Thank you for the explanation, I learned something new.

Very marginally, but yes, experiments have proven that time dilation is real, and appreciable, even at the level of Earth's satellites. Satellites and the ISS are affected by time dilation due to both general relativity (gravity) and special relativity (their velocity while orbiting Earth). The exact dilation is marginal, on the scale of microseconds per day, but is important to adjust for in systems such as our GPS navigation system, without which the accuracy of the system would be entirely worthless.

https://science.howstuffworks.com/explosion-land-water1.htm

Differential density. Your cavities (such as your lungs) and the gasses within get compressed when the shock wave hits and your tissues rupture when the pressure is transmitted through the water and through your body. Differential density is also the reason why things like shaped charges kill everyone inside a tank (using a shaped charge, a high explosive generates a shock wave which penetrates the armor of the tank via the Munroe effect, the energy of which is transferred to anything inside it as the pressure of the shock wave compresses and destroys your tissues) even if the tank armor remains intact (no or incomplete penetration).

The reason why you need a similar density to water is because of differential density. With a similar density, forces will be exerted roughly equally but when there are non-uniform densities, those effects can be felt. Why does oil float on top of water? Because of the difference in density and the application of buoyant force. Oil is less dense than water and so it floats to the top. But what happens when a person has a different density than the fluid both inside (the cavities) and out? Imagine for a moment if your fluid density is more dense (you "sink") and if your fluid density is less dense (you "float") relative to the fluid immersing you. Higher/lower density doesn't really matter as the only thing that really changes is the direction you go in but regardless, you'll feel the sum total of all the different forces on your body, all at the same time, as your body tries desperately to resist the laws of physics and fails.

Humans are largely composed of fluid. Yes, the fluid is tucked away by membranes (cells) and we think of ourselves as solid, but we are still almost 60% water. Do you know how we use centrifugal force to separate red blood cells from the rest of the plasma? Same concept, differential density, only now the fluids and precipitates that comprise your being are being separated by ascending/descending density.

That's why you need a fluid with a similar density as water, because we're made of water and we need to keep that water inside our cells.

Yes. Forces applied to fluids are distributed as omnidirectional pressures as fluids are difficult to compress. Because fluids are difficult to compress, there's no appreciable change in density under high acceleration. This concept has already been applied to high G flight suits, namely the Libelle G suit, which has allowed pilots to remain conscious and functioning during maneuvers as high as 10 G's.

The practical acceleration protection limit via liquid immersion is hypothesized to be approximately 15-20 G's. Beyond that, cavities such as your lungs will collapse, so you'd need to fill your cavities with a human compatible oxygenated immersion fluid which simultaneously has a similar density to water. There is practical upper limit as the differential density of tissues inside the human body will eventually be reached, but hypothetically, if you filled a person with this fluid in all their cavities (lungs, stomach, intestines, etc.), they could survive outrageous amounts of acceleration. Of course, this is all contingent on finding an immersion fluid which is both lung-compatible and has a density similar to water, so it'll probably never happen.

What constitutes a disruption? Does it have to exert a secondary tidal effect rivaling Luna, or can any alteration to the current tidal pattern, no matter how marginal, be considered a disruption? Also, how measurable does this effect have to be? Thirdly, does this object have to follow the same trajectory as Luna's natural orbit? Luna's orbit around the Earth is elliptical and not equidistant. At what distance exactly are you referring to?

I'm going to assume you're taking about Newtonian physics here and not general relativity. Taking the literal understanding of your question, any introduction of any kind of mass into Earth's system will disrupt the Earth's tides and also Luna's orbit. This effect could be minuscule to the point where it cannot be measured by our instruments but the introduction of something new in the system will affect the existing system. Earth and Luna's tidal forces are also not constant as celestial objects such as the Sun or other planets also exert forces on each other at non-constant rates. The orbital path of the object and its velocity are also factors of consideration but the exact disruption will have to take place at an exact time and place.

The force of attraction (gravity) is stronger the closer you are to an object so the closer this object is, the stronger it's effect (inverse square law). To calculate the exact disruption, you will need to input the mass and distance but any mass at any distance will alter the system, no matter how small (even if it's not measurable).

We can calculate the approximate disruption of an inputted mass at an inputted distance but to be honest, it's difficult to answer your question in a meaningful way. We can try to calculate the tidal force of an object (to simplify the calculation, we input a new mass, distance, and orbital path into the local Earth-Luna system) and run the calculation from there but basically, any change will affect the system and while we can calculate the approximate change to the system as a result, in the end, we need more specific conditions (ex. assuming the introduction of a new tidally locked mass opposite of Luna's normal trajectory, at a distance of 360,000 km, how much mass is required to alter the tidal force of Luna by +/-1%?). There are also other factors to consider here such as measurement errors or rounding errors so I can't tell you the exact minimum amount of mass needed for the change but them monkeys at NASA are getting REALLY good at running these kinds of calculations (orbital mechanics).

This right here is the answer. The Rehbinder Effect basically describes the observation that surfacants (a chemical that reduces the surface tension between substances such as soap) reduces the hardness (a measure of localized plastic deformation) and the ductility (how easily a substance can be drawn) of a material, thus making it easier to deform and manipulate. By submerging the glass inside water, you can reduce the cutting force of the drill and better control the rate of abrasion. In this scenario, water is being used as a lubricant.

Human history is pretty short, beyond advances in technology (ex. telescopes, corrective lenses, etc.) and light pollution, I don't think there are any noticeable changes. The moon's orbit is pretty stable, even if it's gradually slowing down the rotation of the Earth and moving away at like, 4 cm a year. Maybe there are more footprints and craters on the moon's surface? But to the naked eye, I honestly don't think there's much of a difference. A few thousand years is nothing on a cosmic level.

The majority of histamine allergies are on H1 and H2. H3 and H4 are pretty rare. H1 are where most allergic reactions take place while H2 is the gastric stuff. I imagine if you're taking H1, most of your other histamine allergies will also be impacted. H3 is mostly found in the brain and H4 is kind of special. H4 was found while combing through the human genome and it seems to affect the shape of some white blood cells and the movement of mast cells. H4 is not well understood as it was only discovered in 2000. H4 receptor antagonists are being studied for the potential treatment of asthma.

The simple answer is yes but the more complex answer is maybe.

To understand what an antihistamine is, you have to first understand what a histamine is. A histamine, in simplest terms, is a compound involved in local immune responses and a neurotransmitter. It is this compound which triggers many allergic reactions, mainly by binding a cell's histamine receptor. There are 4 types of histamine receptors, aptly numerated by H1-H4.

An antihistamine is a classification of drugs which counters the activation of a cell's histamine receptor by blocking the receptor without triggering a response (receptor antagonist). Though it is commonly understood that antihistamines are used in the prevention/treatment of allergic reactions, an antihistamine is not synonymous with anti-allergy drugs as there are drugs out there which treat allergies/inflammations which are not triggered by histamines, such as corticosteroids (antihistamines do not work on non-histamine allergies/inflammations). Silver allergies for example, is not a histamine allergy and is treated by corticosteroids.

You mentioned that you're taking levocetrizine, which targets H1 receptors. It would not be effective if you had allergies on H2-H3 or any other non-histamine allergy triggers. Mosquito bites, in particular the itching reaction, is strongly correlated to be affected by the activation of the H1 receptor. By taking levocetrizine, you've blocked the H1 receptor and thus, have suppressed the itch activation.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3684411/

Thus, to answer your question, first of all, it would depend on which type of antihistamine you're taking (which type of histamine inhibition, from H1-H4) to see what other potential allergic/inflammatory reactions you're also suppressing). A H1 inhibitor antihistamine will not work on a H2-H4 histamine reaction or vice versa (it must be targeted). Secondly, antihistamines will only work on allergies/inflammations caused by histamines - it is not a cure-all for allergies as there are many different types of allergens (such as silver). Lastly, you are correct in identifying that taking an antihistamine for one allergen may reduce the effect of another potential allergen if they are both triggered via similar pathway. However, you should not preemptively self-medicate without proper medical guidance as each allergic reaction and subsequent treatment should be taken by a case by case basis. Also, taking antihistamines in the long-term can be detrimental to your health so please take care when you're using drugs and only use drugs in the manner prescribed.

https://www.mayoclinic.org/diseases-conditions/conjoined-twins/symptoms-causes/syc-20353910#:~:text=Conjoined%20twins%20may%20be%20joined,hearts%20but%20share%20other%20organs.

I think it would depend on three factors: the type of conjoining, the type of drug, and thirdly, the dose but yes, in theory, both people could feel the effect of drugs.

Thoracopagus (being joined in the chest) is the most common type of conjoined twins and they typically have a shared heart and liver. As their circulatory system (heart) and waste disposal system (liver) are connected, it stands to reason that a significant dose that is being metabolized by one twin will also affect the other due to the connected systems though likely at different rates. Something like alcohol for example, taken orally, should in theory, affect both twins but inebriate the ingesting twin more heavily as the alcohol is being absorbed through that twin's mouth and stomach and should reach the ingesting twin's brain faster.

Rachipagus (being connected along the spine) is a rare type of conjoined twin and will likely not result in the other twin being affected by the ingestion of alcohol due to the separation of their circulatory system and GI.

Basically, anyone who shares the same GI and circulatory system should in theory, be affected though the rate and effect of that drug would be different. I don't believe there is any research that studies this in depth so I am only offering my conjecture.

I don't imagine there would be anything conclusive for a variety of reasons.

By virtue of being prehistoric, it can't, by definition, be referenced by a written record. This means that any record of such a hypothetical pandemic would have to be based on residual physical evidence, which would be extremely scarce.

Pandemics are differentiated from other disease outbreaks in the sense that it has to be spread out and affect a large region. This means that to find physical evidence of disease spread over a large region, you would have to actually find multiple instances of that disease being spread over a large region. However, both bodies and pathogens naturally degrade over time so it would be extremely hard to find any physical evidence at all.

While it may be hypothetically possible for evidence of a mass dying caused by sickness (ex. while rare, a mass grave with preserved active/inert pathogens, perhaps preserved by cold conditions such as glaciers or permafrost could potentially be discovered), to assert that a pandemic had occurred, you would need to find additional evidence (other intact burial sites or other physical evidence) over a large region, which occurred at roughly the same time. An anthropological find like this would probably be worth a Nobel prize.

Herds of animals or human tribes dying out from illness is a pretty common occurrence in nature but geography and other natural barriers would've discouraged most pathogens from becoming pandemic. Diseases affecting animal populations tend to self-limit due to a variety of factors (such as geography, climate, vectors, predation, population collapse, etc.) so spreading a disease to the point that it becomes pandemic seems rather implausible in prehistoric times.

Your immune system, in particular antibodies, recognizes and attacks things based on the presence of these things called antigens. Things like viruses, bacteria, or even pollen (i.e. allergies) possess antigens which your antibodies can detect via a receptor. Antigens come in all forms of shapes, sizes, and chemical compositions whether it's proteins, peptides, saccharides, etc., but what triggers the antibody to attack is when an antigen binds to the antibody's receptor. If the antibody receptor does not bind, the antibody does not attack. This is why your body doesn't usually destroy itself (except for autoimmune diseases), as a normally functioning immune system will only attack things that trigger it (anything else will not be attacked). Think of it as a reverse IFF (Identification Friend or Foe), where your immune system assumes everything is friendly except for when it detects a threat.

Modern pharmaceuticals are formulated so that when used in treatment, they will be effective. If it's not effective, it's not considered medicine - it's as simple as that. The biotech engineering takes into account things like delivery method (ex. oral ingestion, IV, etc.), potential interactions (ex. drug to drug), and how well tolerated it will be when taken (i.e. whether it causes an adverse reaction and if so, the extent of it). Thus, the first filter (reason) why drugs work is because they are specifically engineered to work and won't be passed off as medicine until it has passed drug trials and has been approved by whatever regulatory body your country has.

Secondly, drugs/medicine can have an effect on your body that is not limited to immune responses - these are usually referred to as side-effects. In regards to specifically to drugs activating an immune response though, certain drugs may or may not illicit an immune response, and if they do, it could either be a big response, or a small response, or they could even shut down a response all together. It is extremely varied and it all depends on the context. For example, certain drugs, such as chemotherapy meds, obliterate your white blood cells and weaken your immune response as an unintentional effect of killing cancer. Other drugs can trigger an immune response if the drug's antigen is bound and your immune system can actively try to rid itself of the drug, such as in the case of Bococizumab (a cholesterol control drug developed by Pfizer, which failed its trial as while the drug was initially effective, the trial participants started developing antibodies against it, which is why drug trials happen in the first place, to see what happens). This is also one of the reasons why certain drugs lose effectiveness over time (another reason is tolerance, such as in the case of opioids).

Thirdly, certain drugs are formulated to intentionally tone down an immune response, such as antihistamines or steroids to control inflammation. This category of drugs are commonly referred to as immunosuppressants, which are usually used to treat autoimmune diseases. Drugs, like man, are not made the same. The mode of action is a consideration.

In summation:

a) Your immune system will not attack anything that doesn't have a detectable trigger (an antigen) and this function is not limited to drugs and thus pathogens (ex. bacteria, viruses, etc.) which can evade detection will also evade destruction.

b) Drugs are engineered specifically to be effective and well-tolerated. Any drug that is not effective won't make it to market due to regulatory bodies.

c) The assertion that drugs don't provoke an immune response is based on an incorrect parameter. Many drugs do in fact, provoke an immune response and can be expressed as a side-effect, though side-effects are not limited only to immune responses.

d) Certain drugs are specifically formulated to tone down or disable an immune response (immunosuppressants).