Tuesday, June 8, 2021

Quantum Cosmology



“The argument that Hawking has offered may be conveyed by question-and-answer:

Q: From what did our universe evolve? A: Our universe evolved from a much smaller, much emptier mini-universe. You may think of it as an egg. Q: What was the smaller, emptier universe like? A: It was a four-dimensional sphere with nothing much inside it. You may think of that as weird. Q: How can a sphere have four dimensions? A: A sphere may have four dimensions if it has one more dimension than a three-dimensional sphere. You may think of that as obvious. Q: Does the smaller, emptier universe have a name? A: The smaller, emptier universe is called a de Sitter universe. You may think of that as about time someone paid attention to de Sitter. Q: Is there anything else I should know about the smaller, emptier universe? A: Yes. It represents a solution to Einstein’s field equations. You may think of that as a good thing. Q: Where was that smaller, emptier universe or egg? A: It was in the place where space as we know it did not exist. You may think of it as a sac. Q: When was it there? A: It was there at the time when time as we know it did not exist. You may think of it as a mystery. Q: Where did the egg come from? A: The egg did not actually come from anywhere. You may think of this as astonishing. Q: If the egg did not come from anywhere, how did it get there? A: The egg got there because the wave function of the universe said it was probable. You may think of this as a done deal. Q: How did our universe evolve from the egg? A: It evolved by inflating itself up from its sac to become the universe in which we now find ourselves. You may think of that as just one of those things. This catechism, I should add, is not a parody of quantum cosmology. It is quantum cosmology.”