I am also interested in “Level II: Universes with different physical constants”. Do you happen to know if there’s actually good ways to approach that question — ie any methodology much better than wild speculation? I would love to learn about such a method
Well, slightly better than wild speculation. We observe broken symmetries in particle physics. This suggests that the corresponding unbroken symmetries existed in the past and could have been broken differently, which would correspond to different (apparent) laws of physics, meaning particles we call “fundamental” might have different properties in different regions of the Cosmos, although this is thought to be far outside our observable universe.
The currently accepted version of the Big Bang theory describes a universe undergoing phase shifts, particularly around the inflationary epoch. This wouldn’t necessarily have happened everywhere at once. In the Eternal Inflation model, in a brief moment near the beginning of the observable universe, space used to be expanding far faster than it is now, but (due to chance) a nucleus of what we’d call “normal” spacetime with a lower energy level occurred and spread as the surrounding higher-energy state collapsed, ending the epoch.
However, the expansion of the inflating state is so rapid, that this collapse wave could never catch up to all of it, meaning the higher-energy state still exists and the wave of collapse to normal spacetime is ongoing far away. Due to chance, we can expect many other lower-energy nucleation events to have occurred (and to continue to occur) inside the inflating region, forming bubbles of different (apparent) physics, some probably corresponding to our own, but most probably not, due to the symmetries breaking in different directions.
Each of these bubbles is effectively an isolated universe, and the collection of all of them constitutes the Tegmark Level II Multiverse.
I am also interested in “Level II: Universes with different physical constants”. Do you happen to know if there’s actually good ways to approach that question — ie any methodology much better than wild speculation? I would love to learn about such a method
Well, slightly better than wild speculation. We observe broken symmetries in particle physics. This suggests that the corresponding unbroken symmetries existed in the past and could have been broken differently, which would correspond to different (apparent) laws of physics, meaning particles we call “fundamental” might have different properties in different regions of the Cosmos, although this is thought to be far outside our observable universe.
The currently accepted version of the Big Bang theory describes a universe undergoing phase shifts, particularly around the inflationary epoch. This wouldn’t necessarily have happened everywhere at once. In the Eternal Inflation model, in a brief moment near the beginning of the observable universe, space used to be expanding far faster than it is now, but (due to chance) a nucleus of what we’d call “normal” spacetime with a lower energy level occurred and spread as the surrounding higher-energy state collapsed, ending the epoch.
However, the expansion of the inflating state is so rapid, that this collapse wave could never catch up to all of it, meaning the higher-energy state still exists and the wave of collapse to normal spacetime is ongoing far away. Due to chance, we can expect many other lower-energy nucleation events to have occurred (and to continue to occur) inside the inflating region, forming bubbles of different (apparent) physics, some probably corresponding to our own, but most probably not, due to the symmetries breaking in different directions.
Each of these bubbles is effectively an isolated universe, and the collection of all of them constitutes the Tegmark Level II Multiverse.
Your explanation is much appreciated! It’s probably time that I properly go and understand the broken symmetries stuff.