From: mk_thisisit
Orthodox quantum mechanics is fundamentally a theory of our observations of the microworld [00:02:50]. All knowledge about the world stems from observations, and theories are considered valid if they align with these observations, whether sensory or enhanced by experimental devices [00:02:53].
Classical World vs. Quantum World
The classical world is characterized by large objects, eventually breaking down into smaller objects until atoms are reached [00:00:53]. Atoms are incredibly small, and their behavior differs significantly from macroscopic objects like trams or ping-pong balls [00:01:34]. The quantum world, where atoms reside, operates completely differently from our everyday experience [00:02:01]. It is an “alien” world to which humanity, despite being composed of atoms, does not have direct access [00:02:16].
The Professor's Anecdote
The speaker recalls a professor’s statement: “If we were to lose all of humanity’s knowledge, this one sentence should [remain]: the world is made of atoms” [00:00:00]. This highlights the foundational importance of atoms in understanding the world.
The Role of Observation
A key distinction between the classical and quantum realms lies in the impact of observation:
- Macroscopic Objects: For large-scale objects, acts of observation have virtually no effect [00:03:15].
- Microscopic Objects: In the case of microscopic objects, observation profoundly changes our knowledge about the object [00:03:30]. It can even alter the object’s state [00:03:41]. Photons, used to observe quantum phenomena, are capable of disrupting what is being observed [00:03:47]. This active role of observation is crucial at the microscopic level [00:05:31].
Einstein’s Dilemma and Heisenberg’s Story
The concept is illustrated by the famous (though poorly formulated) Einstein’s dilemma: “If I do not look at the moon, it does not exist” [00:04:04]. While the moon’s existence isn’t dependent on observation (it exists even when not illuminated), the act of observing it with a telescope or eyes requires light, which has a negligible effect on the moon’s shape or movement [00:04:41].
However, in a “Heisenberg story” scenario, if one wanted to observe a single electron, illuminating it would cause it to scatter, thereby disturbing its state [00:05:07]. The act of observation in the microscopic stage actively changes the information we have about the object [00:05:34].
This perspective is key to understanding quantum mechanics [00:05:46]. The Copenhagen interpretation of quantum mechanics is accepted as a true picture of nature by the speaker, unlike some, such as Einstein, who conducted research to disprove it [00:14:29]. The natural states described by quantum mechanics reveal situations that are paradoxical in the macroscopic world [00:15:00].
Bell’s Theorem and Quantum Entanglement
Research on the basic foundations of quantum mechanics, specifically Bell’s theorem, highlights the gap between phenomena explainable by classical mechanics plus relativity theory, and what quantum mechanics reveals [00:41:35]. When the speaker began research on quantum entanglement, the term wasn’t even common in literature, and many advised against studying it [00:42:05]. However, the intellectual shock of the topic drove him to delve deeper [00:42:46].
The speaker and his colleague, Anton, focused on understanding how to force interference between independent single photons [00:20:55]. They initially believed it was impossible, but discovered that by breaking the assumption of time resolution being on the order of the photon coherence time, independent photons could be forced to interfere [00:22:31]. This led to showing the possibility of “exchange of entanglement,” where two independent sources of entangled photons could become entangled through a specific measurement [00:23:14].
This research contributed to the understanding of quantum information, including teleportation and quantum cryptography [00:21:50]. The Nobel Prize was awarded to Anton and others for their work on entangled states, showing the violation of Bell inequalities, and pioneering experiments on quantum information [00:21:26].