May 16, 2018 04:26 PM
https://www.scientificamerican.com/artic...cientists/
EXCERPT: What began as a debate over astronomical measurements is on the verge of becoming a full-blown crisis in how we understand the cosmos. Two data sets—one from the newborn universe nearly 14 billion years ago, the other from stars as we see them today—are yielding contradictory answers to a deceptively simple question: How fast is the universe expanding?
The gap between answers is only 9 percent, but that far exceeds each data set’s estimated uncertainties. Researchers on each side of the gap call it “the tension,” and are digging in their heels about the validity of their observations. This tension is the stuff of scientific dreams—and nightmares.
“If the tension isn’t a fluke and it’s not an error in measurement, it implies we’re missing something in our models,” says Adam Riess [...] “Making this measurement for the early universe and then comparing it to today’s is an end-to-end test of the whole story we’ve constructed about the universe. The trouble is, if something definitely doesn’t fit, we don’t know where exactly the story diverges.”
[...] The Hubble constant reflects the sum total of all the stuff in the universe and the forces acting on it—weighing in on whether gravity or the void will ultimately win this intergalactic tug-of-war. The universe’s contents could eventually reverse the expansion—a scenario called the “big crunch,” in which gravity pulls everything back into an infinitely hot and dense point like the one that birthed the big bang. Or the universe might steadily expand indefinitely, growing ever colder and listless in a “big chill” that offers endless space and time—but ultimately very little to do. Or just maybe the cosmic expansion will dramatically speed up, becoming so unruly that it bucks all its riders. [...] until even the fabric of reality itself splits at its seams in a “big rip” that leaves practically nothing behind. Will the universe end in fire, ice or emptiness? The Hubble constant knows—but until the tension is resolved, the answer is unclear....
MORE: https://www.scientificamerican.com/artic...cientists/
EXCERPT: What began as a debate over astronomical measurements is on the verge of becoming a full-blown crisis in how we understand the cosmos. Two data sets—one from the newborn universe nearly 14 billion years ago, the other from stars as we see them today—are yielding contradictory answers to a deceptively simple question: How fast is the universe expanding?
The gap between answers is only 9 percent, but that far exceeds each data set’s estimated uncertainties. Researchers on each side of the gap call it “the tension,” and are digging in their heels about the validity of their observations. This tension is the stuff of scientific dreams—and nightmares.
“If the tension isn’t a fluke and it’s not an error in measurement, it implies we’re missing something in our models,” says Adam Riess [...] “Making this measurement for the early universe and then comparing it to today’s is an end-to-end test of the whole story we’ve constructed about the universe. The trouble is, if something definitely doesn’t fit, we don’t know where exactly the story diverges.”
[...] The Hubble constant reflects the sum total of all the stuff in the universe and the forces acting on it—weighing in on whether gravity or the void will ultimately win this intergalactic tug-of-war. The universe’s contents could eventually reverse the expansion—a scenario called the “big crunch,” in which gravity pulls everything back into an infinitely hot and dense point like the one that birthed the big bang. Or the universe might steadily expand indefinitely, growing ever colder and listless in a “big chill” that offers endless space and time—but ultimately very little to do. Or just maybe the cosmic expansion will dramatically speed up, becoming so unruly that it bucks all its riders. [...] until even the fabric of reality itself splits at its seams in a “big rip” that leaves practically nothing behind. Will the universe end in fire, ice or emptiness? The Hubble constant knows—but until the tension is resolved, the answer is unclear....
MORE: https://www.scientificamerican.com/artic...cientists/
