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Saturday Citations: The universe doesn't care about your precious standard model

This week, ALMA researchers reported the discovery of oxygen in the most distant known galaxy. Geologists believe unusual structures in rock in the desert regions of Namibia, Oman and Saudia Arabia may be evidence of an unknown microorganism. And a group of physicists may have generated a tiny charge of electricity using the Earth's rotational energy. But the biggest story by far is the second release of data from the DESI survey of the universe, which could upend the standard model:

DESI is coming for the standard model

An emerging generation of cosmological surveys launched this week with the second release of data from the Dark Energy Spectroscopic Instrument at Kitt Peak National Observatory in Arizona, which is mapping an unprecedentedly huge number of galaxies spanning 11 billion years of cosmic history in order to better understand dark energy.

Astronomers have known for many decades that the universe is expanding; in the 1990s, the first image of the cosmic microwave background—the echo of the big bang—revealed that this expansion is accelerating for unknown reasons. Astronomers call this expansion "dark energy," which translates to "we don't understand what this energy is."

The new data from the DESI collaboration, much of which comprises refinement of the first data release, indicates tensions emerging between observations of the expansion of the universe. When the collaboration combined the new data with previous observations, they found signs that the impact of dark energy on universal expansion may be weakening over time.

"When we combine all the cosmological data, it favors that the universe's expansion was accelerating at a slightly higher rate around 7 billion years ago," said Arnaud de Mattia, a French physicist on the team analyzing the data. However, the researchers emphasize that they do not have absolute certainty for this yet—meaning the research effort has not yet met the "five sigma" statistical threshold physicists use as a marker for certainty.

This new theory of "evolving dark energy" will impact the standard cosmological model, which will require substantial changes to incorporate new findings.

OK, but let's speculate

So let's say this result—that dark energy evolves over time—is confirmed by DESI and the forthcoming next-gen surveys later in the decade. Right now, the standard model suggests expansion until the ultimate heat death of the universe. But now, we can consider more exciting, cinematic possibilities for the fate of the universe: if the universal expansion acceleration increases over time, the universe could tear apart in a "big rip." Alternatively, it could reach a point of maximum expansion and collapse inward in a "big crunch."

In the "big rip" scenario, as the acceleration of universal expansion increases toward infinity within a finite time, all matter down to the scale of atoms and subatomic particles, and spacetime itself, are (as the best dungeon masters put it) "torn asunder."

As the universe approaches this point, galaxies would become gravitationally unbound as matter dispersed; ultimately, the same thing would happen to planetary systems; then military squadrons, families and married couples. Then atoms would become ionized as their electrons were ripped away. Finally, atomic nuclei themselves would disassociate.

By contrast, in the "big crunch," the expansion of the universe reverses and all matter and spacetime reconverge toward a singularity, or at least toward a singular point. If the universe contains a high enough density of matter, gravity would stop universal expansion and all matter would fall back in on itself.

This leads to a third theory, the "big bounce," which suggests that the universe itself is a cycle of expansions, collapses and re-expansions. At the smallest point of convergence, general relativity demands the emergence of a singularity.

However, physicists theorize that quantum effects become highly important at that stage, preventing the formation of a singularity and instead resulting in a highly energetic and explosive expansion (and the birth of a new universe). This theory is currently so far away from the "five sigma" threshold as to effectively exist in another universe, but it is indisputably the prettiest of the theories of the nature of the universe.

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