Ten thousand world systems

In the early Buddhist texts a world is that in the world through which one perceives & conceives the world, eg mind, eye, ear.

A world which is a thousandfold system is thus a perception of a thousandfold percepients.

Special relativity and principle of non-simultaneity do well in explaining why and how it is world.

"If the mind makes no discriminations, the ten thousand things are as they are, of single essence." -from the early Chinese Zen poem The Xinxin Ming

Compare also

"The named is the mother of ten thousand things." -from The Tao Te Ching

It is interesting to look at the soteriological role of numbers in Indian thought, as discussed in this episode of In Our Time: Indian Mathematics. A kalpa in Buddhist thought has been estimated at millions of years, and a maha-kalpa at tens or hundreds of billions of years - appropriate for geological time, the current age of the universe, and the stelliferous era over which stars will form, respectively. But what is notable is these were not presented as exact:

"it would not be equal to a Maha Kalpa" "even that number will be less than the number of passed kalpas" "will be filled even before the kalpa end"

are typical phrasings. So like with the number of realms, I'd say the import here is to understand our situation in general terms, to gain a sense of perspective.

Physics is very much a work in progress, what we are sure of about time and gravity, is that they don't fit with the other forces which we have a nice integrates quantum field of. A fifth force turned up from muon behaviour a few weeks ago. Dark energy and dark matter are big challenges to our picture of the past and future. Yet in 1900 Lord Kelvin declared:

“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”

just five or so years before the beginning of quantum mechanics, and two decades before relativity.

Mixing and matching between physics and Buddhist thought is not I think generally useful. Buddhist thinking forms a coherent whole, best understood in reference to itself, as tools aimed at cultivating awakening.

It is remarkable that Buddhist cosmology seems to have the most accurate timescale from long before Hubble, and point not to an infinite cosmos but one very very large (there are likely a lot more than 10,000 planets with intelligent life in the universe). It is highly well suited to a universe encountering alien species, and to Earth's own animals developing human-level consciousness. But it is better I'd say approached as a way of thinking, rather than as a set of results, or declarations. What I'd say is remarkable, is what is indicated about the power of regular meditation practice to give us good answers to deep questions.

In physics there is no agreement or clarity about the multiverse, the existence of Many Worlds, brane collisions, fracture planes in the E8 mathematical structure, multiple time dimensions, whether the past and future are 'real', whether there are multiple dimensions of time, or why the time dimension behaves differently from space dimensions. Buddhist thought is not waiting for those answers. Like in The Parable Of The Poison Arrow, next to the problem of suffering these are like asking about the material the bow was made from, when we have been struck by an arrow. It may be good to know the poison, to understand why someone might fire such an arrow - but don't forget why: to benefit all sentient beings.

If there is one thing we can be sure of, it is that our words are not sufficient to communicate the understanding of an enlightened person to someone who isn't. The cosmos will doubtless prove stranger and more beautiful than we are even beginning to imagine. I suggest a playfulness about cosmology, an inquiry into it for how it can help us be better. This Kurzgesacht video 'The Egg' is a nice example of how different traditions may have been like the blind men who approached the elephant in different ways.