Hackerspace (page-2)
Waterloo, Ontario, Canada.

  1. StarTalk: Neil deGrasse Tyson reminds us why we celebrate Earth Day

    Learn how a NASA selfie in 1968 and moon-landing in 1969 triggered new agencies (EPA, and NOAA) to protect our air and water.
    quote: we journied to discover the moon but then we discovered the Earth


    Laying the ground-work: Winner of 8 awards, Rachel Carson's 1962 book "Silent Spring" is the history making bestseller that stunned the world with its terrifying revelation about our contaminated planet. No science-fiction nightmare can equal the power of this authentic and chilling portrait of the unseen destroyers which have already begun to change the shape of life as we know it. "Silent Spring" is a devastating attack on human carelessness , greed and irresponsibility. It should be read by every American who does not want it to be the epitaph of a world not very far beyond us in time.”

  2. When I was a teenager in the 1960s, many people (except medical and legal professionals) aspired to be scientists, engineers, technologists or technicians. It seemed that everyone was reading magazines like Scientific American, Popular Science and Popular Mechanics. A real "can do" attitude existed everywhere in our society. For example, when President John F Kennedy announced America's intention to visit the Moon before the end of the decade, naysayers complained that the goal was impossible because the technology did not exist. Meanwhile, once funding was in place, other "can do" engineers and scientists simply created the technology. Both the internet and "personal computers" are two spin-off technologies which were never dreamed of by anyone when Kennedy publically gave his moon shot speech in 1962 but by the mid 1970s it appeared that everyone was building computer kits (like the Altair 8800 or the Heathkit H8) or were buying personal computers (like the Apple-2 or the Radio Shack TRS-80). Within 5 years it seemed that everyone was reading Byte magazine and/or attending nightly college courses to learn computer programming and/or digital electronics. Life today is much different. It appears to me that life this side of 1995 is considerably different with many people aspiring to be politicians, political advisors, political aids, or just political pundits with a YouTube channel. The "can do" attitude has been replaced with a "can't do" political divisiveness with wannabe millionaires calling for taxes cuts and austerity (why should I be expected to pay for that?). Just at a time when humanity has become dependent upon science and technology, western civilization has decided to replace scientific facts with political opinion.
    Now watch this video: https://www.youtube.com/watch?v=D99qI42KGB0
  3. Science is Bigger Than Politics. Neil deGrasse Tyson on The rise (and fall?) of America (from Abraham Lincoln's founding of the National Academy of Sciences in 1863, to the US currently leading the world in the Nobel Prize count (a third of which we owe to immigrants), America was built on science. What happens when we doubt and defund it?
    Transcript: I have to chuckle a little bit when I'm approached by anybody, but in particular journalists, and say, “Are scientist worried that the public is in denial of science or is cherry-picking it?” And I chuckle not because it's funny but because they're coming to me as a scientist when they should be going to everyone. Everyone should be concerned by this, not just scientists. In fact, scientists will just continue as they're doing. You might withdraw funding, but then there isn't any science done—okay. You are transforming your civilization if you choose to either stand in denial of science or withdraw science funding from those who are actually doing the research. Everything we care deeply about that defines modern civilization pivots on innovations in science, technology, engineering and the math that is the foundational language for it all. Everything: transportation, your health, your communication through smart phones that talk to GPS satellites to find out where Grandma is. To make a left turn to find her address or the nearest Starbucks. Whatever is your need, whatever is your want, the emergent innovations in science and technology are not only enabling it, they are creating for you solutions to challenges you always lived with but never thought that they could be solved. The message is clear: if you do not understand what science is and how and why it works—by the way, I'm not even blaming you. I look back as an educator, I look back to K through 12, kindergarten through 12th grade, and I say there's something missing there. If you, as an educated adult, can say, "This is what these scientists agree to, but I don't agree with them." If that sentence even comes out of your mouth it's like: oh my gosh. Okay, well, we live in a free country, you can say and think what you want. I'm not even going to stop you. But if you rise to power and have influence over legislation and that legislation references what you think science is but is not, that is a recipe for the unraveling of an informed democracy. So I'm not even going to blame you. It's not your fault. Click here to read more
  4. George Clooney speaks against Rampant DUMBF**KERY on ABC's Jimmy Kimmel Live! while promoting: UDUMASS (United to Defeat Untruthful Misinformation And Support Science)

    NSR comments:
    • If your idea of "doing research" involves looking up stuff on the internet then this message is for YOU!
    • If you think you are smarter than climate scientists or vaccine scientists then this message is for YOU!
    • If you only see the world through the prism of politics then this message is for YOU!
    • If you are an American, Canadian, or British politician then this message is for YOU!
    • If you are permanently tied to one political party (left or right) then this message is for YOU!
    • If you believe that "any" internet-based news outlet or podcast " does real journalism" then this message is for YOU!
      • do you really think that these outlets triple-checks the accuracy of their sources the same way traditional newspapers did before they lost business to fire-and-forget websites? On top of that, website publishers seem to be more interested in money than accuracy. In the 1970s a small group of newspaper publishers stuck together to publish the truth. Their readers where able to convince Congress to begin impeachment hearings against Richard Nixon which resulted in him resigning. I do not think this could ever happen in the era of the internet.
    • If you believe everything you see on television then this message is for YOU!
      • there are times when FOX NEWS appears to act like the official propaganda arm of the "far right". This should be troubling for anyone with knowledge of propaganda during world-war-2
  5. I just heard this on the CBC radio program IDEAS which I publish as food-for-thought: Reclaiming Marxism in an Age of Meaningless Work
    https://www.cbc.ca/radio/ideas/reclaiming-marxism-in-an-age-of-meaningless-work-1.5175707
    comment: While it is true that Marx published some wacky stuff (the communist manifesto first springs to mind), Marx's description of how capitalism failed Europeans of the 1840s (after the promises  by Adam Smith in the middle to late 1700s) sounds very familiar to how extreme capitalism is failing most people today, except the very rich. In Marx's time, he worried that the very rich "didn't ever think about the rest of humanity" and I fear the same is true today. Listen to the program at least once even if you don't agree with everything that is presented. At least you might get a handle on some of the ideas of the economic theory known as Marxism.
  6. beach covered with one-time use plasticThe European Union announced that they will ban one-time use plastic products by 2021.

    This includes: stir-sticks, drinking straws, cutlery, soft-drink containers, and shopping bags.

    They stated:  if something isn't done now, then by 2050 there would be more plastic in the ocean than fish.

    Canada announced it will follow Europe's lead and also ban single-use plastics by 2021.

    Comment: Most people would agree that using petroleum (a non-renewable resource) to create single-use plastic products (drinking straws, knives, forks, spoons, coffee cup lids, and cream containers) is wasteful as well as stupid. This is made worse by the fact that less than 9% of all plastic is recycled with the remaining amount going to land fills or, eventually, the ocean. Did you know that those resin identification codes imprinted upon plastic products is almost useless? Numbers "1" and "2" can be easily recycled while numbers "3" through "7" can only be recycled with great difficulty so are usually shipped elsewhere or discarded.
     
    Ecologic Brands
    1) Almost all powered protein supplements are retailed in large, heavy (thick) plastic containers so view the container pictured to the right. This is not a plastic bottle. It is a much lighter, crushable cardboard container employing a thin plastic bag to protect the powered protein inside (too bad they have not yet ditched the plastic lid). Although the protein is from Bodylogix, the container was manufactured by Ecologic Brands. Click here, here and here to learn more.

    2) Question: What's wrong with these pictures of two competing toothpaste products? Answer: the second product employs more waste plastic in the lid which YOU pay for then discard. Suggestion: always buy the product with the smallest ecological foot print.
    crest colgate

    coffee creamer3) More Insanity: Manu people drink multiple cups a coffee each day then throw in one to two creamers each time. Now you have really got to think about this one: an inexpensive biologically replaceable resource (cow's milk) is served up in a one-time use plastic made from a non-renewable resource (petroleum). Suggestion: until dairy producers move their product into cardboard containers, we must reduce or eliminate the use of plastic creamers

  7. co2 across the ice agesChildren born now could live to see the oceans rise well over 1 m (3.2 ft) by 2100. Even conservative forecasts of sea level by 2100 are now rising above the meter mark for high emission scenarios. The last report from the Intergovernmental Panel on Climate Change in 2013 concluded that sea level could rise between 0.3 and 1 meter by 2100 depending on how much carbon dioxide we emit. Now a study by Tamsin Edwards of King’s College London has added 0.2 meters [to the IPCC report]. “Our likely range is about 20 centimeters higher” says Edwards. Other studies have come to similar conclusions. In fact, the IPCC is set to up its projections: according to a leaked version of an upcoming IPCC report, sea level will rise by as much as 1.3 meters by 2100. In the US alone, a 0.9 meter rise in sea level rise would displace 4 million people. Global average sea level has already risen around 0.3 meters since 1880. There are three key questions about what happens next: How much higher will the sea rise for a given amount of warming? How fast will it rise? And will the loss of some ice sheets become unstoppable once set in motion, as several recent studies suggest? The only way to find out is by looking at the past and using computer models. But our knowledge of past sea level changes is poor, and computer models of ice sheets are relatively new and crude, so there are huge uncertainties. The 2013 IPCC estimate of up to 1 meter assumes hardly any contribution from Antarctica. However, as the report itself acknowledged, many researchers think the unstable West Antarctic sheet could start to lose a lot of ice long before 2100. continued here...

    comments:
    1) according to tide gauges by sea-faring nations, sea level increased by 19.5 cm (~ 7.7 in) between 1870 and 2004 which equates to 1.44 mm per year. Radar measurements by satellites show the new value as 3.3 mm per year. So even if you do not accept the fact that the rate-of-rise is accelerating, sea level is absolutely guaranteed to rise an additional 33 cm (~ 13 in) in the next 100 years but remember that this rise is vertical. Beaches are sloped which means that tide-surges will make things a lot worse much sooner.
    2) Ocean rise should not be a surprise to anyone educated in ice ages where CO2 levels normally bounce between 180 ppm (when in an ice age) vs. 280 ppm (when in an interglacial). Why? During an ice age a lot of water accumulates in glacial ice. But humanity's industrial age has pushed co2 levels more than 130 units past 280 which is pushing "the melting of ice" to a totally new place. Had we known this earlier, then none of us would have built large cities so close to the coast. I fear that Venice Italy stands as a symbol for American cities like New York, San Francisco and Miami to only name three of many.
    3) Some climatologists have hypothesized that sea level on Earth (where water covers 70% of the globe) has a near-linear relationship with co2 levels where 100 pm translates into ~ 100 ft. When I first heard this I was skeptical of the units and values until I later learned that "one foot" was just their lowest starting point. But where did they get that number? Well, is now commonly accepted that humans walked to North America via the Bering Straight at a time when the ocean level was much lower than it is today. These migrations happened numerous times so it is difficult to determine the exact time periods BUT some ancient human artifacts have been located 120 ft below the current surface. So here's what worries me: let's assume that an increase in co2 levels triggers new melting which causes the ocean levels to rise even more. The industrial age increased co2 from 280 to the current value of 410 so can we assume that we will see the oceans rise another 128 feet?

  8. In his latest book titled Light of the Stars, astronomer Adam Frank presents convincing information that variable 'L' in the Drake Equation should be changed from " self destruction through nuclear war" to " self destruction though climate change". He argues that even if some extraterrestrial civilizations had never developed nuclear weapons (as humanity did), all would eventually grow to a size where their collective actions would change their climates, and possibly outstrip their natural resources. This is an extrapolation of the predator-prey model (described in the book) which was previously used to model the collapse of various civilizations where local people outstripped their resources ( Easter Island, The Mayans, etc.)

    comment-1: What does this say about what humanity is currently doing to planet Earth? In the era of mutually assured destruction (MAD), a large number of western citizens advocated for nuclear de-escalation because the thought of an accidental conflict seemed too great. Today, many people seem to think that a healthy economy is more important than a healthy biosphere. In fact, many people with financial ties to the old economy are actively working to speed the collapse by denying that the climate is warming or that is is human induced.
    comment-2: Many climate deniers do not believe it is possible for modern humans to change Earth's atmosphere. And yet, it was the action of microscopic stromatolites (cyanobacteria) that added oxygen to Earth's atmosphere ~ 3.5 billion years ago.
  9. Computers speak a simple language known as binary. The lexicon is built from digital 0s and 1s, so the 'C' letter at the start of this box would be represented as an elaborate code: '01000011'. The dominance of binary is partly due to computers being built from transistors, electrical switches that either allow current to flow or not, and nothing in between. These two well-defined states stand in neatly for 0 and 1. But there’s a newer electrical component on the scene called a memristor (see main story). These devices are becoming more and more useful in computers built to mimic the brain, and they are plenty more versatile than the transistor. Rather than being simply on or off, they can adopt several different states of resistance. Last year, researchers led by Vikas Rana at the Peter Grünberg Institute in Jülich, Germany, got a set of memristors successfully performing calculations in a ternary language, which uses the digital equivalent of 0s, 1s and 2s. This means memristors could allow computers to compute much more efficiently. And it doesn’t have to stop at base 3; memristors can reliably adopt at least seven, and possibly more, resistive states.

    Continued here: New Scientist (2 August 2017)

    Comment: quantum computing (as opposed to quantum communications) is the focus of much research because (entanglement aside) it primarily moves from two digital states (0+1) to three (0-middle-1) but most punters overlook the huge liquid nitrogen cooling tanks. It seems to me that memristor-based technology (with 7 or more states) might be a better candidate for certain applications like neural nets and artificial intelligence. Sci-fi author, Isaac Asimov, employed the phrase "positronic brain" as at literary device meaning "fill in the blank". I wonder if memristor technology could fill this roll
    • Size differences in two brain structures, the amygdala (larger in conservatives) and the anterior cingulate (larger in liberals), bias human perspective of the world. Therefore ...
    • Conservatives see most issues as "black and white" while liberals see "shades of gray"
    • Conservatives play politics as a team sport so will almost always "vote their party" while Liberals will split their vote choosing alternate parties (now you know how Trump got in)
    • Conservatives (larger amygdala) are more fearful of others so are more easily encouraged to vote for POPULIST issues like "building the wall" or BREXIT (funny point: Britain had the lowest number of Syrian immigrants but apparently the highest political reaction against them)
    • Since conservatives only see things as black and white, they try (and sometimes succeed) in converting liberals over to their way of voting. It seems to me that the reverse never happens
  10. Skeptic Magazine ( http://www.skeptic.com/magazine/archives/20.3/ ) contains a story about a contest Alfred Russel Wallace entered in 1870 to prove the Earth was round. (see: https://en.wikipedia.org/wiki/Alfred_Russel_Wallace#Flat_Earth_wager for a less detailed version of the story)

    Every citizen today should read this story paying special attention to the reactions of his opponent, John Hampden, who believed data from Wallace's experiment proved the Earth was flat. Wallace was declared the winner and so won 500 pounds but lost it all in court costs when Hampden would not stop personal attacks while refusing to acknowledge the evidence. Why would the courts allow this? Remember that this occurred in Victorian England at a time where many respectable people were seance-attending spiritualists. I find it difficult to understand that this could happen in the country of Isaac Newton approximately 150 years after Newton's death. The point I am trying to make is this: today's climate change deniers claim to be on the side of Galileo but they are really Flat Earthers
  11. Isaac Asimov on PBS

    Isaac Asimov PhD
    (Biochemistry)

    "There is a cult of ignorance in the United States, and there always has been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."

    -- Isaac Asimov (Column in Newsweek, 21 January 1980)

    Excerpt from Wikipedia: Isaac Asimov was an atheist, a humanist, and a rationalist. He did not oppose religious conviction in others, but he frequently railed against superstitious and pseudoscientific beliefs that tried to pass themselves off as genuine science. During his childhood, his father and mother observed Orthodox Jewish traditions, though not as stringently as they had in Petrovichi, Smolensk Oblast, Russia; they did not, however, force their beliefs upon young Isaac. Thus he grew up without strong religious influences, coming to believe: "that the Torah represented Hebrew mythology in the same way that the Iliad recorded Greek mythology". When he was age 13, he chose not to have a bar mitzvah. As his books Treasury of Humor and Asimov Laughs Again record, Asimov was willing to tell jokes involving God, Satan, the Garden of Eden, Jerusalem, and other religious topics, expressing the viewpoint that a good joke can do more to provoke thought than hours of philosophical discussion.

    comment: I wished fundamentalist Christians considered the same perspective
  12. Facts, Hypothesis, Theory, Law: Explained!  https://www.youtube.com/watch?v=lqk3TKuGNBA
    1. Facts are observations
      • the Sun rises in the morning then sets in the evening
    2. Hypothesis ( hypo-thesis literally means 'below thesis') is a proposed explanation; here are three of many:
      1. the Sun moves around the Earth (jump to step 3a)
      2. the Earth moves around the Sun (jump to step 3b) in circles
      3. all planets moves around the Sun in elliptical orbits (although they all have different elliptical eccentricities)
    3. Theory is the result of an experimentally tested Hypothesis; at this point a scientist will write, then publish, a thesis 
      1. experimental test of hypothesis 2a...
        • passes (until the era of precision measurements) so jump to step 4 to build models (mathematical, mechanical, computer-based, etc.)
        • fails during the era of precision measurements (Tycho Brahe) so go back to step 2 to develop hypothesis 2b
      2. experimental test of hypothesis 2b...
        • passes for a time (we have a theoretical understanding of the issue) so jump to step 4
        • fails during the era of evermore precise measurements so jump to hypothesis 2c
    4. Law is a detailed mathematical description
      • develop a model to test the hypothesis with greater precision (early physical models were machines; modern models employ computers)
      • many times, a successful theory produces yet-unobserved predictions (eg. Atomic Theory, Quantum, Theory of Gravitation)
      • improved observations (new facts) through newer instrumentation may force us back to step 2 (eg. General Relativity morphs into General Relativity)
  13. A.I. has been shifting from an "engineering discipline" (expert systems was the most visible practical success before IBM's Watson) to a "cognitive science" discipline for a while now. This shift has forced researchers to view the human mind from a different perspective. One proposal by Daniel Kahneman separates the human mind into two abstractly labeled modules colloquially referred to as system-1 and system-2 (abbreviated: S1 and S2). S1 is a high-speed parallel processor evolved for avoiding hungry lions but also handles wrote intelligence ( what is "2 plus 2"?) while S2 is a serial processor which deals with higher level procedural intelligence ( what is "19 times 21"?).
     
    S2 requires more energy and concentration (not something you want to be doing while being chased by a lion) so idles until activated by S1.
    • Example 1
      • "S1 immediately engages S2 but fails to pass accurate information to S2 (causing S2 to make an error)"
    • Examples 2-5
      • "S1 will answer incorrectly without ever engaging S2"
    • Example 6
      • "S1 immediately engages S2; S2 employs a little algebra to compute the answer then notifies S1; S1 doesn't believe S2 so requests S2 to double-check; S2 repeats the solution then notifies S1; S1 still doesn't believe S2 so requests S2 to perform a detailed rationalization of where S1 had gone wrong"
    • Example 7
      • "S1 will do a preliminary scan of the facts then will usually give up as soon as it notices one facts is missing; Sometimes S1 will defer to S2 which may dig deeper then make the same mistake; However, sometimes experienced "logicians" or "digital circuit designers" will notice that "since two of three facts were provided" that a possible solution might exist. So those people will reengage S2 to produce the correct answer.

    Examples:
    algebra with fruit
    1. This graphical algebra problem employs picture symbols rather than x, y and z. (answer)
      step-1: "Apple = 7"; step-2: "Pear = (7+5) = 12"; step-3: "Three Bananas = (7-1) = 6"; therefore: One Banana = 2; step-4: "2 + 12 + 7 = 21";
    2. "All flowers need water. All roses need water. Therefore, all roses are flowers". Is this logically true? (answer)
      S1 usually answers "yes" but this is logcially false as many things require water
    3. A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost? (answer)
      S1 usually answers 10 cents but the correct answer is 5 cents (Proof: 1.05 + 0.05 = 1.10)
    4. If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets? (answer)
      S1 usaully answers 100 but the correct answer is 5
    5. A lily is placed in a lake. Every day the lillies doubles in number. If it takes 48 days for the litty patch to cover the entire lake, how long would it take for the patch to cover half of it? (answer)
      S1 usually answers 24 but the correct answer is 47
    6. Three people check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later the clerk realizes the bill should only be $25. To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realizes that he cannot divide the money equally. As the guests didn't know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $2 as a tip for himself. Each guest got $1 back: so now each guest only paid $9; bringing the total paid to $27. The bellhop has $2. And $27 + $2 = $29 so, if the guests originally handed over $30, what happened to the remaining $1? (answer)
      The misdirection in this riddle is at the end of the description, where a bunch of unrelated totals are added together, and the listener assumes these numbers should add to 30 (should be 27 after the 1 dollar refund)
    7. Jack is looking at Anne but Anne is looking at George. Jack is married but George is not. Is a married person looking at an unmarried person? Possible answers are: "yes", "no", and "cannot be determined" (answer)
      At first their appears to be insufficient information. But let's assume that Anne is unmarried. In this case the question would be true. Now let's assume that Anne is married. Once again, the question is true. This reducation in the size of logic happens all the time when digital engineers employ "boolean algebra"
  14. chloroplastThe computed World Human Population Limit
     
    A little math proves the current human population is already too large at 7.57 billion (this is a real-time counter BTW). Anything higher (caveat: humanity adds 1 billion every 12 years) is certainly out of the question. Why?

    Higher temperatures reduce the efficiency of photosynthesis resulting in a loss of agricultural productivity (biologists estimate a 10% drop for every degree increase). This is a shift in the direction of famine, disease (due to compromised immune systems), war (due to food and water shortages), and death. Since photosynthesis is required to replenish atmospheric O 2 (oxygen), then we can expect O 2 to drop as well. So I guess it should be no surprise that...

    Atmospheric oxygen levels have been dropping ever since measurements began in 1990. While CCS (carbon capture and storage) technologies promise to limit some CO 2 releases, any burning of fuel will continue to consume atmospheric oxygen. So when calculating the optimum human population we also need to include the number of large internal combustion engines. (for now, just think about the number of ocean-going boats, jet airplanes, locomotive engines, and one billion functional automobiles). Now for one additional thought...

    Many people mistakenly believe higher CO 2 levels "are good for plants" and "will trigger plant growth" (some people call CO 2 the gas of life). First off, atmospheric CO 2 levels have risen from 315 to 405 ppm (an increase of 28.5%) ever since direct annual measurement began in 1958 but humanity has not noticed any explosion of plant life to compensate for the increase (if we did, we might not have seen an increase in CO 2 levels). Secondly, this schematic diagram of photosynthesis shows the first stage involves the photolysis of water by sunlight (this is the only place where oxygen is released to the atmosphere). This diagram is proof that sunlight (input 1) and H 2O (input 2) are more important than CO 2 (input 3) but each ingredient is considered a limiting factor to maximum photosynthetic productivity (it goes without saying that there is no release of oxygen on short days, cloudy days, or at night). The majority of plant life acquires water through roots rather than the atmosphere. Higher temperatures will evaporate a greater volume of water into the atmosphere making it bio-unavailable to plants. While more evaporation usually translates into more rain fall, higher temperatures will send it back into the atmosphere sooner.
  15. Baruch Spinoza was a 17th century Dutch Jewish philosopher (1632-1677). He was known for his radical views on religion and politics. As a young man, he was banned by his own religious community for his scandalous ideas. He made his living by grinding precision lens for scientists. He died young, at the age of 44, presumably from inhaling glass dust. Spinoza did not believe that God created the heavens and earth - the universe.  For Spinoza, God was equivalent to all of nature. He believed that "false religion" created superstition.  A "true religion," on the other hand, was liberating because it allowed freedom of thought. The Europe of 17th century was a place  of stifling religious orthodoxies, strife and war. Spinoza believed in freedom of thought and the principle of religious tolerance. Spinoza also had radical ideas about the nature of politics. He believed in democracy. He is credited with helping to shape the revolution in human thought known as The Enlightenment.
     
    CBC IDEAS host Paul Kennedy explores how Spinoza's thoughts on God, the universe, ethics and politics helped ignite the flame what became known as the Enlightenment.
    http://www.cbc.ca/radio/ideas/spinoza-1.2913483 Audio: 53:59
  16. RadiometerIn 1873, while investigating infrared radiation and the element thallium, the eminent Victorian experimenter Sir William Crookes developed a special kind of radiometer, an instrument for measuring radiant energy of heat and light. Crookes's Radiometer is today marketed as a conversation piece called a light-mill or solar engine. It consists of four vanes each of which is blackened on one side and silvered on the other. These are attached to the arms of a rotor which is balanced on a vertical support in such a way that it can turn with very little friction. The mechanism is encased inside a clear glass bulb where the air has been pumped out to partial vacuum.
    Observations/Explanations:
    • When sunlight falls on the light-mill, the vanes turn with the black surfaces apparently being pushed away by the light (is photon momentum being absorbed?)
    • In 1901, with a better vacuum pump, Pyotr Lebedev showed that the radiometer only works when there is low pressure gas in the bulb but the vanes stay motionless in a hard vacuum. This is proof that the thermal properties of the low pressure gas are responsible for the motion, not the direct action of photons. Climate-Warming Food-for-thought: too much gas traps too much heat causing the machine to stop working.
    • The radiometer can also be made to rotate backwards in a refrigerator.
    • Other mistaken explanations for the radiometer: Since the black side of each vane would absorb heat from infrared radiation more than the silver side, then this would cause the rarefied gas to be heated on the black side.  In that case, the obvious explanation is that the pressure of the gas on the darker side increases with its temperature, creating a higher force on the dark side of the vane which thus pushes the rotor around.  Maxwell analyzed this theory carefully and discovered that, in fact, the warmer gas would simply expand in such a way that there would be no net force from this effect, just a steady flow of heat across the vanes.  So this explanation in terms of warm gas is wrong, but even the Encyclopedia Britannica gives this false explanation today.  A variation on this theme is that the motion of the hot molecules on the black side of the vane provide the push.  Again this is not correct, and could only work if the mean free path between molecular collisions were as large as the container, instead of its actual value of typically less than a millimeter.
    • The correct solution to the problem was provided qualitatively by Osborne Reynolds in 1879 in a paper to the Royal Society in which he considered what he called "thermal transpiration". To explain the radiometer, therefore, one must focus attention not on the faces of the vanes, but on their edges.  The faster molecules from the warmer side strike the edges obliquely and impart a higher force than the colder molecules.  Again, these are the same thermo-molecular forces responsible for Reynolds' thermal transpiration.  The effect is also known as thermal creep, since it causes gases to creep along a surface that has a temperature gradient.  The net movement of the vane due to the tangential forces around the edges is away from the warmer gas and towards the cooler gas, with the gas passing around the edge in the opposite direction.  The behavior is just as if there were a greater force on the blackened side of the vane (which as Maxwell showed is not the case); but the explanation must be in terms of what happens not at the faces of the vanes, but near their edges.

Neil Rieck
Waterloo, Ontario, Canada

Yes, this is the old "Laptops and Lederhosen" site