Physics
- Physics and the Search for ET
- Serendipity in Science
- Origin of Term Black Hole
- Size and Mass of Black Holes
- Cell Phones and Brain Tumors
- Arthur C. Clarke
- Battleships in Bathtubs
- Weather Predictions and Chaos
- Eclipses and the Power of Science
- Why Satellites Fall from Orbit
Posted by
Paul A. Heckert
Paul A. Heckert
How physics contributes to the scientific search for extraterrestrial life elsewhere in the universe.
Is there anyone out there or are we alone in the universe? We don't yet know, but physics is an important tool in finding out. For questions about life, most people normally think of biology, biochemistry, and similar sciences. However the best ways to search for extraterrestrial life combine all areas of science.
The search for life in the solar system involves sending robotic probes to other planets, mostly Mars. After landing, the probes rely on biochemistry to search for life. However getting the probe to another planet involves quite a bit of physics, such as rocket propulsion and orbital mechanics.
Outside the solar system, searches for life have traditionally looked for radio signals from possible extraterrestrial civilizations. That uses the physics of electromagnetic radiation. Special relativity and the speed of light limit keeps us from sending probes to other stars.
The April 2008 Scientific American has a nice article about a new strategy. Author Nancy Kiang discusses work that she and coworkers are doing on strategies for detecting vegetation on extrasolar planets. We have detected water on extrasolar planets using spectroscopy. Why not try to detect lush vegetation on a planet with similar techniques. NASA satellites use this tool and the spectral signature of chlorophyll to map vegetation on Earth. Increasing sensitivity and resolution might allow us to try this on extrasolar planets.
The trick is that plant life on extrasolar planets may have different spectral signatures. The green pigments on Earth plants are most efficient for the Sun's energy spectrum. Planets orbiting stars of different temperatures will have different spectra of natural light. Therefore plants on these planets are likely to have a different color chlorophyll and different spectral signatures. Knowing the physics of blackbodies is crucial to this analysis.
The search for life in the solar system involves sending robotic probes to other planets, mostly Mars. After landing, the probes rely on biochemistry to search for life. However getting the probe to another planet involves quite a bit of physics, such as rocket propulsion and orbital mechanics.
Outside the solar system, searches for life have traditionally looked for radio signals from possible extraterrestrial civilizations. That uses the physics of electromagnetic radiation. Special relativity and the speed of light limit keeps us from sending probes to other stars.
The April 2008 Scientific American has a nice article about a new strategy. Author Nancy Kiang discusses work that she and coworkers are doing on strategies for detecting vegetation on extrasolar planets. We have detected water on extrasolar planets using spectroscopy. Why not try to detect lush vegetation on a planet with similar techniques. NASA satellites use this tool and the spectral signature of chlorophyll to map vegetation on Earth. Increasing sensitivity and resolution might allow us to try this on extrasolar planets.
The trick is that plant life on extrasolar planets may have different spectral signatures. The green pigments on Earth plants are most efficient for the Sun's energy spectrum. Planets orbiting stars of different temperatures will have different spectra of natural light. Therefore plants on these planets are likely to have a different color chlorophyll and different spectral signatures. Knowing the physics of blackbodies is crucial to this analysis.
Posted by
Paul A. Heckert
Paul A. Heckert
Serendipity has played an important role in a surprising number of scientific discoveries, but it also takes an exceptional scientist to follow up on the lucky break.
I once read a definition of serendipity: when you want to go fishing, dig for worms, and strike oil. If this happened in real life, there are many who would bemoan the black goo and their inability to catch fish. Only a few would recognize the value of the black goo.
Sometimes scientific discovery is like this. Serendipity plays a large role, but the scientist must take advantage of the lucky break to make a discovery. Examples of serendipitous discoveries in science abound.
In 1820, Hans Christian Oersted performed an electrical demonstration for a class he was teaching, when a nearby magnetic compass started behaving strangely. Oersted could have declared the compass broken and tossed it in the trash. Instead he investigated further and discovered a long sought connection between electricity and magnetism.
In 1967 Jocelyn Bell-Burnell was a student worker on a large radio observation project. She noticed what she called "a bit of scruff" in her data. Her fellow students told her to ignore the scruff, finish her project, and graduate. She chose to ignore the well meaning advice instead of the scruff. For her efforts, she discovered pulsars, which turned out to be the neutron stars that had been predicted more than 30 years earlier but never found. After her discovery, it turned out that a few other astronomers had observed similar effects in their data, but ignored them.
Bell-Burnell found the equivalent of black goo in her data. Her reward for not going fishing and instead investigating the nature of the black goo was the scientific equivalent of finding oil - a major new discovery.
How many scientists missed out on an important discovery because they ignored the black goo or scruff in their data?
Sometimes scientific discovery is like this. Serendipity plays a large role, but the scientist must take advantage of the lucky break to make a discovery. Examples of serendipitous discoveries in science abound.
In 1820, Hans Christian Oersted performed an electrical demonstration for a class he was teaching, when a nearby magnetic compass started behaving strangely. Oersted could have declared the compass broken and tossed it in the trash. Instead he investigated further and discovered a long sought connection between electricity and magnetism.
In 1967 Jocelyn Bell-Burnell was a student worker on a large radio observation project. She noticed what she called "a bit of scruff" in her data. Her fellow students told her to ignore the scruff, finish her project, and graduate. She chose to ignore the well meaning advice instead of the scruff. For her efforts, she discovered pulsars, which turned out to be the neutron stars that had been predicted more than 30 years earlier but never found. After her discovery, it turned out that a few other astronomers had observed similar effects in their data, but ignored them.
Bell-Burnell found the equivalent of black goo in her data. Her reward for not going fishing and instead investigating the nature of the black goo was the scientific equivalent of finding oil - a major new discovery.
How many scientists missed out on an important discovery because they ignored the black goo or scruff in their data?
Posted by
Paul A. Heckert
Paul A. Heckert
Prior to 1967 black holes were called either frozen stars or collapsed stars. Neither term captures the imagination like the name black hole.
Few astronomical objects capture the public imagination like black holes. These exotic stellar corpses are so dense that their gravity prevents anything, even light, from escaping. It took a while for the idea to catch on. During World War I, Karl Schwarzschild's solution to Einstein's general relativity equations predicted the possibility of black holes and their event horizons, but few scientists took the idea seriously until the 1960s.
John A. Wheeler, who is usually credited with coining the name black hole, died last week at age 96. Despite providing the name and doing much to popularize the study of black holes, Wheeler did not buy the idea at first. At a scientific meeting in 1958, Wheeler disagreed with Robert Oppenheimer and said that such objects could not exist. Wheeler however eventually came to accept the possibility that such highly collapsed stars could exist and came up with the perfect name for them.
In his book, Black Holes and Warped Spacetime, Kip Thorne, a former student and colleague of Wheeler, describes how the term originated. They had been called collapsed stars by western researchers and frozen stars by Russian workers. According to Thorne, Wheeler pondered until he found the perfect name for these exotic objects. Wheeler then simply started using the name during a 1967 meeting, as if they had always been called black holes.
How much did finding this perfect name contribute to exciting the public imagination about black holes?
John A. Wheeler, who is usually credited with coining the name black hole, died last week at age 96. Despite providing the name and doing much to popularize the study of black holes, Wheeler did not buy the idea at first. At a scientific meeting in 1958, Wheeler disagreed with Robert Oppenheimer and said that such objects could not exist. Wheeler however eventually came to accept the possibility that such highly collapsed stars could exist and came up with the perfect name for them.
In his book, Black Holes and Warped Spacetime, Kip Thorne, a former student and colleague of Wheeler, describes how the term originated. They had been called collapsed stars by western researchers and frozen stars by Russian workers. According to Thorne, Wheeler pondered until he found the perfect name for these exotic objects. Wheeler then simply started using the name during a 1967 meeting, as if they had always been called black holes.
How much did finding this perfect name contribute to exciting the public imagination about black holes?
Posted by
Paul A. Heckert
Paul A. Heckert
Recent news articles about a black hole discovery use size and mass as if they were the same thing, but they are not. They are two completely different properties.
I recently read some news articles about the discovery of the smallest black hole. It is an interesting discovery, but the headlines should read the lowest mass black hole rather than the smallest black hole.
Reading the articles, I notice that no distinction is made between size and mass. The two words are used as if they are interchangeable terms. They are not. Size and mass are two distinct properties. We can measure an objects mass, which is in grams or kilograms, with a scale. We measure its size, which is in meters or similar units, with a ruler or similar device. An object with a larger mass is not always bigger in size. For example a 10 kilogram lead weight will be smaller in size than a feather pillow having a mass of 1 kilogram.
The astronomers who discover a black hole measure its mass from its gravitational effects. They then use the mass to infer its size, which we can not measure directly. It turns out that the size of a black hole is directly proportional to its mass. Hence, a more massive black hole will be larger in size, as long as we are referring to the size of the event horizon or Schwarzschild radius rather than the central singularity point.
Not all stars however have this property. For white dwarf stars or neutron stars the size decreases as the mass increases. Using the words size and mass as synonyms for these stars will result in many incorrect statements.
Language in physics is must be very precise. Words have very specific meanings that should not be interchanged. Science writers and journalists need to use the terms correctly to avoid confusing their readers.
Reading the articles, I notice that no distinction is made between size and mass. The two words are used as if they are interchangeable terms. They are not. Size and mass are two distinct properties. We can measure an objects mass, which is in grams or kilograms, with a scale. We measure its size, which is in meters or similar units, with a ruler or similar device. An object with a larger mass is not always bigger in size. For example a 10 kilogram lead weight will be smaller in size than a feather pillow having a mass of 1 kilogram.
The astronomers who discover a black hole measure its mass from its gravitational effects. They then use the mass to infer its size, which we can not measure directly. It turns out that the size of a black hole is directly proportional to its mass. Hence, a more massive black hole will be larger in size, as long as we are referring to the size of the event horizon or Schwarzschild radius rather than the central singularity point.
Not all stars however have this property. For white dwarf stars or neutron stars the size decreases as the mass increases. Using the words size and mass as synonyms for these stars will result in many incorrect statements.
Language in physics is must be very precise. Words have very specific meanings that should not be interchanged. Science writers and journalists need to use the terms correctly to avoid confusing their readers.
Posted by
Paul A. Heckert
Paul A. Heckert
What should one look for when evaluating claims on the possibility that cell phones cause brain tumors and other health claims?
I just read an article claiming that cell phone usage increases the risk of brain tumors. I have also read contradictory research reports claiming no connection. Contradictory claims for health research are common; so how does one evaluate health claims?
News articles often leave out crucial details. Look for in-depth articles that give necessary details, or better yet, the original article. Articles in peer reviewed medical/scientific journals are best.
The human body is extremely complex making epidemiological studies complex. Small effects are difficult to isolate causing many contradictory studies. For claims about health effects of cell phones, or anything else, don't rely on a single study. Look at many studies for overall trends.
When evaluating studies consider the following points:
News articles often leave out crucial details. Look for in-depth articles that give necessary details, or better yet, the original article. Articles in peer reviewed medical/scientific journals are best.
The human body is extremely complex making epidemiological studies complex. Small effects are difficult to isolate causing many contradictory studies. For claims about health effects of cell phones, or anything else, don't rely on a single study. Look at many studies for overall trends.
When evaluating studies consider the following points:
- How large is the study sample? Larger samples are more likely to be accurate.
- Is there a control sample? Controlled double blind studies are the gold standard for medical research.
- Are variables properly isolated? A good study isolates or corrects for other variables so that only the tested variable changes.
- To claim an effect, there should be a correlation, the stronger the better. However that is not enough. Correlation does not prove causation. So to claim something causes a health effect, good or bad, there should also be a plausible mechanism. In the case of cell phones, they send their signals via microwaves. Microwaves are very low energy electromagnetic waves, but there is a very small possibility repeated exposure could cause cellular damage.
- How long did the study last? Very small effects, such as from cell phones, may take decades to cause problems.
Posted by
Paul A. Heckert
Paul A. Heckert
Science fiction and science writer Arthur C. Clarke dies at age 90.
Arthur C. Clarke died today at age 90. Clarke was best known as a science fiction writer and I have enjoyed reading his science fiction since childhood. Clarke's science fiction combined excellent science with excellent story telling. Like many scientists, I prefer science fiction that is based on solid science.
Clarke's best known science fiction story may very well be 2001: A Space Odyssey. The book and movie, which was produced in collaboration with Stanley Kubrick, came out at time when 2001 seemed impossibly far in the future. Many science fiction books are based on good science, but the movie remains a rarity in that it is one of the few Hollywood science fiction movies with accurate science.
In addition to science fiction, Arthur C. Clarke did good science. His contribution to science that most affects us on a daily basis is the idea of communications satellites in geosynchronous orbits. At the time Clarke suggested the idea, it was more science fiction than science. The first satellite would not be launched into orbit for over a decade.
Like many brilliant ideas, it is elegantly simple. Launch a satellite to an orbital distance with an orbital period of 24 hours so that it stays above the same location on Earth. It is a relatively simple physics problem to figure out the required orbital distance. Satellites in geosynchronous orbits are very useful for communications satellites, because satellite TV and communications antennae do not have to move to track the satellite.
How many more of Clarke's science fiction ideas will someday become reality?
Clarke's best known science fiction story may very well be 2001: A Space Odyssey. The book and movie, which was produced in collaboration with Stanley Kubrick, came out at time when 2001 seemed impossibly far in the future. Many science fiction books are based on good science, but the movie remains a rarity in that it is one of the few Hollywood science fiction movies with accurate science.
In addition to science fiction, Arthur C. Clarke did good science. His contribution to science that most affects us on a daily basis is the idea of communications satellites in geosynchronous orbits. At the time Clarke suggested the idea, it was more science fiction than science. The first satellite would not be launched into orbit for over a decade.
Like many brilliant ideas, it is elegantly simple. Launch a satellite to an orbital distance with an orbital period of 24 hours so that it stays above the same location on Earth. It is a relatively simple physics problem to figure out the required orbital distance. Satellites in geosynchronous orbits are very useful for communications satellites, because satellite TV and communications antennae do not have to move to track the satellite.
How many more of Clarke's science fiction ideas will someday become reality?
Posted by
Paul A. Heckert
Paul A. Heckert
Locks in the Panama Canal provide a good experimental answer to the question: Can a battleship float in a bathtub?
In the excellent book, Thinking Physics, one question asks if a battleship can float in a bathtub. Ignore the obvious fact that no real bathtubs are as large as a battleship. The question is really about the amount of water required for a ship to float.
Very little water is really required. According to Archimedes's principle, the buoyant force on a ship or other object in water equals the weight of the water displaced. If the weight of the displaced water exceeds the ship's weight, the buoyant force is enough to float the ship. Ships weighing more than the displaced water sink.
Reading that statement might lead one to think that there must be at least enough water surrounding the ship to equal the weight of the ship, but that is not the case. The weight of the water displaced, not the weight of the water surrounding the ship, determines if the ship will float. The displaced water does not actually need to be there, hence there does not need to be much water actually surrounding the ship.
If there were a battleship-bathtub combination allowing the ship to just barely fit inside the tub, a thin layer of water between the outside of the battleship and the inside of the bathtub would be enough to float the battleship.
The locks in the Panama Canal are a good example of this principle. On a recent trip, I watched a ship going into the Miraflores locks of the canal. Even ships that barely fit into the locks float on the very small amount of water surrounding the ship in the lock. Observations confirm the theory.
Yes it is possible for a battleship to float in a bathtub.
Very little water is really required. According to Archimedes's principle, the buoyant force on a ship or other object in water equals the weight of the water displaced. If the weight of the displaced water exceeds the ship's weight, the buoyant force is enough to float the ship. Ships weighing more than the displaced water sink.
Reading that statement might lead one to think that there must be at least enough water surrounding the ship to equal the weight of the ship, but that is not the case. The weight of the water displaced, not the weight of the water surrounding the ship, determines if the ship will float. The displaced water does not actually need to be there, hence there does not need to be much water actually surrounding the ship.
If there were a battleship-bathtub combination allowing the ship to just barely fit inside the tub, a thin layer of water between the outside of the battleship and the inside of the bathtub would be enough to float the battleship.
The locks in the Panama Canal are a good example of this principle. On a recent trip, I watched a ship going into the Miraflores locks of the canal. Even ships that barely fit into the locks float on the very small amount of water surrounding the ship in the lock. Observations confirm the theory.
Yes it is possible for a battleship to float in a bathtub.
Posted by
Paul A. Heckert
Paul A. Heckert
The mathematical field of chaos arose from Edward Lorenz's early attempts to use computers for long range weather forecasts.
My last blog entry was about eclipses as an example of the predictive power of science. I was able to watch the eclipse however because another prediction was wrong. The weather report for my location predicted rain or snow but was wrong. It cleared up just in time to see the eclipse and the clouds moved back in when the eclipse ended.
In principle weather should be as predictable as eclipses. Weather also results from basic laws of physics. Weather however results from a much more complex system. We therefore do not have the computing power needed to accurately predict the weather. Accurate weather predictions would require a computer as complex as Earth's atmosphere.
This complexity makes weather a good example of a chaotic system. It is in fact the original example. In the early 1960's, Edward Lorenz started using computers to try to compute long range weather forecasts. It didn't work at the time, and still doesn't work, because our atmosphere is too complex. Very minor, almost immeasurable, differences in initial conditions can compound into significant differences. That is essentially the definition of a chaotic system and the origin of the term "butterfly effect". In a chaotic system, a butterfly in Brazil might cause a tornado in Texas.
This chaotic compounding of very small effects makes it impossible to accurately forecast weather. Science can predict things very accurately in principle, but in practice it does not work for extremely complex systems. That is the basic idea behind the mathematical field of chaos.
In principle weather should be as predictable as eclipses. Weather also results from basic laws of physics. Weather however results from a much more complex system. We therefore do not have the computing power needed to accurately predict the weather. Accurate weather predictions would require a computer as complex as Earth's atmosphere.
This complexity makes weather a good example of a chaotic system. It is in fact the original example. In the early 1960's, Edward Lorenz started using computers to try to compute long range weather forecasts. It didn't work at the time, and still doesn't work, because our atmosphere is too complex. Very minor, almost immeasurable, differences in initial conditions can compound into significant differences. That is essentially the definition of a chaotic system and the origin of the term "butterfly effect". In a chaotic system, a butterfly in Brazil might cause a tornado in Texas.
This chaotic compounding of very small effects makes it impossible to accurately forecast weather. Science can predict things very accurately in principle, but in practice it does not work for extremely complex systems. That is the basic idea behind the mathematical field of chaos.
Eclipses and the Power of Science
Posted by
Paul A. Heckert
Paul A. Heckert
Eclipses are a good example of the predictive power of science. Nature follows certain laws rather than being random or capricious.
The lunar eclipse occurred on schedule last Wednesday night. It started and stopped just when the predictions said it would. Eclipses can be predicted correctly well into the future. That is part of the nature and power of science. Natural phenomena follow very specific laws of nature that allow us to predict what will happen. Mathematical statements of the laws of nature coupled with mathematical tools allow us to make specific quantitative predictions.
Before we understood these laws, nature seemed capricious. Our ancestors, with no understanding of how orbits work, looked at eclipses and saw random events, which they often attributed to capricious gods. They then performed various rituals to appease these gods in hopes the gods would return the Sun or Moon.
Scientists however try to understand natural events and their causes. This understanding allows us to predict natural events. As our understanding of natural laws has increased throughout history, our ability to predict natural phenomena has also increased. Our belief in the capriciousness of nature has correspondingly declined. Complex natural phenomena still elude prediction, but we at least usually understand their causes and are working on the predictions.
There are limitations to the power, but much of the power of science comes from the ability to accurately predict what will happen in a specific situation. Otherwise we are, like our ancestors, at the mercy of capricious nature.
Before we understood these laws, nature seemed capricious. Our ancestors, with no understanding of how orbits work, looked at eclipses and saw random events, which they often attributed to capricious gods. They then performed various rituals to appease these gods in hopes the gods would return the Sun or Moon.
Scientists however try to understand natural events and their causes. This understanding allows us to predict natural events. As our understanding of natural laws has increased throughout history, our ability to predict natural phenomena has also increased. Our belief in the capriciousness of nature has correspondingly declined. Complex natural phenomena still elude prediction, but we at least usually understand their causes and are working on the predictions.
There are limitations to the power, but much of the power of science comes from the ability to accurately predict what will happen in a specific situation. Otherwise we are, like our ancestors, at the mercy of capricious nature.
Why Satellites Fall from Orbit
Posted by
Paul A. Heckert
Paul A. Heckert
With no friction a satellite will orbit forever without engines, but Earth's upper atmosphere provides some friction.
Many years ago I watched a Star Trek episode with a group of science types. The crew was trying to get Enterprise's engines working again, otherwise the Enterprise and her good crew would crash into the planet they were orbiting.
Because we understood how orbits work, we laughed at the writers' lack of physics knowledge. Once something is orbiting a planet or star, it needs no engines to keep it in orbit. Earth doesn't have an engine to orbit the Sun and the Moon does not need engines to orbit Earth. These orbits have been stable for nearly 5 billion years.
Why then do satellites fall from orbit? Lately the possibility of a spy satellite falling from orbit has been in the news. Those of us who are old enough might remember the Skylab falling into the Pacific in the late 1970s. Occasionally other small satellites streak down from orbit.
The key is friction. Orbits remain stable as long as no frictional forces slow the satellite. Rather than ending abruptly; Earth's atmosphere just gradually gets thinner. In a low Earth orbit the atmosphere is very thin but not quite a vacuum. Hence there is a small amount of atmospheric resistance to slow the satellite. As the orbital speed slows, the orbit decays to a closer distance. The atmosphere is thicker, increasing the atmospheric resistance. The orbit decays faster and the satellite streaks down to Earth. Let's hope it doesn't hit a populated area.
If the Star Trek writers had written something into the script about atmospheric friction, we would not have made fun of them.
Because we understood how orbits work, we laughed at the writers' lack of physics knowledge. Once something is orbiting a planet or star, it needs no engines to keep it in orbit. Earth doesn't have an engine to orbit the Sun and the Moon does not need engines to orbit Earth. These orbits have been stable for nearly 5 billion years.
Why then do satellites fall from orbit? Lately the possibility of a spy satellite falling from orbit has been in the news. Those of us who are old enough might remember the Skylab falling into the Pacific in the late 1970s. Occasionally other small satellites streak down from orbit.
The key is friction. Orbits remain stable as long as no frictional forces slow the satellite. Rather than ending abruptly; Earth's atmosphere just gradually gets thinner. In a low Earth orbit the atmosphere is very thin but not quite a vacuum. Hence there is a small amount of atmospheric resistance to slow the satellite. As the orbital speed slows, the orbit decays to a closer distance. The atmosphere is thicker, increasing the atmospheric resistance. The orbit decays faster and the satellite streaks down to Earth. Let's hope it doesn't hit a populated area.
If the Star Trek writers had written something into the script about atmospheric friction, we would not have made fun of them.
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