Time is perhaps the greatest mystery of all and is deeply wrapped up in our conscious experience of things. For Newton time was absolute, with Einstein time became more flexible and relative in scope. However, no one has been able to fully explain what it is really.
1: Time Is The Fourth Dimension
Simply stated, the first three dimensions are used to specify an object’s location/movement in space (forward-backwards, left-right and up-down), while the fourth dimension locates its position in time. All four dimensions are used to specify completely the location or dynamism of an object in space. Collectively the four dimensions are inseparably interlinked and known as space-time.
2: Three Dimensional Creatures
Being three dimensional creatures (possessing length, width and height), humans are unable to see the fourth dimension as our physical world is constructed within these three physical dimensions. We might feel or intuit time’s presence, but we can never actually detect it with our three-dimensional senses because it extends beyond our universe. Humans only perceive the fourth dimension time as memories lodged at variable intervals, the result of which is our apparent perception of time moving forward in a straight line. However, time still exists as a dimension and objects can cross it in a similar way as they do the others, although three dimensional like humans can only move in one direction forward through time. If we could see an object’s fourth dimensional space-time (or world-line) it may resemble a spaghetti-like line stretching from the past to the future showing the spatial location of the object at every instant in time.
3: Space And Time Inseparable
Space And Time are simultaneous phenomena (like mass and energy), and together form the fabric of the universe known as space-time. A demonstration of four dimensional space-time’s inseparability is the fact that, as astronomers often remind us, we cannot look into space without looking back into time. We see the Moon as it was 1.2 seconds ago and the Sun as it was 8 minutes ago.
Also, in accordance with Einstein’s general theory of relativity, a massive object in space stretches the fabric of both the space and time around it. For example, our Sun’s mass bends its surrounding space so that the Earth moves in a straight line but also circles within the Sun’s curvature in space. The Sun’s affect on time is to slow it down, so time runs slower for those objects close to the massive object. Interestingly, gravity is the result of mass stretching the fabric of the space-time around it. Gravity also has an infinite range such that no matter how far apart two masses are in space they will always experience some gravitational pull towards each other. Theoretical physicists have tried to explain this phenomena in terms of gravitons, S-Theory, and M-Theory, but even today a successful quantum theory of gravity is yet to be found.
4: Time And The Speed Of Light
A property of light is that it always travels at the same constant speed in a vacuum of 186,000 miles a second (700 million mph) and you can’t go any faster. The reason for this is that mass increases with speed all the way to infinity and so an infinite amount of energy would then be needed to travel beyond the speed of light.
The mathematical equations states that Speed = Distance ÷ Time. However, the Speed of light (c) is fixed, and as you travel at relativistic speeds, or those speeds in which the relativistic effect becomes significant, then the Distance and Time values in the equation start to change. What actually happens is that Time and Distance are ‘relative’ to one another, and as you travel close to the speed of light, distances become shortened while time is lengthened. This is explained in Einstein’s theory of special relativity.
For a person traveling at 99% the speed of light, Time slows for them by a factor of 7. If they were to travel to a star 7 light years away, at 99% speed of light, it would take them 1 year, but to an observer on Earth it would have seemed like 7 years. However, if that person attained 99.999% the speed of light, only 1 year would pass on-board for every 223 years back on Earth. Finally, You don’t need to travel at light speed for time dilation to occur but you won’t notice the effects until you go extremely fast.