For centuries humanity has been measuring and marking the passage of time. Cultures and religions in many cases evolved independently of one another, giving rise to differences in measuring the passage of years. This can be seen in the differing years and dates across calendars in Buddhist, Christian, Islamic, Jewish, Maori, and other cultures. Despite cultural differences in measuring years, as in the example of the Islamic calendar’s 355 days or fewer per year, the measurement of hourly time is a relative constant.
This is because hourly time is based on a system where every day consists of 24 hours, each hour is made up of 60 minutes, and every minute lasts 60 seconds. On paper it is an extremely precise measurement, but in reality it is more of a very precise average. It is an average due to variances in the earth’s rotational speed, which change based on differences in climate, or geologic activity. While that change is minimal, it does result in the occasional need for a leap second to be inserted so our tracking of time remains accurate.
Every country has its own system for establishing the exact time at its location, but people don’t always use those systems. That tends to create minor variations in observed time from place to place in a given region, but generally each government will have a central point of time measurement that is more or less drawn from or equal to the accepted international standard. This allows citizens of every nation to keep relatively consistent and accurate measurement of the time in respect to one another, despite the occasional minor variations regionally.
If, however, one travels internationally, keeping track of the current time brings with it a whole new set of problems. For starters, the majority of the world no longer observes daylight savings time, but they know what it is. On the other hand, some countries have never observed the practice, and others continue to use it. In fact, some countries have regions that observe it and others that don’t. Couple that with slight differences in time standards across the various zones of the planet, and many travelers resort to the use of internet-based systems to help them track time.
Of course, helpful as these applications are, they only enable one to monitor and react to changes in the time. What about actually understanding it? While time is something everyone understands as a tool for measuring the passage of a day, it is rare for anyone to actually question just what time is. Those who do raise questions quickly discover that there is much more to time than clocks. It is a difficult subject to wrap one’s mind around, and the last real breakthrough on the subject centered on Einstein’s theory of general relativity.
The reason time is hard to understand has to do with how humans naturally observe the world. For example, no matter how quickly or slowly a person throws a baseball, the ball and the objects around it don’t change, and no one would expect them to change. The ball, whether at motion or stationary, is still just a ball, and the person throwing it is still the same person both before and after he throws it. Time, however, does not operate that way, because it is relative to the observer and his position in relation to the object. To oversimplify with the example of the baseball, the faster the ball is thrown, the slower it will travel through time – but the person watching would only see a ball moving very fast. This is known as time dilation, and it is one of the reasons time is perhaps the least understood subject of modern science.
One reason it is so hard to understand is that there are two types of time dilation. There is gravitational time dilation, which is basically how close you are to the center of gravity in your gravitational field, and then there time dilation due to relative velocity, which is how fast an object is traveling. This was explained earlier in the example of the baseball. As you might expect, both can occur simultaneously; therefore an object like Earth has gravitational time dilation due to its gravitational field, which slows time down the closer one gets to the center of the planet. Because the earth is moving, it also has time dilation from relative velocity, also slowing time down.
A gross oversimplification of this in practice, would be that of a spaceship moving at 90% of the speed of light. For everyone on the spaceship, time would pass normally, and they would age normally. Everyone back on earth would experience their version of the same thing: Time would pass normally for them, and they would age normally. However, because the the spaceship is moving so fast, time dilation due to relative velocity would cause time to slow down on the ship relative to the people back on earth. To be precise, every year the ship was in space, two years would pass for the people on earth. Both groups of people would basically be existing in two separate instances of time. None of them would notice any difference in themselves or the things around them, and everyone would age at the exact same rate – relative to their positions in time.
That means that if the ship were in space for 20 years, the crew would return home 20 years older, but everyone back on earth would have aged 40 years, because the position in time they were occupying was moving faster than the position in time of the people on the ship. It it’s confusing, don’t worry, you’re not alone. The equations and supporting theories that make these seemingly impossible calculations possible are quite complex, and there are enormous numbers of variables that come into play. Many theories exist about how time works, and the research supporting or refuting them grows every day.
So, the next time you look at the time, consider how different it is than anything else you’ve probably ever learned about the laws of physics and the universe as a whole. As a species we’re constantly expanding our understanding of the world around us and how we relate to it, thanks to science, a bit of luck, and good timing.
Image Credits: Feature Image: ’Scorpius and the Milky Way‘ Article Image: ‘Time Travel Haikus 5-7-5‘ Article Image: ‘Most Amazing High Definition Image of Earth – Blue Marble 2012‘ Article Image: ‘Warp Speed‘ Found On: flickrcc.net