# Could a ball lying on the ground spontaneously bounce?

• LogicX

#### LogicX

My textbook tells me that balls don't randomly bounce upward because it is improbable that all of the thermal motion of the particles suddenly align in one direction (upward). But it is just improbable right, or is it impossible?

I guess what I'm asking is, is entropy only a statistical expression and thus the ball could bounce, or would this violate the second law?

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My textbook tells me that balls don't randomly bounce upward because it is improbable that all of the thermal motion of the particles suddenly align in one direction (upward). But it is just improbable right, or is it impossible?

I guess what I'm asking is, is entropy only a statistical expression and thus the ball could bounce, or would this violate the second law?

EDIT: Oh wow, how did this end up here? Please move this thread, I'm sorry.

All objects above absolute zero are jittering with molecular motion. Essentially, at a very tiny scale, the ball is spontaneously bouncing from the occasional accumulation of molecules bouncing on the same direction. It's just really tiny.

Have you ever seen Brownian motion act on grains of pollen?

I believe the answer is that it is indeed vanishingly improbable. Like on the order of the age of the universe.

So entropy really is just a statement of probability then? And the ball, however improbable it is, can violate the second law? Or is this not a violation of the second law?

Or is this not a violation of the second law?

It is not. The system is not closed.

But it is just improbable right, or is it impossible?

It is not impossible, but it is very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very improbable. (Maybe a mole of "very"s would be enough.)

Fundamentally, the second law of thermodynamics is a statistical statement. With ten molecules, violations are uncommon but do occasionally occur. With a hundred molecules, they become highly unlikely. With a thousand molecules, you're probably more likely to win the Powerball jackpot. With a mole of molecules... well...

There is no way that heat will apply a downward force to a ball of any normal size sufficient to flex it. Work must be done to store energy. This work must not violate the third law of motion. There is nothing in the air, nor anything else, which can absorb the force of the heat in such a manner to supply this downward force. Absent of external thrust or a light enough ball, say with a nano-thin flexible shell with great elasticity, it will *never* happen.

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My textbook tells me that balls don't randomly bounce upward because it is improbable that all of the thermal motion of the particles suddenly align in one direction (upward). But it is just improbable right, or is it impossible?

I guess what I'm asking is, is entropy only a statistical expression and thus the ball could bounce, or would this violate the second law?

Any time you question whether or not something is "possible," the answer(in todays Quantum view of the universe) the answer is yes.

Is it possible for the ball to morph into a hungry lion and eat you? Yes. How possible? Thats intuitive...

That of course is not going to happen, let alone spontaneously.

That of course is not going to happen, let alone spontaneously.

Just because its not GOING to happen, doesn't mean it CAN'T happen.

What are the odds of a small dense point of matter and energy expanding into an entire inhabitable universe? Not very good.

A ball spontaneously changing into a hungry lion is impossible by physics as we know it.

A ball spontaneously jumping off the ground is fabulously unlikely, but there is no principle - except that of cumulative probabilities - preventing it from happening.

What are the odds of a small dense point of matter and energy expanding into an entire inhabitable universe?
One.

One.

just because it occurred does not mean its probability was one.

Rolling a dice and getting a four does not mean there was a one hundred percent chance of getting a four.

I would say the chances of the ground and rubber ball suddenly disappearing, or exploding, or turning into a lion, are no less likely than a small point of energy winking into existence on the quantum scale(or however you believe the story went before the big bang) and suddenly expanding into and cooling into a universe with a set of rules favorable to the evolution of intelligent life.

P never is one or zero in a quantum universe

Walking through a wall is also possible but it's splendidly unlikely.

Walking through a wall is also possible but it's splendidly unlikely.

Correct. If you had an infinite amount of time, and walked into the wall over and over, you would walk through it an infinite number of times.

Given eternity within the sea of vagueness (state of pre-exisitence, pre-something/nothing) a chance for Universe to arise (e.g. via Big Bang) is surely one. (Since it did happen once.)

A ball to turn into an lion within our Universe which isn't eternal cannot have a chance of one.

In short, Universe happens infinite times, while each Universe isn't lasting forever... Only if it could then I'd agree that a ball can suddenly morph into a lion or whatever.

Given eternity within the sea of vagueness (state of pre-exisitence, pre-something/nothing) a chance for Universe to arise (e.g. via Big Bang) is surely one. (Since it did happen once.)

A ball to turn into an lion within our Universe which isn't eternal cannot have a chance of one.

Yes, but then again, (since we're talking about the same universe), you have to give the ball the same domain. It will surely at some point turn into a man eating lion...given an infinite amount of time.

Considering nothing about the universe, or its origins, is known to be infinite, the odds of either are highly unlikely.

We got lucky once.

Correct. If you had an infinite amount of time, and walked into the wall over and over, you would walk through it an infinite number of times.

And that's in addition to the fact that you would ALSO likely spend an infinite amount of time in the emergency room getting your nosed fixed on all the times when it didn't work.

And that's in addition to the fact that you would ALSO likely spend an infinite amount of time in the emergency room getting your nosed fixed on all the times when it didn't work.

This is correct. Except that your monetary resources are probably not as infinite as they would need to be to support such an endeavor.

Partly we seem to agree, that is, in case when we consider SAME Universe being eternal, as I added in my above post while you were answering me:
"In short, Universe happens infinite times, while each Universe isn't lasting forever... Only if it could then I'd agree that a ball can suddenly morph into a lion or whatever."

Also, if we consider that pre-conditions for Big Bang are eternal and each Universe is not, then we have a disagreement.

But who cares right, we won't live long enuff to see who's right, right? Or will we? ;)

Partly we seem to agree, that is, in case when we consider SAME Universe being eternal, as I added in my above post while you were answering me:
"In short, Universe happens infinite times, while each Universe isn't lasting forever... Only if it could then I'd agree that a ball can suddenly morph into a lion or whatever."

Also, if we consider that pre-conditions for Big Bang are eternal and each Universe is not, then we have a disagreement.

But who cares right, we won't live long enuff to see who's right, right? Or will we? ;)

Well, the singularity is near...

Any time you question whether or not something is "possible," the answer(in todays Quantum view of the universe) the answer is yes.

Is it possible for the ball to morph into a hungry lion and eat you? Yes. How possible? Thats intuitive...

Physical systems always obey conservation of 4-momentum. As long as your transmutation from ball to lion does that, you can talk transition rates...

BBB

It is not. The system is not closed.

How is it not closed? The system is the ball and the ground. The atoms in the ball all randomly align and make it move upward.

So do we have here a spontaneous process, however unlikely, in which there is a decrease in entropy.

Should the second law really read "It is probable that for spontaneous processes, entropy increases"?

That doesn't seem like a great "law" then...

How is it not closed? The system is the ball and the ground. The atoms in the ball all randomly align and make it move upward.

How do they do that without violating the conservation of momentum?

BBB

By the way, the 2nd law has already been violated experimentally at small time-energy scales. It is true that it is statistical in nature, but in every case, it eventually wins. So I wouldn't add "probable" to the 2nd law, but merely the caveat that it (like energy conservation) can be broken for a very short time.

In order for the momentum vectors of ball's atoms to align and point up, they will have to bump into each other in an extremely unlikely fashion so that they first push down against the floor (or the atoms below them) en masse, and the resulting elastic collision sends the atoms' momentum up. So yes, they need the floor bounce off of to align themselves in the up direction. Essentially, the ball bounces itself.

Statements such as "very improbable" have quantitative practical meaning. For a given event, one can conceivably calculate the transition probability rate for the system to go from the pre-event state to the post-event state. The inverse of the transition rate is the transition lifetime. If, upon calculation, a transition lifetime is longer than the total amount of time the experiment will be run/system will be observed/machine will be used, than for practical purposes, the transition is so improbable that it is considered impossible. For instance, strictly speaking, all heavy elements on the periodic table are unstable and will eventually experience nuclear decay. But some of them have half-lives older than than the age of the universe, so they are considered stable for practical purposes.

By the way, the 2nd law has already been violated experimentally at small time-energy scales. It is true that it is statistical in nature, but in every case, it eventually wins. So I wouldn't add "probable" to the 2nd law, but merely the caveat that it (like energy conservation) can be broken for a very short time.

In order for the momentum vectors of ball's atoms to align and point up, they will have to bump into each other in an extremely unlikely fashion so that they first push down against the floor (or the atoms below them) en masse, and the resulting elastic collision sends the atoms' momentum up. So yes, they need the floor bounce off of to align themselves in the up direction. Essentially, the ball bounces itself.

Well, if we are depending on thermal collisions to generate the improbable event, I would put this a different way. Thermal fluctuations in the kinetic energy of the ball are on the order of kT (or just T, when using the correct units where k=1). So in that sense the ball is always jumping up and down and sideways, it's just that for a macroscopic ball the movement is very tiny. So it's not that movement is improbable to the point of being "impossible", it's that the probability of a given state declines exponentially with the square of the velocity, in accordance with the Boltzmann factor exp(-0.5*M*v2/T)...