If the Earth's temperature suddenly dropped to absolute zero (which is -273.15 degrees Celsius or 0 Kelvin), it would have catastrophic consequences for life as we know it. Absolute zero represents the complete absence of heat energy, and such extreme cold temperatures would cause virtually all molecular and atomic activity to cease. Under these conditions, it is highly unlikely that any existing bunker or human-made structure would provide a suitable environment for survival.
Even if there were bunkers designed to withstand extreme temperatures, they would need to be equipped with advanced life-support systems capable of generating heat and sustaining the necessary atmospheric conditions for human survival. Such bunkers would require a continuous and abundant energy source to maintain habitable conditions, which is currently beyond our technological capabilities.
Furthermore, the sudden drop to absolute zero would have devastating effects on the Earth's ecosystem. Most plants and animals are adapted to specific temperature ranges, and the complete absence of heat would likely cause widespread death and extinction. The food chain would collapse, and ecosystems would be unable to support life.
If, hypothetically, the Earth's temperature were to suddenly rise again after reaching absolute zero, it would still present immense challenges for the survival and recovery of human civilization. The Earth's environment and ecosystems would be drastically altered, and it would take a significant amount of time for life to reestablish itself. The odds of returning to "normal" lives would depend on various factors, including the availability of resources, the ability to adapt to new conditions, and the resilience and ingenuity of human beings. It would likely be a long and complex process requiring significant technological advancements and cooperation among survivors.