Modern physics is forcing us to rethink existence | Michelle Thaller: Full Interview

Michelle Thaller, an astronomer at NASA's Goddard Space Flight Center, discusses how astronomers explore the universe's biggest questions. She clarifies that "astronomer" and "astrophysicist" are largely interchangeable terms today, both focusing on understanding stars and celestial mechanics, unlike a century ago when astronomers primarily mapped stars and astrophysicists studied their underlying science. Thaller's own doctoral research focused on binary stars, specifically massive ones (15 to 50 times the sun's mass) in close orbits, which produce colliding stellar winds of high-energy particles, creating giant shockwaves. She used observational astronomy, traveling to observatories in Australia and Arizona, and analyzing data from X-ray satellites and the Hubble Space Telescope. A significant part of an astronomer's life involves extensive writing—proposals for telescope time and grant applications for funding. This means that while training emphasizes math, physics, and computer science, the day-to-day work often involves administration and securing resources. She describes the unique satisfaction of being a young astronomer, making minor but unprecedented discoveries while observing the night sky. Original research is a requirement for a doctorate, often achieved by joining a professor's research and taking on a piece of it, gradually developing one's own questions. Her research on binary star shockwaves, using tomography (similar to medical CAT scans) to map their three-dimensional structure, helps understand how stars work. These shockwaves are crucial for producing molecules in space, including water, with some binary stars in the Orion Nebula generating enough water daily to fill Earth's oceans 60 times over (in molecular gas form). This research contributes to understanding the origins of life's essential molecules. While most astronomers study concrete phenomena like star formation, galactic evolution, and stellar remnants, only a few delve into theoretical cosmology, addressing questions about the multiverse or events before the Big Bang. Thaller notes that while these grand questions are intriguing, much of astronomy focuses on more observable phenomena. She emphasizes that science aims to approach reality, acknowledging that human perception and understanding are limited and constantly evolving. Scientific "truth" can change with new information, as demonstrated by the shift from a static universe theory to an expanding one. Physics, especially in the last century, has challenged common sense notions of space and time. Newton described gravity as a force, but Einstein later redefined it as a curvature of spacetime. This led to the profound question: what *is* spacetime? Modern physicists are exploring radical ideas, such as spacetime being a consequence of quantum mechanics, rather than a separate entity. This perspective suggests that relativity and quantum mechanics, which traditionally clash, might be unified if spacetime emerges from quantum phenomena like entanglement. Quantum entanglement, observed and replicated in labs, describes how two interacting particles become part of the same quantum system, regardless of distance. If one particle's property (like spin) changes, the other instantly responds, not via a signal, but because they are fundamentally one system. This leads to the speculative idea that everything in the universe might be entangled, and what we perceive as space and time is merely the degree of that entanglement. The closer the entanglement, the closer things appear in space and time. This concept could imply that distance isn't fundamental, and advanced civilizations might manipulate entanglement for "travel" without propulsion. Intriguingly, equations of gravity are now emerging from quantum mechanics based on entanglement, suggesting a potential unification of these theories. Thaller explains that a photon, traveling at the speed of light, experiences no space or time; all points in space and time are one to it. Yet, humans, made of components that can be converted to photons, experience space and time as extended properties. This duality suggests a deeper reality beyond human perception. The famous equation E=mc² signifies that mass is a concentrated form of energy, and the two are interchangeable. This is seen in nuclear reactions where mass converts to energy, and in particle accelerators where high energy collisions create new particles, demonstrating energy manifesting as mass. Virtual particle pairs (e.g., electron and positron) constantly pop in and out of existence from the energy of space itself, annihilating each other almost immediately. Around extreme objects like neutron stars, intense magnetic fields can separate these virtual particles, creating beams of energy and making the vacuum of space itself incredibly dense (e.g., three times the density of iron near a neutron star). Neutron stars are fascinating remnants of massive stars that didn't quite collapse into black holes. They are composed mainly of neutrons, formed when gravity crushes electrons into protons. These objects are incredibly dense, with a teaspoonful having the mass of Mount Everest, and spin rapidly (up to 500 times a second). Recently, neutron stars have been linked to fast radio bursts (FRBs)—mysterious, powerful radio emissions lasting only a millisecond but radiating energy equivalent to the sun's output in a week. Scientists hypothesize that FRBs are caused by "neutron star quakes," where stresses in the star's neutron crust send energetic compression waves through its fluid interior, releasing massive amounts of energy. Studying these FRBs could provide insights into the internal structure of neutron stars, much like earthquakes reveal Earth's interior. Thaller also discusses solar winds, a constant stream of high-energy particles from the sun, first predicted by Eugene Parker (after whom the Parker Solar Probe is named). This wind profoundly affects planets; it stripped Mars of its atmosphere and contributed to Venus's hellish environment. Earth is protected by its strong magnetic field. However, powerful solar storms, called coronal mass ejections (CMEs), can pose risks. While a normal solar wind is harmless, a direct hit from a major CME could be fatal for unprotected astronauts and could severely damage Earth's power grids, as evidenced by the 1859 Carrington Event. Scientists are actively monitoring the sun with a fleet of satellites and developing prediction models to provide warnings, allowing for protective measures like astronaut sheltering or power grid shutdowns. Asteroids are described as "time capsules" of the early solar system, preserving the original chemistry and physical conditions, unlike planets that have undergone significant geological changes. While asteroids contain valuable elements like gold and platinum that sank to Earth's core, the economic feasibility of asteroid mining remains questionable due to the challenges of space travel and extraction. Regarding navigation in space, Thaller explains that compasses respond to magnetic fields. While planets, stars, and even the galaxy have magnetic fields, there is no universal magnetic north. In the vastness between galaxies, where no detectable magnetic field exists, direction is relative. The only absolute reference point for motion in the universe is the cosmic microwave background radiation, the oldest light observable from about 400,000 years after the Big Bang. Finally, Thaller addresses common misconceptions about the Big Bang. She clarifies that scientists do not believe the universe came from "nothing." Instead, the early universe, containing all observable matter and energy, was compressed into a volume smaller than an atom. Current physics cannot fully describe this extreme state, but future theories integrating gravity and extreme energy densities might provide answers. She also highlights that the Big Bang is believed to have created not just space, but time itself, meaning there was no "before" in the conventional sense. Furthermore, the observable universe is only a tiny fraction of the entire universe, which could be infinitely large. The idea of a "holographic universe," where our 3D reality is an emergent property of a 2D surface of information, is gaining traction in physics, stemming from attempts to reconcile black hole physics. This concept implies that space and time as we perceive them might not be fundamental, but rather a human interpretation of an underlying reality. Thaller concludes by emphasizing the humility required in science, acknowledging that the human brain, like a grasshopper's, has limitations in perceiving the universe's full reality. The universe was not designed to be comprehensible to us, and much remains beyond our immediate grasp, pushing us to constantly question and expand our understanding.