If the Universe is expanding, we can understand why distant galaxies recede from us as they do. But then why aren’t stars, planets and even atoms expanding, too? (C. FAUCHER-GIGUÈRE, A. LIDZ, AND L. HERNQUIST, SCIENCE 319, 5859 (47))

This Is Why We Aren’t Expanding, Even If The Universe Is

The Universe is expanding, but we, our planet, solar system and galaxy all aren’t. Here’s why.

Take a look out at almost any galaxy in the Universe, and you’ll find it’s moving away from us. The farther away it is, the faster it appears to recede. As light travels through the Universe, it gets shifted to longer and redder wavelengths, as though the fabric of space itself is being stretched. At the largest distances, galaxies are being pushed away so rapidly by this expanding Universe that no signals we can possibly send will ever reach them, even at the speed of light.

But even though the fabric of space is expanding throughout the Universe — everywhere and in all directions — we aren’t. Our atoms remain the same size. So do the planets, moons, and stars, as well as the distances separating them. Even the galaxies in our Local Group aren’t expanding away from one another; they’re gravitating towards one another instead. Here’s the key to understanding what is (and isn’t) expanding in our expanding Universe.

The original conception of space, thanks to Newton, as fixed, absolute and unchanging. It was a stage where masses could exist and attract. (AMBER STUVER, FROM HER BLOG, LIVING LIGO)