Thanks to Emerson for supporting this episode of SciShow.

To learn more, visit Emerson.com/WeLoveSTEM. [♪ INTRO]. After many years of ignoring their stories, the world has finally started to talk about women in science — which is amazing!

Everyone should know about all the women in the past and present who have kicked butt doing amazing research. But we really can't talk about women in STEM enough — and we definitely don't talk as often as we should about women who have done cool work in science's more applied sibling, engineering. It's a pretty wide-ranging field, and like with more basic science, it's had women making big advances in it for a long time.

And the coolest part? Lots of the stuff they work on and have worked on affects your day-to-day life. We're talking train travel, your Bluetooth headphones, your hybrid cars.

So buckle up for five fantastic women in engineering. Hedy Lamarr was a lot more brilliant than people often gave her credit for. She's best known for being a famous 1940s actress, but she also helped come up with the idea that today underlies secure WiFi and Bluetooth technology.

This part of Lamarr's story began in the 1930s, when she was unhappily married to an Austrian arms dealer. She often hosted her husband's dinner parties or attended meetings with him. And while she wasn't a fan of playing hostess to literal Nazis at these events, she did end up learning a lot about weapons control systems from just being there.

With World War II on the horizon, that was a pretty big deal. See, at this time, radio waves were starting to play an important role in these control systems. And at some point, Lamarr quietly came up with an idea that would make these signals much harder to jam or intercept.

It was an early form of what we today call frequency hopping spread spectrum. Rather than sending all of your information over one frequency, you spread it out by sending little packets of info over different frequencies. The information you're sending hops from frequency to frequency — and in order to get the whole message, you have to know when and on which frequencies bits of information will arrive.

That makes your data much more secure. It also means that it's harder to jam your signal, because the jammer has to block lots of radio frequencies instead of just one. Now, fast-forward to the 1940s.

By this point, Lamarr had left her husband, gone to Hollywood, and become friends with a composer named George Antheil. And finally, she started talking to him about her radio ideas, and how they could be used to help the U. S. military.

The two agreed that hopping frequencies could solve the problem of people intercepting or jamming weapons frequencies… but of course, you needed a way to know which frequency the signal would be on at what time. Together, Lamarr and Antheil came up with the idea of using player piano rolls to synchronize the sender and the receiver. If you're not familiar, these are big paper rolls that you could plug in to a piano that would then play a song.

They each had little cut-outs to tell the piano which notes to play when. The idea was that each of the 88 keys on the piano could be used to represent a different frequency. And in 1942, this team got a patent for it.

Unfortunately, the U. S. military didn't take it too seriously, and Lamarr didn't receive wide recognition for her work until much later, when plays and movies were being written about it. Today, though, this idea of sending packets of information over a broad range of frequencies is what makes our WiFi secure and helps sync our Bluetooth devices.

So thanks, Hedy. Olive Wetzel Dennis graduated from Cornell University in 1920 with a degree in civil engineering, then promptly went and got herself a railroad job. That all might sound relatively normal now, but it wasn't really done at that time.

Dennis was only the second woman to graduate from Cornell's civil engineering program, and women didn't really work for railroads. But, hey, that didn't stop her. She got a job working as a draftsman for the Baltimore & Ohio Railroad and helped build bridges in rural Ohio.

Then, not long after, she became a service engineer with the B&O. That meant she rode the line for tens of thousands of kilometers a year, paying attention to details, testing things out, and making all kinds of improvements. Her work led to stain-resistant upholstery, ceiling lights that could be easily dimmed, air conditioning, better meals, window vents that brought in fresh air and kept out dust, and reclining chairs.

Of course, when Dennis got kind of famous for her work, newspapers gave her nicknames like “the Lady Engineer” and the “world's greatest housekeeper.” Yikes. But! She was awesome at her job.

And today, everybody appreciates that train cars are air-conditioned. Dennis was super detail oriented, an advocate for women pursuing their dreams, and proof that engineers don't have to invent a bunch of stuff to have a big impact. Because really, she didn't just change trains.

Small improvement by small improvement, she also changed the way we think about transportation and set a new standard for comfortable travel. Annie Easley isn't a household name, and she doesn't have a huge movie about her. But she was another one of NASA's hidden figures.

She always knew that she was good at math, but she thought she wanted to go into pharmacy — that is, until one day in 1955, when she read about the human computers at NASA's predecessor, NACA. These were people who did the calculations necessary for spaceflight. And right away, she knew that's what she wanted to do.

Easley worked as a computer until machines replaced humans… and then she just became awesome at programming computers instead. As a programmer, she helped analyze alternative energy, including wind and solar power, and she also worked to understand the storage life of batteries. The code she wrote for analyzing energy-conversion systems actually contributed to the development of the kinds of batteries that we use in hybrid cars today.

Easley also helped develop software for Centaur, a high-energy rocket that would become known as “America's Workhorse in Space.” The Centaur was designed to use liquid hydrogen as a fuel, which was kind of a big deal at the time. Hydrogen is really light - it's the lightest element - and liquid hydrogen also really burns. This makes it a super efficient rocket fuel, providing a lot of power for not that much weight.

But liquid hydrogen — and the Centaur — got off to a rocky start. When the rocket was first tested, it was buggy and prone to problems… mostly because liquid hydrogen is so hard to work with. It needs to be stored at less than negative 250 degrees Celsius, expands quickly when heated, and is so cold that it can make metal brittle.

So the engineers at Lewis Research Center, including Annie Easley, became responsible for “taming” liquid hydrogen by testing it and analyzing data about it. Eventually, Centaur rockets would be used in over 100 uncrewed launches, boosting satellites into orbit and probes into space. The Centaur would be responsible for sending the Cassini mission to Saturn in 1997, as well as probes and fly-bys to Mercury, Venus, Mars, Jupiter, Uranus, and Neptune.

So like, no big deal or anything. Lynn Conway literally wrote the textbook on microchip design. She helped kickstart the development of the kinds of computers and cell phones we have today — and, on a different note, her work as an activist for transgender rights has also been influential.

Working in the Xerox Palo Alto Research Center in the 1970s, Conway invented scalable design rules for VLSI chip design. That stands for Very-Large-Scale-Integration, and it's where millions of transistors get combined into a single chip to increase its processing power. She also pioneered teaching these methods at MIT.

Conway's way of thinking was that the chip itself wasn't the invention. Instead, it was the idea of using the best computing technology available to figure out a newer and better way to make the next chip. She deeply understood that the computing industry would constantly reinvent itself.

Based on her teaching at MIT, and in collaboration with Carver Mead of Caltech, Conway wrote. Introduction to VLSI Systems, which pretty much set in motion chip design as we know it. Also, it led to Moore's law, which suggests that the computing power of chips doubles every two years.

Yes, that Moore's law. All of this is amazing, but another remarkable part of Conway's story is that, by this point, she had already had a whole other career in the 60s. Back in those days, she invented dynamic instruction scheduling, which is basically where hardware can rearrange a set of instructions to execute them in the most efficient way possible.

It's another fundamental component of computer architecture and modern computing, but up until recently, nobody really knew that Lynn Conway was also responsible for that. That's because she had done the work before coming out as transgender and transitioning. And with the way people viewed gender in the 60s and 70s, it didn't feel safe for her to claim that work.

But despite that, she still managed to become one of the leading thinkers in computer engineering. Finally, Treena Livingston Arinzeh studied mechanical engineering as an undergrad, and it was only later that she became interested in applying engineering principles to medicine. But once she did?

She became an extremely influential researcher in the field of stem cells. These are sort of blank-slate cells that can differentiate into specialized types of cells. And Arinzeh's primary interest is in using them to repair injuries.

You can't just throw a bunch of stem cells in a wound and hope they'll fix things, though. So an important part of Arinzeh's research is the development of tiny, synthetic biostructures that can serve as a kind of scaffolding for stem cells. She's made some great advancements in this field, but her most well-known finding so far was actually published back in 2003.

That year, she was able to show that a large bone defect in a dog could be repaired by transplanting stem cells from another dog. And, maybe most importantly, immunosuppressant drugs weren't needed to keep the body of the transplant recipient from rejecting those cells. This finding laid the groundwork for a big idea: that adult stem cells from one person can be implanted into another person without being rejected or causing an adverse immune reaction.

This is huge. Without the help of immunosuppressant drugs, most transplants from donors are rejected by the body because the immune system recognizes them as foreign and tries to fight them off. But Arinzeh's work suggests that isn't true for so-called mesenchymal stem cells.

These are stem cells that can differentiate into things like bone and cartilage cells, and Arinzeh's work supports the fact that they might be immune-privileged. In other words, molecules on the surface of the cells tell the immune system that they shouldn't be destroyed, which allows them to go about their business of differentiating and repairing without interruption. Since her landmark study, Arinzeh has also studied therapies for treating cartilage and neurons, both of which are notoriously tricky to repair.

In addition to her research, Arinzeh also runs a summer program for high school students. Growing up, she didn't have a lot of understanding of what an engineer does… but this program can help make sure that these kids will. And that's why it's so important to talk about women in engineering, too.

Because, of course, as Olive Wetzel Dennis once said, “There is no reason that a woman can't be an engineer simply because no other woman has ever been one.” And of course now, there have been female engineers, and they've changed our lives — so we'll keep celebrating their stories and the amazing research they've done. Thanks for watching this episode of SciShow, and special thanks to Emerson for helping us make it! If you want to learn more about who Emerson is and what they're about, you can go to.

Emerson.com/WeLoveSTEM. [♪ OUTRO].