"universe"

Everything we can see in the universe has an internal structure and they are all made up of smaller matter, so what is the smallest matter in the universe?

Below the solar system, there is a star system labeled "alpha Centauri".

Whichever way you look at it, humans cannot be the only intelligent creatures in the universe. As far as we know, the universe has existed for at least tens of billions of years, so a reasonable speculation is that there is probably an advanced civilization in the universe that is hundreds of millions or even billions of years ahead of humans, and if that is the case, their level of technology is something that we humans simply cannot imagine.

After the sun evolves into a red giant, the hydrogen in its core is almost completely fused into helium, so the nuclear fusion inside the sun stops, after which the sun loses its internal radiation pressure and continues to collapse, leading to a constant increase in temperature and pressure in its core, while the helium in the central region of the sun is gradually compressed into the condensed state.

If we make the space station in space into a ring and let it rotate, then the humans in it will also feel the "centrifugal force" to "push" themselves towards the outer wall of the space station

The mass of a star cannot grow indefinitely, it can only reach the "Eddington limit" at most, so beyond this threshold, it will soon "eject" the extra material

The universe is so unimaginably large that even if humans were able to travel at infinitely close to the speed of light, they would not be able to penetrate its mysteries. Fortunately, the speed of light is not the speed limit of the universe, so it is entirely conceivable that in the distant future, humans may somehow be able to escape the shackles of the speed of light.

Between the Earth and the Moon there exists a much more empty space than imagined, so what can be put down in this space?

The reason we don't see time travelers is actually because they are not in our timeline

NASA's Jet Propulsion Laboratory's Near Earth Object Research Center has such a database, which is called the "Fireball Database."