Theory: solids passing through solids?

July 24, 2007 8:08 AM

I read somewhere that, in theory, two solids coming into repeated contact should at some point (assume we're dealing with infinity) pass through each other. Nearest I can come is molecular harmonic resonance, or this slightly dubious writeup. Is this a observed phenomenon? Or is there a formal theory for this?
posted by ikebowen to science & nature (14 comments total)

All i have ever heard on the subject is that they might pass through each other as no one has ever been able to test the theory for an infinite amount of time. Therefore they are unable to prove it can't happen.

When i heard it, it sounded like a load of bunk to me.
posted by unsurmountable at 8:18 AM on July 24, 2007

Yeah I'd say "dubious" is right.

I think the idea about 'matter passing through matter' springs from realizing that matter is, by volume anyway, mostly empty space, but at the same time not understanding that the "empty space" contains fields and interactions -- it's "empty" only in the sense of not having nuclei there.

If you take two solids and push them against each other, they don't run into each other because the atomic nuclei themselves are hitting each other, but because the fields (which fill the 'empty space' between atoms) run into each other.

The best way I've heard it described, in terms of a non-technical analogy, is to say that solid matter is like a chain-link fence. A fence is mostly (by volume) empty space, but yet you can't walk through it. Likewise, solids are configured in such a way so that even though they have their mass in very small, discrete volumes, you still can't pass another solid through them.

There might be some very rare exceptions to this (probably occurring in the very limiting cases of how "solid" matter is defined), but the link's descriptions of weather phenomena that cause rocks/trees/etc to pass through other matter is baseless.
posted by Kadin2048 at 8:26 AM on July 24, 2007

It's probably related to quantum tunnelling - things can pass through a barrier that would classically require them to have more energy to do so.

If you tried to throw a ball through a wall you'd have to try a number of times so large that to call it 'astronomical' would be an astronomical understatement. And it's not clear to me that it wouldn't be more likely that the ball would not make it through intact.
posted by edd at 8:39 AM on July 24, 2007

The link is dubious, but it isn't theoretically ruled out just very, very, very, very unlikely. It's less a matter about the atomic nuclei passing through the spaces between them and more about quantum tunneling:

Consider rolling a ball up a hill. If the ball is not given enough velocity, then it will not roll over the hill. This scenario makes sense from the standpoint of classical mechanics, but is an inapplicable restriction in quantum mechanics simply because quantum mechanical objects do not behave like classical objects such as balls. On a quantum scale, objects exhibit wavelike behavior. For a quantum particle moving against a potential energy "hill", the wave function describing the particle can extend to the other side of the hill. This wave represents the probability of finding the particle in a certain location, meaning that the particle has the possibility of being detected on the other side of the hill. This behavior is called tunneling; it is as if the particle has 'dug' through the potential hill.

Quantum tunneling has been observed with electrons. Naturally, the odds that every particle in an object -- electrons and all -- would do this are infinitesimal.

(note: this is based on casual "I occasionally read science mag" knowledge)
posted by mkn at 8:39 AM on July 24, 2007

This is discussed by Brian Greene in The Elegant Universe (which is certainly worth reading anyway). It took me a while, but I found the relevant passage:

"....[I]f you walked into a solid wall every second, you would have to wait longer than the current age of the universe to have a good chance of passing through it on one of your attempts. With eternal patience (and longevity), though, you could--sooner or later--emerge on the other side" (116).

Of course, he has a very good explanation of why this is the case, which you certainly ought to read.
posted by Ms. Saint at 8:46 AM on July 24, 2007

Couple of points:
'quantum mechanical objects do not behave like classical objects such as balls'
To clarify this a bit, the way a ball behaves is entirely quantum mechanical, even if it also fits the classical prediction perfectly well. It's just that at those scales quantum mechanics predicts the same thing as classical mechanics. This is the correspondence principle.

'Quantum tunneling has been observed with electrons.'
That would be something of an understatement - tunnelling has many important practical applications that depend upon it all the time.
posted by edd at 8:47 AM on July 24, 2007

I feel like I should point out that for anything small enough that quantum mechanics is important, tunneling is a very important effect and one well-established enough to be engineering. For example, scanning-tunneling microscopy, one of the main ways of imaging surfaces with atomic-scale resolution, is based on measuring the current from tunneling electrons and using that to infer distance. For anything larger than a subatomic particle, however, the probabilities involved basically define "impossible."
posted by Schismatic at 8:53 AM on July 24, 2007

Besides quantum tunnelling, you may be thingking of The Adventures of Buckaroo Banzai Across the 8th Dimension. Besides being one of the greatest movies ever, the physics weren't that far off. Carry Sneider, a physicist at Berkeley, had some thoughts on it.
posted by FuManchu at 9:21 AM on July 24, 2007 [1 favorite]

You don't need quantum mechanics for this. You just have to realize all the molecules of thing "a" are in motion just as all the molecules of thing "b" are in motion. Wait long enough and both will be a in state such that the two objects can merge into one thing and then re-emerge as two objects. It will just take very, very, very unpredictably long time. IANAP.
posted by rdr at 9:42 AM on July 24, 2007

It looks like your question has been answered, but just to put it into perspective:

Your body (by a really rough estimate) has something like 7x10^27 atoms in it. That's 7 billion billion billion atoms. Think about the chances of them all tunneling to a different point in roughly the same configuration...pretty dismal for those of us who would love to walk through walls on a semi-regular basis, huh?
posted by invitapriore at 9:43 AM on July 24, 2007

Pitifully dismal. Shame.

Thanks guys -
posted by ikebowen at 10:01 AM on July 24, 2007

Looking at it another way, any two homogeneous solids A and B that are placed in contact will tend to mix by diffusion until the free energy of the system is minimized. At that point, unmixing and subsequent separation of A and B is forbidden by the Second Law of Thermodynamics. (The Second Law is only a tendency for entropy to increase in a closed system, but for any reasonable piece of matter, the probability of spontaneous unmixing is so tiny as to be essentially zero.)
posted by Mapes at 10:02 AM on July 24, 2007

If you increase the energy of a bunch of electrons, the depth and rate of tunneling increase.

So, imagine a really strong home run hitter at the plate, and a 100 mile an hour fastball pitcher on the mound. You know how sometimes it looks like the batter swings right through the ball?

Exactly!   :)
posted by Chuckles at 10:04 AM on July 24, 2007

My high school physics teacher once had us calculate the wavelength of a fastball. (not an uncommon question). The answer: 8.8 x 10-35 m
posted by PercussivePaul at 10:47 AM on July 24, 2007