Galaxies may simply exchange between themselves particles which they cannot trap. There is no obvious reason why the spectrum of particles above this critical energy for galactic trapping should fit smoothly to the spectrum of trapped particles, but it does.
Other theories of the origin of cosmic rays have been proposed; Ginzburg , for example, suggests that the cosmic ray flux is a re- sult solely of supernovae acceleration and diffusion throughout the galactic halo; this averts the first difficulty mentioned above but not the second and third, and it introduces many problems of its own such as an expected cutoff in the proton spectrum at ev.
But in any event it is challeng- ing to realize that in studying the cosmic ray energy and mass spectra we are gaining valuable information about element synthesis and stellar evo- lution not only from our own Galaxy, but from other galaxies as well. Cameron: It would be worthwhile to seek. Cocconi, G. Ginzburg, V. Singer, S. Paris , Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.
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That might indicate the material there is of a different chemical composition, or a different grain size. Small grains are more reflective than larger ones. Data collected during the fly-by confirm that MU 69 is dark reddish, as scientists had suspected. The colour is probably a result of sunlight irradiating its icy surface for billions of years, says team member Carly Howett, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.
New Horizons visited its first Kuiper belt object, Pluto , in July But MU 69 is special because it hails from an undisturbed part of the Solar System known as the cold classical Kuiper belt. Scientists think that objects there have been in a deep freeze since the Solar System formed, more than 4. Data from the MU 69 fly-by will give scientists their most direct look at these pristine relics of planetary formation. One of its undergraduates, Isaac Newton, went back home to Woolsthorpe, where he spent the next eighteen months opening the door to the modern world.
We live in a technological era that would be impossible without the ability to make quantitative predictions. And the first great example of quantitative prediction was to be found in Newton's theory of universal gravitation.
Starting from the hypothesis that the gravitational attraction between two masses is directly proportional to the product of the masses and inversely proportional to the square of the distance between them, Newton figured out that the orbit of a planet was an ellipse with the sun at one of the foci. Johannes Kepler had reached this conclusion from years of painstaking observations, but Newton was able to do so with no more than the assumption of gravitational attraction and the mathematical tool of calculus which he had invented for this purpose. Curiously, though the gravitational constant, G, was the first constant to be discovered, it is the least accurately known of all 13 constants.
That is because of the extreme weakness of the gravitational force when compared with the other basic forces. Consider that though mass of the earth is approximately 6 x 10 24 kilograms, by —about three centuries after Newton left plague-ravaged London—humans overcame the earth's gravitational attraction by using a simple chemical-powered rocket to place Sputnik, the first artificial satellite, in orbit.
The invention of the cannon during the Middle Ages showed that the speed of sound was finite; you could see a cannon fire long before you heard the sound of the explosion.
Cosmos - The science of everything
Shortly thereafter, several scientists, including the great Galileo, realized the possibly that the speed of light was finite as well. Galileo devised an experiment that might well have proved this, involving telescopes and men pointing lights at each other over a great distance. But the extreme rapidity of the speed of light, combined with the technological limitations of the s, made this experiment unworkable.
By the end of the nineteenth century, technology and ingenuity had advanced so far that it was possible to measure the speed of light within 0. This enabled Albert Michelson and Edward Morley to demonstrate that the speed of light was independent of direction. This startling result led eventually to Einstein's theory of relativity, the iconic intellectual achievement of the 20th century and perhaps of all time.
It is often said that nothing can travel faster than light. Indeed, nothing physical in the universe can travel faster than the speed of light, but even though our computers process information at near light speed, we still wait impatiently for our files to download. The speed of light is fast, but the speed of frustration is even faster. In the 17th century, scientists understood three phases of matter—solids, liquids and gases the discovery of plasma, the fourth phase of matter, lay centuries in the future.
Back then, solids and liquids were much harder to work with than gases because changes in solids and liquids were difficult to measure with the equipment of the time. So many experimentalists played around with gases to try to deduce fundamental physical laws. Robert Boyle was perhaps the first great experimentalist, and was responsible for what we now consider to be the essence of experimentation: vary one or more parameter, and see how other parameters change in response. It may seem obvious in retrospect, but hindsight, as the physicist Leo Szilard once remarked, is notably more accurate than foresight.
Boyle discovered the relationship between the pressure and volume of a gas, and a century later, the French scientists Jacques Charles and Joseph Gay-Lussac discovered the relationship between volume and temperature. This discovery was not simply a matter of donning a traditional white lab jacket which hadn't yet been invented and performing a few measurements in comfortable surroundings.
To obtain the required data, Gay-Lussac took a hot-air balloon to an altitude of 23, feet, possibly a world record at the time. The results of Boyle, Charles and Gay-Lussac could be combined to show that in a fixed quantity of a gas, temperature was proportional to the product of pressure and volume. The constant of proportionality is known as the ideal gas constant.
It's easy to make heat. Humans have been able to capture or create fire since prehistoric times. Producing cold is a much more difficult task. The universe as a whole has done a very good job of it, as the average temperature of the universe is only a few degrees above absolute zero. And it has done so the way that we do it in our refrigerators: through the expansion of gas. Michael Faraday , who is far better known for his contributions to the study of electricity, was the first to suggest the possibility of producing colder temperatures by harnessing the expansion of a gas.
Faraday had produced some liquid chlorine in a sealed tube, and when he broke the tube and thereby lowered the pressure , the chlorine instantly transformed into a gas. Faraday noted that if lowering the pressure could transform a liquid into a gas, then perhaps applying pressure to a gas could transform it into a liquid—with a colder temperature.
That's basically what happens in your refrigerator; gas is pressurized and allowed to expand, which cools the surrounding material. Pressurization enabled scientists to liquefy oxygen, hydrogen and, by the beginning of the 20th century, helium. That brought us to within a few degrees of absolute zero. But heat is also motion, and a technique of slowing down atoms by using lasers has enabled us to come within millionths of a degree of absolute zero, which we now know to be slightly more than — degrees Fahrenheit.
Absolute zero falls in the same category as the speed of light.
Scratching the surface
Material objects can get ever so close, but they can never reach it. Unlocking the secrets of chemistry was not unlike unlocking a safe-deposit box. It took two keys to accomplish the task. The first key, the atomic theory, was discovered by John Dalton at the dawn of the 19th century. The renowned physicist Richard Feynman felt that the atomic theory was so important that he said, "If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words?
I believe it is the atomic hypothesis that all things are made of atoms—little particles that move around in perpetual motion. These are the 92 naturally occurring elements that are the fundamental building blocks of all the matter in the universe. However, almost everything in the universe is a compound; a combination of different kinds of elements. Thus, the second key to modern chemistry was the discovery that each compound was a collection of identical molecules.
The Cosmic Machine: The Science That Runs Our Universe and the Story Behind It
For example, a batch of pure water is made of lots and lots of identical H 2 O molecules. But just how many molecules? Getting the bookkeeping right so that we could predict the result of chemical reactions proved to be a major roadblock to the advancement of chemistry. The Italian chemist Amadeo Avogadro proposed that at the same temperature and pressure equal volumes of different gases contained the same number of molecules. This hypothesis was largely unappreciated when it was first announced, but it enabled chemists to deduce the structure of molecules by measuring volumes at the start and finish of a chemical reaction.