This SciShow video is about to debate the most important Pi(e) known to humanity. And that's because pi(e) in all of its forms is important to humanity. So to show our appreciation for pi, we are launching a pi-themed calendar. This is not a drill! You can get it for a limited time at complexlycalendars.com.

Pi may be the most useful number ever. It helps us find the path of an artificial satellite, the size of an object in space, and the best way to achieve a light, fluffy crust. I may have gotten a little lost on that one. There's two kinds of pi(e). The ratio of a circle's circumference to its diameter and the delectable sugary treat. But to figure out which one is more essential to life, the universe, and everything, we'll need some science and an impartial moderator.

First up in the great debate, is pie the dessert outlined in scientific detail by our very own pie enthusiast and science communicator Hank Green. 

In honour of pi day, we thought that we would talk today about pie. No not pi, pie. Tender crust with fruit inside. The filled dessert that is superior to other desserts, that pie. Fron the crust, to the filling, to the presentation, there is a science to making the perfect pie.

Let's start with that crust. The best pie crusts tend to be light, crisp, and above all else, flaky. And the key to making a light, crispy, flaky pie crust? Vodka.

Normally, two of the main ingredients in pie crust are wheat flour and water. But wheat flour contains two proteins, gliadin and glutenin that can combine to form a delicate pie crust's worst enemy gluten. The proteins combine when they're exposed to water and the more you work the dough, the more gluten will develop. 

Generally, more gluten is a good thing. If you're baking bread that is. Gluten is sticky and elastic. It makes bread dough chewy. But gluten also makes pie crust tough. So what you want is a pie crust dough that sticks together enough to roll out properly but stays flaky. And replacing about half of the water with vodka turns out to be a great way to do that.

Vodka is 40% ethanol and those proteins that make up gluten won't dissolve in ethanol the way they do in water. But, since the ethanol still adds moisture, you can still work the dough. Most, though not all, the alcohol will cook off in the oven so you won't end up with a particularly boozy pie crust, just a delicious one.

Then there's the filling. Which you probably don't want getting all runny and soggy. Problem is, fruit has a lot of water in it and plant cells tend to break down when you cook them and that lets the water loose inside your pie.

One ingredient that can help keep the water from escaping is something that occurs naturally in the fruit itself. A carbohydrate called pectin which normally helps hold cell walls together. In pie filling, will form a jelly-like mesh that holds water in place. So more pectin means a thicker pie filling which in turn means a pie bottom that is less soggy.

For thicker pie filling you can choose fruits that have more pectin naturally like apples. You can even add an apple to a pie made with low-pectin fruits like strawberries for more thickening power. And a little acid will make pectin stronger and more stable so some bakers add lemon juice to pie filling.

However, heat destroys pectin. So even a pie with lots of pectin can turn to mush if you overcook it. Finally, you can improve both the look and flavour of your finished pie with what's known as the Maillard reaction AKA the most delicious chemical reaction of all time. 

It was named after an early 20th century French chemist who was trying to figure out how to make proteins. And it's actually more than just one chemical reaction, it's a whole category of them. The Maillard reaction is what happens when proteins react with certain sugars at around 140 degrees Celsius. The reaction can form all kinds of different products depending on the proteins and sugars involved. But generally, it's what makes bread develop a crust and cooked food turn brown.

It's also usually considered something that makes food extra delicious and there's an easy way to help the reaction along in your pie, or pretty much any pastry for that matter. All you gotta do is brush a little bit of egg white over your crust while it bakes. The protein in the egg white will react with the sugars in the crust setting up a Maillard reaction and giving your pie that deep golden brown colour.

So happy pi day everybody! And we hope these tips help you impress your friends with a pi pie. 

There you have it! Pie, the dessert involves the Maillard reaction which requires protein and sugar. Those are two of the most valuable building blocks for life. So pie with an 'e' is coming out of the gates strong. To give pi, the number, a fighting chance, let's discuss its merit on the most relevant day of the century, March 14th, 2015.

Lately, astronomers have found loads of exoplanets; or planets outside of our solar system. They can find them because when a planet moves in front of its host star a portion of that star's light is blocked out. Then, as the plant clears, the star's brightness returns to normal.

The graph of how we see that light twinkle from Earth is called a light curve and to figure out how to interpret this light curve they need to know how big the host star is. So how on Earth do astronomers figure out the area of a star? With the equation for the surface area of a sphere: four pi r squared (?), the 'r' being the star's radius. 

Once they know how big that star is, they can use that combined with how much its light fluctuated to figure out things like the exoplanet's size, and maybe even what's in the atmosphere. Since knowing an exoplanet's size can help scientists guess whether it's habitable or not, pi is kind of essential to our search for planets that might support alien life. 

So pi is obviously crucial to studying anything that's spherical, like stars, because spheres are just circles swept(?) around in three dimensions. And as it happens, the way we calculate the forces of physics has a lot to do with spheres too. 

Take the electrostatic force for example, which is the force between two electric charges. It's calculated using a handy equation you may have heard of called Coulomb's Law. So let's say you have two electrons just floating out in the middle of space. Each electron is exerting a force in all directions, so basically its force forms a sphere. And we call that an electric field. 

But you only see the effect of these fields when they interact. In this case, by repelling each other.  If you want to calculate how much electrostatic force is driving those electrons apart, you're gonna have to find out how much of each electron's invisible sphere is touching the other. And since we're dealing with spheres again, there is pi!

To figure out how much of their electric fields are touching, you need to divide the total force from both electrons by the same formula we used to find the surface area of a star: four pi r squared (?). 

Now, no discussion of the use of pi in science would be complete without talking about how it was used to describe the universe itself by one Albert-no-middle-name-Einstein. Einstein published his theory of general relativity a century ago in 1915. Which happens to be the last time that Pi Day was 3/14/15(?).

And you know what Einstein's birthday is? Just give me a guess. March 14. Dude was born on Pi Day. 

And Einstein's theory of general relativity calls on pi to describe how all forms of momentum and energy can curve space-time. Now we often talk around here and on SciShow Space about huge masses like stars and galaxies can curve space and time with their gravity. But Einsteins's theory actually says that just like a ball sitting on a bed sheet, any form of momentum and energy can also curve space-time around it. 

And the equation that Einstein used to describe that fact uses pi. This equation basically defines the physical universe so it's got a lot going on in it. But one of its main points is that there's a fixed ratio, a constant, that helps explain the relationship between gravity, momentum, and energy. 

And pi has to be part of that constant because Einstein was talking about physics in terms of Field Theory. Just like electrons, each tiny part of an object generates its own gravitational field in every direction and together they form a spherical field of force around that object. And where there's a sphere, there's pi.

For such an important number it seems sad that pi only gets one day a year for official celebrations and a Pi Day this special won't show up again until 2115. But at practically any moment, you can be sure that somewhere in the world there's a mathematician or scientist using pi for something important. 

3.14 has a lot of value when it comes to our understanding of the universe. So it may be a close call between the number and the dessert when it comes to which is more essential. But here's the tiebreaker, pi the number might not really be as special as we think. It may just be taking all the credit for the power of another number, known as Tau. Here's Hank with the final word.

Are you like me? Do you love pi(e)? I don't get it as often as I like anymore but scientists get to have pi day every day. Pi, as you know, is the ratio of a circle's circumference to its diameter. No matter how big or small a circle is or where in the universe the circle might be, this ratio is always the same. You might remember it from 9th-grade geometry as 3.14, but of course, pi actually goes on forever. Kind of like 9th-grade geometry. 

And like all rational numbers, the digits that make up pi never end and never repeat in patterns. The standing record for reciting pi is 67, 890 places. To which I say, challenge accepted! No. 

But if you think pi is just for high school freshmen and dateless loners with excellent memories, you've got another thing coming,  buddy. Because we couldn't do science, any of it, without pi. Name anything in the universe that's round, circular, spherical, 
globular, even roundish, and we use pi to measure, study, or predict the behaviour of that thing. 

Say you have an artificial satellite in a circular orbit above Earth, like the International Space Station, and you want to measure the path it travels? Easy-peasy, to get the circumference of a circle you just multiply its radius by 2 pi. 

Maybe you're observing the night sky and find a planet passing in front of a star. You want to know what area it covers? Pi times the square of its radius is all you need to know. Not only that, you can use those same two numbers, pi and the radius, to figure out the surface area of this new planet that you just discovered as well as its volume without having to fly all the way out there. 

And of course, we're not just talking about astronomy. You can find pi at work in the measurements of in nature of anything that curves. One of your DNA molecules for instance is 1.5 pi times shorter when it's bundled up inside your cells than it would be if it were stretched out. Electromagnetic waves can be measured in terms of pi. The 'p' word even shows up in Einstein's formula for how energy and mass curve space-time. 

Now you'll notice, that in these awesome applications, pi almost always appears in multiples of two. 2piR, 4pi, 8piG(?). Because of that, scientists argue that the real magic number in mathematics is not pi, but 2pi or about 6.28. Members of this camp point out that the defining feature of a circle is really its radius, not its diameter. And it makes sense when you think about it, every measure of a circle its circumference, area, volume or surface area is expressed as a function of its radius. 

So the mathematical constant that we should be using, is really just twice pi. Proponents call this number the ratio of a circle's circumference to its radius Tau. So instead of measuring the space 
station's orbit as 2piR, it would just be TauR. They even propose just as some people celebrate Pi Day on March 14th, we should observe Tau Day on June 28th. So I guess I'll see you then! 

So we should still celebrate pi, the numerical value, for all that it tells us about life, the universe, and everything. But since it really should share the spotlight with Tau, I'm calling this one a draw. 

We have created a pi calendar. It's an entire year devoted to pi without the 'e'. Yes, a real physical calendar that you can touch and hang on your wall and look at every day. The photos are high-quality and accompanied by awesome science-related facts and thoughts from your friends at SciShow. Each month represents one digit of pi. So we don't have a chance to cover the endless digits that follow 3.14, but there may be more than you can rattle off the top of your head.

You can test your pi knowledge and get more sweet stuff from the people who made this video by ordering a pi calendar before they run out. Find them at complexlycalendars.com or click the link in the description. 

Thanks for watching this video and thanks for supporting SciShow.