Because E=mc2

Featured Blogger / by Ethan Siegel /

On the beauty and significance of the world’s most oft-cited but less oft-understood equation.

Seed’s Elizabeth Cline reviews Brian Cox and Jeff Forshaw’s new book, Why Does E=mc2? Instead of a straightforward review, Cline keeps a comprehensive, chapter-by-chapter log of the book through the eyes of a non-physicist, putting to test the authors’ intention of creating a truly accessible account of the world’s most famous equation.

Whenever I bring up the subject of Einstein to my friends who aren’t physicists, I typically only get one of two responses. Either it’s something like, “Oh, the science guy with the weird hair?”

Or they say, “Eee equals emm see squared!”

Yes, Einstein was the science guy with the weird hair, and he did discover the equation E=mc2. But what does it actually mean, and what makes it so important that even people who don’t know the first thing about matter, energy, or even algebra can recite it?

When Einstein discovered that equation, that energy was equal to mass times the speed of light squared, there were a lot of different possible physical meanings that it could have. Which one was right? Did it mean:

  • That one could simply convert mass into energy, and energy back into mass?
  • That energy—pure, massless energy—would be affected by gravity and would cause gravity just as mass does?
  • That, because radioactive materials emitted energy, their mass was being destroyed?
  • That, because the Sun was emitting energy, its mass was being converted into energy?

Remarkably, E=mc2 means all of these things. What’s more, E=mc2 tells us how much mass it takes to make a certain amount of energy. The speed of light is a huge, huge quantity. Square it, and it’s even bigger. What this tells us is that a small, insignificant amount of mass can generate an amount of energy so fantastic it’s barely fathomable.

The most powerful nuclear weapon ever detonated, the Tsar Bomba, with a yield of 60 megatons, was the equivalent of only 47 grams (less than 2 ounces) of matter being converted into energy.

The Sun—our seemingly endless source of energy for the entire 4.5 billion years of the solar system’s life—has burned up less than 0.03 percent of its mass to burn as brightly as it does for all of the eons that it’s burned.

Inside of every atom—every proton, every neutron, every electron in the universe—lies the secret of this energy. The idea that we could turn mass into energy brought us an understanding of not only radioactivity, and not just the source of power within Sun, but everything from the bombs of nuclear fission to the hope of clean, pollution-free power from nuclear fusion.

But the reverse idea—the idea that we could turn energy itself into mass—has given us even more bizarre things, like antimatter. Because E=mc2, if you take enough energy, you can use it to create mass. Some of that mass comes out as normal matter, like all of the things we find on Earth. But fully half of that mass comes out wrong, and comes out as antimatter, the most volatile substance ever manufactured. All antimatter has to do to normal matter is touch it, and it immediately detonates, turning both the antimatter and the normal matter into pure energy, making use of E=mc2 once again.

This reverse idea—that we can turn energy into both matter and antimatter—led to the birth of particle accelerators, which now use tremendous amounts of energy to try and create new, more exotic types of matter and antimatter. This is the very frontier of what we know and what we understand. As the LHC nears the brink of its full operation, it’s worth taking a look back. When you do, you’ll realize that the only reason we have any of this is because of the realization that energy and mass can be transformed into one another. How is this possible?

Because E=mc2.

Originally published August 25, 2009

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