A philosophical theory stating that when you have no reason to believe one outcome is more likely than another, all outcomes should be considered equally probable.
From Latin 'equi-' (equal) + 'probabilis' (probable) + '-ism' (doctrine). The concept emerged in 17th-century probability theory when mathematicians like Laplace formalized the principle of indifference.
This principle is why a fair coin flip has 50-50 odds—but it gets tricky! Scientists realized equiprobabilism can lead to paradoxes when you're not careful about how you set up your equally-likely possibilities.
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