Physics has declined in popularity among pupils at school and students at university, research suggests.
The researchers identified a "spiral of decline"
A-level entries have fallen from 55,728 in 1982 to 28,119 in 2005, according to researchers at Buckingham University.
Girls accounted for less than a quarter (22.4%) of applications. Compounding the problem, fewer graduates in physics than other sciences went into teaching.
But the Department for Education and Skills said sciences were among the more popular courses at A-level.
The researchers said the decline was noted across all types of schools and colleges, but was sharpest in further education colleges and was least noticeable in independent schools and grammar schools.
Co-author Professor Alan Smithers said the falling numbers of pupils taking up physics was a matter of grave concern.
"It looks as though physics is in the grip of a long-term downward spiral and it's urgent that we find ways of breaking into it."
Prof Smithers said the downturn was impacting on higher education, with numbers at universities down by 28%.
He said: "Not enough young people come through to take physics degrees, which means that the pool from which to recruit teachers is not large enough and science teaching is left to biologists to a greater extent than is desirable."
As a result, many young people did not get sufficient opportunity to discover if they were good at physics, and were naturally disinclined to take what they believed was a difficult subject at A-level.
"Consequently, there is an insufficient platform to support the university studies to a level where there would be enough graduates from which to recruit the teachers."
Martin Rees, president of the Royal Society said: "Teachers who are both enthused and knowledgeable about their subjects are key to breaking the cycle of decline that physics is experiencing."
Sir Richard Friend, Cavendish professor of physics at Cambridge University, said while there were concerns about declining numbers of pupils taking physics at A-level, where physics was practised it was "robust".
But he said more must be done to make pupils aware of the choice and number of jobs available to physics graduates.
A spokesman for the Department for Education and Skills said sciences continued to be among the more popular courses at A-level.
Last year maths, chemistry and physics made up a greater proportion of A- level entries than communication studies, computing, expressive arts/drama, ICT, media studies and psychology put together.
"Moreover, far greater percentages of A to C grades are awarded for maths and science A-levels than for media studies, communication studies and ICT."
The Buckingham University research was funded by the Gatsby Charitable Foundation.