Is Entanglement the Key to a Theory of Quantum Gravity? with Sean Hodgman

Sean Hodgman's group conducts experiments using atoms, specifically helium, to observe entanglement. Unlike measurements relying on photons which travel at the speed of light, their approach utilizes slower-moving atoms, allowing for more controlled and observable quantum phenomena. This method involves cooling helium atoms to extremely low temperatures, nearly absolute zero, to facilitate the observation of entanglement.

To study quantum phenomena, Sean Hodgman's team cools helium atoms to temperatures just a millionth of a degree above absolute zero. This process removes thermal motion and creates what’s known as a Bose-Einstein condensate – a state where atoms behave collectively as one macroscopic quantum object. At this temperature, the atoms form a single coherent quantum state, effectively acting as a 'fuzzy smeared out' blob.

Normally, we don’t observe wave-like behavior of particles due to their tiny wavelengths. By cooling atoms to extremely low temperatures and forming a Bose-Einstein condensate, scientists can create macroscopic quantum states where the wavelength becomes large enough to be observable. This allows for phenomena like atoms expanding over distances of 0.1 millimeters after being released from a trap.

Elementary particles are classified as either bosons or fermions, each governed by different statistical rules. Bose-Einstein condensates are formed using bosons (named after Satyendra Nath Bose), while other quantum phenomena involve fermions. Despite Einstein's initial skepticism of quantum physics, the concept of Bose-Einstein condensation and the associated particle types bear his name due to his contributions to understanding these concepts.

Sean Hodgman explains that in their experiment, entanglement isn't based on position but rather the momentum states of atoms. Specifically, it’s the direction they are traveling – northeast/southwest or northwest/southeast – that establishes the entangled relationship. This means two atoms can be linked by their movement directions simultaneously, creating a correlated state.

Albert Einstein famously disliked the concept of entanglement, which he termed 'spooky action at a distance.' He found it unsettling that measuring one entangled particle could seemingly instantaneously influence the state of another, leading to what appeared to be faster-than-light communication and a collapse of superposition. This challenged his understanding of locality and causality.

John Bell devised an experiment to test whether entangled particles exist in a superposition or not. The core idea is to take the superposed states of entangled particles and make them interfere with each other, creating a measurable interference pattern if they are truly in a superposition. This approach allowed for experimental verification of entanglement's existence.

Sean Hodgman clarifies that entanglement typically requires particles to be identical, such as helium atoms in their experiment. However, it's not strictly necessary; collisions between non-identical particles can also create entangled states where one particle moves in one direction and the other in the opposite direction, establishing a correlated relationship.

Researchers are actively exploring the limits of entanglement as it applies to larger particles. While entanglement has been observed with collections of atoms and molecules, current estimates suggest a limit around a thousand atoms, though this number is subject to ongoing research and refinement. The goal is to understand where and how entanglement breaks down at larger scales.

Sean Hodgman references George Gamow’s 'Mr. Tompkins in Wonderland,' a thought experiment illustrating how altering fundamental physical constants, like the speed of light or Planck’s constant, could drastically change our perception and experience of reality. The analogy highlights that if we had a way to adjust these constants, macroscopic phenomena, such as diffraction through doors, would become commonplace.

Despite initial excitement, entanglement cannot be used for faster-than-light communication due to the 'no-communication theorem.' The act of measurement inherently contains information, and transmitting that information requires a classical channel – essentially negating any potential speed advantage. The theorem states that entangled states can’t be exploited to send signals faster than light.

While entanglement cannot facilitate faster-than-light communication, it *can* be utilized for quantum encryption. This approach leverages the fact that measuring one entangled particle alters its partner; by sending one photon from an entangled pair and keeping the other, a secure key can be established through shared measurements.

Sean Hodgman discusses the emerging possibility that quantum entanglement plays a role in various biological processes. He mentions speculation about DNA stability, where entanglement within molecules might contribute to its robustness. Additionally, he highlights research suggesting entanglement may be involved in bird navigation, particularly during migration, potentially explaining how birds know which direction to fly. While acknowledging this area is still under investigation and not his direct expertise, Hodgman emphasizes the growing evidence pointing towards quantum physics' importance in biological systems.

Sean Hodgman explains that measuring entanglement using photons, which travel at the speed of light, can lead to potential explanations that circumvent Einstein's concerns about instantaneous communication. To avoid such interpretations, physicists measure entanglement using slower-moving atoms, typically moving at a few centimeters per second – an inch per second for American audiences. This allows them to rule out explanations based on the photons’ velocity and reinforces the implications of non-local correlations.

Sean Hodgman emphasizes that rigorous scientific experimentation requires publication and peer review. He explains that publishing research allows other scientists to scrutinize the methods, identify potential errors, and suggest alternative approaches. This process of critical evaluation is crucial for ensuring the validity and reliability of experimental results and preventing unintentional biases or overlooked factors.

Sean Hodgman clarifies that 'loopholes' exist within Bell’s theorem experiments, representing potential ways to preserve locality and avoid instantaneous communication. These loopholes include concerns about experimental conspiracies or the observer influencing results through subtle interactions. To address these, researchers implement rigorous testing protocols and seek independent verification from other scientists.

The discussion highlights the significant uncertainty surrounding the future impact of quantum computing. While there's considerable investment and excitement, it’s acknowledged that its ultimate utility remains an open question, ranging from massive economic and security implications to potentially being a 'fun physics exercise' with limited practical application. The potential applications include drug development, data processing, and more, but the outcome is far from certain.

The conversation draws a parallel between current enthusiasm for quantum computing and the historical reception of early quantum physics. A century ago, quantum mechanics was dismissed as a fringe curiosity with no practical use, yet it has since become foundational to modern technology. This emphasizes the importance of investing in basic research even when its immediate applications are unclear.

The speaker expresses concern about the decline in basic physics research within the United States and Australia, stating they 'don't know what that is anymore'. This reflects a shift away from fundamental scientific inquiry towards more applied or commercially driven projects, potentially hindering long-term innovation. They lament the lack of support for exploratory research.