How Does Cryptocurrency Work?

iStock/Marc Bruxelle
iStock/Marc Bruxelle

In September 2018, the Official Scrabble Players Dictionary added hundreds of new words—one of which was “bitcoin.” Sure, you can get a double letter score for it, but how does cryptocurrency work? And what about the other equally mysterious cryptocurrencies, which have been called everything from the future of money to a pyramid scheme? What is all this fuss about?

THE ISLAND OF YAP

One of the most popular metaphors for how cryptocurrencies work involves the Pacific island of Yap. According to NPR, the residents long ago learned of a distant island with large limestone deposits. The islanders brought back large discs of rock which they eventually turned into a form of currency—not for every day purchases, but for major outlays.

That may sound simple, but it’s not quite that easy. These rocks could weigh as much as a car, so when they changed hands they were rarely actually moved. The society just recognized that “this rock now belongs to person B.”

There’s even a story in which a giant rock brought back to Yap was lost when the boat it was on sank. The islanders dealt with this conundrum by having an oral transaction history, so everyone knew that the rock was not lost. It did have a new owner. In fact, you could argue that they had a kind of public ledger, because everyone knew how many rocks everyone had. Disagreements rarely arose because of the distributed nature of that information. This is akin to one of the most important elements of cryptocurrency: the blockchain.

At its core, the blockchain is just a ledger distributed across a network of computers, which are called nodes. Every time any transaction occurs, the network checks to make sure that it’s a valid transaction and the blockchain gets updated with a new "block," which serves as a permanent record of the transaction. This gets sent to all of the relevant computers—like the Yap islanders telling everyone about the change of ownership of a rock. The block is added to the blockchain alongside a code called a hash.

SECURITY

The hash is essentially a digital fingerprint generated by complex mathematics. This is part of the system’s security, as it takes time and energy to generate these hashes. As Reuters explains, any change to the input creates a new hash. By way of example, they explained that the extremely long novel War and Peace might have a hash like:

a948904f2f0f479b8f8197694b30184b0d2ed1c1cd2a1ec0fb85d299a192a447

While just deleting one comma from the text changes it to:

40115cc2aecc43ea86a7e54be6f7257abff7b43959cd728f06c0c7423039166r

By itself, this is not necessarily secure. But every new block also contains the previous hash as a kind of error check. If someone goes in to retroactively change a transaction (say, by deleting that comma in War and Peace), that block's hash gets updated to a new code. But the next block will have a different hash code on record from the previous block (it will be looking for the old hash, the one beginning with a948—but seeing the new hash, the one starting with 4011), so in theory the nefarious action will be discovered. There are potential ways to cheat this system. A computer faster than the other nodes combined may be able to rewrite blocks fast enough to work, but MIT Technology Review cautioned that even then “success isn’t guaranteed.”

CRYPTOCURRENCY

But cryptocurrencies and blockchains are not synonymous. Similarly to how the internet and world wide web are not synonymous, blockchain is a technology chiefly used for cryptocurrencies, though this may not always be the case. It’s increasingly being examined for use in other fields—and some even argue cryptocurrency is one of the least promising fields.

The crypto in cryptocurrency is a reference to the cryptography used to ensure that the transactions are secure. Up until this stage, it’s not particularly different from any other digital currency—when you send U.S. dollars over the internet, physical dollars are not changing hands. That’s true for any digital currency, of which cryptocurrencies are one.

But there are key differences—including that, traditionally, money is issued by the government or some powerful institution. Cryptocurrencies are created by algorithms. Another important distinction is how ownership is traced. Because there’s nothing physical to a cryptocurrency, the blockchain ledger is used to determine ownership.

There are also more nuanced differences. Because the blockchain ledger has to be transparent, all transactions are public, leading to many suggestions for how to best manage privacy expectations. As another distinction, many cryptocurrencies are limited to a set number—only 21 million bitcoins will ever exist, and it remains unclear what will happen when the final bitcoin is "mined." Contrast that with traditional currency, which can be produced in limitless quantities.

Not everyone is convinced that cryptocurrencies are the future. Speaking to Vox, Nicholas Weaver of the International Computer Science Institute at UC Berkeley explained that miners—the people who create the blocks and get paid for their efforts—are disproportionately powerful and serve as the central agency that cryptocurrencies are trying to avoid. Also, he argues that outside of nefarious purchases (like assassins or illegal drugs), there isn’t a point to cryptocurrencies. Due to price volatility, they don’t fundamentally work as a currency. There’s a famous story about a programmer buying two pizzas for 10,000 bitcoin—a sum that would be worth more than $80 million just a few years later. This volatility, according to Weaver, means that most companies claiming they accept bitcoin aren’t actually accepting bitcoin per se, they just instantly sell it for conventional currency.

Cryptocurrency fans immediately pounced on these comments, arguing that it’s an oversimplification and could be used to argue against other forms of currency as well. No matter what, the debates will continue.

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How Is a Sunscreen's SPF Calculated?

Rawpixel/iStock via Getty Images
Rawpixel/iStock via Getty Images

I’m a pale person. A very pale person. Which means that during these hot summer months, I carry sunscreen with me at all times, and apply it liberally. But I’ve never really understood what those SPF numbers meant, so I asked some sun care to break it down for me—and to tell me how to best apply the stuff so that I can make it through the summer without looking like a lobster.

Soaking up the sun ... safely

SPF stands for Sun Protection Factor, and it indicates a sunscreen’s ability to block UVB rays. The concept was pioneered at the Coppertone Solar Research Center in 1972; in 1978, the FDA published an SPF method based on Coppertone’s system, according to Dr. David Leffell, chief of Dermatologic Surgery and Cutaneous Oncology at Yale.

The numbers themselves stand for the approximate measure of time a person who has applied the sunscreen can stay out in the sun without getting burned. Say you get burned after 20 minutes in the sun without sunscreen; if properly applied (and reapplied), SPF 30 will allow you to stay in the sun 30 times longer without burning than if you were wearing no protection at all. So, theoretically, you should have approximately 600 minutes, or 10 hours, in the sun. But it’s not an exact science because the amount of UV light that reaches us depends on a number of factors, including cloud cover, the time of day, and the reflection of UV rays off the ground, so it’s generally recommended that you reapply sunscreen every two hours (or even sooner).

What gives a sunscreen a higher SPF comes down to the product’s formulation. “It’s possible that an SPF 50 might contain slightly more of one or more sunscreen active ingredients to achieve that higher SPF,” Dr. Patricia Agin, president of Agin Suncare Consulting, says. “But it’s also possible that the SPF 50 might contain an additional active ingredient to help boost the SPF performance to SPF 50.”

No matter what SPF your sunscreen is, you’ll still get a burn if it’s not properly applied. So let’s go over how to do that.

How to apply sunscreen

First, make sure you have a water-resistant, broad spectrum sunscreen—which means that it protects against both UVB and UVA radiation—with an SPF of at least 30. “Typically, you don’t have to buy sunscreen that has an SPF higher than that unless you have very sun sensitive skin,” Leffell says. “That’s a very small percentage of the population.” (Redheads, people with light eyes, and those who turn pink after just a few minutes in the sun—you’ll want to load up on SPF above 30.)

Twenty minutes before you go out to the beach or the pool, begin to apply your sunscreen in an even coat. “Don’t apply it like icing on a cake,” Leffell says. “I see these patients and they’ve got the tops of their ears covered with thick, unevenly applied sunscreen, and that’s not a good sign.” Sunscreen sprays will easily give you that even coat you need.

Whether you’re using lotion or a spray, when it comes time to apply, Leffell recommends starting with your scalp and face, even if you plan on wearing a hat. “Make sure you’ve covered the ears and nose and under the eyes,” Leffell says. “Then, I would move down to the shoulders, and make sure that someone can apply the sunscreen on your back beyond the reach of your hands.”

Other areas that are important that you may forget to cover, but shouldn’t, are the tops of your feet, the backs of your hands, and your chest. “We see it all the time now—the v of the chest in women has become a socially and aesthetically huge issue when they are 50 and beyond. Because even though they can treat their faces with all sorts of cosmetics and procedures, the chest is much harder, and they are stuck with the face of a 40-year-old and the chest of a 60-year-old. You want to avoid that using sunscreen.”

Another important thing to keep in mind: Water-resistant doesn’t mean waterproof. “I always tell patients to reapply every couple of hours while you’re active outdoors," Leffell says, "and always reapply when you come out of the water or if you’ve been sweating a lot, regardless of whether the label says water resistant."

Determining whether or not you’ve succeeded in properly applying your sunscreen is easy: “You know you’re applying your sunscreen properly if, after the first time you’ve used it, you haven’t gotten a burn,” Leffell says.

Agin has a caveat, though: "It’s not a good idea to think of sunscreens only as a way to extend your time in the sun," she says. "One must also understand that even before becoming sunburned, your skin is receiving UV exposure that causes other damage to the skin. At the end of the 600 minutes, you will have accrued enough UV to cause a sunburn—one Minimal Erythema Dose or MED—but there is pre-MED damage done to skin cells’ DNA and to the skin’s supporting structure of collagen and elastin that is not visible and happens even before you sunburn. These types of damage can occur without sunburning. So you can’t measure all the damage done to your skin by only being concerned about sunburn."

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An earlier version of this post ran in 2014.

What's the Difference Between Ice Cream and Gelato?

iStock/Getty Images/zoff-photo
iStock/Getty Images/zoff-photo

'Tis the season for beach reads, tan lines, and ice-cold desserts. You know it's summer when going to the local ice cream or gelato shop becomes part of your daily routine. But, what exactly is the difference between these two frozen treats?

One of the key differences between the two is butterfat. While ice cream's main ingredients include milk, cream, sugar, and egg yolks, the secret to making gelato is to use much less cream and sometimes little to no egg yolk. This leads to a much smaller percentage of butterfat in gelato. The FDA rules say that ice cream cannot contain less than 10 percent milkfat (though it can go as high as 25 percent) while gelato, much like soft serve, stays in the 4- to 9-percent range.

The churning method for both also differs, which affects the treat's density. Ice cream is churned at a much faster pace, leading to more air being whipped into the mixture. Ice cream's higher butterfat content comes into play here—due to all of that milkfat, the mix absorbs the air more readily. Gelato, on the other hand, is churned at a slower pace and absorbs far less air, creating a much denser dessert.

You also might have noticed that the serving style for the two treats aren't the same, either. In order to get those perfectly stacked ice cream scoops on a cone, buckets of ice cream must be stored at around 0°F to maintain its consistency, while the softer gelato is stored at a warmer 10°F to 22°F. Ice cream is then scooped into fairly uniform balls with the round ice cream scooper, whereas a spade or paddle is best for molding gelato into mound in a cup or a cone.

You can't really go wrong with either gelato or ice cream on a sweltering summer day, but there is one more difference to keep in mind while you debate which to get: taste. If you want a bolder flavor, you'll want to go with gelato. Because of the density of the cream and because there's less butterfat to coat your taste buds, gelato can seem to have more intensity to its flavors.

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