Time is such a consistent, dependable and uncontrollable part of life’s background that there doesn’t seem to be much need to worry about what it is. But just as the Bible tries to stretch our concepts of God and life beyond what we’ve derived from this palpable universe, it tries to stretch our simplistic views of time with varying degrees of success. As a result people argue over a number of religious issues involving time: whether creation took 7 days of 24 hours, or 7 eons; the timing of events in the Apocalypse1; what happens to people after death; and others. Perhaps it would change the character of the debates if we take into account what we’ve learned lately about the nature of time.
The objective of this post is just to provide the background we need and get those little gray cells doing a few warm-up stretches.
Since we measure time with human built clocks, we will be talking a lot about clocks. They are simply devices that quantify the passage of existence.
Our natural inclination, based on experience, is to think that a perfectly running clock will always measure the same extent of time no matter where we take it. A minute or an hour should always be the same as long as the clock’s mechanism works correctly, right? Well, our present knowledge of physics throws a wrinkle in that assumption. If you hold a perfect clock2 in your hands, it will always appear to you to run at the same rate. But when you look at someone else’s clock, and they look at yours, well now, you may be surprised, because what you see will depend upon where each of you are in the universe and what speed you two are moving at in relation to each other.
Let’s take a run through time…er.. history.
Before the time of Christ, people generally thought the world was the center of the universe. Whatever their conception of the universe, it included the ideas that the earth was at its center and that what is seen in the sky moves past the earth. This implied two comforting thoughts, the idea that something could be at “absolute rest” (the cessation of all motion) and a closely related concept of there being a physically unique absolute reference point in the universe – the one place that’s not moving.
When Kepler, Copernicus, and Newton came along in the 16th century things changed. It became clear that many heavenly objects were not just mysterious lights moving in the sky but roughly spherical bodies at great distance from the earth moving in orbits around the sun according to predictable rules of motion and a mysterious gravitational force. It was problem enough that their findings required giving up the idea that the Earth was the center of the universe, but the real profound change that comes from their work is the conclusion that there can be no object in the universe at absolute “rest” and therefore there can be no center to the universe. Everything is moving in relation to everything else!
Let’s see what this might mean. Imagine you are in a space suit floating in a place in a spot where there is no gravity and where you cannot see any background whatsoever – everything around you is pure black. As you shine your flashlight, – you brought batteries right? – out into the void and notice another space-suited person whizzing by with their flashlight pointed at you. It turns out there is no way to prove who’s moving. Are you at rest and they are moving? Or are they at rest and you are moving? Or are you both moving? You see there is no concept of a place that is at “rest” in the universe and since all objects are moving, there is no natural point of reference, just an arbitrary one we might choose to designate for the sake of convenience.
That’s two absolutes gone: nothing is at rest and there’s no center to the universe. OK, you’re a modern person, no big deal, you can handle it. Eventually people accepted all this but were still comforted with the idea that the entire whirring universe was traveling through time at the same rate because time is, well time. It passes at the same rate everywhere and every-when, right?
But when scientists became convinced that Einstein’s theories were true, that sacred absolute had to go, yup, right in ye ol’ trash bin. Wave goodbye as the trash man takes it down the street. Your time (as measured by a clock) will pass along at the same rate as far as you can tell. However when your clock is observed by another person, that person could discover that it is faster or slower than their clock and vice versa (remember both clock mechanisms are working perfectly). Time does not pass at the same rate everywhere in the universe. That means that the universe doesn’t pass through time, but that time is part of the universe in some weird way. Still awake? Hang in there for a just a bit longer.
Time flies, or crawls. I can never tell.
If person A is very close to a very massive body like a planet or star, observer B who is far away, will think that A’s clock is running very slow. B sees A running in slow motion. A, on the other hand will think that person B’s clock is running fast. B looks like they just drank a gallon of caffè espresso. The more massive the body near person A, the more the difference each sees. Yet both people will think that time is passing at a normal rate for themselves.
Believe it or not, this has practical use. The well known Global Positioning System (GPS) uses satellites located 12,000 miles above the earth to locate objects with an accuracy of several feet. To accomplish this, a receiver on earth picks up and processes time signals from extremely precise clocks on several satellites and compares them. These satellites are so far from earth, and the time signals require such precision that the system has to account for the fact that there is a difference in the rate at which the satellite clocks (far from a massive body) appear to run compared to clocks on earth (close to a massive body). The difference is not noticeable to humans, but if not accounted for, GPS devices would be much less accurate.
OK, so the intensity of gravity somehow has an affect on clocks.
Ready for another one? You like travel right? Let’s pick a star that is 4.45 light years from Earth like Alpha Centauri. That means that light from this star, traveling at 186,000 miles per second, takes 4.45 years to
reach Earth. Suppose one of two twins3 was placed in a space ship at birth and that the ship instantly accelerated to 86.6% the speed of light, traveled to the star and returned4 (with no layover). From Earth’s perspective the trip will have taken 10.28 years so when the ship returns, the twin on Earth is 10.28 years old. However the traveling twin turns out to be physically 5.14 years old! Yet measurements taken by the doctors on the journey show that their kid’s heart rate and biological growth were absolutely normal. How did this happen?
Those clocks again. The ones on earth didn’t run at the same rate as the ones on the ship. It isn’t just the clocks. Something about the very nature of the universe caused the actual passage of time to be different for the two twins. Where did it change? On the ship? That would assume the Earth is the reference. But the universe doesn’t care about reference points. As far as the people on the space ship are concerned they stayed still and the Earth rushed away from them so the ship was their reference point. The change was a function of their relationship. This gets very weird and requires lengthy explanations and lots of rest between each point, so let’s just say that time depends upon relative speed between the observers. We are not normally aware of this because none of us has any friends or relatives that travel past us fast enough – do we?.
This isn’t just theory. Scientists have found that when they create a high velocity head-on collision of two certain atomic particles, the wreckage spits out a new object that self destructs in exactly 2 billionths of a second. This is very repeatable. So they decided to conduct the entire experiment close to the speed of light. It would be as if you had two cars in a head on collision while the entire roadway was moving near the speed of light. Guess what happened. The object now appeared to live 9 billionths of a second. Did it live longer? Well, according to its own clock, it self destructed right on schedule, in two billionths of a second, but to us it took longer, just as in the twin paradox.
Let’s review. Two observers watching each other will find that the other person’s clock doesn’t function at the same rate as their own if they are either 1) moving in relation to each other, or 2) if the intensity of gravity is different between them5. Yet each observer will think their own clock is ticking away normally.
How fast does time go when you’re asleep?
Ok one more thing and then you can put some ice on your overheating brain. Apart from clocks which 
provide an objective measurement of time, human perception of time is highly dependent upon our conscious state and some chemical processes inside the body.6 For example as we grow older, we perceive days as passing faster because they become a smaller percentage of our lifetime. In addition, perception of time is affected by our level of consciousness, drugs, illness and body temperature.
The bottom line
There are no natural absolute points of reference in either space or time. Not only does time itself actually pass at different rates in different circumstances but human perception of time is very subjective. (That’s why we have clocks.)
For now the only physical reference in the universe is the speed with which light travels. Everyone will measure it to be the same no matter where they are and how they are moving. Unfortunately it is this very fact requires that both physical space and time be flexible (not fixed) at least as far as we now understand the physical attributes of our universe.
Go rest for awhile (how long? – well now that depends….) while I write the next post.
Footnotes- The Revelation, also called The Apocalypse, is the last book of the Bible complicates analysis because it describes events on Earth from Heaven’s dimension [↩]
- A perfect clock has no defects and always runs at the exact same rate [↩]
- The Twin Paradox [↩]
- Assume the ship can instantly reverse course at full speed when it arrives at Alpha Centauri and instantly stop when it returns to Earth. [↩]
- Again I’ve oversimplified the issue because actually motion and gravity are interrelated in a way that is not intuitive to us [↩]
- Links: Stanford Encyclopedia of Philosophy The Subjective Scale of Life [↩]
