Is there any simple way to understand it? If our universe was a free fall model would the planet fall for an eternity? And if it isn’t infinite what lies outside the boundary is there any research to study around it

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Infinity is a place holder, its a way to describe a potential value beyond our ability to calculate. Or something that has an expanding value which appears to never have an end, or an end we dont yet know.

There are other asymptotes that might be easier to explain. Looking at a graph of 1/x as x gets near 0. The value becomes very large, but it’s hard to put a specific value on it. We can use ∞ for that.

I’ll try to give an answer that will help you understand the concept. I don’t think a 5 year old would get this though.

There are only so many ways that you can organize protons, neutrons, and electrons. That is the building block of all matter. Basically you have 3 legos that are really tiny and can only fit together in a certain way. Everything is built out of those 3 pieces. Because the number of ways to build matter are finite, there essentially must be an infinite number of Milky Way galaxies with every atom in the same spot as our galaxy if the universe is infinite (and the laws of physics don’t change in infinite ways or something silly).

And if the universe is actually infinite, we can estimate the average distance between our galaxy and the next identical galaxy. That number is something like 10 to the power of 10 to the power of 26 light years. Something absurd and too big to really fathom. But because the universe is infinite, there would still be infinite identical Milky Way galaxies with infinite me’s typing this to infinite you’s.

In addition to those identical Milky Way galaxies, there will be more infinite numbers of galaxies with 1 atom difference. And more with a million atoms difference. There are also infinite numbers of them, but there are MORE of them even though both have infinite numbers. It is a more common infinite to find milky ways with some differences than ours.

But there are still infinite numbers of our exact galaxy, or even our exact known universe. That is, if the universe is infinite and the laws of physics are the same. Which we don’t know.

Infinity is anything bigger than the biggest thing anyone can observe or perceive.

As soon as you observe it to be a value, infinity gets further away, at an infinite distance away each time.

Infinity is a mathematical concept of a number so large it cannot be quantified. It goes on forever. This is separate than what you ask in the description. Which is to ask if the universe is infinite, and how that could be.

Assuming the universe is infinite, the earth will not “fall” anywhere. All matter in the universe is constantly moving away from all other matter. Only gravity keeps things together. Eventually, all matter will spread out and cool off. The universe will “burn out” and die a cold quiet death.