Thu 5 Mar 2009
Is time immutable, or is it subjective? Philosophers have debated the nature of time, and whether it is intrinsically ordered and has tense. I have devised a mind experiment to show that time depends not only on the observer, but the observer’s position, that before, after and simultaneous are subjective.
Visualize two observers on opposite sides of a town, one north, one south. Both have clocks that were synchronized, and the observers moved slowly apart, so that relativistic effects on their clocks is insignificant, and flash detectors connected to the clocks to properly record the time of lightning flashes.
A storm comes up, and a lightning stroke hits in the middle of the town. The two observer’s flash detectors record the time of the flash, and agree on the time. The light from the flash travels to the flash detectors at the speed of light, producing a time delay of approximately 3.33 microseconds per kilometer. Lets say the the observers are 6 km apart so the delay from the stroke until the observers detect it is 10 microseconds, and both of them agree on the time of the lightning stroke.
Lets now assume that there are two lightning strokes, one near the north observer and the other near the south observer, and from the “god’s eye view” (lets say, from the point of view of an astronaut on the moon) the north stroke took place at Time = T and the south stroke took place at Time = T + 5 us. “God” would say that the north stroke took place first. The north observer would agree, but would claim that the south stroke took place 25 microseconds before the south stroke.
The south observer would disagree, the south stroke took place 15 microseconds BEFORE the north stroke!
The speed of light is the limit of the rate of information flow in the universe, and is the basis for the visualization of the “time cone” where occurances at a distance from an observer are experienced at a later time than it would have been experienced by a proximate observer
Looking at our example, you might say: “Well, what is a few microseconds among friends? My senses cannot register microseconds – I would need a fancy chronometer to gauge that kind of error.” Well, lets look at things on a bigger scale, an astronomical scale.
Let us now assume that it is January 2011, when Mars is generally on one side of the sun, and Earth is generally on the other – with nearly maximum distance between the planets, and assume that we have an astronomer on earth and an astronaut on Mars, and they both have their clocks set to Universal Coordinated Time, and both clocks were moved slowly. Both astronauts are looking at Antares, a large star in the constellation Scorpio about 600 light years from earth. The earthbound astronomer would also see Mars, as Antares is in nearly same direction as Mars is from Earth (in January 2011).
Let us imagine that in 1411 CE while Joan of Arc was raising her armies here on Earth, the folks living on a planet orbiting Antares were seared by their star going supernova. A supernova is a sudden and extreme explosion of a star. Before the light from the supernova got to the astronomer and the astronaut, they would have no knowledge of the event. For them it happens when the light gets to where they are. The astronaut would log Antares as going supernova twenty minutes before our astronomer. If instead they were looking at a star in Ares going supernova, the astronomer would be twenty minutes ahead of the Martian astronaut. If it had been Polaris going supernova (the pole star – at an angle perpendicular to the ecliptic) they would have agreed on the time of the nova.
What has all this got to do about time? My intention was to point out that simple Newtonian time (without even getting into relativistic effects) cannot be treated as a constant, but depends not only on the clock, but the observer’s position. You and I, even sitting across the room from each other do not inhabit the same time, merely a similar time, as our “time cones” originate from different positions. When these positions are further apart, the discrepancy becomes greater.
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