Complex sentence: In the sciences, TANSTAAFL means that the universe as a whole is ultimately a closed system--there is no magic source of matter, energy, light, or indeed lunch, that does not draw resources from something else, and will not eventually be exhausted.
Split into simpler sentences: In the sciences, TANSTAAFL means that the universe as a whole is ultimately a closed system. There is no magic source of matter, energy, light, or indeed lunch, that does not draw resources from something else, and that will not eventually be exhausted.