Spoiler alert – in the future there never will be artificial gravity – astronauts won’t be able to walk around in spaceships.
In the movies most spaceships like the Starship Enterprise employ a convenient technology they call “artificial gravity” to overcome this weightlessness problem. In a few movies they even rotate parts of the ship, though the part of the ship that rotates often has no relevance to the part of the space ship people are walking around in.
No matter. Walking around is a convenient way to avoid a big budget.
Weightlessness is a pesky little problem and we’ve become comfortable accepting that on spaceships of the future you’ll be solidly on the floor. Venture outside to fix anything and you’ll be weightless maybe (unless you use something they call “gravity boots”) but inside, put something on a table and it stays on the table. People won’t be weightless in spaceships in the future.
That’s why they call this stuff science fiction. There won’t be any artificial gravity and to the dismay of Kirk and Spock a spaceship that looks like their’s will have weightless people inside.
Another design, a real design, for a spaceship that would actually have “artificial gravity” is called the Von Braun spacewheel, and envisioned in movies wanting more realism. The Von Braun spacewheel looks like this contraption. Of course, it spins and as it does the occupants inside experience centripetal acceleration, also sometimes known as artificial gravity.
So why doesn’t NASA build one of these?
Well, along comes the real world, pushing Hollywood right outta there.
They don’t have the lifting power to get all the parts up there. It’s doubtful the Falcon-heavy will be utilized for such a project.
Assembly and then pressuring it inside are formidable obstacles. This is not impossible, but beyond available budgets.
Zero gravity laboratories, like the present International Space Station have taught us that research in microgravity environments is valuable.
With exercise, astronauts do just fine, so why bother?
Alas, we may send people to Mars one day, but those poor ol’ chaps will be weightless all the way, and exercise like they do on the ISS.
If aliens had something like hands with something like opposable thumbs and intelligence and a few hundred thousand years, then possibly they might develop technology similar to ours.
So what is an opposable thumb? According to an article on NSTA News: “Human thumbs are called opposable thumbs. They are called opposable because the thumb can be moved around to touch the other fingers, which gives people the ability to grasp things. Most primates (humans, apes, and Old World monkeys) and some other animals have opposable thumbs.”
You ask if aliens exists in the universe, however you should know not all aliens need be intelligent. Most of them are probably germs. Just look at Earth. Not all creatures here are human! Most of them are insects, plankton, germs, fish, mammals and birds.
The law of probability suggests that there exists alien biodiversity somewhere else because the universe is pretty big. However, there is no proof or hard evidence that even an alien microbe exists at present. Maybe we’ll discover something growing on Titan one day.
Perhaps we’ll even discover another intelligent self-aware life form out there.
Great question, but let’s bring it down to Earth so we can see from the perspective of history.
American Indians lived in North America for centuries and knew no other people from other parts of the world. When the first Europeans settled they were from the other side of the ocean – a vast inconceivable distance and place. The Europeans were aliens.
The Europeans started to encroach on native lands, pushing natives back into territories occupied by other natives. War between natives broke out. Eventually war with the descendants of the Europeans broke out. It was a mess. Most Indian tribes did combine, sharing the common enemy: The United States of America.
In terms of the modern world, united we stand, divided we fall. We’re divided.