Superfluidity is briefly mentioned in the article, but it&#x27;s a quantum effect that&#x27;s visible in very large systems.<p>A system exhibits zero viscosity when its particles condense into a single quantum mechanical state. Superconductivity is an instance of this, where electrons pair up and flow without resistance.<p>Buckets of liquid helium show superfluidity. [1]<p>Labs cool blobs of alkali gas to superfluidity. [2]<p>Entire cores of neutron stars are superfluid. [3]<p>There&#x27;s even a theory of quantum gravity where physical vacuum is a superfluid. [4]<p>[1] <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=2Z6UJbwxBZI" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=2Z6UJbwxBZI</a><p>[2] <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=1RpLOKqTcSk" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=1RpLOKqTcSk</a><p>[3] <a href="http:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;1012.0045" rel="nofollow">http:&#x2F;&#x2F;arxiv.org&#x2F;abs&#x2F;1012.0045</a><p>[4] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Superfluid_vacuum_theory" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Superfluid_vacuum_theory</a>