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Comment by ck2 | Hacker News Reader

You know what blows my mind but everyone takes for granted?

Inertia. Sure, gravity is an amazing, mysterious force, but inertia in a vacuum boggles my comprehension. Why does something with physical mass keep going without any additional energy applied to it - forever?

Think about Voyager - if no other force got in its way, it could literally keep cruising for 50 billion light-years and maybe "bounce" off the wall of the universe like something out of The Truman Show. (of course since the universe keeps expanding it might have to go more than 50 billion light-years)

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What blows my mind even more is to imagine the sheer immensity in the scale here: A tiny speck of a probe in the vastness of space.

No matter whether those aliens are hostile or not, kudos to them if they can even find the damn thing!

How about this:

When you throw a ball, you are converting the potential energy in your body to a kinetic energy stored in the ball. In order for the ball to slow down, something has to get that energy out of it. Since energy can't be destroyed, the ball is forced to keep going forever until the kinetic energy is taken away.

It's actually quite simple.

When you throw a ball, it only slows down because of friction with the air surrounding it or because it hits something.

When you give an object force, it will just keep going because there is no opposing force to diminish the force you gave it in the first place.

Hope that makes some semblance of sense!

Oh I understand the physics of it and why it's harder to grasp the concept on earth with gravity and friction.

But stop and think about it - the universe is like some kind of infinite iced-over pond where something will keep going and going and going once given momentum.

I mean in space it's sliding endlessly across "nothingness" - doesn't that kinda freak you out when you really think about it?

It makes sense if you accept that there is no concept of absolute rest. The state of "moving" is really the natural state...when you apply force to something, you are just changing the parameters of that state.

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