"universe"

A rigorous discussion of the unknown is not possible, so it is necessary to narrow down the universe we are discussing to only the universe we can see

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

Scientists using modern observation equipment have determined the size, position, distance and other data of most of the objects in our galaxy

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

Although the Earth is just a "grain of dust suspended in the sun" in the universe, for us humans, this "grain of dust" is irreplaceable.

Further research shows that this mysterious force accounts for 68.3% of the total mass energy of the universe, and it is because of this that it is able to overcome gravity and become the dominant force controlling the operation of the universe

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

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.

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.

In theory, when a civilization develops into a civilization that can cross the stars, there is basically no risk of extinction