Over the past decade, two very different ways of calculating the rate at which the universe is expanding have come to be at odds, a disagreement dubbed the Hubble tension, after 20th-century astronomer Edwin Hubble. Experts have speculated that this dispute might be temporary, stemming from subtle shortcomings in observations or analyses that will eventually be corrected rather than from some flawed understanding of the physics of the cosmos. Now, however, a new study that relies on an independent measure of the properties of galaxies has strengthened the case for the tension. Quite possibly, it’s here to stay.
For some researchers, the word “tension” fails to convey the problem’s increasing severity.
“We’ve been at this ‘Hubble tension’ level for a long time. At some point the community needs to say, ‘This is more serious,’” says physicist Dan Scolnic of Duke University, who was not associated with the new study. “And the step up from ‘tension’ is ‘crisis.’”
Worsening these woes are the latest results based on observations of the large-scale structure of the universe: dark energy, which is thought to be causing the expansion of the universe to accelerate, may be changing with time. This only serves to aggravate the Hubble tension—or Hubble crisis, if you prefer.
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