Imagine being a Perfect Observer, a PO, able to observe and not disturb small stuff (as well as big stuff). Imagine having the perceptual capability of perceiving directly and instantaneously all things and events without the perceptual problems inherent in our perceptual senses of sight/hearing/touch/smell/taste/etc., with the result that what is perceived is perceived immediately and without distortion.

NOTE: If you are not willing to accept the premises of this gedankenexperiment (German: thought experiment, intuitive imagining), then you will miss the logic of how the premises of the PO Theory lead to the conclusion of the PO Theory.

What would we find?

Would we find chaos, or would we find determinism, properly called causality, in which the things and events present in the Now, the current configuration of the matter/energy present in the universe, as effects from previous causes are causes of future effects?

Would we observe every possible configuration of matter/energy (all possible universes) or only the one-and-only actual configuration (the one-and-only universe)?

I vote for causality, and, therefore, the one-and-only universe.

Quantum Mechanics probability theory is derived from the fact that when dealing with small stuff we cannot observe and not disturb small stuff [the physical necessities inre observing small stuffs cause disturbances of the positions and/or the velocities of small stuffs] and therefore, theoretically, we cannot determine a particle's position and velocity simultaneously.

Hence, not being able to determine both a particle's velocity and position, we are limited to probabilistic predictions instead of true deterministic predictions.

But is determinism alive and well at the level of small stuff?

The fact is that QM probabilistic theories work well. Where we cannot directly observe individuals members of a crowd of small stuffs, we can observe the crowd and develop averages of the crowd's behavior and therefore make predictions based upon that knowledge, inductive reasoning leading to deductive reasoning.

The PO Theory nevertheless shows us the reality of causality at all levels of observation including the level(s) of small stuffs.

The trick is, of course, learning how to be, and becoming, Perfect Observers. 

Imagine being a Perfect Observer [PO].

You have a perceptual capability (similar to touch) by which you instantly perceive the position and velocity (location and motion—direction and speed) of each and every quantum and any and all quanta in the universe. [Your ability to perceive the precise position and velocity of a quantum is not distorted by time delays resulting from light-based information transmission, and, therefore, you observe the true position/velocity of each and every quantum and any and all quanta.]

You can observe and not disturb quanta. [The Heisenberg Uncertainty Principle does not apply to you.]

You can observe at any scalar level. [No exceptions!]

You can move instantly from one location to another; instantaneous changes of location means you can travel at superluminal speeds, or faster-than-light [FTL]. [The limitations of c/SOL do not apply to you—No exceptions!]

You recognize a force to be a push or a pull.

You recognize the law of inertia [LoI]: an object in the inertial state [IS] of being at rest or in the IS of being in uniform motion retains its IS until acted upon by a force.

You recognize the Corollaries to the Law of Inertia [CLoI]:

(1) Only a force can cause a change of an object's IS;
(2) The observation/measurement of a change of an object's IS implies the cause to be a force.

You recognize the laws of the conservation of matter, energy, electric charge, and momentum.

You recognize therefore that matter and energy are indestructible [the laws of the conservation of matter and energy].

You recognize that matter and energy are convertible; that matter can be converted into energy [m = e/c2] and energy can be converted into matter [e = mc2].

You recognize that matter and energy are two forms of the same phenomena, matter/energy [m/e].

You define an open m/e system to be an m/e system ...

(A) to which m/e can be added;
(B) from which m/e can be removed;
(C) in which the sum total of m/e is variable.

You define a closed m/e system as an m/e system ...

(A) to which m/e cannot be added (where would the additional m/e come from?);
(B) from which m/e cannot be removed (where would the removed m/e go?);
(C) the sum total of m/e is a constant (the quantity of m/e does not change].

You recognize that people/objects/events are comprised of matter/energy [m/e].

You define causality as people/objects/events who/which are comprised of m/e and who/which are causes cause the effects of changes in pre-existing people/objects/events and/or new people/objects/events.

You define infinite as having no physical or mathematical limits; you define finite as having physical and/or mathematical limits.

You define space as a volume of infinite radius, the infinite volume or i-volume.

You define the unit of measurement of space to be a length, or distance, or space-interval [SI], as found in foot-rulers/metre-sticks/yard-sticks/etc.

You recognize there are two SIs: (A) The variable SI [VSI], which varies inversely with accelerations/decelerations; (B) The invariable SI [ISI], which does not vary with accelerations/decelerations.

You define time as the use of a duration called a time-interval [TI] for the measurement of the occurrences of events [causal relationships between/among people/objects comprised of matter/energy].

You recognize there are two TIs: (A) The variable time-interval [VTI], which varies inversely with accelerations/decelerations; (B) The invariable time-interval [ITI], which does not vary regardless of accelerations/decelerations.

You recognize there are two kinds of clocks: (A) The variable time-interval clock [VTIC] which uses a VTI; (B) The invariable time-interval clock [ITIC] which uses an ITI.

You recognize (A) that when time is measured using VTIs [in VTICs] the resulting time is local time [LT] within an inertial reference frame [IRF] and therefore different in different IRFs and (B) that when time is measured using ITIs [in ITICs] the resulting time is absolute time [AT] within each and every IRF and any and all IRFs.

You recognize that time is a temporal process by which a TI can be used to measure the occurrences of events and, therefore, time is not a physical process, and time is not a causal process.

You recognize that time can be measured as a Timepoint [T, as T1, T2, ..., etc., or as T+1, T+2, ... etc., or as T-1, T-2, ... etc.].

You recognize that a series of Timepoints, Ts, generates a Timemap, or Timeline: T0 [Origin] -> T1 -> T2 -> T3 -> ..., etc.

You recognize that an ITI can be used in ITICs to create a series of Timepoints which generates a Timemap/Timeline which is The Continuum of Time [CoT]:

Past Infinity <- ... <- T-2 <- T-1 <- T0 [Origin/Present Timepoint] -> T+1 -> T+2 -> ... -> Infinity Future

You recognize that by The Continuum of Time/CoT there is an arrow of time [AoT] which is caused by causality and which moves only from the past through the present into the future.

You recognize that mass is a resistance to a change of inertia/motion (position + velocity).

You recognize that mass is the unit of measurement of the resistance to a change of inertia/motion.

You recognize that mass consists of matter/energy [m/e].

You recognize that the science of physics consists of the study of m/e.

You define universes all reality.

You recognize that there is one-and-only-one universe. [Multiple/parallel universes are nonsense, because they would have to fit within the one-and-only universe which is defined/specified to be comprised of all reality.]

You recognize that the universe is comprised of three realities: (1) Space, the Spatial Reality; (2) Time, the Temporal Reality; (3) Physics (M/E), the Physical Reality.

As a PO, you will observe that for each and every Timepoint/T and any and all Timepoints/Ts there is an universal m/e configuration [M/EC] which can be measured by the use of an ISI and a unit of mass.

As a PO, you will observe that time travel is impossible because (A) any time travel would occur at later Timepoints than the previous Timepoint to which an individual or machine desires to travel, and, therefore, no 'travel' to a previous Timepoint can occur from a future Timepoint, and (B) time travel by an individual/machine to a previous Timepoint would cause the M/EC of that previous Timepoint to be different to account for the additional mass/(m/e) of the individual/machine who/which is the time traveler, i.e., the M/EC or the previous Timepoint would be increased [M/EC -> M/EC + m/e].

As a PO, you will observe that all the m/e of the M/EC at a Timepoint is accounted for, you will observe the M/ECs of previous Timepoints moving through space/time coordinates in a predictable series of positions and with predictable velocities; and because the M/ECs and the positions/velocities of the M/ECs of previous Timepoints are accounted for there is no possibility of a reversal of the position and velocity [direction and speed] of the M/EC.