General Science Articles

Cheat Sheet / Updated 09-27-2022

Whether you're talking about evolution — or any other element of science — you should understand the process of scientific investigation, which proves or disproves a scientific theory. Take a look at a chart of our hominid ancestors as discovered through fossil records, and learn some key terms to grasp the course of evolution.

Cheat Sheet / Updated 03-27-2016

Albert Einstein revolutionized science with his famous writings on relativity and quantum physics. But Einstein was more than a scientist — he was also a complex and well-respected man and an NAACP member who called racism America's "worst disease."

Article / Updated 03-26-2016

How do the scientists know what they know? When it comes to gathering information, scientists usually rely on the scientific method. The scientific method is a plan that is followed in performing a scientific experiment and writing up the results. It is not a set of instructions for just one experiment, nor was it designed by just one person. The scientific method has evolved over time after many scientists performed experiments and wanted to communicate their results to other scientists. The scientific method allows experiments to be duplicated and results to be communicated uniformly. As you're about to see, the format of the scientific method is very logical. Really, many people solve problems and answer questions every day in the same way that experiments are designed. Hypothetically speaking When preparing to do research, a scientist must form a hypothesis, which is an educated guess about a particular problem or idea, and then work to support it and prove that it is correct, or refute it and prove that it is wrong. Whether the scientist is right or wrong is not as important as whether he or she sets up an experiment that can be repeated by other scientists, who expect to reach the same conclusion. The value of variables Experiments must have the ability to be duplicated because the "answers" the scientist comes up with (whether it supports or refutes the original hypothesis) cannot become part of the knowledge base unless other scientists can perform the exact same experiment(s) and achieve the same result; otherwise, the experiment is useless. "Why is it useless," you ask? Well, there are things called variables. Variables vary: They change, they differ, and they are not the same. A well-designed experiment needs to have an independent variable and a dependent variable. The independent variable is what the scientist manipulates in the experiment. The dependent variable changes based on how the independent variable is manipulated. Therefore, the dependent variable provides the data for the experiment. Experiments must contain the following steps to be considered "good science." 1. A scientist must keep track of the information by recording the data. The data should be presented visually, if possible, such as through a graph or table. 2. A control must be used. That way, results can be compared to something. 3. Conclusions must be drawn from the results. 4. Errors must be reported. Suppose that you wonder whether you can run a marathon faster when you eat pasta the night before or when you drink coffee the morning of the race. Your hunch is that loading up on pasta will give you the energy to run faster the next day. A proper hypothesis would be something like, "The time it takes to run a marathon is improved by consuming large quantities of carbohydrates pre-race." The independent variable is the consumption of pasta, and the dependent variable is how fast you run the race. Think of it this way: How fast you run depends on the pasta, so how fast you run is the dependent variable. Now, if you eat several plates of spaghetti the night before you race, but then get up the next morning and drink two cups of coffee before you head to the start line, your experiment is useless. Why is it useless? By drinking the coffee, you introduce a second independent variable, so you will not know whether the faster race time is due to the pasta or the coffee. Experiments can have only one independent variable. If you want to know the effect of caffeine (or extra sleep or improved training) on your race time, you would have to design a second (or third or fourth) experiment. Checking your stats Of course these experiments would have to be performed many times by many different runners to demonstrate any valid statistical significance. Statistical significance is a mathematical measure of the validity of an experiment. If an experiment is performed repeatedly and the results are within a narrow margin, the results are said to be significant when measured using the branch of mathematics called statistics. If results are all over the board, they are not that significant because one definite conclusion cannot be drawn from the data. Tracking the information Once an experiment is designed properly, you can begin keeping track of the information you gather through the experiment. In an experiment testing whether eating pasta the night before a marathon improves the running time, suppose that you eat a plate of noodles the night before and then drink only water the morning of the race. You could record your times at each mile along the 26-mile route to keep track of information. Then, for the next marathon you run (boy, you must be in great shape), you eat only meat the night before the race, and you down three espressos on race morning. Again, you would record your times at each mile along the route. What do you do with the information you gather during experiments? Well, you can graph it for a visual comparison of results from two or more experiments. The independent variable from each experiment is plotted on the x-axis (the one that runs horizontally), and the dependent variable is plotted on the y-axis (the one that runs vertically). In experiments comparing the time it took to run a marathon after eating pasta the night before, getting extra sleep, drinking coffee, or whatever other independent variable you may want to try, miles 1 to 26 would be labeled up the y-axis. The factor that does not change in all the experiments is that a marathon is 26 miles long. The time it took to reach each mile would be plotted along the x-axis. This data might vary based on what the runner changed before the race, such as diet, sleep, or training. You can plot several independent variables on the same graph by using different colors or different styles of lines. Your graph might look something like the one in Figure 1. Figure 1: Graph showing the time each mile of a marathon was reached for a runner who consumed pasta (white dotted line), a runner who consumed coffee (squared line), and a runner who slept four extra hours prior to the race (black dotted line). Taking control of your experiment How would you know if your race times were improved either by eating pasta or drinking coffee? You would have to run a marathon without eating pasta the night before or drinking coffee the morning of the race. (Exhausted yet?) This marathon would be your control. A control is a set of base values against which you compare the data from your experiments. Otherwise, you would have no idea if your results were better, worse, or the same. Drawing conclusions So, maybe it took you less time to reach each mile along the marathon route after the night of pasta eating, but your race times after drinking the coffee matched those of the control. That would support your initial hypothesis, but it would refute your second hypothesis. There's nothing wrong with being wrong, as long as the information is useful. Knowing what doesn't work is just as important as knowing what does. Your conclusion to these two experiments would be something like: "Consuming pasta the night before a 26-mile marathon improves race time, but consuming caffeine has no effect." However, in scientific experiments you have to confess your mistakes. This confession lets other scientists know what could be affecting your results. Then, if they choose to repeat the experiment, they can correct for those mistakes and provide additional beneficial information to the knowledge base. In the pasta-caffeine-race experiment, if you had consumed the pasta the night before and then the caffeine the morning of the race, your major error would be that of including more than one independent variable. Another error would be having too small of a sample. A more accurate determination could be made by recording the race times at each mile for many runners under the same conditions (i.e., having them eat the same amount of pasta the night before a race or consuming the same amount of caffeine the morning of a race). Of course, their individual control times without those variables would have to be taken into account. Science. It's all in the details.

Article / Updated 03-26-2016

When Einstein began his research as an amateur scientist, there were two major problems: Light was known to be a wave but had to be considered as made up of lumps — not waves — to explain the ultraviolet catastrophe (the observation that hot objects emit less ultraviolet light and more light of other colors). In mechanics, the results of experiments are identical in motion or at rest (all motion is relative, and there is no absolute motion). Not so in electromagnetism, because you can be at rest in the ether (there is absolute motion). Scientists were struggling to make existing theories work, but more and more they were becoming aware of their inadequacies. The stage was set for Einstein to make history, and in 1905, he did just that. What did Einstein achieve during his year of miracles? He wrote and published five scientific papers that would change physics forever: 1. March 17: "On a heuristic point of view concerning the production and transformation of light." This paper laid the foundation for quantum theory with the introduction of the concept of quanta of energy, or photons. 2. April 30: "A new determination of molecular dimensions." This was Einstein's PhD dissertation, which the University of Zurich accepted in July. Although not revolutionary, this paper helped establish the existence of molecules. 3. May 11: "On the motion of small particles suspended in a stationary liquid." This paper not only explained the zigzag motion of a speck in a liquid (called Brownian motion), which had puzzled scientists for a long time, but also showed the reality of molecules. 4. June 30: "On the electrodynamics of moving bodies." This was Einstein's first paper on the theory of relativity. 5. September 27: "Does an object's inertia depend on its energy content?" This second paper on the theory of relativity contained Einstein's most famous equation: E = mc2. Even before the first paper was published, Einstein suspected that what he was about to do was of great importance. In May of 1905, he wrote to one of his closest friends: I promise you four papers . . . the first of which I might send you soon, since I will be receiving the free reprints. The paper deals with radiation and the energy properties of light and is very revolutionary, as you will see . . . The first paper of 1905 certainly was revolutionary. It laid the foundation for quantum theory. Einstein won the Nobel Prize in physics several years later for this work. As if that weren't enough, the fourth paper and fifth papers that Einstein published that year were also revolutionary. The other two papers were also very important because they helped to establish the existence of atoms and molecules, which were not yet universally accepted. But unlike the other three, they didn't turn the scientific world upside down. Defining the nature of light Einstein solved the first major problem in physics with thefirst paper of his miracle year, the paper on the light quantum. German physicist Max Planck had used a mathematical trick to explain radiation in the ultraviolet part of the spectrum; he bundled light into quanta of energy. In the first paper of 1905, Einstein made Planck's quanta a property of light and of all electromagnetic radiation (radio waves, x-rays, ultraviolet and infrared light, and so on). It isn't that light is lumpy in some instances. Light is always lumpy, like a particle. It comes in bundles. The light emitted by hot objects isn't somehow split into these bundles. Light is made up of these bundles, these photons as they are called, that can't be split. By making lumpiness a property of light, Einstein paved the way for the development of quantum theory that would take place in the 1920s. Quantum theory would later explain that light is both a wave and a particle. Light behaves like a wave under certain conditions, and under other conditions, it behaves like a particle. Quantum theory integrates both behaviors seamlessly. Even though Einstein's first paper was read with a great deal of interest, most physicists didn't believe his idea of photons of light, including Planck himself initially. For the next 15 years, Einstein was almost the only one who believed in the light quantum idea. But quantum theory, developed by other physicists in the 1920s based on Einstein's work, would become the most successful physics theory ever. Einstein's first paper of 1905 also explained a phenomenon called the photoelectric effect in a clever but simple way. In 1921, after Einstein had already become world famous, the Nobel committee awarded him the Nobel Prize in physics for this discovery. Eliminating the ether A key contradiction between mechanics and electromagnetism was the existence of absolute motion. According to Newton, all motion is relative — absolute motion can't exist. But according to Maxwell, it can. Einstein sided with mechanics. In his fourth paper of 1905, commonly referred to as the relativity paper (even though the word relativity doesn't appear in the title), Einstein reformulated electromagnetism so that it would also remain unchanged whether the person observing was at rest or moving at a constant velocity. In other words, he modified electromagnetism so that its description would depend only on relative motion, without any need for the ether. Light does not need a substance to move through. It can move in the empty space between the stars. With the publication of this paper, the ether was gone from physics. According to Einstein, absolute motion does not exist. When you are on an airplane, you have no way to tell, without looking out the window, whether you are moving or at rest. All the laws of physics, those of mechanics and those of electromagnetism, are the same everywhere in the universe, no matter how you move (provided that you don't accelerate). Einstein extended the idea of relative motion to light itself. Anybody, anywhere in the universe, whether at rest or in motion with a constant velocity, always measures the same speed of light. All of thephysics known at the timefollowed the simple principles that Einstein put forward in his relativity paper. And all the physics discoveries since then have followed those principles. Einstein's paper didn't just fix the problems with electromagnetism; it actually created a new way of looking at the world. Introducing E = mc2 Einstein's final paper of 1905, which was also the last of his revolutionary papers, contained the famous E = mc2 equation. This paper was more of a follow-up to the first relativity paper than an introduction to a new equation. In this beautiful three-page paper, Einstein used electromagnetic equations from his first relativity paper to explain that energy has mass. Two years later, he realized that the opposite should also be true, that mass of any kind must have energy. According to Einstein, mass and energy are equivalent. An object's mass is a form of energy, and energy is a form of mass. Here are a few examples of how this tiny little equation has changed our lives in big ways: Scientists spent more than 40 years finding a way to demonstrate the reality of E = mc2. World events made this demonstration very dramatic with the development of the nuclear bomb, which was first tried in the desert in Alamogordo, New Mexico, in July of 1945. One month later, the bomb was dropped for real in Hiroshima and Nagasaki, Japan. The energy released by the bomb comes from nuclear fission, the splitting of the uranium-235 nucleus. E = mc2 gives the recipe for the conversion of part of the uranium nucleus into energy. The same recipe applies to a nuclear reactor, except that the production of energy is controlled with very precise procedures. Together with the later development of quantum physics, E = mc2 helped explain another long-standing problem: understanding how the sun burns its fuel and generates the energy that makes possible life on earth.

Article / Updated 03-26-2016

Einstein obviously had a tremendous influence on the scientific community and the entire world. Einstein enjoyed people's company and learned a great deal from those around him – including the two women whom he married over the course of his life. First wife, Mileva Mileva Maric was the only female physics major at the Polytechnic in Zurich, where Einstein went to college. During their second semester, Einstein and Mileva began to take interest in each other. Their relationship developed into a romance that eventually led to marriage, in spite of strong opposition from Einstein's family (especially his mother). Einstein and Mileva's romance is well-documented in letters they wrote to each other between 1897 and 1903, which were discovered only in 1987. Not much was known about Mileva before the appearance of these letters. In her early letters, Mileva wrote with enthusiasm about the physics she was learning in class. As time went on, the focus on physics disappeared, and her letters became love letters, showing her feelings for Einstein and her preoccupation with their relationship. Einstein wrote to her about his love for her, about his family's reaction to their affair, and about physics. The letters are an invaluable and direct record of Einstein's early intellectual development. He proudly told Mileva about his ideas on relativity and about his discoveries of inconsistencies in some of the physics papers that he read. Mileva, with her understanding of physics, seemed to be his sounding board. Starting a family After graduating from the Polytechnic and before starting his job at the Bern patent office, Einstein took a temporary job away from Zurich, while Mileva stayed at the Polytechnic. (She had failed final exams and was preparing to try them again.) During those few months, Einstein came to see Mileva in Zurich every Sunday. During one of those visits, Mileva told Einstein that she was pregnant. The pregnancy didn't help Mileva in her studies, which had been a struggle for years. She took her finals again and failed. She was devastated, and she quit school. Depressed, she went home to her parents in Hungary, who weren't happy with either piece of news. Initially, her father angrily prohibited Mileva from marrying Einstein. During the winter of 1902, Mileva gave birth to a girl, Lieserl. The birth was difficult, and Einstein wasn't present. He learned about it in a letter from Mileva's father. No one knows what happened to Einstein's only daughter. Soon after her birth, she disappeared, and no record of her has ever been found. Mileva may have given her up for adoption. About a year later, on January 6, 1903, Einstein and Mileva got married in a civil ceremony at the court house in Bern. Einstein was working at the patent office, making an adequate salary as a civil servant. Life was relatively good for them. A little more than a year after their marriage, Mileva gave birth to their first son, Hans Albert. Although he initially tried to help Mileva with the baby, overall Einstein wasn't a good husband. He was interested in his work and paid little attention to Mileva or to his son. It became worse during the burst of creativity in 1905, referred to as his "miracle year." Their relationship began to suffer. Struggling with depression Einstein took refuge in his work. Mileva became depressed. According to one visitor, their house was a mess. Einstein tried to help, but his heart wasn't in it. He would carry the baby while trying to write his equations on a pad. On July 28, 1910, Einstein and Mileva's second son, Eduard, was born. For a while, things improved between them, but that didn't last. Mileva continued to be depressed and was becoming jealous of the women Einstein flirted with. In 1911, Einstein and his family moved to Prague, where he'd accepted a nice offer from the university. Mileva hated the city. A year later, Einstein accepted an offer from his alma mater and moved back to Zurich. Mileva was delighted. That lasted only a couple of years. In 1914, Einstein accepted an offer from the University of Berlin and moved his family there. Mileva was extremely unhappy about moving to Berlin. Einstein's cousin, Elsa, lived there, and Mileva was jealous of her. Besides, Germans looked down on people of Serbian origin, like Mileva. Heading toward divorce Mileva was right about Elsa. Einstein started seeing her often, and that was the beginning of the end for Einstein's marriage. After a fight, Einstein moved out, and some time later, he wrote a contract for their separation that detailed the support he would provide. Mileva and the boys moved back to Zurich. In 1916, during one of his visits to see the boys, Einstein asked Mileva for a divorce, which led her to have nervous breakdown. She recovered slowly, but their son Eduard then became a cause for concern. Eduard was extremely gifted. He read Goethe and Friedrich Schiller in first grade and had a photographic memory. He learned anything that he set out to learn with breathtaking speed. But he was troubled. (Eduard had to be placed in a psychiatric hospital in 1933 after he showed signs of mental instability. He died at the hospital in 1965.) Mileva and Einstein divorced on February 14, 1919. After the divorce, Mileva spent a great deal of her life taking care of Eduard. In 1947, her health began to deteriorate. The next year, she suffered a stroke that left her paralyzed on one side of the body. On August 4, 1948, Mileva died. Mileva had started out as Einstein's intellectual equal; they read, studied, and discussed physics together. By 1902, their partnership had changed, because Einstein's thinking had developed to a different level. But until then, her presence helped him shape his thoughts by providing him with the loving ears of another physicist. Second Wife, Elsa Elsa was Einstein's cousin, the daughter of his "rich uncle" Rudolf Einstein and his aunt Fanny (Pauline's sister). Elsa was first married to Max Loewenthal, a textile trader from Berlin with whom she had two daughters, Ilse and Margot, and a son who died shortly after birth. Einstein and Elsa met often while they were growing up but lost contact as adults. During one of Einstein's visits to Berlin while he was still married to Mileva, he met his cousin again. She was divorced and living with her two daughters in an apartment right above her parents. Einstein felt comfortable with Elsa in this family environment. When he moved to the University of Berlin, he continued seeing her with some frequency. After his separation from Mileva, Einstein saw Elsa often, and he moved in with her in September of 1917. Elsa was clearly interested in Einstein and kept the pressure on him to divorce Mileva. After the divorce took place in 1919, Einstein felt free to marry Elsa. His main attraction to her was her cooking. He also felt grateful to her because she had taken care of him when he was ill with stomach problems. There was no passion between them. Nevertheless, they were married on June 2, 1919, three and a half months after his divorce from Mileva. Einstein was 40 and Elsa was 43. Their marriage seems to have been platonic. Although some of Einstein's friends criticized Elsa's eagerness for fame, she was receptive of her husband's importance and was able to create a nice environment for Einstein to work in. Her efficiency in running the household made Einstein's life much easier. As happened during his marriage to Mileva, problems developed because of Einstein's flirting with other women. He was very famous, and women all over the world were attracted to him. In 1935, after Einstein and Elsa had moved to the United States, she fell ill with heart and kidney problems. She died on December 20, 1936. Einstein had been very attentive and caring during Elsa's last months of her life. After she died, he adjusted quickly. "I have got used extremely well to life here," he wrote. "I live like a bear in my den . . . This bearishness has been further enhanced by the death of my woman comrade, who was better with other people than I am."

Article / Updated 03-26-2016

For those of us who keep our eyes fixed to the heavens, Einstein's theory of special relativity has thrilling implications. Namely, the relativity of time and space allows for the possibility of human interstellar travel. The nearest stars to Earth, the binary stars Proxima and Alpha Centauri, are about four light-years away. In other words, light from these stars, traveling at 300,000 km (186,000 mi) per second, takes four years to reach us. And there are other interesting stars for us to visit beyond our closest neighbors. Over the past ten years, astronomers have discovered more than 125 planets orbiting around stars similar to our sun. They've been able to "see" them by studying the tiny motions that these planets cause on their suns as they move around them. Among these newly discovered planets, there is a very young one — a planet in orbit around the star CoKu Tau 4, about 420 light-years from Earth. There is even one that astronomers have actually seen directly with the European Southern Observatory Very Large Telescope in Chile. It orbits its sun at some 230 light-years from us. We may also want to visit the center of our galaxy, which is hidden from our eyes by interstellar dust but visible to our x-ray, infrared, and radio telescopes. Scientists have discovered a super massive black hole there. (A black hole is an object with such strong gravity that not even light can escape.) In the future, human beings may also want to tour our entire galaxy and even visit other galaxies. However, even if we design a spaceship that can travel at 0.99c, interstellar travel beyond the nearest stars seems impossible for the foreseeable future. Crossing our own galaxy will take more than 100,000 years, and a trip to Andromeda, the nearest galaxy, will take more than 2 million years. That timeline is accurate for those of us staying behind. But, on the moving ship, time will be dilated. A future spacecraft, using technologies that we haven't even dreamed of, may use an engine that could sustain a constant acceleration of 1 g until the ship reaches relativistic speeds. With such an engine, a trip even to Andromeda may be possible within a human lifetime. For those astronauts, however, returning back home is out of the question. Back on Earth, entire civilizations would've come and gone, while the astronauts who left in their 20s would be only in their 80s. Table 1 shows several possible trips on a ship constantly accelerating at 1 g. The figure for "Distance in Light-Years" is also the time that would pass on Earth while the ship traveled to its destination. Table 1: Ship Time for Interstellar Travel at 1 g Destination Distance in Light-Years Ship Time in Years Alpha Centauri 4 3 Sirius 9 5 Epsilon Eridani 10 5 2M1207: Star with first visible planet 230 11 CoKu Tau 4 420 12 Galactic center 30,000 20 Andromeda galaxy 2,000,000 28

Article / Updated 03-26-2016

The energy of a nuclear bomb comes from inside the nucleus of the atom. Mass is converted into energy according to E = mc2. This energy is the binding energy of the nucleus, the glue that keeps the nucleus of the atom together. Radiating particles In some cases, the nuclear force is not able to keep a nucleus all together, and the nucleus loses some of its particles. French physicist Henri Becquerel accidentally discovered this effect in 1896. He'd been intrigued by the experiments with x-rays that Wilhelm Roentgen had been doing in Germany. Becquerel obtained a uranium salt to see if he could observe these x-rays. In his laboratory at the Museum of Natural History in Paris (where his father and grandfather had also been physics professors), Becquerel started his experiments by exposing to the sun a photographic plate with the uranium salt sprinkled on it, thinking that sunlight would activate the x-rays. One cloudy day when he couldn't perform one of his experiments, he placed the photographic plate with the uranium salt in a drawer. A few days later, he went ahead and developed the plate anyway, thinking that he was going to get a faint image. But the image was very sharp, with high contrast. He soon realized that he'd discovered a new type of energetic radiation. When Pierre and Marie Curie heard of Becquerel's experiment, they began to search for other elements that could emit similar rays. They found that thorium and uranium emit the same radiation. And in 1898, they discovered two new elements: polonium (named after Marie's native Poland) and radium. The Curies named the effect radioactivity. In England, Ernest Rutherford designed experiments to investigate this new radioactivity phenomenon and was able to show that these rays come in two varieties, one more penetrating than the other. The less penetrating one, which he called alpha, has positive electric charge. The Curies in Paris discovered that the other one, called beta, is negatively charged. Realizing limitations of the nuclear force Why are these nuclei giving off particles? The nuclear force is supposed to be extremely strong. Why isn't it able to keep all these particles inside the nucleus? The answer is that the nuclear force has a very short range of action. It's able to tie in particles that are close to each other. If the particles are too far apart, the force stops working. If the particles happen to be protons, which have positive charges, the electric force acting alone will push them apart. When the nuclear particles are bundled up in a nucleus of an atom, each particle interacts only with its nearest neighbors. In a nucleus with more than 30 particles, a particle in the middle of the nucleus won't feel the nuclear force of a particle at the edges. Each of the nuclear particles in the cluster feels the nuclear attraction of the other particles in the cluster (its immediate neighbors). However, these particles don't feel the force of the particle near the edge. Think of it this way: Imagine that you and a group of several friends are trying to stay together while swimming in rough waters. If you all decide to hold hands, each one of you will be holding on to the two nearest neighbors. The grip of a swimmer at one end of the large chain, no matter how strong it seems to his immediate neighbor, has no influence on a swimmer at the other end. If the water gets too rough, the whole group may break apart, creating small groups of two, three, or maybe four. Like the rough waters that break apart your group, the electrical repulsion of the protons tries to break apart a large nucleus. However, in the nucleus, certain helpers try to keep the whole thing together: the neutrons. Neutrons don't have an electric charge, and the only force they feel is the nuclear attraction. They are the skilled swimmers who won't be pushed away by the rough waters. If you have enough of them in your group, it will stay together. Studying alpha decay Like the swimming group with the skilled swimmers, a nucleus with a balanced number of protons and neutrons is stable and stays together. But if a nucleus has too many protons, the total electric repulsion can overwhelm the attraction of the nuclear force, and a piece of the nucleus can fly apart. The piece that leaves the nucleus is usually in the form of an alpha particle, a cluster of two protons and two neutrons. (This particle is also the nucleus of the helium atom.) It turns out that these four particles are held together very tightly by the nuclear force, so this cluster is a very stable configuration of nuclear particles. These are the particles that Rutherford identified as alpha radiation. Physicists call the effect of the alpha particles leaving the nucleus alpha decay. Detecting beta decay It seems as if having a lot of neutrons is good for a nucleus because neutrons don't feel the electrical repulsion but do feel the nuclear attraction. They are the skilled swimmers in rough waters. However, these skilled swimmers don't have a lot of stamina. A neutron on its own, away from the nucleus, lasts for only about 15 minutes. After these 15 minutes, it changes into a proton, an electron, and another small particle called the neutrino. This effect is called beta decay. Inside the nucleus, surrounded by the other particles, neutrons last much longer. When there are enough protons around, a quantum physics effect prevents neutrons from creating more protons. Quantum physics describes it by giving each proton in the nucleus its own space or slot. When there are enough protons, all the slots are taken and no additional protons are allowed. In a nucleus with too many neutrons, a neutron at the outer edges of the nucleus can decay into a proton because there will be empty slots for this new proton to stay in. Therefore, A nucleus with too many neutrons is unstable and decays into a proton, an electron, and a neutrino. The protons created by this decay stay in the nucleus. The electrons don't belong in the nucleus; there are no slots for them there. The same goes for the neutrinos. Therefore, the electrons and neutrinos are both ejected. Neutrinos are extremely difficult to detect. They can go through the entire Earth and come out at the other end without a single collision. But electrons are easy to detect. These breakaway electrons create the beta rays that the Curies and Rutherford saw. In both cases, the alpha and beta decays, the radioactive nucleus changes into the nucleus of another element when it gives off the alpha or the beta particle. A third type of radioactive decay exists in which the unstable nucleus gives off only very energetic radiation, but no particles are ejected. The radiation is electromagnetic and is called gamma rays. In this case, the nucleus simply gives back some energy that it gained previously, but it doesn't lose its identity.

Article / Updated 03-26-2016

Boy, put biology, geology, and chemistry together, and you get biogeochemical! When you talk about the "circle of life," the circle to which you are referring is a biogeochemical cycle. The plants and animals that live and then die are the bio part; the earth that they decompose into comprises the geo part; and the process by which organic matter returns to the chemical elements in the earth is explained by the chemical part. There are four biogeochemical cycles, and each of them returns to the earth important elements that are required in living organisms. The hydrologic (water) cycle Plants absorb water from soil, and animals drink water or eat animals, which are made mostly of water. When plants go through the process of transpiration (that's when water evaporates from a leaf and more water is pulled up from the roots of the plant and out through the cells on the surface of the leaf), they give off water. When animals create perspiration, they release water, which is evaporated into the atmosphere. Water also is released from plants and animals as they decompose. Decomposing tissue becomes dehydrated, which is what causes the dried-out tissues to break down and fall off into the soil. As water evaporates into the air, wind moves air over bodies of water, and precipitation (rain, snow, sleet, hail) releases water into larger bodies of water such as lakes, rivers, oceans, and even glaciers. Water from precipitation and decomposing tissue also gets into groundwater, which ultimately supplies larger bodies of water. The carbon cycle Plants take in carbon dioxide for photosynthesis. Animals consume plants or other animals, and all living things contain carbon. Carbon is what makes organic molecules organic (living). Carbon is necessary for the creation of molecules such as carbohydrates, proteins, and fats. Plants release carbon dioxide when they decompose. Animals release carbon dioxide when they decompose or respire. (Animals take in oxygen and release carbon dioxide when they breathe.) Carbon dioxide also is released when organic matter such as wood, leaves, coal, or oil are burned. The carbon dioxide returns to the atmosphere, where it can be taken in by more plants that are then consumed by animals. Decomposing animals and plants leach carbon into the ground, forming fossil fuels such as coal or oil. Peat also forms from the decomposition of organic matter. Some carbon is stored in the form of cellulose in the wood of trees and bushes. The phosphorus cycle ATP, that ubiquitous energy molecule created by every living thing, needs phosphorus. You can tell that by its name; triphosphate indicates that it contains three molecules of phosphate, which requires phosphorus. DNA and RNA, the genetic molecules present in every living thing, have phosphate bonds holding them together, so they require phosphorus, too, as does bone tissue. Plants absorb inorganic phosphate from the soil. When animals consume plants or other animals, they acquire the phosphorus that was present in their meal. Phosphorus is excreted through the waste products created by animals, and it is released by decomposing plants and animals. When phosphorus gets returned to the soil, it can be absorbed again by plants, or it becomes part of the sediment layers that eventually form rocks. As rocks erode by the action of water, phosphorus is returned to water and soil. The nitrogen cycle Because amino acids build proteins, nitrogen is pretty important. Nitrogen also is present in the nucleic acids DNA and RNA. Life could not go on without nitrogen. The nitrogen cycle (Figure 1) is the most complex biogeochemical cycle because nitrogen can exist in several different forms. Nitrogen fixation, nitrification, denitrification, and ammonification are all parts of the nitrogen cycle. Figure 1: The nitrogen cycle. Nitrogen fixation: In the soil, as well as in the root nodules of certain plants, nitrogen is "fixed" by bacteria, lightning, and ultraviolet radiation. The "fixing of nitrogen" does not mean nitrogen was broken; a better term might be "fixated," because the bacteria put elemental nitrogen into a form that can be used by living organisms and do not allow it to leave that form and revert to elemental nitrogen. Nitrification: Certain bacteria take the forms into which nitrogen was fixated and further process it (oxidization). Oxidation provides energy for the nitrogen cycle to take place — the bacteria that live in soil cannot harness energy from the sun. The energy they use during their work in the nitrogen cycle comes from this process. Denitrification and ammonification. Plants absorb nitrates or ammonium ions from the soil and turn them into organic compounds. Animals obtain nitrogen by consuming plants or other animals. Therefore, the waste products of animals contain nitrogen. Ammonium ions, ammonia, urea, and uric acid all contain nitrogen. So regardless of what form of excretion an animal has, some nitrogen is released back into the ecosystem through excrement. Dead plants and animals are food for decomposing bacteria.

Article / Updated 03-26-2016

James Clerk Maxwell's theory of electromagnetism tells us that light is an electromagnetic wave traveling at 300,000 kilometers per second (kps). Maxwell's equations tell us that changing electric and magnetic fields create and sustain each other even in regions where there are no electric charges to accelerate or magnets to move. Maxwell showed how these two fields, interlocked in a dance, create their own light show. The fields spread out through space as light or as any other electromagnetic wave. But before Maxwell, other scientists made their own attempts to identify the nature of light and to calculate its speed. Galileo: Hanging lanterns How fast does light travel through space? The modern value for the speed of light is 300,000 kps (186,000 mps). Actually, it's 299,792.458 kps, but that's a tough number to remember. The circumference of the earth is about 40,000 km (25,000 mi), so it would take light slightly longer than a tenth of a second to travel around the world. With modern instruments, the extremely large value of the speed of light can be measured. But how did anyone measure it before those instruments were created? Galileo was the first person who tried. He had two people stand on distant hills flashing lanterns. Clearly, Galileo's experiment didn't work — he couldn't even measure seconds accurately, much less the tiny fraction of a second that it took for light to travel between the two hills. But Galileo was Galileo, and with his crude approach to this very difficult experiment, he was still able to show that the speed of light is finite. His contemporary, French philosopher René Descartes, had been saying that it was infinite. Roemer: Timing a satellite Some 70 years after Galileo's experiment, the young Danish astronomer Olaus Roemer was able to get the first value of the speed of light. But he had to go farther than a distant hill to get it. He used the satellites of Jupiter instead. And he also had to fight with his boss — the famous astronomer Jean-Dominique Cassini, for whom the Saturn rings are now named. Tackling an inconsistency Roemer was a bright 21 year old who was hired by one of Cassini's assistants to help at the Paris Observatory, which was headed by Cassini. But Roemer didn't just help; he tackled one of the observatory's major problems. Cassini's observations were showing a problem with the motion of one of Jupiter's satellites, the one named Io (after one of the many lovers of Zeus, who is called Jupiter in Roman mythology). It seemed as if Io's orbit was a bit unpredictable. The times when the satellite came out from behind the planet changed inexplicably. Cassini ordered his assistants to make better observations and to do more calculations. Roemer doubted that the observations or calculations were the problem. The problem was that no one had taken into account the relative distance of the Earth and Jupiter as the two planets went around the sun. At different places in their orbits, the planets are sometimes closer and sometimes farther apart. When Io comes out from behind Jupiter, the distance that light travels from the satellite to the Earth depends on the separation of the planets at that time. Cassini didn't agree with his assistant. He believed that light traveled from place to place instantaneously, without delays. It didn't matter how far Jupiter was. Roemer stuck with his idea. He went back and reviewed many years' worth of data taken in Cassini's observatory. With this data, he was able to calculate the changes in the eclipsing times for Io as it went around in its orbit. He was sure that he was right and wanted to go public. Going around the boss What to do? Normally, the lab director would make the public presentation of new findings, along with the researcher who made the discovery. But Cassini didn't agree with Roemer's work, so Roemer decided to go alone. He'd been in Cassini's observatory for five years and felt cocky. He appeared before the Academy of Sciences in Paris and announced that Io was going to come out from behind Jupiter exactly ten minutes after Cassini said it would. Cassini had calculated that Io was going to come out of the eclipse on November 9, 1676, at 5:25:45. The astronomers went out to look that night. 5:25:45 came and went, and Io wasn't there. At 5:30, there were still no signs of it. But at 5:35:45, Io reappeared. Roemer had been right. Roemer's friend Christian Huygens used this data to come up with the first measured value for the speed of light. His number was 227,000 km (140,000 mi) per second, which is about 24 percent lower than the modern value. Cassini never admitted his error. Most European astronomers followed Cassini and didn't believe that the speed of light was finite. Some 50 years later, other methods to measure the speed of light showed that Roemer had been correct. By the time Einstein was in school, the speed of light had been measured with fairly good accuracy. This speed, represented in Einstein's work by the letter c, ended up at the very foundation of his special theory of relativity.

Article / Updated 03-26-2016

Albert Einstein shared his scientific theories and discoveries through numerous books and papers. His theory of relativity made its first appearance in 1905 but was expanded upon and explained in many subsequent writings. The most important of Einstein's writings are listed here: 1905 March 17. The light quantum paper: "On a heuristic point of view concerning the production and transformation of light." This paper gave birth to quantum theory. 1905 June 30. The special theory of relativity: "On the electrodynamics of moving bodies." In this paper, Einstein stated that the laws of physics are the same for all observers in non-accelerated motion and that, for these observers, the speed of light never changes. 1905 September 27. The E = mc2 paper: "Does an object's inertia depend on its energy content?" This paper explained Einstein's discovery that mass and energy are aspects of the same thing; mass and energy are equivalent, and one can be converted into the other. 1911 June. The bending of light prediction: "On the effect of gravity on the propagation of light." This prediction (which was confirmed in 1919) was based on the idea that large objects, like the sun, warp space. 1915 November 15. "On the general theory of relativity." This paper extended Einstein's special theory of relativity to include all types of motion. It took Einstein four years to develop the general theory. 1915 March 20. Einstein's first book, The Foundation of the General Theory of Relativity. This book provided the first complete description of his general theory of relativity. 1916 December. Einstein's best known book, Relativity: The Special and General Theory. This book, which has been reprinted continuously in every major language in the world, contains an accessible description of the two theories of relativity. It uses simple high school mathematics to explain the theories. 1917 The cosmological constant: "Cosmological observations on the general theory of relativity." In this paper, Einstein introduced a correction term to prevent his equations from describing an expanding universe. Although he failed to predict the expansion of the universe (which was discovered later), his cosmological constant is now helping to explain observations about the shape of space and the rate of expansion of the universe. 1935 April. The quantum reality problem: "Can the quantum-mechanical description be considered complete?" Einstein wasn't convinced that quantum theory described reality. Most physicists disagreed with him on this issue. In this paper, he proposed a clever experiment to settle the argument. This experiment was finally performed in the 1980s, and the results indicate that Einstein may have been wrong in this case.