Your questions seem rather nonsensical to me, because unicorns and mermaids have never been observed to actually exist anywhere in our universe. Hence, experiments can not be conducted on unicorns in order to determine if they sweat nor could experiments be conducted on mermaids in order to determine the frictional coefficient value of their bodies.
Do we live in a simulated universe with an underlying grid?
Some physicists have proposed a method for testing if we are in a numerical simulated cubic space-time lattice Matrix or simulated universe with an underlying grid.
[1210.1847] Constraints on the Universe as a Numerical Simulation
Based on the assumption that there'd be finite computational resources, a simulated universe would be performed by dividing up the space-time continuum into individually separate and distinctive points. Analogous to mini-simulations that lattice-gauge theorists conduct to construct nuclei based on Quantum Chromodynamics, observable effects of a grid-like space-time have been studied from these computer simulations which use a 3-D grid to model how elementary particles move and collide with each other. Anomalies found in these simulations suggest that if we are in a simulation universe with an underlying grid, then there'd be various amounts of high energy cosmic rays coming at us from each direction; but if space is continuous, then there'd be high energy cosmic rays coming at us equally from every direction.
High Energy Physics - Phenomenology
Constraints on the Universe as a Numerical Simulation
Silas R. Beane,
Zohreh Davoudi,
Martin J. Savage
(Submitted on 4 Oct 2012 (
v1), last revised 9 Nov 2012 (this version, v2))
Oh, this is easy. Just ask the unicorns and mermaids if they exist.
Or, we could do what my theist friend did....climb a pile of rocks, find a rock, and assert that it is proof that God exists.
No one is really asserting that the grid of space is there. But, in order to understand the expansion of the universe, it helps to think of a grid.
Cosmic noise - Wikipedia
The link above discusses cosmic noise (electromagnetic radiation, like a radio wave, of about 15 MHz, from the big bang). Parts of the universe were blown off course (like our sun, and therefore like earth) from supernova explosions. But, if not blown off course, mass remained where it was as the universe expanded and that expansion accelerated. To calculate when the universe exploded, it helps to find parts of the universe that have not moved since the universe started to expand. These parts are called co-moving observers. Thus, two distant co-moving observers could move apart due to expansion of the universe, but they haven't really moved at all since the universe started. Thus, the Twin Paradox can not be used with co-moving observers because neither moved relative to the universe, thus time did not dilate for either one of them, though they are moving away from each other due to the expansion of the universe.
We can determine if a star is a co-moving observer by detecting (with a radio-telescope) the cosmic background radiation. Co-moving observers have an even amount of background radiation (not lopsided as it is at the sun or earth).
There are two main ways of doing quantum mechanics (quantum chromodynamics and quantum electrodynamics). Each way correctly predicts some results, and incorrectly predicts other results. Electrodynamics assumes that the small world of quantum mechanics is about electromagnetic fields. Chromodynamics, on the other hand, assumes that the small world of quantum mechanics is about subatomic particles (which could be electromagnetism trapped in tiny loops which we call particles).
That is, subatomic particles could be trapped light. After all, E=mc^2 is about the energy produced when mass is changed to energy (or vice versa). Pair production is about electromagnetic energy converting to a matter and antimatter pair (a process that is well known and commonly observed). Matter/antimatter annihilation is about a particle and its antimatter counterpart turning into pure energy when they collide. Again, it is commonly observed.
If you ask me, I think that quantum mechanics is a combination of chromodynamics and electrodynamics (sometimes we are dealing with electromagnet waves (aka light), and sometimes we are dealing with particles).
The concept of a simulated universe (such as the movie The Matrix) which means that we are all living in a holodeck (from Star Trek), is accepted and promoted by unlikely people (Neil De Grasse Tyson, for example). But wouldn't that allow us to detect the matrix? Couldn't we somehow manipulate or change the matrix?