The Bomb.

It's the end of the world. It's not a fantasy or a cliche. It's a nightmare rooted in reality. It could happen here and now.

Since it exploded over Hiroshima on Aug. 6, 1945, the atomic bomb has dominated global politics, created a cultural climate of fear and paranoia and turned war cold and ultimate.

It still sparks the imagination of filmmakers today. ''Hiroshima'' is on Showtime on Sunday and many stations are airing films on this topic to mark its 50th anniversary.

Films about the bomb fall into four main categories: developing and dropping the bomb, its impact on its creators and victims, the threat of nuclear attack and the horror of the aftermath.

The story begins with ''The Day After Trinity'' (1980), a superb documentary about the scientists who built the first atomic bomb and the personal and political fallout from their achievement.

What began as a race to end the war and defeat the Nazi demon became an unstoppable quest to prove scientific theory with little thought to its consequences until it was too late.

It is also the story of J. Robert Oppenheimer, an intellectual, scholarly, theoretical physicist who became an unlikely national hero for leading the massive effort to develop the bomb.

After the war, he futilely fought to control its use, only to find himself condemned as a Communist sympathizer and his creation the focus of an escalating arms race and Cold War.

Through interviews with scientists who worked on the Manhattan Project, the fascinating, dramatic film details their personalities, daily lives, and regrets over their success.

It took them just 18 months to build the bomb. It fell on Japan three weeks later. The film ends with scenes of the bomb's The film ends with scenes of the bomb's awesome power and beauty and Oppenheimer invoking Hindu deities: ''Now I am become Death, the destroyer of worlds.''

The city destroyed by the first atomic bomb is the setting for ''Hiroshima, Mon Amour'' (1959), Alain Resnais' thought-provoking love story about how the past influences the present and how war can destroy one person or an entire city with equal swiftness.

It opens with a famous sequence contrasting a couple making love with newsreel footage showing Hiroshima after the bombing. She is a French actress making a film about the bomb; he is a Japanese architect whose family perished from it.

Their brief encounter recalls how her love for a young German soldier in occupied France during the war cost his life and left her publicly humiliated and emotionally scarred.

Moving from past to present, Resnais parallels her private horror and the public horror of Hiroshima and how both continue to influence events years later.

In Hollywood, the Atomic Age spawned new evils, from giant insects created by radioactive fallout to all-too-real scenarios about Cold War tensions leading to World War III.

The latter inspired two unforgettable 1964 classics with similar plots but different tones: ''Fail-Safe'' and ''Dr. Strangelove: or, How I Learned to Stop Worrying and Love the Bomb.''

Both track a single bomber group ordered to attack Russia. Action rotates between the lead plane, the military leaders trying to stop it and strategists advising the president.

Mechanical error launches one attack, and a paranoid general starts the other.

Both feature memorable conversations between U.S. presidents and Soviet premieres, veteran pilots using old-fashioned American ingenuity to reach their targets and advisors arguing that nuclear war is winnable.

One is a deformed ex-Nazi scientist. The other a bitter Jewish intellectual who has grown as cold and heartless as his enemy.

Both films are brilliantly written, directed and acted.

One is deadly serious and the other blackest comedy.

''Fail-Safe'' is a tragedy of men taking responsibility for creating the circumstances leading to a crisis and for the agonizing decisions and personal sacrifices needed to end it.

"Strangelove" began as serious drama. But director Stanley ''Strangelove'' began as serious drama. But director Stanley Kubrick and screenwriter Terry Southern turned it into a stylish satirical nightmare about humanity's self-destruction.

Both films end with the bombs falling. A few filmmakers have imagined what happens to the people below.

Peter Watkins' ''The War Game'' (1965) is a harrowing, 50-minute documentary about life before, during and after nuclear war.

Based on government plans and scientific and historical evidence, Watkins uses newsreel-like footage and interviews to graphically detail expected human casualties, social chaos and futility of Civil Defense preparation and relief efforts.

One critic called the film a ''dress rehearsal for Hell.'' The made-for-TV film was so disturbing that the BBC banned it, but it won the Oscar as Best Documentary feature.

The human cost of nuclear war is heart-wrenchingly portrayed in The human cost of nuclear war is heart-wrenchingly portrayed in ''Testament'' (1983), the story of a typical, small-town American family coping with life after a sudden nuclear attack.

It is impossible to watch without being moved by the mounting deaths, the collapsing of a once-close community, and the ham radio going silent, as the last pockets of humanity fade away.

This is poignantly shown through a young widow (Jane Alexander, in an Oscar-nominated role) and her children as they lose the struggle to survive and face a future without hope and a past filled only with memories recalled as grainy home movies.

''On the Beach'' (1959) recalls the final months of people preparing for nuclear fallout to drift over Australia, mankind's last outpost following a nuclear war.

An American submarine captain can't accept his wife and kids are dead, a lonely woman faces the end alone, a young couple agonizes about taking their newborn baby's life, and a scientist who worked on the bomb tries to meet his fate in a racecar.

There are no violent scenes of death and destruction, only quiet images of hospital staff dispensing suicide pills, a deserted San Francisco glimpsed through a periscope, the declining number of men meeting in a club, and a not-so-subtle sign warning audiences that ''There's still time, brother.''

As in T.S. Eliot's ''The Wasteland,'' the world ends not with a bang but with a whimper and a wistful ''Waltzing Matilda.''

It is understated yet powerful, a sad reminder of the grim legacy that the world is still living with five decades later.

• ''Above and Beyond'' (1952)
  
• ''Atomic Cafe'' (1982)
  
• ''The Bedford Incident'' (1965)
  
• ''The Beginning or the End'' (1947)
  
• ''Blue Sky'' (1991)
  
• ''By Dawn's Early Light'' (1990)
  
• ''Countdown to Looking Glass'' (1984)
  
• ''Crimson Tide'' (1995)
  
• ''The Day After'' (1983)
  
• ''Day One'' (1989)
  
• ''Desert Bloom'' (1986)
  
• ''Akira Kurosawa's Dreams'' (1990)
  
• ''Enola Gay: The Men, The Mission, The Atomic Bomb'' (1980)
  
• ''Ground Zero'' (1987)
  
• ''Hiroshima: Out of the Ashes'' (1990)
  
• ''I Live in Fear'' (1955)
  
• ''Insignificance'' (1985)
  
• ''Kiss Me Deadly'' (1955)
  
• ''Lord of the Flies'' (1963)
  
• ''The Missiles of October'' (1974)
  
• ''Nightbreaker'' (1989)
  
• ''Rhapsody in August'' (1991)
  
• ''Seven Days to Noon'' (1950)
  
• ''Threads'' (1984)
  
• ''World War III'' (1982)