끌개장 이론(Attractor Field Theory)

                 끌개장 이론(Attractor Field Theory) 

  마음 속에 떠오르거나 상상한 것을 책이나 현실에서 발견하는 경우가 더 많는 것 같다. 주관적이고 직관적인 성향이 강하고 뇌의 구조상으로 우측과 앞쪽이 발달한 것으로 보인다. 세상을 자기중심적으로 사는, 제멋대로 사는 부류에 속한다. 끌개장이론이라는 것은 유유상종이라는 말을 양자역학이나 카오스이론를 연구하는 학자들이 이론화한 것이라는 생각이 든다. 많은 현상을 설명해주는 포괄적인 이론들 중 하나라고 생각된다.( 생각하는 것이 아닌 생각된다..) 

  간단히, 내가 끌개장을 생각하기 시작하자 그와 관련된 아이디어들이 줄줄이 흘러 나오는 것도 우주에 존재하는 공명의 원리를 설명하는 끌개장이론이 맞아들어가는 경우라 할 수 있을 것이다.  육상에서  과거에는 "깰 수 없는 기록"이 어느 한 선수가 기록을 깨면 그 다음에 많은 선수들이 기록을 깨기시작한다.   육상계라는 한 장(field)에서 끌개장이 형성되면서 에너지레벨이 높아지고 선수들의 신념과 운동능력이 급상승을 하는 것이다.   

  일본 한 섬에서 원숭이 한 녀석이 고구마를 씻어 먹기 시작하자 그 것을 옆에 녀석이 모방하여 그 섬 전체 원숭이들이 고구마를 씻어 먹는 것은 그 섬에 하나의 끌개장이 형성되었기 때문이다.  더 나아가 지리적으로  떨어져있는 근처 섬의 원숭이들도 끌개장 안에 들어가면서 고구마를 씻어 먹는 것이 관찰되었다고 한다. 지리적으로 떨어져 있어도 하나의 끌개장에 들어가면 자기도 모르는 집단최면에 걸리는 것이다. 집단무의식을 공유하여 텔레파시가 이루어지고 그 장안의 개체들의 의식속에 그런 아이디어가 공유된다. 끌개장의 범위는 다양하다. 두 사람 사이, 마을, 국가, 지구전체, 태양계 전체, 우주에 이르기 까지 각 장에서 개체들은 하나의 큰 개체를 이루며 한몸처럼 공명하는 것이다.   

 나의 상상과 관찰에 의하면 지구인 대부분이  세 끼 식사를 하는 것, 이집트와 중남미 지역에 유사한 형태의 피라미드가 건설된 것 등은 끌개장에 의하여 아이디어들이 보편적으로 무선통신으로 공유된 것이라는 생각이다. 같은 주파수를 가진 파동은 공명한다. 사람과 사람의 인연, 사람과 사건의 인연은 서로 끌리는 장을 통해서 엮여지고 흩어진다. 그러니 끌리는 일을 하고 끌리는 사람과 어울리면 될 것이다. 생명은 자신의 영혼의 파동따라 흘러간다.  

 내가 끌리고 있는  아이디어 장은 친환경적이고 영적인 삶을 추구하는 장이다. 많은 사람들이 이 장에 끌리게 되면 세상이 좀더 깨끗하고 평화로울 것이라는 생각을 나도 모르게 하게 되고 그 생각에 따라 행동하게 되는 것이다. 그 생각과 행동이 나의 생각과 행동이라고 생각할 수도 없다. 인연에 따라 이루어지는 업일 것이다. 세상에 나의 것이라고 할만한 것은 없어보인다. '나의 것'이라고 임시적으로 가정하며 살아가는 것이다. 
사자성어로 흔히 사용하는 말 중에, 자동기상구[ 同氣相求 ] 마음이 맞는 사람끼리는 서로 찾아 친하게 모임. -출전 易經(역경),      유유상종,   유유상종의 근원은 알 수 없으나, 《주역(周易)》의 〈계사(繫辭)〉 상편에서 그 전거를 찾을 수 있다. 방이유취 물이군분 길흉생의(方以類聚 物以群分 吉凶生矣), 즉 "삼라만상은 그 성질이 유사한 것끼리 모이고, 만물은 무리를 지어 나뉘어 산다. 거기서 길흉이 생긴다" 하였다.  

 얼마전 전세계적으로 <Secret>이라는 영상물과 책이 인기를 모은 적이 있다. 그 책에 담긴 비밀을 한 마디로 말하면 위의 두 사자성어랄 할 수 있다.  위의 두 사자성어도 우주의 원리를 적었다고 하는 주역에서 유래하였다고 되어있다.  오래 전부터 신지학, 양자역학, 중국과 인도철학, 카발라 등 동서양의 신비주의 서적들을  읽으면서 우주의 원리에 관한 주장들을 살펴오고 있다.  그 가운데 가장 핵심적이고 공통적으로 주장되는 원리가 바로 유유상종의 법칙이다.  영어로는 The Law of Attractiond이다. 같은 것끼리 서로 어울린다는 것이다. 모든 민족들 사이에 떠도는 명언, 속담 들 가운데에서 이 원리를 담고 있는 말들이 가장 많아 보인다. 끼리끼리 뭉친다..

   "콩 심은데 콩 나고, 팥 심은데 팥 난다"도 자세히 보면 같은 원리를 말하는 속담이다. 최근 양자역학에서는 끌개장(attractor field) 개념이 이를 설명해준다. 유사한 파장을 가진 사물과 아이디어, 파동체는 서로 이끌려서 일을 도모한다는 것이다.  악의 파장을 품고 있는 자, 악행을 저지를 것이고, 선의 파장을 품고 있는 사람은 선행을 할 것이다. 우주의 수 많은 별 가운데 태양계에 함께 어울려 살 가능성도 매우 희박한 것인데, 같은 시대에 한반도 땅에서 대한민국 국민이 될 인연은 참으로 계산하기 힘든 인연의 끌개장이 작용한 결과이다.  

  하물며 한 가족이 될 인연은 너무도 귀중한 매력(attraction)이 작용한 결과이다. 무심코 만나게 되는 사람들과 사건들이 아무런 원인 없이 이루어지지 않는다.  수 많은 생에서 쌓아 온 영혼의 파장에 따라 공명하고 끌어들이고, 그 반대로 밀어내기도 하면서 삶이 이루어져 간다. 

   세계적인 성공학의 거장 나폴레옹 힐의 책을 집중하여 읽고 있는데,  그가 밝힌 성공원리 또한 the law of attraction이라 할 수 있다. 자신이 이루고자 하는 일에 대한 강한 신념을 가지고, 생각의 파장을 강하게 형성하면 그 일이 이루어 진다는 것이다.  신념을 지속적으로 유지하기 위해 언어의 힘을 사용하고, 꾸준한 자기충전이 필요한 것이다. 긍정적인 마음으로 긍정적인 삶을 살고, 자신이 원하는 것을 선명한 비전(vision)으로 가지고 최선을 다하면 원하는 것은 반드시 이루어진다.  포기하지 않고 될때까지 최선을 다하는 것이다. 생각대로 이루어진다. 같은 기는 서로 어우러지기 때문이다.

EFT

[ Emotional Freedom Techniques ]

요약

 미국의 게리 크레이그(Gary Craig)가 창안한 심리치료법으로 동양의 경락이론을 바탕으로 하고 있다. 부정적 감정은 신체에너지시스템(경락기능)이 혼란된 것이라고 전제하며, 특정 타점(경혈)을 두드림으로써 신체에너지시스템의 혼란을 해소해 치유하는 기법이다.

미국의 게리 크레이그(Gary Craig)가 창안한 심리치료법으로 동양의 경락이론을 바탕으로 하고 있다. 부정적 감정은 신체에너지시스템(경락기능)이 혼란된 것이라고 전제하며, 특정 타점(경혈)을 두드림으로써 신체에너지시스템의 혼란을 해소해 치유하는 기법이다.

EFT는 로저 칼라한(Roger Callahan)이 개발한 TFT(Thought Field Therapy)에서 변형된 것이다. TFT는 로저 칼라한이 물공포증 환자를 치료하다가 우연히 발견하였는데, 환자의 특정 경혈을 두드리자 물공포증이 치료된 경험을 토대로 개발된 것이다. 이후 TFT는 증상에 따라 특정 경혈을 두드리고 이를 통해 경락의 기운을 조절하여 정서적 문제를 해결하는 기법으로 발전하였다. 그러나 TFT는 절차가 복잡한 절차와 고가의 비용으로 널리 이용되지 않았는데 게리 크레이그가 이를 단순화시켜 EFT로 재정립함으로써 대중적으로 알려지게 되었다.

EFT에서는 기본적으로 부정적 감정의 원인은 신체에너지시스템의 혼란이라고 전제한다. 또한 부정적 감정은 육체적 증상까지 야기할 수 있으며, 부정적 사건이 누적되어 부정적 감정이 지속되면 부정적 신념 및 태도를 형성한다고 본다. 따라서 신체에너지시스템의 소통을 원활하게 하면 부정적 감정 뿐 아니라 육체적 증상까지 치료되며 신념과 태도도 바뀔 수 있다고 한다.

EFT를 시행하는 기본과정은 6단계로 나눌 수 있다.

1) 문제확인: 부정적인 감정의 원인이 되는 사건을 구체적으로 떠올린다. 그리고 그 사건을 떠올릴 때 일어나는 감정에 대한 SUD(주관적고통지수: 특정 감정의 강도를 본인이 주관적으로 측정하는 것으로 대개 0~10까지의 수치로 표현함)를 기록한다.

2) 준비작업: "나는 비록 __하지만 나 자신을 마음속 깊이 진심으로 받아들입니다."와 같은 수용확언과 함께 손의 날타점을 두드리거나 가슴의 압통점을 문지른다.(3회 정도 반복)

3) 연속두드리기: 연상어구(부정적인 감정을 잘 이끌어낼 수 있는 단어 또는 어구)를 반복해 말하며, 몸통의 7개 타점과 손의 5타점을 각 타점당 7회 정도 두드린다. 

4) 뇌조율과정: 부가적으로 뇌를 자극하여 EFT의 효과를 배가시키는 단계이다. 눈동자의 움직임으로 뇌를 활성화시키고 숫자를 통해 좌뇌를, 콧노래를 통해 우뇌를 자극한다. 이 때는 손등타점을 두드리면서 아홉가지 동작을 한다.

① 눈을 감는다.

② 눈을 뜬다.

③ 머리를 움직이지 않은 채 눈은 오른쪽 아래를 바라본다.

④ 머리를 움직이지 않은 채 눈은 왼쪽 아래를 바라본다.

⑤ 머리를 움직이지 않은 채 눈동자를 시계방향으로 크게 돌린다.

⑥ 머리를 움직이지 않은 채 눈동자를 시계반대방향으로 크게 돌린다.

⑦ 2초 정도 콧노래를 한다.

⑧ 1에서 5까지 숫자를 센다.

⑨ 다시 2초 정도 콧노래를 한다.

5) SUD 재측정: 1)번에서 느꼈던 부정적 감정에 대한 SUD를 다시 한 번 측정한다.

6) 추가조정작업: 1)번과 5)번의 SUD를 비교했을 때 수치가 떨어지지 않았다면 수용확언, 연상어구를 재조정하여 위 과정을 반복한다. 또는 부정적 감정과 관련된 다른 사건을 떠올려

 위의 기본과정을 반복한다. 

위의 6단계의 EFT 시행방법은 기본적인 과정이며 이를 단축시킨 과정도 있다. 또한 선택확언, 내적평화과정 등의 심화된 방법이 있으며 이는 EFT 전문 트레이너의 지도를 받으면 

 정확하고 효과적으로 진행이 가능하다.

• 번역 의뢰하기

[네이버 지식백과] EFT [Emotional Freedom Techniques] (두산백과)

영적 세계와 소통

지구에 사는 사람들 중에는 영적인 세계와 소통을 하는 사람들이 있다. 

http://welovebh.blog.me/221500879590

한가로운 삶

도서관에서 컴퓨터만 보다가 머리를 식히기 위해 

주변을 걸어본다. 

길가에 핀 민들레가 눈에 들어온다. 

생기 넘치는 노란 꽃이 마음을 기쁘게 한다.

자연과 꽃에 마음이 이끌리는 것은 

그 아름다움을 창조하는 힘, 

생명력 때문 일 것이다. 

문득 생각해본다. 

도서관 공부하는 일이 중요한 것인지, 

이렇게 한가롭게 꽃을 감상하는 것이 중요한 것인지?

   하얀 털에 씨앗을 달고,

바람 부는 날을 기다려,

멀리멀리 날아가,

바람이 보내준 곳에 

싫다 말 한 마디 않고,

조용히 뿌리를 내리고,

꽃을 피우는 민들레,

신의 섭리를 따르는 군!

도서관 옆 개울에는 물오리 한 쌍이 

한가로이 물고기를 잡기도 하고, 

따뜻한 햇살을 받으며 오간다. 

저들의 마음 속이 복잡할 지 모르지만 

내 눈엔 평화로워 보인다. 

 생계 걱정을 하며, 

이런 저런 분주한 마음으로 있는 나에게 

저들은 부러움의 대상이 된다.

번잡한 일과 욕망을 줄이고, 

배를 채우기 위한 기본 활동만 하며

한가로이 자연에 머무는 저들처럼 살고 싶네!

환상과 실재

  플라톤의 "동굴의 우화"는 이 주제를  시작하기에 안성맞춤인 듯하다. 우리가 실재라고 보고 있는 것은 실재의 그림자일 가능성이 높다. 무지의 동굴에 갖힌 인간은 허상을 실재라 믿고 산다. 플라톤은 동굴의 우화를 통해 동영상에서 처럼 잘 보여주고 있다.

오늘날에는 기기의 발달로 영화나 자료를 스마트 폰 같은 것으로 보니 이해가 빠르다. 사진은 그 사람의 실재가 아닌 그림자인데 우리는 실재로 착각한다. 영화나 드라마도 가상인데, 가끔 실재로 착각한다. 우리의 지구에서 삶도 한 편의 드라마처럼 사라진다. 이 모든 것 가운데 무엇이 실재이고 무엇이 환상인지 구분할 수 있는가? 현실이라고 믿는 것도 나중에 알고보면, 혹은 전체 차원에서 보면 허상이고 그림자인 것이 대부분이다. 우리의 육체적 모습과 물리적 삶은 영적인 여러 차원의 껍데기나 그림자이다. 그 영적 차원에도 에너지의 순도에 따라 다른 실재와 환상이 존재한다. 양파만 겹겹이 층을 이룬 생명체가 아니다. 플라톤은 이를 잘 보여준다.

아카식 레코드를 이해하면 우리가 지상에 창조하는 것은 영적 세계를 투사한 것에 지나지 않음을 알 수 있다. 감수성있고 열정적인 사람의 두뇌를 통해 아이디어(이데아)가 흘러나오고 같은 주파수를 가진 사람들이 동조하면서 세상에 일이 이루어진다. 기계의 발명이든, 피라미드의 건설이든, IT 산업의 발전이든  지구상에 떠도는 아이디어와 물질적 구축물들은 우주의 프로그램의 일부이며, 일정 시기가 지나면 드라마처럼 사라진다. 

 공상과학 소설의 원조라 여겨지고 있는 쥘 베른의 소설 <해저 2만리>는 150년 전에 쓰여진 것인데, 네모 선장이 노틸러스호라는 첨단 잠수함을 타고 세계의 해저를 누빈다. 쥘 베른의 정신이 우주 정보 창고에 있는 이 잠수함 아이디어에 닿은 것이다. 그는 아이디어를 나른 사람이다. 같은 주파수를 가진 것이다. 이 소설 속에 아틀란티스 대륙의 위치까지 대서양 어느 곳으로 언급하고 있는 데, 그가 관련 자료를 기록으로 알았거나 상상으로 우주 정보를 열어보았을 가능성이 높다.  그는 우주선을 소재로 한 소설을 쓰기도 하였다. 시간은 과거에서 현재, 미래로 흐르지 않는다. 우주에 통으로 존재한다. 시간과 공간은 없다. 사람들이 편의상 사용하는 망상적 개념이다. 의식은 과거 미래 상관없이 우주 공간을 누빌 수 있다.

  장자가 나비가 된 꿈을 꾸고, 나비인 자기가 이 세상 꿈을 꾼 것인지, 자기가 나비 꿈을 꾼 것인지 헷갈린다. 이 세상이 꿈 속인지 내가 밤에 꾼 꿈이 실재인지 구분이 쉽지 않다. 이 세상은 내가 꾸는 여러 꿈들 가운데 하나이다.

  몇 번 읽은 이 책에는 우리가 이곳에 있으면서 동시에 여러 곳에 존재할 수 있음을 설명하고 있다. 홍길동이 도술을 부리는 어릴 적 본 드라마가 생각난다. 배우 이승현이 홍길동으로 주연하는 데, 도술을 부려 여러 곳에 나타나서 선행을 한다. 우리는 우리가 모르는 사이에 여러 곳에 존재한다. 유체이탈이라는 것도 그 사례 중의 하나다. 즉, 내가 지금 이글을 쓰고 있지만 교6ㅅ6내 영혼의 일부, 혹은 다른 껍데기는 다른 차원이나 장소로 순식 간에 투사가 가능한다. 진동하는 것이다. 양자역학의 연구에서도 이 사실을 서서히 밝히고 있다. 무선통신으로 영화나 다른 데이터 파일이 날아가는데 인간의 뇌파나 영혼이 우주 공간으로 광자나 우리가 모르는 매질을 통해 시공간을 초월하여 진동하지 못한다는 것이 오히려 이상하다. 우리가 상상하는 생각은 우주의 그림을 보는 것이다. 즉, 내가 지나온 과거 아름다운 추억을 상상하는 것은 실재 우주에 기록된 비디오를 다시 꺼내 보는 것이다. 컴퓨터 파일에서 동영상 열어서 보는 것과 같다. 이 세상 사물은 우리 정신의 표현이고, 정신은 우주심(아카식 레코드)의 파일에 접속되는 것이다. 홀로그램 이론으로 생각해보면, 부분 속에 전체가 포함될 수 있으니, 우리 영혼의 일부나 세포 하나의 미세칩 속에(무선 인터넷을 타고 날아가는 파일처럼) 우리의 생각이 담겨 동시적으로 광자를 타고 우리가 생각하는 다른 시공간에 도달하는 것이 가능하지 않겠는가? 생각하는 순간 동조가 이루어진다. 우주와 자연에 대해 우리는 아직 모르는 것이 너무 많다.

  휴대폰으로 선이 연결되지 않았는 데 통화를 한다거나, 우주선을 띄운다거나, 무선으로 데이터를 주고 받는 다는 것은 불과 몇 십년 전만 하더라도 공상과학 소설의 소재였다. 1980년 대초에 V라는 외국 영화에 보면 팔찌에 오늘날 우리가 사용하는 것과 같은 무선통신기를 사용하며 외계인과 싸우는 장면이 나온다. 이 영화에서 대부분 지휘관들이 여자들이다.  앞으로 지구는 여자들이 더 힘차게 활동할 것이다. 실제로 그렇게 되고 있지 않는가? 남자와 수컷들의 생식기능이 저하되고 무력화되고 두뇌가 약화되고 있다. 지구에 흐르는 에너지 패턴이 바뀌고 있기 때문이다. 

주제에 다시 집중하자면, 환상과 실재는 구분이 없다. 극단적으로 말하면 실재하는 것은 없다. 잠시 에너지가 뭉쳐 형상을 그림자나 드라마처럼 보이다 사라지는 것들이다. 모두가 아침이슬과 같은 존재임을 인정해야 한다. 그러니 집착하고 영원할 것 처럼 매달리는 어리섞음을 버려야 한다. 자기가 모르는 것에 마음의 문을 닫는 무지의 습관을 벗어야 한다. 류시화와 이상무가 번역한 저 책 앞부분에 장님 코끼리 더듬기 일화가 생각난다. 인간은 실재나 실재의 허망함을 이해하기에는 근원적으로 무지할 수 밖에 없다. 이 모든 것이 또한 허튼 소리이고 스치는 바람과 같은 것이라네. 답은 바람 속에 흩날리네....

나노 기술과 내부우주

 이너 스페이스 1988년 용산 미군정보부대에 근무하던 겨울에 동료들과 본 영화..

데니스 퀘이드와 맥 라이언이 주연한 SF 영화 제목이다. 극소화비행실험에 비행사로 실험에 참가한 다크가 난 비행선이 재채기 콧물분자 크기로 축소되어 한 남자의 몸 안을 비행한다. 나노 기술을 상상한 흥미로운 영화이다. 미세한 우주선이 몸이라는 거대한 우주를 누빈다. 남자가 여자친구와 키스를 하는 순간 우주선은 여자의 입속으로 옮겨가서 여자 몸 속을 여행한다. 

 물리적 크기를 상대화하는 상상이 나노기술의 발달로 현실이 되어 가고 있다. 미세한 로봇이 인체 내부를 누비며 질병을 찾아내고 치료까지 해내는 일들이 조만간 현실이 것으로 보인다.

 아래 뉴스 참고...

‘스마트팩토리’·‘로봇 의사’…미래?직업?성큼!

출처 : KBS 뉴스 | 네이버 뉴스

‘스마트팩토리’·‘로봇 의사’…미래?직업?성큼!

4차 산업 혁명이 발 빠르게 진행되면서 영화 속에서만 봤던 '미래직업'도 우리 곁으로 성큼 다가오고 있습니다. 미래직업 체험관부터 전문인력 교육 현장까지, 이종완 기자가 취재했습니다. "선생님 장기 나옵니다. 보이죠

이 영화는 우주가 수 천의 차원으로 크기를 초월하여 상대적으로 존재할 수 있다는 것을 시사한다. 금강경에서 붓다가 "삼천대천세계 "를 수보리에게 언급하는 장면이 연상된다. 우리 몸 속에 우주 만한 또다른 세계가 존재할 수 있다. 수 십 편의 영화가 칩 하나에 들어가는 것 처럼... 우리의 영혼은 여러 편의 영화에 연속 출현하기도 하고, 심지어 겹치기 출현도 가능하다.

이 세상은 모두 꿈이고 환상이며 한 편의 드라마이다. 사물이나 세상은 보는 위치나 보는 도구에 따라 다르다. 현미경으로 보는 세포는 거대한 우주이고, 천체망원경으로 보는 은하계는 미세한 점들일 뿐이다. 아인슈타인이 장황하게 이론화한 상대성이론의 기본개념이다. 우주 속에는 삼천대천세계, 즉, 헤아릴 수 없는 우주가 중첩되어 있다. 시공을 의식으로 상대화하거나 절대화하는 것이 가능하다. 마음상태에 따라 매우 큰 것이 미세하게 보이기도 하고 인생이 찰나처럼 느껴지거나 한 시간이 한 평생처럼 지겨울 수 있다. 마음 밖에 물건이 없다. 공허한 것들이다.    
 *자연의학 번역가-김일용 

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광자(photon)에 관하여

*물리학에서 광자에 대한 논쟁도  많고, 빛과 관련된 것이라 아직도 정체가 제대로 파악되지 않은 듯하다. 그래서 이해도 안된다. 이해할 수 있는 만큼 시도해보고자 한다. 양자역학이 우주론과 연계될 수 밖에 없다는 것이 나의 육감이고, 연구결과도 비슷하게 진행되고 있는 것 같다.  양자에 대한 이해를 이 공간에 정리해보고자 한다. 과학적 이해와  영적인 감성이 있는 분들이 도와주시면 감사하겠다. 빛과 관련된 것이니 빛은 순식 간에 거의 동시에 우주 끝에 닿을 수 있다. 그런데 빛을 구성하는 미립자들은 빛의 속도보다 빠를 것이라는 것이 추정된다. 우리의 뇌파 같은 것도 양자와 같은 속성을 지닌 입자들에 의해 정보를 나르는 것으로 보인다. 이 미지의 세계를 논하려고 하니 모든 것이 미확정적인 언어로 묘사할 수 밖에 없다. 내가 무지해서 이기도 하고 양자가 야누스같고, 말그대로 빛입자라 전광석화처럼 움직이니 인간 두뇌로 쉽게 이해가  되지 않은 것 같기도 하다. 양자역학자들이 동양의 선(禪)에 관심을 가지게 된 것도 이런 때문이라고 들었다.

  *일단, 위키피디아에 있는 광자(photon)에 관한 설명을 번역하며 이해를 시도해볼까한다.

*출처-https://en.wikipedia.org/wiki/Photon

광자(photon)

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이글은 빛의  기본 입자로써 광자에 관한 것입다. 다른  용도로 광자를 이해하려면 ,  광자-모호함 없애기( Photon disambiguation)를 보기 바랍니다.

 광자는  빛이나 전자기력 전달물과 같은 전자기 방사를 포함한 전자기장의 양자인 기본 입자 중 하나이다. The photon has zero rest mass and always moves at the speed of light within a vacuum.

Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time as per Heisenberg's uncertainty principle. The photon's wave and quantum qualities are two observable aspects of a single phenomenon—they cannot be described by any mechanical model;^[2] a representation of this dual property of light that assumes certain points on the wavefront to be the seat of the energy is not possible. The quanta in a light wave are not spatially localized.

The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical wave model of light. The benefit of the photon model is that it accounts for the frequency dependence of light's energy, and explains the ability of matter and electromagnetic radiation to be in thermal equilibrium. The photon model accounts for anomalous observations, including the properties of black-body radiation, that others (notably Max Planck) had tried to explain using semiclassical models. In that model, light is described by Maxwell's equations, but material objects emit and absorb light in quantized amounts (i.e., they change energy only by certain particular discrete amounts). Although these semiclassical models contributed to the development of quantum mechanics, many further experiments^[3][4] beginning with the phenomenon of Compton scattering of single photons by electrons, validated Einstein's hypothesis that light itself is quantized.^[5] In December 1926, American physical chemist Gilbert N. Lewis coined the widely-adopted name "photon" for these particles in a letter to Nature.^[6][7][8] After Arthur H. Compton won the Nobel Prize in 1927 for his scattering studies,^[9] most scientists accepted that light quanta have an independent existence, and the term "photon" was accepted.

In the Standard Model of particle physics, photons and other elementary particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass, and spin, are determined by this gauge symmetry. The photon concept has led to momentous advances in experimental and theoretical physics, including lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, and for applications in optical imaging and optical communication such as quantum cryptography.

Contents

• 1Nomenclature
• 2Physical properties
  • 2.1Experimental checks on photon mass
• 3Historical development
• 4Einstein's light quantum
• 5Early objections
• 6Wave–particle duality and uncertainty principles
• 7Bose–Einstein model of a photon gas
• 8Stimulated and spontaneous emission
• 9Second quantization and high energy photon interactions
• 10The hadronic properties of the photon
• 11The photon as a gauge boson
• 12Contributions to the mass of a system
• 13Photons in matter
• 14Technological applications
• 15Recent research
• 16See also
• 17Notes
• 18References
• 19Further reading
• 20External links

Nomenclature[edit]

The word quanta (singular quantum, Latin for how much) was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1900, the German physicist Max Planck was studying black-body radiation, and specifically the Ultraviolet Catastrophe: he suggested that the experimental observations would be explained if the energy carried by electromagnetic waves could only be released in "packets" of energy. In his 1901 article ^[10] in Annalen der Physik he called these packets "energy elements". In 1905, Albert Einstein published a paper in which he proposed that many light-related phenomena—including black-body radiation and the photoelectric effect—would be better explained by modelling electromagnetic waves as consisting of spatially localized, discrete wave-packets.^[11] He called such a wave-packet the light quantum (German: das Lichtquant).^[a]

The name photon derives from the Greek word for light, φῶς (transliterated phôs). Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, who coined the term in a letter to Nature on December 18, 1926.^[6][12] In fact, the same name was used earlier but was never widely adopted before Lewis: in 1916 by the American physicist and psychologist Leonard T. Troland, in 1921 by the Irish physicist John Joly, in 1924 by the French physiologist René Wurmser (1890–1993), and in 1926 by the French physicist Frithiof Wolfers (1891–1971).^[8] The name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolfers's and Lewis's theories were contradicted by many experiments and never accepted, the new name was adopted very soon by most physicists after Compton used it.^[8][b]

In physics, a photon is usually denoted by the symbol γ (the Greek letter gamma). This symbol for the photon probably derives from gamma rays, which were discovered in 1900 by Paul Villard,^[14][15]named by Ernest Rutherford in 1903, and shown to be a form of electromagnetic radiation in 1914 by Rutherford and Edward Andrade.^[16] In chemistry and optical engineering, photons are usually symbolized by hν, which is the photon energy, where h is Planck constant and the Greek letter ν (nu) is the photon's frequency.^[17] Much less commonly, the photon can be symbolized by hf, where its frequency is denoted by f.

Physical properties[edit]

See also: Special relativity

The cone shows possible values of wave 4-vector of a photon. The "time" axis gives the angular frequency (rad⋅s⁻¹) and the "space" axis represents the angular wavenumber (rad⋅m⁻¹). Green and indigo represent left and right polarization

A photon is massless,^[c] has no electric charge,^[18][19] and is a stable particle. A photon has two possible polarization states.^[20] In the momentum representation of the photon, which is preferred in quantum field theory, a photon is described by its wave vector, which determines its wavelength λ and its direction of propagation. A photon's wave vector may not be zero and can be represented either as a spatial 3-vector or as a (relativistic) four-vector; in the latter case it belongs to the light cone (pictured). Different signs of the four-vector denote different circular polarizations, but in the 3-vector representation one should account for the polarization state separately; it actually is a spin quantum number. In both cases the space of possible wave vectors is three-dimensional.

The photon is the gauge boson for electromagnetism,^[21]:29–30 and therefore all other quantum numbers of the photon (such as lepton number, baryon number, and flavour quantum numbers) are zero.^[22] Also, the photon does not obey the Pauli exclusion principle,^[23]:1221 but instead obeys Bose–Einstein statistics.

Photons are emitted in many natural processes. For example, when a charge is accelerated it emits synchrotron radiation. During a molecular, atomic or nucleartransition to a lower energy level, photons of various energy will be emitted, ranging from radio waves to gamma rays. Photons can also be emitted when a particle and its corresponding antiparticle are annihilated (for example, electron–positron annihilation).^{[23]:572,1114,1172}

In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p. This derives from the following relativistic relation, with m = 0:^[24]

${\displaystyle E^{2}=p^{2}c^{2}+m^{2}c^{4}.}$

The energy and momentum of a photon depend only on its frequency (ν) or inversely, its wavelength (λ):

${\displaystyle E=\hbar \omega =h\nu ={\frac {hc}{\lambda }}}$

${\displaystyle {\boldsymbol {p}}=\hbar {\boldsymbol {k}},}$

where k is the wave vector (where the wave number k = |k| = 2π/λ), ω = 2πν is the angular frequency, and ħ = h/2π is the reduced Planck constant.^[25]

Since p points in the direction of the photon's propagation, the magnitude of the momentum is

${\displaystyle p=\hbar k={\frac {h\nu }{c}}={\frac {h}{\lambda }}.}$

The photon also carries a quantity called spin angular momentum that does not depend on its frequency.^[26] The magnitude of its spin is √2ħ and the component measured along its direction of motion, its helicity, must be ±ħ. These two possible helicities, called right-handed and left-handed, correspond to the two possible circular polarization states of the photon.^[27]

To illustrate the significance of these formulae, the annihilation of a particle with its antiparticle in free space must result in the creation of at least two photons for the following reason. In the center of momentum frame, the colliding antiparticles have no net momentum, whereas a single photon always has momentum (since, as we have seen, it is determined by the photon's frequency or wavelength, which cannot be zero). Hence, conservation of momentum (or equivalently, translational invariance) requires that at least two photons are created, with zero net momentum. (However, it is possible if the system interacts with another particle or field for the annihilation to produce one photon, as when a positron annihilates with a bound atomic electron, it is possible for only one photon to be emitted, as the nuclear Coulomb field breaks translational symmetry.)^[28]:64–65 The energy of the two photons, or, equivalently, their frequency, may be determined from conservation of four-momentum. Seen another way, the photon can be considered as its own antiparticle. The reverse process, pair production, is the dominant mechanism by which high-energy photons such as gamma rays lose energy while passing through matter.^[29] That process is the reverse of "annihilation to one photon" allowed in the electric field of an atomic nucleus.

The classical formulae for the energy and momentum of electromagnetic radiation can be re-expressed in terms of photon events. For example, the pressure of electromagnetic radiation on an object derives from the transfer of photon momentum per unit time and unit area to that object, since pressure is force per unit area and force is the change in momentum per unit time.^[30]

Each photon carries two distinct and independent forms of angular momentum of light. The spin angular momentum of light of a particular photon is always either +ħ or −ħ. The light orbital angular momentum of a particular photon can be any integer N, including zero.^[31]

Experimental checks on photon mass[edit]

Current commonly accepted physical theories imply or assume the photon to be strictly massless. If the photon is not a strictly massless particle, it would not move at the exact speed of light, c, in vacuum. Its speed would be lower and depend on its frequency. Relativity would be unaffected by this; the so-called speed of light, c, would then not be the actual speed at which light moves, but a constant of nature which is the upper bound on speed that any object could theoretically attain in spacetime.^[32] Thus, it would still be the speed of spacetime ripples (gravitational waves and gravitons), but it would not be the speed of photons.

If a photon did have non-zero mass, there would be other effects as well. Coulomb's law would be modified and the electromagnetic field would have an extra physical degree of freedom. These effects yield more sensitive experimental probes of the photon mass than the frequency dependence of the speed of light. If Coulomb's law is not exactly valid, then that would allow the presence of an electric field to exist within a hollow conductor when it is subjected to an external electric field. This thus allows one to test Coulomb's law to very high precision.^[33] A null result of such an experiment has set a limit of m ≲ 10⁻¹⁴ eV/c².^[34]

Sharper upper limits on the speed of light have been obtained in experiments designed to detect effects caused by the galactic vector potential. Although the galactic vector potential is very large because the galactic magnetic field exists on very great length scales, only the magnetic field would be observable if the photon is massless. In the case that the photon has mass, the mass term 1/2m²A_μA^μ would affect the galactic plasma. The fact that no such effects are seen implies an upper bound on the photon mass of m < 3×10⁻²⁷ eV/c².^[35] The galactic vector potential can also be probed directly by measuring the torque exerted on a magnetized ring.^[36] Such methods were used to obtain the sharper upper limit of 1.07×10⁻²⁷ eV/c² (the equivalent of 10⁻¹⁸ atomic mass units) given by the Particle Data Group.^[37]

These sharp limits from the non-observation of the effects caused by the galactic vector potential have been shown to be model-dependent.^[38] If the photon mass is generated via the Higgs mechanism then the upper limit of m ≲ 10⁻¹⁴ eV/c² from the test of Coulomb's law is valid.

Photons inside superconductors develop a nonzero effective rest mass; as a result, electromagnetic forces become short-range inside superconductors.^[39]

See also: Supernova/Acceleration Probe

Historical development[edit]

Main article: Light

Thomas Young's double-slit experiment in 1801 showed that light can act as a wave, helping to invalidate early particle theories of light.^[23]:964

In most theories up to the eighteenth century, light was pictured as being made up of particles. Since particle models cannot easily account for the refraction, diffraction and birefringence of light, wave theories of light were proposed by René Descartes (1637),^[40] Robert Hooke (1665),^[41] and Christiaan Huygens (1678);^[42]however, particle models remained dominant, chiefly due to the influence of Isaac Newton.^[43] In the early nineteenth century, Thomas Young and August Fresnelclearly demonstrated the interference and diffraction of light and by 1850 wave models were generally accepted.^[44] In 1865, James Clerk Maxwell's prediction^[45] that light was an electromagnetic wave—which was confirmed experimentally in 1888 by Heinrich Hertz's detection of radio waves^[46]—seemed to be the final blow to particle models of light.

In 1900, Maxwell's theoretical model of light as oscillating electric and magnetic fields seemed complete. However, several observations could not be explained by any wave model of electromagnetic radiation, leading to the idea that light-energy was packaged into quantadescribed by E=hν. Later experiments showed that these light-quanta also carry momentum and, thus, can be considered particles: the photon concept was born, leading to a deeper understanding of the electric and magnetic fields themselves.

The Maxwell wave theory, however, does not account for all properties of light. The Maxwell theory predicts that the energy of a light wave depends only on its intensity, not on its frequency; nevertheless, several independent types of experiments show that the energy imparted by light to atoms depends only on the light's frequency, not on its intensity. For example, some chemical reactions are provoked only by light of frequency higher than a certain threshold; light of frequency lower than the threshold, no matter how intense, does not initiate the reaction. Similarly, electrons can be ejected from a metal plate by shining light of sufficiently high frequency on it (the photoelectric effect); the energy of the ejected electron is related only to the light's frequency, not to its intensity.^[47][d]

At the same time, investigations of blackbody radiation carried out over four decades (1860–1900) by various researchers^[48] culminated in Max Planck's hypothesis^[10][49] that the energy of any system that absorbs or emits electromagnetic radiation of frequency ν is an integer multiple of an energy quantum E = hν. As shown by Albert Einstein,^[11][50] some form of energy quantization must be assumed to account for the thermal equilibrium observed between matter and electromagnetic radiation; for this explanation of the photoelectric effect, Einstein received the 1921 Nobel Prize in physics.^[51]

Since the Maxwell theory of light allows for all possible energies of electromagnetic radiation, most physicists assumed initially that the energy quantization resulted from some unknown constraint on the matter that absorbs or emits the radiation. In 1905, Einstein was the first to propose that energy quantization was a property of electromagnetic radiation itself.^[11] Although he accepted the validity of Maxwell's theory, Einstein pointed out that many anomalous experiments could be explained if the energy of a Maxwellian light wave were localized into point-like quanta that move independently of one another, even if the wave itself is spread continuously over space.^[11] In 1909^[50] and 1916,^[52]Einstein showed that, if Planck's law of black-body radiation is accepted, the energy quanta must also carry momentum p = h/λ, making them full-fledged particles. This photon momentum was observed experimentally^[53] by Arthur Compton, for which he received the Nobel Prize in 1927. The pivotal question was then: how to unify Maxwell's wave theory of light with its experimentally observed particle nature? The answer to this question occupied Albert Einstein for the rest of his life,^[54] and was solved in quantum electrodynamics and its successor, the Standard Model (see § Second quantization and § The photon as a gauge boson, below).

Einstein's light quantum[edit]

Unlike Planck, Einstein entertained the possibility that there might be actual physical quanta of light—what we now call photons. He noticed that a light quantum with energy proportional to its frequency would explain a number of troubling puzzles and paradoxes, including an unpublished law by Stokes, the ultraviolet catastrophe, and the photoelectric effect. Stokes's law said simply that the frequency of fluorescent light cannot be greater than the frequency of the light (usually ultraviolet) inducing it. Einstein eliminated the ultraviolet catastrophe by imagining a gas of photons behaving like a gas of electrons that he had previously considered. He was advised by a colleague to be careful how he wrote up this paper, in order to not challenge Planck, a powerful figure in physics, too directly, and indeed the warning was justified, as Planck never forgave him for writing it.^[55]

Early objections[edit]

Up to 1923, most physicists were reluctant to accept that light itself was quantized. Instead, they tried to explain photon behavior by quantizing only matter, as in the Bohr model of the hydrogen atom (shown here). Even though these semiclassical models were only a first approximation, they were accurate for simple systems and they led to quantum mechanics.

Einstein's 1905 predictions were verified experimentally in several ways in the first two decades of the 20th century, as recounted in Robert Millikan's Nobel lecture.^[56] However, before Compton's experiment^[53] showed that photons carried momentum proportional to their wave number (1922), most physicists were reluctant to believe that electromagnetic radiation itself might be particulate. (See, for example, the Nobel lectures of Wien,^[48] Planck^[49] and Millikan.^[56]) Instead, there was a widespread belief that energy quantization resulted from some unknown constraint on the matter that absorbed or emitted radiation. Attitudes changed over time. In part, the change can be traced to experiments such as Compton scattering, where it was much more difficult not to ascribe quantization to light itself to explain the observed results.^[57]

Even after Compton's experiment, Niels Bohr, Hendrik Kramers and John Slater made one last attempt to preserve the Maxwellian continuous electromagnetic field model of light, the so-called BKS model.^[58] To account for the data then available, two drastic hypotheses had to be made:

1. Energy and momentum are conserved only on the average in interactions between matter and radiation, but not in elementary processes such as absorption and emission. This allows one to reconcile the discontinuously changing energy of the atom (the jump between energy states) with the continuous release of energy as radiation.
2. Causality is abandoned. For example, spontaneous emissions are merely emissions stimulated by a "virtual" electromagnetic field.

However, refined Compton experiments showed that energy–momentum is conserved extraordinarily well in elementary processes; and also that the jolting of the electron and the generation of a new photon in Compton scattering obey causality to within 10 ps. Accordingly, Bohr and his co-workers gave their model "as honorable a funeral as possible".^[54] Nevertheless, the failures of the BKS model inspired Werner Heisenberg in his development of matrix mechanics.^[59]

A few physicists persisted^[60] in developing semiclassical models in which electromagnetic radiation is not quantized, but matter appears to obey the laws of quantum mechanics. Although the evidence from chemical and physical experiments for the existence of photons was overwhelming by the 1970s, this evidence could not be considered as absolutely definitive; since it relied on the interaction of light with matter, and a sufficiently complete theory of matter could in principle account for the evidence. Nevertheless, all semiclassical theories were refuted definitively in the 1970s and 1980s by photon-correlation experiments.^[e] Hence, Einstein's hypothesis that quantization is a property of light itself is considered to be proven.

Wave–particle duality and uncertainty principles[edit]

See also: Wave–particle duality, Squeezed coherent state, Uncertainty principle, and De Broglie–Bohm theory

Photons in a Mach–Zehnder interferometerexhibit wave-like interference and particle-like detection at single-photon detectors.

Photons, like all quantum objects, exhibit wave-like and particle-like properties. Their dual wave–particle nature can be difficult to visualize. The photon displays clearly wave-like phenomena such as diffraction and interference on the length scale of its wavelength. For example, a single photon passing through a double-slit experiment exhibits interference phenomena but only if no measure was made at the slit. A single photon passing through a double-slit experiment lands on the screen with a probability distribution given by its interference pattern determined by Maxwell's equations.^[61] However, experiments confirm that the photon is not a short pulse of electromagnetic radiation; it does not spread out as it propagates, nor does it divide when it encounters a beam splitter.^[62] Rather, the photon seems to be a point-like particle since it is absorbed or emitted as a whole by arbitrarily small systems, systems much smaller than its wavelength, such as an atomic nucleus (≈10⁻¹⁵ m across) or even the point-like electron. Nevertheless, the photon is not a point-like particle whose trajectory is shaped probabilistically by the electromagnetic field, as conceived by Einstein and others; that hypothesis was also refuted by the photon-correlation experiments cited above. According to our present understanding, the electromagnetic field itself is produced by photons, which in turn result from a local gauge symmetry and the laws of quantum field theory (see § Second quantization and § The photon as a gauge boson below).

Heisenberg's thought experiment for locating an electron (shown in blue) with a high-resolution gamma-ray microscope. The incoming gamma ray (shown in green) is scattered by the electron up into the microscope's aperture angle θ. The scattered gamma ray is shown in red. Classical opticsshows that the electron position can be resolved only up to an uncertainty Δx that depends on θ and the wavelength λ of the incoming light.

A key element of quantum mechanics is Heisenberg's uncertainty principle, which forbids the simultaneous measurement of the position and momentum of a particle along the same direction. Remarkably, the uncertainty principle for charged, material particles requires the quantization of light into photons, and even the frequency dependence of the photon's energy and momentum.

An elegant illustration of the uncertainty principle is Heisenberg's thought experiment for locating an electron with an ideal microscope.^[63] The position of the electron can be determined to within the resolving power of the microscope, which is given by a formula from classical optics

${\displaystyle \Delta x\sim {\frac {\lambda }{\sin \theta }}}$

where θ is the aperture angle of the microscope and λ is the wavelength of the light used to observe the electron. Thus, the position uncertainty ${\displaystyle \Delta x}$ can be made arbitrarily small by reducing the wavelength λ. Even if the momentum of the electron is initially known, the light impinging on the electron will give it a momentum "kick" ${\displaystyle \Delta p}$ of some unknown amount, rendering the momentum of the electron uncertain. If light were not quantized into photons, the uncertainty ${\displaystyle \Delta p}$ could be made arbitrarily small by reducing the light's intensity. In that case, since the wavelength and intensity of light can be varied independently, one could simultaneously determine the position and momentum to arbitrarily high accuracy, violating the uncertainty principle. By contrast, Einstein's formula for photon momentum preserves the uncertainty principle; since the photon is scattered anywhere within the aperture, the uncertainty of momentum transferred equals

${\displaystyle \Delta p\sim p_{\text{photon}}\sin \theta ={\frac {h}{\lambda }}\sin \theta }$

giving the product ${\displaystyle \Delta x\Delta p\,\sim \,h}$, which is Heisenberg's uncertainty principle. Thus, the entire world is quantized; both matter and fields must obey a consistent set of quantum laws, if either one is to be quantized.^[64]

The analogous uncertainty principle for photons forbids the simultaneous measurement of the number ${\displaystyle n}$ of photons (see Fock state and the Second quantizationsection below) in an electromagnetic wave and the phase ${\displaystyle \phi }$ of that wave

${\displaystyle \Delta n\Delta \phi >1}$

See coherent state and squeezed coherent state for more details.

Both photons and electrons create analogous interference patterns when passed through a double-slit experiment. For photons, this corresponds to the interference of a Maxwell light wave whereas, for material particles (electron), this corresponds to the interference of the Schrödinger wave equation. Although this similarity might suggest that Maxwell's equations describing the photon's electromagnetic wave are simply Schrödinger's equation for photons, most physicists do not agree.^[65][66] For one thing, they are mathematically different; most obviously, Schrödinger's one equation for the electron solves for a complex field, whereas Maxwell's four equations solve for real fields. More generally, the normal concept of a Schrödinger probability wave function cannot be applied to photons.^[67] As photons are massless, they cannot be localized without being destroyed; technically, photons cannot have a position eigenstate ${\displaystyle |\mathbf {r} \rangle }$, and, thus, the normal Heisenberg uncertainty principle ${\displaystyle \Delta x\Delta p>h/2}$ does not pertain to photons. A few substitute wave functions have been suggested for the photon,^{[68][69][70][71]} but they have not come into general use. Instead, physicists generally accept the second-quantized theory of photons described below, quantum electrodynamics, in which photons are quantized excitations of electromagnetic modes.

Another interpretation, that avoids duality, is the De Broglie–Bohm theory: known also as the pilot-wave model. In that theory, the photon is both, wave and particle.^[72] "This idea seems to me so natural and simple, to resolve the wave-particle dilemma in such a clear and ordinary way, that it is a great mystery to me that it was so generally ignored", J.S. Bell.^[73]

Bose–Einstein model of a photon gas[edit]

Main articles: Bose gas, Bose–Einstein statistics, Spin-statistics theorem, and Gas in a box

In 1924, Satyendra Nath Bose derived Planck's law of black-body radiation without using any electromagnetism, but rather by using a modification of coarse-grained counting of phase space.^[74] Einstein showed that this modification is equivalent to assuming that photons are rigorously identical and that it implied a "mysterious non-local interaction",^[75][76] now understood as the requirement for a symmetric quantum mechanical state. This work led to the concept of coherent states and the development of the laser. In the same papers, Einstein extended Bose's formalism to material particles (bosons) and predicted that they would condense into their lowest quantum state at low enough temperatures; this Bose–Einstein condensation was observed experimentally in 1995.^[77] It was later used by Lene Hau to slow, and then completely stop, light in 1999^[78] and 2001.^[79]

The modern view on this is that photons are, by virtue of their integer spin, bosons (as opposed to fermions with half-integer spin). By the spin-statistics theorem, all bosons obey Bose–Einstein statistics (whereas all fermions obey Fermi–Dirac statistics).^[80]

Stimulated and spontaneous emission[edit]

Main articles: Stimulated emission and Laser

Stimulated emission (in which photons "clone" themselves) was predicted by Einstein in his kinetic analysis, and led to the development of the laser. Einstein's derivation inspired further developments in the quantum treatment of light, which led to the statistical interpretation of quantum mechanics.

In 1916, Albert Einstein showed that Planck's radiation law could be derived from a semi-classical, statistical treatment of photons and atoms, which implies a link between the rates at which atoms emit and absorb photons. The condition follows from the assumption that functions of the emission and absorption of radiation by the atoms are independent of each other, and that thermal equilibrium is made by way of the radiation's interaction with the atoms. Consider a cavity in thermal equilibrium with all parts of itself and filled with electromagnetic radiation and that the atoms can emit and absorb that radiation. Thermal equilibrium requires that the energy density ${\displaystyle \rho (\nu )}$ of photons with frequency ${\displaystyle \nu }$ (which is proportional to their number density) is, on average, constant in time; hence, the rate at which photons of any particular frequency are emitted must equal the rate at which they absorb them.^[81]

Einstein began by postulating simple proportionality relations for the different reaction rates involved. In his model, the rate ${\displaystyle R_{ji}}$ for a system to absorb a photon of frequency ${\displaystyle \nu }$ and transition from a lower energy ${\displaystyle E_{j}}$ to a higher energy ${\displaystyle E_{i}}$ is proportional to the number ${\displaystyle N_{j}}$ of atoms with energy ${\displaystyle E_{j}}$ and to the energy density ${\displaystyle \rho (\nu )}$ of ambient photons of that frequency,

${\displaystyle R_{ji}=N_{j}B_{ji}\rho (\nu )\!}$

where ${\displaystyle B_{ji}}$ is the rate constant for absorption. For the reverse process, there are two possibilities: spontaneous emission of a photon, or the emission of a photon initiated by the interaction of the atom with a passing photon and the return of the atom to the lower-energy state. Following Einstein's approach, the corresponding rate ${\displaystyle R_{ij}}$ for the emission of photons of frequency ${\displaystyle \nu }$ and transition from a higher energy ${\displaystyle E_{i}}$ to a lower energy ${\displaystyle E_{j}}$ is

${\displaystyle R_{ij}=N_{i}A_{ij}+N_{i}B_{ij}\rho (\nu )\!}$

where ${\displaystyle A_{ij}}$ is the rate constant for emitting a photon spontaneously, and ${\displaystyle B_{ij}}$ is the rate constant for emissions in response to ambient photons (induced or stimulated emission). In thermodynamic equilibrium, the number of atoms in state i and those in state j must, on average, be constant; hence, the rates ${\displaystyle R_{ji}}$ and ${\displaystyle R_{ij}}$ must be equal. Also, by arguments analogous to the derivation of Boltzmann statistics, the ratio of ${\displaystyle N_{i}}$ and ${\displaystyle N_{j}}$ is ${\displaystyle g_{i}/g_{j}\exp {(E_{j}-E_{i})/(kT)},}$ where ${\displaystyle g_{i,j}}$ are the degeneracy of the state i and that of j, respectively, ${\displaystyle E_{i,j}}$ their energies, k the Boltzmann constant and T the system's temperature. From this, it is readily derived that ${\displaystyle g_{i}B_{ij}=g_{j}B_{ji}}$ and

${\displaystyle A_{ij}={\frac {8\pi h\nu ^{3}}{c^{3}}}B_{ij}.}$

The A and Bs are collectively known as the Einstein coefficients.^[82]

Einstein could not fully justify his rate equations, but claimed that it should be possible to calculate the coefficients ${\displaystyle A_{ij}}$, ${\displaystyle B_{ji}}$ and ${\displaystyle B_{ij}}$ once physicists had obtained "mechanics and electrodynamics modified to accommodate the quantum hypothesis".^[83] In fact, in 1926, Paul Dirac derived the ${\displaystyle B_{ij}}$ rate constants by using a semiclassical approach,^[84] and, in 1927, succeeded in deriving all the rate constants from first principles within the framework of quantum theory.^[85][86] Dirac's work was the foundation of quantum electrodynamics, i.e., the quantization of the electromagnetic field itself. Dirac's approach is also called second quantization or quantum field theory;^[87][88][89] earlier quantum mechanical treatments only treat material particles as quantum mechanical, not the electromagnetic field.

Einstein was troubled by the fact that his theory seemed incomplete, since it did not determine the direction of a spontaneously emitted photon. A probabilistic nature of light-particle motion was first considered by Newton in his treatment of birefringence and, more generally, of the splitting of light beams at interfaces into a transmitted beam and a reflected beam. Newton hypothesized that hidden variables in the light particle determined which of the two paths a single photon would take.^[43] Similarly, Einstein hoped for a more complete theory that would leave nothing to chance, beginning his separation^[54] from quantum mechanics. Ironically, Max Born's probabilistic interpretation of the wave function^[90][91] was inspired by Einstein's later work searching for a more complete theory.^[92]

Second quantization and high energy photon interactions[edit]

Main article: Quantum field theory

Different electromagnetic modes (such as those depicted here) can be treated as independent simple harmonic oscillators. A photon corresponds to a unit of energy E=hν in its electromagnetic mode.

In 1910, Peter Debye derived Planck's law of black-body radiation from a relatively simple assumption.^[93] He correctly decomposed the electromagnetic field in a cavity into its Fourier modes, and assumed that the energy in any mode was an integer multiple of ${\displaystyle h\nu }$, where ${\displaystyle \nu }$ is the frequency of the electromagnetic mode. Planck's law of black-body radiation follows immediately as a geometric sum. However, Debye's approach failed to give the correct formula for the energy fluctuations of blackbody radiation, which were derived by Einstein in 1909.^[50]

In 1925, Born, Heisenberg and Jordan reinterpreted Debye's concept in a key way.^[94] As may be shown classically, the Fourier modes of the electromagnetic field—a complete set of electromagnetic plane waves indexed by their wave vector k and polarization state—are equivalent to a set of uncoupled simple harmonic oscillators. Treated quantum mechanically, the energy levels of such oscillators are known to be ${\displaystyle E=nh\nu }$, where ${\displaystyle \nu }$ is the oscillator frequency. The key new step was to identify an electromagnetic mode with energy ${\displaystyle E=nh\nu }$ as a state with ${\displaystyle n}$ photons, each of energy ${\displaystyle h\nu }$. This approach gives the correct energy fluctuation formula.

In quantum field theory, the probability of an event is computed by summing the probability amplitude (a complex number) for all possible ways in which the event can occur, as in the Feynman diagramshown here; the probability equals the square of the modulus of the total amplitude.

Dirac took this one step further.^[85][86] He treated the interaction between a charge and an electromagnetic field as a small perturbation that induces transitions in the photon states, changing the numbers of photons in the modes, while conserving energy and momentum overall. Dirac was able to derive Einstein's ${\displaystyle A_{ij}}$ and ${\displaystyle B_{ij}}$ coefficients from first principles, and showed that the Bose–Einstein statistics of photons is a natural consequence of quantizing the electromagnetic field correctly (Bose's reasoning went in the opposite direction; he derived Planck's law of black-body radiation by assuming B–E statistics). In Dirac's time, it was not yet known that all bosons, including photons, must obey Bose–Einstein statistics.

Dirac's second-order perturbation theory can involve virtual photons, transient intermediate states of the electromagnetic field; the static electric and magneticinteractions are mediated by such virtual photons. In such quantum field theories, the probability amplitude of observable events is calculated by summing over allpossible intermediate steps, even ones that are unphysical; hence, virtual photons are not constrained to satisfy ${\displaystyle E=pc}$, and may have extra polarization states; depending on the gauge used, virtual photons may have three or four polarization states, instead of the two states of real photons. Although these transient virtual photons can never be observed, they contribute measurably to the probabilities of observable events. Indeed, such second-order and higher-order perturbation calculations can give apparently infinite contributions to the sum. Such unphysical results are corrected for using the technique of renormalization.

Other virtual particles may contribute to the summation as well; for example, two photons may interact indirectly through virtual electron–positron pairs.^[95] In fact, such photon–photon scattering (see two-photon physics), as well as electron–photon scattering, is meant to be one of the modes of operations of the planned particle accelerator, the International Linear Collider.^[96]

In modern physics notation, the quantum state of the electromagnetic field is written as a Fock state, a tensor product of the states for each electromagnetic mode

${\displaystyle |n_{k_{0}}\rangle \otimes |n_{k_{1}}\rangle \otimes \dots \otimes |n_{k_{n}}\rangle \dots }$

where ${\displaystyle |n_{k_{i}}\rangle }$ represents the state in which ${\displaystyle \,n_{k_{i}}}$ photons are in the mode ${\displaystyle k_{i}}$. In this notation, the creation of a new photon in mode ${\displaystyle k_{i}}$ (e.g., emitted from an atomic transition) is written as ${\displaystyle |n_{k_{i}}\rangle \rightarrow |n_{k_{i}}+1\rangle }$. This notation merely expresses the concept of Born, Heisenberg and Jordan described above, and does not add any physics.

The hadronic properties of the photon[edit]

Measurements of the interaction between energetic photons and hadrons show that the interaction is much more intense than expected by the interaction of merely photons with the hadron's electric charge. Furthermore, the interaction of energetic photons with protons is similar to the interaction of photons with neutrons^[97] in spite of the fact that the electric charge structures of protons and neutrons are substantially different. A theory called Vector Meson Dominance (VMD) was developed to explain this effect. According to VMD, the photon is a superposition of the pure electromagnetic photon which interacts only with electric charges and vector mesons.^[98] However, if experimentally probed at very short distances, the intrinsic structure of the photon is recognized as a flux of quark and gluon components, quasi-free according to asymptotic freedom in QCD and described by the photon structure function.^[99][100] A comprehensive comparison of data with theoretical predictions was presented in a review in 2000.^[101]

The photon as a gauge boson[edit]

Main article: Gauge theory

The electromagnetic field can be understood as a gauge field, i.e., as a field that results from requiring that a gauge symmetry holds independently at every position in spacetime.^[102] For the electromagnetic field, this gauge symmetry is the Abelian U(1) symmetry of complex numbers of absolute value 1, which reflects the ability to vary the phase of a complex field without affecting observables or real valued functions made from it, such as the energy or the Lagrangian.

The quanta of an Abelian gauge field must be massless, uncharged bosons, as long as the symmetry is not broken; hence, the photon is predicted to be massless, and to have zero electric charge and integer spin. The particular form of the electromagnetic interaction specifies that the photon must have spin ±1; thus, its helicity must be ${\displaystyle \pm \hbar }$. These two spin components correspond to the classical concepts of right-handed and left-handed circularly polarized light. However, the transient virtual photons of quantum electrodynamics may also adopt unphysical polarization states.^[102]

In the prevailing Standard Model of physics, the photon is one of four gauge bosons in the electroweak interaction; the other three are denoted W⁺, W⁻ and Z⁰ and are responsible for the weak interaction. Unlike the photon, these gauge bosons have mass, owing to a mechanism that breaks their SU(2) gauge symmetry. The unification of the photon with W and Z gauge bosons in the electroweak interaction was accomplished by Sheldon Glashow, Abdus Salam and Steven Weinberg, for which they were awarded the 1979 Nobel Prize in physics.^{[103][104][105]} Physicists continue to hypothesize grand unified theories that connect these four gauge bosons with the eight gluon gauge bosons of quantum chromodynamics; however, key predictions of these theories, such as proton decay, have not been observed experimentally.^[106]

Contributions to the mass of a system[edit]

See also: Mass in special relativity and Mass in general relativity

The energy of a system that emits a photon is decreased by the energy ${\displaystyle E}$ of the photon as measured in the rest frame of the emitting system, which may result in a reduction in mass in the amount ${\displaystyle {E}/{c^{2}}}$. Similarly, the mass of a system that absorbs a photon is increased by a corresponding amount. As an application, the energy balance of nuclear reactions involving photons is commonly written in terms of the masses of the nuclei involved, and terms of the form ${\displaystyle {E}/{c^{2}}}$ for the gamma photons (and for other relevant energies, such as the recoil energy of nuclei).^[107]

This concept is applied in key predictions of quantum electrodynamics (QED, see above). In that theory, the mass of electrons (or, more generally, leptons) is modified by including the mass contributions of virtual photons, in a technique known as renormalization. Such "radiative corrections" contribute to a number of predictions of QED, such as the magnetic dipole moment of leptons, the Lamb shift, and the hyperfine structure of bound lepton pairs, such as muonium and positronium.^[108]

Since photons contribute to the stress–energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound–Rebka experiment. However, these effects are not specific to photons; exactly the same effects would be predicted for classical electromagnetic waves.^[109]

Photons in matter[edit]

See also: Group velocity and Photochemistry

Light that travels through transparent matter does so at a lower speed than c, the speed of light in a vacuum. For example, photons engage in so many collisions on the way from the core of the sun that radiant energy can take about a million years to reach the surface;^[110] however, once in open space, a photon takes only 8.3 minutes to reach Earth. The factor by which the speed is decreased is called the refractive index of the material. In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and that new light interfering with the original light wave to form a delayed wave. In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitations of the matter to produce quasi-particles known as polariton (other quasi-particles are phonons and excitons); this polariton has a nonzero effective mass, which means that it cannot travel at c. Light of different frequencies may travel through matter at different speeds; this is called dispersion (not to be confused with scattering). In some cases, it can result in extremely slow speeds of light in matter. The effects of photon interactions with other quasi-particles may be observed directly in Raman scattering and Brillouin scattering.^[111]

Photons can also be absorbed by nuclei, atoms or molecules, provoking transitions between their energy levels. A classic example is the molecular transition of retinal (C₂₀H₂₈O), which is responsible for vision, as discovered in 1958 by Nobel laureate biochemist George Wald and co-workers. The absorption provokes a cis-trans isomerization that, in combination with other such transitions, is transduced into nerve impulses. The absorption of photons can even break chemical bonds, as in the photodissociation of chlorine; this is the subject of photochemistry.^[112][113]

Technological applications[edit]

Photons have many applications in technology. These examples are chosen to illustrate applications of photons per se, rather than general optical devices such as lenses, etc. that could operate under a classical theory of light. The laser is an extremely important application and is discussed above under stimulated emission.

Individual photons can be detected by several methods. The classic photomultiplier tube exploits the photoelectric effect: a photon of sufficient energy strikes a metal plate and knocks free an electron, initiating an ever-amplifying avalanche of electrons. Semiconductor charge-coupled device chips use a similar effect: an incident photon generates a charge on a microscopic capacitor that can be detected. Other detectors such as Geiger counters use the ability of photons to ionize gas molecules contained in the device, causing a detectable change of conductivity of the gas.^[114]

Planck's energy formula ${\displaystyle E=h\nu }$ is often used by engineers and chemists in design, both to compute the change in energy resulting from a photon absorption and to determine the frequency of the light emitted from a given photon emission. For example, the emission spectrum of a gas-discharge lamp can be altered by filling it with (mixtures of) gases with different electronic energy levelconfigurations.

Under some conditions, an energy transition can be excited by "two" photons that individually would be insufficient. This allows for higher resolution microscopy, because the sample absorbs energy only in the spectrum where two beams of different colors overlap significantly, which can be made much smaller than the excitation volume of a single beam (see two-photon excitation microscopy). Moreover, these photons cause less damage to the sample, since they are of lower energy.^[115]

In some cases, two energy transitions can be coupled so that, as one system absorbs a photon, another nearby system "steals" its energy and re-emits a photon of a different frequency. This is the basis of fluorescence resonance energy transfer, a technique that is used in molecular biology to study the interaction of suitable proteins.^[116]

Several different kinds of hardware random number generators involve the detection of single photons. In one example, for each bit in the random sequence that is to be produced, a photon is sent to a beam-splitter. In such a situation, there are two possible outcomes of equal probability. The actual outcome is used to determine whether the next bit in the sequence is "0" or "1".^[117][118]

Recent research[edit]

See also: Quantum optics

Much research has been devoted to applications of photons in the field of quantum optics. Photons seem well-suited to be elements of an extremely fast quantum computer, and the quantum entanglement of photons is a focus of research. Nonlinear optical processes are another active research area, with topics such as two-photon absorption, self-phase modulation, modulational instabilityand optical parametric oscillators. However, such processes generally do not require the assumption of photons per se; they may often be modeled by treating atoms as nonlinear oscillators. The nonlinear process of spontaneous parametric down conversion is often used to produce single-photon states. Finally, photons are essential in some aspects of optical communication, especially for quantum cryptography.^[f]

Two-photon physics studies interactions between photons, which are rare. In 2018, MIT researchers announced the discovery of bound photon triplets, which may involve polaritons.^[119][120]

See also[edit]

• Physics portal

• Advanced Photon Source at Argonne National Laboratory
• Ballistic photon
• Dirac equation
• Doppler effect
• Electromagnetic radiation
• EPR paradox
• High energy X-ray imaging technology
• Laser
• Light
• Luminiferous aether
• Medipix
• Phonon
• Photography
• Photon counting
• Photon energy
• Photon epoch
• Photon polarization
• Photonic molecule
• Photonics
• Single-photon source
• Static forces and virtual-particle exchange
• Two-photon physics

Notes[edit]

1. ^ Although the 1967 Elsevier translation of Planck's Nobel Lecture interprets Planck's Lichtquant as "photon", the more literal 1922 translation by Hans Thacher Clarke and Ludwik Silberstein Planck, Max (1922). The Origin and Development of the Quantum Theory. Clarendon Press. (here) uses "light-quantum". No evidence is known that Planck himself used the term "photon" by 1926 (see also).
2. ^ Isaac Asimov credits Arthur Compton with defining quanta of energy as photons in 1923.^[13]
3. ^ The mass of the photon is believed to be exactly zero. Some sources also refer to the relativistic mass, which is just the energy scaled to units of mass. For a photon with wavelength λ or energy E, this is h/λc or E/c². This usage for the term "mass" is no longer common in scientific literature. Further info: What is the mass of a photon?
4. ^ The phrase "no matter how intense" refers to intensities below approximately 10¹³ W/cm² at which point perturbation theory begins to break down. In contrast, in the intense regime, which for visible light is above approximately 10¹⁴ W/cm², the classical wave description correctly predicts the energy acquired by electrons, called ponderomotive energy. (See also: Boreham et al. (1996). "Photon density and the correspondence principle of electromagnetic interaction".) By comparison, sunlight is only about 0.1 W/cm².
5. ^ These experiments produce results that cannot be explained by any classical theory of light, since they involve anticorrelations that result from the quantum measurement process. In 1974, the first such experiment was carried out by Clauser, who reported a violation of a classical Cauchy–Schwarz inequality. In 1977, Kimble et al. demonstrated an analogous anti-bunching effect of photons interacting with a beam splitter; this approach was simplified and sources of error eliminated in the photon-anticorrelation experiment of Grangier et al. (1986). This work is reviewed and simplified further in Thorn et al. (2004). (These references are listed below.)
6. ^ Introductory-level material on the various sub-fields of quantum optics can be found in Fox, M. (2006). Quantum Optics: An Introduction. Oxford University Press. ISBN 978-0-19-856673-1.

References[edit]

1. ^ Jump up to:^{a b c d e f} Amsler, C.; et al. (Particle Data Group) (2008). "Review of Particle Physics: Gauge and Higgs bosons" (PDF). Physics Letters B. 667 (1): 1. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018.
2. ^ Joos, George (1951). Theoretical Physics. London and Glasgow: Blackie and Son Limited. p. 679.
3. ^ Kimble, H.J.; Dagenais, M.; Mandel, L. (1977). "Photon Anti-bunching in Resonance Fluorescence" (PDF). Physical Review Letters. 39 (11): 691–695. Bibcode:1977PhRvL..39..691K. doi:10.1103/PhysRevLett.39.691.
4. ^ Grangier, P.; Roger, G.; Aspect, A. (1986). "Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences". Europhysics Letters. 1 (4): 173–179. Bibcode:1986EL......1..173G. CiteSeerX 10.1.1.178.4356. doi:10.1209/0295-5075/1/4/004.
5. ^ Compton, Arthur H. (1965) [12 Dec 1927]. "X-rays as a branch of optics". From Nobel Lectures, Physics 1922-1941 (PDF). Amsterdam: Elsevier Publishing Company.
6. ^ Jump up to:^a b "December 18, 1926: Gilbert Lewis coins "photon" in letter to Nature". www.aps.org. Retrieved 2019-03-09.
7. ^ "Gilbert N. Lewis". Atomic Heritage Foundation. Retrieved 2019-03-09.
8. ^ Jump up to:^a b c Kragh, Helge (2014). "Photon: New light on an old name". arXiv:1401.0293 [physics.hist-ph].
9. ^ "Arthur H. Compton – Facts". Nobelprize.org. Nobel Media AB 2014. Web. 4 Mar 2017. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1927/compton-facts.html>
10. ^ Jump up to:^a b Planck, M. (1901). "Über das Gesetz der Energieverteilung im Normalspectrum". Annalen der Physik (in German). 4 (3): 553–563. Bibcode:1901AnP...309..553P. doi:10.1002/andp.19013090310.English translation
11. ^ Jump up to:^a b c d Einstein, A. (1905). "Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt" (PDF). Annalen der Physik (in German). 17 (6): 132–148. Bibcode:1905AnP...322..132E. doi:10.1002/andp.19053220607.. An English translation is available from Wikisource.
12. ^ "Discordances entre l'expérience et la théorie électromagnétique du rayonnement." In Électrons et Photons. Rapports et Discussions de Cinquième Conseil de Physique, edited by Institut International de Physique Solvay. Paris: Gauthier-Villars, pp. 55–85.
13. ^ Asimov, Isaac (1983). The Neutrino: Ghost Particle of the Atom. Garden City, NY: Avon Books. ISBN 978-0-380-00483-6.and Asimov, Isaac (1971). The Universe: From Flat Earth to Quasar. New York: Walker. ISBN 978-0-8027-0316-3. LCCN 66022515.
14. ^ Villard, P. (1900). "Sur la réflexion et la réfraction des rayons cathodiques et des rayons déviables du radium". Comptes Rendus des Séances de l'Académie des Sciences (in French). 130: 1010–1012.
15. ^ Villard, P. (1900). "Sur le rayonnement du radium". Comptes Rendus des Séances de l'Académie des Sciences (in French). 130: 1178–1179.
16. ^ Rutherford, E.; Andrade, E.N.C. (1914). "The Wavelength of the Soft Gamma Rays from Radium B". Philosophical Magazine. 27(161): 854–868. doi:10.1080/14786440508635156.
17. ^ Andrew Liddle (2015). An Introduction to Modern Cosmology. John Wiley & Sons. p. 16. ISBN 978-1-118-69025-3.
18. ^ Frisch, David H.; Thorndike, Alan M. (1964). Elementary Particles. Princeton, NJ: David Van Nostrand. p. 22.
19. ^ Kobychev, V.V.; Popov, S.B. (2005). "Constraints on the photon charge from observations of extragalactic sources". Astronomy Letters. 31 (3): 147–151. arXiv:hep-ph/0411398. Bibcode:2005AstL...31..147K. doi:10.1134/1.1883345.
20. ^ Matthew D. Schwartz (2014). Quantum Field Theory and the Standard Model. Cambridge University Press. p. 66. ISBN 978-1-107-03473-0.
21. ^ Role as gauge boson and polarization section 5.1 inAitchison, I.J.R.; Hey, A.J.G. (1993). Gauge Theories in Particle Physics. IOP Publishing. ISBN 978-0-85274-328-7.
22. ^ See p.31 inAmsler, C.; et al. (2008). "Review of Particle Physics" (PDF). Physics Letters B. 667: 1–1340. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018.
23. ^ Jump up to:^a b c Halliday, David; Resnick, Robert; Walker, Jerl (2005), Fundamental of Physics (7th ed.), John Wiley and Sons, Inc., ISBN 978-0-471-23231-5
24. ^ See section 1.6 in Alonso & Finn 1968, Section 1.6
25. ^ Davison E. Soper, Electromagnetic radiation is made of photons, Institute of Theoretical Science, University of Oregon
26. ^ This property was experimentally verified by Raman and Bhagavantam in 1931: Raman, C.V.; Bhagavantam, S. (1931). "Experimental proof of the spin of the photon" (PDF). Indian Journal of Physics. 6 (3244): 353. Bibcode:1932Natur.129...22R. doi:10.1038/129022a0. hdl:10821/664.
27. ^ Burgess, C.; Moore, G. (2007). "1.3.3.2". The Standard Model. A Primer. Cambridge University Press. ISBN 978-0-521-86036-9.
28. ^ Griffiths, David J. (2008), Introduction to Elementary Particles(2nd revised ed.), WILEY-VCH, ISBN 978-3-527-40601-2
29. ^ Alonso & Finn 1968, Section 9.3
30. ^ E.g., Appendix XXXII in Born, Max; Blin-Stoyle, Roger John; Radcliffe, J.M. (1989). Atomic Physics. Courier Corporation. ISBN 978-0-486-65984-8.
31. ^ Alan E. Willner. "Twisted Light Could Dramatically Boost Data Rates: Orbital angular momentum could take optical and radio communication to new heights". 2016.
32. ^ Mermin, David (February 1984). "Relativity without light". American Journal of Physics. 52 (2): 119–124. Bibcode:1984AmJPh..52..119M. doi:10.1119/1.13917.
33. ^ Plimpton, S.; Lawton, W. (1936). "A Very Accurate Test of Coulomb's Law of Force Between Charges". Physical Review. 50(11): 1066. Bibcode:1936PhRv...50.1066P. doi:10.1103/PhysRev.50.1066.
34. ^ Williams, E.; Faller, J.; Hill, H. (1971). "New Experimental Test of Coulomb's Law: A Laboratory Upper Limit on the Photon Rest Mass". Physical Review Letters. 26 (12): 721. Bibcode:1971PhRvL..26..721W. doi:10.1103/PhysRevLett.26.721.
35. ^ Chibisov, G V (1976). "Astrophysical upper limits on the photon rest mass". Soviet Physics Uspekhi. 19 (7): 624. Bibcode:1976SvPhU..19..624C. doi:10.1070/PU1976v019n07ABEH005277.
36. ^ Lakes, Roderic (1998). "Experimental Limits on the Photon Mass and Cosmic Magnetic Vector Potential". Physical Review Letters. 80 (9): 1826. Bibcode:1998PhRvL..80.1826L. doi:10.1103/PhysRevLett.80.1826.
37. ^ Amsler, C; Doser, M; Antonelli, M; Asner, D; Babu, K; Baer, H; Band, H; Barnett, R; et al. (2008). "Review of Particle Physics⁎"(PDF). Physics Letters B. 667: 1. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018. Summary Table
38. ^ Adelberger, Eric; Dvali, Gia; Gruzinov, Andrei (2007). "Photon-Mass Bound Destroyed by Vortices". Physical Review Letters. 98(1): 010402. arXiv:hep-ph/0306245. Bibcode:2007PhRvL..98a0402A. doi:10.1103/PhysRevLett.98.010402. PMID 17358459.preprint
39. ^ Wilczek, Frank (2010). The Lightness of Being: Mass, Ether, and the Unification of Forces. Physics Today. 62. Basic Books. p. 212. Bibcode:2009PhT....62d..61W. doi:10.1063/1.3120899. ISBN 978-0-465-01895-6.
40. ^ Descartes, R. (1637). Discours de la méthode (Discourse on Method) (in French). Imprimerie de Ian Maire. ISBN 978-0-268-00870-3.
41. ^ Hooke, R. (1667). Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon ... London: Royal Society of London. ISBN 978-0-486-49564-4.
42. ^ Huygens, C. (1678). Traité de la lumière (in French).. An English translation is available from Project Gutenberg
43. ^ Jump up to:^a b Newton, I. (1952) [1730]. Opticks (4th ed.). Dover, NY: Dover Publications. Book II, Part III, Propositions XII–XX, Queries 25–29. ISBN 978-0-486-60205-9.
44. ^ Buchwald, J.Z. (1989). The Rise of the Wave Theory of Light: Optical Theory and Experiment in the Early Nineteenth Century. Physics Today. 43. University of Chicago Press. p. 78. Bibcode:1990PhT....43d..78B. doi:10.1063/1.2810533. ISBN 978-0-226-07886-1. OCLC 18069573.
45. ^ Maxwell, J.C. (1865). "A Dynamical Theory of the Electromagnetic Field". Philosophical Transactions of the Royal Society. 155: 459–512. Bibcode:1865RSPT..155..459C. doi:10.1098/rstl.1865.0008. This article followed a presentation by Maxwell on 8 December 1864 to the Royal Society.
46. ^ Hertz, H. (1888). "Über Strahlen elektrischer Kraft". Sitzungsberichte der Preussischen Akademie der Wissenschaften (Berlin) (in German). 1888: 1297–1307.
47. ^ Frequency-dependence of luminiscence pp. 276ff., photoelectric effect section 1.4 in Alonso & Finn 1968
48. ^ Jump up to:^a b Wien, W. (1911). "Wilhelm Wien Nobel Lecture". nobelprize.org.
49. ^ Jump up to:^a b Planck, M. (1920). "Max Planck's Nobel Lecture". nobelprize.org.
50. ^ Jump up to:^a b c Einstein, A. (1909). "Über die Entwicklung unserer Anschauungen über das Wesen und die Konstitution der Strahlung" (PDF). Physikalische Zeitschrift (in German). 10: 817–825.. An English translation is available from Wikisource.
51. ^ Presentation speech by Svante Arrhenius for the 1921 Nobel Prize in Physics, December 10, 1922. Online text from [nobelprize.org], The Nobel Foundation 2008. Access date 2008-12-05.
52. ^ Einstein, A. (1916). "Zur Quantentheorie der Strahlung". Mitteilungen der Physikalischen Gesellschaft zu Zürich. 16: 47.Also Physikalische Zeitschrift, 18, 121–128 (1917). (in German)
53. ^ Jump up to:^a b Compton, A. (1923). "A Quantum Theory of the Scattering of X-rays by Light Elements". Physical Review. 21 (5): 483–502. Bibcode:1923PhRv...21..483C. doi:10.1103/PhysRev.21.483.
54. ^ Jump up to:^a b c Pais, A. (1982). Subtle is the Lord: The Science and the Life of Albert Einstein. Oxford University Press. ISBN 978-0-19-853907-0.
55. ^ Einstein and the Quantum: The Quest of the Valiant Swabian, A. Douglas Stone, Princeton University Press, 2013.
56. ^ Jump up to:^a b Millikan, R.A (1924). "Robert A. Millikan's Nobel Lecture".
57. ^ Hendry, J. (1980). "The development of attitudes to the wave-particle duality of light and quantum theory, 1900–1920". Annals of Science. 37 (1): 59–79. doi:10.1080/00033798000200121.
58. ^ Bohr, N.; Kramers, H.A.; Slater, J.C. (1924). "The Quantum Theory of Radiation". Philosophical Magazine. 47 (281): 785–802. doi:10.1080/14786442408565262. Also Zeitschrift für Physik, 24, 69 (1924).
59. ^ Heisenberg, W. (1933). "Heisenberg Nobel lecture".
60. ^ Mandel, L. (1976). E. Wolf, ed. The case for and against semiclassical radiation theory. Progress in Optics. 13. North-Holland. pp. 27–69. Bibcode:1976PrOpt..13...27M. doi:10.1016/S0079-6638(08)70018-0. ISBN 978-0-444-10806-7.
61. ^ Taylor, G.I. (1909). Interference fringes with feeble light. Proceedings of the Cambridge Philosophical Society. 15. pp. 114–115.
62. ^ Saleh, B.E.A. & Teich, M.C. (2007). Fundamentals of Photonics. Wiley. ISBN 978-0-471-35832-9.
63. ^ Heisenberg, W. (1927). "Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik". Zeitschrift für Physik (in German). 43 (3–4): 172–198. Bibcode:1927ZPhy...43..172H. doi:10.1007/BF01397280.
64. ^ E.g., pp. 10ff. in Schiff, L.I. (1968). Quantum Mechanics (3rd ed.). McGraw-Hill. ISBN 978-0-07-055287-6.
65. ^ Kramers, H.A. (1958). Quantum Mechanics. Amsterdam: North-Holland. ISBN 978-0-486-49533-0.
66. ^ Bohm, D. (1989) [1954]. Quantum Theory. Dover Publications. ISBN 978-0-486-65969-5.
67. ^ Newton, T.D.; Wigner, E.P. (1949). "Localized states for elementary particles" (PDF). Reviews of Modern Physics. 21 (3): 400–406. Bibcode:1949RvMP...21..400N. doi:10.1103/RevModPhys.21.400.
68. ^ Bialynicki-Birula, I. (1994). "On the wave function of the photon" (PDF). Acta Physica Polonica A. 86: 97–116.
69. ^ Sipe, J.E. (1995). "Photon wave functions". Physical Review A. 52(3): 1875–1883. Bibcode:1995PhRvA..52.1875S. doi:10.1103/PhysRevA.52.1875.
70. ^ Bialynicki-Birula, I. (1996). Photon wave function. Progress in Optics. 36. pp. 245–294. Bibcode:1996PrOpt..36..245B. doi:10.1016/S0079-6638(08)70316-0. ISBN 978-0-444-82530-8.
71. ^ Scully, M.O.; Zubairy, M.S. (1997). Quantum Optics. Cambridge: Cambridge University Press. ISBN 978-0-521-43595-6.
72. ^ The best illustration is the Couder experiment, demonstrating the behaviour of a mechanical analog, see Video on YouTube
73. ^ Bell, J.S. (2004). Speakable and Unspeakable in Quantum Mechanics: Collected Papers on Quantum Philosophy. Cambridge: University Press. Cambridge University Press. Bibcode:1987suqm.book.....B. ISBN 978-0-521-52338-7.
74. ^ Bose, S.N. (1924). "Plancks Gesetz und Lichtquantenhypothese". Zeitschrift für Physik (in German). 26 (1): 178–181. Bibcode:1924ZPhy...26..178B. doi:10.1007/BF01327326.
75. ^ Einstein, A. (1924). "Quantentheorie des einatomigen idealen Gases". Sitzungsberichte der Preussischen Akademie der Wissenschaften (Berlin), Physikalisch-mathematische Klasse (in German). 1924: 261–267.
76. ^ Einstein, A. (1925). Quantentheorie des einatomigen idealen Gases, Zweite Abhandlung. Sitzungsberichte der Preussischen Akademie der Wissenschaften (Berlin), Physikalisch-mathematische Klasse (in German). 1925. pp. 3–14. doi:10.1002/3527608958.ch28. ISBN 978-3-527-60895-9.
77. ^ Anderson, M.H.; Ensher, J.R.; Matthews, M.R.; Wieman, C.E.; Cornell, E.A. (1995). "Observation of Bose–Einstein Condensation in a Dilute Atomic Vapor". Science. 269 (5221): 198–201. Bibcode:1995Sci...269..198A. doi:10.1126/science.269.5221.198. JSTOR 2888436. PMID 17789847.
78. ^ "Physicists Slow Speed of Light". News.harvard.edu (1999-02-18). Retrieved on 2015-05-11.
79. ^ "Light Changed to Matter, Then Stopped and Moved". photonics.com (February 2007). Retrieved on 2015-05-11.
80. ^ Streater, R.F.; Wightman, A.S. (1989). PCT, Spin and Statistics, and All That. Addison-Wesley. ISBN 978-0-201-09410-7.
81. ^ Einstein, A. (1916). "Strahlungs-emission und -absorption nach der Quantentheorie". Verhandlungen der Deutschen Physikalischen Gesellschaft (in German). 18: 318–323. Bibcode:1916DPhyG..18..318E.
82. ^ Section 1.4 in Wilson, J.; Hawkes, F.J.B. (1987). Lasers: Principles and Applications. New York: Prentice Hall. ISBN 978-0-13-523705-2.
83. ^ Einstein, A. (1916). "Strahlungs-emission und -absorption nach der Quantentheorie". Verhandlungen der Deutschen Physikalischen Gesellschaft (in German). 18: 318–323. Bibcode:1916DPhyG..18..318E. p. 322: Die Konstanten ${\displaystyle A_{m}^{n}}$ and ${\displaystyle B_{m}^{n}}$ würden sich direkt berechnen lassen, wenn wir im Besitz einer im Sinne der Quantenhypothese modifizierten Elektrodynamik und Mechanik wären."
84. ^ Dirac, P.A.M. (1926). "On the Theory of Quantum Mechanics". Proceedings of the Royal Society A. 112 (762): 661–677. Bibcode:1926RSPSA.112..661D. doi:10.1098/rspa.1926.0133.
85. ^ Jump up to:^a b Dirac, P.A.M. (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proceedings of the Royal Society A. 114 (767): 243–265. Bibcode:1927RSPSA.114..243D. doi:10.1098/rspa.1927.0039.
86. ^ Jump up to:^a b Dirac, P.A.M. (1927b). The Quantum Theory of Dispersion. Proceedings of the Royal Society A. 114. pp. 710–728. Bibcode:1927RSPSA.114..710D. doi:10.1098/rspa.1927.0071.
87. ^ Heisenberg, W.; Pauli, W. (1929). "Zur Quantentheorie der Wellenfelder". Zeitschrift für Physik (in German). 56 (1–2): 1. Bibcode:1929ZPhy...56....1H. doi:10.1007/BF01340129.
88. ^ Heisenberg, W.; Pauli, W. (1930). "Zur Quantentheorie der Wellenfelder". Zeitschrift für Physik (in German). 59 (3–4): 139. Bibcode:1930ZPhy...59..168H. doi:10.1007/BF01341423.
89. ^ Fermi, E. (1932). "Quantum Theory of Radiation". Reviews of Modern Physics. 4 (1): 87. Bibcode:1932RvMP....4...87F. doi:10.1103/RevModPhys.4.87.
90. ^ Born, M. (1926). "Zur Quantenmechanik der Stossvorgänge". Zeitschrift für Physik (in German). 37 (12): 863–867. Bibcode:1926ZPhy...37..863B. doi:10.1007/BF01397477.
91. ^ Born, M. (1926). "Quantenmechanik der Stossvorgänge". Zeitschrift für Physik (in German). 38 (11–12): 803. Bibcode:1926ZPhy...38..803B. doi:10.1007/BF01397184.
92. ^ Pais, A. (1986). Inward Bound: Of Matter and Forces in the Physical World. Oxford University Press. p. 260. ISBN 978-0-19-851997-3. Specifically, Born claimed to have been inspired by Einstein's never-published attempts to develop a "ghost-field" theory, in which point-like photons are guided probabilistically by ghost fields that follow Maxwell's equations.
93. ^ Debye, P. (1910). "Der Wahrscheinlichkeitsbegriff in der Theorie der Strahlung". Annalen der Physik (in German). 33 (16): 1427–1434. Bibcode:1910AnP...338.1427D. doi:10.1002/andp.19103381617.
94. ^ Born, M.; Heisenberg, W.; Jordan, P. (1925). "Quantenmechanik II". Zeitschrift für Physik (in German). 35 (8–9): 557–615. Bibcode:1926ZPhy...35..557B. doi:10.1007/BF01379806.
95. ^ Photon-photon-scattering section 7-3-1, renormalization chapter 8-2 in Itzykson, C.; Zuber, J.-B. (1980). Quantum Field Theory. McGraw-Hill. ISBN 978-0-07-032071-0.
96. ^ Weiglein, G. (2008). "Electroweak Physics at the ILC". Journal of Physics: Conference Series. 110 (4): 042033. arXiv:0711.3003. Bibcode:2008JPhCS.110d2033W. doi:10.1088/1742-6596/110/4/042033.
97. ^ Bauer, T.H.; Spital, R.D.; Yennie, D.R.; Pipkin, F.M. (1978). "The hadronic properties of the photon in high-energy interactions". Reviews of Modern Physics. 50 (2): 261. Bibcode:1978RvMP...50..261B. doi:10.1103/RevModPhys.50.261.
98. ^ Sakurai, J.J. (1960). "Theory of strong interactions". Annals of Physics. 11 (1): 1–48. Bibcode:1960AnPhy..11....1S. doi:10.1016/0003-4916(60)90126-3.
99. ^ Walsh, T.F.; Zerwas, P. (1973). "Two-photon processes in the parton model". Physics Letters B. 44 (2): 195. Bibcode:1973PhLB...44..195W. doi:10.1016/0370-2693(73)90520-0.
100. ^ Witten, E. (1977). "Anomalous cross section for photon–photon scattering in gauge theories". Nuclear Physics B. 120 (2): 189–202. Bibcode:1977NuPhB.120..189W. doi:10.1016/0550-3213(77)90038-4.
101. ^ Nisius, R. (2000). "The photon structure from deep inelastic electron–photon scattering". Physics Reports. 332 (4–6): 165–317. arXiv:hep-ex/9912049. Bibcode:2000PhR...332..165N. doi:10.1016/S0370-1573(99)00115-5.
102. ^ Jump up to:^a b Ryder, L.H. (1996). Quantum field theory (2nd ed.). Cambridge University Press. ISBN 978-0-521-47814-4.
103. ^ Sheldon Glashow Nobel lecture, delivered 8 December 1979.
104. ^ Abdus Salam Nobel lecture, delivered 8 December 1979.
105. ^ Steven Weinberg Nobel lecture, delivered 8 December 1979.
106. ^ E.g., chapter 14 in Hughes, I.S. (1985). Elementary particles (2nd ed.). Cambridge University Press. ISBN 978-0-521-26092-3.
107. ^ E.g., section 10.1 in Dunlap, R.A. (2004). An Introduction to the Physics of Nuclei and Particles. Brooks/Cole. ISBN 978-0-534-39294-9.
108. ^ Radiative correction to electron mass section 7-1-2, anomalous magnetic moments section 7-2-1, Lamb shift section 7-3-2 and hyperfine splitting in positronium section 10-3 in Itzykson, C.; Zuber, J.-B. (1980). Quantum Field Theory. McGraw-Hill. ISBN 978-0-07-032071-0.
109. ^ E.g. sections 9.1 (gravitational contribution of photons) and 10.5 (influence of gravity on light) in Stephani, H.; Stewart, J. (1990). General Relativity: An Introduction to the Theory of Gravitational Field. Cambridge University Press. pp. 86 ff, 108 ff. ISBN 978-0-521-37941-0.
110. ^ Naeye, R. (1998). Through the Eyes of Hubble: Birth, Life and Violent Death of Stars. CRC Press. ISBN 978-0-7503-0484-9. OCLC 40180195.
111. ^ Polaritons section 10.10.1, Raman and Brillouin scattering section 10.11.3 in Patterson, J.D.; Bailey, B.C. (2007). Solid-State Physics: Introduction to the Theory. Springer. ISBN 978-3-540-24115-7.
112. ^ E.g. section 11-5 C in Pine, S.H.; Hendrickson, J.B.; Cram, D.J.; Hammond, G.S. (1980). Organic Chemistry (4th ed.). McGraw-Hill. ISBN 978-0-07-050115-7.
113. ^ Nobel lecture given by G. Wald on December 12, 1967, online at nobelprize.org: The Molecular Basis of Visual Excitation.
114. ^ Photomultiplier section 1.1.10, CCDs section 1.1.8, Geiger counters section 1.3.2.1 in Kitchin, C.R. (2008). Astrophysical Techniques. Boca Raton, FL: CRC Press. ISBN 978-1-4200-8243-2.
115. ^ Denk, W.; Svoboda, K. (1997). "Photon upmanship: Why multiphoton imaging is more than a gimmick". Neuron. 18 (3): 351–357. doi:10.1016/S0896-6273(00)81237-4. PMID 9115730.
116. ^ Lakowicz, J.R. (2006). Principles of Fluorescence Spectroscopy. Springer. pp. 529 ff. ISBN 978-0-387-31278-1.
117. ^ Jennewein, T.; Achleitner, U.; Weihs, G.; Weinfurter, H.; Zeilinger, A. (2000). "A fast and compact quantum random number generator". Review of Scientific Instruments. 71 (4): 1675–1680. arXiv:quant-ph/9912118. Bibcode:2000RScI...71.1675J. doi:10.1063/1.1150518.
118. ^ Stefanov, A.; Gisin, N.; Guinnard, O.; Guinnard, L.; Zbiden, H. (2000). "Optical quantum random number generator". Journal of Modern Optics. 47 (4): 595–598. doi:10.1080/095003400147908.
119. ^ Hignett, Katherine (16 February 2018). "Physics Creates New Form Of Light That Could Drive The Quantum Computing Revolution". Newsweek. Retrieved 17 February 2018.
120. ^ Liang, Qi-Yu; et al. (16 February 2018). "Observation of three-photon bound states in a quantum nonlinear medium". Science. 359 (6377): 783–786. arXiv:1709.01478. Bibcode:2018Sci...359..783L. doi:10.1126/science.aao7293. PMID 29449489. Retrieved 17 February 2018.

Further reading[edit]

By date of publication:

• Alonso, M.; Finn, E.J. (1968). Fundamental University Physics Volume III: Quantum and Statistical Physics. Addison-Wesley. ISBN 978-0-201-00262-1.
• Clauser, J.F. (1974). "Experimental distinction between the quantum and classical field-theoretic predictions for the photoelectric effect". Physical Review D. 9 (4): 853–860. Bibcode:1974PhRvD...9..853C. doi:10.1103/PhysRevD.9.853.
• Pais, A. (1982). Subtle is the Lord: The Science and the Life of Albert Einstein. Oxford University Press.
• Feynman, Richard (1985). QED: The Strange Theory of Light and Matter. Princeton University Press. ISBN 978-0-691-12575-6.
• Grangier, P.; Roger, G.; Aspect, A. (1986). "Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences". Europhysics Letters. 1 (4): 173–179. Bibcode:1986EL......1..173G. CiteSeerX 10.1.1.178.4356. doi:10.1209/0295-5075/1/4/004.
• Lamb, W.E. (1995). "Anti-photon". Applied Physics B. 60 (2–3): 77–84. Bibcode:1995ApPhB..60...77L. doi:10.1007/BF01135846.
• Special supplemental issue of Optics and Photonics News (vol. 14, October 2003) article web link
  • Roychoudhuri, C.; Rajarshi, R. (2003). "The nature of light: what is a photon?". Optics and Photonics News. 14: S1 (Supplement).
  • Zajonc, A. "Light reconsidered". Optics and Photonics News. 14: S2–S5 (Supplement).
  • Loudon, R. "What is a photon?". Optics and Photonics News. 14: S6–S11 (Supplement).
  • Finkelstein, D. "What is a photon?". Optics and Photonics News. 14: S12–S17 (Supplement).
  • Muthukrishnan, A.; Scully, M.O.; Zubairy, M.S. "The concept of the photon – revisited". Optics and Photonics News. 14: S18–S27 (Supplement).
  • Mack, H.; Schleich, W.P. "A photon viewed from Wigner phase space". Optics and Photonics News. 14: S28–S35 (Supplement).
• Glauber, R. (2005). "One Hundred Years of Light Quanta" (PDF). 2005 Physics Nobel Prize Lecture. Archived from the original (PDF) on 2008-07-23. Retrieved 2009-06-29.
• Hentschel, K. (2007). "Light quanta: The maturing of a concept by the stepwise accretion of meaning". Physics and Philosophy. 1 (2): 1–20.

Education with single photons:

• Thorn, J.J.; Neel, M.S.; Donato, V.W.; Bergreen, G.S.; Davies, R.E.; Beck, M. (2004). "Observing the quantum behavior of light in an undergraduate laboratory" (PDF). American Journal of Physics. 72 (9): 1210–1219. Bibcode:2004AmJPh..72.1210T. doi:10.1119/1.1737397.
• Bronner, P.; Strunz, Andreas; Silberhorn, Christine; Meyn, Jan-Peter (2009). "Interactive screen experiments with single photons". European Journal of Physics. 30 (2): 345–353. Bibcode:2009EJPh...30..345B. doi:10.1088/0143-0807/30/2/014.

External links[edit]

광자

[ Photon ]

광자는 입자로서의 빛으로, 빛알이라고도 한다. 그러나 이는 고전역학에서 기술하는 입자, 즉 고전 입자(classical particle)와는 다르다. 고전 입자는 주어진 시간에 위치와 속도를 동시에 기술할 수 있다. 양자역학의 입자는, 파동으로서의 성질과 함께 상보적으로 이해해야 한다. 입자물리학의 표준 모형에서는 광자를 전자기력을 매개하는 기본입자라고 보고 있다. 광자의 운동과 상호작용은 양자장론으로 기술한다.

---

광자를 이야기할 때 빛은 좁은 의미인 가시광선이 아니라 넓은 의미인 전자기파를 뜻한다. 양자역학의 발전을 통해, 빛은 개수를 셀 수 있는 입자, 즉 양자(quantum)로 볼 수 있게 되었다.

목차

1. 1.역사와 발견
2. 2.성질
3. 3.참고 자료

역사와 발견

뉴턴(I. Newton, 1643-1727)은 빛을 입자로 보고 반사 등의 많은 물리현상을 설명할 수 있었다. 그러나 간섭을 설명할 수 없었고, 뉴턴 당대에도 하위헌스(C. Huygens, 1629-1695)등이 빛을 파동으로 보는 입장이 존재했다. 그러나 영의 실험을 통해 빛은 파동이라고 결론지어지고 논쟁이 끝나는듯 했다. 외르스테드(H. C. Ørsted, 1777-1851)와 패러데이(M. Faraday, 1791-1867)는 전기와 자기 현상이 서로 연관이 있음을 밝혔으며, 맥스웰(J. C. Maxwell, 1831-1879)이 최종적으로 빛은 전자기파의 일종이며, 진공 중에서 라고 부르는 속력으로 전파된다는 것을 보였다.

1901년 플랑크(M. Planck, 1858-1947)의 흑체복사 분석을 통해, 빛이 양자화되어야 한다는 것을 발견하게 되었다. 온도가 정해진 흑체의 파장에 따른 복사량을 설명해야 하는데, 관측된 양을 설명하는 유일한 방법은 빛은 고전적인 파동처럼 연속적인 것이 아니며, 개수를 셀 수 있는 것으로 보는 것이었다. 1905년 아인슈타인(A. Einstein, 1879-1955)이 광전효과를 설명하기 위하여 역시 빛이 양자화 되어야 한다는 것을 알아낸다. 빛이 금속에 흡수되어 흐르는 전류는 연속적인 것이 아니라, 한 개의 빛이 금속에 흡수되느냐 되지 않느냐 하는 이산적인 양이다. 또한 1924년 콤프턴(A. Compton, 1892-1962)이 콤프턴효과를 빛 입자로 설명하게 되었다. 드브로이(L. de Broglie, 1892-1987)가 모든 물질은 파동으로 이해해야 한다는 물질파이론을 제창하였다. 따라서 반대로 파동도 물질로 이해할 수 있다.

성질

양자전기역학을 통해 빛을 입자로 이해할 수 있다. 입자들의 성질은 질량, 스핀, 전하만으로 분류할 수 있으며, 광자는 질량이 0, 스핀이 1, 전하는 0이다.

광자의 질량은 실험을 통해 검측되지 않았으므로, 0이라고 생각해도 아직 모순이 없다. 질량이 있다고 가정했을 때 나타나는 여러 현상들에 따라 다른데, 표준모형에서 광자의 질량항을 관측할 수 없다는 결과를 바탕으로 하는 실험 한계는 보다 작아야 한다는 것이다. 1)이다. 양자장론에서는 U(1) 게이지 대칭성을 통해 광자를 기술하는데, 게이지 대칭성이 존재하기 위해서 광자의 질량은 정확히 0이어야 한다.

양자역학에 따르면, 파장이 인 광자 하나의 운동량의 크기 는

이다. 여기에서 는 플랑크상수이다. 광자가 이동하는 방향을 고려하여 운동량 벡터를 생각할 수도 있다. 이 광자 하나의 에너지는

는 진공 중 빛의 속력이며, 는 빛의 진동수이다. 이 양은 로런츠 네성분 벡터를 이룬다. 이들은 광자 하나의 물리량이기는 하지만, 이 물리량은 파동의 특성인 파장과 진동수를 통해 주어진다. 따라서 파동의 성질과 함께 상보적으로 이해해야 한다. 영의 실험이라고 부르는 이중 슬릿 실험을 통해, 광자 하나도 파동의 고유한 성질인 간섭현상을 일으킨다는 것을 알 수 있다.

광자는 스핀 1을 갖는다. 벡터양으로 기술이 되어 힘을 매개하는 벡터 보손 가운데 하나이다. 양자장론에서는 U(1)게이지 대칭성을 통해 전자기력을 기술한다. 따라서 전자기 전하를 띤 입자와 상호작용한다.

참고 자료

1. Amsler, C; Doser, M; Antonelli, M; Asner, D; Babu, K; Baer, H; Band, H; Barnett, R et al. (2008). 'Review of Particle Physics '. Physics Letters B 667: 1.

[네이버 지식백과] 광자 [Photon] (물리학백과)