Image credit: Hyper-Mathematics – Uzayzaman / Spacetime.

Why the Universe needs Dark Matter (and not MOND) in one graph

Posted by Ethan Siegel on January 18, 2013

“The cosmos is all that is or ever was or ever will be. Our feeblest contemplations of the Cosmos stir us—there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, or falling from a height. We know we are approaching the greatest of mysteries.” -Carl Sagan

If you looked out at the planets in the Solar System orbiting our Sun, you’d expect that if you know where they are right now and how quickly they’re moving, you can figure out exactly where they’re going to be at any time-and-date arbitrarily far into the future. That’s the great power that comes with understanding the laws of nature that underlie any physical system: in this case, the laws of gravity that governs the motion of planets in our Solar System.

And if the planet you were observing wasn’t where it appeared to be, you’d assume that one of two things were amiss.

Either there’s extra mass somewhere in the Solar System that’s throwing off the motion of the planet you’re looking at, due to the effects of its gravity, or

Your understanding of the laws of gravity are incomplete, and need to be upgraded or modified in some way.

Believe it or not, this has actually happened twice before in our own discovery of the Solar System.

Read more: Why the Universe needs Dark Matter (and not MOND) in one graph – Starts With A Bang.

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