Is action and reaction instantanious?

Main Question or Discussion Point

I know very little about physics, so I hope this is a pretty easy question.

Action is always acting and reaction is always equal. Is this action and reaction instantanious, and if not, why not?

I read around quite a bit but this alludes me.

I hope my query is worthy of consideration. I can't quantify for myself if its a good question or not.

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russ_watters
Mentor
Yes, they are instantaneous.

So all action and reaction in the entire universe is within an instant.

And action is reaction.

Which is not even action, since it is zero in an instant.

Is this logically flawed?

And are we within the bounds of physics?

Doc Al
Mentor
The terms "action" and "reaction" are somewhat problematic (and outdated) as they imply that first comes the "action", followed by the "reaction" (as the terms are used in non-physics, everyday contexts). A better term is "3rd law pair". For example, consider a contact force between two bodies: Body A and Body B exert forces on each other. The two "3rd law pairs" are: The force that A exerts on B and the force that B exerts on A. There is no implication of time order--they are two parts of a single interaction.

(Of course the 3rd law gets a bit more complicated when fields are involved.)

fluidistic
Gold Member
If you are talking about Newton's third law, then it is instantaneous. But this doesn't describe our universe well at such speeds (I'm talking about the speed of light in vacuum). At most it could have the speed of light. That means that if the sun suddenly disappear, the Earth would suffer changes in its orbit about 8 minutes later and not instantaneously as Newton could have thought. I'll study this law more in details very soon, but I guess I'm right saying that the gravitation is an action-reaction law. If I made an error, just tell me, thanks.

rcgldr
Homework Helper
The 3rd pair law action and reaction are simultaneous. However there is a delay between the time a force is initially applied to a system and the time when the system stabilizes, due to deformation of the objects involved (compression or tension at the point of application of forces).

Thank you everyone.

My thoughts are:

The first action is simultaneous with the last, and all action in between (universally speaking), so all action is instantaneous and singular in nature. (like in 3rd pair law).

Action is not of time (and perception of seemingly endless action and reaction is remarkable.)

So action itself is not of matter.

The action apon "matter" made frequency movement in a photon (massless) and light speed established energy form transfer rates equal to time and the "rate of perception".

The quantum thoeries seem heavily dependent on the observer.

So time itself is within the first (and only) action which is zero in that instant.

So perception is more a prerequisite for time/space/matter and not so much a consequence of the movement of "matter". (However, the action itself is singular.)

Do my logical steps still hold water and are they in keeping with quantum theories?

I deeply appreciate your indulging me as I am not well versed in physics. (oh, you noticed).

And I apologise in advance if this post is inappropriate.

russ_watters
Mentor
Honestly, I can't make heads or tails of what you are trying to say there. It just looks like gibberish to me.

HallsofIvy
Homework Helper
Thank you everyone.

My thoughts are:

The first action is simultaneous with the last, and all action in between (universally speaking), so all action is instantaneous and singular in nature. (like in 3rd pair law).
Where did "singular" suddenly come from?

Action is not of time (and perception of seemingly endless action and reaction is remarkable.)
No, no one has said that. Action (and reaction) certainly can occur over time. The only thing that has been said is that the "action" and "reaction" occur at the same time.

So action itself is not of matter.

The action apon "matter" made frequency movement in a photon (massless) and light speed established energy form transfer rates equal to time and the "rate of perception".
That's gibberish. "action" and "reaction" do not necessarily have anything to do with photons and I have no idea what you mean by "rate of perception".

The quantum thoeries seem heavily dependent on the observer.

So time itself is within the first (and only) action which is zero in that instant.

So perception is more a prerequisite for time/space/matter and not so much a consequence of the movement of "matter". (However, the action itself is singular.)

Do my logical steps still hold water and are they in keeping with quantum theories?
I cannot say anything about your "logical steps" since I see none here.

I deeply appreciate your indulging me as I am not well versed in physics. (oh, you noticed).

And I apologise in advance if this post is inappropriate.

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I cannot say anything about your "logica steps" since I see none here.
yes, I have been told is is off.

I tried to edit the post and couldn't so I hope to re-direct soon.

I must have lost the edited post so I'll try again.

I see that action and reaction are a single action by the 3rd pair law.

If the first action reacts instaneously and so on, all action is instantanous.

All action is momentary.

The primary particals (strings, loops, photons etc) are massless.

So an infinitely small amount of energy or action is required for movement as matter is infinitely massless.

The entirety of time is the duration between the first and last actions which is instantaneous. (By a chain of action and reaction begun by the first action.)

Perception of time is the observation of movement, but in fact no time elapses between the first and last actions as they are a chain reaction of instant 3rd pairs.

I'm suggesting that time/space if of perception, and 3rd pair instant action is the reality.

I hope this is clear. If it is just gibberish I'll refrain, I think there's logic in it and would appreciate if the flaws could be pointed out.

Thanks everyone for indulging my rather naive notions and I hope my post is appropriate.

HallsofIvy
Homework Helper
I must have lost the edited post so I'll try again.

I see that action and reaction are a single action by the 3rd pair law.
What "3rd pair law" are you talking about. No, no one has said that "action and reaction are a single action". They are separate "actions" that occur at the same time.

If the first action reacts instaneously and so on, all action is instantanous.
"Simultaneously", not "instantaneously". Those are very different words.

All action is momentary.
You have been told repeatedly now that "action" and "reaction" occur simultaneously. That does not imply either "instantaneous" or "momentary".

The primary particals (strings, loops, photons etc) are massless.
You must be using the wrong word here. Primary particles are not all massless nor are strings and loops particles.

So an infinitely small amount of energy or action is required for movement as matter is infinitely massless.
Where did you get that idea? I'm made of particles and I am definitely not massless!

The entirety of time is the duration between the first and last actions which is instantaneous. (By a chain of action and reaction begun by the first action.)
What do you mean by "first and last action"? If you mean an action and reaction, there is no "duration between the first and last actions".

Perception of time is the observation of movement, but in fact no time elapses between the first and last actions as they are a chain reaction of instant 3rd pairs.
Now, what do you mean by "3rd pairs"? It is hard to understand what you mean because you keep introducing new terms ("first and last actions", "3rd pairs") without defining them.

I'm suggesting that time/space if of perception, and 3rd pair instant action is the reality.

I hope this is clear. If it is just gibberish I'll refrain, I think there's logic in it and would appreciate if the flaws could be pointed out.

Thanks everyone for indulging my rather naive notions and I hope my post is appropriate.

Doc Al
Mentor
I see that action and reaction are a single action by the 3rd pair law.
"Action" and "reaction" are two forces associated with a single interaction. The terms "action" and "reaction" are leading you astray--I advise dropping them.
If the first action reacts instaneously and so on, all action is instantanous.
Again, you are taking the everyday meaning of the words "action" and "reaction" as if one happens first, followed by the other, which "reacts" to the first. Not so. They act together.

Example: My hand hits the wall. Which happens first: My hand hitting the wall or the wall hitting my hand? Neither. They are aspects of the same interaction.

There is no "chain" of 3rd law pairs. There can, of course, be a causal chain of interactions: My shoulder pushes my arm, my arm pushes my hand, my hand pushes the wall. But these are not third law pairs. And they are certainly not "instantaneous".

Thanks everyone,

It is very helpful. I'm not very eloquent having little maths "language".

I hope I'm not imposing by furthur posting but am left with one query.

Please indulge me even though my previous posts have eroded my credibility.

If the first action simultaneously reacted with the second which in turn simutaneously propagated the third and so on, would the very last action be simultaneous with the very first?

And being simultaneous, would this have an instantaneous effect, seeing it is simutaneous for the duration of first action?

I would think the very first instant of action is simultaneous with the very last instant.

Thanks again all. I have developed a great interest in physics now I realise that it lends credibility to "whack" theory. I like the site, but will study more so I can communicate more effectively before further posting. I look forward to reading the insightful posts of everyone here in the meantime.

In appreciation, Throng.

russ_watters
Mentor
If the first action simultaneously reacted with the second which in turn simutaneously propagated the third and so on, would the very last action be simultaneous with the very first?

And being simultaneous, would this have an instantaneous effect, seeing it is simutaneous for the duration of first action?

I would think the very first instant of action is simultaneous with the very last instant.
What are these other actions and why would they necessarily be simultaneous with the first? What you are saying implies to me that you think forces propagate through an object instantaneously. They don't.

It may be instructive to consider what happens in the real-world situation of a hammer hitting a nail. Metals are almost perfectly elastic over a certain range of forces, so in this case, the objects can be modeled as collections of tiny springs. The action and reaction that occur simultaneously at impact are a force at the impact point and compression of the spring. But the compression takes a finite time to happen - the force takes time to build, and the particles time to accelerate. So the force and acceleration of the objects propagate through the objects in a pressure wave that travels at the speed of sound.

Doc Al
Mentor
If the first action simultaneously reacted with the second which in turn simutaneously propagated the third and so on, would the very last action be simultaneous with the very first?
Nope. If the first and second "actions" are 3rd law pairs, then the second and third are not. There are only two forces in a 3rd law pair, not a chain of forces.

You can certainly have a causal chain of forces (as I and Russ have been pointing out), but that is not a chain of "action/reaction" pairs and they do not happen simultaneously.

HallsofIvy
Homework Helper
Thanks everyone,

It is very helpful. I'm not very eloquent having little maths "language".

I hope I'm not imposing by furthur posting but am left with one query.

Please indulge me even though my previous posts have eroded my credibility.

If the first action simultaneously reacted with the second which in turn simutaneously propagated the third and so on, would the very last action be simultaneous with the very first?
You have been told several times now that there is no "first" or "second" in the so-called "action" and "reaction". Now what do you mean by "third and so on"? What forces are you talking about?

And being simultaneous, would this have an instantaneous effect, seeing it is simutaneous for the duration of first action?
You seem to be thinking now of a series of forces. What does that have to do with your original question about "action" and "reaction"?

I would think the very first instant of action is simultaneous with the very last instant.

Thanks again all. I have developed a great interest in physics now I realise that it lends credibility to "whack" theory. I like the site, but will study more so I can communicate more effectively before further posting. I look forward to reading the insightful posts of everyone here in the meantime.

In appreciation, Throng.
??What do you mean by "whack" theory? I do hope that's not some "whacky" theory you made up yourself- after telling us you know nothing about physics.

Nope. If the first and second "actions" are 3rd law pairs, then the second and third are not. There are only two forces in a 3rd law pair, not a chain of forces.

You can certainly have a causal chain of forces (as I and Russ have been pointing out), but that is not a chain of "action/reaction" pairs and they do not happen simultaneously.

Thanks, I am now far better informed and appreciate that.

Though the OP is, apparently, satisfied by the response on this thread, the issue itself warrants further examination.

Action/reaction scenarios do not have a simple, single answer, as this universe is not made of billiard balls.

Whereas A/R(Action/Reaction) could be considered a paired event, it could be argued that action precedes reaction. In the macroscopic world, a judicial reaction to a criminal act can normally only occur after the criminal action.

In that sense, A/R is valid, whereas R/A is not. Therefore, in that scenario action and reaction is paired but action comes first.

Or, one starts a small fire(action) within a dry forest and the fire spreads to a thousand acres(reaction)
It would be absurd to assume that the entire forest is burned down before the action of the initial small fire.

But back to physics, the question is if A/R can be "flipped" to R/A and remain integrity.

HallsofIvy
Homework Helper
You seem to think that there is some objective distinction between "action" and "reaction". There is not. When I push against a wall, it pushes against me. Either can be considered the "action" and either can be considered the "reaction".

stewartcs
Or, one starts a small fire(action) within a dry forest and the fire spreads to a thousand acres(reaction)
It would be absurd to assume that the entire forest is burned down before the action of the initial small fire.
No, that would be cause and effect, not the typical physics definition of action and reaction.

As previously pointed out by the mentors, these concepts are quite different. Don't fall for the semantics of the language.

CS

russ_watters
Mentor
...this universe is not made of billiard balls.
Yeah, it really is.
Whereas A/R(Action/Reaction) could be considered a paired event, it could be argued that action precedes reaction. In the macroscopic world, a judicial reaction to a criminal act can normally only occur after the criminal action.
That's true, but it has nothing to do with physics.
But back to physics, the question is if A/R can be "flipped" to R/A and remain integrity.
I don't see how introducing concepts that are utterly unrelated to the underlying physics are helpful. In the context here, these terms have specific and unequivocable meanings.

You seem to think that there is some objective distinction between "action" and "reaction". There is not. When I push against a wall, it pushes against me. Either can be considered the "action" and either can be considered the "reaction".
Objective distinction? Of course there is!
It is IMPOSSIBLE for the 'wall" to push against your hand without your hand first pushing against it.

That is the problem.

Doc Al
Mentor
Objective distinction? Of course there is!
It is IMPOSSIBLE for the 'wall" to push against your hand without your hand first pushing against it.
There's no "first". It is IMPOSSIBLE for the wall to push against your hand without your hand simultaneously pushing the wall.

You're getting hung up on the colloquial, non-physics meaning of the words "action" and "reaction".

OK, let's get hardball.

There has to be a "first"... otherwise even common reactions could not take place and develope into a more complex status.

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