What will happen if gravity vanishes?
Mass and gravity are linked with each other. Many times we have some fun thought experiments where a certain mass like a star is removed from the solar system and the effects are studied. But let’s remove the gravity and keep the mass of everything as is. So now all of a sudden, no mass will attract other mass by gravity. Alright?
In an instant!
Your local effects:
You will feel the effects instantly! You maybe sitting down or standing up. But in some way you are connected with the floor (gravity). But when gravity vanishes, you will instantly begin to move without any action. You will first rise a bit and then all other objects around you will also move around and rise with gentle speed. Anything that is not linked by electromagnetic force will move independently. Things will collide. You will struggle to grasp at something as that is your first instinct but every object is moving too. If you are inside your house, then you can hold on to the wall for some time as the earth and the crust and the land is weakly linked by electromagnetic force. But that will change soon too.
If you are out, you will rise, but actually you are moving sideways too, you just don’t realise it as your reference point is the ground below you which is also rotating. In short you have inertia of the rotational motion of the earth. Earth is revolving around the sun and you have that inertia too. The combination of both of these will make you move away from the ground if you are in certain parts of the world, and it will make you move with the ground in other parts of the world. Imagine people on opposite side of the earth.
Mostly, you will, with all other objects around, rise up and the ground will begin to slowly move away from you. Or so you observe. The air is no more held by gravity and it moves just like you, its density decreasing. You will now experience some difficulty in breathing. And soon enough you will suffocate.
The earth will, in hundreds of years, tear up due to complicated motion of its molten core but mostly it will stay intact.
Even though the gravity vanished suddenly and you felt its effects immediately, on large distances, you will not observe what you were expecting.
Let’s assume you do not die of suffocation and somehow stay alive.
If you are on the sun facing side of earth, you will not see anything weird immediately in the sky. The sun is still burning for you. But in the sun, the fusion stops. No new fusion takes place and so no new energy is formed. But the sun still has a lot of light and energy trapped inside and the energy begins to move out without hinderance. In 8 minutes, you will see the sun first glow up more and then dim away soon. The sun then disappears from your vision and the world turns black.
Now you will not see this, but due to the end of influence of the sun on the planets, every planet and orbiting object will begin to move away in straight lines with the tangential speed they had before gravity disappeared. The stuff in the sun will just drift apart over the course of millions of years like smoke drifts apart in an enclosed room.
If you are still alive somehow (impossible, we know) you will still see the distant stars shine as the light from them is travelling in straight line and you get that light. Depending upon the distances between you and the stars, you will start to see one by one stars going out. It will be a really slow process and you are just drifting in dark space without any footing on where you are heading. Perhaps you will collide with some object now and then. But after a while it will be a slow lonely drifting in space. To see the last of the light go out, you will have to wait billions of years! Think about why this is even though gravity vanished instantly from everywhere in the universe.