Quantum Physics: The Double-Slit Experiment and Quantum Entanglement

 Quantum physics is the study of the smallest particles in nature, such as atoms, electrons, photons, and so on. These particles behave in very strange and fascinating ways that are different from the things we see in everyday life. One of the most famous examples is called the double-slit experiment. It shows that light can act as both a wave and a particle, depending on how we observe it.

Well, imagine you have a source of light, like a flashlight, and you shine it on a wall that has two narrow slits cut into it. Behind the wall, there is another screen that can detect where the light hits it. What do you think you will see on the screen?

Two bright spots, one for each slit?

That’s what you would expect if light was just a stream of particles, like bullets. But if you do the experiment, you will see something different. You will see a pattern of many bright and dark stripes on the screen.

Why does that happen?

That happens because light is also a wave, like a ripple on water. When waves pass through the slits, they interfere with each other and create the stripes on the screen. This is called interference.

But how can light be both a wave and a particle at the same time? That doesn’t make sense. 

That’s the tricky part. The truth is, we don’t really know what light is. We only know how it behaves in different situations. Sometimes it acts like a wave, sometimes it acts like a particle, and sometimes it acts like something else entirely. This is one of the mysteries of quantum physics. 

Something else entirely? 

 Well, there is another aspect of quantum physics that is even more bizarre than the double-slit experiment. It’s called quantum entanglement. It means that two particles can be linked together in such a way that they share the same state, even if they are far apart from each other. It means that if you measure one of them, you will instantly know the state of the other one, without having to measure it directly. For example, if you have two entangled photons, and you measure the polarization of one of them, you will immediately know the polarization of the other one, even if it is on the other side of the galaxy. They are just in sync with each other, because they were created together in a special way. This is called quantum nonlocality. It means that quantum physics does not obey the usual rules of space and time.