inteligence. In okno v katerem smo velikodušno sevali kilovate v vesolje, je trajalo zgolj dobrih 50 let, kar je tren očesa v primerjavi s starostjo in velikostjo vesolja.

Ker I v SETI pomeni inteligenco, zgolj življenje ni dovolj. Biti mora tudi dovolj inteligentno, da bo pustilo neko sled, po kateri ga bo mogoče zaznati. In do razvoja inteligence vodi po ocenah številnih strokovnjakov niz 5-6 zelo neverjetnih dogodkov, od katerih lahko vsak zahteva več sto milijonov let. Če se vsi dogodki ne zvrstijo preden potencialni planet “umre”, se inteligentno življenje ne zgodi. Na žalost nimamo nobene metrike kaj je verjetno in kaj ne. Edini primer smo mi sami¹, in statistika na osnovi enega vzorca ni vredna nič. Kljub temu obstaja možnost, da so se vsi neverjetni dogodki na Zemlji po naključju zgodili neverjetno hitro, in da smo v tem pogledu statistični ubežnik. Če je tako, smo najbrž sami precej daleč naokrog.

Na spodnji sliki je tak pesimističen scenarij. Če drži, potem nam je na Zemlji za las uspelo pridobiti inteligenco tik (800 milijonov let) pred koncem planeta. Lahko, da večina planetov nima te sreče.

Eden izmed takih zelo neverjetnih dogodkov je bil pred kratkim dokaj dobro povzet na Slo-techu — razvoj evkariontske celice:

Razvoj na Zemlji kaže, da gre za skrajno neverjeten pojav, saj se je v celotni zgodovini planeta primeril samo enkrat. Vso večcelično življenje (rastline, glive, živali) je namreč potomec prve evkariontske celice.

Po drugi strani pa, če temu ni tako, mora biti vesolje polno življenja — morda celo inteligentnega. Enačba, ki jo je sestavil znani astrofizik Frank Drake poskuša oceniti število inteligentnih civilizacij, ki razpolagajo z radijsko tehnologijo, in ki ta hip obstajajo v naši galaksiji. Pomemben faktor v tej enačbi predstavlja tudi verjetnost, da se civilizacija uniči. Če sklepamo po nas samih, smo v relativno kratkem času prišli od odkritja radijskih valov do izuma atomske bombe. Spet pa ne vemo, koliko časa bomo zdržali brez samouničenja, ali koliko časa bi zdržala povprečna civilizacija.

V spodnjem posnetku Carl Sagan lepo razloži faktorje Drakove enačbe in poda ocene zanje.

Toda problem lahko predstavlja še nek drug trend. Kljub milijonom let evolucije smo samo v zadnjih dobrih 100 letih odkrili večino znanosti: elektriko, radijske valove, relativnost, kvantno mehaniko, laserje, računalnike, internet, ipd. Če verjamemo Moorovemo zakonu in napovedim Raya Kurzweila, bomo v kratkem dosegli tehnološko singularnost, kjer bo vsaka sposobnost napovedovanja prihodnosti odpovedala.

Ta vedno večja hitrost napredka je lepo razvidna s spodnje slike.

Kdo pravi, da bi civilizacija, milijon let starejša od naše, sploh komunicirala s tako primitivno tehnologijo kot so radijski valovi? Sevanje ozadja in pulzarji, ki oddajajo radijske valove, predstavljajo naravne vire šuma, ki moti komunikacijo galaktičnega interneta. Primer obetavne komunikacijske tehnologije, ki bi jo napredna civilizacija lahko uporabljala, je curek nevtrinov, kar bi podobno razvita civilizacija brez težav zaznala (mi pa zaenkrat še ne).

Druga dimenzija napredka se lahko nanaša na nivo zaznavanja. Danes npr. jasno ločujemo dva konceptualna nivoja: materialnega in informacijskega. Delo lahko opravljamo ne samo z manipulacijo snovi, ampak tudi z obdelavo informacij. Pred samo 500 leti bi se stroj za obdelavo informacij (in koncept softvera) zdel nekaj nepojmljivega. Kako lahko vemo, da se ne bo v naslednjih 500 letih razvil še višji nivo, ki bo npr. temeljil na premikanju informacij, tako kot obdelava informacij danes temelji na premikanju elektronov? Takega procesa ne bi mogli prepoznati niti na nivoju fizičnega sveta (premikanje elektronov), niti na nivoju informacij (tako kot že danes ne moremo razbrati npr. naslova spletne strani neposredno iz opazovanja premikov elektronov).

Nenazadnje pa, kdo pravi, da bi miljon let naprednejša civilizacija sploh rada komunicirala z nami? Preradi predpostavljamo, da so na isti razvojni stopnji kot mi, to je vsaj v cca. letu 1950. To je, da poznajo radijsko tehniko, da se zavedajo, da lahko iz vesolja pride radijski signal, ter da poslušajo. Če so vesoljci že dosegli svojo singularnost in nadomestili naravno evolucijo z umetno, so najbrž postali pametni stroji (megaračunalniki). Biološka inteligenca je, po vseh napovedih, le prehodno obdobje do nastanka intelignetnih strojev.

Torej, če so vesoljci tako ali drugače miljon let pred nami, zakaj bi sploh hoteli komunicirati z nami? Konec koncev tudi mi ne poskušamo komunicirati s šimpanzi, ki so po evoluciji milijon let za nami (ali npr. z glivami, če upoštevamo še eksponentno pospeševanje napredka). Ali se lahko od gliv česarkoli koristnega naučimo? Ali nam lahko razkrijejo poenoteno teorijo vsega ali razložijo nastanek vesolja? Če ne, zakaj bi iskali načine za komunikacijo z njimi. In podobno, zakaj bi se samozadosten megaračunalnik v velikosti planeta, ki bi se zabaval z reševanjem matematičnih problemov, ukvarjal s komunikacijo z biološkimi bitji, ki so v primerjavi z njim na razvojni stopnji glive.

Pod črto, nad knjigo sem bil navdušen; napisana je zanimivo in berljivo ter upoštevaje vsa zadnja in predzadnja znanstvena dognanja s tega področja, vključno z domnevnim Nasinim odkritjem življenja na osnovi arzena. Osvežujoče branje, ki na sistematičen in znanstveno skeptičen način obdela kopico možnih scenarijev in jih podpre s poljudno razlago, številne ZF koncepte pa bodisi kritično razdela ali z dvema stavkoma zdrave pameti postavi na trdna tla. Priporočam!

Za konec pa še en poetičen posnetek iz Nasine Carl Sagan serije na to temo. Life looks for life.

1. To ima za posledico tudi našo antropocentričnost. Ker znamo razmišljati samo v človeških okvirih, si tudi vesoljce najraje predstavljamo kot humanoide, čeprav je verjetnost za to izjemno majhna. [↩]

As promised, Electrons is in the App store, and it’s just amazing.

It’s a charged particle simulator for iPad. It allows you to create dozens of positively or negatively charged particles, either freely roaming in space, or contained within conducting bodies. You can observe complex particle interactions and resulting electric forces, create capacitors, simulate a lightning rod, a cathode ray tube (CRT) and much, much more. Through play, you can effortlessly gain deeper understanding of many natural phenomena. Following the included guided tour of 10 experiments will give you further insights into the world of electricity.

A perfect companion for students and teachers of physics and electrical engineering, or anyone interested in understanding one of the four fundamental forces — the one without which there would be no lightbulbs or elevators, no radio and television, no computers, no Internet, and for that matter—no life.

Electrons app includes an 11-page guide, explaining the basics of electric forces and Coulomb’s law, and provides 10 guided experiments, which you can try on your own. By following them, you will systematically unravel many of the seemingly puzzling mysteries of nature.

By following the guide, you can:
⊕ Get acquainted with the basics of attractive and repulsive forces.
⊕ Learn why electric field inside conductors equals zero.
⊕ Learn why electric field is stronger in corners and pointy edges.
⊕ Simulate an electrostatic shock (redistribution of charge).
⊕ Create a capacitor and observe its homogenous electric field.
⊕ Learn how to create a do-it-yourself electric field probe.
⊕ Learn how to neutralize electric field.
⊕ Demonstrate how a cathode ray tube deflects particles.
⊕ Simulate a lightning rod and observe how it “attracts” lightning.

Disclaimer
Such great teaching aid could not be possible without a true visionary — my professor of Fundamentals of Electrical Engineering (about 10 years ago), late prof. Vojko Valenčič. He has, at the turn of the millenium, envisioned and developed a simulator, ten times more powerful than the Electrons. It was called JaCoB, and is still available freely at jacob.fe.uni-lj.si. Although JaCoB source code is available under GNU GPL, it has not been used in any way in development of the Electrons, which is purely an extension of Gravity Lab. Solely the concepts that prof. Valenčič taught, explained and demonstrated during his courses, and the basic idea behind JaCoB — to make learning of science fun — were used in making of this project. I sincerely wish someone will find it at least a bit as useful as I did JaCoB.

With Gravity Lab, I’ve built what I think is a decent particle simulation framework. Which brings me to my hidden agenda: something I’ve wanted to do for a long time, but could only do incrementally, since the complexity of the entire task was just too overwhelming. So I present to you another particle simulator, codenamed Charges.

It was a no-brainer, really. Ok, sure — there’s no money in educational apps. There’s that. But the thing was practically already done. Electric forces are just like gravitational forces: obeying inverse square law (read more here, or here). There’s just a matter of inverting the polarity, i.e., introducing “negative masses”. And change some constants.

Or so I thought.

It turns out a charged particle simulator is pretty useless by itself: particles always recombine (i.e., neutralize each other), or fly far away from each other until they get garbage-collected.

What I needed were solid (metallic) objects, which could trap the particles — so I could observe the forces, make capacitors, simulate cathode ray tubes (CRT), and generally bring the “static” into “electrostatic”. So I decided to implement objects. And this is an epic journey of a developer, struggling with an interesting problem and generating much flow™ in the process.

Simple enough, I decided to support rectangles and circles only. Why? Because this way, it can be quite easily checked whether a particle has hit the wall. When you tap the screen, I simply loop through an array of all objects and check if you tapped inside a body. If I find that to be true, I set the parent of the particle to the ID of the body. Then, when calculating the motion of the particle (which is done by summing all the forces of all the other particles), I only need to check if the particle has hit the parent object’s wall. If parent object is a rectangle, it’s really simple, like this:

if rectangle
    if parent.left_wall.x < particle.x < parent.right_wall.x
        move freely (left or right)
    else
        dont move along x axis
    end

    if parent.bottom_wall.y < particle.y < parent.top_wall.y
        move freely (up or down)
    else
        dont move along y axis
    end
end

With circles, I’ve already hit the first obstacle. You can’t separate x and y coordinate checking into separate conditions, because they are dependent. I tried many options without real success and particles always got stuck in some kind of deadlocked state. What finally proved to be the most efficient solution, was checking if the particle’s future position is too far away from the circle center (more than circle radius away), and projecting it back onto the circle boundary. Like this:

if circle
    if (x^2 + y^2 < circle.radius^2)
        move freely along x and y
    else
        phi = atan2(y,x)
        x = circle.radius * cos(phi)
        y = circle.radius * cos(phi)
    end
end

It worked like a charm. But I faced a more dire problem, one that could not be solved in my limited particle-has-a-single-parent model. Namely, my particles couldn’t migrate from one parent to the next. Which would, of course, happen in nature: if you bring together a charged metallic object and an uncharged metallic object, some of the charge from the first one will be forced out into the second one.

I wanted that, and it obviously couldn’t be done. Indeed, the composite objects made of circles and rectangles can become quite complex; how could one force the particles to stay within an object in such simple terms as shown above?

I slept on it, and slept some more. And for the first time I can remember, the solution suddenly blinded me one morning. Yesterday’s morning, that is. And it goes like this.

Timesharing.

Let me explain. If a particle happens to be inside an overlap of two or more metallic objects (i.e, inside two or more objects at the same time), cycle through all of them every n frames of the animation. Let them all be parents, but not at the same time. And let the electrostatic forces that drive the particles away from each other do all the work.

The bottom right particle in the picture above desperately wants to break away, to the South-East direction (down and to the right). If we bring in another body, the particle now has 2 parents (overlap). We iterate through both of them and let the particle just savor the moment for a while. And the moment it is assigned to object 2 above, it is propelled towards South-East, no longer bound by the first object. When there’s no more overlap, the time-sharing doesn’t happen any more. Voila.

So hopefully, a new and amazing simulator will soon hit the App store. Stay tuned.

It’s been well over a month since Gravity Lab 1.0 was released. Now it has received a nice update with particle trails and a solar system preset. The solar system is actually just a set of bodies with preset masses and initial velocities¹. The resulting setup is quite a faithful representation of the real solar system, down to the orbiting times (i.e., the lengths of planetary years) in correct proportions. And there’s also a satellite preset.

Now you can test first-hand the effects of a stray sun wandering into our planetary system and ejecting Earth into outer space.

There’s also a new and interesting setting — adjustable gravitational constant, which allows you to distort the simulated universe and observe the consequences.

1. planetary masses courtesy of Wolfram Alpha; initial velocities were determined such that a stable orbit was ensured [↩]

Gravity Lab is an iPad gravity simulator. It allows you to create massive bodies on a 2-D plane and set their initial velocities by dragging your finger. Their attraction is then simulated, which causes them to accelerate (and combine) according to Newton’s law of universal gravitation. Newton’s law states that every massive body in the universe attracts every other massive body; such attraction is proportional to masses of both bodies and inversely proportional to the square of the distance between them.

All beings living on Earth’s surface become, through life’s experience, intimately acquainted with the force of gravity. Gravity keeps us from drifting freely into space. Yet there’s something extremely limiting in our perception: the only significant gravitational force that we can perceive is that of the Earth, which has mass approximately 60,000,000,000,000,000,000,000 times greater than an average human being standing on its surface. The gravitational attraction doesn’t feel very mutual (although the forces of attraction of both bodies are equal in size), which is due to the much higher mass and consequently higher inertia of the Earth.

Gravitational force is also the weakest force in nature, either compared to electromagnetic, weak or strong force. Take a look at the comparison here. The strength of the gravitational attraction is for a factor of 10³⁶ (or 1,000,000,000,000,000,000,000,000,000,000,000,000) times weaker than the electromagnetic force (which also works universally — that is, with unlimited range). The value of the gravitational constant G used to calculate the force in the Newton’s equation: F=Gm₁m₂/r² is 0.00000000006674, which means the masses have to be extremely large and distances reasonably short for force F to become noticeable.

That’s where a simulator can help. Generating large massive bodies has never been easier. The simulator then calculates and updates the forces between them in real-time and, besides helping you get a feeling of how gravity works on a larger and more massive scale, also allows you to perform different experiments and demonstrate various phenomena:

• create your own solar system
• demonstrate complex interaction patterns of multiple massive bodies
• collide massive bodies and demonstrate the conservation of momentum
• display vectors of acceleration due to gravitational forces and observe the acceleration of orbiting bodies
• observe first two of the three Kepler’s laws of planetary motion
• demonstrate gravitational slingshot (gravity assist) for increasing the spacecraft’s velocity, etc.

More info and purchase: