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The Direction of Time

time-directionDespite most of things we do is dependent on time, we still don’t fully comprehend what time is really is! Our everyday experiences condition us to view the flow of time to be toward one direction, the future. So why can’t time flow towards the past? Why do events unfold in only one direction? Common sense dictates that this reverse flow goes against the laws of physics. Or does it?

The laws of physics are the mathematical equations used to measure anything in the universe. These include the movement of the stars, how atoms behave, and the formation of galaxies. Centuries of observation and experiments have been performed in order to come up with these equations. And even if it is a widely accepted principle, there is nothing in the laws of physics which state that events have to flow towards the future. Actually, these equations dictate that events can also flow in the reverse.

In reality, most of the equations we use to describe the universe don’t have an arrow of time assigned to them. As a matter of fact, some equations function equally well for both forward and backward motions. It just becomes harder for us to understand this concept because the laws of physics appear to be reversible while several aspects of our lives feel like they are irreversible.

To better explain this, imagine dropping a glass bottle onto the ground. Common sense dictates the bottle will explode into pieces if you drop it from a high enough level. It would seem incredibly far-fetched for the shattered pieces of glass to move in a reverse motion in order to form the glass again. Nevertheless, the laws of physics state this may be done. The only thing needed is to reverse the velocities of everything. The glass bottle will return to its original form by reversing the velocities of each piece of shattered glass, any liquid, air, every atom and molecule.

Confused? That’s usually the initial reaction of people who learn about this theory. One of the most common questions people ask is “if it doesn’t matter to the laws of physics whether the glass bottle is shattered or not, how come we don’t see them form back from a shattered state?” To understand how the arrow of time works, we must align the laws of physics with our everyday experiences.


To answer this mystery, experts have turned to the tombstone of 19th century Austrian physicist Ludwig Boltzmann. The graveyard where his remain lie is also the final resting place for other great minds such as Beethoven and Strauss. The equation S=K log W is engraved neatly on the top of Boltzmann’s tombstone. This is the mathematical formulation for the formidable concept of entropy. Even in death, Professor Ludwig Boltzmann wanted to spread the world about the concept of entropy. So what is entropy and how does its concept tie up with the laws of physics?

Entropy is the measurement of the number of specific ways a certain system may be arranged and is often governed by randomness or disorder. This is considered a valuable aspect in the study of physics because everything in the universe has a tendency to move from order to disorder.

For example, the pages of a book are bound together in an orderly fashion. They usually arranged from the first page up to the last page. However, if you tear off the pages and throw them in the air, entropy will do its work and the pages will be scattered which will make them every disordered. There is only one way for the pages to land in order but there are several ways for them to land in a total mess. So there is a bigger possibility for the pages to land in a disorderly manner.

This also happens in our daily lives. Everything in the universe can move from order to disorder and the entropy that surrounds us only increases as time goes by. This is manifested in numerous ways such as the melting of ice into water, burning of dry leaves which turn into ash, the decomposition of dead animals, smoke from cigarettes disappearing in thin air. This transition of states from order to disorder seems to be the direction of the arrow of time. And because of entropy, we see disorder tends to increase in only one direction of time. This is what gave Boltzmann the idea about the movement of time.

Some experts point to entropy as the answer. It’s possible that the arrow of time moves according to the natural tendency of things to move towards disorder. However, there’s a slight drawback to this conclusion. This doesn’t make sense because the laws of physics do not discriminate between the past and the future. This means entropy can increase both towards the past and the future.

In the next article, entropy will be further explained and more clues to the direction of time will be discussed.

By: Jeffrey Slayter

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