There is an old saying “seeing is believing”. When we see something, we believe what we see. Can this be really true? We see objects around us when there is light. When there is no light, we see nothing. If you have ever experienced being in a dark room where photographers develop film, you know what the total darkness is, that is until you turn on the red light. This brings up a good question, what does this mean? We cannot see anything when there is no light. Why not?
The mechanisms of eyesight are relatively simple. Let’s assume that there is an object in front of our eyes. As we turn the light on, the light will travel to the object and hit the object. As the light bounces off the object, it will lose some energy and will produce visible range of light (about 390 – 750 nm). This bounced visible light will travel to our eyes so we can see the object in front of us. However, the important question is “Are we really seeing the true objects themselves?” Strictly speaking, the answer is “NO”. We see the objects because the bounced light traveled from the object and reached to our eyes. This means that if the visible light didn’t travel from the object to our eyes, we won’t be able to see it. What we are seeing is the bounced visible light that reflects the objects – not the objects themselves.
When we see, we are seeing the past of what we see
We understand that light travels fast. The speed of light is about 300,000 Km/Sec. Having measurable speed indicates that it is travelable. In other words, if we have advanced technologies, we may be able to travel faster than the speed of light as we overcame the speed of the sound. We are aware of the speed of sound very well. For example, when we look at an airplane passing by (doesn’t have to be a supersonic) we hear the delayed sound because sound travels slower than light. When we try to locate the airplane using only our sense of hearing, we will be pointing at the location where the airplane had already passed; the speed of sound is not fast enough to provide us the real time information. This indicates that what we are hearing is the past of the airplane. We can apply the very same ideas to the speed of light. To picture the speed of light, let us consider light traveling from the sun to earth. The distance between the sun and earth is 149,597,900 (km/sec). The calculated time for the light from the sun to reach earth is about eight minutes. The eight-minute-difference is due to the distance between the sun and earth and due to the traveling speed of the light. Thus we are looking at the sun that was eight minutes ago. In other words, we won’t be able to see the present sun unless we fly to the sun and land on it physically.
What does this “we are looking at the past of the sun all the time” mean to us, then? If we could fly to the sun, we would see the present sun. Doesn’t this mean we just made time travel – moving toward the present from the past? We can consider the situation as shown in figure 1a where there are two planets with the same distance from the sun (planet A and planet B). Since both planets are at the same distance from the sun, the sunlight will reach these planets at the same time. We assume that these planets are ten-light-minutes apart (takes ten minutes to travel with speed of light) and we are planning to fly from planet A to planet B. Since we are starting at the planet A, we are at the present of planet A but we are looking at the ten-minute-past of planet B (figure 1a). As we travel toward planet B and when we are at the half way to planet B, we are looking at the five-minute-past of both planets (figure 1b). As we get closer to the destination (planet B), we are arriving to the present of planet B but we are about ten-light-minutes away from planet A thus, we are looking at ten-minute-past of the planet A (figure 1c). Here we just made time travel. As we move from planet A to planet B, we started moving toward the past of the planet A but we are moving toward the present of planet B. When we arrived at the planet B, we are at the present of planet B but we are at the ten-minute-past of the planet A.
We can easily extend this idea to the current universe. We understand that the stars we look at are probably not there anymore. The stars we look at everyday are the past of the stars. If we, somehow, able to travel to these stars, we will be moving toward the present of these stars but we will be traveling toward the past of earth or solar system. This indicates that traveling the three dimensional space includes traveling the time but in relative way. For example, let’s say you are traveling from Montreal to Vancouver. As you come closer to Vancouver, you are getting close to present of Vancouver but you are traveling toward Montreal’s past. We simply don’t realize this because the speed of light is too fast for us to detect the differences. Due to the speed of light which goes around the earth about 7.5 times per second, we consider both Montreal and Vancouver as present at the same time. However, in reality, the concept of present depends on where you are at the moment.
What if we travel faster than the speed of light?
What phenomenon would be observed if we travel faster than the speed of light? To explore this, we can put ourselves back into figure 1 but only consider that we are traveling faster than the speed of light. From the previous example, we did not have to define the traveling speed because the consequences should be the same except the duration of the travel. However, if we consider that we are traveling faster than the speed of light, the results come out differently. From the destination (planet B) point of view, nothing changes since we are at the present of planet B as soon as we land on it. Only the traveling time is shorter. From the departure (planet A) point of view, however, we are traveling towards further past of planet A. For example, if we assume that we travel two times faster than the speed of light, it will take only five minutes for us to move from planet A to planet B. This indicates that we will see the fifteen-minutes-past of planet A instead of ten-minute-past. It will be very hard to detect in reality because the limitations of our detection tools, namely relying on the light – means that we will be detected to be present on both planets at the same time.
Are we time traveling yet?
“YES”. As we move from a place to a place, we are moving toward the present of one place and moving away from the present of another. As Einstein pointed out, time is as relative as space.