Made with some breadcrumbs, egg, and 20,000 lab-grown cow muscle cells, the world's first lab-grown burger made its debut last year. It was a proof of concept, evidence that you can make meat in lab. The technology is too difficult and expensive to show up grocery stores any time soon. In the future, however, proponents hope so-called cultured meat will get cheaper. If it does, making beef from stem cells could be an environmentally friendly alternative to, you know, killing animals for food. Raising cattle takes up a lot of arable land and water and creates greenhouse gas emissions. Engineers working on in vitro meat hope their creations will be less harmful on the environment. But will they ever get there?