Short answers, pulled from the story.
The three main branches of ethics are normative ethics, applied ethics, and metaethics. Normative ethics investigates fundamental principles of moral conduct, applied ethics examines concrete moral problems in real-life situations, and metaethics explores the underlying assumptions and concepts of morality, including whether objective moral facts exist.
Consequentialism holds that an act is right if it produces the best consequences, while deontology holds that certain actions are inherently right or wrong regardless of their outcomes. Consequentialism was given its name by G. E. M. Anscombe in the 20th century; its most well-known form is utilitarianism, formulated by Jeremy Bentham in the late 18th century. Deontology's most influential proponent was Immanuel Kant (1724-1804), who argued that morality is grounded in categorical imperatives applying to all rational agents.
Utilitarianism was initially formulated by Jeremy Bentham (1748-1832) and further developed by John Stuart Mill (1806-1873). It holds that an act is morally right if it produces the greatest good for the greatest number by increasing happiness and reducing suffering. Bentham introduced the hedonic calculus to measure pleasure by intensity and duration; Mill refined this by distinguishing higher pleasures, such as intellectual satisfaction, from lower sensory ones.
Metaethics examines the nature, foundations, and scope of moral judgments rather than which actions are right. It asks whether moral facts are objective and whether moral statements can be true or false. G. E. Moore (1873-1958) made influential early contributions by arguing that moral values differ fundamentally from natural properties. R. M. Hare (1919-2002) developed prescriptivism, J. L. Mackie (1917-1981) proposed that all moral statements are false, and Derek Parfit (1942-2017) argued for moral realism.
The trolley problem was devised by Philippa Foot. It presents a situation in which a person can flip a switch to redirect a trolley from one track to another, sacrificing the life of one person to save five. The scenario is used to explore how the distinction between doing and allowing harm affects moral obligations.
Ethics began in ancient civilizations: Egypt used the concept of Maat to guide behavior; India's Vedas, composed from the 2nd millennium BCE, discussed duty and consequences; Buddhist ethics emerged between the 6th and 5th centuries BCE; and ancient China's 6th century BCE saw the rise of Confucianism and Daoism. In ancient Greece, Socrates (c. 469-399 BCE) and Aristotle (384-322 BCE) shaped Western ethics. Medieval thought was dominated by religious philosophy, including Thomas Aquinas (1224-1274 CE) and Islamic philosophers like Avicenna (980-1037 CE). The modern period shifted toward secular approaches, with thinkers like Hobbes (1588-1679), Hume (1711-1776), and Kant (1724-1804).