Random thoughts: We are only able to see the past

Imagine that you are taking a walk. You are in no hurry and therefore you have time to observe what’s around you. What you may not realize is that everything that you see is in your past, even if you think that is happening right in front of you.

Our universe has a speed limit. A high one to be sure, but a speeed limit nonetheless. It is the speed of light (about 186,000 miles/second or if you are metrically-inclined, about 300,000 km/second).

Humans are mainly visual beings. We realy heavily on our sight, to the extent that when it does not work well or at all, it is a real handicap. This means that we often rely on sight to interact with the world around us by perceiving light reflected on well, everything!

Let’s say you are having coffee with a friend; you sit in front of each other at a table roughly one meter across. if you look at your friend’s face, you see her face as it was about 0.000003 seconds ago (1 meter x 1 second / 300,000 meters). This is the time that reflected light from her face took to reach your visual system. There is an additional time lag while your nervous system processes this information, but we can safely ignore this lag, as it does not invalidate this argument. Even so, the nice thing about visual perception is that for all practical purposes it is equivalent with real time. A person cannot do much in 0.000003 seconds after all, but to my mind, oh my overactive mind, it is 0.000003 seconds in the past nonetheless.

It gets worse (or better, depending in your point of view). A few minutes ago, I went out to walk our dog, Ginger (she is nuts, by the way). It is a cold, crisp night! Anyway, very single time that I go out of the house at night, I like looking at the stars. I do not know why. I just do. Even if it is a little cloudy, if I only see one star, I get happy. Am I weird? (hint: the answer starts with the letter y…).


Tonight I saw the planet Jupiter, precisely as it was about 35 minutes before. Jupiter does not emit energy as visible light. It can only reflect sunlight, which takes about 43 minutes to get from the Sun to Jupiter and in turn this reflected light takes about 35 minutes to reach earth (we are about 8 light minutes away from the Sun ourselves).

What about the stars themselves? Interstellar distances are so vast that we commonly use a special unit of measurement, the light year. A light year is how far light travels in a year. I will let you do the math to figure out this distance, but trust me, it is a BIG distance.

The thing is that I realized that when I look at the stars and planets, I am not seeing them as they are at the moment. I see Jupiter as it was 35 minutes ago, while I may see a particular star as it was 6 years ago, another star as it was 500 years ago and I can even see the Andromeda galaxy, albeit as it was about 2.5 million years ago.

I am fully aware that I am not first person to think or write about this. Still it is a sobering thought, a really sobering thought indeed…


The Andromeda galaxy


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  1. When Jessica, my firstborn, was a toddler, she would sing “Twinkle twinkle, little star, how I wonder where (instead of what) you are.” When I thought about it, it was as legit a question as the original lyrics.

    If you keep looking and see nothing, it might not be the end of the universe but that you have gone back to the big bang.


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