Posts Tagged ‘Cosmology’
“All you really need to know for the moment is that the universe is a lot more complicated than you might think, even if you start from a position of thinking it’s pretty damn complicated in the first place”*…
When you gaze out at the night sky, space seems to extend forever in all directions. That’s our mental model for the universe, but it’s not necessarily correct. There was a time, after all, when everyone thought the Earth was flat, because our planet’s curvature was too subtle to detect and a spherical Earth was unfathomable.
Today, we know the Earth is shaped like a sphere. But most of us give little thought to the shape of the universe. Just as the sphere offered an alternative to a flat Earth, other three-dimensional shapes offer alternatives to “ordinary” infinite space.
We can ask two separate but interrelated questions about the shape of the universe. One is about its geometry: the fine-grained local measurements of things like angles and areas. The other is about its topology: how these local pieces are stitched together into an overarching shape.
Cosmological evidence suggests that the part of the universe we can see is smooth and homogeneous, at least approximately. The local fabric of space looks much the same at every point and in every direction. Only three geometries fit this description: flat, spherical and hyperbolic…
Alternatives to “ordinary” infinite space: “What Is the Geometry of the Universe?”
* Douglas Adams, The Hitchhiker’s Guide to the Galaxy
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As we tinker with topology, we might recall that it was on this date in 1811 that Percy Bysshe Shelley was expelled from the University of Oxford for publishing the pamphlet The Necessity of Atheism. Shelley, of course, went on to become a celebrated lyric poet and one of the leaders of the English Romantic movement… one who had a confident (if not to say exalted) sense of his role in society:
Poets are the hierophants of an unapprehended inspiration; the mirrors of the gigantic shadows which futurity casts upon the present; the words which express what they understand not; the trumpets which sing to battle, and feel not what they inspire; the influence which is moved not, but moves. Poets are the unacknowledged legislators of the world.
“Every why hath a wherefore”*…
Physicists have started to realise that causality might not be as straightforward as we thought. Instead of cause always preceding effect, effects can sometimes precipitate their causes. And, even more mindbogglingly, both can be true at once. In this version of events, you would be opening the fridge because the butter was already on the table, and your toast would be perfectly golden both before and after you put it in the toaster. You wouldn’t just be making breakfast – your breakfast would also be making you.
Playing fast and loose with causality does more than make for confusing mornings. It could shake physics to its very foundations. No longer having a definite order of events goes against the picture of the universe painted by general relativity, and even hints at a reality beyond quantum mechanics, the best model we have of the subatomic world. Allowing causality to operate in both directions could allow us to combine these two theories into a single framework of quantum gravity, a goal that has eluded us for over a century. The end of causality as we know it …
In everyday life, causes always precede effects. But new experiments suggests that things might be different when things get very, very tiny: “In the quantum realm, cause doesn’t necessarily come before effect.”
* Shakespeare, Comedy of Errors
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As we get small, we might recall that it was on this date in 1564 that results of the Council of Trent (Concilium Tridentinum) were published, condemning what the Catholic Church deemed to be the heresies of Protestants. The embodiment of the Counter-Reformation, it established a firm and permanent distinction between the two practices of faith.
Council of Trent (painting in the Museo del Palazzo del Buonconsiglio, Trento)
“Oh how wrong we were to think immortality meant never dying”*…
Quantum simulation (Verresen et al., Nature Physics, 2019)
Further (in a fashion) to yesterday’s post…
Nothing lasts forever. Humans, planets, stars, galaxies, maybe even the Universe itself, everything has an expiration date. But things in the quantum realm don’t always follow the rules. Scientists have found that quasiparticles in quantum systems could be effectively immortal.
That doesn’t mean they don’t decay, which is reassuring. But once these quasiparticles have decayed, they are able to reorganise themselves back into existence, possibly ad infinitum.
This seemingly flies right in the face of the second law of thermodynamics, which asserts that entropy in an isolated system can only move in an increasing direction: things can only break down, not build back up again.
Of course, quantum physics can get weird with the rules; but even quantum scientists didn’t know quasiparticles were weird in this particular manner…
Maybe some things are forever. More at “Scientists Find Evidence a Strange Group of Quantum Particles Are Basically Immortal.”
Read the underlying Nature Physics article, by physicist Ruben Verresen and his team at the Technical University of Munich and the Max Planck Institute for the Physics of Complex Systems, here.
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As we ponder perpetuity, we might send carefully-deduced birthday greetings to Richard Bevan Braithwaite; he was born on this date in 1900. A Cambridge don who specialized in the philosophy of science, he focused on the logical features common to all sciences. Braithwaite was concerned with the impact of science on our beliefs about the world and the appropriate responses to that impact. He was especially interested in probability (and its applications in decision theory and games theory) and in the statistical sciences. He was president of the Aristotelian Society from 1946 to 1947, and was a Fellow of the British Academy.
It was Braithwaite’s poker that Ludwig Wittgenstein reportedly brandished at Karl Popper during their confrontation at a Moral Sciences Club meeting in Braithwaite’s rooms in King’s College. The implement subsequently disappeared. (See here.)
“Nothing happens until something moves”*…
What determines our fate? To the Stoic Greek philosophers, fate is the external product of divine will, ‘the thread of your destiny’. To transcendentalists such as Henry David Thoreau, it is an inward matter of self-determination, of ‘what a man thinks of himself’. To modern cosmologists, fate is something else entirely: a sweeping, impersonal physical process that can be boiled down into a single, momentous number known as the Hubble Constant.
The Hubble Constant can be defined simply as the rate at which the Universe is expanding, a measure of how quickly the space between galaxies is stretching apart. The slightest interpretation exposes a web of complexity encased within that seeming simplicity, however. Extrapolating the expansion process backward implies that all the galaxies we can observe originated together at some point in the past – emerging from a Big Bang – and that the Universe has a finite age. Extrapolating forward presents two starkly opposed futures, either an endless era of expansion and dissipation or an eventual turnabout that will wipe out the current order and begin the process anew.
That’s a lot of emotional and intellectual weight resting on one small number…
How scientists pinned a single number on all of existence: “Fate of the Universe.”
[Readers might remember that the Big Bang wasn’t always an accepted paradigm— and that on-going research continues to surface challenges.]
* Albert Einstein
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As we center ourselves, we might spare a thought for Kurt Friedrich Gödel; he died on this date in 1978. A logician, mathematician, and philosopher, he is considered (along with Aristotle, Alfred Tarski— whose birthday this also is– and Gottlob Frege) to be one of the most important logicians in history. Gödel had an immense impact upon scientific and philosophical thinking in the 20th century. He is, perhaps, best remembered for his Incompleteness Theorems, which led to (among other important results) Alan Turing’s insights into computational theory.
Kurt Gödel’s achievement in modern logic is singular and monumental – indeed it is more than a monument, it is a landmark which will remain visible far in space and time. … The subject of logic has certainly completely changed its nature and possibilities with Gödel’s achievement. — John von Neumann
“There is a size at which dignity begins”*…
The spectrometer for the KATRIN experiment, as it works its way through the German town of Eggenstein-Leopoldshafen in 2006 en route to the nearby Karlsruhe Institute of Technology
Isaac Asimov dubbed neutrinos “ghost particles.” John Updike immortalized them in verse. They’ve been the subject of several Nobel Prize citations, because these weird tiny particles just keep surprising physicists. And now we have a much better idea of the upper limit of what their rest mass could be, thanks to the first results from the Karlsruhe Tritium Neutrino experiment (KATRIN) in Germany. Leaders from the experiment announced their results last week at a scientific conference in Japan and posted a preprint to the physics arXiv.
“Knowing the mass of the neutrino will allow scientists to answer fundamental questions in cosmology, astrophysics, and particle physics, such as how the universe evolved or what physics exists beyond the Standard Model,” said Hamish Robertson, a KATRIN scientist and professor emeritus of physics at the University of Washington…
Physicists get small: “Weighing in: Physicists cut upper limit on neutrino’s mass in half.”
* Thomas Hardy, “Two on a Tower”
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As we step onto the scales, we might spare a thought for Max Karl Ernst Ludwig Planck; he died on this date in 1947. A theoretical physicist, he is best remembered as the originator of quantum theory. It was his discovery of energy quanta that won him the Nobel Prize in Physics in 1918.
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