The ‘raisin bread’ model of the expanding Universe, where relative distances increase as the space (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what’s been known all the way back since the 1920s. (Credit: NASA/WMAP Science Team)

What is “early dark energy” and can it save the expanding Universe?

There are two fundamentally different ways of measuring the Universe’s expansion, and they disagree. “Early dark energy” might save us.

Whenever you have a puzzle, you have every right to expect that any and all correct methods should lead to you to same solution. This applies not only to the puzzles we create for our fellow humans here on Earth, but to even the deepest puzzles that nature itself has to offer. One of the greatest challenges we can dare to take on is to uncover how the Universe has expanded throughout its history: from the Big Bang all the way up through the present day.

You can imagine starting at the beginning, evolving the Universe forward according to the laws of physics, and measuring those earliest signals and their imprints on the Universe to determine how it’s expanded over time. Alternatively, you can imagine starting here-and-now, and looking out at the distant objects as we see them receding from us, and then drawing conclusions as to how the Universe has expanded from that.

Both of these methods rely on the same laws of physics, the same underlying theory of gravity, the same cosmic ingredients, and even the same equations as one another. And yet, when we actually…