出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/07/18 18:10:22」(JST)
| 出典は列挙するだけでなく、脚注などを用いてどの記述の情報源であるかを明示してください。記事の信頼性向上にご協力をお願いいたします。（2010年6月） |
| 物理学 |
|---|
| ウィキポータル 物理学 執筆依頼・加筆依頼 |
|
|
| カテゴリ |
| 物理学 - （画像） |
| ウィキプロジェクト 物理学 |
物理学（ぶつりがく、physics）は、自然科学の一分野である。自然界に見られる現象には、人間の恣意的な解釈に依らない普遍的な法則があると考え、自然界の現象とその性質を、物質とその間に働く相互作用によって理解すること（力学的理解）、および物質をより基本的な要素に還元して理解すること（原子論的理解）を目的とする。化学、生物学、地学などほかの自然科学に比べ数学との親和性が非常に強い。
古代ギリシアの自然学 (φύσις physis) にその源があり、"physics"という言葉も、元々は自然についての一般的な知識の追求を意味しており、天体現象から生物現象までを含む幅広い概念だった。現在の、物理現象のみを追求する"physics"として自然哲学から独立した意味を持つようになったのは19世紀からである。
物理学の古典的な研究分野は、物体の運動、光と色彩、音響、電気と磁気、熱、波動、天体の諸現象（物理現象）である。
物理学では物理現象を微視的な視点と巨視的な視点とから研究する[要出典]。
[要出典]微視的な視点の代表的なものは素粒子物理学で、自然界に存在するさまざまな物質が分子や原子、電子といった種類の限られた基本要素の組み合わせによって構成されていることを突き止めてきた。素粒子物理学は核子よりさらに基本的な要素であるクォークが存在することを解明し、さらにもっと基本的な要素であるストリングなどが研究されている。また、こうした物質要素の間に働く力が、重力、電磁気力、弱い力、強い力（又は核力）の四種類の力に還元できることも明らかにされてきた。現在知られている相互作用は以上の四つのみである。
[要出典]巨視的な視点からは、液体や気体、熱エネルギー、エントロピー、波といった巨視的な物理現象が研究される。こうした巨視的現象も原理的には無数の粒子の微視的現象の積み重ねの結果であると考えられているが、構成粒子数が極端に多いために、すべての素過程を記述して、そこから巨視的な現象を導くことは事実上不可能である。一方、こうした巨視的現象には構成粒子の従う法則とは関係なく、物質の巨視的な振る舞いを支配する別個の法則が存在するように見える。例えば、水や雲、蜂蜜といった液体は、原子レベルにさかのぼらなくても、液体として同じ法則に従って振る舞い、それらの物質的な特性の違いは粘性のような巨視的なパラメータとして表される。
材料力学や流体力学はそうした巨視的現象の法則からなる独立した物理学上の理論体系である。巨視現象を説明しながら微視現象との親和性が高い巨視物理学は統計熱力学のみである。ここで注意しなければならないのは材料力学や流体力学はそれらの適用範囲においては、他の理論から完全に閉じた理論体系として存在していることである。
現代の物理学は、たとえば素粒子論がある一方で熱力学があるように、巨視的現象の理論と微視的現象を記述する力学とをつなぐ理論や現象も、重要なテーマとして研究されている。一般的にこの分野では統計物理学と呼ばれる強力な手法が使われる。ルートヴィッヒ・ボルツマンらによって開発されたこの手法は、構成粒子の振る舞いを統計的に処理することによって、巨視的現象と結びつけるものである。統計力学の基礎づけは、古典力学によっては不可能であり、量子力学は欠かせない。また、量子力学の発見には、黒体放射を説明するプランクの法則など、当時の古典統計力学における問題とも深い関わりがあった。
大量の数値計算を可能にするスーパーコンピュータによって、大量の粒子の理論的振る舞いを数値的にシミュレートして巨視的な振る舞いを再現させようとする計算物理学の試みが20世紀後半から勃興している。
物理学では、理論やモデルを数式として表現することが多い。これは、自然言語で記述するとどうしても厳密さに欠け、定量的な評価や複雑な推論をすることが難しいためである。数学は非常に強力な記号操作体系であるため、推論を一連の計算として実行することが可能なことと、複雑なモデルを正確・簡潔に表現することに適している。このように言語としての数学は、物理学を記述するのに適した特性を備えているが、学問としての物理学と数学は扱う対象も方法論も異なる。
物理学の研究において最も重要なステップの一つは、物理法則を数式に表現する前の段階、観測された事実の中から記述すべき基本的な要素を抽出する行為である[要出典]。電磁気学に貢献したマイケル・ファラデーが正規の教育を受けなかったため、数学的知識がなかったにもかかわらず、さまざまな発見を成し遂げたことや、ノーベル賞を受賞したリチャード・P・ファインマンが液体ヘリウムについて論じた論文やジョージ・ガモフが初めてビッグバン理論を提唱した論文には数式が出てこないことは、自然界の中に記述すべき対象を見つけ出す営みが物理学において重要なステップであるということを示している[要出典]。
物理学の歴史は一見異なって見える現象を、同一の法則の異なる側面であるとして、統一的に説明していく歴史でもあった[要出典]（物理学の歴史そのものについては後述）。
地上付近での物体の落下と月の運動を同じ万有引力によるものとしたニュートンの重力の理論は、それまであった惑星の運動に関するケプラーの法則や、ガリレイの落体運動の法則が万有引力の別の側面であることを示した。 マクスウェルは、それまでアンペールやファラデーらが個別に発見していた電気と磁気の法則が、電磁気という一つの法則にまとめられることを導き、電磁波の存在を理論的に予言し、光が電磁波の一種であることを示した。
20世紀に入るとアインシュタインが相対性理論によって、時間と空間に関する認識を一変させた。彼はさらに重力と電磁気力に関する統一場理論の研究に取り組んだが実現しなかった。しかし、その後も統一場理論に関する研究は他の研究者たちによって続けられ、新しく発見された核力も含めて統一しようとする努力が続けられた。1967年頃電磁気力と弱い力に関する統一場理論（ワインバーグ・サラム理論）が提唱され、後の実験的な検証により理論の正当性が確立した。この理論により、電磁気力と弱い力は同じ力の異なる側面として説明されることになった。
自然界に存在する重力、電磁気力、強い力、弱い力の四つの相互作用のうち、上記の電弱統一理論を超えて、電磁気力、強い力、弱い力に関する統一場理論である大統一理論、重力、電磁気力、強い力、弱い力の四つの相互作用全てに関する統一場理論（例えば、超弦理論が候補）が研究されているが、実験的に検証されておらず、現在においても確立には至っていない（しばしば、上記の四つの相互作用に関する統一場理論は、既存の物理現象がその理論一つを基礎として理解できると考えられるため、万物の理論と呼ばれることがある）。
古典的な物理学では、物理現象が発生する空間と時間は、物理現象そのものとは別々のものと考えられてきたが、重力の理論（一般相対性理論）によって、物質の存在が空間と時間に影響を与えること、物質とエネルギーが等価であることが解明されたことから、現代物理学では、物理現象に時間と空間、物質とエネルギーを含める。
物理学はほかの自然科学と密接に関係している。物理学で得られた知見が非常に強力なために、他の自然科学の分野の問題の解決に寄与することも多く、生物学、医学など他の分野との連携も進んでいる。
特に化学においては密接に関連する分野が多く、特に物理学的な手法を用いる分野として物理化学という分野が設けられている。
生物学においても、生物の骨格や筋肉を力学的に考察したり、遺伝子レベルでの解析や進化の物理的考察を行う分子生物学がある。
地球科学においても地球を物理的な手法を用いて研究する地球物理学があり、地震学・気象学・海洋物理学・地球電磁気学等は地球物理学の代表的な分野であるといえる。
今日の物理学は自然科学のみならず人文科学・社会科学とも関係している。人文科学においては「哲学との学際領域に自然哲学があり、自然哲学から今日の哲学と自然科学が分離した[要出典]」という見方もある。また、心理学も精神物理学を通じて物理学と関係している。
社会科学においては中学校・高等学校における教科としての物理は教育学と密接に関係しており、経済現象を物理的に解明する経済物理学は経済学との学際的分野であるといえる。
総合的なものとして、物理学用語一覧を参照。
| この節は検証可能な参考文献や出典が全く示されていないか、不十分です。出典を追加して記事の信頼性向上にご協力ください。（2010年6月） |
古代から人々は物質の振る舞いを理解しようと努めていた。なぜ支持しない物は地面におちるのか？なぜ異なった物質は異なった性質を持つのか？など。宇宙の特徴はまた神秘であった。地球の成り立ちや太陽や月といった天体の動き。いくつかの理論が提唱されたが、そのほとんどは間違っていた。それらの理論は哲学の言葉でおおむね述べられており、系統だった試行的な試験によって変えられることはなかった。例外として、例えば古代ギリシアの思想家アルキメデスは力学と静水学に関して多くの正確で定量的な説明をした。
16世紀後半に、ガリレイは物理理論を立証するために実験を用いた。実験は科学的研究法における重要な概念である。ガリレイは力学に関するいくつかの結果を定式化し、成功裏に試験した。とくに、慣性の法則について。1687年にニュートンはプリンキピアを出版した。それは二つの包括的かつ成功した理論を詳述していた。その一つ、ニュートンの運動方程式は古典力学の起こりとなった。もう一つ、万有引力の法則は基本的な力である万有引力を記述する。両理論は実験と良く一致した。ラグランジュ、ハミルトンらは古典力学を徹底的に拡張し、新しい定式化、原理、結果を導いた。重力の法則によって宇宙物理学の分野が起こされた。宇宙物理学は物理理論をもちいて天体現象を記述する。
18世紀から、ボイル、ヤングら大勢の学者によって熱力学が発展した。1733年に、ベルヌーイが熱力学的な結果を導くために古典力学とともに統計論を用いた。これが統計力学の起こりである。1798年に、トムソンは力学的仕事が熱に変換されることを示した。1847年に、ジュールは力学的エネルギーを含めた熱についてのエネルギーの保存則を提示した。
電気と磁気の挙動はファラデー、オーム、他によって研究された。1855年にマクスウェルはマクスウェル方程式で記述される電磁気学という単一理論で二つの現象を統一的に説明した。この理論によって光は電磁波であると予言された。
1895年に、レントゲンはX線を発見し、それが高い周波数の電磁波であることを明らかにした。放射能はベクレルによって1896年に発見された。さらに、ピエール・キュリーとマリ・キュリーほかによって研究された。これが核物理学の起こりとなった。
1897年に、トムソンは回路の中の電流を運ぶ素粒子である電子を見つけた。1904年に、原子の最初のモデルを提案した。それはプラムプリン模型として知られている（原子の存在は1808年にドルトンが提案していた）。
1905年に、アインシュタインは特殊相対性理論を定式化した。その中では時間と空間は時空という一つの実体に統一される。相対性理論は古典力学とは異なる慣性座標系間の変換を定める。それ故、古典力学の置き換えとなる相対論的力学を構築する必要があった。低（相対）速度領域においては二つの理論は一致する。1915年に、アインシュタインは特殊相対性理論を拡張し、一般相対性理論で重力を説明した。それはニュートンの万有引力の法則を置き換えるもので、低質量かつ低エネルギーの領域では二つの理論は一致する。
1911年に、ラザフォードは散乱実験から陽子と呼ばれる正の電荷の構成物質でぎっしりと詰まった原子核の存在を推定した。中性の核構成物質である中性子は1932年にチャドウィックによって発見された。
1900年代初頭に、プランク、アインシュタイン、ボーアたちは量子論を発展させ、離散的なエネルギー準位の導入によってさまざまな特異な実験結果を説明した。1925年にハイゼンベルクらが、そして1926年にシュレーディンガーとディラックが量子力学を定式化し、それによって前期量子論は解釈された。量子力学において物理測定の結果は本質的に確率的である。つまり、理論はそれらの確率の計算法を与える。量子力学は小さな長さの尺度での物質の振る舞いをうまく記述する。
また、量子力学は凝縮系物理学の理論的な道具を提供した。凝縮系物理学では誘電体、半導体、金属、超伝導、超流動、磁性体、といった現象、物質群を含む固体と液体の物理的振る舞いを研究する。凝縮系物理学の先駆者であるブロッホは結晶構造中の電子の振る舞いの量子力学的記述を1928年に生み出した。
第二次世界大戦の間、核爆弾を作るという目的のために、研究は核物理の各方面に向けられた。ハイゼンベルクが率いたドイツの努力は実らなかったが、連合国のマンハッタン計画は成功を収めた。アメリカでは、フェルミが率いたチームが1942年に最初の人工的な核連鎖反応を達成し、1945年にアメリカ合衆国ニューメキシコ州のアラモゴードで世界初の核爆弾が爆発した。
場の量子論は、特殊相対性理論と整合するように量子力学を拡張するために定式化された。それは、ファインマン、朝永、シュウインガー、ダイソンらの仕事によって1940年代後半に現代的な形に至った。彼らは電磁相互作用を記述する量子電磁力学の理論を定式化した。
場の量子論は基本的な力と素粒子を研究する現代の素粒子物理学の枠組みを提供した。1954年にヤンとミルズはゲージ理論という分野を発展させた。それは標準模型の枠組みを提供した。1970年代に完成した標準模型は今日観測される素粒子のほとんどすべてをうまく記述する。
場の量子論の方法は、多粒子系を扱う統計物理学にも応用されている。松原武生は場の量子論で用いられるグリーン関数を、統計物理学において初めて使用した。このグリーン関数の方法はロシアのアブリコソフらにより発展され、固体中の電子の磁性や超伝導の研究に用いられた。
2003年時点において、物理学の多くの分野で研究が進展している。
スーパーカミオカンデの実験からニュートリノの質量が0でないことが判明した。このことを理論の立場から理解しようとするならば、既存の標準理論の枠組みを越えた理解が必要である。質量のあるニュートリノの物理は現在理論と実験が影響しあい活発に研究されている領域である。今後数年で粒子加速器によるTeV（テラ電子ボルト）領域のエネルギー尺度の探査はさらに活発になるであろう。実験物理学者はそこでヒッグス粒子や超対称性粒子の証拠を見つけられるのではないかと期待している。
量子力学と一般相対性理論を量子重力の単一理論に統合するという半世紀以上におよぶ試みはまだ結実していない。現在の有望な候補はM理論とループ量子重力理論である。
宇宙物理学の分野でも1990年代から2000年代にかけて大きな進展が見られた。特に1990年代以降、大口径望遠鏡やハッブル宇宙望遠鏡・COBE・WMAP などの宇宙探査機によって格段に精度の良い観測データが大量に得られるようになり、宇宙論の分野でも定量的で精密な議論が可能になった。ビッグバン理論及びインフレーションモデルに基づく現代のΛ-CDM宇宙モデルはこれらの観測とよく合致しているが、反面、ダークマターの正体や宇宙の加速膨張を引き起こしていると考えられるダークエネルギーの存在など、依然として謎となっている問題も残されている。これ以外に、ガンマ線バーストや超高エネルギー宇宙線の起源なども未解決であり、これらを解明するための様々な宇宙探査プロジェクトが進行している。
凝縮物質の物理において、高温超伝導の理論的説明は、未解明の問題として残されている。量子ドットなど単一の電子・光子を用いたデバイス技術の発展により、量子力学の基礎について実験的検証が可能になってきており、さらにはスピントロニクスや量子コンピュータなどへの応用展開が期待される。
| ウィキペディアの姉妹プロジェクトで 「物理学」に関する情報が検索できます。 |
|
| ウィクショナリーで辞書項目 | |
| ウィキブックスで教科書や解説書 |
|
| ウィキクォートで引用句集 |
|
| ウィキソースで原文 |
|
| コモンズでメディア |
|
| ウィキニュースでニュース |
|
| ウィキバーシティで学習支援 |
|
|
||||||||||||||||||||
|
||||||||
Various examples of physical phenomena.
Physics (from Ancient Greek: φυσική (ἐπιστήμη) phusikḗ (epistḗmē) "knowledge of nature", from φύσις phúsis "nature"[1][2][3]) is the natural science that involves the study of matter[4] and its motion through space and time, along with related concepts such as energy and force.[5] More broadly, it is the general[disputed – discuss] analysis of nature, conducted in order to understand how the universe behaves.[a][6][7][8]
Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[9] Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches of mathematics, and biology, but during the scientific revolution in the 17th century, the natural sciences emerged as unique research programs in their own right.[b] Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms of other sciences[6] while opening new avenues of research in areas such as mathematics and philosophy.
Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs. For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons;[6] advances in thermodynamics led to the development of industrialization, and advances in mechanics inspired the development of calculus.Pages with a transclusion of Template:Reflistp that should be removed
Astronomy is the oldest of the natural sciences. The earliest civilizations dating back to beyond 3000 BCE, such as the Sumerians, ancient Egyptians, and the Indus Valley Civilization, all had a predictive knowledge and a basic understanding of the motions of the Sun, Moon, and stars. The stars and planets were often a target of worship, believed to represent their gods. While the explanations for these phenomena were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy.[9]
According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy.[10] Egyptian astronomers left monuments showing knowledge of the constellations and the motions of the celestial bodies,[11] while Greek poet Homer wrote of various celestial objects in his Iliad and Odyssey; later Greek astronomers provided names, which are still used today, for most constellations visible from the northern hemisphere.[12]
Natural philosophy has its origins in Greece during the Archaic period, (650 BC – 480 BC), when Pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause.[13] They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment;[14] for example, atomism was found to be correct approximately 2000 years after it was first proposed by Leucippus and his pupil Democritus.[15]
Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics.[16]
Major developments in this period include the replacement of the geocentric model of the solar system with the helio-centric Copernican model, the laws governing the motion of planetary bodies determined by Johannes Kepler between 1609 and 1619, pioneering work on telescopes and observational astronomy by Galileo Galilei in the 16th and 17th Centuries, and Isaac Newton's discovery and unification of the laws of motion and universal gravitation that would come to bear his name.[17] Newton also developed calculus,[c] the mathematical study of change, which provided new mathematical methods for solving physical problems.[18]
The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased.[19] The laws comprising classical physics remain very widely used for objects on everyday scales travelling at non-relativistic speeds, since they provide a very close approximation in such situations, and theories such as quantum mechanics and the theory of relativity simplify to their classical equivalents at such scales. However, inaccuracies in classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century.
Modern physics began in the early 20th century with the work of Max Planck in quantum theory and Albert Einstein's theory of relativity. Both of these theories came about due to inaccuracies in classical mechanics in certain situations. Classical mechanics predicted a varying speed of light, which could not be resolved with the constant speed predicted by Maxwell's equations of electromagnetism; this discrepancy was corrected by Einstein's theory of special relativity, which replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light.[20] Black body radiation provided another problem for classical physics, which was corrected when Planck proposed that light comes in individual packets known as photons; this, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to the theory of quantum mechanics taking over from classical physics at very small scales.[21]
Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger and Paul Dirac.[21] From this early work, and work in related fields, the Standard Model of particle physics was derived.[22] Following the discovery of a particle with properties consistent with the Higgs boson at CERN in 2012,[23] all fundamental particles predicted by the standard model, and no others, appear to exist; however, physics beyond the Standard Model, with theories such as supersymmetry, is an active area of research.[24]
In many ways, physics stems from ancient Greek philosophy. From Thales' first attempt to characterize matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics was known as natural philosophy until the late 18th century.[25]
By the 19th century, physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on philosophy of science to give an adequate description of the scientific method.[26] The scientific method employs a priori reasoning as well as a posteriori reasoning and the use of Bayesian inference to measure the validity of a given theory.[27]
The development of physics has answered many questions of early philosophers, but has also raised new questions. Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism.[28]
Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism,[29] and Erwin Schrödinger, who wrote on quantum mechanics.[30][31] The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking,[32] a view Penrose discusses in his book, The Road to Reality.[33] Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.[34]
Though physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories were experimentally tested numerous times and found correct as an approximation of nature (within a certain domain of validity). For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research, and a remarkable aspect of classical mechanics known as chaos was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton (1642–1727).
These central theories are important tools for research into more specialised topics, and any physicist, regardless of their specialisation, is expected to be literate in them. These include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.
Classical physics includes the traditional branches and topics that were recognised and well-developed before the beginning of the 20th century—classical mechanics, acoustics, optics, thermodynamics, and electromagnetism. Classical mechanics is concerned with bodies acted on by forces and bodies in motion and may be divided into statics (study of the forces on a body or bodies not subject to an acceleration), kinematics (study of motion without regard to its causes), and dynamics (study of motion and the forces that affect it); mechanics may also be divided into solid mechanics and fluid mechanics (known together as continuum mechanics), the latter including such branches as hydrostatics, hydrodynamics, aerodynamics, and pneumatics. Acoustics is the study of how sound is produced, controlled, transmitted and received.[35] Important modern branches of acoustics include ultrasonics, the study of sound waves of very high frequency beyond the range of human hearing; bioacoustics the physics of animal calls and hearing,[36] and electroacoustics, the manipulation of audible sound waves using electronics.[37] Optics, the study of light, is concerned not only with visible light but also with infrared and ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion, and polarization of light. Heat is a form of energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy. Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an electric current gives rise to a magnetic field, and a changing magnetic field induces an electric current. Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest.
| Modern physics |
|---|
|
Schrödinger equation
|
| History of modern physics |
|
Founders
Max Planck · Albert Einstein · Niels Bohr · Max Born · Werner Heisenberg · Erwin Schrödinger · Louis de Broglie · Satyendra Nath Bose · Wolfgang Pauli · Paul Dirac
|
|
Concepts
space · time · energy · work
randomness · information · entropy · mind |
|
Branches
Philosophy of Science · Philosophy of physics
Mathematical logic · Mathematical physics |
|
Scientists
Röntgen · Becquerel · Lorentz · Planck · Curie · Wien · Skłodowska-Curie · Sommerfeld · Rutherford · Soddy · Onnes · Einstein · Wilczek · Born · Weyl · Bohr · Schrödinger · de Broglie · Laue · Bose · Compton · Pauli · Walton · Fermi · Waals · Heisenberg · Dyson · Zeeman · Moseley · Hilbert · Gödel · Jordan · Dirac · Wigner · Hawking · P.W Anderson · Lemaître · Thomson · Poincaré · Wheeler · Penrose · Millikan · Nambu · von Neumann · Higgs · Hahn · Feynman · Lee · Lenard · Salam · 't Hooft · Bell · Gell-Mann · J. J. Thomson · Raman · Bragg · Bardeen · Shockley · Chadwick · Lawrence · Zeilinger
|
|
Classical physics is generally concerned with matter and energy on the normal scale of observation, while much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on a very large or very small scale. For example, atomic and nuclear physics studies matter on the smallest scale at which chemical elements can be identified. The physics of elementary particles is on an even smaller scale since it is concerned with the most basic units of matter; this branch of physics is also known as high-energy physics because of the extremely high energies necessary to produce many types of particles in large particle accelerators. On this scale, ordinary, commonsense notions of space, time, matter, and energy are no longer valid.
The two chief theories of modern physics present a different picture of the concepts of space, time, and matter from that presented by classical physics. Quantum theory is concerned with the discrete, rather than continuous, nature of many phenomena at the atomic and subatomic level and with the complementary aspects of particles and waves in the description of such phenomena. The theory of relativity is concerned with the description of phenomena that take place in a frame of reference that is in motion with respect to an observer; the special theory of relativity is concerned with relative uniform motion in a straight line and the general theory of relativity with accelerated motion and its connection with gravitation. Both quantum theory and the theory of relativity find applications in all areas of modern physics.
While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.
Mathematics is the language used for compact description of the order in nature, especially the laws of physics. This was noted and advocated by Pythagoras,[38] Plato,[39] Galileo,[40] and Newton.
Physics theories use mathematics[41] to obtain order and provide precise formulas, precise or estimated solutions, quantitative results and predictions. Experiment results in physics are numerical measurements. Technologies based on mathematics, like computation have made computational physics an active area of research.
Ontology is a prerequisite for physics, but not for mathematics. It means physics is ultimately concerned with descriptions of the real world, while mathematics is concerned with abstract patterns, even beyond the real world. Thus physics statements are synthetic, while mathematical statements are analytic. Mathematics contains hypotheses, while physics contains theories. Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data.
The distinction is clear-cut, but not always obvious. For example, mathematical physics is the application of mathematics in physics. Its methods are mathematical, but its subject is physical.[42] The problems in this field start with a "mathematical model of a physical situation" and a "mathematical description of a physical law". Every mathematical statement used for solution has a hard-to-find physical meaning. The final mathematical solution has an easier-to-find meaning, because it is what the solver is looking for.
Physics is a branch of fundamental science, not practical science.[43] Physics is also called "the fundamental science" because the subject of study of all branches of natural science like chemistry, astronomy, geology and biology are constrained by laws of physics,[44] similar to how chemistry is often called the central science because of its role in linking the physical sciences. For example, chemistry studies properties, structures, and reactions of matter (chemistry's focus on the atomic scale distinguishes it from physics). Structures are formed because particles exert electrical forces on each other, properties include physical characteristics of given substances, and reactions are bound by laws of physics, like conservation of energy, mass and charge.
Physics is applied in industries like engineering and medicine.
Applied physics is a general term for physics research which is intended for a particular use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. It usually differs from engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.
The approach is similar to that of applied mathematics. Applied physicists can also be interested in the use of physics for scientific research. For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics.
Physics is used heavily in engineering. For example, statics, a subfield of mechanics, is used in the building of bridges and other static structures. The understanding and use of acoustics results in sound control and better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic flight simulators, video games, and movies, and is often critical in forensic investigations.
With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty. For example, in the study of the origin of the earth, one can reasonably model earth's mass, temperature, and rate of rotation, as a function of time allowing one to extrapolate forward and backward in time and so predict prior and future conditions. It also allows for simulations in engineering which drastically speed up the development of a new technology.
But there is also considerable interdisciplinarity in the physicist's methods, so many other important fields are influenced by physics (e.g., the fields of econophysics and sociophysics).
Physicists use the scientific method to test the validity of a physical theory, using a methodical approach to compare the implications of the theory in question with the associated conclusions drawn from experiments and observations conducted to test it. Experiments and observations are collected and compared with the predictions and hypotheses made by a theory, thus aiding in the determination or the validity/invalidity of the theory.
A scientific law is a concise verbal or mathematical statement of a relation which expresses a fundamental principle of some theory, such as Newton's law of universal gravitation.[45]
Theorists seek to develop mathematical models that both agree with existing experiments and successfully predict future experimental results, while experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena. Although theory and experiment are developed separately, they are strongly dependent upon each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot explain, or when new theories generate experimentally testable predictions, which inspire new experiments.
Physicists who work at the interplay of theory and experiment are called phenomenologists. Phenomenologists look at the complex phenomena observed in experiment and work to relate them to fundamental theory.
Theoretical physics has historically taken inspiration from philosophy; electromagnetism was unified this way.[d] Beyond the known universe, the field of theoretical physics also deals with hypothetical issues,[e] such as parallel universes, a multiverse, and higher dimensions. Theorists invoke these ideas in hopes of solving particular problems with existing theories. They then explore the consequences of these ideas and work toward making testable predictions.
Experimental physics expands, and is expanded by, engineering and technology. Experimental physicists involved in basic research design and perform experiments with equipment such as particle accelerators and lasers, whereas those involved in applied research often work in industry developing technologies such as magnetic resonance imaging (MRI) and transistors. Feynman has noted that experimentalists may seek areas which are not well-explored by theorists.[46]
Physics covers a wide range of phenomena, from elementary particles (such as quarks, neutrinos, and electrons) to the largest superclusters of galaxies. Included in these phenomena are the most basic objects composing all other things. Therefore physics is sometimes called the "fundamental science".[44] Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things observable to humans to root causes, and then connect these causes together.
For example, the ancient Chinese observed that certain rocks (lodestone) were attracted to one another by some invisible force. This effect was later called magnetism, and was first rigorously studied in the 17th century. A little earlier than the Chinese, the ancient Greeks knew of other objects such as amber, that when rubbed with fur would cause a similar invisible attraction between the two. This was also first studied rigorously in the 17th century, and came to be called electricity. Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force—electromagnetism. This process of "unifying" forces continues today, and electromagnetism and the weak nuclear force are now considered to be two aspects of the electroweak interaction. Physics hopes to find an ultimate reason (Theory of Everything) for why nature is as it is (see section Current research below for more information).
Contemporary research in physics can be broadly divided into condensed matter physics; atomic, molecular, and optical physics; particle physics; astrophysics; geophysics and biophysics. Some physics departments also support physics education research and physics outreach.
Since the 20th century, the individual fields of physics have become increasingly specialized, and today most physicists work in a single field for their entire careers. "Universalists" such as Albert Einstein (1879–1955) and Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare.[f]
The major fields of physics, along with their subfields and the theories they employ, are shown in the following table.
| Field | Subfields | Major theories | Concepts |
|---|---|---|---|
| Astrophysics | Astronomy, Astrometry, Cosmology, Gravitation physics, High-energy astrophysics, Planetary astrophysics, Plasma physics, Solar Physics, Space physics, Stellar astrophysics | Big Bang, Cosmic inflation, General relativity, Newton's law of universal gravitation, Lambda-CDM model, Magnetohydrodynamics | Black hole, Cosmic background radiation, Cosmic string, Cosmos, Dark energy, Dark matter, Galaxy, Gravity, Gravitational radiation, Gravitational singularity, Planet, Solar system, Star, Supernova, Universe |
| Atomic, molecular, and optical physics | Atomic physics, Molecular physics, Atomic and Molecular astrophysics, Chemical physics, Optics, Photonics | Quantum optics, Quantum chemistry, Quantum information science | Photon, Atom, Molecule, Diffraction, Electromagnetic radiation, Laser, Polarization (waves), Spectral line, Casimir effect |
| Particle physics | Nuclear physics, Nuclear astrophysics, Particle astrophysics, Particle physics phenomenology | Standard Model, Quantum field theory, Quantum electrodynamics, Quantum chromodynamics, Electroweak theory, Effective field theory, Lattice field theory, Lattice gauge theory, Gauge theory, Supersymmetry, Grand unification theory, Superstring theory, M-theory | Fundamental force (gravitational, electromagnetic, weak, strong), Elementary particle, Spin, Antimatter, Spontaneous symmetry breaking, Neutrino oscillation, Seesaw mechanism, Brane, String, Quantum gravity, Theory of everything, Vacuum energy |
| Condensed matter physics | Solid state physics, High pressure physics, Low-temperature physics, Surface Physics, Nanoscale and Mesoscopic physics, Polymer physics | BCS theory, Bloch wave, Density functional theory, Fermi gas, Fermi liquid, Many-body theory, Statistical Mechanics | Phases (gas, liquid, solid), Bose-Einstein condensate, Electrical conduction, Phonon, Magnetism, Self-organization, Semiconductor, superconductor, superfluid, Spin, |
| Applied Physics | Accelerator physics, Acoustics, Agrophysics, Biophysics, Chemical Physics, Communication Physics, Econophysics, Engineering physics, Fluid dynamics, Geophysics, Laser Physics, Materials physics, Medical physics, Nanotechnology, Optics, Optoelectronics, Photonics, Photovoltaics, Physical chemistry, Physics of computation, Plasma physics, Solid-state devices, Quantum chemistry, Quantum electronics, Quantum information science, Vehicle dynamics | ||
Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter.[47] In particular, it is concerned with the "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.[48]
The most familiar examples of condensed phases are solids and liquids, which arise from the bonding by way of the electromagnetic force between atoms.[49] More exotic condensed phases include the superfluid[50] and the Bose–Einstein condensate[51] found in certain atomic systems at very low temperature, the superconducting phase exhibited by conduction electrons in certain materials,[52] and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.[53]
Condensed matter physics is the largest field of contemporary physics. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields.[54] The term condensed matter physics was apparently coined by Philip Anderson when he renamed his research group—previously solid-state theory—in 1967.[55] In 1978, the Division of Solid State Physics of the American Physical Society was renamed as the Division of Condensed Matter Physics.[54] Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.[48]
Atomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions on the scale of single atoms and molecules. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales. All three areas include both classical, semi-classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).
Atomic physics studies the electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions,[56][57][58] low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the nucleus (see, e.g., hyperfine splitting), but intra-nuclear phenomena such as fission and fusion are considered part of high-energy physics.
Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light. Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.
Particle physics is the study of the elementary constituents of matter and energy and the interactions between them.[59] In addition, particle physicists design and develop the high energy accelerators,[60] detectors,[61] and computer programs[62] necessary for this research. The field is also called "high-energy physics" because many elementary particles do not occur naturally but are created only during high-energy collisions of other particles.[63]
Currently, the interactions of elementary particles and fields are described by the Standard Model.[64] The model accounts for the 12 known particles of matter (quarks and leptons) that interact via the strong, weak, and electromagnetic fundamental forces.[64] Dynamics are described in terms of matter particles exchanging gauge bosons (gluons, W and Z bosons, and photons, respectively).[65] The Standard Model also predicts a particle known as the Higgs boson.[64] In July 2012 CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson,[66] an integral part of a Higgs mechanism.
Nuclear physics is the field of physics that studies the constituents and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those in nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.
Astrophysics and astronomy are the application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the solar system, and related problems of cosmology. Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
The discovery by Karl Jansky in 1931 that radio signals were emitted by celestial bodies initiated the science of radio astronomy. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the earth's atmosphere make space-based observations necessary for infrared, ultraviolet, gamma-ray, and X-ray astronomy.
Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. In the early 20th century, Hubble's discovery that the universe is expanding, as shown by the Hubble diagram, prompted rival explanations known as the steady state universe and the Big Bang.
The Big Bang was confirmed by the success of Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the cosmological principle. Cosmologists have recently established the ΛCDM model of the evolution of the universe, which includes cosmic inflation, dark energy, and dark matter.
Numerous possibilities and discoveries are anticipated to emerge from new data from the Fermi Gamma-ray Space Telescope over the upcoming decade and vastly revise or clarify existing models of the universe.[67][68] In particular, the potential for a tremendous discovery surrounding dark matter is possible over the next several years.[69] Fermi will search for evidence that dark matter is composed of weakly interacting massive particles, complementing similar experiments with the Large Hadron Collider and other underground detectors.
IBEX is already yielding new astrophysical discoveries: "No one knows what is creating the ENA (energetic neutral atoms) ribbon" along the termination shock of the solar wind, "but everyone agrees that it means the textbook picture of the heliosphere — in which the solar system's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing 'galactic wind' of the interstellar medium in the shape of a comet — is wrong."[70]
Research in physics is continually progressing on a large number of fronts.
In condensed matter physics, an important unsolved theoretical problem is that of high-temperature superconductivity. Many condensed matter experiments are aiming to fabricate workable spintronics and quantum computers.
In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost among these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem, and the physics of massive neutrinos remains an area of active theoretical and experimental research. Particle accelerators have begun probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the Higgs boson and supersymmetric particles.[71]
Theoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet been decisively resolved. The current leading candidates are M-theory, superstring theory and loop quantum gravity.
Many astronomical and cosmological phenomena have yet to be satisfactorily explained, including the existence of ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe and the anomalous rotation rates of galaxies.
Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena involving complexity,[72] chaos,[73] or turbulence[74] are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics remain unsolved; examples include the formation of sandpiles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections.[75]
These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. Complex physics has become part of increasingly interdisciplinary research, as exemplified by the study of turbulence in aerodynamics and the observation of pattern formation in biological systems. In 1932, Horace Lamb said:[76]
I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.
—Horace Lamb, Annual Reviews in Fluid Mechanics
| Physics portal | |
| Cosmology portal |
|
|
|
mathematical physics — that is, the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories.
Physics is the study of your world and the world and universe around you.
| This article's use of external links may not follow Wikipedia's policies or guidelines. Please improve this article by removing excessive or inappropriate external links, and converting useful links where appropriate into footnote references. (July 2015) |
| Look up physics in Wiktionary, the free dictionary. |
| Wikibooks has a book on the topic of: Physics |
| Wikibooks has a book on the topic of: Physics Study Guide |
| Wikibooks has a book on the topic of: FHSST Physics |
| Wikisource has original works on the topic: Physics |
| Wikiversity has learning materials about Category:Physics |
General
Organizations
|
||||||||||
|
||||||||||||||||||||||
|
||||||
|
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
| リンク元 | 「物理」「物理学」 |
| 拡張検索 | 「biophysics」「psychophysics」 |