Kecepatan Cahaya

Kecepatan cahaya merupakan sebuah konstanta yang disimbolkan dengan huruf c, singkatan dari celeritas (yang dirujuk dari dari bahasa Latin) yang berarti "kecepatan". Kecepatan cahaya dalam sebuah ruang hampa udara didefinisikan saat ini pada 299.792.458 meter per detik (m/s)[1]atau 1.079.252.848,8 kilometer per jam (km/h) atau 186.282.4 mil per detik (mil/s) atau 670.616.629,38 mil per jam (mil/h), yang ditetapkan pada tahun 1975 dengan toleransi kesalahan sebesar 4×10−9.[2] Pada tahun 1983, satuan meter didefinisikan kembali dalam Sistem Satuan Internasional (SI) kemudian ditetapkan pada 17th Conférence Générale des Poids et Mesures sebagai ... the length of the path travelled by light in vacuum during a time interval of 1⁄299.792.458 of a second[3][4][5][6] , sehingga nilai konstanta c dalam meter per detik sekarang tetap tepat dalam definisi meter, sebagai jarak yang ditempuh oleh cahaya dalam ruang hampa pada 1⁄299.792.458 detik[7][8][9]. Observasi Rømer dengan mengamati gerakan planet Jupiter dan menghitung pergeseran periode orbit dari salah satu bulan satelitnya yang bernama Io, dan kemudian Rømer dapat memperkirakan jarak tempuh cahaya dari diameter orbit bumi [sunting] Kronologis Beragam ilmuwan sepanjang sejarah telah mencoba untuk mengukur kecepatan cahaya. * Pada tahun 1629, Isaac Beeckman melakukan pengamatan sinar flash yang dipantulkan oleh cermin dari jarak 1 mil (1,6 kilometer). * Pada tahun 1638, Galileo Galilei berusaha untuk mengukur kecepatan cahaya dari waktu tunda antara sebuah cahaya lentera dengan persepsi dari jarak cukup jauh. * Pada tahun 1667, percobaan Galileo Galilei diteliti oleh Accademia del Cimento of Florence, dengan rentang 1 mil, tetapi tidak terdapat waktu tunda yang dapat diamati. Berdasarkan perhitungan modern, waktu tunda pada percobaan itu seharusnya adalah 11 mikrodetik. Dan Galileo Galilei mengatakan bahwa pengamatan itu tidak menunjukkan bahwa cahaya mempunyai kecepatan yang tidak terhingga, tetapi hanya menunjukkan bahwa cahaya mempunyai kecepatan yang sangat tinggi.[10][11] * Pada tahun 1676, sebuah percobaan awal untuk mengukur kecepatan cahaya dilakukan oleh Ole Christensen Rømer, seorang ahli fisika Denmark dan anggota grup astronomi dari French Royal Academy of Sciences. Dengan menggunakan teleskop, Ole Christensen Rømer mengamati gerakan planet Jupiter dan salah satu bulan satelitnya, bernama Io[12][13]. Dengan menghitung pergeseran periode orbit Io, Rømer memperkirakan jarak tempuh cahaya pada diameter orbit bumi sekitar 22 menit[14]. Jika pada saat itu Rømer mengetahui angka diameter orbit bumi, kalkulasi kecepatan cahaya yang dibuatnya akan mendapatkan angka 227×106 meter/detik. Dengan data Rømer ini, Christiaan Huygens mendapatkan estimasi kecepatan cahaya pada sekitar 220×106 meter/detik. Penemuan awal penemuan grup ini diumumkan oleh Giovanni Domenico Cassini pada tahun 1675, periode Io, bulan satelit planet Jupiter dengan orbit terpendek, nampak lebih pendek pada saat Bumi bergerak mendekati Jupiter daripada pada saat menjauhinya. Rømer mengatakan hal ini terjadi karena cahaya bergerak pada kecepatan yang konstan. Pada bulan September 1676, berdasarkan asumsi ini, Rømer memperkirakan bahwa pada tanggal 9 November 1676, Io akan muncul dari bayang-bayang Jupiter 10 menit lebih lambat daripada kalkulasi berdasarkan rata-rata kecepatannya yang diamati pada bulan Agustus 1676.[15]. Setelah perkiraan Rømer terbukti,[16] dia diundang oleh French Academy of Sciences[17] untuk menjelaskan metode yang digunakan untuk hal tersebut.[18] Diagram di samping adalah replika diagram yang digunakan Rømer dalam penjelasan tersebut.[19] * Pada tahun 1704, Isaac Newton juga menyatakan bahwa cahaya bergerak pada kecepatan yang konstan. Dalam bukunya berjudul Opticks, Newton menyatakan besaran kecepatan cahaya senilai 16,6 x diamater Bumi per detik (210.000 kilometer/detik). Teori James Bradley Diagram Hippolyte Fizeau * Pada tahun 1725, James Bradley mengatakan, cahaya bintang yang tiba di Bumi akan nampak seakan-akan berasal dari sudut yang kecil, dan dapat dikalkulasi dengan membandingkan kecepatan Bumi pada orbitnya dengan kecepatan cahaya. Kalkulasi kecepatan cahaya oleh Bradley adalah sekitar 298.000 kilometer/detik (186.000 mil/detik). Teori Bradley dikenal sebagai stellar aberration.[20] Sinar cahaya yang datang bintang 1 membutuhkan waktu untuk mencapai bumi, dan pada saat sinar tersebut tiba, bumi telah bergeser pada orbitnya, sehingga seolah-olah kita melihat sinar cahaya tersebut datang dari bintang di lokasi 2. * Pada tahun 1849, pengukuran kecepatan cahaya, yang lebih akurat, dilakukan di Eropa oleh Hippolyte Fizeau. Fizeau menggunakan roda sprocket yang berputar untuk meneruskan cahaya dari sumbernya ke sebuah cermin yang diletakkan sejauh beberapa kilometer. Pada kecepatan rotasi tertentu, cahaya sumber akan melalui sebuah kisi, menempuh jarak menuju cermin, memantul kembali dan tiba pada kisi berikutnya. Dengan mengetahui jarak cermin, jumlah kisi, kecepatan putar roda, Fizeau mendapatkan kalkulasi kecepatan cahaya pada 313×106 meter/detik. * Pada tahun 1862, Léon Foucault bereksperimen dengan penggunaan cermin rotasi dan mendapatkan angka 298×106 meter/detik. * Albert Abraham Michelson melakukan percobaan-percobaan dari tahun 1877 hingga tahun 1926 untuk menyempurnakan metode yang digunakan Foucault dengan penggunaan cermin rotasi untuk mengukur waktu yang dibutuhkan cahaya pada 2 x jarak tempuh antara Gunung Wilson dan Gunung San Antonio, di California. Hasil pengukuran menunjukkan 299.796.000 meter/detik. Beliau wafat lima tahun kemudian pada tahun 1931. * Pada tahun 1946, saat pengembangan cavity resonance wavemeter untuk penggunaan pada radar, Louis Essen dan A. C. Gordon-Smith menggunakan gelombang mikro dan teori elektromagnetik untuk menghitung kecepatan cahaya. Angka yang didapat adalah 299.792±3 kilometer/detik. * Pada tahun 1950, Essen mengulangi pengukuran tersebut dan mendapatkan angka 299.792.5±1 kilometer/detik, yang menjadi acuan bagi 12th General Assembly of the Radio-Scientific Union pada tahun 1957. Angka yang paling akurat ditemukan di Cambridge pada pengukuran melalui kondensat Bose-Einstein dengan elemen Rubidium. Tim pertama dipimpin oleh Dr. Lene Vestergaard Hau dari Harvard University and the Rowland Institute for Science. Tim yang kedua dipimpin oleh Dr. Ronald L. Walsworth, dan, Dr. Mikhail D. Lukin dari the Harvard-Smithsonian Center for Astrophysics. Notasi kecepatan cahaya (c) mempunyai makna "konstan" atau tetap[21] yang digunakan sebagai notasi kecepatan cahaya dalam ruang hampa udara, namun terdapat juga penggunaan notasi c untuk kecepatan cahaya dalam medium material sedangkan c0 untuk kecepatan cahaya dalam ruang hampa udara.[22] Notasi subskrip ini dimaklumkan karena dalam literatur SI [23] sebagai bentuk standar notasi pada suatu konstanta, ada juga berbentuk seperti: konstanta magnetik µ0, konstanta elektrik e0, impedansi ruang kamar Z0. Menurut Albert Einstein dalam teori relativitas, c adalah konstanta penting yang menghubungkan ruang dan waktu dalam satu kesatuan struktur dimensi ruang waktu. Di dalamnya, c mendefinisikan konversi antara materi dan energi[24] E=mc2.[25], dan batas tercepat waktu tempuh materi dan energi tersebut.[26][27] c juga merupakan kecepatan tempuh semua radiasi elektromagnetik dalam ruang kamar[28] dan diduga juga merupakan kecepatan gelombang gravitasi.[29][30] Dalam teori ini, sering digunakan satuan natural units di mana c=1, [31][32] sehingga notasi c tidak lagi digunakan.

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Cahaya

Gelombang elektromagnetik dapat digambarkan sebagai dua buah gelombang yang merambat secara transversal pada dua buah bidang tegak lurus yaitu medan magnetik dan medan listrik. Merambatnya gelombang magnet akan mendorong gelombang listrik, dan sebaliknya, saat merambat, gelombang listrik akan mendorong gelombang magnet. Diagram di atas menunjukkan gelombang cahaya yang merambat dari kiri ke kanan dengan medan listrik pada bidang vertikal dan medan magnet pada bidang horizontal. Onde electromagnetique.svg Cahaya adalah energi berbentuk gelombang elekromagnetik yang kasat mata dengan panjang gelombang sekitar 380–750 nm.[1] Pada bidang fisika, cahaya adalah radiasi elektromagnetik, baik dengan panjang gelombang kasat mata maupun yang tidak. [2][3] Cahaya adalah paket partikel yang disebut foton. Kedua definisi di atas adalah sifat yang ditunjukkan cahaya secara bersamaan sehingga disebut "dualisme gelombang-partikel". Paket cahaya yang disebut spektrum kemudian dipersepsikan secara visual oleh indera penglihatan sebagai warna. Bidang studi cahaya dikenal dengan sebutan optika, merupakan area riset yang penting pada fisika modern. Studi mengenai cahaya dimulai dengan munculnya era optika klasik yang mempelajari besaran optik seperti: intensitas, frekuensi atau panjang gelombang, polarisasi dan fasa cahaya. Sifat-sifat cahaya dan interaksinya terhadap sekitar dilakukan dengan pendekatan paraksial geometris seperti refleksi dan refraksi, dan pendekatan sifat optik fisisnya yaitu: interferensi, difraksi, dispersi, polarisasi. Masing-masing studi optika klasik ini disebut dengan optika geometris (en:geometrical optics) dan optika fisis (en:physical optics). Pada puncak optika klasik, cahaya didefinisikan sebagai gelombang elektromagnetik dan memicu serangkaian penemuan dan pemikiran, sejak tahun 1838 oleh Michael Faraday dengan penemuan sinar katoda, tahun 1859 dengan teori radiasi massa hitam oleh Gustav Kirchhoff, tahun 1877 Ludwig Boltzmann mengatakan bahwa status energi sistem fisik dapat menjadi diskrit, teori kuantum sebagai model dari teori radiasi massa hitam oleh Max Planck pada tahun 1899 dengan hipotesa bahwa energi yang teradiasi dan terserap dapat terbagi menjadi jumlahan diskrit yang disebut elemen energi, E. Pada tahun 1905, Albert Einstein membuat percobaan efek fotoelektrik, cahaya yang menyinari atom mengeksitasi elektron untuk melejit keluar dari orbitnya. Pada pada tahun 1924 percobaan oleh Louis de Broglie menunjukkan elektron mempunyai sifat dualitas partikel-gelombang, hingga tercetus teori dualitas partikel-gelombang. Albert Einstein kemudian pada tahun 1926 membuat postulat berdasarkan efek fotolistrik, bahwa cahaya tersusun dari kuanta yang disebut foton yang mempunyai sifat dualitas yang sama. Karya Albert Einstein dan Max Planck mendapatkan penghargaan Nobel masing-masing pada tahun 1921 dan 1918 dan menjadi dasar teori kuantum mekanik yang dikembangkan oleh banyak ilmuwan, termasuk Werner Heisenberg, Niels Bohr, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Wolfgang Pauli, David Hilbert, Roy J. Glauber dan lain-lain. Era ini kemudian disebut era optika modern dan cahaya didefinisikan sebagai dualisme gelombang transversal elektromagnetik dan aliran partikel yang disebut foton. Pengembangan lebih lanjut terjadi pada tahun 1953 dengan ditemukannya sinar maser, dan sinar laser pada tahun 1960. Era optika modern tidak serta merta mengakhiri era optika klasik, tetapi memperkenalkan sifat-sifat cahaya yang lain yaitu difusi dan hamburan.

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Kids' views on Science

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Date: Mon, 5 Jun 1995 09:18:54 -0700 (PDT)
From: Sonia P Mistry
Subject: just for smiles...kid science! (fwd)

Okay, so here's another contribution....I just wanted to make sure i sent it in before anyone else did. It's cute, along the lines of that "kids opinions on love" thingy..

Sonia

The beguiling ideas about science quoted here were gleaned from essays, exams, and class room discussions; most were from fifth- and sixth-graders. They illustrate Mark Twain's contention that the "most interesting information comes from children, for they tell all they know and then stop."

Q: What is one horsepower?
A: One horsepower is the amount of energy it takes to drag a horse 500 feet in one second.

- You can listen to thunder after lightening and tell how close you came to getting hit. If you don't hear it you got hit, so never mind.

- When they broke open molecules, they found they were only stuffed with atoms. But when they broke open atoms, they found them stuffed with explosions.

- When people run around and around in circles we say they are crazy. When planets do it we say they are orbiting.

- While the earth seems to be knowingly keeping its distance from the sun, it is really only centrificating.

- Most books now say our sun is a star. But it still knows how to change back into a sun in the daytime.

- A vibration is a motion that cannot make up its mind which way it wants to go.

- Many dead animals of the past changed to fossils, others preferred to be oil.

- Vacuums are nothings. We only mention them to let them know we know they're there.

- Some people can tell what time it is by looking at the sun. But I have never been able to make out the numbers.

- We say the cause of perfume disappearing is evaporation. Evaporation gets blamed for a lot of things people forget to put the top on.

- I am not sure how clouds get formed. But the clouds know how to do it, and that is the important thing.

- Rain is saved up in cloud banks.

- Cyanide is so poisonous that one drop of it on a dog's tongue will kill the strongest man.

- Thunder is a rich source of loudness.

- Isotherms and isobars are even more important than their names sound.

- It is so hot in some parts of the world that the people there have to live other places.

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Radio Interview of Neil Armstrong and Buzz Aldrin

Interviewer: Neil and Buzz, thanks for joining us today to chat about this intriguing news story about ice on the moon. Buzz, did you ever have any suspicions that there might be water on the moon?

(Scuffling sound as if both Armstrong and Aldrin were trying to grab hold of the microphone.)

Aldrin: Well, the first time I suspected there might be water on the moon was when the windshield of the lunar module started icing up on our descent to the moon. I yelled over to Armstrong to turn up the windshield defroster fan a few seconds after I first noticed ice crystals forming on our windshield.

Armstrong: Gee, I can't recall the ice on the windshield, Buzz, but I do remember seeing a lake-shaped blue object on the horizon as the lunar module descended.

Aldrin: I can't recall seeing that, Neil, but I do recall that when I first stepped on the moon my foot slid along something I thought might be black ice. Fell right on my butt.

Armstrong: Sure, I remember you falling on your butt, Buzz, but that's because you forgot to tie your shoelaces before the moonwalk. How many times did I tell you, "Tie your shoelaces. Tie your shoelaces. Four billion people will be watching this moonwalk. Tie your shoelaces."?

Aldrin: Sure, I fell on my butt once on the moon, but you fell over more than a dozen times.

(At this point the interview seems to degenerate as the astronauts sound as if they're wrestling for control of the microphone.)

Armstrong: Yes, but I suspected ice on the moon after I had to use de-icing spray on the door handle of the lunar module.

Aldrin: I suspected water on the moon after the third thunderstorm.

Armstrong: But I first suspected water on the moon when I saw the recreational vehicle water hookup near the campsite where we landed on the moon.

Aldrin: I first suspected ice on the moon when I spotted Wayne Gretzky hanging around the launchpad.

Armstrong: True enough, but I first suspected ice on the moon when I noticed a fleet of Zamboni's parked not far from the lunar module landing site.

Armstrong: I suspected water on the moon when I picked up an object that looked like a seashell, held it to my ear, and heard a distinct gurgling sound.

Aldrin: I suspected water on the moon right after I stepped in a huge puddle.

Armstrong: I suspected water on the moon the moment I saw a small waterfall.

Aldrin: I suspected water on the moon after our drink cooler accidentally tipped over.

Armstrong: I suspected water on the moon when my astronaut suit visor kept fogging up on the inside.

Aldrin: I suspected water on the moon when I saw what appeared to be a discarded Brita filter.

Armstrong: I suspected ice on the moon when I spotted a popsicle stick.

(At this point both astronauts are giggling and elbowing each other in the ribs.)

Armstrong: Yes, but I first suspected ice on the moon when I stubbed my toe on a glacier.

Aldrin: I suspected ice on the moon shortly after I put on my skates.

Armstrong: I suspected water on the moon when I came across a rock that looked very much like a water slide from a theme park.

Armstrong: Oh sure. I first suspected water on the moon after I finished doing my first laundry load.

Aldrin: Neil, I first suspected ice on the moon when our lunar rover slid off the road.

Armstrong: I first suspected water on the moon when I saw a rock that looked very similar to a fire hydrant.

Aldrin: I first suspected ice on the moon when Houston replaced their entire Mission Control staff with figure skating announcers.

Armstrong: Speaking of ice skating, Buzz, I hear that you've signed a five year contract to tour with the Ice Capades?

Aldrin: Well, if you're going to bring up the subject of contracts, I might mention the rumor that you've signed a ten year contract to dress up as Goofy for the new hastily planned "Ice on the Moon" attraction at Disneyworld.

Armstrong: Did not!

Aldrin: Did too!

Armstrong: Not!

Aldrin: Too!

Armstrong: Not! Not!

Aldrin: Too! Too!

By Phil Shapiro
http://www.his.com/~pshapiro/

pshapiro@his.com
(Note: The above radio interview is entirely fictional.)
Return to Phil's home page.

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Five Great Problems in Theoretical Physics

In his controversial 2006 book The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, theoretical physicist Lee Smolin points out "five great problems in theoretical physics."

1. The problem of quantum gravity: Combine general relativity and quantum theory into a single theory that can claim to be the complete theory of nature.
2. The foundational problems of quantum mechanics: Resolve the problems in the foundations of quantum mechanics, either by making sense of the theory as it stands or by inventing a new theory that does make sense.
3. The unification of particles and forces: Determine whether or not the various particles and forces can be unified in a theory that explains them all as manifestations of a single, fundamental entity.
4. The tuning problem: Explain how the values of the free constants in the standard model of particle physics are chosen in nature.
5. The problem of cosmological mysteries: Explain dark matter and dark energy. Or, if they don't exist, determine how and why gravity is modified on large scales. More generally, explain why the constants of the standard model of cosmology, including the dark energy, have the values they do.

Problem 1: The Problem of Quantum Gravity

Quantum gravity is the effort in theoretical physics to create a theory that includes both general relativity and the standard model of particle physics. Currently, these two theories describe different scales of nature and attempts to explore the scale where they overlap yield results that don't quite make sense, like the force of gravity (or curvature of spacetime) becoming infinite. (After all, physicists never see real infinities in nature, nor do they want to!)

Problem 2: The Foundational Problems of Quantum Mechanics

One issue with understanding quantum physics is what the underlying physical mechanism involved is. There are many interpretations in quantum physics - the classic Copenhagen interpretation, Hugh Everette II's controversial Many Worlds Interpretation, and even more controversial ones such as the Participatory Anthropic Principle. The question that comes up in these interpretations revolves around what actually causes the collapse of the quantum wavefunction. (The puzzle of the curious aspect of human consciousness's role in resolving these questions is related in Quantum Enigma.)

Most modern physicists who work with quantum field theory no longer consider these questions of interpretation to be relevant. The principle of decoherence is, to many, the explanation - interaction with the environment causes the quantum collapse. Even more significantly, physicists are able to solve the equations, perform experiments, and practice physics without resolving the questions of what exactly is happening at a fundamental level, and so most physicists don't want to get near these bizarre questions with a 20 foot pole.

Problem 3: The Unification of Particles and Forces

There are four fundamental forces of physics, and the standard model of particle physics includes only three of them (electromagnetism, strong nuclear force, and weak nuclear force). Gravity is left out of the standard model. Trying to create one theory which unifies these four forces into a unified field theory is a major goal of theoretical physics.

Since the standard model of particle physics is a quantum field theory, then any unification will have to include gravity as a quantum field theory, which means that solving problem 3 is connected with the solving of problem 1.

In addition, the standard model of particle physics shows a lot of different particles - 18 fundamental particles in all. Many physicists believe that a fundamental theory of nature should have some method of unifying these particles, so they are described in more fundamental terms. For example, string theory, the most well-defined of these approaches, predicts that all particles are different vibrational modes of fundamental filaments of energy, or strings.

Problem 4: The Tuning Problem

A theoretical physics model is a mathematical framework that, in order to make predictions, requires that certain parameters are set. In the standard model of particle physics, the parameters are represented by the 18 particles predicted by the theory, meaning that the parameters are measured by observation.

Some physicists, however, believe that fundamental physical principles of the theory should determine these parameters, independent of measurement. This motivated much of the enthusiasm for a unified field theory in the past and sparked Einstein's famous question "Did God have any choice when he created the universe?" Do the properties of the universe inherently set the form of the universe, because these properties just won't work if the form is different?

The answer to this seems to be leaning strongly toward the idea that there is not only one universe that could be created, but that there are a wide range of fundamental theories (or different variants of the same theory, based on different physical parameters, original energy states, and so on) and our universe is just one of these possible universes.

In this case, the question becomes why our universe has properties that seem to be so finely tuned to allow for the existence of life. This question is called the fine-tuning problem and has promoted some physicists to turn to the anthropic principle of explanation, which dictates that our universe has the properties it does because if it had different properties, we wouldn't be here to ask the question. (A major thrust of Smolin's book is the criticism of this viewpoint as an explanation of the properties.)

Problem 5: The Problem of Cosmological Mysteries

The universe still has a number of mysteries, but the ones that most vex physicists are dark matter and dark energy. This type of matter and energy is detected by its gravitational influences, but can't be observed directly, so physicists are still trying to figure out what they are. Still, some physicists have proposed alternative explanations for these gravitational influences, which do not require new forms of matter and energy, but these alternatives are unpopular to most physicists.

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Hypothesis, Model, Theory & Law

In common usage, the words hypothesis, model, theory, and law have different interpretations and are at times used without precision, but in science they have very exact meanings.

Hypothesis

Perhaps the most difficult and intriguing step is the development of a specific, testable hypothesis. A useful hypothesis enables predictions by applying deductive reasoning, often in the form of mathematical analysis. It is a limited statement regarding the cause and effect in a specific situation, which can be tested by experimentation and observation or by statistical analysis of the probabilities from the data obtained. The outcome of the test hypothesis should be currently unknown, so that the results can provide useful data regarding the validity of the hypothesis.

Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable. The concept of atoms was proposed by the ancient Greeks, who had no means of testing it. Centuries later, when more knowledge became available, the hypothesis gained support and was eventually proven, though it has had to be amended many times over the year. Atoms are not indivisible, as the Greeks supposed.

Model

A model is used for situations when it is known that the hypothesis has a limitation on its validity. The Bohr model of the atom, for example, depicts electrons circling the atomic nucleus in a fashion similar to planets in the solar system. This model is useful in determining the energies of the quantum states of the electron in the simple hydrogen atom, but it is by no means represents the true nature of the atom.

Theory & Law

A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a law uses a handful of fundamental concepts and equations to define the rules governing a set of phenomena.

Scientific Paradigms

Once a scientific theory is established, it is very hard to get the scientific community to discard it. In physics, the concept of ether as a medium for light wave transmission ran into serious opposition in the late 1800s, but it was not disregarded until the early 1900s, when Einstein proposed alternate explanations for the wave nature of light that did not rely upon a medium for transmission.

The science philosopher Thomas Kuhn developed the term scientific paradigm to explain the working set of theories under which science operates. He did extensive work on the scientific revolutions that take place when one paradigm is overturned in favor of a new set of theories. His work suggests that the very nature of science changes when these paradigms are significantly different. The nature of physics prior to relativity and quantum mechanics is fundamentally different from that after their discovery, just as biology prior to Darwin’s Theory of Evolution is fundamentally different from the biology that followed it. The very nature of the inquiry changes.

One consequence of the scientific method is to try to maintain consistency in the inquiry when these revolutions occur and to avoid attempts to overthrow existing paradigms on ideological grounds.

Occam’s Razor

One principle of note in regards to the scientific method is Occam’s Razor (alternately spelled Ockham's Razor), which is named after the 14th century English logician and Franciscan friar William of Ockham. Occam did not create the concept - the work of Thomas Aquinas and even Aristotle referred to some form of it. The name was first attributed to him (to our knowledge) in the 1800s, indicating that he must have espoused the philosophy enough that his name became associated with it.

The Razor is often stated in Latin as:

entia non sunt multiplicanda praeter necessitatem or, translated to English:
entities should not be multiplied beyond necessity

Occam's Razor indicates that the most simple explanation that fits the available data is the one which is preferable. Assuming that two hypotheses are presented have equal predictive power, the one which makes the fewest assumptions and hypothetical entities takes precedence. This appeal to simplicity has been adopted by most of science, and is invoked in this popular quote by Albert Einstein:

Everything should be made as simple as possible, but not simpler.

It is significant to note that Occam's Razor does not prove that the simpler hypothesis is, indeed, the true explanation of how nature behaves. Scientific principles should be as simple as possible, but that's no proof that nature itself is simple. However, it is generally the case that when a more complex system is at work there is some element of the evidence which doesn't fit the simpler hypothesis, so Occam's Razor is rarely wrong as it deals only with hypotheses of purely equal predictive power. The predictive power is more important than the simplicity.

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Introduction to the Scientific Method

The scientific method is a set of techniques used by the scientific community to investigate natural phenomena by providing an objective framework in which to make scientific inquiry and analyze the data to reach a conclusion about that inquiry.

Steps of the Scientific Method

The goals of the scientific method are uniform, but the method itself is not necessarily formalized among all branches of science. It is most generally expressed as a series of discrete steps, although the exact number and nature of the steps varies depending upon the source. The scientific method is not a recipe, but rather an ongoing cycle that is meant to be applied with intelligence, imagination, and creativity. Frequently, some of these steps will take place simultaneously, in a different order, or be repeated as the experiment is refined, but this is the most general and intuitive sequence:

1. Ask a question – determine a natural phenomenon (or group of phenomena) that you are curious about and would like to explain or learn more about, then ask a specific question to focus your inquiry.
2. Research the topic – this step involves learning as much about the phenomenon as you can, including by studying the previous studies of others in the area.
3. Formulate a hypothesis – using the knowledge you have gained, formulate a hypothesis about a cause or effect of the phenomenon, or the relationship of the phenomenon to some other phenomenon.
4. Test the hypothesis – plan and carry out a procedure for testing the hypothesis (an experiment) by gathering data.
5. Analyze the data – use proper mathematical analysis to see if the results of the experiment support or refute the hypothesis.

If the data does not support the hypothesis, it must be rejected or modified and re-tested. Frequently, the results of the experiment are compiled in the form of a lab report (for typical classroom work) or a paper (in the case of publishable academic research). It is also common for the results of the experiment to provide an opportunity for more questions about the same phenomenon or related phenomena, which begins the process of inquiry over again with a new question.

Key Elements of the Scientific Method

The goal of the scientific method is to get results that accurately represent the physical processes taking place in the phenomenon. To that end, it emphasizes a number of traits to insure that the results it gets are valid to the natural world.

• objective – the scientific method intends to remove personal and cultural biases by focusing on objective testing procedures.
• consistent – the laws of reasoning should be used to make hypotheses that are consistent with broader, currently known scientific laws; even in rare cases where the hypothesis is that one of the broader laws is incorrect or incomplete, the hypothesis should be composed to challenge only one such law at a time.
• observable – the hypothesis presented should allow for experiments with observable and measurable results.
• pertinent – all steps of the process should be focused on describing and explaining observed phenomena.
• parsimonious – only a limited number of assumptions and hypothetical entities should be proposed in a given theory, as stated in Occam's Razor.
• falsifiable – the hypothesis should be something which can be proven incorrect by observable data within the experiment, or else the experiment is not useful in supporting the hypothesis. (This aspect was most prominently illuminated by the philosopher of science Karl Popper.)
• reproducible – the test should be able to be reproduced by other observers with trials that extend indefinitely into the future.

It is useful to keep these traits in mind when developing a hypothesis and testing procedure.

Conclusion

Hopefully this introduction to the scientific method has provided you with an idea of the significant effort that scientists go to in order to make sure their work is free from bias, inconsistencies, and unnecessary complications, as well as the paramount feat of creating a theoretical structure that accurately describes the natural world. When doing your own work in physics, it is useful to reflect regularly on the ways in which that work exemplifies the principles of the scientific method.

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What are the Fields of Physics?

Question: What are the Fields of Physics?
Answer:

Physics is a diverse area of study and in order to make sense of it scientists have been forced to focus their attention on one or two smaller areas of the discipline. This allows them to become experts in that narrow field, without getting bogged down in the sheer volume of knowledge that exists regarding the natural world.

Below is a list - by no comprehensive - of different disciplines of physics. The list will be updated with new additions and definitions as appropriate.

• Acoustics - the study of sound & sound waves
• Astronomy - the study of space
• Astrophysics - the study of the physical properties of objects in space
• Atomic Physics - the study of atoms, specifically the electron properties of the atom
• Biophysics - the study of physics in living systems
• Chaos - the study of systems with strong sensitivity to initial conditions, so a slight change at the beginning quickly become major changes in the system
• Chemical Physics - the study of physics in chemical systems
• Computational Physics - the application of numerical methods to solve physical problems for which a quantitative theory already exists
• Cosmology - the study of the universe as a whole, including its origins and evolution
• Cryophysics / Cryogenics / Low Temperature Physics - the study of physical properties in low temperature situations, far below the freezing point of water
• Crystallography - the study of crystals and crystalline structures
• Electromagnetism - the study of electrical and magnetic fields, which are two aspects of the same phenomenon
• Electronics - the study of the flow of electrons, generally in a circuit
• Fluid Dynamics / Fluid Mechanics - the study of the physical properties of "fluids," specifically defined in this case to be liquids and gases
• Geophysics - the study of the physical properties of the Earth
• High Energy Physics - the study of physics in extremely high energy systems, generally within particle physics
• High Pressure Physics - the study of physics in extremely high pressure systems, generally related to fluid dynamics
• Laser Physics - the study of the physical properties of lasers
• Mathematical Physics - applying mathematically rigorous methods to solving problems within physics
• Mechanics - the study of the motion of bodies in a frame of reference
• Meteorology / Weather Physics - the physics of the weather
• Molecular Physics - the study of physical properties of molecules
• Nanotechnology - the science of building circuits and machines from single molecules and atoms
• Nuclear Physics - the study of the physical properties of the atomic nucleus
• Optics / Light Physics - the study of the physical properties of light
• Particle Physics - the study of fundamental particles and the forces of their interaction
• Plasma Physics - the study of matter in the plasma phase
• Quantum Electrodynamics - the study of how electrons and photons interact at the quantum mechanical level
• Quantum Mechanics / Quantum Physics - the study of science where the smallest discrete values, or quanta, of matter and energy become relevant
• Quantum Optics - the application of quantum physics to light
• Quantum Field Theory - the application of quantum physics to fields, including the fundamental forces of the universe
• Quantum Gravity - the application of quantum physics to gravity and unification of gravity with the other fundamental particle interactions
• Relativity - the study of systems displaying the properties of Einstein's theory of relativity, which generally involves moving at speeds very close to the speed of light
• Statistical Mechanics - the study of large systems by statistically expanding the knowledge of smaller systems
• String Theory / Superstring Theory - the study of the theory that all fundamental particles are vibrations of one-dimensional strings of energy, in a higher-dimensional universe
• Thermodynamics - the physics of heat

It should become obvious that there is some overlap. For example, the difference between astronomy, astrophysics, and cosmology can be virtually meaningless at times ... to everyone, that is, except the astronomers, astrophysicists, and cosmologists, who can take the distinctions very seriously.

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Why Study Physics?

Question: Why Study Physics?
Why should you study physics? What is the use of a physics education? If you aren't going to become a scientist, do you still need to understand physics?
Answer:

The Case for Science

For the scientist (or aspiring scientist), the question of why to study science doesn't need to be answered. If you're one of the people who get science, then no explanation is required. Chances are that you already have at least some of the scientific skills necessary to pursue such a career, and the whole point of study is to gain the skills which you don't yet have.

However, for those who are not pursuing a career in the sciences, or in technology, it can frequently feel as if science courses of any stripe are a waste of your time. Courses in the physical sciences, especially, tend to be avoided at all cost, with courses in biology taking their place to fill necessary science requirements.

The argument in favor of "scientific literacy" is amply made in James Trefil's 2007 book Why Science?, focusing on arguments from civics, aesthetics, and culture to explain why a very basic understanding of scientific concepts is necessary for the non-scientist. Specifically, he presents a set of grand ideas that could be used to form the basis of this scientific literacy ... many of which are firmly rooted concepts of physics.

The Case for Physics

Trefil refers to the "physics first" approach presented by 1988 Nobel Laureate Leon Lederman in his Chicago-based educational reforms. Trefil's analysis is that this method is especially useful for older (i.e. high school age) students, while he believes the more traditional biology first curriculum is appropriate for younger (elementary & middle school) students.

In short, this approach emphasizes the idea that physics is the most fundamental of sciences. Chemistry is applied physics, after all, and biology (in it's modern form, at least) is basically applied chemistry. You can of course extend beyond that into more specific fields ... zoology, ecology, & genetics are all further applications of biology, for example.

But the point is that all of science can, in principle, be reduced down to fundamental physics concepts such as thermodynamics and nuclear physics. In fact, this is how physics developed historically: basic principles of physics were determined by Galileo while biology still consisted of various theories of spontaneous generation, after all.

Therefore, grounding a scientific education in physics makes perfect sense, because it is the foundation of science. From physics, you can expand naturally into the more specialized applications, going from thermodynamics & nuclear physics into chemistry, for example, and from mechanics & material physics principles into engineering.

The path cannot be followed smoothly in reverse, going from a knowledge of ecology into a knowledge of biology into a knowledge of chemistry and so on. The smaller the sub-category of knowledge you have, the less it can be generalized. The more general the knowledge, the more it can be applied to specific situations. As such, the fundamental knowledge of physics would be the most useful scientific knowledge, if someone had to pick which areas to study.

And all of this makes sense, because physics is the study of matter, energy, space and time, without which there would be nothing in existence to react or thrive or live or die. The entire universe is built upon of the principles revealed by a study of physics.

Why Scientists Need Non-Science Education

While on the subject of well rounded education, I suppose I should also point out that the opposite argument holds just as strongly: someone who is studying science needs to be able to function in society, and this involves understanding the entire culture (not just the techno-culture) involved. The beauty of Euclidean geometry is not inherently more beautiful than the words of Shakespeare ... it's just beautiful in a different way.

In my experience, scientists (and physicists especially) tend to be fairly well rounded in their interests. The classic example is the violin-playing virtuoso of physics, Albert Einstein. One of the few exceptions is perhaps medical students, who lack diversity more due to time constraints than lack of interest.

A firm grasp of science, without any grounding in the rest of the world, provides little understanding of the world, let alone appreciation for it. Political or cultural issues do not take case in some sort of scientific vacuum, where historical & cultural issues need not be taken into account.

While I've known many scientists who feel that they can objectively evaluate the world in a rational, scientific manner, the fact is that important issues in society never involve purely scientific questions. The Manhattan Project, for example, was not purely a scientific enterprise, but also clearly triggered questions that extend far outside of the realm of physics.

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What Is Physics?

Question: What Is Physics?

Answer: Physics is the scientific study of matter and energy and how they interact with each other.
This energy can take the form of motion, light, electricity, radiation, gravity . . . just about anything, honestly. Physics deals with matter on scales ranging from sub-atomic particles (i.e. the particles that make up the atom and the particles that make up those particles) to stars and even entire galaxies.

How Physics Works

As an experimental science, physics utilizes the scientific method to formulate and test hypotheses that are based on observation of the natural world. The goal of physics is to use the results of these experiments to formulate scientific laws, usually expressed in the language of mathematics, which can then be used to predict other phenomena.

The Role of Physics in Science

In a broader sense, physics can be seen as the most fundamental of the natural sciences. Chemistry, for example, can be viewed as a complex application of physics, as it focuses on the interaction of energy and matter in chemical systems. We also know that biology is, at its heart, an application of chemical properties in living things, which means that it is also, ultimately, ruled by the physical laws.

Major Concepts in Physics

Because physics covers so much area, it is divided into several specific fields of study, such as electronics, quantum physics, astronomy, and biophysics.

• Major Laws of Physics
• 10 Weirdest Physical Theories
• Thermodynamics Overview

Why Is Physics (Or Any Science) Important?

• Why Study Physics?
• Grand Ideas of Science (adapted, with permission, from the book Why Science? by James Trefil)

Physics - major concepts

• Fields of Physics
• Major Laws of Physics
• Fundamental Forces of Physics

Physics - modern physics theories

• Quantum Physics Overview
• Einstein's Theory of Relativity
• 10 Weirdest Physical Theories

Physics - other useful information

• What Skills Do I Need to Study Physics?
• Scientific Method
• Popular Physics Myths

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