How is synthesized Vacuum different from the one in the Universe? This question is with reference to Torricelli's Vacuum Barometer which was one of the first experiments involving vacuum creation in Laboratories. The Atmospheric pressure causes a rise in the mercury in the column. By manipulating the length of the column, Torricelli first synthesized vacuum.
However I'm not very certain about the difference between this synthetically created vacuum and the natural Void of space. Several researches and accountable sites guarantee that we on Earth cannot create a better vacuum (in terms of particles per unit area) than what naturally exists in space. But the vacuum in the Universe contains Dark Energy which seems to be the cause of its expansion. So in a vacuum that is created in any experiment in laboratories such as the one done by Torricelli, can there be the presence of dark energy along with the empty space. If that is the case, shouldn't there be quantum fluctuations or expansions by the dark energy in that vacuum which would make a Mercury Barometer highly unstable as the vacuum will press against the mercury and will try to expand to infinity?
If in case the vacuum that we created possesses no dark matter or energy, then haven't we been able to produce a more efficient void than the one in the Universe. Doesn't that contradict the fact that the spatial vacuum is the "purest of all"?
 A: Ultra High Vacuum goes down to pressures of perhaps $10^{-12}$mbar, which corresponds to a particle density of some $10^4$ molecules per cm$^3$. The interstellar medium has densities of perhaps 1 particle per cm$^3$ (Wikipedia agrees). So indeed the number density of particles in outer space can be much lower than that of a very good vacuum in a lab. Unless you are in a molecular cloud or such, in which case it might as well be much higher of course.
The mass-energy density of dark energy is tiny in comparison to, well, in comparison to anything really: About $10^{-29}$g/cm$^3$ which is another factor $10^6$ or $10^7$ lower than the density number of particles in interstellar space quoted above.
Any quantum fluctuations in the vacuum of a mercury barometer are utterly negligible. One can however measure the Casimir effect in the lab, but this is the infamously "worst model in physics" for dark energy, so again, no information about dark energy from that at all.
So then there is the question whether the vacuum chamber in your lab would contain dark energy or not. Since dark energy is believed to be a property of spacetime itself, the answer is expected to be "yes". So, no, you not would expect the vacuum we create to be "purer" than the vacuum in outer space. However, given the above order-of-magnitudes, it should be clear why there can be no experimental evidence to support that.
Finally, you mention dark matter. Dark matter interacts only very weakly, so we would expect that it simply passes through any vacuum vessel you build. In other words, just like with dark energy but for other reasons, the density of dark matter is also expected to the same, whether you are in outer space, in your lab breathing air, or in some vacuum vessel. Specifically, that density is of order $10^{-25}$g/cm$^3$ in the vicinity of our Sun.
