The circumference of the Earth's equator is 40,000 kilometers, and from the Earth to the Moon is 380,000 kilometers.
An astronomical unit is 150 million kilometers, which is also the distance from the earth to the sun, and after leaving the solar system, the astronomical unit will give way to light years, for example, Proxima Centauri is 4.22 light years away from us, and the diameter of the Milky Way is 180,000 light years.
One second can fly 300,000 kilometers, and after one year of continuous flight, we can get that one light year is 9.46 trillion kilometers, a number that is difficult for the human brain to imagine, and it has been completely distorted, so we will use some practical examples to set off how far a light year is.
If a car can maintain a speed of 200 kilometers per hour for a long time, then it will take 5.4 million years to cover a light year, which is almost from the time when our ancestors first appeared and has just ended now.
The fastest probe to fly at present, the Parker solar probe can reach a speed of 192 kilometers per second, in which case it takes 1,500 years to fly a light year, as for the more familiar Voyager 1 and 2, their speed is only 17 kilometers per second, and it takes 18,000 years to fly a light year.
Interestingly, the radius of the Oort cloud, the outermost part of the solar system, is exactly one light-year, so neither Voyager 1 nor Voyager 2 actually flew out of the solar system, but only out of the heliosphere of the sun, and they are still tens of thousands of years away from true interstellar space.
Let's not forget that the closest star world to the solar system is Proxima Centauri 4.22 light-years away, the closest galaxy of the same magnitude to the Milky Way is the Andromeda Galaxy 2.54 million light-years away, and the entire observable universe has a diameter of 93 billion light-years, of which there are at least 2 trillion galaxies, all of which are millions of light-years away on average.
At this time, if you look at another light year, you will find that it is only a very short distance in the universe, and there is a parsec above it, all the way to a million parsecs, a second gap is 3.26 light years, and a million parsecs is 3.26 million light years.
You may think that the speed of light of 300,000 kilometers per second is the speed of a snail in the face of the vast universe, and even a light-speed spaceship cannot effectively explore the universe, but this sentence is actually only half true, because although the speed of light is very slow in the universe, the time dilation effect of light-speed travel will make the time lapse speed of the people in the spacecraft infinitely close to 0.
This phenomenon, which Einstein called time dilation, will allow the person driving the light-speed spaceship to reach any place in the universe in an instant, but he himself will not feel the passage of time.
In fact, for the photons in the universe, they also arrived at the earth at the moment of birth, and reached anywhere in the universe, because time is stationary for them, only us on the earth, in a low-speed reference frame, will think that the sunlight flew for 8 minutes and 20 seconds to reach the earth, and the photons of the Andromeda galaxy flew for 2.54 million years to reach the earth.
Overall
If humans want to travel in the vast universe, the speed of light is a threshold that must be crossed, such as curvature drive, such as wormholes, these are the current theories allow for faster-than-light methods, the only problem is that we don't know how to achieve them.