3084: Unstoppable Force and Immovable Object

Unstoppable Force and Immovable Object

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Title text: Unstoppable force-carrying particles can't interact with immovable matter by definition.

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Explanation

This explanation is incomplete: The last paraph about quantum physics might be too technical for some users. Don't remove this notice too soon. If you can fix this issue, edit the page!

An "unstoppable force meeting an immovable object" is a common expression and thought experiment when two things with mutually exclusive properties are forced to interact. In the comic, this is depicted with three drawings, with an arrow representing an unstoppable force moving toward an object that is immovable. The next two images depict how they interact - or rather, not interact, with the force passing right through the object as if it weren't there. In a caption below the comic, Randall states that he cannot understand why people find this scenario to be tricky

The comic plays on the word "force", which has different definitions depending on context. To a physicist like Randall it describes a fundamental influence between particles of matter. Not all forces interact with all types of matter, nor can they be stopped (only depleted, by interaction and dispersion over their effective distance); as a result, although "unstoppable forces" seem like an impossible thing, they are in fact quite common (again, provided one is using the physics definition), something Randall exploits in line with prior informative comics of this ilk. In casual language however, a "force" is an entity with a large amount of (usually kinetic) energy, hence the question might better be phrased as "what happens if one attempts to apply kinetic energy to an object whose velocity cannot be changed?".

A lot of times, the "unstoppable force / immovable object" expression is just that, an expression, to indicate that two parties who have contradictory goals and are unwilling or unable to compromise. Other times it's an exaggeration for large and powerful forces that are not literally unstoppable but still cause massive damage when they run into each other.

In the title text, Randall clarifies what he means in that the force-carrying particles cannot interact with the matter by definition. If such objects did exist, being intangible to each other is the only possible answer that would be compatible with how we understand physics to work, as force-carrying particles can only interact with some particles. (An further explanation of this situation is described in a video by Minute Physics.) In quantum physics, all forces are mediated by force-carrying particles, but this is not usually something that is relevant to consider, when macroscopic objects interact.

Transcript

[In one panel there are three drawings representing the same scenario at three different times. The first drawing shows a right-pointing arrow at the left, and a rounded trapezium-like object set slightly to the right of center. They are each labeled with a line going from a label above down to the respective shape:]

Unstoppable Force

Immovable Object

[In the second drawing the arrow is shown in the process of moving through the trapezoid, the part of the arrow within the trapezoid is drawn in gray lines.]

[In the third drawing the arrow has moved a similar distance, now being to the right of the trapezoid.]

[Caption below the panel:]

I don't see why people find this scenario to be tricky.

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Discussion

lol, i remember this explanation from a minutephysics video. however, the version of the problem i heard, which is actually paradoxical, is "what happens when an immovable object meets an irresistible force?" Not without text (talk) 00:03, 3 May 2025 (UTC)

That was also literally my first thought. 169, anyone? --Coconut Galaxy (talk) 05:37, 3 May 2025 (UTC)

How do connect this comic with 169: Words that End in GRY? I see no connection! --Kynde (talk) 16:43, 4 May 2025 (UTC)

Communicating poorly and then acting smug. --Coconut Galaxy (talk) 11:52, 5 May 2025 (UTC)

The MinutePhysics video: on Nebula or on YouTube --NeatNit (talk) 09:55, 3 May 2025 (UTC)

Come on, it's just an arrow made of W- bosons, right? TheTrainsKid (talk) 03:22, 3 May 2025 (UTC)

Is there no joke here? Is it just the solution? Broseph (talk) 06:52, 3 May 2025 (UTC)

I remember an explanation by Isaac Asimov in one of his books which was like "by definition, an immovable object will not move at all under any force in the universe, and an unstoppable force will move all of the objects in this way" and then explained how the definitions conflicted each other and as such prevented both from being able to register for the hypothetical at the same time 172.64.236.161 06:55, 3 May 2025 (UTC)

In the first MMO games, collision was a big problem. A player could block a doorway, and nobody else could go through. It was even worse if the player had "follower" characters or pets. One solution was to have characters automatically "push" stationary characters out of the way, but that caused other problems. Modern MMO's such as World of Warcraft simply allow characters to pass through each other, as depicted in this xkcd comic. Our eyes fool us into "seeing" that two characters somehow slid past each other. 172.68.228.132 07:29, 3 May 2025 (UTC)

Our eyes, or the programmers? I don't have that much experience with MMO's but they probably do render it in specific way to make that effect. -- Hkmaly (talk) 02:59, 4 May 2025 (UTC)

It's been a few years since I played WoW, but at that time there wasn't anything hiding the fact that the characters were clipping through each other. although I'm not sure what the other poster was talking about being fooled "into 'seeing' that two characters somehow slid past each other" since to me it always looked like two characters passed right through each other.172.70.126.111 20:31, 6 May 2025 (UTC)

When the two things pass through each other, at the instant where they both occupy exactly the same space, is there one object or two? 162.158.216.159 08:02, 3 May 2025 (UTC)

Given that force is not an object, one. Just like there was when they weren't colocated. 172.69.43.220 08:29, 3 May 2025 (UTC)

OK, but what about the 'unstoppable force carrying particles' in the title text? 172.69.194.204 19:00, 3 May 2025 (UTC)

I understand it as if a particle interacting with the object counts as 'stopping', in which case an unstoppable force-carrying particle wont have any effect. --162.158.120.157 20:40, 3 May 2025 (UTC)

Two, if you're counting particles as "objects". At the level of particle interactions, two particles aren't merely distinguished by their spatial extent, but also by all their other "quantum numbers" -- charge, flavor, and others. You can absolutely have two particles, even two fermions, that have exactly the same wavefunction in space, but are distinguished by differing in other ways. (And in practice, something like this would be a fermion and a boson anyway.) Linkhyrule5 (talk) 06:24, 6 May 2025 (UTC)

The force could simply go around the object. The object hasn't moved, and the force wasn't stopped. Rtanenbaum (talk) 11:17, 3 May 2025 (UTC)

Redirecting would imply the force could be redirected, allowing us to trap it inside a closed loop, effectively stopping it. 172.70.57.132 15:38, 3 May 2025 (UTC)

This is like the Chinese saying the spear and the shield. Using this comic, I guess spear wins Aprilfoolsupdate! (talk) 14:02, 3 May 2025 (UTC)

Gonna be honest, I think this is my least favorite comic of the last 500 or so. It's a solution already given by minutephysics, except with all the perspective about reference frames, and what people actually mean with these terms replaced by a caption with a superiority complex. I suppose it gets pretty hard 3000 comics in, but c'mon. 172.68.35.83 19:18, 3 May 2025 (UTC)

--Comment by Darth Vader (talk) 22:07, 3 May 2025 (UTC) deleted--

Ok, as we're giving personal opinions, I can't let it stand. Some might not exactly be total belly-laughs, but I think they each still have something to them and I prefer a mix of tones (and a wider spatter of focuses and treatments) to them all being exactly the same aspect of 'high-humour'. Not that I'd care to rank them, anyway, but I'm nowhere near ready to go off and make disparaging comments as if this site was bitchaboutxkcd.com, or whatever.

I won't try to tell you what to think, yourself, though maybe you should just roll with it. If you really don't like a comic, there'll be another along in two or three days. That might be even 'worse', as well as 'better', but then you can be even more unchill about that. 141.101.98.82 22:45, 3 May 2025 (UTC)

All forces are irresistable. No objects are immovable. If any force acts on any object, the object moves (or deforms). 172.68.84.145 22:22, 3 May 2025 (UTC)

Can we not say that Dark Matter, if that's what we imagine it might be, entirely resists the electromagnetic force? (It's one of my possible interpretations of the comic, though without enough hint that it was intended to have me annotate the Explanation accordingly.)

That said, it's unstoppable force (and there's are no Cavorite-like forceproof barriers), and it's rather that immovable objects are awkward to imagine under Relativity and there being no actual preferable frame of reference in the first place. 172.69.195.113 22:50, 3 May 2025 (UTC)

I would say that, since a force is mass*acceleration, the force cannot yet be stated while passing through the immovable object, because the object have to accelerate to calculate the force. Therefore, the "force" is only potential or kinetic energy at this point.162.158.127.25 12:54, 4 May 2025 (UTC)

I would say that nothing happens. If you think of Pressure and immoveable object: An infinite force would acting on an immoveable (think infinite mass) object would lead to no movement at all. Well, actually a black hole would be created, swallowing up the object and the force. Since the object's further behavior now cannot be seen from outside mass could be reduced anf the black hole could simply evaporate. Result: Force and objects actual mass would simply be converted into energy, representing a bomb. 104.23.187.224 16:42, 4 May 2025 (UTC)

Did someone pull out ChatGPT again for this explanation? The claim that the humor derives from the contrast between the casual meaning of "force" and its meaning in physics is ridiculous and patently false. A "force" in physics doesn't have a physical position to begin with and so it can't "pass through" anything. At this point I really feel like there should be some kind of policy on writing explanations using LLMs like ChatGPT because it almost never adds anything of value and it just complicates the explanation and makes the process of real people digging into the actual meaning and themes more difficult.172.71.102.223 18:45, 4 May 2025 (UTC)

Looking at what it replaced, it was an improvement, if not described as well as I think it should be. I believe it means to talk of the flux from a point-originated field (e.g. the most common fields normally deplete by inverse-square rule, all the way to infinity, from the point(s) of origin, though nuclear forces are... different).

Given the depiction of the "unstoppable force" as actually 'moving', it has to be looked at as some kind of propagating pulse of 'forceness', albeit one that does not interact with the object seen as in its path (which would therefore neither react to the 'force' nor attenuate its potential effects). But that might need to be said in similarly short fashion (if my interpretation is even agreed with). Good luck! 172.70.162.52 20:47, 4 May 2025 (UTC)

Agree! The physical explanation of force is plainly wrong in the explanation text. Sebastian --172.68.110.207 23:18, 4 May 2025 (UTC)

Could the objects be in front of each other instead of colliding? -- Dardafus1 (talk) 18:00, 5 May 2025 (please sign your comments with ~~~~)

Not both at the same time... 172.69.224.82 19:49, 5 May 2025 (UTC)

I contemplated this years ago while watching a Newton's cradle, and I came to the conclusion that the irresistible force would transform into an immovable object, and the immovable object would transform into an irresistible force. But honestly, a variation of what he proposes also makes sense, that the immovable object would conduct the irresistible force and retransmit it out the other side. The Black box view of the interaction would be the same either way. SammyChips (talk) 20:07, 6 May 2025 (UTC)

Except an irresistible force is different from an unstoppable one: if the force is irresistible, the force must have an effect on the object. I guess I could see how retransmitting the force would be a type of effect, but it's a bit of a stretch. Not without text (talk) 14:09, 15 May 2025 (UTC)
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