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Why half of the life you experience is over by age 7

Have you ever observed that time seems to be going by faster as you get older?

There's a reason that one summer seems to stretch out forever when you're a kid, but zips by before you know it when you're 30. That reason is perspective, as a gorgeous interactive visualization, by Austrian designer Maximilian Kiener, demonstrates.

When you're one year old, a year is literally forever to you -- it's all the time that you've ever known. But as you grow older, one year is a smaller and smaller fraction of your total life. It's like watching something shrink in your rear view mirror.

This idea has stunning implications. It means that parents actually see their children grow up much faster than children perceive themselves to be.

It means that waiting 24 days for Christmas at age 5 literally feels like waiting a year at age 54. It might also explain why kids on car trips are always asking that annoying question, "Are we there yet?" A car journey actually feels longer to kids than it does to adults.

It's a simple concept, but the feeling is explained beautifully by Kiener's interactive. The interactive has you painstakingly scroll through each year, and experience how time seems to speed up as you "get older."

For example, when you are one year old, a year is 100 percent of your life. As Kiener writes, this theory was first put forth by Paul Janet in 1897. (Click on the image to enlarge.)

But the proportion falls sharply as you age. As you scroll through the years, you notice that each year takes significantly less time to pass by than the first. By the time you're eight, a year is only 12.5 percent of your life.

By 18, that proportion has fallen by half again. One year is now 5.56 percent of your life. As Kiener writes, your summer vacation in your first year of college feels as long as your whole 76th year.

After 30, the proportion begins to level off, and each year of your life is similarly short. By the time you're 35, one year is 2.86 percent of your life.

At 98, it's about 1 percent.

Kiener attributes this idea to Paul Janet, a French philosopher. The idea is that we perceive time by comparing it with our life span: The apparent length of a period of time is proportional to our life span itself.

We perceive our first few years to be much longer in duration than the years that come later -- as the graphic above this shows. If you measure your life this way, in "perceived" time rather than actual time, half of your "perceived life" is over by age 7. If you factor in the fact that you don't remember much of your first three years, then half of your perceived life is over by the time you turn 18, Kiener writes.

In mathematical terms, our time perception is logarithmic -- stretched out at the beginning and compressed at the end -- rather than linear, in which each year has the same length. If you don't know, or don't want to think about math, it's basically the difference between the graph on the left, which is how time proceeds according to calendars, and the graph on the right, which starts slow and then ramps up:

Perception likely isn't the only reason we experience time the way we do. One problem with Janet's theory is that we're not constantly experiencing our lives as a whole. We live in the moment, and we're not always thinking of or remembering our 20, 30 or 40-plus years.

More recent theories about how we experience time draw on psychology and science. One says that our sense of time is governed by biological processes that run the body. Researchers have long shown that we experience time as going by much slower when our body temperature is higher. So perhaps it's not a coincidence that children have higher body temperatures than adults, and also experience time more slowly.

Other theories have to do with attention, memory and emotion. One idea is that the passage of time speeds up with familiarity. As we get older, things become more familiar to us, and time slips by as a result. There is some evidence that we tend to remember events between the ages of 15 and 25 most vividly because we experience so many new things in that time. A related idea is that we can actually slow down our experience of time through paying attention to the present moment, what people call mindfulness.

There's likely some truth in all these theories -- our sense of time is very complex. Still, perception is an important, and particularly haunting, piece. Many of us feel that our birthday arrives "one day earlier each year," as this video by The Dictionary of Obscure Sorrows, says:

John Koenig explores the idea of time appearing to go by faster as we get older. (Video: The Dictionary of Obscure Sorrows, by John Koenig)

This might seem depressing -- it kind of is. But it's also a reminder to savor our time and remember that it is precious.

"Like many things, this will require some patience to get through," Kiener says of his graphic. "But in the end it'll be over faster than you thought or hoped it would be."

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