How It All Ends | Crash Course Pods: The Universe #11

Potential Fates of the Universe

• The universe is theorized to be moving towards an end state of structureless disorder due to the second law of thermodynamics. (2m9s)
• The expansion of the universe will eventually result in a dark cosmos where only our immediate surroundings are observable. (5m46s)
• The ultimate fate of the universe is uncertain and depends in part on the nature and behavior of dark energy. (6m5s)
• The current best guess for the nature of dark energy is that it is a cosmological constant, similar to what Einstein first proposed. (6m53s)
• While a cosmological constant, where every bit of spacetime has some stretchiness, fits the current data well, dark energy could be something else entirely. (9m25s)
• One possibility is that dark energy is a scalar field, similar to the inflaton field thought to have driven cosmic inflation, that affects the universe's expansion rate. (10m26s)
• There are three potential outcomes for dark energy: it could increase in strength, decrease in strength, or remain constant. (12m40s)
• The Dark Energy Spectroscopic Instrument (DESI) has produced data that suggests dark energy may be weakening over time, though further research is needed to confirm this. (14m11s)

The Big Crunch

• A Big Crunch scenario, where the expansion of the universe reverses and everything collapses in on itself, is considered a less likely but nonetheless frightening possibility. (16m9s)
• Martin Rees, an astronomer, calculated that in a big crunch scenario, the universe would reach a point where the ambient radiation is so intense that it would trigger thermonuclear explosions on the surfaces of stars. (18m25s)
• In a standard big crunch, the universe collapses into a singularity, representing a definitive end without a new beginning. (19m41s)

Heat Death

• If dark energy remains constant, the universe will continue to expand at an accelerated rate, causing galaxies to move further apart and eventually leading to a state where matter becomes insignificant. (21m50s)
• As the universe expands and stars exhaust their fuel, everything will eventually decay into radiation, including white dwarfs, black holes (through Hawking evaporation), ultimately resulting in a universe dominated by waste heat. (23m7s)
• Protons are believed to decay, though this has never been observed, and in 10⁴⁰ years, they will begin to decay, leaving nothing but diffused radiation. (23m52s)
• As entropy increases over time, according to the Second Law of Thermodynamics, the universe will reach maximum entropy, resulting in a "heat death" where nothing meaningful can occur. (24m36s)
• While random fluctuations might lead to temporary decreases in entropy and the brief appearance of particles, the overall state of maximum entropy, or "heat death," will persist, even as spacetime continues to exist. (25m7s)

Other Potential Endings

• The universe could repeat itself, with every point in the past recurring at some point in the future. (29m35s)
• The Boltzmann brain problem suggests that it is more likely for a single brain imagining the universe to exist than for the entire universe to have fluctuated into existence. (31m26s)
• The heat death of the universe, while a definitive end, is a gentle one compared to other possibilities like the Big Crunch. (33m7s)

Potential Endings Based on Dark Energy

• The Big Crunch: If dark energy decreases, the universe could stop expanding and contract, causing space to become hotter and light to blue shift. (36m7s)
• Heat Death: If dark energy remains constant, the universe will continue expanding, matter will become diffuse, stars will die, and entropy will reach its maximum, resulting in a thermodynamic equilibrium where nothing further occurs. (36m50s)
• The Big Rip: If dark energy, referred to as Phantom Dark Energy, increases, it could overcome the binding energy of structures, tearing apart galaxy clusters, galaxies, solar systems, and eventually even atoms. (38m30s)
• The Big Rip could occur in at least 200 billion years based on current calculations of dark energy. (42m7s)

Vacuum Decay

• Vacuum Decay is a theoretical event where the Higgs field, an energy field throughout space, could change states. (44m31s)
• This transition in the Higgs field could result in changes to particle physics, potentially impacting the existence of particles, mass, and the fundamental forces of the universe. (45m1s)
• The Higgs field could transition to a different state through a process called Quantum tunneling. This transition is unpredictable, but it would involve the Higgs field shifting to a state known as a true vacuum. (46m12s)
• The current state of the Higgs field is referred to as a false vacuum, implying that it is not the most stable configuration. The universe might be metastable, meaning it is currently stable but could transition to a more stable state, similar to a cup balanced precariously on the edge of a table. (47m24s)
• If a Quantum tunneling event were to occur, a bubble of true vacuum would form and expand at approximately the speed of light, encompassing and transforming the universe. This event would be instantaneous and undetectable until it reached an observer. (50m4s)
• If the universe exists within a false vacuum, a change in the Higgs field could cause it to transition to a true vacuum state, destroying the universe in the process. (55m31s)
• This destruction would occur rapidly, at the speed of light, and would be imperceptible to observers within the universe. (55m40s)
• Current estimates suggest that, even if the universe exists within a false vacuum, the decay time is on the order of 10^100 to 10^500 years, making it extremely unlikely to occur within any timeframe relevant to human existence. (53m20s)

Cyclical Models of the Universe

• Some theorists, including the speaker's PhD advisor Paul Steinhardt, propose a cyclical model of the universe where a contraction leads to a smaller universe that then re-expands, preserving information like gravitational waves. (57m52s)
• Roger Penrose, a Nobel laureate, suggests the "conformal cyclic cosmology" where a new Big Bang emerges from the heat death of the previous universe, with information potentially passing through supermassive black holes. (58m21s)
• The concept of cosmic inflation suggests that multiple universes could arise from a larger universe, with some universes ending in heat death while others are just beginning. (1h0m31s)

The End of the Universe and Its Meaning

• The end of the universe means that nothing we do will ultimately matter and there will be no memory or persistence of human existence. (1h2m58s)
• Knowing about the end of the universe is a relatively new concept for humanity, existing for a small fraction of human history. (1h4m4s)
• The inevitability of the universe's end highlights the importance of finding meaning in the present moment, appreciating joy, love, and connection, and sharing those experiences with others. (1h7m47s)
• The universe will eventually be empty, cold, and dark, but humans should still find meaning in connection with each other. (1h9m27s)

Credits

• John Green and Dr. Katie Mack hosted the show, which was produced by Hannah West. (1h12m53s)
• The show was edited by Lonus Openhouse, with music and mix by Joseph Tuna Medis. (1h12m58s)