How is it possible for ISP's to know we are doing online? Isn't HTTPS supposed encrypt content so it can't be read?

The ISP (Internet Service Provider) is your mailman. They need to get packages to where they need to go. HereBeAnswers, for example, is sending you a package containing this answer. You pay the mailman monthly for a rate at which they send packages from you and to you.

HTTPS encrypts the package's contents, however the ISP's responsibility is still to move the package from A to B, and therefore needs to know what these A and B are. Therefore the postage address cannot be encrypted, and your ISP can track who you are exchanging packages with, be it HBA or YouTube or Netflix.

So your ISP can't actually see what you are viewing on HBA, YouTube, or Netflix, but they can see which sites you are accessing.

Why is CO2 added to carbonated water/soda and not other gasses? Why not add just air?

Originally beverages were carbonated via fermentation, which produces CO2 as the yeast. Some beverages still are done this way, such as beer. CO2 is still used because it's cheap and adds the acidic flavour. Some of the CO2 in the drink forms carbonic acid.

Air couldn't be used because it contains oxygen, which will allow for the beverage to spoil. Other gases can be used though. Guinness beer for example uses a mix of CO2 and nitrogen, giving it a more foamy head.

In general, for a gas to be used for "carbonation", it would need to:

* not cause the food to spoil (which is pretty much just oxygen)

* not cause some sort of undesirable chemical reaction with the beverage. CO2 will make some carbonic acid which is fine, but others may make more of worse chemicals.

* not have any negative odour or taste. You wouldn't want sulfur based gases that smell like rotten eggs.

* they would obviously need to readily dissolve in water. Helium for example would probably work fine, if you could actually get it to dissolve as well as CO2.

* not be flammable would be nice too, as even if methane (aka natural gas) or hydrogen could work, they would also be a little dangerous. 

* Also in the extreme, you wouldn't want it being poisonous. We add a little chlorine to water to kill bacteria, but you wouldn't want a rupture of chlorine coming out of a beverage or it will kill you. Lots of other toxic gases you wouldn't want in there.

* Again in the extreme end, you wouldn't want the gas to be a environmental issue. Something like SF6 may very well work, but you wouldn't exactly want a lot of that getting into the atmosphere.

A lot of gases wouldn't work for one of these reasons or another. I'm sure there's some other gas out there other than CO2 and to a lesser extent N2, they however most likely wouldn't be as cheap and easy.

What is the difference between noise isolating and noise cancelling headphones?

Noise Isolating

Consider the earphones that have earbuds in them. They block outside noise by providing a noise reducing barrier.

Noise Cancelling

Headphones that essentially listen to ambient noise and produce an opposite sound wave to blank out the unwanted sound. Fill your bathtub with water. Drop two rocks into the tub one at each end.  When the waves collide you will see a spot where the water seems calm because the waves are cancelling each other out. Noise cancelling headphones produce this negative wave by listening in to the outside noise and producing the opposite wave to cancel out the wave just like in the water.

Why are canned foods high in sodium? Doesn't canning eliminate the need for preservatives?

Not entirely.

First, depending on the food we're talking about, salt might be an inherent part of the process, either of canning in particular or just the food in general. Pickles? Olives? Gotta have salt. Salt is also a critical ingredient in any number of fermented foods, many of which are canned.

Second, salt is a flavor enhancer. Processed food manufacturers have tended to add loads of salt to a wide variety of foods for the better part of a century as a way of making their products tastier. Canned foods are hardly unique here.

Third, while canned vegetables are certainly saltier than their raw counterparts, they're not necessarily as salty as you might think. One 30g slice of white bread has a little less than three times as much sodium as 28g of canned green beans.

Fourth, while canning certainly tends to kill biological organisms, it's not magic. Some organisms are merely weakened. Some may even survive, though in small enough numbers that they can't cause a problem if the food is eaten within a year or two. A little salt goes a long way towards ensuring that fewer bacteria survive, and those that do stay dormant.

But lastly, bacteria aren't the only things that contribute to food spoilage. There are other chemical processes that have nothing to do with bacteria that can make food go bad, or at least lose quality over time. Discoloration comes immediately to mind, but that's not the only thing. Flavors can change. Textures can break down. Foods can take on flavors from their containers. Salt creates an environment inhospitable to bacteria, to be sure, but it also tends to interfere with some of these other processes, making it useful as a preservative even in a largely sterile environment.

How do we know what materials the interior of the Earth is made of if the farthest we have dug is 8 miles?

One of the main ways we have learned about the earth's interior is by studying earthquakes.

Scientists have learned a lot about how vibrations (which is what earthquakes are) travel through different types of materials (solids, liquids, semi-solids.) 

Imagine you take a big rock and put your hands on the side of it, while somebody else taps it with a hammer. You would sense different things if the person tapped right next to your hands, or if they tapped further away, or if they tapped on the far side of the rock.  If your hands were really sensitive, and you kept a detail of what you felt, you would learn a lot about that. Then imagine doing the same thing with different materials, maybe a big jello mold, or an inflated basketball, or a bucket of water. You would pretty soon know what kind of vibrations would feel like from different kinds of taps in different places on different materials. 

Scientists have sensors all around the world that measure earthquakes and other vibrations in the earth very precisely. Let's say a big earthquake happens in Japan, it will be detected in Japan and the nearby region, but also in America, and Australia and Europe. By comparing the types of vibrations detected in those different parts of the world, and looking at how long they took to travel, scientists can infer quite a lot about the types of material that the vibrations were traveling through. 

Then they take information from other scientists who have studied the kinds of stuff the earth is made of, and how those materials behave under heat and pressure. When the different groups of scientists put their data together they are able to form a pretty clear understanding of the composition of the interior of the planet without having to observe it directly.

How do baggage scanners at the airport work? What do the different colors on the x-ray mean?

The x-ray devices in luggage scanners are a bit more complicated than the x-ray medical imaging devices. In particular, they're set up to identify and distinguish between different kinds of objects, whereas medical x-rays are pretty much only interested in one: bones.

The trick is that not all x-rays are created equal. The x-ray source will send out x-rays in a range of energy levels. Organic objects block some low-energy x-rays, but not higher-energy x-rays. Plastics block low-energy x-rays better than organic objects, but not as effectively as metal objects, which pretty much block everything.

The device is set up so that the x-rays pass through your luggage and then hit the first detector, which sends an image to the computer. But the x-rays then pass through a filter that blocks out all low-energy x-rays before hitting a second detector. That sends another image to the computer, this time only showing those objects that block high-energy x-rays. By combining these two images, the software can distinguish between organics, inorganics (e.g., plastics), and metals. It then assigns different colors to each.

Most manufacturers use black for metal and orange for organics, but it could vary from machine to machine.

What are noir and neo-noir genres of movies?

Film noir is a genre of movies from the 1940's and 1950's. These movies were pessimistic, gritty, and dark (noir is French for dark). The characters, even the protagonists, were often corrupt in some form, such as being alcoholics, lonely, or depressed. Common characters were corrupt policemen and corrupt politicians. The plot was often crime based, such as police or a private investigator trying to solve a crime.

The protagonist would often fail to accomplish his goals during the movies, sometimes thwarted by a femme fatale, or by a friend he trusted. The cinematography would be dark and menacing, for example, a dark and smoky alley in a big but empty city.  Movies like Double Indemnity and the Malatese Falcon are examples of film noir.

Neo-noir is a modern recreation of those movies. It follows the same theme is a noir film, but was made after the 1950's.  Movies like Chinatown and LA Confidential are set in the time period of noir films (the 30's, 40's, and 50s), but were made outside of that time period. Blade Runner has the theme of a noir film, but set in the future. Another example is Who Framed Roger Rabbit, which is a noir film set in the 50's, but has cartoon characters.

In short, if a movie has dark cinematography, corrupt protagonists, an unsolvable mystery or conflict, and if the villains win or at least force the "good guys" to do bad things, then it is noir.


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