I'm studying Cosmology Lectures of Prof. Leonard Susskind (no GR involved at the moment). Vacuum energy density was introduced as $\rho_0$ and related to the Cosmological Constant $\Lambda$. I know this is also connected to Quantum Mechanics results, which does not particularly cease to amaze me.
I understand that this term of energy when modeling the Universe has an attractive effect (or a negative pressure) that is trying to "hold" Universe's expansion. I commented this to my younger brother and he immediately asked: "Ok. but, can it be used?".
Question: What would you answer to that? Cosmological effects can be seen (indirectly) from Hubble law at large scales, which is not something you could measure on Earth, to say something. Anyways, this energy term actually exerts pressure and does work so, only for pedagogical (and self-learning) purposes, could you think of an experiment (not necessarily one that could be done) in which Vacuum Energy could be related or converted to any other form of energy, in a way it can be understood for someone who is not familiarized with the expansion of the Universe? In other words: how would you attempt to explain Vacuum Energy more palpably, not necessarily going through the mathematics of it?
Might be related: Vacuum energy conversion to heat