There is a mistaken belief that I want to deny, people usually believe that by leaving the Earth's atmosphere and arriving in space, a phenomenon occurs that makes gravity disappear and allows astronauts to float freely; Well, this is not necessarily true.

Source
Public Domain - Author: NASA

First of all, and to make it easier to digest, we need to understand precisely what it is zero gravity, this term refers to a situation where the effect of gravity is counteracted by another effect. For example in general in space, zero gravity does not exist, unless the ship where our hypothetical astronauts are, is orbiting around the earth at an adequate speed.

Source
CC BY 2.0

A vivid example of this compensation of forces was when the astronauts who traveled to the moon felt a weaker gravity than the one exerted inside the earth, but that was not zero at all.

This is explained because when orbiting around the earth, that is to say in an accelerated system (uniform circular movement orbiting), the effect of gravity is almost exactly counterbalanced by the inertial forces associated with that system. So in fact, they do not perceive gravity even though they are within a gravitational field.

Source
Public Domain – Author: NASA

These statements were made known then, through the quantification and prediction that allowed physicists to make accurate calculations about what might happen at certain times.

So understanding now, that theoretically there is no zero gravity within the solar system, and that it depends on many factors of action, and that the sun also has enough gravity to keep an entire aligned system of planets orbiting around it.

Source
Public Domain – Author: NASA

Weightlessness.

The weightlessness that can be observed in videos of the Space Station, is not more than a mere illusion.

Source
Public Domain – Author: NASA

A simple way to understand this phenomenon is that the international space station is in a constant free fall. This was undoubtedly what Isaac Newton concluded when he observed an apple fall: If the apple falls towards the Earth, will the Moon also be falling?

Let's look at it better.

It is more than obvious that if you release an object, it simply falls to the ground, due to the gravity exerted on the inside of the earth (Blue)

Image made by me, from this image
Source
Public Domain

But if you add a horizontal speed to that same object, that object will fall at a point farther from where it originally fell, and without a doubt, from a certain horizontal speed, the curvature of the Earth begins to make a presence. (Red)

Image made by me, from this image
Source
Public Domain

However when the object reaches an orbital speed, it will continue to fall but it turns out that in the end, it will end up "finishing" the Earth to fall, so it will continue to fall to the ground but without hitting it. (Purple)

Image made by me, from this image
Source
Public Domain

This phenomenon of free fall is responsible for doing even when the ISS is in fall inside the crew feel a weightless space

Gravity reduction.

The force exerted by gravity contracts rapidly according to a scale that is inversely proportional to distance. That is to say that if we move away from the earth at an X distance and duplicate this distance, the gravity would be half, and so on progressively. However, gravity will never reach zero, no matter how far we go, it will always get smaller.

A graphic example of how gravity reduction works in relation to distance.

Assumption.

Let's suppose something for a moment, perhaps at some point in space the value of gravity is zero, this could be possible due to two main factors:

• The distance with a very large star.
• Very small gravity.

Another theory could be that indeed at some point in time and some time in the universe, gravity was zero, such as when the universe expanded as a result of dark energy, whose energy proportion was so great that it accelerated the space between objects faster than the speed of light, so gravitational waves, which also travel at that speed, do not have time to interact on objects.

Conclusion.

In summary, as I said, in no part of the universe, gravity is zero, what happens is that it gives the feeling of being because our body receives a different force. All this because the mass of our body is more minute, and is far from any object with a larger mass.

---

I hope you liked my explanation, if you have any doubt, opinion or contradiction feel free to share it and to the extent of my knowledge, I will try to answer them.

---

References.

• https://wonderopolis.org/wonder/why-is-there-no-gravity-in-space
• https://www.wired.com/2011/07/why-do-astronauts-float-around-in-space/
• https://www.space.com/23017-weightlessness.html
• https://physics.stackexchange.com/questions/231441/weightlessness-in-satellites
• https://en.wikipedia.org/wiki/Weightlessness
• https://www.britannica.com/science/weightlessness
• https://www.sciencedirect.com/science/article/pii/S0422989408711565
• Gravitation, by Charles W. Misner, Kip S. Thorne , John Archibald Wheeler and David I. Kaiser.