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Nov 16
2009
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One of the major discoveries of relativity is that the Universe is a four dimensional construct, three of space and one of time, spacetime. It was also a surprise to find that the dimensions of space and time are connected, that changes in one can effect changes in the other. In addition, relativity plus experimental evidence demonstrate that the Newtonian concepts of Absolute Space and Time are incorrect and that spacetime is malleable, although it has an independent existence as proposed by the philosophical view of substantivalism.
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However, these descriptions of the fabric of spacetime go against our common sense. Space as a void was rejected for many years with the argument that a vacuum is nothing, and what is nothing does not exist (nonexistence is a property of nothing). Aristotle believed that space had to be `dressed', meaning that a continuous covering of material substances are required to make space real. For Aristotle, this dressing was the fifth element, ether.
Leibniz continued this idea of the link between space and matter by stating that this is no space where there is no matter, called relationism. For Leibniz, space has no absolute reality and, in particular, no
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Aristotle
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This view held till the middle of the seventeenth century when experiments with air pumps convinced many scientists that space could exist without material covering. Newton developed the idea of an `undressed' space, a continuum existing in its own right, absolute and independent of all it contains. Descartes combined geometry and algebra into analytical geometry, a mathematical tool that uses coordinate systems to determine relationships in space (i.e. the Cartesian x, y and z coordinates).
Thus, space became, for Newton, the thing that surrounds us, stretching off into infinite, in which objects are distributed. It is spanned by intervals of distance that can be measured in units such as miles or meters.
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Newtonian Time:
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Time is not so simple to understand as space because we can not observe bodies distributed in it. We do not observe time with the same five senses that we use to observe space. The nature of time is a perplexing subject and has provoked endless philosophical discussion. Modern physics deals with time as an addition dimension to our reality. The typical tool to study time is a space-time diagram.
In a spatial diagram, a point represents a location in space. In a spacetime diagram, a point represents an event, something that has a location in space and time. An example of an events is a movie time, it has a location (the theater) and a time (the showtime). A line in a spacetime diagram, called a world line, represents something that exists through time, an object.
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The fact that time is treated as an extra, fourth dimension does not mean that it has identical properties to the other three spatial dimensions. The formula for calculating spacetime distances is not the same as the one to calculate spatial distances (the speed of light comes into play). Causality is also strongly dependent on the distinction between space and time. The special nature of time prevents cause and effect from being hopelessly jumbled. And unlike the spatial directions, the future is at least partially determinate or else all would be chaos.
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The Present or `Now':
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The physical view of time is one where a 4D spacetime continuum exists as one entity. Thus, our everyday notion that time passes or is in flux is an illusion. While this is difficult to understand, or accept, there are numerous examples where our conscious perceptions differ from physical reality. For example, perception of color differs slightly from individual to individual, however, the physical interpretation of color is simply the wavelength of light emitted or reflected by an object.
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Of course the key moment in our conscious perception of time is the present or now. The present marks the boundary being the past, which we have memory of, and the future which we have little or no knowledge. In a spacetime diagram, the present is indicated by a line horizontal to the spatial axis. As time passes or flows, we represent this by moving the present line upward at a rate of one sec per sec. For human minds, the present line is not perfectly thin. Our perception of time is fuzzy at about the 1/16 of a sec interval. For this reason, single images can be strung together at speeds greater than 1/16 sec to create the illusion of motion and time in videos.
Its not uncommon for our common sense view of the Universe to differ from the more exacting view presented by physics. The psychologically manifestation of physical events is what makes up our perception of the world around us. Take, for example, the old riddle of when a tree falls in a forest and noone is there to hear it, does it make a sound? A physics response to this riddle is that the falling tree does indeed make a wave of compression of air. But it takes a psychological view to explain that the compression of air on a human ear produces the perception of sound in the brain.
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The problem of our perception of time flowing involves a mixture of metaphors concerning the nature of time and the confusion surrounding the ideas of `being' and `becoming'. So far, despite the efforts of centuries of philosophical inquiry, we have been unable to connect the concepts of temporal continunity (states of being) and transience (states of becoming). For example, are you the same person that you were 10 years ago? In some ways, yes, in many ways, no.
Physics deals with this problem by claiming that transience is a non-physical peculiarity of living creatures, following the Parmenidean doctrine that the real world is unchanging and transitory experiences are illusions. The concept of `now' was destroyed with special relativity. Einstein predicted, and experiments confirmed, that the definition of the present varyed with observer, and with the motion of the observer. This also confirms the poor meaning behind the phrase `the passage of time'. The notion of time flux is internally inconsistent. Since flux refers to motion, a change in space with time. What does it mean to speak of the movement of time? Relative to what does it move? How fast does time move? One sec per sec is a trivial and meaningless answer. These arguments have led support to the idea that the flow of time is unreal, but time itself is as real as space. Motion through 4D spacetime occurs at one speed, the speed of light. When we have zero spatial |
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