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What does “law” mean in “laws of nature?” ELA and Science
What does the word “law” mean in the phrase “laws of nature?” We won’t be able to understand the science until we understand the English.
In our English language arts classes we have learned about homographs – words spelled the same but have different meanings.
For instance, what is a “bow?” With the same spelling it used for 4 entirely different words.
bow – noun, the front of a boat
bow – verb, to bend at the waist.
bow – noun, a type of ribbon we used to decorate a present.
bow – noun, sporting equipment used to shoot arrows.
The same is true for the word “law.” It can refer to three different things:
Laws made up by people
City, state, or national “laws” aren’t real in any scientific sense. They aren’t part of the universe. They don’t even stay the same. They change all the time.
How old does one have to be in order to vote? How fast can you drive a car on the road? How much property tax does a homeowner have to pay on a house?
None of those rules are part of the universe. These “laws” are just things that people agree on. Nothing more. People get together in communities, clubs, or governments, and decide upon rules so that (hopefully) their society runs safely and smoothly.
Natural law
The idea of natural law is a somewhat controversial idea in philosophy, ethics, and religion. The idea is that there are universal moral laws in nature that mankind is capable of learning, and obligated to follow.
This idea is held by some religious groups and some schools of philosophy.
It isn’t necessarily related to religion; there are many non-religious people who believe in the necessary existence of natural law.
image from commons.wikimedia.org
Laws of nature
In physics, a law of nature is something scientists have learned about how things in our physical world actually work.
A law of nature is a precise relationship between physical quantities, and is expressed as an equation.
Laws of nature are relationships universally agreed upon – but not agree upon because we want this relationship to exist. Rather, the law is only accepted because repeated experiments show us that this relationship exists.
People don’t decide what nature’s laws are. People can only investigate and discover what they are.
Here’s an example: Electrical charge is conserved. The total electric charge in an isolated system never changes. People can’t pass a law that says “positive charges can now be created.” That won’t work. Nothing humans say changes the way that the universe works,
Laws of nature are true for every time and every place. They are just as true in Michigan, Moscow, or Miami, just as true on the Moon or on Mars. They are just as true 10,000 years ago as today, and as next year.
We explore the concept of laws of nature in more detail here – What are laws of nature? What are theories?
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Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Rotating space stations in fact and science fiction
This resource – rotating space stations in fact and science fiction – may be used with our resource on Artificial gravity in a space station.
Some people prefer to start here, learning the ideas and designs first, and then look at the physics in more detail. Others prefer the reverse order. Both ways are fine.
Big idea: Building a rotating space station with artificial gravity isn’t a far-out sci-fi idea. The idea has its roots in firm, realistic engineering & science. Most of the designs based on this idea are quite realistic (at least until we get to the world-sized megastructures at the end of this unit.)
NASA 1950s concept
From Dan Beaumont Space Museum
In a 1952 series of articles written in Collier’s, Dr. Wernher von Braun, then Technical Director of the Army Ordnance Guided Missiles Development Group at Redstone Arsenal, wrote of a large wheel-like space station in a 1,075-mile orbit.
This station, made of flexible nylon, would be carried into space by a fully reusable three-stage launch vehicle. Once in space, the station’s collapsible nylon body would be inflated much like an automobile tire.
The 250-foot-wide wheel would rotate to provide artificial gravity, an important consideration at the time because little was known about the effects of prolonged zero-gravity on humans.
Von Braun’s wheel was slated for a number of important missions: a way station for space exploration, a meteorological observatory and a navigation aid. This concept was illustrated by artist Chesley Bonestell.
Graphic – NASA/MSFC Negative Number: 9132079. Reference Number MSFC-75-SA-4105-2C
2001 A Space Odyssey
Perhaps the most classic design of a rotating space ship comes from 2001: A Space Odyssey. This was a 1968 epic science fiction film by Stanley Kubrick, and the concurrently written novel by Arthur C. Clarke. The story was inspired by Clarke’s 1951 short story “The Sentinel.”
The film is noted for its scientifically accurate depiction of space flight. The space station was based on a 1950s conceptual design by NASA scientist Wernher Von Braun.
Classic rotating spacestation designs
The High Frontier: Human Colonies in Space is a 1976 book by Gerard K. O’Neill, a road map for what the United States might do in outer space after the Apollo program, the drive to place a man on the Moon and beyond.
It envisions large manned habitats in the Earth-Moon system, especially near stable Lagrangian points. Three designs are proposed:
Island one (a modified Bernal sphere)
Island two (a Stanford torus)
Island 3, two O’Neill cylinders. See below.
These would be constructed using raw materials from the lunar surface launched into space using a mass driver and from near-Earth asteroids. The habitats spin for simulated gravity. They would be illuminated and powered by the Sun.
O’Neill cylinder
Consists of two counter-rotating cylinders. The cylinders would rotate in opposite directions in order to cancel out any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun.
Each could be 5 miles (8.0 km) in diameter and 20 miles (32 km) long, connected at each end by a rod via a bearing system. They would rotate so as to provide artificial gravity via centrifugal force on their inner surfaces.
The space station in the TV series Babylon 5 is modeled after this kind of design.
(This section adapted from Wikipedia.)
A pair of O’Neill cylinders. NASA ID number AC75-1085
–
Rick Guidice, NASA Ames Research Center; color-corrector unknown
Inhabitants on the inside of the outer edge experience 1 g. When at halfway between the axis and the outer edge they would experience only 0.5 g. At the axis itself they would experience 0 g.
https://www.youtube.com/watch?v=qD3GMwg4qZo
Visions Of The High Frontier Space Colonies of 1970
Rama
In his 1973 science fiction novel Rendezvous with Rama, Arthur C. Clarke provides a vivid description of a rotating cylindrical spaceship, built by unknown minds for an unknown purpose.
http://www.nss.org/settlement/space/rama.htm
Rama video – artist’s homepage and resources
Babylon 5
Babylon 5 was an American hard sci-fi, space-opera, TV series created by J. Michael Straczynski, that aired in the 1990’s. It was conceived of as a novel for television, each episode would be a single chapter. A coherent story unfolds over five 22-episode seasons. The station is modeled after the O’Neil design (above.)
It is an O’Neill cylinder 5 miles (8.0 km) long and 0.5–1.0 mile (0.80–1.61 km) in diameter.
Ringworld
Ringworld is a 1970 science fiction novel by Larry Niven, a classic of science fiction literature. It tells the story of Louis Wu and his companions on a mission to the Ringworld, a rotating wheel space station, an alien construct in space 186 million miles in diameter – approximately the diameter of Earth’s orbit. It encircles a sun-like star.
It rotates to provide artificial gravity and has a habitable, flat inner surface – equivalent in area to approximately three million Earths. It has a breathable atmosphere and a temperature optimal for humans.
Night is provided by an inner ring of shadow squares. These are far from the surface of the ringworld, orbiting closer to the star. These squares are connected to each other by thin, ultra-strong wire.
Halo
Halo is a science fiction media franchise centered on a series of video games. The focus of the franchise builds off the experiences of Master Chief. The term “Halo” refers to the Halo Array: a group of immense, habitable, ring-shaped superweapons.
They are similar to the Orbitals in Iain M. Banks’ Culture novels, and to a lesser degree to author Larry Niven’s Ringworld concept.
ELA/Literary connections
Short Story – “Spirals” by Larry Niven and Jerry Pournelle. First appeared in Jim Baen’s Destinies, April-June 1979. Story summary – Cornelius Riggs, Metallurgist, answers an ad claiming “high pay, long hours, high risk. Guaranteed wealthy in ten years if you live through it.”
The position turns out to be an engineering post aboard humanity’s orbiting habitat. The founders of “the Shack” dream of a livable biosphere beyond Earth’s gravity, a permanent settlement in space. However, Earth’s the economic conditions are getting worse, and the supply ships become more and more infrequent.
See the short story Spirals by Larry Niven and Jerry Pournelle.
Computer & math connections
The O’Neill Cylinder Simulator, by David Kann, Australia.
“In our discussion we came across the thought of what it might look like to throw a ball in the air in a zero-gravity rotating space station. I was stumped so I brought the question to my colleagues. They were stumped. Eventually I was able to make a pair of parametric equations for position in time to model the motion of the ball but it didn’t tell me much unless I could visualize the graph of the equations. The next logical step was to simulate the equations in software. Enter the O’Neill Cylinder Simulator:”
“When I saw the parametric equation animated (like above) it blew my mind a little. Here we see someone throwing a ball up and to the left, it circles above their head, and returns to them from the right. Throwing a ball in an O’Neill Cylinder apparently is nothing like on Earth. You can do some really sweet patterns:”
Also see Rotating space stations with counter rotating segments
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
SAT Subject Test in Physics
Circular motion, such as uniform circular motion and centripetal force
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
HS-PS2-1. Analyze data to support the claim that Newton’s second law of motion is a
mathematical model describing change in motion (the acceleration) of objects when
acted on by a net force.
HS-PS2-10(MA). Use free-body force diagrams, algebraic expressions, and Newton’s laws of motion to predict changes to velocity and acceleration for an object moving in one dimension in various situations
Massachusetts Science and Technology/Engineering Curriculum Framework (2006)
1. Motion and Forces. Central Concept: Newton’s laws of motion and gravitation describe and predict the motion of most objects.
1.8 Describe conceptually the forces involved in circular motion.
Female sexual anatomy
It is of critical importance for high school students to graduate high school with knowledge of how their bodies work. This includes sexual anatomy. In this resource we present anatomical information on external and internal female sexual anatomy.
There is a difference in student population between college level and high school level health and science classes. As such, we have taken care to select images that are anatomically correct yet not quite overt.
The vulva – external female sexual anatomy
The vulva includes
The inner and outer lips of the labia.
The clitoris.
The opening to the vagina (although the vagina itself is technically the long muscular opening moving back from this opening, see below.)
Vaginal glands, which are between the vulva and anus (the perineum).
The urethral opening. This is the opening to the urethra (the tube that carries urine outside of the body).
Image from Memorial Sloan Kettering Cancer Center
Above image from Memorial Sloan Kettering Cancer Center
Internal female reproductive system
Vagina (birth canal) – A muscular tube leading inside a woman’s body. Where sperm enters a woman. Also is where a baby is born from.
Cervix – The muscular wall at the end of the vagina. It has a tiny hole that sperm can swim through.
Uterus (womb) -A thick muscular organ. Has two purposes
(a) Allows sperm to pass, from the vagina, up towards the fallopian tubes
(b) If a woman becomes pregnant, the fetus will attach to the wall of the uterus and grow here.
Fallopian tubes – Tubes that connect the uterus to the ovary
(a) sperm swim up into these tubes. If the woman has recently released an egg, this is where the egg and sperm meet.
Ovary – these are where a woman’s eggs are stored. After puberty, women usually mature one egg a month.
Also see Human reproductive system
Also see Female reproductive system, Teens Health
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consciousness
It is easy to ask “what is the brain, and how does it work?” A much more difficult question is “what is the mind?,” and “what is consciousness?”
Introduction
Consciousness is “awareness or sentience of internal or external existence”.
Despite centuries of analyses, definitions, and debates by philosophers and scientists, consciousness remains puzzling and controversial. It is “at once the most familiar and most mysterious aspect of our lives”.
Perhaps the only widely agreed notion about the topic is the intuition that it exists. Opinions differ about what exactly needs to be studied and explained as consciousness.
Sometimes “consciousness” is synonymous with ‘the mind’, other times just an aspect of mind.
In the past it was one’s “inner life”, the world of introspection, of private thought, imagination and volition.
Today, with modern research into the brain it often includes any kind of experience, cognition, feeling or perception.
There might be different levels or orders of consciousness, or perhaps different kinds of consciousness – or just one kind with different features.
Other questions include whether only humans are conscious or all animals or even the whole universe. The disparate range of research, notions and speculations raises doubts whether the right questions are being asked.
( – Wikipedia, adapted, Consciousness)
Are there levels of consciousness?
Consciousness isn’t binary (It exists, or it doesn’t exist.)
Rather, it seems to exist on a smooth continuum from not at all, all the way up to what we humans experience.
There’s no reason to assume that our awareness & consciousness is the highest level – there may be higher levels, or different kids that we can’t imagine.
Image below from A better way to test for consciousness?
How does this relate to our bodies? What if we look at consciousness on the level of a person, and then down to smaller biological components?
Or what if we look at this on the level of a person, and then see how this changes when we look at how many people think when they interact?
“The scale problem of consciousness: Human conscious experience does not reflect information from every scale. Only information at a certain coarse-grained scale in the neural system is reflected in consciousness.”
Image from Chang, Acer & Biehl, Martin & Yu, Yen & Kanai, Ryota. (2019)
Information Closure Theory of Consciousness.
The hard problem of consciousness
“The meta-problem of consciousness is (to a first approximation) the problem of explaining why we think that there is a problem of consciousness.”
– Chalmers on the Meta-Problem
The hard problem of consciousness is the problem of explaining how atoms and molecules work together to create a living being – like us! – that actually feels and experiences the world.
How does a living person – like us! – experience awareness? How can we feel alive, experience our own thoughts – when we are built out of parts that have no awareness at all?
How the brain works is one thing – that’s the (relatively!) “easy” problem. We already have learned much about the anatomy of the brain and what kind of cells it is made of.
We’re learning how information is sent from our eyes, ears, skin, etc. to the brain. We have even begin to learn how the brain mechanically follows the laws of physics to store, recall, and process information.
But how can we humans (and presumably, animals) experience qualia – instances of subjective, conscious experience?
The philosopher David Chalmers is the first to clearly and forcefully make people aware of what an amazingly hard question is, this hard problem of consciousness.
Easy problems are (relatively) easy because all that is required for their solution is to specify a mechanism that can perform the function.
That is, regardless of how complex the phenomena of easy problems may be, they can eventually be understood by following science as we have always known it.
But the hard problem of consciousness will “persist even when the performance of all the relevant functions is explained”.
Chalmers, David (1995). “Facing up to the problem of consciousness” Journal of Consciousness Studies. 2 (3): 200–219.
On the other hand, the very existence of this hard problem is controversial. It has been accepted by many philosophers of mind but its existence is disputed by others.
Facing Up to the Problem of Consciousness, David J. Chalmers
Moving Forward on the Problem of Consciousness, David J. Chalmers
Consciousness as a State of Matter, Max Tegmark
Panpsychism: You are conscious but so is your coffee mug
Qualia Formalism in the Water Supply: Reflections on The Science of Consciousness 2018
Is consciousness an illusion?
(Text tba)
Has science shown that consciousness is an illusion?
Is Consciousness Real? Scientific American
The ‘me’ illusion: How your brain conjures up your sense of self
The consciousness illusion
There’s No Such Thing as Consciousness, According to Philosopher Daniel Dennett
Physical correlates of consciousness
If consciousness if real, then presumably it correlates to something going on in our brain.
What are the physical correlates of consciousness?
The controversial correlates of consciousness, George A. Mashour, Science 04 May 2018:
Vol. 360, Issue 6388, pp. 493-494, DOI: 10.1126/science.aat5616
https://science.sciencemag.org/content/360/6388/493/tab-figures-data
Neuroscience Readies for a Showdown Over Consciousness Ideas: To make headway on the mystery of consciousness, some researchers are trying a rigorous new way to test competing theories. Philip Ball, 3/6/2019, Quanta Magazine
Neuroscience Readies for a Showdown Over Consciousness Ideas
Visualizing how consciousness might work
Consciousness might be explained by it being an emergent phenomenon,
Analogy – we can’t predict the existence or behavior of oceans from looking at a single molecule of water.
Yet when enough liquid water molecules come together, an ocean – with all of its complex behavior – emerges.
Perhaps consciousness is similar. It might emerge from the interplay of dynamics that we already are beginning to learn about.
“Psychologist and neuroscientist Grit Hein and Ernst Fehr from the Department of Economics, University of Zurich teamed up with Yosuke Morishima, Susanne Leiberg, Sunhae Sul and found that the way relevant brain regions communicate with each other is altered depending on the motives driving a specific behavioral choice.”
Hein G, Morishima Y, Leiberg S, Sul S, & Fehr E (2016). The brain’s functional network architecture reveals human motives. Science, 351 (6277), 1074-8 PMI
and
Elucidating the Nature of Human Consciousness Through Art: interview with Greg Dunn
Do we really need new physics to understand consciousness?
Are the laws of physics, as we currently understand them, truly insufficient to explain what consciousness is? Many philosophers and writers make this claim. If so then we would need to postulate, look for, and prove the existence of undiscovered laws of physics.
Many claims in this area have been raised over the last two centuries. But physicist Sean Carroll warns us to be very careful if we make any such claim.
He writes – “Consciousness and the Laws of Physics” is a new paper where I review how we understand physics pretty well, and consciousness not so well, so altering physics to account for consciousness should be a last resort. And that if you try to alter the ontology of the world by adding intrinsically mental aspects to it, *without* modifying the laws of physics, you don’t really explain anything at all. The very first thing any attempt to account for consciousness should do is to be honest about whether it implies a modification of the known laws of physics. If yes, be very specific about how the equations change; if no, you’re not helping.
Philosophical zombies
In physics and philosophy, one way to learn about something is to create a gedankenexperiment (“thought experiment.”).
It may be possible to learn more about minds and consciousness by creating philosophical/biological thought experiments. The most well known one is the question of the philosophical zombie:
A philosophical zombie is a hypothetical being who is physically identical to a normal human being, but completely lacks conscious experience. – David Chalmers.
If a philosophical zombie is possible, then conscious experience is independent of physical world.
This image from Masatoshi Yoshida the-hard-problem-of-consciousness
Consciousness and the universe
“The universe is sentient. We all know that. We are the sentient bit. What could consciousness be, except the universe witnessing itself?”
– Steven Moffat
“We believe that the universe itself is conscious in a way that we can never truly understand. It is engaged in a search for meaning. So it breaks itself apart, investing its own consciousness in every form of life. We are the universe trying to understand itself.”
– J. Michael Straczynski
Related articles
Consciousness in Human and non-Human Animals
Possible minds
Consciousness creep Our machines could become self-aware without our knowing it
External articles
What Is Consciousness? Scientists are beginning to unravel a mystery that has long vexed philosophers, By Christof Koch, Scientific American, June 1, 2018
New Scientist articles
What Is Consciousness?
Consciousness, Stanford Encyclopedia of philosophy
Consciousness. Internet Encyclopedia of Philosophy
Articles on consciousness from New Scientist
Why can’t the world’s greatest minds solve the mystery of consciousness? The Guardian (article), UK
Why we need to figure out a theory of consciousness. The Conversation
Science catalog & supplier list
American Surplus and Supplies (Sciplus)
https://www.sciplus.com/
Arbor Scientific
https://www.arborsci.com/
Carolina
https://www.carolina.com/
Daydream Education (great science posters)
https://www.daydreameducation.com/
Delta Education (K-8)
https://www.deltaeducation.com/
Edmund Optics
https://www.edmundoptics.com/
Educational Innovations (Teachersource)
https://www.teachersource.com/
Fisher Scientific
https://www.fishersci.com/
Flinn Scientific
https://www.flinnsci.com/
Frey Scientific & CPO Science
http://www.freyscientific.com/
Hand2mind (K-8)
https://www.hand2mind.com/
Lab-aids
https://store.lab-aids.com/
Kelvin Educational
http://kelvin.com/
NASCO (STEM, STEAM products)
https://www.enasco.com/c/Education-Supplies/Steam
PASCO
https://www.pasco.com/index.cfm
Pittsco
https://www.pitsco.com/
School Speciality
https://www.schoolspecialty.com/?param=ssi
STEMfinity (technology, engineering, robotics)
https://www.stemfinity.com/
ThermoFisher Scientific (Massachusetts)
https://www.thermofisher.com/us/en/home/order.html
Trend Enterprises posters
https://www.trendenterprises.com/home.cfm
Vernier
https://www.vernier.com/
VWR
https://us.vwr.com/store/product?keyword=educational%20classroom%20kits
Wards’s Science / SK Science Kit & Boreal Laboratories
https://www.wardsci.com/
Easy labs and manipulatives
Easy labs and manipulatives
Astronomy
TBA
Biology
Chemistry
Precipitates: Coca Cola and milk
Teaching about the Periodic Table
Creating the periodic table
Element Data Cards Lab instructions
Element Data Cards the cards themselves
Electrochemistry: Two potato clock
TBA
Earth Science
TBA
Physics
Gravity and tides: Why Is There a Tidal Bulge Opposite the Moon?
Inertial mass and gravitational mass lab
Measuring data with smartphone apps
Engineering/Simple machines
Catapult and Trebuchet build project
General science
Teaching science with augmented reality
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Exploratorium Science Snacks
(San Francisco, California)
Simple DIY masks could help flatten the curve. We should all wear them in public.
Also see How do viruses spread? Airborne vs non-airborne
Jeremy Howard writes
When historians tally up the many missteps policymakers have made in response to the coronavirus pandemic, the senseless and unscientific push for the general public to avoid wearing masks should be near the top.
The evidence not only fails to support the push, it also contradicts it. It can take a while for official recommendations to catch up with scientific thinking. In this case, such delays might be deadly and economically disastrous.
It’s time to make masks a key part of our fight to contain, then defeat, this pandemic. Masks effective at “flattening the curve” can be made at home with nothing more than a T-shirt and a pair of scissors. We should all wear masks — store-bought or homemade — whenever we’re out in public.
At the height of the HIV crisis, authorities did not tell people to put away condoms. As fatalities from car crashes mounted, no one recommended avoiding seat belts. Yet in a global respiratory pandemic, people who should know better are discouraging Americans from using respiratory protection.
… There are good reasons to believe DIY masks would help a lot. Look at Hong Kong, Mongolia, South Korea and Taiwan, all of which have covid-19 largely under control. They are all near the original epicenter of the pandemic in mainland China, and they have economic ties to China.
Yet none has resorted to a lockdown, such as in China’s Wuhan province. In all of these countries, all of which were hit hard by the SARS respiratory virus outbreak in 2002 and 2003, everyone is wearing masks in public.
George Gao, director general of the Chinese Center for Disease Control and Prevention, stated, “Many people have asymptomatic or presymptomatic infections. If they are wearing face masks, it can prevent droplets that carry the virus from escaping and infecting others.”
My data-focused research institute, fast.ai, has found 34 scientific papers indicating basic masks can be effective in reducing virus transmission in public — and not a single paper that shows clear evidence that they cannot.
Studies have documented definitively that in controlled environments like airplanes, people with masks rarely infect others and rarely become infected themselves, while those without masks more easily infect others or become infected themselves.
Masks don’t have to be complex to be effective. A 2013 paper tested a variety of household materials and found that something as simple as two layers of a cotton T-shirt is highly effective at blocking virus particles of a wide range of sizes.
Oxford University found evidence this month for the effectiveness of simple fabric mouth and nose covers to be so compelling they now are officially acceptable for use in a hospital in many situations. Hospitals running short of N95-rated masks are turning to homemade cloth masks themselves; if it’s good enough to use in a hospital, it’s good enough for a walk to the store.
The reasons the WHO cites for its anti-mask advice are based not on science but on three spurious policy arguments.
First, there are not enough masks for hospital workers.
Second, masks may themselves become contaminated and pass on an infection to the people wearing them.
Third, masks could encourage people to engage in more risky behavior.
None of these is a good reason to avoid wearing a mask in public.
Yes, there is a shortage of manufactured masks, and these should go to hospital workers. But anyone can make a mask at home by cutting up a cotton T-shirt, tying it back together and then washing it at the end of the day. Another approach, recommended by the Hong Kong Consumer Council, involves rigging a simple mask with a paper towel and rubber bands that can be thrown in the trash at the end of each day.
… the idea that masks encourage risky behavior is nonsensical. We give cars anti-lock brakes and seat belts despite the possibility that people might drive more riskily knowing the safety equipment is there. Construction workers wear hard hats even though the hats presumably could encourage less attention to safety. If any risky behavior does occur, societies have the power to make laws against it.
Papers about effectiveness of basic masks #masks4all
About the author – Jeremy Howard is a distinguished research scientist at the University of San Francisco, founding researcher at fast.ai and a member of the World Economic Forum’s Global AI Council.
Simple DIY masks could help flatten the curve. We should all wear them in public.
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More reason to wear face masks:
Experts said the choir outbreak is consistent with a growing body of evidence that the virus can be transmitted through aerosols — particles smaller than 5 micrometers that can float in the air for minutes or longer.
The World Health Organization has downplayed the possibility of transmission in aerosols, stressing that the virus is spread through much larger “respiratory droplets,” which are emitted when an infected person coughs or sneezes and quickly fall to a surface.
But a study published March 17 in the New England Journal of Medicine found that when the virus was suspended in a mist under laboratory conditions it remained “viable and infectious” for three hours — though researchers have said that time period would probably be no more than a half-hour in real-world conditions.
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Nell Greenfieldboyce writes
the question of whether or not the coronavirus can be “airborne” is extremely contentious right now — and it’s a question that has real implications for what people should do to avoid getting infected.
… a committee of independent experts convened by the National Academies of Sciences, Engineering, and Medicine has weighed in, in response to a question from the White House Office of Science and Technology Policy about whether the virus “could be spread by conversation in addition to sneeze/cough-induced droplets.”
“Currently available research supports the possibility that SARS-CoV-2 could be spread via bioaerosols generated directly by patients’ exhalation,” says a letter from the committee chair. By bioaerosols, they are referring to fine particles emitted when someone breathes that can be suspended in the air rather than larger droplets produced through coughs and sneezes.
Even if additional research shows that any virus in such tiny particles is viable, researchers still won’t how much of it would need to be inhaled to make someone sick. But the committee experts also caution that uncertainty about all this is almost a given—because there’s currently no respiratory virus for which we know the exact proportion of infections that come from breathing the virus in versus coming into contact with droplets in the air or on surfaces.
“I personally think that transmission by inhalation of virus in the air is happening,” says Linsey Marr, an aerosol scientist at Virginia Tech. But she says so far, health experts have largely discounted the possibility of transmitting this coronavirus in this way.
“From an infection prevention perspective, these things are not 100% black and white. The reason why we say ‘droplet’ versus ‘airborne’ versus ‘contact’ is to give overall guidance on how to manage patients who are expected to be infectious with a specific pathogen,” said Dr. Hanan Balkhy, assistant director-general for antimicrobial resistance at WHO, in an interview with NPR earlier this week.
As an expert who worked to contain an outbreak of the deadly MERS coronavirus in Saudi Arabia, she believes that this new virus should behave similarly to other severe coronaviruses — and that means, unless health-care workers are doing invasive procedures like putting in breathing tubes, the virus is expected to primarily spread through droplets.
Droplets are larger respiratory particles that are 5 to 10 micrometers in size. Those are considered “big,” even though a 5 micrometer particle would still be invisible to the naked eye. Traditionally, those droplets are thought to not travel more than about three feet or so after exhalation. That would mean the virus can only spread to people who get close to an infected person or who touch surfaces or objects that might have become contaminated by these droplets. This is why public health messages urge people to wash their hands and stand at least 6 feet away from other people.
An “airborne” virus, in contrast, has long been considered to be a virus that spreads in exhaled particles that are tiny enough to linger in the air and move with air currents, letting them be breathed in by passersby who then get sick. Measles is a good example of this kind of virus — an exhaled measles pathogen can hang suspended in a room for a couple hours after an infected person leaves.
The reality of aerosol generation, however, is far more complex than this “droplet” versus “airborne” dichotomy would suggest, says Marr. People produce a wide range of different-sized particles of mucus or saliva. These particles get smaller as they evaporate in the air and can travel different distances depending on the surrounding air conditions.
“The way the definitions have been set up, this “droplet” vs “airborne” distinction, was first established in the 1950s or even earlier,” says Marr. “There was a more limited understanding of aerosol science then.”
Even a 5 micrometer droplet can linger in the air. “If the air were perfectly still, it would take a half hour to fall from a height of 6 feet down to the ground. And, of course, the air isn’t perfectly still,” says Marr. “So it can easily be blown around during that time and stay in the air for longer or shorter.”
What’s more, coughs and sneezes create turbulent clouds of gas that can propel respiratory particles forward.
“For symptomatic, violent exhalations including sneezes and coughs, then the droplets can definitely reach much further than the 1 to 2 meter [3 to 6 feet] cutoff,” says Lydia Bourouiba, an infectious disease transmission researcher at MIT, referring to the distance typically cited as safe for avoiding droplet-carried diseases.
In fact, studies show that “given various combinations of an individual patient’s physiology and environmental conditions, such as humidity and temperature, the gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet,” she wrote in a recent article published online by the Journal of the American Medical Association.
…. Some of the strongest evidence that an airborne route of transmission might be possible for this virus comes from a report published last month by the New England Journal of Medicine that described mechanically generating aerosols carrying the SARS-CoV-2 virus in the laboratory. It found that the virus in these little aerosols remained viable and infectious throughout the duration of the experiment, which lasted 3 hours.
WHO mentioned this study in its recent review of possible modes of transmission and noted that “this is a high-powered machine that does not reflect normal human cough conditions … this was an experimentally induced aerosol-generating procedure.”
It may have been artificial, says Marr, but “the conditions they used in that laboratory study are actually less favorable for survival compared to the real world. So it’s more likely that the virus can survive under real world conditions.”
Scientists Probe How Coronavirus Might Travel Through The Air
Reference: Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19
Lydia Bourouiba, JAMA insights, March 26, 2020. doi:10.1001/jama.2020.4756
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Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1
March 17, 2020 , DOI: 10.1056/NEJMc2004973
A novel human coronavirus that is now named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (formerly called HCoV-19) emerged in Wuhan, China, in late 2019 and is now causing a pandemic. We analyzed the aerosol and surface stability of SARS-CoV-2 and compared it with SARS-CoV-1, the most closely related human coronavirus.
… We found that the stability of SARS-CoV-2 was similar to that of SARS-CoV-1 under the experimental circumstances tested. This indicates that differences in the epidemiologic characteristics of these viruses probably arise from other factors, including high viral loads in the upper respiratory tract and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic.
Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed).
These findings echo those with SARS-CoV-1, in which these forms of transmission were associated with nosocomial spread and super-spreading events, and they provide information for pandemic mitigation efforts.
Neeltje van Doremalen, Ph.D., Trenton Bushmaker, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT
Dylan H. Morris, M.Phil., Princeton University, Princeton, NJ, Myndi G. Holbrook, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT
Amandine Gamble, Ph.D.
University of California, Los Angeles, Los Angeles, CA
Brandi N. Williamson, M.P.H.
National Institute of Allergy and Infectious Diseases, Hamilton, MT
Azaibi Tamin, Ph.D., Jennifer L. Harcourt, Ph.D.
Natalie J. Thornburg, Ph.D., Susan I. Gerber, M.D.
Centers for Disease Control and Prevention, Atlanta, GA
James O. Lloyd-Smith, Ph.D.
University of California, Los Angeles, Los Angeles, CA, Bethesda, MD
Emmie de Wit, Ph.D., Vincent J. Munster, Ph.D.
National Institute of Allergy and Infectious Diseases, Hamilton, MT
Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1
#NEJM
Buoyancy of balloons in Up
Up is a 2009 American computer-animated comedy-drama film produced by Pixar Animation Studios and released by Walt Disney Pictures.
In this movie, the hero releases many, many helium filled balloons out of the house. Could that actually be enough to make a house float?
In Physics and the movie UP – floating a house, 6/3/2009, Wired Magazine, Rhett Allain writes
…The first time I saw this trailer I thought the balloons were stored in his house. After re-watching in slow motion, it seems the balloons were maybe in the back yard held down by some large tarps. … [but] what if he had the balloons in his house and then released them? Would that make the house float more? Here is a diagram:
There is a buoyancy force when objects displace air or a fluid. This buoyancy force can be calculated with Archimedes’ principle which states: The buoyancy force is equal to the weight of the fluid displaced.
The easiest way to make sense of this is to think of some water floating in water. Of course water floats in water. For floating water, it’s weight has to be equal to it’s buoyant force. Now replace the floating water with a brick or something. The water outside the brick will have the exact same interactions that they did with the floating water. So the brick will have a buoyancy force equal to the weight of the water displaced. For a normal brick, this will not be enough to make it float, but there will still be a buoyant force on it.
What is being displaced? What is the mass of the object. It really is not as clear in this case. What is clear is the thing that is providing the buoyancy is the air. So, the buoyancy force is equal to the weight of the air displaced.
What is displacing air? In this case, it is mostly the house, all the stuff in the house, the balloons and the helium in the balloons.
In the two cases above, the volume of the air displaced does not change. This is because the balloons are in the air in the house. (Remember, I already said that I see that this NOT how it was shown in the movie).
So, if you (somehow) had enough balloons to make your house fly and you put them IN your house, your house would float before you let them outside.
Why doesn’t the balloon house keep rising?
The reason the balloon reaches a certain height is that the buoyant force is not constant with altitude.
As the balloon rises, the density of the air decreases. This has the effect of a lower buoyant force.
At some point, the buoyant force and the weight are equal and the balloon no longer changes in altitude.
http://scienceblogs.com/dotphysics/2009/06/03/physics-and-the-movie-up-floating-a-house/
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https://en.wikipedia.org/wiki/Larry_Walters
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Mythbusters : Lets talk buoyancy – Pirates of the Carribean
Adam and Jamie explore the possibility of raising a ship with ping-pong balls, originally conceived in the 1949 Donald Duck story The Sunken Yacht by Carl Barks.
MythBusters S02E13 Pingpong Rescue, 2004
Doing the math of MythBusters – Warning: Science content
More on the movie Up! (or Upper)
Rhett Allain on June 9, 2009
If the house were lifted by standard party balloons, what would it look like? The thing with party balloons is that they are not packed tightly, there is space between them. This makes it look like it takes up much more space. Let me just use Slate’s calculation of 9.4 million party balloons….
Pixar said they used 20,600 balloons in the lift off sequence. From that and the picture I used above and the same pixel size trick, the volume of balloons is about the same as a sphere of radius 14 meters. This would make a volume of 12,000 m3…
And then this would lead to an apparent volume of the giant cluster of 9.4 million balloons:
If this were a spherical cluster, the radius would be 110 meters. Here is what that would look like:
How long would it take this guy to blow up this many balloons? You can see that there is no point stopping now. I have gone this far, why would I stop? That would be silly.
The first thing to answer this question is, how long does it take to fill one balloon. I am no expert, I will estimate low. 10 seconds seems to be WAY too quick.
But look, the guy is filling 9.4 million balloons, you might learn a few tricks to speed up the process. If that were the case, it would take 94 million seconds or 3 years….
What if it was just 20,600 balloons like Pixar used in the animation? At 10 seconds a balloon, that would be 2.3 days (and I think that is a pretty fast time for a balloon fill). Remember that MythBusters episode where they filled balloons to lift a small boy? Took a while, didn’t it?
How many tanks of helium would he need? According this site, a large helium cylinder can fill 520 of the 11″ party balloons and costs about $190. If he had to fill 9.4 million balloons, this would take (9.4 million balloons)(1 tank)/(520 balloons)= 18,000 tanks at a cost of 3.4 million dollars.
http://scienceblogs.com/dotphysics/2009/06/09/more-on-the-movie-up-or-upper/
Tidal power
Content objective:
What are we learning? Why are we learning this?
content, procedures, skills
Vocabulary objective
Tier II: High frequency words used across content areas. Key to understanding directions, understanding relationships, and for making inferences.
Tier III: Low frequency, domain specific terms
Building on what we already know
What vocabulary & concepts were learned in earlier grades?
Make connections to prior lessons.
Ocean tides are caused by tidal forces.
What are “tides”?
Types of tidal power
Tidal barrages may be the most efficient way to capture energy from the tides.
Here, a dam utilizes the potential energy generated by the change in height between high and low tides.
In this example, the motion of the water spins a propeller.
image from technologystudent.com/images5/tidal1.gif
The spinning propeller spins an axle, which transmits the motion up to the generator.
Inside the generator, this motion is used to rotate wires inside a magnet (or vice-versa)
The wire feels the magnetic field changing;
this produces an electrical current inside the wires.
Thus we have converted the energy of moving water into electrical energy.
Tidal fences
Turbines that operate like giant turnstiles.
The spinning turnstiles spins an axle, which transmits the motion up to the generator.
Inside the generator, this motion is used to rotate wires inside a magnet (or vice-versa) as shown above.
Tidal turbines
Similar to wind turbines but these are underwater.
The mechanical energy of tidal currents is used to turn turbines.
These are connected to a generator that produces electricity
Other possible designs
Many other designs are possible, for instance:
Fluid Pumping Apparatuses Powered By Waves Or Flowing Currents
Great animations
Many types of tidal energy convertors (European Marine Energy Centre)
Advantages of tidal power
Environmentally friendly
Relatively small amount of space
Ocean currents generate relatively more energy than air currents. Why? Because ocean water is 832 times more dense than air. It therefore applies greater force on the turbines.
Disadvantages of tidal power
High construction costs
The amount of energy produced is not constant per hour, or even per week.
It requires a suitable site, where tidal streams are consistently strong.
The equipment must be capable of withstanding strong tides and storms.
It can be expensive to maintain and repair.
Related topics
Why Is There a Tidal Bulge Opposite the Moon?
SETI notes
The search for extraterrestrial intelligence (SETI) is a collective term for any scientific searches for intelligent extraterrestrial life.
It is done by monitoring radio signals for signs of transmissions from civilizations on other planets.
Topics
The history of SETI
Where could other forms of life exist in our solar system?
Where could other forms of life exist in our galaxy?
How likely is it that life would exist? The Drake Equation
What exactly is our galaxy?
How could we detect sings of intelligent life from outside of our solar system?
scanning radio waves
Why don’t any Earthly organisms detect radio waves?
so what are radio waves, and how do we detect them?
The Water hole: What radio frequencies should we listen to?
Misconceptions about listening with radio telescopes
How can we differentiate between natural or artificial (intelligent) signals?
scanning infrared for signs of Dyson spheres or other megastructures
so what is IR, and how do we detect it?
Where might we find life?
Goldilocks Zone/Circumstellar habitable zone – single star systems
Habitable zones for binary star systems
Atmosphere of brown dwarf stars
surface of neutron stars (very speculative)
Could we realistically ever travel to other star systems? physics of interstellar travel
Where would other forms of intelligent life exist?
There may be other forms of life even here in our own solar system, but almost certainly that would be only primitive, single celled organisms.
That being said, the number of worlds in our own solar system where life may exist, even right now, is larger than more people think. For a variety of reasons, scientists believe that there is a possibility of life existing on
Europa, a moon of Jupiter
https://europa.nasa.gov/why-europa/ingredients-for-life/
NASA Europa Clipper expedition
Europa: A World of Ice, With Potential for Life. NASA
NASA Europa in depth
Enceladus, a moon of Saturn
https://solarsystem.nasa.gov/missions/cassini/science/enceladus/
https://solarsystem.nasa.gov/resources/17649/ingredients-for-life-at-enceladus/
https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/
Mars
https://mars.nasa.gov/news/8863/searching-for-life-in-nasas-perseverance-mars-samples/
https://en.wikipedia.org/wiki/Life_on_Mars
https://www.nature.com/immersive/d41586-021-00321-7/index.html
https://mars.nasa.gov/science/goals/
https://www.smithsonianmag.com/science-nature/life-on-mars-78138144/
NASA Viking mission: Evidence of Life on Mars in the 1970s
Jupiter – ideas about how life could exist in its upper cloud layers.
Carl Sagan, Cosmos. Possibility of life on Jupiter. Video
Particles, environments, and possible ecologies in the Jovian atmosphere.. Carl Sagan
https://www.centauri-dreams.org/2009/02/25/edwin-salpeter-and-the-gasbags-of-jupiter/
What exactly is our solar system? See our resource the Solar system.
When we talk about SETI, we’re not looking for life in general, but we’re looking for very complex forms of life that have evolved intelligence and the ability to communicate with the electromagnetic spectrum.
Such life could exist on other planets, or large moons, around other stars in our galaxy, the Milky Way.
At this point we should take a look at what we mean by “galaxy”.
Here is a view of our galaxy as seen from Earth, New Hampshire.
This is what our galaxy would look like if we were above the galactic center, looking down at it.
There are approximately 100 billion stars in our galaxy, with perhaps one trillion planets and large moons, each of which has existed for billions of years. Many scientists believe it likely that life has evolved on many of these worlds.
For a variety of reasons, we have reason to believe that many of these worlds would in many ways be Earth-like, some of them larger than Earth. These are often called super earths.
Dimitar D. Sasselov and Diana Valencia, Planets We Could call home, Scientific American, 303, 38 – 45 (2010)
Current – and even any other potentially feasible – technology is unable to let us detect SETI signals from life on planets in other galaxies. If we were to consider other galaxies, the odds of intelligent life existing somewhere out there is considered near certain.
Observations with the Hubble Space Telescope reveal that there are about two trillion galaxies in the observable universe – each of these galaxies likely having billions of planets and large moons.
This photo shows the Sombrero galaxy, m104. The other points of light around it are not stars, but entire galaxies!
A Hubble Space Telescope image of the Sombrero galaxy, M104 (credit: NASA)
At this point we should stop and clarify precisely what we mean by the word “universe.” – The universe
What are radio waves?
Radio waves are just a part of the EM (electromagnetic) spectrum.
That sounds dandy, except, what exactly is the “electromagnetic spectrum”?
All parts of the EM spectrum – radio, visible light, etc. – are oscillating electric and magnetic fields.
For details see Light is an electromagnetic field.
How are radio waves different from other parts of the EM spectrum?
They’re made of the same thing, behaving in exactly the same way.
The only difference is that radio waves are hundreds of meters to thousands of meters long.
Other parts of the EM spectrum have longer or shorter waves.
What creates radio waves?
With a radio receiver we can hear radio waves coming from all around us. They are naturally produced, and comes from all over the Earth, and outer space.
Radio waves are naturally created by:
* Wind whipping over a surface, creating static electricity
(Here’s a more mundane example of static electricity.)
* Lightning
* atoms trapped in the magnetic fields around the Earth, and around all other planets as well.
* The Sun (it puts out all frequencies of EM radiation!)
* All stars
* Ionized interstellar gas surrounding bright, hot stars
HST (Hubbble Space Telescope) Image: Gaseous Pillars In M16-Eagle Nebula Pillars Of Creation In A Star- Forming Region
* Supernovas
* There are also more complex radio waves that are naturally generated. See Natural and man-made terrestrial electromagnetic noise
By the late 1800’s humans had learned not only how to receive radio waves, but how to generate them.
Today we artificially create radio waves for all sorts of purposes, including
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Traditional, over-the-air, radio stations (AM and FM radio)
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Traditional, old-fashioned, TV (television)
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Wi-Fi
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Bluetooth
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Cellphone communication (cell towers and the phones)
Cornell.edu: Observational-astronomy. SETI and extraterrestrial life
Kaiserscience – All about the electromagnetic spectrum
What is a radio telescope?
The technology of how we detect radio waves.
http://abyss.uoregon.edu/~js/glossary/radio_telescope.html
Image from website of James Schombert, Dept of Physics, Univ. Oregon
How does an antenna pick up radio waves?
“If we place a conducting material on the path of such a wave, the passing wave will create an oscillating electric field inside the material; and that field will accelerate charges back and forth through the conductor.”
https://en.wikipedia.org/wiki/Antenna_(radio)
http://spiff.rit.edu/classes/ast613/lectures/radio_ii/radio_ii.html
The history of SETI
This section has been adapted from “Search for extraterrestrial intelligence.” Wikipedia, The Free Encyclopedia. 4 Mar. 2019
There have been many earlier searches for extraterrestrial intelligence within the Solar System. In 1896, Nikola Tesla suggested that an extreme version of his wireless electrical transmission system could be used to contact beings on Mars. He conducted an experiment at his Colorado Springs experimental station.
In the early 1900s, Guglielmo Marconi, Lord Kelvin and David Peck Todd also stated their belief that radio could be used to contact Martians, with Marconi stating that his stations had also picked up potential Martian signals.
On August 21–23, 1924, Mars entered an opposition closer to Earth than at any time in the century before or the next 80 years. In the United States, a “National Radio Silence Day” was promoted during a 36-hour period from August 21–23, with all radios quiet for five minutes on the hour, every hour.
At the United States Naval Observatory, scientists used a radio receiver, miles above the ground in a dirigible, to listen for any potential radio messages from Mars.
A 1959 paper by Philip Morrison and Giuseppe Cocconi first pointed out the possibility of searching the microwave spectrum, and proposed frequencies and a set of initial targets.
In 1960, Cornell University astronomer Frank Drake performed the first modern SETI experiment, named “Project Ozma”, after the Queen of Oz in L. Frank Baum’s fantasy books. Drake used a radio telescope at Green Bank, West Virginia, to examine the stars Tau Ceti and Epsilon Eridani.
Soviet scientists took a strong interest in SETI during the 1960s and performed a number of searches. Soviet astronomer Iosif Shklovsky wrote the pioneering book in the field, Universe, Life, Intelligence (1962), which was expanded upon by American astronomer Carl Sagan as the best-selling book Intelligent Life in the Universe (1966).
In the March 1955 issue of Scientific American, John D. Kraus described an idea to scan the cosmos for natural radio signals using a radio telescope. Ohio State University soon created a SETI program.
In 1971, NASA funded a SETI study that involved Drake, Bernard M. Oliver of Hewlett-Packard Corporation, and others. The resulting report proposed the construction of an Earth-based radio telescope array with 1,500 dishes known as “Project Cyclops”. It was not built, but the report formed the basis of much SETI work that followed.
Why don’t any organisms detect radio waves?
Much life on earth can see in visible light. Some organisms can see IR (infrared) or UV (ultraviolet) light – but as far as we know none can see the radio part of the EM spectrum. Why not?
See Why don’t any organisms detect radio waves?
How difficult will this be?
It is very difficult to pick up Earth’s radio waves from another solar system. As such, we can imagine that it would very difficult to pick up radio waves here, from some other solar system.
That’s why we aren’t really looking for random radio waves that happen to escape out into space. Rather, the current projects are looking for much more powerful signals, that we hope would be sent out on purpose.
https://io9.gizmodo.com/are-we-screwing-ourselves-by-transmitting-radio-signals-493800730
“That’s a rather extraordinary claim, so I spoke to SETI expert and scifi novelist David Brin about it — and he’s not convinced detection is this easy. He told me that, even if an ETI had a one square kilometer array, they would have to point it a at Earth for the duration of an entire year. “
Because it would take that long,” he told io9. “But why stare if you don’t already have a reason to suspect?”
Like SETI Institute’s Seth Shostak, Brin believes that Earth is not detectable beyond five light years. “With one exception: Narrow-focused, coherent (laser-like) planetary radars that are aimed to briefly scan the surfaces of asteroids and moons,” he says, “
And not to be confused with military radars that disperse.””
How can we differentiate between natural or artificial (intelligent) signals?
Consider listening to the sound of radio static. Compare that to the sound of a song, or a person giving a speech. Both are sounds – how are they similar? How are they different?
Come up with ideas on how we could differentiate between natural or artificial (intelligent) signals.
“Humanity has received some odd signals in the past. We’ve also sent out some signals ourselves. How could we determine that a signal we’d received was artificial in origin? Or of course inversely, how could an extraterrestrial civilization determine a signal we had sent out was was artificial?”
Listening for Extraterrestrial Blah Blah: At the cosmic dinner party, intelligence is the loudest thing in the room. By Laurance R. Doyle, Illustrations by Tianhua Mao
Listening for Extraterrestrial Blah Blah
The Water hole: What radio frequencies should we listen to?
Tba
Hailing Frequencies Open, Captain! What is the “water hole”?
Misconceptions about listening with radio telescopes
Radio signals diminish in strength very rapidly with distance – they decrease according to the inverse square law. What does that mean?
Consider cooking oil that is sprayed. The cooking spray hits a piece of toast and deposits an even layer of butter, 1 mm thick.
Hewitt textbook
When the butter gets twice as far, it becomes only 1/4 as this.
If it travels 3 times as far, it will spread out to cover 3 x 3, or 9, pieces of toast.
So now the butter will only be 1/9th as thick. (1/9 is the inverse square of 3)
This pattern is called an inverse-square law.
The same is true for a can of spray paint: as the paint travels further, it covers a wider area, so the paint per area is inversely less thick.
Hewitt Conceptual Physics worksheets
The same pattern of spreading out and weakening, the inverse square laws, is true for radio waves.
Animations of the inverse-square law – animated clip: Inverse-square law for light
Okay – so by the time that radio signals reach even the next solar system they would be unbelievably weak. The radio signals would be even millions of times weaker by the time they travelled across even 1% of the galaxy.
Our radio telescopes could never pick up such radio signals.
So if that’s the case, what then are SETI researchers listening for?We are looking for a civilization that wants to be known, one that has deliberately built a high power radio beacon, aimed in one direction at a time.
A tightly beamed signal would be millions of times stronger – if by chance we happen to be in its path.
Do SETI researchers believe that someone out there is deliberately sending a signal to us here on Earth specifically? No. However, we know that there are billions of stars, and tens of billions of planets. Many of these planets might support life.
Therefore, at any given time there could be many thousands of other worlds with intelligent life. The hope is that some of them would want to communicate, sending a tight, beamed radio signal out into space. If so, then one day we might intercept such a communication.
Article: Is there anybody out there? Jason Davis, October 25, 2017, The Planetary Society Planetary.org – Is there anybody out there?
Goldilocks Zone/Circumstellar habitable zone
This section from evolution.berkeley.edu, A Place for Life: A special astronomy exhibit of Understanding Evolution
From the known properties of stars and of the chemistry of water, astronomers can define “habitable zones” around stars where liquid water (and hence life) could exist on the surface of planets.
Too close to the star, and water will boil; too far, and it will freeze. This so-called Goldilocks zone, where the temperature is just right, depends on both the distance from the star and the characteristics of the star itself.
The habitable zone around luminous giant stars is further from the star than the habitable zone around faint dwarfs.
Of course, as noted previously, life may also exist outside these zones, for example in subsurface oceans on icy moons heated from the moon’s interior.
We know that there are around 200 billion stars in our Galaxy. Recent research has revealed that most of them have planets, and that tens of billions of these planets are likely similar in size to Earth, made of rock, and orbit in their stars’ habitable zones.
The question that remains to be answered is what fraction of those potentially habitable worlds host life.
https://www.e-education.psu.edu/astro801/content/l12_p4.html
from the NASA Kepler Mission
https://en.wikipedia.org/wiki/Circumstellar_habitable_zone
https://www.nasa.gov/content/kepler-multimedia
Habitable Zones of Different Stars. NASA/Kepler Mission/Dana Berry.
https://www.nasa.gov/ames/kepler/habitable-zones-of-different-stars
Habitable zones for binary star systems
What about planets in a solar system with two stars?
Most stars in the Galaxy have at least one stellar companion—binary or multiple star systems. Stars like our Sun with no stellar companion are in the minority.
It would probably be difficult for there to be stable, only slightly elliptical planet orbits in a binary or multiple star system.
Complex life (multi-cellular) will need to have a stable temperature regime to form so the planet orbit cannot be too eccentric.
Simple life like bacteria might be able to withstand large temperature changes on a planet with a significantly elliptical orbit but complex life is the much more interesting case.
Suitable binary stars would be those systems where either:
(a) the binary stars orbit very close to each other with the planet(s) orbiting both of them at a large distance (called a “circumbinary planet”)
or (b) the binary stars orbit very far from each other so the planet(s) could reside in stable orbits near each of the stars—the one star’s gravity acting on a planet would be much stronger than that of the other star.
Image by Nick Strobel
image from https://www.astronomynotes.com/lifezone/s2.htm
A cool article on this subject: I Built a Stable Planetary System with 416 Planets in the Habitable Zone
Strong magnetic fields may be necessary
Earth has a strong magnetic field.
It turns out that this might be necessary on a planet if complex life is to evolve.
v
Why does Earth have such a strong magnetic field? Earth’s core is still hot and molten. Metal still moves inside it, and moving metal has moving free electrons.
Electrons moving around – by definition – are an electrical current. And it turns out that electrical currents create their own magnetic field!
Image from S-cool revision. GCSE » Physics » Magnetism and Electromagnetism
Inside the earth
This field protects the Earth’s atmosphere from some of the Sun’s radiation.
Without such a field most of a planet’s atmosphere is likely to be blown away into space, as happened to Mars.
Mars now has very little atmosphere, and its surface is constantly irradiated by solar radiation.
What else may be necessary for life to evolve?
How do tectonic plates make Earth hospitable to life?
The Drake Equation
An equation named after Frank Drake, who first summarized the things we need to know to answer the question, “how many possible extraterrestrial civilizations are out there?”
The equation breaks this complex question into small parts. The Drake Equation
Matthew Bobrowsky says “I introduce the Drake Equation not to actually estimate the number of technological civilizations in the Galaxy, but to provide an indication of the kinds of things to consider when deciding about the likelihood of finding life on another world.”
“It’s also interesting to note that the most uncertain factor in the Drake equation is the average lifetime of a technological civilization. We have no idea how long we (humans) will last, but I have an interesting discussion with students about the various ways — both natural (e.g., an asteroid impact) and by our own hands (e.g., global nuclear war) that our species could become extinct at any time.”
Astrobiology: Life elsewhere in the universe
Here we will link to lessons about the realistic possibility of life existing elsewhere in our galaxy, The idea is far more mainstream than most people realize.
Why would anyone think that it is likely that life would also evolve elsewhere in the universe?
(A) Why not? We have no data to assume otherwise.
(B) We do have enormous amounts of data available on what life on Earth is made of, and how it evolved over time. We have enormous amounts of data available on biochemistry and organic chemistry. enormous amounts of data available on how stars work and how planetary systems form.
The most common chemical elements in life are the most common elements in the universe
Discussions on how atoms naturally form molecules, including precursors to the organic molecules here on Earth
Evidence that this same chemistry happens elsewhere in the galaxy
Class discussion: What conditions would life need to evolve on another world?
What conditions would life need to evolve into advanced forms of life?
Even if advanced forms of life evolve, would they necessarily be able to develop technology?
Example: Dolphins and whales on earth have near human-like intelligence, awareness, and emotions, but they don’t have hands. They can’t manipulate their environment; can’t mine minerals or metals, and this can’t develop technology.
needs for energy – what possible energy sources?
needs for a solvent – water seems to be the only likely solvent, although we can investigate other options
protection from radiation (from stars, supernovas, et.)
how long would it take for life to evolve? How long are the lives of stars?
Given this, what kinds of stars could we expect to possibly have intelligent life?
(likely not around O-type stars, they burn out too quickly)
What kind of biochemistry would exist?
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probably carbon based
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we can investigate other possibilities
What kind of conditions could life thrive under? Consider conditions necessary for human life in specific, then animal life in general. Then compare to range of conditions that archaea can survive in.
Potential habitats for life
Terrestrial planets
Super Earths
Worlds like Europa, Enceladus
Atmosphere of brown dwarf stars
Alien life could thrive in the clouds of failed stars: cold brown dwarf stars
Cold brown dwarf star no hotter than a summer’s day
Atmospheric Habitable Zones in Y Dwarf Atmospheres, Jack S. Yates, Paul I. Palmer, Beth Biller, Charles S. Cockell , The Astrophysical Journal
Megastructures (Dyson swarms, etc.)
Evidence for ET intelligent life
None currently exists
UFO fads in the late 1800s, 1950s, and today. Extremely low quality photographs, evidence is considered at best very poor.
The WOW signal and other somewhat more realistic events that could be interpreted as evidence
Possible significant downside to contacting ET intelligence
TBA
Could we realistically ever travel to other star systems?
Here we learn about the potentially realistic physics of interstellar travel
Learning Standards
Common Core, English Language Arts Standards » Science & Technical Subjects
CCSS.ELA-LITERACY.RST.9-10.1 – Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
CCSS.ELA-LITERACY.RST.9-10.2 – Determine the central ideas or conclusions of a text; trace the text’s explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
CCSS.ELA-LITERACY.RST.9-10.4 – Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context.
CCSS.ELA-LITERACY.RST.9-10.5 – Analyze the structure of the relationships among concepts in a text, including relationships among key terms (e.g., force, friction, reaction force, energy).
CCSS.ELA-LITERACY.RST.9-10.6 – Analyze the author’s purpose in providing an explanation, describing a procedure, or discussing an experiment in a text, defining the question the author seeks to address.
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
HS-PS2-5. Provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.
6.MS-PS4-1. Use diagrams of a simple wave to explain that (a) a wave has a repeating pattern with a specific amplitude, frequency, and wavelength, and (b) the amplitude of a wave is related to the energy of the wave.
HS-PS4-1. Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling within various media. Recognize that electromagnetic waves can travel through empty space (without a medium) as compared to mechanical waves that require a medium.
HS-PS4-5. Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy.
Next Generation Science Standards: Science & Engineering Practices
● Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
● Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
● Ask questions to determine relationships, including quantitative relationships, between independent and dependent variables.
● Evaluate a question to determine if it is testable and relevant.
● Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of the design
Common Core Math Standards (Inverse-square law)
CCSS.Math.Content.7.RP.A.2a ( Grade 7 ): Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.
CCSS.Math.Content.7.RP.A.2c ( Grade 7 ): Represent proportional relationships by equations.
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