Opinion | Is There a Crisis in Cosmology?
Category: News & PoliticsVia: john-russell • 3 weeks ago • 13 comments
By: Adam Frank and Marcelo Gleiser (nytimes)
Sept. 2, 2023, 7:00 a.m. ETVideoCreditCredit...Virginia Gabrielli
By Adam Frank and Marcelo Gleiser
Dr. Frank is an astrophysicist at the University of Rochester. Dr. Gleiser is a theoretical physicist at Dartmouth College.
Not long after the James Webb Space Telescope began beaming back from outer space its stunning images of planets and nebulae last year, astronomers, though dazzled, had to admit that something was amiss. Eight months later, based in part on what the telescope has revealed, it's beginning to look as if we may need to rethink key features of the origin and development of the universe.
Launched at the end of 2021 as a joint project of NASA, the European Space Agency and the Canadian Space Agency, the Webb, a tool with unmatched powers of observation, is on an exciting mission to look back in time, in effect, at the first stars and galaxies. But one of the Webb's first major findings was exciting in an uncomfortable sense: It discovered the existence of fully formed galaxies far earlier than should have been possible according to the so-called standard model of cosmology.
According to the standard model, which is the basis for essentially all research in the field, there is a fixed and precise sequence of events that followed the Big Bang: First, the force of gravity pulled together denser regions in the cooling cosmic gas, which grew to become stars and black holes; then, the force of gravity pulled together the stars into galaxies.
The Webb data, though, revealed that some very large galaxies formed really fast, in too short a time, at least according to the standard model. This was no minor discrepancy. The finding is akin to parents and their children appearing in a story when the grandparents are still children themselves.
It was not, unfortunately, an isolated incident. There have been other recent occasions in which the evidence behind science's basic understanding of the universe has been found to be alarmingly inconsistent.
Take the matter of how fast the universe is expanding. This is a foundational fact in cosmological science — the so-called Hubble constant — yet scientists have not been able to settle on a number. There are two main ways to calculate it: One involves measurements of the early universe (such as the sort that the Webb is providing); the other involves measurements of nearby stars in the modern universe. Despite decades of effort, these two methods continue to yield different answers.
At first, scientists expected this discrepancy to resolve as the data got better. But the problem has stubbornly persisted even as the data have gotten far more precise. And now new data from the Webb have exacerbated the problem. This trend suggests a flaw in the model, not in the data.
Two serious issues with the standard model of cosmology would be concerning enough. But the model has already been patched up numerous times over the past half century to better conform with the best available data — alterations that may well be necessary and correct, but which, in light of the problems we are now confronting, could strike a skeptic as a bit too convenient.
Physicists and astronomers are starting to get the sense that something may be really wrong. It's not just that some of us believe we might have to rethink the standard model of cosmology; we might also have to change the way we think about some of the most basic features of our universe — a conceptual revolution that would have implications far beyond the world of science.
A potent mix of hard-won data and rarefied abstract mathematical physics, the standard model of cosmology is rightfully understood as a triumph of human ingenuity. It has its origins in Edwin Hubble's discovery in the 1920s that the universe was expanding — the first piece of evidence for the Big Bang. Then, in 1964, radio astronomers discovered the so-called Cosmic Microwave Background, the "fossil" radiation reaching us from shortly after the universe began expanding. That finding told us that the early universe was a hot, dense soup of subatomic particles that has been continually cooling and becoming less dense ever since.
Over the past 60 years, cosmology has become ever more precise in its ability to account for the best available data about the universe. But along the way, to gain such a high degree of precision, astrophysicists have had to postulate the existence of components of the universe for which we have no direct evidence. The standard model today holds that "normal" matter — the stuff that makes up people and planets and everything else we can see — constitutes only about 4 percent of the universe. The rest is invisible stuff called dark matter and dark energy (roughly 27 percent and 68 percent).
Cosmic inflation is an example of yet another exotic adjustment made to the standard model. Devised in 1981 to resolve paradoxes arising from an older version of the Big Bang, the theory holds that the early universe expanded exponentially fast for a fraction of a second after the Big Bang. This theory solves certain problems but creates others. Notably, according to most versions of the theory, rather than there being one universe, ours is just one universe in a multiverse — an infinite number of universes, the others of which may be forever unobservable to us not just in practice but also in principle.
There is nothing inherently fishy about these features of the standard model. Scientists often discover good indirect evidence for things that we cannot see, such as the hyperdense singularities inside a black hole. But in the wake of the Webb's confounding data about galaxy formation, and the worsening problem with the Hubble constant, you can't be blamed for starting to wonder if the model is out of joint.
A familiar narrative about how science works is often trotted out at this point to assuage anxieties. It goes like this: Researchers think they have a successful theory, but new data show it is flawed. Courageously rolling up their sleeves, the scientists go back to their blackboards and come up with new ideas that allow them to improve their theory by better matching the evidence.
It's a story of both humility and triumph, and we scientists love to tell it. And it may be what happens in this case, too. Perhaps the solution to the problems the Webb is forcing us to confront will require only that cosmologists come up with a new "dark" something or other that will allow our picture of the universe to continue to match the best cosmological data.
There is, however, another possibility. We may be at a point where we need a radical departure from the standard model, one that may even require us to change how we think of the elemental components of the universe, possibly even the nature of space and time.
Cosmology is not like other sciences. It's not like studying mice in a maze or watching chemicals boil in a beaker in a lab. The universe is everything there is; there's only one and we can't look at it from the outside. You can't put it in a box on a table and run controlled experiments on it. Because it is all-encompassing, cosmology forces scientists to tackle questions about the very environment in which science operates: the nature of time, the nature of space, the nature of lawlike regularity, the role of the observers doing the observations.
These rarefied issues don't come up in most "regular" science (though one encounters similarly shadowy issues in the science of consciousness and in quantum physics). Working so close to the boundary between science and philosophy, cosmologists are continually haunted by the ghosts of basic assumptions hiding unseen in the tools we use — such as the assumption that scientific laws don't change over time.
But that's precisely the sort of assumption we might have to start questioning in order to figure out what's wrong with the standard model. One possibility, raised by the physicist Lee Smolin and the philosopher Roberto Mangabeira Unger, is that the laws of physics can evolve and change over time. Different laws might even compete for effectiveness. An even more radical possibility, discussed by the physicist John Wheeler, is that every act of observation influences the future and even the past history of the universe. (Dr. Wheeler, working to understand the paradoxes of quantum mechanics, conceived of a "participatory universe" in which every act of observation was in some sense a new act of creation.)
It is not obvious, to say the least, how such revolutionary reconsiderations of our science might help us better understand the cosmological data that is flummoxing us. (Part of the difficulty is that the data themselves are shaped by the theoretical assumptions of those who collect them.) It would necessarily be a leap of faith to step back and rethink such fundamentals about our science.
But a revolution may end up being the best path to progress. That has certainly been the case in the past with scientific breakthroughs like Copernicus's heliocentrism, Darwin's theory of evolution and Einstein's relativity. All three of those theories also ended up having enormous cultural influence — threatening our sense of our special place in the cosmos, challenging our intuition that we were fundamentally different than other animals, upending our faith in common sense ideas about the flow of time. Any scientific revolution of the sort we're imagining would presumably have comparable reverberations in our understanding of ourselves.
The philosopher Robert Crease has written that philosophy is what's required when doing more science may not answer a scientific question. It's not clear yet if that's what's needed to overcome the crisis in cosmology. But if more tweaks and adjustments don't do the trick, we may need not just a new story of the universe but also a new way to tell stories about it.
Adam Frank (@AdamFrank4) is a professor of astrophysics at the University of Rochester and the author of the forthcoming book "The Little Book of Aliens." Marcelo Gleiser (@MGleiser) is a professor of physics and astronomy at Dartmouth College and the author of "The Dawn of a Mindful Universe: A Manifesto for Humanity's Future."
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