Kenji Miyazawa's Universe (69) What lies at the very end of the blue sky?

Kenji Miyazawa's Mental Sketch [At the Very End of the Blue Sky]

There is a short mental sketch by Kenji Miyazawa titled [At the Very End of the Blue Sky].

1074 [At the Very End of the Blue Sky] June 12, 1927,
At the very end of the blue sky
Above the atmosphere where even hydrogen is too sparse
"I am the whole world
The world is a shifting shadow of a blue dream"
Even thoughts like these
Are too heavy to contemplate
Where groups of eternal and transparent creatures dwell (The [New] Collected Works of Kenji Miyazawa, Vol. 4, Chikuma Shobo, 1995, p. 266)

What lies beyond the blue sky? What lies beyond the night sky? Hasn't everyone thought about this at least once? And Kenji thought about it too. That is [At the Very End of the Blue Sky].

Above the atmosphere where even hydrogen is too sparse

This expression likely refers to the space beyond the atmosphere. Kenji loved the word 'kiken' (atmosphere), but this refers to the atmospheric layer. Above the atmosphere, there is no more air, just sparse gas drifting about. Since hydrogen is the most abundant element in the universe, he likely expressed it as 'even hydrogen is too sparse.' But do groups of eternal and transparent creatures really dwell there?

Where is the very end of the blue sky?

By the way, is the space outside the atmosphere the very end of the blue sky? 'End' implies a conclusion. For example, the 'end of a journey' refers to the destination. It would be lonely if the end of the blue sky were just outside the atmosphere. Can't we go further?

Heliopause — The Edge of the Solar System

Let's leave Earth and think from the perspective of the solar system. We find that there is an edge called the heliopause. A wind blows from the sun. It is the solar wind. The solar wind collides and mixes with the interstellar gas (the sparse gas existing between stars) within the Milky Way galaxy. This boundary surface is called the heliopause (Figure 1).

In other words, the range reached by the solar wind is only inside the heliopause. This region is also called the 'heliosphere' because it is the range influenced by the sun.

Oort Cloud

The size of the heliopause is about 100 times the distance between the Earth and the Sun (a distance called 1 astronomical unit, approximately 150 million kilometers). We could call this the very end of the blue sky. However, the solar system has a much larger extent. It is called the 'Oort cloud' (Figure 2). It is believed that there are many planetesimals captured by the sun's gravity at its edge. Because these planetesimals interact gravitationally with each other, their orbits are sometimes changed, bringing them closer to the sun. At that time, the ice and dust particles on the surface of the planetesimals are stripped away by the sun's radiation and appear as comets. In other words, the 'Oort cloud' is the home of comets.

The size of the 'Oort cloud' reaches tens of thousands of astronomical units in diameter. It seems we have come quite far to the edge.

Do you want to go even further to the edge?

From here on, it becomes a world of stars and interstellar gas in the Milky Way galaxy. Furthermore, there is a large amount of dark matter (several times that of elemental matter) in the halo surrounding the Milky Way galaxy.

If you leave the Milky Way galaxy, it becomes a world with numerous galaxies. There is also intergalactic gas between galaxies.

The universe we live in is expanding, and its current size is about 47 billion light-years (1 light-year is the distance light travels in one year, about 10 trillion kilometers). If there is a very end of the blue sky, it would be 47 billion light-years away.

Kenji-san, how about here?

What lies beyond that?

What lies beyond that? Can we go even further to the end? It is a point of curiosity.

What we can consider to exist is the neighboring universe. It is not just one. There are many, so it is called the multiverse. The era of calling the cosmos the 'universe' is over ('uni' means one).

So, can we see the neighboring universe? Or can we go to the neighboring universe? That is impossible. We can only perceive this universe in which we live. At present, the multiverse exists only within theory.

By the way, a group of eternal and transparent creatures dwell
where is this referring to?