Is time travel possible?
The laws of physics in the microscopic world suggest that it is because the physical processes they define at the subatomic level appear to be either entirely or mostly time symmetric. In other words the theoretical statements that describe them remain true if the direction of time is reversed. However, the opposite is true in the macroscopic world in that there is an obvious direction (or flow) of time. In others words, process in our macroscopic environment are observed to be asymmetric with respect to the direction of time appearing to rule out the possibility of traveling backwards in it.
Therefore, one way to understand why we as a civilization have been unable devise a mechanism for traveling back in time may be to understand difference between the macroscopic and microscopic worlds with respect to it because in one it seems possible while in the other it appears not to be.
Entropy appears to be the only quantity in the macroscopic world that "picks" a particular direction for time. As one goes "forward" in time, the second law of thermodynamics says the entropy or disorder of an isolated system will increase when no energy is consumed. In other words many in the scientific community believe the reason a system composed of multiple units must always move in forward with respect to time because to go back to a previous configuration one must add energy to it.
However, one cannot apply the concept of entropy to the microscopic world of atoms to determine its direction with respect to time because the entropy or relative disorder of system composed of signal entities such as an atom does not spontaneously increase as it moves through it. Therefore, one cannot use it to define its direction in microscopic systems because it does not quantifiably change as one "moves" through time.
Yet both these definitions define the direction or flow of time in terms of the physical configuration of its spatial components. For example, entropy or relative disorder of system composed of a signal atom does not spontaneously increase as it moves through time because its spatial position can only be reference to itself. This differs form systems that contain multiple entities in that the spatial configuration of its units can be compared to others in that system. The only difference between them with regards to defining their entropy with respect to the movement of time is what their spatial locations are reference to.
However the fact that we have been unable to move backwards in time in the microscopic universe suggests the casualty of time in that environment may not be related to the physical movement of an entity but to the causality of a quantifiable change in the spatial components of a system similar to the one that gives us direction for time in a macroscopic system.
For example in a multiunit system the causality of the increased entropy associated with the forward movement of time is directly related to its thermodynamic energy because it is what quantifies the direction of the changing spatial disorder in a system. Similarly in a single component system the sequential ordering of the causality of it moving to the left and then to the right will always define the direction of time in terms of its changing spatial position. In other words on can define the direction of time in both in terms of the causality of the systems spatial components.
As was mentioned earlier the second law of thermodynamics which defines the passage of time in the macroscopic world is based on a statistical definition was developed by Ludwig Boltzmann does not hold with strict universality: any system can fluctuate to a state of lower entropy.
However scientists have observed billions of particle collisions in which two particles collide to produce other particles however they have never observed two particles spontaneous coming together to form one particle even though statistically speaking they should happen much more often than in multi particle systems because they have considerably less complexity.
Therefore understanding the causality of the change in the position component of entities in both macro and microscope system may tell us if travel time travel is possible.
As was shown in the earlier article "Defining what time is" Sept. 20, 2007 defining the direction of time in terms of the sequential ordering of the causality of events would a provide a consistent direction for time in all environments because the causality of an atom moving to the left in both single or multiple component system would always be proceeded by the causality of that the same atom moving to the right; even though, as was mentioned earlier the behavior of the atom is not qualitatively different in either case. This would be true in both our physical and mathematical perceptions of time.
In other words defining it in terms of the sequential ordering of the causality of an event is consistent with the observation that events appear to always move forward in time in both the macroscopic universe and the microscopic world of particle accelerators because the casualty of particle breaking up into different parts must always proceed those parts coming together.
Some might think that it is not possible to tell the order in which events occurred without using time as a reference. However one can use the spatial properties of a system to determine it because the first event in a series would only be connected to the one before it while all other would be connected not only to that one but to the one after it. In other words one could determine the order in which the events occurred by referencing them to the one that has only one spatial connection and following the single line of events back towards there origin.
However this also rules out any possibility of one traveling through time because if it is only a measure of the sequential ordering of the causality of events then similar to all measurements it does not have physical properties so because one cannot travel through or in something that does not have a physical structure time travel is physically possible.
Copyright Jeffrey O’Callaghan 2016
Vol. 5 — 2014