We are living on this big lump of rock called the Earth, drifting ever so continuously through space.

Now imagine a tiny but immovable object in space, a single atom of 'unexplanium', locked in space-time (relative to our universe or whatever you need). It will not move, bulge or transform; it's just there having indestructible mass. Assume it has the properties of a hydrogen atom (1 proton + 1 electron) for all physical and chemical purposes, except that it is endowed with infinite inertia.

What would happen if our Earth hit that one immovable atom? For simplicity, we may assume that the Earth's movement is linear and that the atom will hit the center of the Earth. I imagine something like a truck hitting a stationary object. If it's super narrow it'll slice the half, if it's broad it'll smash into it.

Would we even know it happened? Or would the amount of energy rip a giant tunnel through the planet? If a single atom is too small for something significant to happen, what would happen if it's the size of a marble or something bigger?


I've found this XKCD, which is somewhat related and might be an interesting read. It also described super fast and tiny particles:

"If a meteor made out of diamond and 100 feet in diameter was traveling at the speed of light and hit the earth, what would happen to it?”

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    Sorry, this is the archetype of opinion based question: a totally fictional object with totally vague properties, and how are you going to pick an answer? – L.Dutch May 23 at 13:20
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    You just need to specify the interactions that your unexplanium has with regular matter (making it less of an unexplanium I guess). – agaitaarino May 23 at 13:22
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    This may have already happened: telegraph.co.uk/news/science/science-news/3294473/… – Thucydides May 23 at 13:24
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    tiny but immovable object in space That makes no sense based on science - so unless you provide us with the physics for your fictional universe, we cannot answer. In the end it is completely up to you. – Renan May 23 at 13:59
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    There is no immovable in space; nothing is 'at rest'. – Jan Doggen May 23 at 14:14

11 Answers 11

up vote 82 down vote accepted

As @Thucydides mentioned, researchers posited a similar magnitude of impact and thought they had found evidence for it, though they later retracted their findings they did calculate the potential effects.

The team, from the Southern Methodist University in Texas, analysed more than a million earthquake reports, looking for the tell-tale signal of strangelets hitting Earth.

While their very high speed gives strangelets a huge amount of energy their tiny size suggests that any effects might be extremely localised, and there is unlikely to be a blast big enough to have widespread effects on the surface.

The scientists looked for events producing two sharp signals, one as it entered Earth, the other as it emerged again. They found two such events, both in 1993. The first was on the morning of October 22. Seismometers in Turkey and Bolivia recorded a violent event in Antarctica that packed the punch of several thousand tons of TNT. The disturbance then ripped through Earth on a route that ended with it exiting through the floor of the Indian Ocean off Sri Lanka just 26 seconds later - implying a speed of 900,000 mph.

The speed of 900,000mph is important here. Since you're determining that the particles are absolutely stationary we need to know how fast the Earth is moving relative to them.

What is the speed of earth relative to absolute space?

In practice we approximate the comoving frame as the frame at rest with respect to the microwave background radiation. Thus we measure the speed of Earth relative to the comoving coordinates assuming, that the background radiation has no "natural" dipole anisotropy.

The speed of Earth wrt the local comoving frame measured this way in of the order of 500 km/s. And, of course, it varies as the Earth orbits the Sun. If we subtract the velocity of Earth in orbit around the sun, velocity of the sun relative to galactic center and velocity of the Milky Way with respect to the centre of the local group of galaxies, we find, that the local group is moving and slightly above 600 km/s relative to the comoving frame.

900,000mph is ~400km/s, you're looking for an impact appropriate to 600km/s, but the orders of magnitude have the same approximation as the incident in the Telegraph article

several thousand tons of TNT

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    And what would happen if it whould be the size of a marble? – Martijn May 23 at 14:36
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    It seems unlikely this has already happened as the researchers later retracted their claim, apparently. en.wikipedia.org/wiki/Strangelet#cite_note-12 – goPlayerJuggler May 23 at 16:22
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    @goPlayerJuggler none the less the answer shows this is hypothetically possible, and what the signs were to look like if this were the case. – opa May 23 at 16:57
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    -1 This doesn't actually answer the right question. You answered what would happen if Earth hit a stationary object. Not an "immovable" object. That's not at all the same. I don't think that question is even answerable. – WakeDemons3 May 24 at 17:23
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    @WakeDemons3 An "immovable" object differs only in that it does not at all change it trajectory/velocity/acceleration relative to anything it collides with, which I think should be mathematically equivalent to a stationary object upon which additional force is magically applied in perfect sync and opposition to the force it experiences from the Earth colliding with it. Fudging for simplicity, this should have roughly the same effect as "stationary object being collided with that much harder". – mtraceur May 25 at 23:51

Conclusion:

In the case of the atom, you wouldn't see anything without special instruments. This is because the object is so small that very few atoms will interact with it, so it imparts almost no energy to any matter that it encounters.

In the case of the marble, there would be a bright flash streaking through the sky, comparable to a large meteor, but much faster. Upon impact, the top layers of soil would be vaporized, resulting in a blast comparable in intensity to a very large conventional explosion (tens of tons of TNT). This would coincide with a small localized earthquake and a ground shockwave comparable to an underground explosion, due to the object passing through the rock at greater depths.

At the exit site, almost identical effects would occur, except there would be a large explosion followed by a flash streaking upward into the sky.

The exit event would happen $34$ seconds after the original impact, assuming the object comes down vertically and is moving at $370 \text{km} / \text{s}$ (see below about these assumptions).

Detailed explanation and calculations:

I. Hydrogen Atom

Let's first do a quick back-of-the-envelope estimate for how much energy would be imparted to the atmosphere.

  1. Object's speed relative to the Earth.

First of all, what does "at rest" mean? Let's suppose the object is at rest with respect to the cosmic microwave background (CMB). The rationale is that if it originated in the primordial Universe, then it would have originally been at rest with respect to the CMB, and if it has infinite inertia, then nothing can change its motion, so it will remain at rest with respect to the CMB. The Earth moves at about $370 \text{km} / \text{s}$ with respect to the CMB, so that's how fast the object would hit.

  1. Interaction with the atmosphere.

When the object passes through the atmosphere, then any atoms it comes into contact with will bounce off at approximately this speed, on average. Let's first calculate how much mass of air it will encounter. A column of Earth's atmosphere (from the surface to space) has a mass of about $10\mathpunct{,}000$ kilograms per square meter of surface. The object is about the size of a hydrogen atom, with a radius of $10^{-10}$ meters, so if it's a sphere, it will take out a cylinder of atmosphere with an area of $\pi R^2 \approx 3\mathrm{x}10^{-20} \text{m}^2$. Multiplying this by $10\mathpunct{,}000$ kilograms gives us $3\mathrm{x}10^{-16} \text{kg}$ of air that directly interacts with the object.

After this object passes, these air molecules will be moving around at about $370 \text{km} / \text{s}$. Using the expression $E = \frac{MV^2}{2}$ for kinetic energy, we get $$E = \frac{(10^{-16} \text{kg})(370\mathpunct{,}000 \text{m} / \text{s})^2}{2} \approx 7 \mathrm{x}10^{-6} \text{J}$$ energy imparted, in Joules. This is an absolutely minuscule amount of energy; for comparison, a normal household 10W halogen bulb emits 10 Joules of light per second.

  1. Effects on rock would also be negligible, so there is no need to calculate them.

The amount of energy deposited when the object strikes the surface will be similarly negligible.

In the above calculation, the energy imparted to an object is proportional to its column mass (mass per surface area).

Consider the first three meters of soil that the object passes. A layer of rock 3 meters deep has about the same column mass as the atmosphere. Therefore, the object would also deposit about $7 \mathrm{x}10^{-6} \text{J}$ in the first three meters of rock that it penetrates. Again, this is practically undetectable. It will, of course, continue depositing these tiny amounts of energy as it passes through the Earth.

II. Marble

In the case of the marble, the calculation is almost the same as above, except the object's radius is now more like $0.01$ meters instead of $10^{-10}$.

So its radius is a factor of $10^{8}$ bigger, the area of the column of atmosphere it takes out is $10^{16}$ times bigger (as it's proportional to the radius squared) and the amount of energy deposited is also $10^{16}$ times bigger.

The marble would therefore deposit $7 \mathrm{x}10^{-6} \text{J} * 10^{16} = 7 \mathrm{x}10^{10} \text{J}$ of energy in the atmosphere, and a similar amount in the first three meters of rock.

Since we're looking at explosive-like effects, let's convert this to tons of TNT. One ton of TNT releases $4.2 \mathrm{x}10^{9} \text{J}$. So, our object would deposit $$(7 \mathrm{x}10^{10} \text{J})(\frac{1 \text{ ton}}{4.2 \mathrm{x}10^{9} \text{J}}) \approx 17 \text{ tons}$$ of TNT in the atmosphere and in the first three meters of soil.

The effects from the atmosphere would be comparable to a sizable meteor fireball. On the ground, the energy from the first few meters will reach the surface, producing an explosion comparable to a few tens of tons of TNT (a very large bomb).

Anything deeper than a few tens of meters would produce a relatively short-range surface rumble, like a small earthquake, but relatively little energy will reach the surface.

The same effects would happen at the exit site but in reverse order. The diameter of the earth is about $12700 \text{km}$, and the object is moving at $370 \text{km} / \text{s}$, so if the object comes down vertically, the exit event would happen $12700 / 370 \approx 34$ seconds after the first impact.

  • Haha, so it would be a case of "I'm telling you, I really saw a faint lightbulk just plow into the grond!" and nobody to believe you – Martijn May 24 at 14:14
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    @Martijn: In the case of the marble, however, it would be far more impressive. Edited the answer to include that case. – Alexey Vlasenko May 24 at 14:39
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    10 Joules of light per second. Light bulbs are not 100% efficient :P Maybe you meant to say that's how much light + heat a 10W bulb emits. – Peter Cordes May 25 at 8:30
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    @Wilf: There shouldn't be any magma leaking, because by the time the object gets deep enough for magma, the pressure in the rock will be so high that the cavity left behind by the object will collapse almost immediately. No magma will reach the surface. Of course, if the marble-sized object hits something important (like a city block), it can cause some serious destruction. Tens of tons of TNT is no joke. – Alexey Vlasenko Jun 4 at 6:41
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    I would expect the effects of the marble to be much bigger due to the (very) supersonic speed of the marble. The molecules in front of it don't have time to "move out of the way", and accumulate in front of it, slowly bleeding around. but as they bleed around, they have the same effect on molecules further in front, in effect making the frontal area larger. The most obvious result would be the mother of all supersonic shockwaves. – Eth Jun 4 at 16:23

With an impactor the size of a hydrogen atom it's probable that we wouldn't even notice overly much. There might be a bright flash as it hits the atmosphere, it's even more probable there'd be on as it hit the ground, hard enough to break some molecular bonds. That flash is going to go all the way through too but we're not going to see it below ground level. It's almost impossible, certainly at such low relative velocities, to get an individual atom to actually hit such an object, even one with no charge, but because of it's exotic nature there might be some atomic fission events. Taken altogether I would expect very little energy to be imparted to the Earth, and very little if any noticeable damage.

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    @JanDoggen Yeah but no it would hit the atmosphere, and then the ground, and then go the whole way through the planet and out the other side, it doesn't move or transform in any way so it's going to hit things all the way along. – Ash May 23 at 14:26
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    @Martijn Yeah no I'll do your marble and then you're on your own, these are not simple equations. – Ash May 23 at 15:58
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    @Ash: What is "the epicenter of the big bang"? The Big Bang happened everywhere. – Beta May 24 at 1:26
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    @Beta: Everywhere was very small back then. – Joe Bloggs May 24 at 6:38
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    @somebody: As far as we know, space itself doesn't have a velocity, i.e. there's no such thing as absolute velocity, and no special frame of reference. Fortunately, for the purposes of this question we can just consider small objects moving relative to the earth at whatever velocity we think is interesting. – Peter Cordes May 25 at 8:08

At first I thought this would be a planet-ending event, but upon further consideration, it wouldn't be that big of a deal.

First off, nothing can really be immovable, and nothing is really stationary in an absolute sense as others have mentioned. However, if we assume that the earth is going around a few hundred thousand miles per hour relative to the cosmic background, that's a number we can work with: let's call it 400,000 mph. That's not a relativistic number, so nuclear reactions are unlikely.

Neutrinos have a small cross section and routinely pass through the earth unimpeded. However, a hydrogen atom has a much larger area; this is the reason hydrogen can be stored in a pressure vessel, because it bounces off the walls of the container.

Now hydrogen has a diameter of about 50 picometers, so at the very least the particle would scrape out a 50 picometer-wide tunnel all the way through the earth. The mass of that tunnel would be about $6\times10^{-10}\text{ kg}$.  If all of that mass were converted to pure energy, which is a worst-case scenario ($\text{E}=\text{mc}^2$), it would be about $5.6\times10^{7}\text{ Joules}$, which is about the amount of energy released by burning a couple liters of gasoline.

So the good news is we'd all survive.

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    Earth's orbital velocity in a Sun-centric reference frame is about 30 km/s, and the Sun's orbital velocity in a reference frame fixed to the centre of the Milky Way is on the order of 200 km/s if I recall correctly. 200 km/s is 720,000 km/h or about 450,000 miles per hour. Or, alternatively, 0.07% of the speed of light. For our purposes, relativistic effects at such velocities should be completely negligible. – a CVn May 23 at 21:04
  • The biggest difference between a neutrino and an H atom (or H2 molecule) is that neutrinos don't interact with matter via the electromagnetic force. Or via the en.wikipedia.org/wiki/Pauli_exclusion_principle, which applies between the electron shell in an H atom and the electron shells of any atoms / molecules it approaches. This is why neutral atoms repel if pushed close together, and why you don't fall through your chair even though at an atomic level even "solid" matter is mostly empty space. Neutrinos can go right through atomic nuclei with a low chance of interacting. – Peter Cordes May 25 at 8:16

As we now know - everything is relative.

A fixed particle in space might as well be a moving particle in space, relative to us, when we are moving.

This being the case, the atom in question would simply be like many other atoms already bombarding the Earth - individually the effect would likely be negligible, collectively a different story.

The only difference in your case is your comment 'infinite inertia' - I presume this atom doesn't interact like normal atoms do then when in proximity or colliding with another atom. Still, one atom is only one atom, it may not directly interact with others at all on its brief journey through the Earth, or if so only imperceptibly.

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    This is not a bad answer, but not an answer to the question that has been asked. It might not have any influence on the fate of mankind, but what would actually happen during the event? – Raditz_35 May 23 at 13:55

Nothing will happen.

Remember, there are (comparatively, when you think about the ratio of macroscopic distances to the sizes of macroscopic objects), huge gaps between atoms, which is why hydrogen will gradually leak out of any container. In much the same way, the fixed hydrogen atom will mostly push other atoms out of the way. In the atmosphere, we might see a parabolic arc of lightning as the the atoms gets knocked away at the speed of the earth's rotation. When it hits the ground, the fixed atom will simply force its way through, displacing atoms where it comes in contact with the nucleus, until it comes out on the other side. Then we might see another parabolic lightning arc going the other way.

  • Thabnks for your answer. Because I sort of expected this outcome, I've added the "what if it would be the size of a marble" :) – Martijn May 24 at 12:18
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    @Martijn: It will be crushed. Immovable isn't indestructible. – nzaman May 24 at 12:20
  • It might be worth noting that the Earth isn't a rigid body -- it's spherical precisely because gravity was able to deform it into a (more or less) evenly-distributed shape, and much of its center is liquid. It seems plausible to me that an indestructible marble with infinite inertia (assuming such a thing could exist) might just plow right through the core of the Earth and come out the other side again, like a bullet flying through a cube of butter. As for how much that would damage the areas near the entry and exit areas, I can't guess. – Jeremy Friesner May 24 at 14:08
  • @JeremyFriesner: Nobody said it was indestructible. Simply that it was moving with sufficient inertia so as not to be deflected by the mass of the earth (which is what immovable actually means in an expanding universe). We know nothing of its density, only its volume and a rough idea of its speed – nzaman May 24 at 14:30
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    @nzaman "immovable" rather implies "indestructible" to me, in that if the object is destroyed, it will no longer be found at the location where it originally was at, and therefore will have been effectively -- moved. – Jeremy Friesner May 24 at 15:06

As the asker of the question has already learned, it was asked using some phraseology which is difficult to mesh with contemporary physics. As such, I am attempting to answer as if “immovable” is describing:

  • an elastic collision in which the relative motion between a third body which does not collide and one participant in the collision is unchanged.

While the Earth is moving in relation to this “immovable atom” — IA — which you propose, each atom of the Earth has a velocity vector with respect to the IA. The distance between the IA center of mass and the Earth's center of mass is decreasing. When any atom considered to be a part of the Earth collides with this IA, the result of that collision does not cause any change of the IA's relative velocity vector with respect to the velocity vector of any other atom.
In simpler language, the incident atom which is not the IA will bounce back with exactly the same speed but with a deflected direction. Any other atom will continue to see the IA as having the same velocity vector as it did prior to the collision.

Ergo, the IA will continue to pass through the Earth with each successive collision — however, the relative velocity vector between the Earth's center of mass and the center of mass of the IA will not be unchanged, but will be apparently slowed, albeit almost immeasurably. Such will occur because the velocity of the Earth's center of mass is composited from the velocity vectors of each atom which is factored in the arbitrarily defined center of mass …

Anyway. So, we have not yet defined exactly what fields are contributing to these aforementioned collisions. If the IA is uncharged, i.e. not ionic, then the collision is simply a result of the repulsion between electrons — which is, in turn, a consequence of the Pauli Exclusion property which electrons have — when its electron orbitals approach the similar orbitals of other atoms. It is very improbable that nuclear orbitals will ever interact, but at higher velocities such interactions become more probable — i.e. like the velocities you'd see in an atom smasher. And, even then, not very likely.

Of course, all that lends problems to considering exactly how the IA is indeed ‘immovable’, and how that pertains to its constituent particles: its electrons, quarks, and all the other stuff that perhaps fluxes about between in unperceived spaces inside. Gluons and photons and whatnot.

What if the IA were larger — like a pea, or a ball-bearing, or a marble? Well, all that really does — aside from making its ‘immovability’ more difficult to define — is give the IA a larger cross–section for its collisions: i.e., collisions are more likely.
Because it is immovable, and any collision with it is perfectly elastic, its own mass is irrevelant. Only its size is relevant.

What would be the state of that big mass of atoms which we call the Earth when the IA has passed through them and produce no further interactions?
Well, it really depends on what the initial relative velocity was between the two centers of mass. Many other answers here seem to confuse ‘immovable’ with ‘motionless’.
Whatever relative velocity you finally decide to use in your world, know that a larger magnitude will cause more deflection and thus more damage.


All in all, the more details you want require a more rigid definition understanding the concept of ‘immovable’. Others have more or less explained why immovability is almost like a physical limit: you can become more or less immovable, but never perfectly immovable.
Unless, of course, you exist outside the laws of physics which are known to contemporary science.

If that is the case, then this answer is really only useful to you if your physical laws operate in any way which allows my explanation to seem reasonable. Obviously.

  • The OP changed the question from an atom to a marble (see comments on my answer) – nzaman May 25 at 5:16
  • I have never chaged it from atom to marble, it has been marble from the first version of the question :) I've had both, in case a single atom would be boring :) – Martijn May 25 at 7:43
  • +1 finally a mention of en.wikipedia.org/wiki/Pauli_exclusion_principle and the en.wikipedia.org/wiki/Exchange_interaction "force" being how (the electron shells of) neutral atoms repel each other when very close together. – Peter Cordes May 25 at 8:36
  • Size of the ‘immovable whatever’ simply gives it a larger cross–section, but the concept is the same — hang on, I'll add that to this answer – can-ned_food May 26 at 6:39

Immovable (relative to the Earth), and potentially indestructible, marble sized object? "Immovable" could only mean it exists at the exact center of the universe, around which everything else is in relative motion.

It would be surrounded by a cloud of dust and asteroid fragments from previous impacts, would it not? Unless it sprang into being shortly before impact with Earth. Dust zone size depending on how long this marble has existed.

We would enter that zone of space dust, causing a massive and unexpected meteor shower. Then a flare of light as the marble passed through the atmosphere, followed by minimal impact, and a shudder as it plowed through Earth.

This would be a "bullet" that did not flatten or break on impact. The collision would be no big deal, but pressure would surely increase as it bulled its way through. Resulting in confusing seismic readings on the opposite side, then a small eruption as the marble exited. Or, if it entered and exited through oceans, no discernable effect on the surface of the ocean.

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    When you say “immovable relative to the Earth”, it seems like you are saying that it doesn't move with respect to the Earth, but simply floats at a constant distance and position. Would that be geosynchronous, or how exactly does the rotation of the Earth in the solar frame of reference contribute here? – can-ned_food Jun 4 at 21:20
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    This marble of unobtanium would have to be at the "center" of the known universe, around which every other object is in relative motion, right? My aim in posting this answer was to bring up the cloud of debris. – Mary C Jun 6 at 4:36
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    Oh, i gotcha. So it could actually appear to move with respect to one thing or another, but if you were able to compute the exact positions and movements of everything, then you'd see that the immovable unobtanite was like the stationary center. I think i disagree with the stuff about the collision, but i like the definition of ‘immovable’. – can-ned_food Jun 6 at 6:39

The answer is known, and it’s that nothing happens at all. If something is immovable, it means that nothing can move it, which can only mean that nothing we know of will interact with it. You’re describing a particle of dark matter, which the Earth undoubtedly hits all the time, but since it doesn’t interact with the matter of the Earth (except gravitationally, which is too weak and too long-range to be noticeable) nothing happens.

  • Not necessarily dark matter — indeed, not at all, I would say — but the premise is sound, albeit a tad pedantic. I like how this answers the question as if it wants something to warrant the adjective “immovable” at the expense of any other properties which it also stipulates. – can-ned_food May 29 at 1:15

This scenario already exists. Neutrinos can travel through dense matter such as the Earth without interacting with a single atom, leaving no trace of their passage. To observe even just a few of the extremely rare interactions of neutrinos with matter, physicists build detectors with massive amounts of target material and operate them for many years. The detectors record the tracks of the particles that emerge from the rare collisions of neutrinos with atoms of the target material.

I remember hearing that if you wanted to block a neutrino, you would need a sheet of lead as thick as the distance the Earth is from the Sun.

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    The premise of the question is an immovable object which interacts like an atom of normal matter. Neutrinos are not immovable, and do not interact like an atom of normal matter. – Sneftel May 24 at 11:14

For every action there is an equal and opposite reaction. If the supposed object is immovable, that tells us that the reaction is zero, and therefore we know that the action is zero; if there is no effect on one of the objects that are colliding, then there can be no effect on the other one either.

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    This seems like a philosophical dodge, and not an attempt to engage the question. – Misha R May 28 at 0:17
  • I'm sorry you see it that way. It's a genuine attempt to see what would happen under Newtonian mechanics if there was such a thing as an "immovable object". My conclusion was that it can't be immovable unless it somehow is incapable of reacting with the other body in a collision, and if it doesn't react with the other body then the collision has no effect on the other body either. (Essentially @MikeScott came to the same conclusions.) – Michael Kay May 28 at 8:25
  • Your conclusion ignores the question, which asks us to consider a scenario that does have an immovable object. If you believe that the objects will have no effect on each other, however, then you are welcome to describe it in practical terms, rather than as an abstract statement. If you cannot do that, then your answer is - like I said - a dodge, and nothing more. – Misha R May 28 at 9:24
  • I absolutely did not ignore the question. I specifically focused on the part of the question regarding the behaviour of an "immovable object", and considered what Newtonian mechanics would have to say about immovable objects. – Michael Kay May 28 at 18:40
  • What the classical approach would say about the impossibility of immovable objects is irrelevant, since an immovable object is present. The hypothetical asks you to suspend that part of Newtonian physics, and your answer, in essence, is "no, I won't." Consider that this is a process scientists are more than familiar with - thinking creatively every time some new piece of information comes in that defies a current accepted model. In this case, the piece of information is that we have an immovable object. To point at the classical model and say "no" is to refuse to engage. – Misha R May 28 at 20:26

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