The “We don’t know what’s going on” by Muhammad Ali Syaifudin

The “We don’t know what’s going on” by Muhammad Ali Syaifudin

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Let say you have a box which can tell you whether a particle is spherical or cuboid. If a particle is spherical, the particle is deflected, and if it’s cuboid, it just passes through. You also have another box that can tell whether a particle is blue or red. If a particle is blue, the particle is deflected, and if it’s red, it just passes through. Here’s the crucial thing. The way we know a particle’s roundness/color is by looking at these boxes. You can’t tell its roundness/color by other means. Now, here’s the experiment.

Fig 1. Box in action


Imagine sending random particles once at a time to the roundness box detector. You find out 50% of them are spherical and 50% are cuboid. Nothing special and everything is going as expected. Now, let’s change the box with a color box detector. You also find out 50/50 chance of particles being blue or red.

Fig 2. Particle and box


Now you arrange the boxes in a row. You first send particles to a roundness box, which is followed by another roundness box. What do you expect in the second box? You find out 100% particles are spherical. The same thing happens to the color boxes.


Fig 3. Box and box


Now, let us see the above configuration (Figure 3). If you replace the second roundness box with a color box. What do you expect the box to do? The particles have a 50/50 chance of being red or blue. If you place the color box below the roundness box, the result is the same. If you exchange the position of the boxes, (color box first then roundness box), you find out that the particles have a 50/50 chance of being spherical or cuboid. What can you conclude from these experiments? You may think that being spherical doesn’t correlate with being red. In other words, you can’t infer whether a particle is red or blue just by knowing its roundness. You must put it into a color box to find out.

Fig 4. Roundness and Color Boxes in action


Now, let’s add one more box at one end with another roundness box (roundness, color, roundness). What do you expect? Unexpectedly, the result is 50/50 chance of being spherical or cuboid. But how? What is your new conclusion then? Now, you may think, being red destroys the information of being round. The particles just do not have any shape anymore. It’s just red.

For the last experiment, imagine this configuration.

Fig 5. Complicated configuration


Mirrors just deflect the particles’ direction and do not affect their properties, such as roundness and color. Then, there is a new beam splitter, which just directs particles directly to the right, nothing else. Now run the experiment. What do you expect?

Here’s our guess. If the particles are red, then it has a 50/50 chance of being spherical or cuboid. If the particles are blue, it also has a 50/50 chance. Therefore, the result should be 50/50 chance of being spherical or cuboid.

It turns out that is 100% spherical. But how? It is like the middle apparatus doesn’t exist. What is going on? You can try to figure out by putting a wall right to the left of the beam splitter, and the result becomes a 50/50 chance. If the wall was above beam splitter, the result is 50/50 as well.

Now, here is the question. Which path the did particles pass through? The red channel or the blue channel? No, if it was one of them, the result must be 50/50. Both? No, because we can tell that the particles are coming from one direction and not the other. (Think of one box and send particles one at a time. We can measure its how spherical or cuboid for each particle and not measure them one at a time.) Does it traverse none of these paths? Nope, because by putting a wall, the result is altered. So what?

The answer is we don’t know. But we know that the particles must be doing something. Something that our languages don’t have a word for. And physicists just come with the conclusion “what about we call this phenomena superposition, which stands for “we don’t know what’s going on”. And this phenomena is one of the ideas of superposition. The mathematics is settled, but the physical interpretation? Let’s find out by studying quantum physics.

Credits: Muhammad Ali Syaifudin (

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