The discovery that the universe is expanding is usually credited to the American astronomer Edwin Hubble , based on his 1929 observations of distant galaxies.

Quick Scoop

  • In 1929, Hubble showed that distant galaxies are generally moving away from us, and that their speed increases with distance.
  • This relationship between a galaxy’s distance and how fast it recedes is now known as Hubble’s law (often called the Hubble–LemaĂŽtre law).
  • Because of this work, Hubble is widely described as the scientist who “discovered the universe is expanding.”

But It’s A Shared Story

  • Years earlier, Vesto Slipher had already measured large redshifts (recession speeds) for “spiral nebulae,” providing crucial velocity data long before Hubble’s famous paper.
  • In 1927, Belgian physicist Georges LemaĂŽtre used Einstein’s general relativity plus early galaxy data to argue that the universe itself should be expanding, but his work in a little‑known journal was largely overlooked at the time.
  • Other theorists, like Alexander Friedmann in 1922, had already shown mathematically that Einstein’s equations naturally allow an expanding universe.

Simple Takeaway

  • If the question is “who discovered the universe is expanding?” the standard short answer is: Edwin Hubble.
  • If the question is “who really contributed to that discovery?” then Hubble built on key ideas and data from Slipher, LemaĂŽtre, Friedmann, and others.

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