Is time an illusion?

Time works by measuring periods between the past, present and future. It has a SI base unit, the second, defined as about 9 billion oscillations of the cesium atom. In physics time is needed for measuring the rate of change, like velocity and acceleration. In the 17th century, physicist Isaac Newton based his laws of motion on the assumption that time must tick from one second to the next, with no difference between the length of any two seconds. In the other words time is constant scalar universally. This is a valid approximation in daily life but no longer when relativistic effects take place. In 1905, Albert Einstein asserted that the speed of light is instead constant. That cause that time must be relative and depend on the observer.  Einstein concluded that distinction between past, present, and future is only a stubbornly persistent illusion.

In the general relativity time is one dimension coupled to the three space dimensions. As discussed in the blog any energy content, especially a black hole, curves the spacetime around resulting in a gravitational effect. That means the spacetime and thus, the coordinate system gets curved, and the basis vectors of the dimensions are going to vary from point to point, which means their length and direction aren’t constant anymore. The basis vectors, including time, are getting shorter when one moves radially towards the black hole. While the space distances remain constant the time intervals must get longer. This then results in the effect we call gravitational time dilation. This shows up that near to a black hole time passes slower relative to observer far from the black hole. At the event horizon the length of the time basis vector actually shrinks to zero, which physically corresponds to time dilation going to infinity. To conclude, time is not scalar neither vector since it is not invariant in the coordinate transformations. Time is fundamentally viewed in modern physics simply as a coordinate label and is only meaningful in the context of spacetime, but not really by itself. 

So is the fourth dimension time at all? This dimension is needed to explain the rate of change. My hypothesis is that it provides a degree of freedom for elementary particles to distribute. Near to the black hole the wave function distributes more along that obscure dimension and less along the more familiar space dimensions. It shows up that observed events happen less frequently. Inside the event horizon of the black hole all elementary particles live in the fourth dimension entirely and are not visible in the space. The rate of change is actually the cause for the gravitation, and it is a direct measure of the difference in the gravitational potential. When there is energy concentrated it slows the rate which leads more energy to be clustered. This determines how the objects in the universe are moving on theirs geodic paths or light rays are deflected in gravitational lensing. Time is not a dimension that can be ever traveled on. Only the rate of change can be controlled by selecting proper conditions. For example, by being in the proximity of a blackhole or by flying nearly at the speed of light a person could age slower compared to relatives on Earth. When coming back to Earth the person can feel being traveled to the future. However, it is not possible to travel back in time by known physics.  However, it has been argued that wormholes would allow traveling into the past, since they can connect very distant locations in space. In theory, a wormhole could provide a short-cut passage to the younger universe. However, getting back to Earth is likely impossible. 

The most of laws of physics are time symmetric including the general relativity. As an example if you take a video recording of a planet orbiting a star, you cannot distinguish if video is played backward or forward. As an exception, the second law of thermodynamics states that everything in the universe tends to move from low to high entropy (more in the blog), or from uniformity to disorder. This is known as the "arrow of time," likely coined by British astronomer Arthur Eddington in 1928. Entropy determines the direction of any change and order of events in the universe, but is not connected to time necessarily. It is questionable if time really exist physically. Or is it purely a human construct to measure the rate of change? In 1908, metaphysician McTaggart presented the idea that time exists only if change exists, and the question then becomes how to represent time. He defines the A-series that orders times according to whether they are past, present or future and by how far into the past or future they are. He also notes that we can order times according to whether they are earlier than or later than one another, giving the B-series. McTaggart argues that time cannot be constructed by neither of the series since they are contradictory themselves, and thus time is unreal. To many physicists, while we experience time as psychologically real, time is not fundamentally real. At the deepest foundations of nature, time is not a primitive, irreducible element or concept required to construct reality.