هوالفتاح العلیم- بهداشت سوال۱
بهداشت - سلامتی - دامپزشکی - پزشکی - اسلامیهوالفتاح العلیم- بهداشت سوال۱
بهداشت - سلامتی - دامپزشکی - پزشکی - اسلامیگلوان -گراویتون - ریز ذرات هسته ای
بسم الله الرحمن الرحیم
از آن نخستین لحظات آتشین خلقت که به نام انفجار بزرگ میشناسیم گرانش نیروی خالق همه ساختار ها بوده است. از مجموعه های کهکشان تا شکل بدن ما و حتی کارهای روزمره مان را بدون آگاهی خودمان کنترل میکند. اما در این میان چهار نیرو هایی که کائنات را کنترل میکنند گرانش از همه ضعیف تر است.اینجا لازم به ذکر است که تازگی نیروی پنجمی به اسم "dark energy" (منو میگه ) نیز کشف شده است! که مسئول افزایش سرعت انبساط کائنات است.
اما چون مدت کمی از کشف این نیرو گذشته ماهیت آن هنوز مشخص نشده و بنابر این در اینجا فهرست نشده است.
این چهار نیرو عبارت اند از:
1: نیروی هسته ای قوی "strong force" که در قلمرو جهان زیراتمی عمل میکند. این نیرو کوارک ها را برای ساختن پروتون ها و نوترون ها در کنار هم نگه میدارد.
2: نیروی هسته ای ضعیف "weak force" که حاکم بر واپاشی هسته ای هست و از طریق ذراتی به نام "بوزون" های ضعیف عمل میکند. این نیرو عامل محرک خورشید و ستاره هاست و انرژی وابسته به هسته اتم هارا حمل میکند.3: "نیروی الکترومغناطیس" که اتم هارا کنار هم نگه میدارد. گستره این نیرو بینهایت است و از طریق فوتون های عامل نور عمل میکند.
4: "نیروی گرانش gravity" که جاذبه جهانی همه اجرام است. این نیرو همیشه جذب میکند و هیچگاه دفع نمیکند.
در سطح هسته ای هرکدام از این نیرو ها را ذره ای حمل میکند که میتوان آن را کوچکترین بسته حامل آن نیرو به حساب آورد.
این ذرات عبارت اند از:
1: نیروی هسته ای قوی از طریق ذراتی به نام "گلوان ها" عمل میکند. چون آن ها همچون قوی ترین و کامل ترین چسب قابل تصور در دنیا عمل میکنند.
نام گلوان از واژه انگلیسی "glue" به معنی چسب گرفته شده است.
2: "نیروی هسته ای ضعیف" را بوزون ها ی ضعیف حمل میکنند. جرم آن ها حدود 86/97 برابر جرم پروتون است.
3: ذرات حامل نیروی الکترومغناطیس فوتون نام دارند.
4: به نظر میرسد که نیروی گرانش را ذراتی به نام "گراویتون" حمل میکنند. این تنها ذره ای از نوع خود است که هنوز آشکار نشده است اما شاید کشف نشدن آن ها به این دلیل باشد که اصلا وجود ندارند! چرا که بر اساس نظریه نسبیت عام "گرانش نیرو نیست" بلکه تظاهری از انحنای فضا زمان در حضور جرم است. در حال حاظر این تصویر رایج درباره ماهیت گرانش است.
بلافاصله پس از انفجار بزرگ فقط یک نیرو به نام "نیروی متحد بزرگ" وجود داشت وقتی ساعت خلقت به 43-^10 ثانیه رسید و دمای کائنات به 23^10 درجه بالای صفر مطلق بود. این نیرو به نام نیروی گرانش و نیروی electro nuclear force ای تقسیم شد.
وقتی در لحظه 35-^10 ثانیه دمای کائنات به 27^10 درجه کلوین رسید نیروی "الکترو هسته ای" به نیروی هسته ای قوی و نیروی نیروی الکترو ضعیف تقسیم شد و دوران تورم آغاز شد.
با سرد شدن بیشتر کائنات تا 15^10 درجه کلوین در زمان 12-^10 ثانیه نیروی الکترو ضعیف به دو نیروی "النیرومغناطیس و هسته ای ضعیف تقسیم شد" و به این ترتیب چهر نیروی موثر امروزی صرف نظر از نیروی تازه کشف شده انرژی تاریک ; شکل گرفتند.
در این زمان همه ذرات بنیادین که کل جرم فعلی کائنات از جمله "زمین" را تشکیل میدهند به وجود آمدند.
نظریه ای که به بحث درباره اتحاد نیروی های خلقت می پردازد نظریه "وحدت نیرو ها" "وحدت میدان" یا نظریه "همه چیز نام دارد"
وجود نیروی الکترو ضعیف با کشف ذره "Z" که حامل آن است اثبات شده است.
این موفقیت در آزمایش هایی که در شتاب دهنده های بزرگ ذرات انجام شدند حاصل شد. در این شتاب دهنده ها فقط در زمان بسیار کوتاهی میتوان به دمایی رسید که این ذرات ظهور پیدا میکنند .
تعداد زیادی از دانشمندان در پی جستجوی ذره "X" هستند که ظهورش حکایت از پیوستن ذره های الکترو ضعیف و هسته ای قوی به یکدیگر و تشکیل نیروی الکترو هسته ای دارد.
پیوستن نیروی گرانش و نیروی الکترو هسته ای در دمای آتش خلقت رخ میدهد این کار احتیاج به یک دستگاه شتاب دهنده به قطر "1000 سال نوری" دارد.
هنوز حتی بررسی های نظری این مسئله هم تکمیل نشده. این نظریه ای است که اینشتین پس از در آوردن نسبیت باقی عمرش را صرف آن کرد اما نتوانست تکمیلش کند.
البته از زمان درگذشت اینشتین در سال 1953 2/3 (دو سوم) نظریه وحدت نیرو ها را دانشمندان دیگر به صورت نظری کار کرده اند و 1/3 آن را از طریق آزمایش اثبات شده است.
در حال حاضر بسیاری از فیزیکدانان نظری در حال تکمیل 1/3 باقی مانده نظریه اند و مطمئن هستند که زمانی در همین قرن قادر خواهند بود که تعیین کنند چگونه "در خیلی ابتدای کائنات!" نیرو های گرانش و الکترو هسته ای باهم متحداً یک نیرو را تشکیل میدادند.
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Well, there is, but it is all relatively simple (simple hey, we'll see
Particle Physics - Structure of a Matter 
In ancient times, people believed that all matter is a variation of earth, air, fire and water. Until early 20th century people believed that the basic building block of matter is an atom, visualized as a sphere. Nowadays, we know that atoms are made of even more fundamental entities. The diagram below show an increaing magnification of an imaginary microscope on an ordinary matter.
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However, the nucleus is made of a mixture of protons and neutrons. The size of a proton and a neutron are similar, in the order of 10-15 m. We now know that they are not the fundamental particles. Take, for example, a proton. It is now believed a proton is made of three fundamental particles called quarks. There are six different types of quarks, of which only up (u) quark and down (d) quark made up of protons: 2 up and 1 down. This is often written as 'duu'. On the other hand, a neutron is made of 'ddu': two down quarks and one up quark. Once again, to our current understanding, a quark is a fundamental particle. These quarks are held very tightly by the strong force carrier called gluon.
In ancient times, people believed that all matter is a variation of earth, air, fire and water. Until early 20th century people believed that the basic building block of matter is an atom, visualized as a sphere. Nowadays, we know that atoms are made of even more fundamental entities. The diagram below show an increaing magnification of an imaginary microscope on an ordinary matter.
*** Beginning with bulk matter, this is the ordinary matter that we can see, down to the nanometer size which can be seen using an electron microscope. At higher magnification, atoms and molecules (atoms grouped into one entity) beginning to manifest, arranged in certain particlar order, which defines the shape of a solid. The range of scale size is large. This is because of different number of atom types and infinitely number of types of molecules of various sizes that made up different matter. |
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| Elementary Particles : | Readings: | particle physics fundamental forces quarks |
| One of the primary goals in modern physics is to answer the question "What is the Universe made of?" Often that question reduces to "What is matter and what holds it together?" This continues the line of investigation started by Democritus, Dalton and Rutherford. Modern physics speaks of fundamental building blocks of Nature, where fundamental takes on a reductionist meaning of simple and structureless. Many of the particles we have discussed so far appear simple in their properties. All electrons have the exact same characteristics (mass, charge, etc.), so we call an electron fundamental because they are all non-unique. The search for the origin of matter means the understanding of elementary particles. And with the advent of holism, the understanding of elementary particles requires an understanding of not only their characteristics, but how they interact and relate to other particles and forces of Nature, the field of physics called particle physics. |
| The study of particles is also a story of advanced technology begins with the search for the primary constituent. More than 200 subatomic particles have been discovered so far, all detected in sophisticated particle accelerators. However, most are not fundamental, most are composed of other, simpler particles. For example, Rutherford showed that the atom was composed of a nucleus and orbiting electrons. Later physicists showed that the nucleus was composed of neutrons and protons. More recent work has shown that protons and neutrons are composed of quarks. |
Generations of Matter:
| A quark is any of a group of subatomic particles believed to be among the fundamental constituents of matter. In much the same way that protons and neutrons make up atomic nuclei, these particles themselves are thought to consist of quarks. Quarks constitute all hadrons (baryons and mesons)--i.e., all particles that interact by means of the strong force, the force that binds the components of the nucleus. According to prevailing theory, quarks have mass and exhibit a spin (i.e., type of intrinsic angular momentum corresponding to a rotation around an axis through the particle). Quarks appear to be truly fundamental. They have no apparent structure; that is, they cannot be resolved into something smaller. Quarks always seem to occur in combination with other quarks or antiquarks, never alone. For years physicists have attempted to knock a quark out of a baryon in experiments with particle accelerators to observe it in a free state but have not yet succeeded in doing so. Throughout the 1960s theoretical physicists, trying to account for the ever-growing number of subatomic particles observed in experiments, considered the possibility that protons and neutrons were composed of smaller units of matter. In 1961 two physicists, Murray Gell-Mann of the United States and Yuval Ne`eman of Israel, proposed a particle classification scheme called the Eightfold Way, based on the mathematical symmetry group SU(3), that described strongly interacting particles in terms of building blocks. In 1964 Gell-Mann introduced the concept of quarks as a physical basis for the scheme, adopting the fanciful term from a passage in James Joyce's novel Finnegans Wake. (The American physicist George Zweig developed a similar theory independently that same year and called his fundamental particles "aces.") Gell-Mann's model provided a simple picture in which all mesons are shown as consisting of a quark and an antiquark and all baryons as composed of three quarks. It postulated the existence of three types of quarks, distinguished by distinctive "flavours." These three quark types are now commonly designated as "up" (u), "down" (d), and "strange" (s). Each carries a fractional electric charge (i.e., a charge less than that of the electron). The up and down quarks are thought to make up protons and neutrons and are thus the ones observed in ordinary matter. Strange quarks occur as components of K mesons and various other extremely short-lived subatomic particles that were first observed in cosmic rays but that play no part in ordinary matter. Most problems with quarks were resolved by the introduction of the concept of color, as formulated in quantum chromodynamics (QCD). In this theory of strong interactions, developed in 1977, the term color has nothing to do with the colors of the everyday world but rather represents a special quantum property of quarks. The colors red, green, and blue are ascribed to quarks, and their opposites, minus-red, minus-green, and minus-blue, to antiquarks. According to QCD, all combinations of quarks must contain equal mixtures of these imaginary colors so that they will cancel out one another, with the resulting particle having no net color. A baryon, for example, always consists of a combination of one red, one green, and one blue quark. The property of color in strong interactions plays a role analogous to an electric charge in electromagnetic interactions. Charge implies the exchange of photons between charged particles. Similarly, color involves the exchange of massless particles called gluons among quarks. Just as photons carry electromagnetic force, gluons transmit the forces that bind quarks together. Quarks change their color as they emit and absorb gluons, and the exchange of gluons maintains proper quark color distribution. |
| Leptons are any member of a class of fermions that respond only to electromagnetic, weak, and gravitational forces and do not take part in strong interactions. Like all fermions, leptons have a half-integral spin. (In quantum-mechanical terms, spin constitutes the property of intrinsic angular momentum.) Leptons obey the Pauli exclusion principle, which prohibits any two identical fermions in a given population from occupying the same quantum state. Leptons are said to be fundamental particles; that is, they do not appear to be made up of smaller units of matter. Leptons can either carry one unit of electric charge or be neutral. The charged leptons are the electrons, muons, and taus. Each of these types has a negative charge and a distinct mass. Electrons, the lightest leptons, have a mass only 0.0005 that of a proton. Muons are heavier, having more than 200 times as much mass as electrons. Taus, in turn, are approximately 3,700 times more massive than electrons. Each charged lepton has an associated neutral partner, or neutrino (i.e., electron-, muon-, and tau-neutrino), that has no electric charge and no significant mass. Moreover, all leptons, including the neutrinos, have antiparticles called antileptons. The mass of the antileptons is identical to that of the leptons, but all of the other properties are reversed. |
| The electron is the lightest stable subatomic particle known. It carries a negative charge which is considered the basic charge of electricity. An electron is nearly massless. It has a rest mass of 9.1x10-28 gram, which is only 0.0005 the mass of a proton. The electron reacts only by the electromagnetic, weak, and gravitational forces; it does not respond to the short-range strong nuclear force that acts between quarks and binds protons and neutrons in the atomic nucleus. The electron has an antimatter counterpart called the positron. This antiparticle has precisely the same mass and spin, but it carries a positive charge. If it meets an electron, both are annihilated in a burst of energy. Positrons are rare on the Earth, being produced only in high-energy processes (e.g., by cosmic rays) and live only for brief intervals before annihilation by electrons that abound everywhere. The electron was the first subatomic particle discovered. It was identified in 1897 by the British physicist J.J. Thomson during investigations of cathode rays. His discovery of electrons, which he initially called corpuscles, played a pivotal role in revolutionizing knowledge of atomic structure. Under ordinary conditions, electrons are bound to the positively charged nuclei of atoms by the attraction between opposite electric charges. In a neutral atom the number of electrons is identical to the number of positive charges on the nucleus. Any atom, however, may have more or fewer electrons than positive charges and thus be negatively or positively charged as a whole; these charged atoms are known as ions. Not all electrons are associated with atoms. Some occur in a free state with ions in the form of matter known as plasma. |
Fundamental Forces :
| The first two you are familiar with, gravity is the attractive force between all matter, electromagnetic force describes the interaction of charged particles and magnetics. Light (photons) is explained by the interaction of electric and magnetic fields. The strong force binds quarks into protons, neutrons and mesons, and holds the nucleus of the atom together despite the repulsive electromagnetic force between protons. The weak force controls the radioactive decay of atomic nuclei and the reactions between leptons (electrons and neutrinos). Current physics (called quantum field theory) explains the exchange of energy in interactions by the use of force carriers, called bosons. The long range forces have zero mass force carriers, the graviton and the photon. These operate on scales larger than the solar system. Short range forces have very massive force carriers, the W+, W- and Z for the weak force, the gluon for the strong force. These operate on scales the size of atomic nuclei. So, although the strong force has the greatest strength, it also has the shortest range. |
Bosons (Force Carriers):
| Bosons are the particles which transmits the different forces between the matter particles, they normally have a whole number spin, 0, 1 or 2. And Fermions which are matter particles they often have spin 1/2. Real particles are the ones you are familiar with, all Fermions are real particles. The Bosons can sometimes be virtual and sometimes real. Virtual particles are the particles which transmits the force between the particles, e.g. virtual photon carries the electromagnetic force between e.g. electrons. They are called virtual particles because they can't be directly detected, you can't 'see' them so to speak. But their effect can be noticed, by e.g. the actual forces between particles. |
Baryons and Mesons:
| Quarks combine to form the basic building blocks of matter, baryons and mesons. Baryons are made of three quarks to form the protons and neutrons of atomic nuclei (and also anti-protons and anti-neutrons). Mesons, made of quark pairs, are usually found in cosmic rays. Notice that the quarks all combine to make charges of -1, 0, or +1. |
| Thus, our current understanding of the structure of the atom is shown below, the atom contains a nucleus surrounded by a cloud of negatively charged electrons. The nucleus is composed of neutral neutrons and positively charged protons. The opposite charge of the electron and proton binds the atom together with electromagnetic forces. |
| The protons and neutrons are composed of up and down quarks whose fractional charges (2/3 and -1/3) combine to produce the 0 or +1 charge of the proton and neutron. The nucleus is bound together by the nuclear strong force (that overcomes the electromagnetic repulsion of like-charged protons) Quarks in baryons and mesons are bound together by the strong force in the form of the exchange of gluons. Much like how the electromagnetic force strength is determined by the amount of electric charge, the strong force strength is determined by a new quantity called color charge. Quarks come in three colors, red, blue and green (they are not actually colored, we just describe their color charge in these terms). So, unlike electromagnetic charges which come in two flavors (positive and negative or north and south poles), color charge in quarks comes in three types. And, just to be more confusing, color charge also has its anti-particle nature. So there is anti-red, anti-blue and anti-green. Gluons serve the function of carrying color when they interact with quarks. Baryons and mesons must have a mix of colors such that the result is white. For example, red, blue and green make white. Also red and anti-red make white. There can exist no free quarks, i.e. quarks by themselves. All quarks must be bound to another quark or antiquark by the exchange of gluons. This is called quark confinement. The exchange of gluons produces a color force field, referring to the assignment of color charge to quarks, similar to electric charge. The color force field is unusual in that separating the quarks makes the force field stronger (unlike electromagnetic or gravity forces which weaken with distance). Energy is needed to overcome the color force field. That energy increases until a new quark or antiquark is formed (energy equals mass, E=mc2). |
| Two new quarks form and bind to the old quarks to make two new mesons. Thus, none of the quarks were at anytime in isolation. Quarks always travel in pairs or triplets. |
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http://www.hupaa.com/forum/viewtopic.php?f=14&t=30832
http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec16.html