Many wildfires are caused by human actions (like an improperly-extinguished campfire, fireworks, or a cigarette).

> Great read but ain’t no five-year old gonna understand that!

Good thing the sub's rules explicitly say that's not what it's for then.

The explosion itself isn't the source of the EMP. Its immediate aftermath is.

The high-energy gamma rays emitted by the explosion strike electrons in the gas molecules in the air. (And any molecules on the ground, too, but the air will be what's relevant for our purposes.) This briefly turns the air into a plasma, with free electrons moving at high speeds from the huge kick they got from absorbing a highly energetic gamma ray.

In the lower atmosphere, the air is dense enough that these free electrons cannot travel very far. But in the upper atmosphere, their mean free path (the average distance they can travel without colliding and recombining with an atom) is rather long, on the order of a hundred meters or so. That's far enough that the electrons can interact with the Earth's magnetic field.

As the electrons travel, they start to move in loops under the influence of the magnetic field, as any charged particle would. Since the electrons are traveling at relativistic speeds, this produces synchrotron radiation, in much the same way that a boat speeding through the water creates ripples. This radiation is spread out at all wavelengths of light, and radiates outward from the moving electrons until they recombine. Since the electrons are traveling at relativistic speeds with a mean free path of ~100 meters, this recombination happens in on the order of a microsecond.

Since the electrons emit all their radiation within such a brief time, and since this is happening on the shock front of the original emitted gamma rays, the radiation from the electrons closest to the blast travels essentially along with the shock front (since they're only nanoseconds behind the gamma rays that weren't absorbed). As the gamma rays continue to travel, they knock more electrons free, and the synchrotron radiation from those electrons stacks on top of the synchrotron radiation from the previous ones.

All this radiation adds up, forming a shock wave of light at all parts of the spectrum - that's your EMP. (Or rather, it's the first and most damaging of a couple of unrelated EMPs.)

In a ground-level or lower-atmospheric blast, however, there are two differences:

• All the gamma rays are quickly absorbed by nearby air, within a few kilometers. That means essentially all the gamma rays are absorbed near the ground, where the air is dense. The mean free path for electrons in such dense air is much shorter, so they have much less time to emit synchrotron radiation.

• What radiation is emitted only hits targets within line of sight of the immediate shock wave, i.e., within line of sight of a few kilometers above ground zero. The horizon from a few kilometers up is not that far away, so the effects of the original blast tend to be more important than the EMP at that range.

But if you detonate a nuclear weapon at high altitude, ~half of its gamma rays will be absorbed in the upper atmosphere (since the Earth occupies ~half of its lines of sight, just as the ground and sky occupy half on the ground). Those electrons all get the nice long mean free path, and the EMP is emitted at such a high altitude that the horizon is hundreds if not thousands of kilometers away. You generate a potentially massive EMP that can affect an entire continent, which is far beyond the direct blast range of even the largest nuclear weapons.

> That is one of the questions where you say, "that is just how it is.".

It's not so much "how it is" as that it's a specific choice of coordinates. The electric field is simply the part that, in a particular choice of coordinates, does not depend on motion. Changes in coordinates to a moving observer will "mix" the electric field into the magnetic and vice-versa.

You can do electromagnetism with fields other than the electric and magnetic fields and get the same result. In fact, if you're a moving observer, electric fields will start to generate magnetic fields and vice-versa.

In reality, electric and magnetic fields are underlying manifestations of the same (coordinate-independent) underlying "thing". This thing, electromagnetism as a unified object, is more properly described by the four-potential, of which the electric and magnetic fields are parts. We call the part that doesn't care whether you're moving "electric" and the part that does "magnetic". But that is only a choice of coordinates, in the same way that you can do your linear algebra with <1,1> and <1,2> as basis vectors rather than <1,0> and <0,1> and everything will work out fine.

It turns out that you can, in a sense, decompose any (non-changing) vector field this way into an "electric-like" field and a "magnetic-like field", in the sense that these fields share some of the important mathematical properties of the electric and magnetic fields respectively.

> To (over)simplify the math, the curl of a thing is perpendicular to the thing

That is not true.

For example, if F is the vector field sin(x) i + 3 k, we have:

• curl(F) = cos(x) k
• F dot curl(F) = 3cos(x) != 0.

Nonzero dot product -> not perpendicular.

...but it still won't have a magnetic field, so it won't be able to hold on to a thick atmosphere regardless.

Mars already isn't that cold. On a warm day near Mars' equator, you could walk around in a sweater quite comfortably provided you had pressurized oxygen to breathe.

Suppose we have a 1% chance that something happens.

The chance it doesn't happen the first time is 99%.

The chance it doesn't happen the second time is 99%, independently of the first (we do need some degree of independence here, or your statement isn't true). So the chance it didn't happen either of the first two times is 99% times 99%, or 0.99 times 0.99, or 0.9801.

The chance it doesn't happen the third time, still 99%. So the chance it didn't happen any of the first three times is now 0.99 times 0.99 times 0.99.

You can hopefully see a pattern. The chance for the event to fail every one of the first n times is 0.99 times 0.99 times ... times 0.99, n times. In other words, that chance is 0.99^(n). And the limit of 0.99^n as n goes to infinity is 0, meaning that the probability that you manage to dodge your low probability outcome gets closer and closer to zero the larger the number of attempts you have.

Nothing about this depended on the exact 1% / 99% probabilities. All we needed was for that 99% to be less than 100%, i.e., for the 1% to be greater than 0%. As long as that's true, given some non-zero probability of success p, (1-p)^n always goes to 0 as n -> infinity (and therefore the chance you fail every time goes to zero as well).

It won't, directly.

Earth, however, will likely be uninhabitable long before then (barring human actions). The Sun is growing hotter as it ages, and Earth has about another billion years left before the Sun's warming trend begins to evaporate our oceans and trigger a Venus-esque runaway greenhouse effect.

The asthenosphere, which makes up most of the mantle, is mostly solid. It's squishy, but solid.

The diagrams you're talking about are simplifications. In reality, magma usually rises through a series of cracks in the rock, filling out hollows within it as it goes. (These hollows mostly weren't actually empty to begin with, but they were weaker areas that cracked open under the high pressure of the intruding magma.) If the magma hardens underground, it forms one of a variety of intrusive rocks in one of a variety of shapes, depending on how much space it could make for itself by cracking open the surrounding rock, and these shapes show us the variety of ways magma can force its way through rock.

In some cases, the cracks are more or less vertical, and the pictures in your textbook are (while still simplified) more or less accurate, with a vertical-ish shaft descending through the crust and down to the source of the magma in the upper mantle. This is the case for most hotspot volcanoes, for example. In other cases, the network of chambers is exceptionally complicated with lots of back-and-forth - you can imagine something like an anthill - and would form a complex network of caves if drained of magma.

It's worth keeping in mind, though, that the mantle isn't actually liquid for the most part. We used to think that it was, because, well, it's where magma (which is a liquid) comes from, but it turns out that the mantle is mostly a squishy hot-wax-like solid. It only melts under volcanoes because there's some unusual condition (more water in the mantle -> lower melting point, less pressure above it -> lower melting point) present.

> Trains already mass over/through both mountain ranges.

They do, but not on routes that could support a high-speed train for the most part. Though OP has actually missed the most difficult mountains, which are the steep, uneroded peaks of the Cascades and Sierra Nevada. To this day, only a couple of rail lines cross them, and all of those involve some pretty curvy paths except for the ones through the Columbia Gorge.

It's obviously not impossible, but it's not as simple as using existing rail lines either.

Well one, no, violet is quite a distinct color from magneta (the color you get by mixing blue and red light, i.e., "purple"). They're not hugely far apart, but e.g. on this chromaticity diagram, violet is at the bottom while mixtures of blue and red light form a magenta shade bottom-right of center. Magenta and violet are as different as red and yellow or green and cyan.

But the answer to your question is that you distinguish blues from purples by how different the signals from your M and L cones are. In both colors, the S cones are stimulated. If L > M, you see purples. If L ~ M, you see violet. If M > L, you see blues. At the far violet end of the spectrum, both L and M are near zero. At the far red end of the spectrum, L > M but both are weak, so combining that with blue produces high S, low-but-positive L-M (as opposed to high S, ~zero L-M for violet). The difference L - M is not hugely different between violet and purple, which is why they are similar-ish looking.

String theory is an attempt to explain the phenomena of current physics as emergent behavior of some underlying objects. The details are beyond my understanding of physics.

> How does the Higgs boson come into play here? Is it merely hypothetical or has it been widely accepted as something that exists?

The Higgs was hypothetical for a long time, but was observed by the LHC in 2012. It's now generally accepted that it exists.

> What I can remmeber, it was the particle responsible for granting all sorts of matter their mass.

More or less, yes. Specifically, it's (among other things) why the W and Z bosons have mass but the photon doesn't.

Recall that mass and energy are two different expressions of the same thing. Potential energy stored in one of the physical fields underlying the universe is mass, and in fact about 99% of the mass of the objects around you comes from the potential energy of quark-quark attraction, not in the bare mass of the quarks themselves. The Higgs mechanism gives some particles mass by effectively "tangling" the Higgs field (one of the underlying physical fields) with the field underlying the weak interaction (one of the four fundamental physical forces) in such a way that neither of them can settle into the zero-energy state that they "want" to settle into.

Again, the details here are extremely complicated.

> Doing some diving into wikipedia there are tons of things like gravitons and fermions and whatnot that make it seem like it's a massive iceberg out there. My question is, what is the most widely accepted theory for quantum mechanics and what subatomic particles have been proved to actually exist?

The basic accepted theory of particle physics today is the Standard Model, which contains the following particles:

• Six quarks, two of which (the "up" and "down" quark, no relation to everyday directions) make up protons (two up, one down) and neutrons (one up, two down) respectively. The others (the charm, strange, bottom, and top quarks) are unstable under normal conditions and are only observed briefly in particle accelerators.

• Six leptons: the electron and its two heavier cousins, and the three types of neutrino. The muon and tau (the two heavier cousins of the electron) are unstable. The three neutrinos are sort of stable, but they actually oscillate (change from one type of neutrino to another) as they travel. Neutrinos are rarely important to everyday events because they interact very weakly with the matter humans are made of.

• The bosons, particles that carry the underlying physical forces of the Universe. These are the photon (carries electromagnetism), the W+, W-, and Z bosons (which carry the weak interaction), the eight types of gluon (which carry the strong interaction), the Higgs boson (which carries the Higgs field, or more properly one component of it), and the still-unobserved graviton (which carries gravity).

Of these, only the graviton has not been observed.

The Standard Model is, however, known to be incomplete. It can't explain some physical phenomena, and it's incompatible with relativity in conditions where both gravity and quantum mechanics become relevant. Theories like string theory are attempts to expand the standard model in ways that cover these gaps.

> Is it theoretically possible to split a subatomic particle? If so, how much energy would it release?

Subatomic, sure, but not fundamental. The only subatomic particles currently known not to be fundamental are protons and neutrons, and you could in principle split them apart...

...but the properties of the strong interaction make the behavior of such a split a bit weird. Instead of seeing free quarks, you'd see new protons and neutrons!

The reason is that the strong interaction (in its full form, not to be confused with the residual strong force that holds the nuclei of atoms together) doesn't fall off with distance the way that electromagnetism or gravity do. The potential energy of two separated charges in electromagnetism, for example, is -1/r, but the potential energy of two separated strong-interacting particles is, roughly, just r. So once quarks get very far apart, it's actually energetically-favorable to just spontaneously produce new quarks from the void to bind them up into protons and neutrons again.

In any case, protons and neutrons are very tightly bound, so you wouldn't release energy by splitting them (you'd have to input a huge amount of energy). The same is true of nuclei, by the way, it's just that sometimes splitting a nucleus results in more tightly bound nuclei.

> Is it true that many subatomic particles are believed to interact with parallel universes (like basically exist in both simultanoeusly)?

This is speculative and depends on your interpretation of quantum mechanics. Unless you're doing the math, this sort of question is more "whooaa duuuuuude" stoner speculation than science.

> And keep them under control. Not at all.

Uh, the world has actually put a huge amount of energy into stopping nuclear proliferation (the term for new countries acquiring nuclear weapons).

Only eight countries are currently believed to have working nuclear weapons. In order of development, they are:

• the US (1945)
• Russia (1949)
• UK (1952)
• France (1960)
• China (1964)
• Israel (sometime in the 1960s or 1970s; unlike the other states on this list Israel does not admit that they have nukes)
• India (1974)
• Pakistan (1998)
• North Korea (2006)

(South Africa also once had them, and would appear on this list somewhere near Israel or India, but South Africa voluntarily disarmed and no longer possesses nuclear weapons.)

No new state has been added to this list in almost 20 years.

Yes. Not everyone who got the plague died, although a large percentage did (plague is fatal ~half the time without treatment), and there can be different degrees of spread for a particular plague epidemic.

As for why the full intensity didn't reoccur: the Black Death killed a third of the people in Europe (for comparison, that's about 100x the death rate of covid in the US), and infected most of the rest. By killing off the most vulnerable parts of the population, it made Europeans particularly resistant to plague, so future plague epidemics were less bad. It's similar to how modern Native American populations are no longer ravaged by diseases that, when their ancestors were first exposed to them, wiped out as much as 90% of the population.

A subatomic particle is just a particle "smaller than" an atom (hence sub + atomic). The three you're familiar with are the three component particles that make up atoms: protons, neutrons, and electrons. It turns out that protons and neutrons (but not electrons, so far as we know) have further internal sub-structure; protons and neutrons are each made of three smaller particles called quarks. The only other example you "see" in everyday life is the photon, the particle of light. Others exist, but none of them are long-lived or seen in everyday life under normal conditions.

What they "really are" is more a matter of philosophy than it is of physics. Physics is interested in describing how they behave. And in modern physics, we model the behavior of particles through quantum mechanics.

It turns out that the way we tend to think of particles in our minds - tiny little spheres bounding around and exerting forces on one another - just doesn't correspond to the way particles actually behave.

In quantum mechanics, the underlying "reality" of a particle is something called its wavefunction. Rather than a particle "being in one position", a wavefunction takes every possible position and assigns a single number to each of them. These numbers are complex numbers (that is, they look like something like 0.2 - 0.4i), and the Schrodinger equation tells us how they evolve over time.

Exactly how we interpret these wavefunctions as corresponding to any of the things we observe day to day is a topic of some debate. In a sense, the ultimate underlying reality is always the wavefunction, and the Universe as a whole has one wavefunction that has just been evolving according to the Schrodinger equation since the beginning of time. But since we often want to consider particles in isolation so that we can talk about an electron without talking about the whole Universe, we have to think about how we can "cut off" the electron from the cosmos. In this sense we try to talk about "the electron's" wavefunction, but in reality, even the existence or non-existence of the electron is a statement about the wavefunction of the entire Universe, so by talking about "an electron" at all we are going to introduce some weirdness.

We do this by thinking in terms of probabilities. The electron, if measured, will appear to be in one of several locations, and the probability of it being in each of them is equal to the square of the magnitude of the number the wavefunction assigns to that location. For example, if a position has wavefunction value 0.1 - 0.4i as mentioned earlier, the electron will be in that location with probability (0.1)^2 + (0.4)^2 = 0.17. Since the wavefunction has non-zero values at many points, in this sense the electron "can be in more than one place at once", or more properly, could be measured to be in any one of several different places at random.

Exactly how this corresponds to our conventional notions of position, velocity, etc is a topic of considerable debate, but this approach to modeling particles works well and describes our world accurately (and no non-probabilistic model can do so).

My guess is that you're thinking of some sort of opponent-process model or something like the CIELAB space. But neither of those corresponds to the physical response curves of cones.

> That said, even returning the rays to parallel does not mean recombining them. At the first surface they are given different angles, splitting one beam. Returning this set of beams to parallel just means that the colors do not spread even further once they've left.

This is true, but the effect is pretty small, much narrower than a typical light beam, and dominated by diffraction, so you just get fringes of very slight color.

> Each of the three has a color it’s best at detecting, and we name them based on that. One for red, one for green, one for blue.

This is incorrect. The three cones in your eye are most sensitive to violet, green, and yellow-green, and they're not called red, green, or blue cones. The usual name is S, M, and L, for short, medium, and long wavelengths.

> But for whatever reason, way down in violet, the red cone has a little bump in sensitivity again, after not seeing green or blue at all. So violet literally is the blue cone sending a strong signal, but a little bit of the red cone too.

Also incorrect. The L cone does not have any particular sensitivity to violet light.

It's worth noting that CO2 levels are far lower than oxygen levels in the atmosphere, so it's much easier to change the (relative) amount of CO2 than it is to change the (relative) amount of O2.

It isn't completely constant over geologic time. Earth's oxygen has been as low as 0 and as high as about 33% at different points during Earth's history.

The oxygen in the air is the result of an equilibrium between plants and other photosynthetic organisms (it's actually mostly microbes in the ocean) producing oxygen as a by-product of photosynthesis. This equilibrium is pretty stable, since organisms are short-lived and organisms will be slightly more successful in environments that are more favorable to them. (As an example, global plant growth has accelerated pretty significantly as humans have added carbon to the atmosphere, although not by enough to compensate for the rate at which we're adding it.) This part is basically a closed cycle: plants produce oxygen in the process of capturing carbon to use in their "bodies", animals eat the plants and burn the plants' "bodies" with oxygen from the air.

Over the very long term, though, there's another important effect: geology. Or more specifically, geology driven by living things. Earth is old enough, and living things dominant enough in its surface chemistry, that life on Earth and Earth's own geology are intimately linked over the longest timescales. (This is, I think, incredibly cool. In a very real sense, the very stones of Earth are part of the biosphere.)

In the processes described above, some organisms manage to die and decompose without returning their carbon to the atmosphere. The corresponding oxygen that was liberated during the capture of that carbon, then, ends up sticking around in the atmosphere over the long term. This is, in effect, what happened during the burying of the organic material that became fossil fuels, and it's part of why the era in which those fuels were produced had the highest oxygen levels in the history of Earth to date.

On the other hand, sometimes geological processes expose this buried carbon to the atmosphere, where it reacts with oxygen. This is the same kind of chemical cycle as the regular biological one, just dominated by geological processes over much, much longer times.

There are a few other minor contributors, like serpentization of certain rocks, but the ones described above are the big drivers.

The net effect of all of this in the Earth we have today is very close to zero if you ignore humans. So, human activity aside, Earth's oxygen levels aren't changing quickly over any timescale remotely relevant to humanity.

But thanks to the fact that we're burning an absolute ton of buried carbon (effectively accelerating one side of the geological processes described above), the oxygen content of the atmosphere has very slightly declined due to human activity. Not by anything significant - a few parts in 10,000 - but some.

Prisms work by refraction.

Light travels at a fixed speed in a vacuum. But within a material, light travels more slowly. You can think of this as something like a wave traveling through a harbor, jostling boats as it goes, and being slowed by the fact that it is transmitted by the way the jostling of one boat reproduces the wave on the other side. The difference in speed is called the refractive index of the material. Air slows light by only about 3 parts in 10,000, but water slows light by about 1/4, glass by about 1/3, and diamond by about 60%.*

When you move a wave, including light, into a region where it travels more slowly, the wave bends. This is refraction, and it's simply what happens when you slow down one side of a wave; there's nothing magical about it. So when light moves from one medium (=material) to another, it bends.

Since the refractive index of some materials depends a bit on the wavelength (=color) of the light, the different colors of light bend by different amounts. That results the different colors (or more properly, different wavelengths of light) in the incoming beam splitting apart and traveling at slightly different angles.

With that model in mind, we can answer your questions:

> If you shine a coloured light what would happen?

In a colored light, not every incoming wavelength would have the same brightness. So you'd still split the beam into its component wavelengths, but some would be brighter than others. Since many possible mixes of wavelengths can produce the same colors, you could actually shine two different (say) yellow lights into a prism and see two different resulting spectrums.

> Why does it need to have an angle if you can use cuboid ones?

Refraction happens even without an angle, but when the light exits the other side of an object at the same angle (as it does if the would-be prism has two parallel sides), the same refraction happens in reverse. This puts the rays back in parallel. Since the rays didn't separate much in their brief travel through the material, all this results in is a very slight violet tinge on one side of the beam and a very slight red tinge on the other, and even that is a result of the fact that the beam has some non-zero width.

If the sides aren't parallel, though, the light doesn't hit the other side at the same angle. This causes the rays to further disperse (more sharply this time, because this time they weren't even striking at the same angle in addition to the wavelength-dependence of the refractive index), which is what produces the widely spaced bands of color you associate with a prism.

> Do different shapes give different affects?

The overall shape isn't important, just the angle at which the light enters and exits.

* You might wonder about the full physics of exactly what's happening here. There are a few ways to think about it.

One is that, in effect, the light is diffracting around all the billions of billions of billions of particles in the material. That diffraction results in an interference pattern, and it turns out that the interference is only constructive at the angle the light apparently "travels" and destructive everywhere else. Since interference patterns are in general wavelength-dependent, it's not too surprising that the refractive index is wavelength-dependent with this idea in mind.

Another is to think of the light as effectively setting up a resonance in the material, with the photons forcing the molecules in the material to vibrate along with the light's frequency. That vibration, which is a vibration in charged particles, produces a vibration in the electromagnetic field - i.e., the original light - but traveling more slowly and with its phase shifted.

> Cubes also have angles.

An object with parallel sides won't act as a prism, because it puts the rays back in parallel as they exit.