Posts Tagged ‘panspermia’
“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?).
“I’m sure the universe is full of intelligent life. It’s just been too intelligent to come here.”*…
The Fermi paradox, named for physicist Enrico Fermi, is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and various high estimates for their probability (e.g., some of the optimistic estimates for the Drake equation). Fermi wondered, “where are they?”
By way of context, Tim Urban in his wonderful Wait But Why?:
As many stars as there are in our galaxy (100 – 400 billion), there are roughly an equal number of galaxies in the observable universe—so for every star in the colossal Milky Way, there’s a whole galaxy out there. All together, that comes out to the typically quoted range of between 1022 and 1024 total stars, which means that for every grain of sand on every beach on Earth, there are 10,000 stars out there.
The science world isn’t in total agreement about what percentage of those stars are “sun-like” (similar in size, temperature, and luminosity)—opinions typically range from 5% to 20%. Going with the most conservative side of that (5%), and the lower end for the number of total stars (1022), gives us 500 quintillion, or 500 billion billion sun-like stars.
There’s also a debate over what percentage of those sun-like stars might be orbited by an Earth-like planet (one with similar temperature conditions that could have liquid water and potentially support life similar to that on Earth). Some say it’s as high as 50%, but let’s go with the more conservative 22% that came out of a recent PNAS study. That suggests that there’s a potentially-habitable Earth-like planet orbiting at least 1% of the total stars in the universe—a total of 100 billion billion Earth-like planets.
So there are 100 Earth-like planets for every grain of sand in the world. Think about that next time you’re on the beach.
Moving forward, we have no choice but to get completely speculative. Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life (if that’s true, every grain of sand would represent one planet with life on it). And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth. That would mean there were 10 quadrillion, or 10 million billion intelligent civilizations in the observable universe.
Moving back to just our galaxy, and doing the same math on the lowest estimate for stars in the Milky Way (100 billion), we’d estimate that there are 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy.1
SETI (Search for Extraterrestrial Intelligence) is an organization dedicated to listening for signals from other intelligent life. If we’re right that there are 100,000 or more intelligent civilizations in our galaxy, and even a fraction of them are sending out radio waves or laser beams or other modes of attempting to contact others, shouldn’t SETI’s satellite dish array pick up all kinds of signals?
But it hasn’t. Not one. Ever…
Perhaps. as we’ve mused here at (R)D before, life is there, but we’re not seeing it because it isn’t a form of life that we recognize: c.f., “Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying” and “That is a very Earthling question to ask, Mr. Pilgrim.”
But there are some who’ve refused to give up on the search for more traditionally-defined life; indeed, a new study quantifies the “fraction” (to which Urban alludes, above) of civilizations that could (should?) be communicating around our galaxy:
One of the biggest and longest-standing questions in the history of human thought is whether there are other intelligent life forms within our Universe. Obtaining good estimates of the number of possible extraterrestrial civilizations has however been very challenging.
A new study led by the University of Nottingham and published [earlier this month] in The Astrophysical Journal has taken a new approach to this problem. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilizations within our own galaxy -the Milky Way. They calculate that there could be over 30 active communicating intelligent civilizations in our home Galaxy…
Details at (the slightly misleadingly-titled): “Research sheds new light on intelligent life existing across the galaxy.”
* Arthur C. Clarke
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As we stay tuned, we might send far-seeing birthday greeting to Fred Hoyle; he was born on this date in 1915. 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 “Big Bang” theory (a term he coined, derisively, in one 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.
“Human DNA spreading out from gravity’s steep well like an oilslick”*…
Could the Earth be a life-exporting planet? That’s the curious question examined in a recent paper written by Harvard University astronomers Amir Siraj and Abraham Loeb.
The researchers take a novel twist on the controversial notion of panspermia – the idea, propelled into the mainstream in the early 1970s by astronomers Fred Hoyle and Chandra Wickramasinghe, that life might have started on Earth through microbes arriving from space.
The theory is generally discounted, although eminent astrophysicists such as Stephen Hawking conceded it was at least possible, and a major paper published in 2018 revived the topic big-time.
In their [late December, 2019] paper, Siraj and Loeb reverse the standard assumption about the direction of the microbial journey and ask whether it is possible to that at some point Earth-evolved bacteria could have been propelled away from the planet, possibly to be deposited somewhere else in the Milky Way…
Astronomers suggest microbes might hitch lifts on interstellar asteroids. More on the hypothesis and the evidence that supports it at “Earth bacteria may have colonised other solar systems.” Read the underlying paper at arXiv.
* William Gibson, Neuromancer
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As we ponder the polarity of proliferation, we might recall that it was on this date in 1921 that Albert Einstein startled his audience at the Prussian Academy of Sciences in Berlin by suggesting the possibility that the universe could be measured. His talk, “Geometry and Experience” (text here), applied some results of the relativity theory to conclude that if the real velocities of the stars (as could be actually measured) were less than the calculated velocities, then it would prove that real gravitations’ great distances were smaller than the gravitational distances demanded by the law of Newton. From that divergence, the finiteness of the universe could be proved indirectly, and could even permit the estimation of its size.
Later that year, Einstein was announced as the 1921 Nobel Laureate in Physics, an award he accepted the following year.
Einstein in 1921
Happy Birthday, Dante, Mozart, and Lewis Carroll!
I, for one, have always wanted to know…
Readers will know the Large Hadron Collider, the massive particle accelerator built to answer such questions as “Is there a ‘God Particle” (Higgs Boson)?” The LHC accelerates two counter-rotating beams of protons to nearly the speed of light and then brings them into collision inside giant, cathedral-sized detectors that study the subatomic debris that comes flying outward. The folks at CERN, who operate the LHC, hold the world’s record for the highest energies ever achieved: the collisions of more than 10 billion protons per bunch at a total energy of 2.36 trillion electron volts, or TeV, per collision.
But the LHC raises as many questions as it hopes to answer…
Who hasn’t wondered, for example, what happens if one puts one’s hand in front of the beam? Happily (if not conclusively), the folks at Sixty Symbols have gathered some answers:
As we think hard about wearing gloves, we might recall that it was on this date in 1969 that a number of meteor fragments fell near Murchison, in Victoria, Australia. Analysis of the fragments has identified over 14,000 compounds in the carbonaceous chondrite; almost 100 of them, different amino acids, only 19 of which are found on earth… encouraging proponents of “panspermia”– the proposition that life on earth was “jump-started” when key ingredients in the primordial soup dropped in from the Heavens.
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