Posts Tagged ‘expanding universe’
“The universe is under no obligation to make sense to you”*…
Still, we try… In a consideration of three new books, the estimable Sean Carroll brings us up to date on the state of play…
Should scientists be embarrassed that they can’t settle on a definition for the Big Bang? The cosmologist Will Kinney describes it as the “physical theory of the hot infant universe,” while Wikipedia goes for the more elaborate “a physical theory that describes how the universe expanded from an initial state of high density and temperature.” The first refers only to early times, while the latter seems to extend to subsequent times as well. The physicist and science writer Tony Rothman offers the pithier “the universe’s origin,” the theoretical physicist Thomas Hertog suggests that it is the “primeval state” of cosmic history, and a NASA website gives us “the idea that the universe began as just a single point.” These seem to refer to one moment at the start of things, rather than the universe’s life since then.
All of these sources (except NASA, unfortunately) capture something correct. The confusion stems both from the inherent ambiguity of using ordinary language to describe novel scientific concepts and from the state of modern cosmology itself. Cosmology is the study of the universe on the largest scales. So it ignores details of stars and planets, focusing on galaxies and even bigger structures, up to the universe as a whole. Modern cosmology is only about a century old, as it wasn’t until the 1920s that astronomers determined that our own Milky Way is just one of a large number of galaxies and the origin and evolution of them all could be studied together. And it wasn’t until the 1990s that the field matured into the one that exists today, featuring precision measurements and ultralarge datasets.
Dealing as it does with some of the most profound questions about the nature of the cosmos, cosmological research has always involved a vigorous give-and-take between rampant speculation and unanticipated discoveries. Its practitioners have long been fond of spinning purportedly inviolate physical principles from their personal intuitions about how reality should work. But cosmology remains an empirical science—a cherished belief can be quickly swept away by a solid measurement.
The present moment in the science of cosmology is one of consolidation, as we have successfully incorporated the lessons of some impressive discoveries made near the turn of the twenty-first century. Yet crucially important questions remain unanswered, especially about what exactly happened at the onset of the expanding space that evolved into our contemporary universe. It is therefore a good time for books that take stock of where we are and what might come next, and that illustrate which puzzles modern physicists choose to take seriously.
This much we know: we live in a galaxy, the Milky Way, containing around 200 billion stars. There are something like a trillion galaxies in our observable universe, distributed almost uniformly through space. Stars and galaxies condensed out of an originally nearly smooth distribution of matter. Distant galaxies are moving apart from one another. Extrapolating backward, we reach a hot, densely packed configuration about 13.8 billion years ago. We can observe the remnants of this early period in nearly uniform cosmic background radiation coming from every direction in the sky.
The Big Bang model is precisely this general picture, of a universe that expands and cools out of a smooth, hot primordial state. It is well understood and almost universally accepted among modern cosmologists. The Big Bang event is a hypothetical moment when the whole thing might have started, at which the temperature and density are supposed to have been literally infinite—a “singularity,” in physics parlance. This is why the NASA definition above is unambiguously wrong: the Big Bang event has nothing to do with “a single point” in space—it refers to a moment in time.
Nobody knows whether there actually was such an event. To be honest, there probably wasn’t. Einstein’s theory of general relativity predicts that such a singularity would have happened, but most physicists think this signals a breakdown in the theory rather than being an accurate description of the physical world. A prediction of infinitely big physical quantities is apt to be a sign that we don’t have the right theoretical understanding…
[Starting with Einstein’s unification of space-time in 1905, Carroll explains the implications of quantum theory, in particular on the question of the expansion of the universe. Using the three (very different, but complementary) books under consideration, he unpacks the issues and demonstrates the way in which scientific theories about the origin of the universe often involve a vigorous give-and-take between speculation and discovery…]
… Taken together, these three books provide an illuminating view of the state of modern cosmology. There are established results, laudable efforts to connect promising hypotheses to a flood of incoming data, and brave speculations about the physical and metaphysical unknown. They are all notably well written for the genre and will keep readers entertained as they are educated. We can marvel at both how much scientists have learned about the universe and how much we have yet to understand.
The state of cosmology (and a look at science at work): “A First Time for Everything,” from @seanmcarroll.bsky.social in @nybooks.com.
* Neil deGrasse Tyson
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As we wrestle with reality, we might spare a thought for a major (if, in the end, incorrect) character in tale that Carroll tells: Fred Hoyle; he died on this date in 2001. A prominent astronomer, he formulated the theory of stellar nucleosynthesis. But he is rather better remembered for his controversial stances on other scientific matters—in particular his rejection of the (as Carroll observes, now widely-accepted) “Big Bang” theory– a term he coined, derisively, in an episode of his immensely-popular series The Nature of the Universe on BBC radio– and his promotion of panspermia as the source of life on Earth (or maybe the traffic was in the other direction?).
“In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.”*…
In the face of cosmologists who are trying to combine string theory with the theory of cosmic inflation to understand the universe-as-we-find-it, Neil Turok suggests a much simpler explanation. Frank Landymore reports…
Our understanding of the universe, as advanced as it is, remains riddled with paradoxes and huge question marks. Physicists have come up with some pretty heady ideas to explain them — we’ll get to those later — but there just might be a far “simpler” solution to all those holes in cosmology.
As Higgs Chair of Theoretical Physics at the University of Edinburgh Neil Turok explains in an essay for The Conversation, there could be a “mirror” universe that existed before the Big Bang and is a reflection of our own, moving backward in time.
It’s a trippy concept to wrap your head around, but simpler on the physics side of things. It would neatly balance out some of the asymmetries we observe in the universe, provide an answer to dark matter, and supplant some of what Turok would characterize as clumsier leading theories in cosmology, like cosmic inflation and string theory.
“Picturing the big bang as a mirror neatly explains many features of the universe which might otherwise appear to conflict with the most basic laws of physics,” wrote Turok, who published his team’s findings in the journal Annals of Physics. “The progress we have already made convinces me that, in all likelihood, there are alternatives to the standard orthodoxy — which has become a straitjacket we need to break out of.”
The physical laws of the universe should exhibit charge, parity, and time reversal — collectively known as CPT — symmetry, which essentially means every physical interaction can be mirrored. So to break down its implications: every particle should have an anti-particle of the opposite charge, every space has its inversion, and time can be reversed.
Except that’s not what we actually observe. Time only goes forward, and there are more particles than anti-matter particles. As far as we can tell, our universe is not symmetrical.
But: “Our mirror hypothesis restores the symmetry of the universe,” Turok argued. He compared it to looking at your reflection: “The combination of you and your mirror image are more symmetrical than you are alone.”
Extrapolating our universe backward in time through the Big Bang, “we found its mirror image, a pre-bang universe in which (relative to us) time runs backward and antiparticles outnumber particles,” Turok wrote.
This could also solve the mystery of dark matter, an invisible substance thought to make up 85 percent of all matter in the universe. Under the mirror hypothesis, weak, subatomic particles called neutrinos would be the ideal candidate to explain it.
Since we’ve only observed left-handed neutrinos, perhaps yet-unseen right-handed could even exist in the mirror universe.
What’s more, this could also tidily explain why the universe appears to be so uniform and flat. The prevailing theory is that a period of accelerated, faster-than-light expansion called cosmic inflation was responsible for shaping how the universe is today — but we’re yet to observe the large gravitational waves this would have produced.
With a handy mirror universe, however, “statistical arguments explain why the universe is flat and smooth and has a small positive accelerated expansion, with no need for cosmic inflation,” Turok wrote.
Of course, there’s a lot more needed to bear out this intriguing hypothesis. But Turok argues that, even if disproven, it demonstrates that there could be more straightforward explanations than what the Standard Model offers…
A mirror of our own, going backwards in time: “Physicist Says There’s Another Universe Hiding Behind the Big Bang,” from @futurism.
Turok’s full essay– longer and more detailed, but very accessible– is here.
* Douglas Adams, The Restaurant at the End of the Universe
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As we size up symmetry, we might send lofty birthday greetings to another ponderer of the cosmos, Carl Edward Sagan; he was born on this date in 1934. An astronomer, cosmologist, astrophysicist, astrobiologist (his contributions were central to the discovery of the high surface temperatures of Venus), he is best remembered as a popularizer of science– via books like The Dragons of Eden, Broca’s Brain and Pale Blue Dot, and the award-winning 1980 television series Cosmos: A Personal Voyage (which he narrated and co-wrote), the most widely-watched series in the history of American public television (seen by at least 500 million people across 60 different countries).
He is also remembered for his contributions to the scientific research of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.
(Readers can enjoy a loving riff on Cosmos here.)
“It is unnatural in a large field to have only one shaft of wheat, and in the infinite Universe only one living world”*…
NASA’s top scientists have a provocative message for the scientific community: that they need a plan in place for if — or when — we find evidence of extraterrestrial life…
James Green, the agency’s chief scientist, coauthored a new article, published in the journal Nature, urging researchers to create a framework for reporting evidence of aliens. In it, the authors stressed the importance of clearly communicating any findings of extraterrestrial life, as well as establishing clear expectations for the public for when it occurs and accurately expressing ambiguity in early evidence.
“As life-detection objectives become increasingly prominent in space sciences, it is essential to open a community dialogue about how to convey information in a subject matter that is diverse, complicated and has a high potential to be sensationalized,” read the paper.
Green and his co-authors propose a confidence of life detection (CoLD) scale to help evaluate any evidence that might be discovered. The scale itself contains seven different levels like a staircase. Each level is a benchmark that must be met before we can proceed to the next step.
For example, level one would be discovering life signatures such as biological molecules. The second level would be ruling out that the sign of life is the result of contamination from Earth. Eventually, the CoLD scale ends with the final step: scientists declaring that they’ve confidently discovered evidence of extraterrestrial life.
“Having a scale like this will help us understand where we are in terms of the search for life in particular locations, and in terms of the capabilities of missions and technologies that help us in that quest,” Green said in a NASA news release.
The paper’s authors stress that the scale is merely a starting point for a larger conversation with scientists and science communicators about the best ways to proceed if and when we discover evidence of alien life.
It also comes in the context of the upcoming launch of the powerful James Webb telescope, along with the Perseverance Mars rover searching for life on the Red Planet, meaning that such a finding might become a reality sooner rather than later.
“The search for life beyond Earth requires broad participation from the scientific community and many kinds of observations and experiments,” Mary Voltek, co-author of the study and head of NASA’s Astrobiology Program, said in the release. “Together, we can be stronger in our efforts to look for hints that we are not alone.”
“NASA Says We Need a Plan for When We Discover Alien Life,” from @futurism.
As to what we’ll do with that knowledge, a complicating factor: “94% of the universe’s galaxies are permanently beyond our reach” (if the speed of light remains an upper limit on travel).
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As we search far and wide, we might send enduring birthday greetings to Sir Hermann Bondi; he was born on this date in 1919. A mathematician and cosmologist, he is best remembered for developing the steady state model of the universe with Fred Hoyle and Thomas Gold as an alternative to the Big Bang theory. In an attempt to explain the paradox: how can the stars continually recede, yet without disappearing, they audaciously proposed an unproven hypothesis: that the universe has an eternal existence, with no beginning and without an end. Further, they argued, the universe is continuously expanding, maintaining a constant density by continually creating new matter from energy. Their model was rendered obsolete when, in 1965, Arno Penzias and Robert Wilson detected a background microwave radiation from all directions in space, as predicted by the “Big Bang” theory of creation that is now accepted. [See here for more on Penzias’ and Wilson’s discovery.)
Bondi also contributed to the theory of general relativity; was the first to analyze the inertial and gravitational interaction of negative mass; and the first to explicate correctly the nature of gravitational waves.
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