Why Do You See Mirrors Flipping Words?

Mirrors flipping words is a common observation, and most of us are quite used to it. Almost all of us were curious about this phenomenon at some point. But we decided not to pursue the reasons behind it deeply. Some of us thought that we understood the phenomenon from our childhood physics classes, but never got to understand the root cause(s). I wish to represent our united curiosity about this topic and will be investigating what is really going on behind this phenomenon in this article. Let’s start by understanding what we typically see in a mirror.

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Does A Mirror Flip Words Horizontally?

There is a common thought among us that a mirror flips words horizontally. When you think about it, we don’t appear upside down in mirror reflections. But words written on our clothes or other objects do appear to be flipped horizontally. Take a look at the following picture:

The actual piece of paper reads “STREET SCIENCE”. But in the reflection, it appears that the words have been flipped horizontally. Contrary to natural intuition, the mirror does NOT flip objects horizontally. In truth, the mirror neither flips horizontally nor vertically. To prove this, take a look at the following picture:

It is clear from the picture that the objects on the left remain on the left in the reflection. Similarly, objects on the right remain on the right in the reflection as well. Furthermore, there seems to be no vertical flipping going on as well. So, what makes reflections of words special? Before we can answer that question, we need to answer the following question.

What Does Mirror Reflection Do?

What the mirror reflection actually does is inverse depth. That is, the mirror flips light inside out. In other words, objects that are farthest from you and closest to the mirror are reflected first and appear closest to you in the reflection. Similarly, objects that are closest to you appear the farthest from you in the reflection. If you find my words confusing, worry not. Let’s take a look at a pictorial explanation. Have a look at the following picture:

In this picture, the blue ball is closest to you, the red ball is in the middle, and the red marker is farthest from you. But in the mirror reflection, you see the red marker as the closest object, the red ball is in the middle, and the blue ball appears farthest from you. So, the mirror has essentially reversed depth. This is how mirrors work. So now that we have answered this question, what about words?

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Why Are Mirrors Flipping Words?

If mirrors inverse depth, how come words appear to be flipped horizontally? The challenge with words is that there is an added layer of rotation applied to them. You see, you don’t actually see the words when you see their reflection typically in a mirror. To prove this point, have a look at the following series of images. In the first image, you can see the text on the piece of paper directly. In the second image, notice how I rotate the paper by 180 degrees around the vertical axis. Finally, in the third image, the text is no longer visible to your eyes; notice the red question mark on the backside of the paper. You are only able to see the reflection, which appears to flip the words horizontally.

So, what if we could somehow replace the red question mark, and see what we would see if the paper were transparent? Why don’t we do just that?!

Reflections of Words on a Transparent Sheet

If the opaque paper were to be replaced by a transparent sheet of paper, you would see the equivalent of the following image.

Now things are getting clearer! You actually see exactly what the mirror reflects. So, the mirror actually never flips the words horizontally. It is you who does the flipping, and just somehow don’t notice it in your head. Now that we’ve come this far, why don’t we take advantage of the transparent strip we have? What if we never rotated the transparent strip, and just placed it in front of the mirror as if we were looking at the strip directly (ignoring the mirror)? The following picture is the result:

As we can clearly see, there is no horizontal flipping in the reflection this time around! This proves the point that it is actually you who flips the words and not the mirror. All the mirror does is inverse depth, and this has no effect on the lateral flipping of words. Since we are not used to writing on transparent objects, we often tend to forget or ignore the fact that the words facing the mirror are actually flipped to our eyes even before we see the reflection. We are typically just unable to see those words directly because of opaque objects. This is the real reason why words appear horizontally flipped in mirrors.

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Further reading that might interest you: Why Does Temperature Have No Upper Limit? and Why Do We Really Use The 12-Hour Clock?