Probably nothing much would 'happen', we would just be even more isolated than we are now.
That would be a galaxy. Our solar system is part of the Milky Way galaxy, which contains billions of stars, planets, and other celestial objects.
The planets would slowly start to randomly go in directions, eventually colliding into the sun, or other planets.
No one knows. Astronomers are scanning the visible stars of our own Milky Way galaxy for planets orbiting faraway stars, but such planets would have to be nearly the size of Jupiter to be detected at such distances
If the planets did not move in their fixed orbits they may dash each other.
It would be impossible to detect them with current technology, but there is not doubt that there are. We have discovered over 900 planets just in a small corner of our own galaxy, and it is belived that there are hundreds of billions more. Other Galaxies are not fundamentally different from our own, so there is no reason they would contain planets.
If all planets are evenly spaced and there are 2,500 planets, they would be about 40 light years apart in the Milky Way.
nothing would happen to other planets if the world ended because the planets are so far apart that the explosion wouldnt reach too other planets and take my advise. the world wont end right now because since when humans exist, the world is still young.
There are millions, possibly billions, of planets in the Milky Way. An exact number will never be known.
No. There are dwarf planets in our own solar system that are smaller than Pluto and there are many undiscovered planets in the Milky Way that would be smaller than it, but are too far away to see.
If there was no gravity, the Sun and and the planets would never have formed.
This question would not exist!
Now, let's get serious. There are no aliens known to exist, just a bunch of anecdotes, and no matter how high you stack anecdotes, they never become evidence. We hope there is other life out there, and we consider it likely. But someone has to be the first form of intelligent life in the universe, and there is no evidence that it isn't us.