The Crier

Time Travel is Possible. Well, Sort of.

What star-gazing can teach us about the fourth dimension

Jeremy Davidson · The Empiricist · Feb 05, 2007

Is time travel possible?

The concept of time as the fourth-dimension is one of the most misunderstood in all of physics.

While writers like H.G. Wells and Kurt Vonnegut explored this dimension in their novels The Time Machine, and Slaughter-House 5, on a day-to-day basis most people think of themselves as purely three-dimensional. Though it’s difficult to see at first, time is actually a distinct dimension. In fact, time and distance are more closely related than you might imagine.

One way to conceptualize time as the fourth dimension is to look at the stars. Scientists measure the distance of stars using light-years, which are defined as the distance light travels in a vacuum in 365.25 days, or one Julian year. This distance is an astronomical 9,460,730,472,580.8 kilometers.

When you look at a star, you’re looking at a burning ball of gas light-years away. The reason you see the star is because of the light it emits. This light has to travel such a long distance, that by the time you see it, you only see what the stars looked like years ago.

The concept of time as the fourth-dimension is one of the most misunderstood in all of physics.

You can think about this in terms of our closest star, the sun. The sun is approximately 93,000,000 miles from the earth. It takes light about 8 minutes to get from the sun to the earth. This means that if the sun somehow disappeared, the earth would still be light for about 8 minutes, as the last rays of light wouldn’t have reached us yet.

The amount of time it takes for light to move from slightly closer sources — your desk lamp or cell phone screen, for instance — is small enough that we appear to be viewing objects near us in real time.

Understanding this, it’s easy to see that when you look at stars that are billions of light years away, you’re seeing what they looked like billions of years ago.

Similarly, if an observer on a star could make out the earth, they would not see the earth as it is today, but as it was in its infancy.

For now, the closest thing we have to time-travel is looking at the stars.