Is light a particle or a wave?

It is true that the concept of wave function collapse and the idea that particles exist in a superposition of different states before they are measured is a key part of the quantum mechanical description of the world. However, it is not just an "explanation" or a theoretical construct. The existence of wave function collapse and superposition states has been confirmed by a wide variety of experiments, including the double-slit experiment and other experiments that demonstrate the probabilistic nature of quantum systems.

One way to understand the idea of superposition is to consider a simple example: suppose you have a coin that you flip, but instead of just two possible outcomes (heads or tails), the coin can land on any of the points on a continuous scale (e.g. a line). According to quantum mechanics, the coin would exist in a superposition of all possible positions on the scale until you observe it and collapse the wave function.

This may seem strange or counterintuitive, but it is a consequence of the mathematics of quantum mechanics and has been confirmed by many experiments. The uncertainty principle, which states that the more precisely we know the position of a particle, the less precisely we can know its momentum, and vice versa, is another consequence of the wave-like nature of quantum systems and the existence of superposition states.

So while it is true that we cannot know the exact position and momentum of a quantum particle with infinite precision, this does not mean that the particle does not have a definite position and momentum. Rather, it means that the position and momentum of a quantum particle are inherently uncertain and subject to a certain amount of randomness due to the wave-like nature of these systems.

You are correct that the interference pattern observed in the double-slit experiment is similar to the interference patterns produced by classical waves, such as water waves or light waves. However, the way in which the interference pattern is produced in the double-slit experiment is fundamentally different from the way it is produced by classical waves.

In the double-slit experiment, the particles do not exhibit wave-like behavior until they are detected. Prior to detection, the particles exist in a superposition of different possible positions and momenta, which is described by a wave function. The wave function encodes the probabilities of finding the particles at different positions, but it does not correspond to a definite position or momentum.

It is only when the particles are detected that their wave function "collapses" into a definite position and momentum. This process is known as wave function collapse, and it is a fundamental feature of quantum mechanics that is not present in classical wave theories.

Therefore, the double-slit experiment does indeed demonstrate that the behavior of quantum particles like electrons is described by wave-like equations such as the Schrödinger equation, even though the interference pattern produced by these particles is similar to the interference patterns produced by classical waves.

No the double slit experiment does not show that the behaviour of the particles is described by the Schrödinger equation, it only shows the creation of an interference pattern which is predicted by classical wave equations.

It is true that the double-slit experiment demonstrates that the behavior of particles like electrons can be described by wave-like equations (namely, the Schrödinger equation). However, the wave-like behavior of these particles is not the same as the wave-like behavior of classical objects such as water waves. In classical wave phenomena, the waves always have a definite position and momentum, and their future evolution can be predicted with certainty.

In contrast, the wave function of a quantum particle does not correspond to a definite position or momentum, and the outcome of a measurement on a quantum system is inherently uncertain. This is a consequence of the uncertainty principle, which states that the more precisely we know the position of a particle, the less precisely we can know its momentum, and vice versa.

The fact that the outcome of a measurement on a quantum system is uncertain means that the future evolution of the system is not fully determined. In other words, there is an element of randomness or indeterminism in the behavior of quantum systems. This is one of the key differences between classical and quantum systems, and it is a fundamental feature of the quantum world that has been extensively tested and confirmed by a wide variety of experiments.

Let me disagree with this explanation of the experiment. The experiment only shows that what we call electrons are just waves, unless they come in contact with electromagnetic waves, in which case we observe them as "particles". I can't see why there is no determinism.

One famous example of an experiment that demonstrates the non-deterministic nature of the universe is the double-slit experiment. In this experiment, a beam of particles (such as electrons) is shone through a screen with two slits in it, and the pattern of the particles on a detector screen on the other side is observed. If the particles behave like classical objects, we would expect them to pass through one slit or the other and create two distinct bands on the detector screen. However, if the particles behave according to the predictions of quantum mechanics, they will interfere with themselves and create a pattern of alternating bright and dark bands on the detector screen. This experiment has been performed many times with various types of particles, and the results are always consistent with the predictions of quantum mechanics. The fact that the particles seem to "know" about the presence of both slits and interfere with themselves even when only one is open at a time is a clear indication that the universe is not deterministic at the quantum level. There are also other phenomena in the quantum world that are inherently non-deterministic, such as quantum tunneling and the decay of radioactive particles. These phenomena cannot be explained by classical mechanics and are further evidence of the non-deterministic nature of the universe at small scales.

Can you name an experiment or test that shows that the universe is not deterministic?

It is certainly possible that our current understanding of quantum mechanics is incomplete, and that there may be deeper theories that could explain the phenomena described by quantum mechanics in a different way. However, it is important to note that the randomness and uncertainty observed in quantum systems has been extensively tested and found to be a robust feature of nature. There is a great deal of evidence that supports the predictions of quantum mechanics, and many of the phenomena that are difficult to understand within the framework of classical physics can be explained quite naturally in the quantum world. So while it is always possible that our current understanding of the universe may be incomplete or subject to revision, it is also important to recognize the successes and predictive power of the theories that we currently have. It is likely that any future theory that succeeds quantum mechanics will have to be able to explain the phenomena described by quantum mechanics as a special case or limit, rather than simply replacing it outright.

We can say that randomness is due to a theory, namely :" quantum mechanics" which might be wrong and it is wrong in my opinion, and not a real feature of nature.

The classical explanation that many physicists believe is that uncertainty is an inherent feature of quantum mechanics, which describes the behaviour of very small particles like electrons. In quantum mechanics, the state of a particle is described using a mathematical object called a wave function. The wave function encodes the probability of finding the particle at a particular location or with a particular energy, but it does not give us a definite prediction of the outcome of an individual measurement. This is known as the uncertainty principle. So, in a sense, the uncertainty involved in measuring the properties of a particle like an electron is a fundamental feature of the quantum world. However, it is also possible to reduce the uncertainty in our measurements by using better instruments or more sophisticated experimental techniques. In this way, we can "shed light" on the properties of particles like electrons to some extent, but there will always be some uncertainty due to the quantum nature of these systems.

What do you have to say about this?

Thank you for the reply Prof. Smith. I think that I like your explanation a lot more, than any other that I have ever read. It is indeed a simple explanation, which shows that at least according to Feynman there is a chance that you actually understand the subject. Of course there are a lot of things that nobody knows (appart from some advanced aliens like phystroid for example lol), however it is a lot better to understand and admit your ignorance, than creating complicated epicycles of ignorance. The way that you have given me answer makes it almost impossible for me to claim that there is even a chance that your statement might be incorrect. I think I will just stop watching random guys on YouTube, and start posting more questions here in this forum.

We have to truly understand what a particle or a wave is in the first place... and I think that modern science does not have an answer for that question. Of course we can give all sorts of different explanations, but that would be something more of a personal opinion that needs to be supported by robust mathematics and future experiments. A wave in general requires a medium for it to be propagated. So if I ask what is this medium in the case of light? Nobody knows. What truly is a particle? Nobody knows. In my opinion, the way out of this logical problem is to assume that what we perceive as a particle is actually a wave in a material medium which we call "space". It is just an opinion that I might evolve further in my brain as I become older and wiser. Of course you might think that the generally accepted science is not an opinion, but look at the history of science. Science is based upon experiments and logic, and conducting as well as explaining experiments requires logic as well, we therefore conclude that science is based entirely upon logic, which in turn is a personal opinion. I am sure that there is a monkey somewhere out there that disagrees with all of that, but that is my point, logic is a personal opinion.