Time And Space As you write you move the pencil through space, and it takes time to trace a word. This is so commonplace that it is not worth mentioning. Yet if some innocent were to ask you,"What is space?" or "What is time?", what would you say? There was a time a mere 100 generations ago, when a day was 24 hours long, because it took the sun 24 hours to move across the sky and return in some obscure fashion to its starting position. The unit was one day. It was arbitrarily divided into 24 subunits. Notice that no attempt was made to state what time is. Although a few educated Greeks of the classical period understood that the earth was spherical and was in motion relative to the sun: as recently as the sixteenth and seventeenth centuries, most people believed that the earth was the fixed center around which everything else moved. So what is time? It is an abstraction, a concept, a product of human imagination. What is the reality behind it? Matter is real. What matter does is real. Matter interacts with matter. The interaction is the cause. The aftermath of the interaction is the effect. We think of the cause as preceding the effect in time. Chemists can depict actual reactions as reactants = products. The equal sign indicates that the reaction can go either way. Does that mean that time can be reversed? No, the proper way to write the reaction is to include such remarks as energy in or energy out, or entropy so and so, or temperature and pressure, etc. Whereas it is true that the reaction can go either way, the reversibility requires a new set of details. There is no turning back to a previous situation. Now let us consider space. Every interaction involves a push or a pull. The strength of a push or pull varies with the distance between the participants. The distance is not a thing. The participants are real things. Reference to them is usually in terms of comparison with other real things, preferably measuring instruments. Many products are sold by the volume: gasoline, milk, orange juice, detergent, etc., in other words, according to the space they occupy. The space is defined by the container. Space is not a thing in itself. When something is moving, it has a velocity measured in centimeters per second. If the observer is moving at the same velocity alongside the thing that is moving, it seems to be stationary. The theory of special relativity states that, from the point of view of the observer, moving bodies behave as if their clocks run slow, their proportions (height vs. width ) , are altered, and their mass has increased. If the moving body were large enough to carry a scientist, that person would report that everything is normal, the clock, the yardstick, and the scales. So what's the big deal? The mathematics that is developed by the stationary observer produces an absolute figure for the speed of light. Nothing that has mass at rest can attain the speed of light, because, at that speed, its mass would be infinite, which is absurd. Accordingly, the photon, which is light, moves at the speed of light, and therefore has no rest mass. Nevertheless it has a mass which can be calculated via its kinetic energy, which is proportional to its frequency. This, by the way, was arrived at by actual experiments in photoelectronics. There is a better reason to say that a photon has no rest mass. A photon never exists at rest. However, the stuff that the photon is made of does have rest mass, but this was unknown before nuclear physics. With the development of particle accelerators, we learned that a body gains mass as it gains speed, regardless of what the observer is doing. Having said that nothing can move faster than the speed of light, the writer of science fiction predicts that, if one moves faster than the speed of light in a vacuum, his clock runs backward. There is one candidate for the office of "time's arrow", and that is entropy. Every process increases the quantity of entropy in the universe. A simple example is the smoke that issues from a chimney. If we could run that backwards, the smoke would reassemble and go down the chimney, and the atmosphere would get a trifle cooler. The theory of general relativity demonstrates that several consistent explanations can be advanced for any natural phenomenon. For example, gravitation and acceleration can be rival explanations for our sticking to the earth. Another example is the bending of light from a star can be due to gravitation or else the curvature of space time. My preference is the neg-pos theory. It serves more purposes , and it does not elevate space and time to the category of possible causes of physical events. For example, the motion of a body is caused by the arrival of neg-pos bits, and the increase in mass when a body gains motion is the mass of the bits received. The gain in mass as a body gains speed is real. It has nothing to do with observers or the state of motion of the observers. Likewise, motion is not merely relative. It is absolute and should be measured by counting the bits or by measuring mass. Unfortunately, we do not have an exact figure for the number of bits in a particle of matter. We do not know how much mass a body should have when perfectly motionless. In any event the bodies of matter that are larger than molecules do not move anywhere near the speed of light, so we can't measure so small a quantity of mass as we are trying to measure. However particles have been observed with great gains of speed and mass. You may have noticed the difference between the statement that mass can be converted into energy and the statement that mass and energy are merely two ways to measure the quantity of matter in a body. The same equation, E = mC2 , applies to both statements. Einstein's mathematics produced the equation. Einstein reasoned that the laws of nature are the same for all observers. The observer in the laboratory will observe that the moving clock is slow. According to natural laws, a clock slows if its parts become massive. Einstein had to calculate the energy required to increase the speed of an object whose mass increases when the speed increases. His mathematics was correct, but his conclusion should have been that an increase in energy and an increase in mass go together. Instead he said that an increase in energy causes an increase in mass, and energy can be converted into mass. Although Einstein signed a letter to President Franklin D. Roosevelt, which stated that nuclear mass can yield energy, Einstein did not participate in the production of the atomic bomb, and relativity was not a factor in the invention of the atomic bomb. However, the textbooks in nuclear physics do use terms like "mass defect" and "missing mass". This only goes to show that practical physics and chemistry can function successfully without any fundamental understanding. An interesting commentary on Einstein and space-time can be found at the nature of gravity essay