How is it theoretically possible for gravity to have infinite range throughout the universe?
In: Physics
Gravity does not have infinite range. Simply put gravity happens when am the mass of a object is significant higher than an other object nearby. If you are hundreds of Km away from any significant mass on the universe, you will not be subject to gravity.
The range of gravity extends infinitely, but the further away it gets the faster the force reduces eventually becoming negligible. The equation is essentially a fraction. Distance is the denominator so as it grows the force continuously sinks, but will never truly reach zero because there will always be a numerator so long as the objects exist and have mass.
I know that might not be a 5yo explanation but it’s the best I could do
Edit: Added the last three words of the first sentence
It can be a bit counter-intuitive at first, given how most interactions in everyday life need some direct interaction between objects, but gravity exists between any 2 objects that have mass, even if they aren’t in any sort of direct contact otherwise.
The force of gravity between objects decreases at an inverse square of the distance between them(meaning, we divide by an ever larger number), but never by a flat amount, so it simply never reaches 0.
How it’s *theoretically* possible for such a thing to even exist? That’s maybe more of a philosophical question, we observed it to be this way consistently, and doesn’t contradict anything we’ve seen, so we kind of just have to assume that it’s possible.
In *practice* however, because the force becomes really really weak really fast with distance, you get interactions where the force of gravity is effectively meaningless in extreme distances. In theory, a huge star really far away exerts gravity on you just the same way as Earth does under you, but if due to the distance between you and that star the force is the same size as between you and a piece of sand next to you, then it doesn’t influence much.
The best analogy I have ever heard to try and visualize this is to imagine a sheet of cloth pulled taught so that it is a flat sheet suspended in the air. Then, drop a bowling ball in the middle. The sheet will bend around the bowling ball, making a pretty massive indentation in the sheet. The further you get from the ball, the less indentation there is, but the sheet is _always_ intended a little bit no matter how far away you get.
That is gravity. Objects with large mass (the bowling ball) create large indentations in space-time (the sheet). The closer you are to the object with mass, the greater the effect of gravity (the indentation) but gravity is always there, no matter how far away you get.
You know those science fiction movies where some alien says “your feeble human mind couldn’t possibly understand…”, well it turns out there are some things that our feeble human brains have a very, very, very, hard time understanding and this is one of them. It’s easy for us to understand particles and if I tell you that a star throws out a handful of photons into space you can understand how those will just go on and on and on.
If I tell you that a force exists that drops exponentially from its source its easy for you to imagine what’s happening near the source. But the idea that the force could drop off and approach zero but never actually reach it? Witch-craft!
Its a bit like a toddler trying to shove a square peg into a round hole again and again and again. To them it should work and its baffling that it doesn’t. That’s basically what you are doing when you try and apply your regular, intuitive, thinking to issues like this. I don’t mean this to be derogatory, quite the opposite. We should think of ourselves like toddlers when it comes to this kind of stuff and appreciate the WONDER AND MYSTERY of the universe we are discovering. Its ok to keep banking the square peg into the round hole because that’s how we learn, so long as you are actually trying to learn from the process.
For myself, I’m just happy and excited that we live in an age where there are still grand mysteries left to be solved.
Like u/SifTheAbyss said the force of gravity decreases at an inverse of the separation squared meaning 1 divided by the separation squared of the two objects and one divided by anything (other than 0 which would break many things) is never nothing. It will be a very very very very small number but it will never be 0
Gravity does not theoretically extend infinitely. This is a classical view of physics.
According to quantum mechanics there must exist a minimum “amount of gravity”, a gravity quantum.
The thing is according to relativity and classical physics, gravity *does* reach infinitely. This is one of the problems in merging relativity and QM, and is one of the great unsolved problems of physics. But this is more a problem of making relativity work at small scales, since we know that QM already works at that scale.
In other words, there is no reason to think that a grain of sand would affect another grain of sand on the opposite end of the universe gravitationally. To be fair, there is yet no evidence of quantum gravity, but if it doesn’t exist, then QM must be wrong, and that would be remarkable.
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