Physics: Research Trivia

%i. If I use my garage door remote on every garage in my block or city, will it work on someone else's garage? Will my TV remote control work on someone else's TV? Or how about between garage remote and TV remote?

Short answer is, garage remote can never work on TV remote and vice versa, as garage remote are in radio waves, while TV remote are in IR (so even sunlight can trigger a TV to turn on).

But in the earlier days, TV remote had a 128 selection, whereas for garage remote, between 256 and 4,096.

%i. What's more dangerous, high voltage low amp, or high amp low voltage?

Higher amps low voltage. Voltage is like the pressure that pumps the danger.

%i. If there is anti-matter, are there anti-photons? No.

If there are dark matter, can there be dark photons? Yes.
Can there be anti-wavelength? No.
Can there be dark wavelength? No evidence.

%i. How will the world end?

Some people say the world will end in fire, some say in ice. According to the Nobel Prize in physics in 2011, probably end in ice.

%i. Does hot water travel through a pipe faster than cold water?

Yes it does, due to friction. But not by much.

%i. What travels faster, 50 C water traveling through 25 C steel pipe, or 25 C water traveling through 50 C pipe?

Metal heats up faster than water, and so 50 C water heats up the pipe faster than the other way around.

%i. What are some insulation materials to use? Fiberglass, vermiculite, and polyurethane foam.

%i. What’s the most dangerous part of a microwave?

Here’s how microwaves work: 117 V comes into the microwave, and into the circuit transformer. 1 part of the voltage is increased to 2000 V, the other is decreased to 3 V. The 2000 V goes to the capacitor, which is the most dangerous part of the microwave. (The 2000 V transformer and 2000 V capacitor is why you never work with while the microwave is plugged in.). It turns the AC to electricity while doubling the voltage. The 4000 V and 3 V goes into the magnetron (a mini particle accelerator). The 3 V heats a metal, while the 4000 V pulls the electrons off a metal into a magnetic field generated by magnets. The microwaves have a frequency of 2.45 GHz, which is a frequency absorbed by water molecules (much like glass absorbs UV-B and heats up), where the electrons rotate 8x slower than the 2.45 GHz frequency. A pulse is generated on each transition.

The magnetron has a very inefficient power-supply, at about 50%. The power-supply design has only 3 components: a transformer, a capacitor, and a diode. These 3 combined are called a half-wave rectifier (rectifiers convert AC electricity from the outlet, into DC). In a magnetron, the electrons jump off a cathode and move freely around the chamber. Then the spiraling electrons reach the anode, they induce a charge separation (a voltage across the anode-resonating cavities). Magnetrons also have a brass reflector, that prevents waves from bouncing back into the magnetron, as well as 2 permanent magnets.

Microwave cavity magnetrons work on the principle of LC oscillations, which occurs when a charged capacitor is placed along an inductor. When an antenna with an inductor attached to it, is placed near an inductor if a LC circuit, the antenna radiates electromagnetic waves. In a magnetron, many electrons are ejected from the cathode by thermionic emission. Thermionic emission is where electrons are emitted from a filament after the current flows through the filament and heats up the cathode. However, without a surrounding anode, the electrons will just come back to the cathode. So with a surrounding anode, the charges produce radiation when they accelerate. (Then, as you put permanent magnets to sandwich the anodes, this is now a hull magnetron.).

Note: there is a most dangerous chemical inside the magnetron of a microwave, which is inside the ceramic insulating material. It contains beryllium oxide, which is dangerous if you breathe it, so you wouldn't want to break into it.

%i. What makes a non-rechargeable battery a non-rechargeable battery, and a rechargeable battery a rechargeable battery?

Rechargeable batteries have reversible chemistry, but have limits. Material buildup can form inside them, which gradually prevents Li ions from attaching to the opposite end of the battery.

%i. Are chandelier lights in series or parallel?

Parallel. If they were in series, then if 1 light bulb burns out, the whole circuit is down. All light bulbs are also equally bright in parallel. In terms of kilowatt-hours, both types of wiring have the same energy effiency and costs.

In parallel, a 60 W bulb will be brighter than a 40 W bulb, but that won't be the case in series. In series both bulbs wil be dimmer than normal if the bulbs have different Watts, and their lifespan could be shortened. In series, different Watts means uneven voltage sharing and therefore overall dimmer.

Christmas lights are also in parallel, but Christmas lights from the 1920s to 1980s were in series.

%i. If 2 cars drive the same distance, but 1 is twice as fast, do they both use the same amount of gasoline?

Air drag increases with the square of velocity. If you increase velocity by 2, then drag increases by 4. So if you travel 41.4% faster, you consume roughly twice the fuel per unit distance (although engine efficiency changes with changing speed). (Engine efficiency is how much of the input energy is converted to the mechanical motion of the wheel, which hits 25% for the most energy-efficient cars.).

While this makes it seem driving slower is better, the counter argument is to keep in mind when you drive on a highway, you avoid stop signs and red lights, which increases your gasoline usage.

With drag and gasoline.

Running AC uses 10% more fuel, but keeping windows open increasing drag increases about 20% more fuel usage.

%i. Is it warmer to drive a black car in the winter, and cooler to drive a white car in the summer? As well as clothing.

For clothing, there’s 2 factors to this, IR light from the sun, and our own body heat emitted. For sunlight, wearing black is the undisputed color to stay warm. But for body heat, the opposite is true. White clothing reflects our body heat back to our body, whereas black clothing does not. If you combine these, the best way to stay warm in the winters, would be to wear white clothing on the inside, and black clothing on the outside.

For summer time, the best color to keep cool, if in the shade, is black, but if under sunlight, then whether wearing black or white, you got contradicting factors.

For cars, the outer paint of the car being black and white is 1 factor, but also the color of the seats and dashboard, being a light or dark color. The disparity will be less in the winter times, and more in a sunny day vs. cloudy day.

%i. Is it harder to start a car in colder weather?

Yes, for 4 reasons.

1 - Batteries cannot produce as much current when they are cold. This means the starter will not apply as much force to turn the engine when you turn the key.
2 - When metals get cold, they shrink. This means that the pieces fit more tightly together. This makes the engine harder for the starter to turn.
3 - When oil gets cold, it gets thicker. This means that it does not as easily get into the small spaces between metal parts. This means that the engine does not lubricate as quickly.
4 - When fuel gets cold, it is harder to atomize. This means that the fuel air mixture does not burn as smoothly and so it produces less force to keep the engine turning.

%i. What is oil used for in a car, and how often should you change it?

Engine oil serves 1 primary functions in your car: it provides lubrication to reduce friction between moving parts and it also helps absorb heat, keeping the engine from overheating. Both functions are crucial to the sustained health of your car.

As for how often should you change your oil, conventional wisdom held that oil should be changed about every 3,000 miles, but that was based on older oils that didn’t last as long. Modern oils, particularly synthetic oils, tend to last significantly longer than that. The standard for that is 5,000 to 7,500 miles, or every 6 months, whichever comes 1st.

Your owners manual may be your best source of information to determine how regularly you need an oil change. It may even list out different scenarios that may require an adjustment to your car maintenance schedule, such as frequent stop-and-go driving or driving in extremely hot and dusty climates. In that case, change it 3,000 to 5,000 miles, or every 3 to 4 months.

%i. Has engine-efficiency increased for cars?

Yes, in the mid-1970s engine-efficiency was about 13%, and has increased to about 25%. The rest being lost as heat.

And while fuel efficiency has also increased during the timeframe, from 13 miles per gallon to 25 miles per gallon, cars today are heavier now. From 1985 to 2022, the weight of average cars in the U.S. increased by 33%, but the horsepower increased by over 100%. In the 1980s, about 10% of cars were all-wheel-drive, compared to 66% in 2022.

%i. What % of hydrocarbons are outputted from vehicles?

For an automobile without pollution control devices, about 65% of hydrocarbons are released from the exhaust, 25% released from the crankcase, and 15% are released from the carburetor from evaporation.

%i. What hits a baseball farther, 1 that is stationary, or 1 that is coming towards you?

1 that is coming towards you. This is because when a baseball is in motion, it has kinetic energy, which can be transferred to the bat upon impact, helping to propel the ball farther. In contrast, a stationary baseball has no kinetic energy, and therefore, there is no energy to transfer to the bat upon impact.

%i. What hits a baseball farther, swinging a bat and baseball both coming at 25 m/s, or both at 25 m/s²?

It turns out the 2nd question is incomplete, as there are certain variables missing. You would need to know the velocity at the point of contact.

%i. What distance will baseballs rebound back when say, 2 baseballs do a head-on collision, 1 travelling at 10 mph, and the other 40 mph?

False question, as only 1 baseball will rebound back. What will happen is, the slower baseball will slow down the faster baseball.

%i. What is the terminal velocity for a penny?

Pennies have 2 terminal velocities, where when its on its face, and when its on its side, so it oscillates, so the most is 80 mph. It can reach that at around 15 m.

A gun firing a bullet straight up, can hit up to 3 km high.

Terminal velocity also depends on how much air is present. In 2012, Felix Baumgartner jumped from a helium balloon 39 km above sea level, and reached free fall at 40 seconds, a terminal velocity of over 1300 km/hour, which is 25% faster than the speed of sound, making him be the 1st person to break the sound barrier outside a vehicle (because of lack of air at that altitude, which is 60x less dense than sea level). But he eventually slowed to 200 km/hour, at lower elevations at 2.5 km above sea level. That's 808 and 125 mph.

%i. Imagine you lift a baseball up 1 meter. You do positive work on the ball because the fore you apply is in the direction of motion, whereas gravity does negative work because its force is in the opposite direction. It's pretty easy to prove using the work energy theorem that the work done by both these forces are equal. Since the total change in kinetic energy from when the ball is on the ground to when you're done lifting it up is 0, the forces must be equal and opposing. Therefore, the total work done on the ball is 0. So where does the potential energy that the ball now has come from? If the total work done on it is 0, then how does the ball gain energy? If you say that the work done by your hand gives the ball its energy, then where did the work of gravity go towards? By the law of conservation of energy, that work must be transformed into some sort of energy.

A common scenario is that in which the amount of work is equal to the decrease in potential energy, regardless of which agents the applied forces are ascribed to. From the point of view of the lifter, they have to inject the same amount of physical energy into the system (a ball subject to the force of gravity), whether they slowly lift the ball or quickly throw it into the air with just enough initial upward velocity that it goes up by 1 meter. The potential energy increases, so the work is negative. Since it is counterintuitive that the lifter's labor thus achieves negative work, sometimes the opposite approach (increase in potential energy) is preferred.

If you really want to know, the energy is stored in the gravitational field surrounding the ball and the Earth, not in the ball itself. But when dealing with balls moving in constant gravity, that's not a very useful approach. For the moment, choose between (1) gravity does no work, the energy is stored in gravitational potential energy in the ball and can be released from there; or (2) there is no gravitational potential energy, there is a gravitational potential, the derivative of which, when multiplied by a mass, gives a gravitational force, which can do work. Just pick the option that's most convenient.

Note that if you move 2 opposing electric charges apart, the energy/work is stored in the electric field between the charges. If you move 2 aligned magnets apart, it's stored in the magnetic field between the magnets. In those cases it's common to deal with the energy of the field itself, but with gravity, this is rarely done because it's mathematically far more complex.

%i. What is the basis for which metal detectors can also detect liquids? Electrical conductivity.

%i. For the ideal gas law PV = nRT, why isn't there a formula for liquids?

There is a molar volume formula for most liquids and solid. V_m = C₁ + C₂T + C₃T² - C₄P - C₅PT, where C1 through C5 are empirical constants, all positive and substance-specific.

But otherwise, the reason is liquids do not behave the same as gases. Liquids have touching atoms, while not compressing or and decompressing well. (They compress a little bit, but not significant amount of work enough during heating and cooling cycles, or pressure increase/decrease cycles.). It's not like in gases, where the work and heat are always comparable. And if the fluids are incompressible, then pressure and temperature do not affect the volume occupied by a constant quantity of mass, which is what compressibility necessarily implies.

%i. Can light waves emit sound, or sound waves emit light? Are they actually the same wave, so a waves emit sound and light at the same time?

Light waves and sound waves are definitely not manifestations of a common underlying physical phenomenon. Light waves are electromagnetic radiation, whereas sound waves are movements of air often arising from physical vibrations. We do convert invisible light to sound when we listen to a radio. Whatever modulation that can be applied to a radio wave, can be applied to a light wave, so light, when modulated, can carry sounds and data. In Europe, where the rest of the world knows Wi-Fi as radio waves, has Li-Fi for light, UV, and IR waves.

%i. Can there be an electric field without a magnetic field, and can there be a magnetic field without an electric field?

In theory, yes for both, but in reality, no magnetic monopole has been created yet. An electric field can exist between 2 charged particles, even if there is no motion or current involved, while a magnetic field arises due to the motion of charged particles, such as an electric current. Therefore, an electric field can exist without a magnetic field if there is no motion of charged particles, while a magnetic field can exist without an electric field if there is motion of charged particles but no net charge.

A moving charge with constant velocity will always develop both a magnetic field and an electric field. Without the electric field, the magnetic field exists in permanent magnets and also with current-carrying conductors, and without magnetic field, electric field exists in charges at rest. (A current-carrying conductor produces a magnetic field around it, so it behaves like a magnet and exerts a force when a magnet is placed in its magnetic field.).

So, it is not possible to create a magnetic field without an electric field, and without a magnet.

%i. What is the pressure of a water main?

About 60 psi (8640 lb/ft²), or 4 bar (400 kPa).

So if 1 were to connect a vertical pipe into a streets water main, how high would the pipe have to be to prevent water from overflowing at the top? About 40 m (140 feet). H = pressure / unit weight of water. The unit weight of water is 62 lb/ft³ (9.8 kN/m³). H = 8,640 / 62 or 400 / 9.8. This concept is called hydrostatic pressure.

It turns out that living at sea level on Earth is about the same absolute pressure as being 35 feet (10 m) under water, according to WolframAlpha.

%i. What's the most photons an electron can release, at rest and such?

An electron at rest is not a well-defined concept, as by Heisenberg's uncertainty principle, an electron whose position is entirely certain, would have an infinite uncertainty in momentum. But an electron that jumps from 1 orbital shell to a lower orbital shell, emits 1 photon, and is now in the ground state. And electrons in their ground state, are not going to be emitting photons at all. They could be excited by various phenomenon such as thermal energy or absorbing a photon, and then undergo a radiation relaxation state to emit another photon.

In general, electrons can emit photons that are constrained by the conservation of energy, conservation of momentum, conservation of angular momentum, and the Pauli exclusion principle. In a hydrogen atom, an electron dropping down 1 energy level at a time, has a total energy of the photons to not exceed 13.6 eV (still 1 photon). If you pump energy into an electron, by having it absorb photons, it can emit photons forever.

%i. When a magnet attracts a metal, what do you call the magnet, and what do you call the metal that is attracted to the magnet?

The metal that is attracted to the magnet is often simply called the "ferrous material" or the "magnetic material." This is because metals that are attracted to magnets are typically those containing iron, nickel, or cobalt, and they are referred to as ferromagnetic materials. The attraction between the magnet and the metal is due to the alignment of magnetic domains within the metal, creating a magnetic force.

Are the magnet, and the magnetic material, both magnets?

No. Magnets have their own magnetic field due to the alignment of its internal magnetic domains, so they are inherently magnetic. The ferromagnetic material being attracted to the magnet doesn't possess a magnetic field until it comes into contact with the external magnetic field of the magnet. The external magnetic field induces a temporary magnetic field in the ferromagnetic material, causing it to be attracted to the magnet.

%i. If the metals that are attracted to magnets are typically those containing iron, nickel, or cobalt, then what materials are magnets made of?

There are 3 main types of magnets, discussed in the materials page.

%i. If I know a lightbulb's watt, volts, and amp, can I calculate its lumens?

With precision no, but you can narrow it by knowing what type of light bulb it is.

Lumens = watts * lumens/watt, where.

-Incandescent bulbs: ~10-15 lumens/watt (or 15).
-Compact fluorescents (CFL): ~50-70 lumens/watt (usually 70).
LEDs: ~60-120 lumens/watt or more (or 80).
Halogens: 20 lumens/watt.
Metal halide: 60 lumens/watt.

For dimmers, the voltage decreases from the maximum.

%i. If d is the distance from a heat source, then what is the temperature as 1 gets farther from the heat source? Is it 1/d?

No, it's 1/d² for cases of no air. This formula is from the surface of a sphere A=4πd².

If you're considering radiative heat transfer (like infrared radiation, from a fire or candle, as well as sunlight once it reaches Earth's atmosphere), the temperature is proportional to the 4th root of the heat intensity: T = 1/d^1/2.

Although fire radiates heat, most of the heat transfer close to the fire is through convection, because hot air rises rapidly and carries heat with it. However, the radiative component dominates at greater distances where convection has less influence.

%i. If d is the distance from a LED light source, then what is the lumens as 1 gets farther from the light source? Is it 1/d?

Illuminance (the amount of light that hits a surface), E = I/d², where I is the total lumens, and E is the illuminance in lux (lumens per square meter).

%i. In airplanes, I see 2 pilots. They sit on a left and right side, none in center. Why are there 2 pilots?

1 drives the airplane while the other is responsible for radio communications. This allows a pilot to use the bathroom while the other takes over. Commercial airlines do not allow 1 pilot to drive the entire route, and airplanes that allow only 1 pilot, have no bathroom.

%i. Can the airline take over the airplane if the pilot is temporarily absent, via a remote auto-pilot?

No, if that were possible you have the issue of hacking. Such a protocol would only allow the pilot to allow it.

%i. Can both pilots control the airplane, from their side?

For flying yes, but for lift-off, there are certain things only the pilot on the left can do. In transport category aircraft (large aircraft of the kind that are used by major airlines and freight carriers) it is universal that only the pilot in the left seat has a tiller for steering the nosewheel. Consequently taxying is performed by the pilot in the left seat, but in flight the aircraft can be flown from either seat. When the pilot in the right seat is performing the take-off, the other pilot will use the nosewheel tiller to keep the aircraft on the center-line until the aircraft reaches about 60 knots when the rudder pedals become adequate for directional control.

%i. What happens when you mix red, blue, and yellow light?

Red, blue, and green light makes white light, but that is not the case for replacing green with yellow.

Yellow light is a mix of red + green. So asking what is red + blue + yellow light is asking what is 1/3rd + 1/3rd blue + 1/6th red + 1/6th green. So, if it were 1/3rd green, that would be white light, but this is similar to white light, but 1/6th more red.

Red + blue light = magenta light.
Blue + green light = cyan light.

Red green and blue do produce a whiter light than red green and violet, due to humans having a blue cone instead of violet.

The rules are different with paint. The combination of red, blue, and yellow paint ideally should give black or dark brown. However, in practice, due to imperfections in the pigments and their absorption properties, you often get a muddy brown or gray.

And while red, blue, and green light become white light as light is additive, it is not the case for pigments, as pigments subtract light rather than add it. When pigments are mixed, they absorb more wavelengths collectively. White paint is therefore made from a compound that reflects nearly all wavelengths of visible light, such as TiO₂, zinc oxide, and lithopone (mixture of barium sulfate and zinc sulfide).

%i. What does blue light and yellow light make?

Many websites say blue paint yellow paint make a fern green color, but also mistakenly say blue light and yellow light make white light. They argue because yellow is red + green, then blue and yellow make white. But that is only for 33%/33%/33% red green blue. A light that is half blue and half yellow, is therefore 50% blue 25% red and 25% green.

Unfortunately, I don't have a real-world image for that color, but it does exist in HTML, as a RGB(128,128,255).

Note that humans having red green and blue cones, instead of red green and violet, explains why in the Doppler effect, we call it blue shift instead of violet shift. Our red and green cones have a closer overlap, meaning we see yellow better because it affects both our red and green cones. 2ndly, our blue cones aren't as good as our red and green cones, so we're less sensitive to blue light.

%i. Can enrgy that used to be a proton, and energy that used to be an electron, be distinguished?

Yes and no. In 1 case, yes, in another case, no.

The yes case is in which a proton or electron collides with their anti-particle. When an electron collides with a positron, 2 photons are created, each having a kEV of 511. A proton can collide with an anti-proton, and this annihilation produces multiple particles such as pions, kaons, and gamma rays, and releasing 938 MeV. The energy of these photons are then measured when the photon hits a solid, and the energy is measured by a photomultiplier tube.

Note that this is not absolute. If 2 photons have the same 511 kEV, then they cannot be distinguished with a different prior origin. But knowing this distinguishability is still statistically useless, as majority of photons produced are when an electron moves down an energy level.

Another way to create energy, is through nuclear fusion and fission. But the nuclear fusion and fission, do not come from the nucleus, as in protons and neutrons, but from the binding energy of the nucleus. This is the force that holds the nucleus together.

%i. Most superconductors are not magnets, and most magnets are not superconductors. But what are some things that are both a superconductor and a magnet at the same time?

True, these materials are rare because superconductors expel magnetic fields (the Meissner effect), while magnets create them. Remarkably, superconductivity can emerge from the alignment of magnetic moments.

URhGe was the 1st discovered metal that becomes superconducting in the presence of an extremely strong magnetic feld. URhGe and UCoGe are heavy-fermion superconductors, and their magnetic properties originate from the behavior of f-electrons in uranium. URhGe was discovered to be superconducting in 1995, UCoGe in 2007.

The 1st iron-based superconductor, LaFeAsO, was discovered in 2008 by a Japanese research team led by Hideo Hosono. Soon after, related compounds such as FeSe were discovered to exhibit superconductivity.

Iron pnictides and iron chalcogenides, can exhibit both superconductivity and magnetism. Compounds like FeSe show an interesting interplay between their superconducting and magnetic phases. The magnetic ordering is typically weak or antiferromagnetic in nature, allowing superconductivity to emerge at the same time.

Sr₂RuO₄ has been of interest because it may have a type of superconductivity that coexists with magnetic ordering. It was was discovered to be superconducting in 1994 by a group led by Yoshiteru Maeno.

NdNiO₂ shows both superconducting and magnetic characteristics, was 1st reported to be superconducting in 2019.

%i. What are some things that are both a superconductor and a antiferromagnet at the same time?

Antiferromagnetism and superconductivity are also generally considered incompatible, as the magnetic ordering in antiferromagnetic materials usually disrupts the formation of Cooper pairs, which are necessary for superconductivity. However, there are some materials where both antiferromagnetism and superconductivity can coexist. This unusual coexistence typically happens in unconventional superconductors, where the nature of superconductivity itself may not follow the traditional BCS theory.

The 1st heavy fermion superconductor, CeCu₂Si₂ (discovered by Frank Steglich in 1978-1979), and CeRhIn₅ (discovered 2001, and is antiferromagnetic below 4 K) are 2 well-known heavy-fermion superconductors that exhibit antiferromagnetic behavior along with superconductivity. The interaction between f-electrons and conduction electrons allows for this coexistence.

BaFe₂As₂ is an example where antiferromagnetism exists in the undoped phase, and superconductivity appears as doping increases. In some cases, traces of antiferromagnetism can coexist with superconductivity.

La₂CuO₄ is a high-temperature cuprate superconductor that, in its undoped state, is a strong antiferromagnet. Upon doping with strontium (to form La_2-xSr_xCuO₄), it becomes superconducting while some antiferromagnetic order persists in certain phases.

UPd₂Al₃ (discovered 1991) and UNi₂Al₃, exhibit antiferromagnetic and unconventional superconductivity at low temperatures (below 14 K and below 5 K).

FeTe is an anti-ferromagnet, and it becomes a superconductor with Bi₂Te₃, but it's not known why.

%i. What is the thing that transforms light into laser?

The device is called a laser cavity or optical resonator, which is part of a laser system. Here's how it works:

1. Gain medium:

The material where the light amplification occurs. It can be a gas, solid (like a crystal), liquid, or semiconductor. Examples are helium-neon gas, ruby crystal, or doped glass fibers. The medium provides the necessary energy states for atoms or molecules to undergo stimulated emission, a process fundamental to laser operation.

2. Energy source (pump):

Supplies energy to the gain medium to excite its atoms or molecules, to higher energy states. It can be a flashlamp, electrical current, or another light source.

3. Optical resonator (cavity):

Made of 2 mirrors placed at opposite ends of the gain medium. q mirror is fully reflective, and the other is partially reflective, allowing some light to escape as the laser beam. This setup bounces light back and forth, amplifying it via stimulated emission with each pass through the gain medium.

4. Stimulated Emission:

When a photon interacts with an excited atom or molecule in the gain medium, it triggers the release of another photon with the same phase, direction, and wavelength, creating coherent light (spontaneous, the excited atoms release photons randomly). These photons stimulate other excited atoms to release photons in sync. The optical cavity reflects photons back and forth through the gain medium, amplifying the light. The partially reflective mirror allows a concentrated, coherent, and monochromatic beam of light (the laser) to escape.

%i. So the mirrors (in a gain medium) are the ultimate thing that transforms regular light into laser light? Yes, the mirrors within the optical cavity of the laser system play a critical role in transforming regular light into laser light, but they work in conjunction with the gain medium and energy source to achieve this. While the mirrors are crucial, they alone cannot create laser light. The gain medium and energy source are also essential. The mirrors ensure that only light waves with the correct phase and direction (coherent light) build up in the cavity. This feedback mechanism enhances coherence, one of the defining features of laser light.

%i. Can I press 2 bricks against each other so they become 1 brick?

No. The atom's electron clouds repel each other, so they push back when they get close (Coulomb repulsion). To merge them, you would have to overcome their repulsion, but also force their atomic wavefunction to overlap substantially. So, you would have to break and reform bonds, like you do when you convert it to a liquid (or at least fusing the surface), and cool it back to a solid. (In a liquid, atoms can diffuse, bond, and rearrange at surfaces.). The energy cost of compressing electron clouds is enormous. And there is a limit of the Bohr radius of .0529 nm, for all states of matter.