From: mk_thisisit
Professor Wojciech Żurek is the creator of the theory of Quantum Darwinism [00:00:13], [00:08:50], which aims to explain how the classical world emerges from quantum mechanics [00:02:20], [00:03:36]. His work, along with his colleagues, has identified a point of contact between classical and quantum physics [00:18:17].
The Problem of Superposition
In quantum mechanics, all possible states of an object are allowed [00:03:12]. This means an object could be in multiple places simultaneously, a concept known as quantum superposition [00:00:00], [00:03:23], [00:04:43]. For example, a glass could exist “both here and there” [00:00:00], [00:03:27], or a coin could be simultaneously “obverse and reverse” [00:03:36]. Albert Einstein found this aspect of quantum mechanics inconsistent with observed reality, believing “something is wrong” with it [00:04:06], [00:04:23].
Decoherence
The phenomenon that resolves this contradiction is decoherence [00:02:34]. Decoherence is the process that deprives a quantum object of its ability to be in multiple places at once, breaking down quantum superposition [00:04:53].
Key aspects of decoherence:
- Measurement: Quantum states are defined every time a measurement is made [00:05:46]. This “measurement” doesn’t require a person or a device; any correlation that transfers information from an object to its environment acts as a measurement [00:05:52], [00:06:00].
- Environmental Interaction: The environment (e.g., photons, air particles) “knows” where an object is, and this knowledge disrupts coherence [00:06:18]. For example, photons hitting our eyes to allow us to see a glass causes its quantum system to cease existing in superposition [00:06:26], [00:06:31].
- State Selection: Certain quantum states are resistant to environmental interactions and can survive [00:07:11]. If the environment tries to find out an object’s position, coherence between different positions is eliminated [00:07:31].
- Pointer States: States that are resistant to the environment are selected and can survive; these are called “Pointer States” [00:09:37].
Quantum Darwinism: Beyond Decoherence
Quantum Darwinism builds upon decoherence, proposing a further mechanism for the emergence of the classical world [00:10:38].
- Environmental Factors: Environmental factors affect the quantum state [00:08:54].
- Selection and Replication: The theory has two main aspects:
- The selection of quantum states that can survive despite continuous environmental observation [00:09:03].
- The replication of information about these stable states into numerous copies [00:10:55], [00:12:36]. This means information is not just “swept away” but made redundant [00:10:47].
- Information Copies: Instead of a single copy, information about surviving states is “replicated in billions of copies” by the environment (e.g., photons reflecting off an object) [00:12:44], which observers then access [00:11:40], [00:11:49]. This allows for selective information transfer [00:10:04].
- “Darwinian” Aspect: The theory is called “Darwinism” because of the “survival of some states” and the selective information dissemination [00:12:29], [00:12:58]. States that are resistant to the environment are also replicated in many copies, unlike their superpositions [00:14:35].
Prohibition of Cloning
A related concept in quantum theory is the “prohibition of cloning,” which states that an unknown state cannot be cloned [00:13:08], [00:13:16]. Quantum Darwinism clarifies that what multiplies is “what is determined by the interaction between the system and the environment” [00:13:32].
Broader Implications
Unification Theory
Professor Żurek’s research brings us closer to understanding what connects classical and quantum physics [00:15:39]. While the concept of a “great unification theory” often refers to a mathematical formula uniting all forces (like electromagnetism, weak, strong, and gravity via string theory), Żurek’s interest lies in deriving why we only observe a limited set of states from the vast possibilities allowed by quantum mechanics [00:15:53], [00:17:42]. Decoherence and Quantum Darwinism largely explain this [00:18:07].
Quantum Computers
A significant challenge for building quantum computers is decoherence [00:24:52]. If a quantum computer has many “kits” (qubits), it becomes very difficult for the quantum system to survive the environment [00:25:00]. There’s a contradiction: quantum systems need to interact strongly internally for computation but must interact very weakly with the outside to avoid decoherence [00:25:37].
A promising alternative to building universal quantum computers is using quantum systems to simulate or emulate various strange quantum systems [00:26:36]. These simulations connect quantum mechanics with solid-state physics [00:26:58].
The Kibble-Żurek Mechanism
Professor Żurek is a co-creator of the Kibble-Żurek mechanism [00:40:42]. This mechanism describes what happens when the universe cools down after the Big Bang, leading to phase transitions and “symmetry breaking” [00:41:43], [00:42:03]. During these transitions, “topological defects” can form, which are very stable and, if abundant, would dominate the universe’s evolution differently than observed [00:43:28], [00:44:44], [00:45:01]. The theory of inflation was invented to dissolve these defects [00:45:11]. The Kibble-Żurek mechanism allows for the calculation of the density of these defects, which can be experimentally verified in laboratory settings like liquid Helium [00:45:34], [00:45:41]. It provides specific predictions for laboratory experiments concerning phase transitions [00:46:15], [00:46:33].
Personal Philosophy and Research Path
Professor Żurek’s career began at Los Alamos National Laboratory after receiving a very good offer [00:31:56]. His early research was also influenced by Professor John Archibald Wheeler, his mentor in Texas [00:33:51]. Wheeler encouraged exploration into topics like measurement theory and understanding the classical universe, which some contemporaries considered a “waste of time” [00:34:02]. Wheeler’s openness to various ideas and his brutal honesty in evaluating assumptions, even when incorrect, were formative experiences for Żurek [00:35:57], [00:36:42]. This highlights the importance of “wandering” in scientific discovery, but also realizing when one has entered a “blind alley” [00:37:25].
Żurek emphasizes that “ignorance condemns a person to originality” [00:01:05], [00:40:06].
Other Philosophical Questions
The discussion also touched on fundamental questions in physics:
- The Source of Gravity: For physicist John Wheeler, gravity is not a force but “simply the way in which space is curved” [00:20:17]. Objects move along straight lines in curved space, which we interpret as gravity [00:20:26].
- The Nature of Information: Professor Żurek believes information is a “secondary category,” not a primary one [00:22:13]. Instead, quantum states have the potential to transmit information and exist [00:22:21].
- Teleportation: While the transmission of information via quantum teleportation is possible over short distances, teleporting objects is not expected in the future due to the immense amount of classical information and quantum entanglement required [00:23:02], [00:23:30].
- Existence of the Universe: Żurek ponders questions like “why is there something or nothing?” and “why something instead of nothing?” [00:27:56], [00:28:03].
- Physical Constants and Laws: The origin of physical constants and laws is a “very interesting question” that influential physicists have asked [00:29:02]. String theory suggests the existence of a vast number of universes, each with slightly different physical laws, but this idea is not particularly convincing as it lacks predictive power for our reality [00:29:35], [00:29:50].
- Consciousness from Matter: The question of how consciousness is born from matter is very interesting [00:30:09], [00:31:13]. However, until consciousness itself is defined, it is difficult to precisely formulate the question or understand its origins [00:31:41]. Some believe consciousness gives birth to matter [00:31:28].