10 More Changes That Star Trek Hoped You Wouldn't Notice

In the classic Original Series episode Arena, Kirk found a deposit of diamonds and referred to them as 'perhaps the hardest substance known in the universe'.

Aside from the fact that scientists in real life have now been able to synthesise substances harder than diamonds, this statement was also contradicted several times in Trek itself. In the episode Balance Of Terror (which aired before Arena), cast rodinium was called the hardest substance known to man. Then, almost a year after Arena aired, tritanium was described as 21.4 times harder than diamond in the episode Obsession.

There are countless other contenders for the hardest substance in the Trek universe, including neutronium (the material used in the planet killer's hull from the episode The Doomsday Machine), and monotanium (the material used in Hirogen ship armour). There's really no way to know which of them is actually the hardest.