Now is the time to ask:
By the early 2000s, it became clear that even if you were to ignore the supernova data entirely, you would still be compelled to conclude that there was an extra type of energy present within the Universe that comprised this “missing” ~70% or so, and that it had to behave in such a way that it was causing distant objects to have a redshift that increased over time, rather than decreased as expected in a Universe without some form of dark energy.
Although the evidence that dark energy behaved as a cosmological constant had initially large uncertainties, by the mid-2000s that was down to ±30%, by the early 2010s it was ±12%, and today it’s down to ±7%. Whatever dark energy is, it sure does look very much like its energy density remains constant in time.
In the near future, observatories like the ESA’s Euclid, the NSF’s Vera Rubin Observatory, and NASA’s Nancy Roman Observatory will improve that uncertainty so that if dark energy departs from a constant by as little as ~1-2%, we’ll be able to detect it. If it strengthens or weakens over time, or varies in different directions, it would be a revolutionary new indicator that dark energy is even more exotic than we currently think.
Sure, the idea of a novel form of energy inherent to the fabric of space itself — what we know today as dark energy — is a wild one, nobody doubts that. But is it truly wild enough to explain the Universe that we have?
Ethan Siegel, “Ask Ethan: Could Dark Energy Simply Be A Misinterpretation Of The Data?” at Forbes
All we’ve really established is that something is out there, not necessarily that dark energy is out there.
See also: Rob Sheldon: Are “multiple measurements ”closing in on dark energy? Nope.
Researchers: Either dark energy or string theory is wrong. Or both are. But dark energy is so glitzy! Isn’t it a line of cosmetics already?
Researchers: The symmetrons needed to explain dark energy were not found
Rob Sheldon: Has dark energy finally been found? In pop science mags?
Are recent dark energy findings a blow for multiverse theory?
and
Science at sunset: Dark energy might make a multiverse hospitable to life… if it exists
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