You get it and live. It was not 100% fatal.

Additionally, if, say, 10% of the population is naturally immune, and you wipe out a third of the population overall with the disease, you end up with 15% of the survivors being naturally immune.

Wanna bet?

Karahan Tepe, Turkey, the oldest known ancient site accurately aligned to the winter solstice is over 11,000 years old.

There is a site in Aberdeenshire, Scotland, with a lunar calendar that used the solstice to keep on track that is about 10,000 years old, though it is not nearly so sophisticated.

There are a number of sites in Great Britain, Mesopotamia, and at least one in Germany aligned with the solstice which are as old or older than the pyramids.

The ancient Egyptians tracked more than 4,000 astronomical events. There are a number of examples of ancient calendars and structures that were aligned with the solstice created by the Egyptians, such as the Sphinx.

Heard of Stonehenge? Tracked quite a bit more than the winter solstice. Not that old considering it appears to be 7,000 years younger than the oldest known example.

If going by technology rather than age, then in the New World, we have Machu Picchu, Chichen Itza, Chaco Canyon, and quite a few others.

Scientific method? Not required. Not even close. Not even Neolithic. Mesolithic. Some of these structures were built prior to the most recent period of the Stone Age.

Patience is required for two things.

1. You must check repeatedly during the shortest days of the year to find out on which one the shadow of the stick is the the longest at noon.

2. You must keep track day after day for a year until the shortest day returns again. Until the shortest days return, however, all you need to do is to add a day to your tally.

You can measure the length of the year to within the correct number of days with a stick, the ground, a way to mark the ground, the ability to count, and patience. It does not take anything sophisticated.

They didn't, not always. Many cultures celebrated, not the solstice, but the day when they could tell that the day was getting longer and thus someday summer would return again.

The solstice wasn't necessarily the shortest day of the year (though it is). To these people, it was the day when the Sun at noon was lowest in the sky. That it was definitely the shortest day seemed likely given what else they knew, but they often could not measure the length of the day.

Measuring the comparative height of the Sun in the sky, however, takes a stick, the ground, something that can mark the ground, and some patience.

Pounds are a unit of force, while kilograms are a measure of mass, true. However, on Earth they are interchangeable because the difference between a measure of force and a measure of mass in this case is gravity. The pound takes into account gravity, and mass does not.

However, so long as they are in the same gravitational field, they are effectively the same unit. You can think of it as adding gravity to kilograms to make it a force or removing gravity from the pound to make it a unit of mass. Either way, you end up with comparable results if the gravity is the same.

It also does not matter what gravity it is, on the Moon, Earth, Jupiter, or a neutron star. So long as the gravity for both is the same, kilograms are effectively a unit of force and pounds a unit of mass.

You can think of jury duty as a tax to pay for the legal system having "a jury of your peers", much as a monetary tax exists to fund the financial side of the government.

As to cameras seeing "much clearer" than the human eye, they are actually so different that they are very difficult to compare. The human eye takes in a much broader picture than a camera, while the camera may bring in more detail in its smaller field of view. This is because the human eye is built so as to see all the bushes a lion might hide behind well enough to catch the suspicious ones, not a really clear view of a lion too far away to be a threat.

Additionally, the human eye was "designed" by a mindless process and honed over millions of years by that process, one that quits whenever the eye was "good enough", while a camera is made to precision in a factory and designed by an intelligent being which can use metal, glass, and plastic rather than having to grow everything from the ground up and going for a pre-determined end goal of making it better.

As for seeing farther, the zoom lenses in/on a camera are like a telescope. This gives them an advantage when focusing on things at a distance. Human eyes have one lens with variable focal length, not a telescope.

First, neutrons hitting the nucleus of most atoms will either do very little or will actually use up energy. Only "fissile" materials will generate more energy, such as some forms of uranium and plutonium.

When an explosive chain reaction happens, two things cause it to end quickly:

1. The fissile atom's nucleus changes when it releases energy. The atom becomes a different element. The elements that result are non-fissile. As a result, the fissile material is used up, leaving no fuel for the chain reaction.
2. In order to have enough neutrons hit other atoms in the fissile core, that core has to be pretty dense. When the explosion happens, the fissile material spreads out in a cloud of superhot plasma. This plasma is not dense enough to maintain fission.

I think that maybe these explanations might be a bit hard to understand, and so I would like to make them simpler. Also, due to the close relationship between these four concepts, many people will tell you that some are the same as others when, in fact, they are not quite the same. It is not uncommon for this to be done in the classroom or in books on math and logic to simplify things, and it is quite possible that the distinction can be lost on, say, a teacher teaching the concepts. However, as these are stated as four distinct things I think that the nitpicky details are being asked for.

(1)= Equal Sign

This is equal to that. Example: 2+2=4

(2) ≡ Equivalence, Identity

If A ≡ B, then if A is true B is true and if A is false B is false. This is often described as "if and only if" and is sometimes written as iff. Example: You get $100 at the end of the semester ≡ Your GPA is over 3.5.

The next two can be a bit tricky as they are not always used exactly the same way in all math and logic. Additionally, both are forms of equivalence, and are thus often used interchangeably with equivalence and each other.

(3) ↔ Material BiConditional

This is used when two statements are connected together in equivalence, such that one is true if and only if the other is true at this time, but not necessarily at a different time or under different circumstances.

Example: Due to a snowstorm this morning (the material condition), Johnny cannot get to school from his house today unless his Dad drives him. Further, once there he will not be able to leave until the end of the school day.

Thus, "Johnny is at school" ↔ "Johnny was driven to school by his father this morning".
On any other day, this may or may not be true, and thus this is material rather than logical.
(4) ⇔ Logical BiConditional

This is when two statements are connected together in equivalence such that one is true if and only if the other is true, period, regardless of any material conditions.

Example: A is equal to 4 ⇔ A is equal to 2+2. If the first part is true, then the second part is, and if the second part is not, neither is the first. No material changes can make that not the case, so it is a logical bi-conditional and not merely a material bi-conditional.

I tried to make this as clear and precise as possible. I hope it helps.

We are working on developing such things, but so far they are still science fiction.

Echolocation can do interesting things, but it cannot really go through an underground tunnel system and give you a map. This is made up for movies and TV, at least at our current level. It would actually be a lot more like what you would get by shining around a big flashlight. It locates things in an area in the dark but doesn't generally go around corners or allow the mapping of anything but what is there in the room.

Sending seismic tremors through the ground so as to find all the empty areas below would be better, but still is quite a bit short of giving you a 3D map. It really isn't that easy.

And if you used seismic tremors, you might damage the catacombs.

Start by figuring out what you want long-term, and then look for that. Many people end up in divorce court because they went after the short-term, and then discovered that being fun to party with or really to run off and have fun regardless of the long-term consequences are not so great when you are sharing your finances and/or home.

Common in dogs and mamma cats with new kittens. So, maybe not common, but common enough.

Nope.

AC can induce muscle tetanus, but while it can cause you to lock a hand to something, DC is quite a bit more likely to do so. AC has a greater chance of causing a spasm that either removes the hand or allows the victim to pull free.

AC, however, is more likely to kill you, as it can trigger ventricular fibrillation. DC is more likely to stop your heart, which can actually be easier to recover from.

As for Edison, he electrocuted the elephant and invented the electric chair to illustrate the dangers of AC current. Not because he thought it would be all that dangerous at household voltages, but because he owned the patents on DC and wanted AC to look bad. Look into Edison a bit, you will see that he was something of a jerk.

However, for local grid purposes, AC is much better and won out in the end.

If the current is DC, the current causes all muscles to contract. This closes your hand and prevents you from letting go.

If the current is AC, the muscles spasm, and you probably will let go.

In power stations and such, high-voltage direct current is common, and a short can electrify almost any piece of metal. To protect themselves workers brush the back of their hands against metal objects before using them. This way, if the muscles contract, they will violently remove your hand from the object, not grab it.

We don't.

What we do know is this:

1. There are ways that are inherently unable to get you to the speed of light. For example, the acceleration of an object having mass will never get you there, because the closer you get the greater your mass becomes. To get to the speed of light you need infinite energy, so getting faster would require more than infinite energy.
2. FTL inherently allows you to set up situations in which you can go back in time and change the past. This is anathema to many people, including physicists.
3. There are things faster than light. Spacetime can expand at a rate faster than light, for example.

However, we do not know for certain that FTL isn't possible for, say, that object having mass mentioned before. What we do know is that it cannot *accelerate* to such a velocity and that it could violate causality if it found another way to get to that velocity.

That depends upon how you are reaching the Internet.

If you use cable or DSL internet, it travels through wires.

If you use 4G, 5G, or WiFi from somewhere outside the walls, it uses radio.