Reports
Emergence: A Review of Research on Condensed Matter and Quantum Gravity and Resonances Between These Fields
George Musser | Dec 31, 2021
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In living organisms, complexity is immediately evident. But in simple objects, such as a balloon filled with air, the appearance is deceptive and masks complex inner workings. Outward simplicity is not in contradiction with inner complexity; in fact, one emerges from the other. A group of things can display features that are not found in any of their components. In many exotic materials, such as the wonder-material graphene, the properties of the whole are greater than the sum of the parts, potentially yielding tremendous practical applications.
This review examines the concept of emergence in both condensed-matter systems and in quantum gravity, where physicists are exploring how quantum entanglement knits space into existence. It then identifies how theoretical developments in understanding the emergence of space have fed back into condensed matter, enriching both research areas and enabling scientists to solve the problems of one area by importing ideas from the other.
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Cosmological Origins
M. Mitchell Waldrop, PhD | Nov 15, 2021
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They are some of the oldest questions that human beings have ever asked–renewed again and again by every child who looks up in wonder at the sun, the moon, the stars, and the planets: What are they? Why do they move and change the way they do? Where do they all come from? And where do we come from? These questions are so fundamental that every culture and every religion provides answers.
Science, however, confines itself to puzzles that can be addressed by reason, experiment, and observation. Yet as we will see, that discipline has guided scientists to a cosmic story that is far stranger than our ancestors could have imagined. Again and again, what are now considered to be foundational discoveries were met with indifference, incomprehension, or even hostility–and achieved widespread acceptance only after accumulating evidence made the new ideas impossible to ignore.
This review walks us through those paradigm shifts and introduces some of the major mysteries facing cosmologists today. We review how physicists established that the universe is expanding and derived the Big Bang model. But then we ask what might have happened before the Big Bang? What is inflation theory? Do we live in a multiverse of many universes? How are astronomers and physicists homing in on the identities of dark matter and dark energy, with new observations and lab experiments? And we discuss one of the biggest cosmic conundrums, the ‘Hubble tension’: Why do different astrophysical observations suggest different ages for our universe? Could resolving this mismatch force us to consider a new cosmological picture?
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Time: A Review of Temporal Research in the Physical and Biological Sciences
Kate Becker | Nov 30, 2021
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What is time?
It is a position of the hands on a clock, and the difference between finding those hands in one position and another. You can be on time, in time, out of time. Time is the thing that makes the past closed and the future open, distinguishes history from prediction, and fixes cause before effect. It is the machine that turns the future into the present and the present into the past. It flows, but not steadily: sometimes it passes in a great rush, sometimes in drowsy drips, and sometimes it almost seems to freeze. It makes beginnings possible and endings inevitable.
Today’s exquisitely precise timekeeping has brought us no closer to understanding the essential nature of time. Physicists are now tackling some of our deepest questions about time head-on: Where does it come from? Is the flow of time real, or an illusion? Why does time’s arrow point in only one direction? Can time be reversed? And how does the human mind perceive time?
Meanwhile, the two great theories of modern physics, general relativity, describing the motion of the heavenly bodies, and quantum theory, describing the behavior of the very small, reveal contradictory faces of time. Ever since the two theories emerged in the early 20th century, physicists have been trying to find ways to unite them into a single, deeper theory of “quantum gravity.” Could this quest also uncover the true nature of time? This review describes some of the latest experiments to build a “quantum clock” that could reveal the answers.
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Fine Tuning
Miriam Frankel | Jan 31, 2022
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Imagine standing before a firing squad, with 50 trained marksmen aiming rifles at your heart. You’re certain that this is your last moment, but somehow the bullets all miss and you survive. Chances are you would feel perplexed about your survival and want to seek answers about how this happened. This metaphor was put forward by John Leslie to demonstrate how the existence of life in the universe similarly relies on improbable cosmic conditions, with physical variables seemingly aligning perfectly to enable the evolution of intelligent beings.
Is our hospitable universe just a fluke? This review explores the complex history of research on fine tuning, including potential explanations–such as the anthropic principle, string theory, and the multiverse–attempts to pin down the key ingredients for life, and ways to test explanations for fine tuning.
The review also examines claims by some physicists that any apparent fine tuning is an illusion. Some scientists have argued that in the absence of a probability distribution for the possible values of parameters that could occur, it’s impossible to argue with conviction that our measured values are actually odd. Another major issue is that we cannot rule out the possibility that some kind of life could arise even in a universe with completely different properties. And if one allows many parameters to vary simultaneously, it could alleviate the apparent fine-tuning problems, enabling the universe to produce life under a wider range of circumstances than first thought.
So, is the universe ultimately fine-tuned for life?
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