Issue 59: Gravity

What makes gravity so elusive?

What is gravity? What makes it so elusive? Why do our theories continue to change? Is it time to consider radical alternatives?

The Nobel prize in physics has just been awarded to three scientists for their work detecting gravitational waves, confirming a prediction of Einstein’s theory of general relativity.

In 2011, the Nobel committee recognized another discovery — the accelerated expansion of the universe — that conflicts with the predictions of Einstein’s theory.

Do Einstein’s ideas truly hold the answers? Insights in quantum mechanics show his theory crumbling at the sub-atomic level while the mystery of the accelerating expansion of the universe must be solved with yet another mystery: dark energy. 

And so despite huge advances - like the detection of gravitational waves - the elusive phenomenon of gravity, considered by many as physics’ greatest challenge, continues to stump the best minds in science.

Will we ever find a solution to this astronomic puzzle? Why is a force so familiar to us so impossible to explain? What would it mean for humanity if we never solve this mystery?

In this issue of IAI News, we tackle gravity. Our contributors interrogate the strengths and weaknesses of current accounts of this fundamental force, and ask what this continuing enigma means for our understanding of the universe and our place in it.

Gravity: The Story So Far

George Ellis, cosmologist and mathematician

Why does gravity not qualify as a force? What is space-time curvature? Is General Relativity the final say? Co-author of The Large Scale Structure of Space and Time with Stephen Hawking, Ellis investigates our theories of gravity.

Is Space-Time Fluid?

Sabine Hossenfelder, theoretical physicist at the Frankfurt Institute for Advanced Studies

Evidence suggests that space-time behaves like a fluid, allowing physicists to study its effects in the laboratory. But what if this comparison is more than analogy? Questioning our assumptions about space-time, Hossenfelder investigates the gravity-fluid analogy.

Gravity: The Popper Problem

David Merritt, astrophysicist at the Rochester Institute of Technology

Einstein’s principles have long been a central part of the standard cosmological model. But does his theory stand up to Karl Popper’s criteria for distinguishing science from non-science? Merritt interrogates the integrity of the theory of general relativity.

Newton’s Leap

Andrew Janiak, professor of philosophy at Duke University

The story of Isaac Newton and the falling apple has become legendary. But is this really how it occurred? Janiak goes beyond the myth to explore how a young 17th century scholar uncovered a fundamental law of the universe.

The Riddle of Gravity

Don Howard, professor of philosophy at the University of Notre Dame

21st century physicists continue to debate the future of our theories of gravity. But how has our understanding of this phenomenon changed over time? Don Howard unravels the history of our struggle to come to grips with gravity.

Beyond Dark Matter

Marcel Pawlowski, Hubble Fellow at UC Irvine

While the chase for conclusive evidence of Dark Matter continues, do the ideas of physicist Mordehai Milgrom offer an escape? Examining this alternative account of gravity, astrophysicist Pawlowski argues for more diverse approaches to the problem.

Gravity and The Dark Side of Science

Valia Allori, philosopher of physics at Northern Illinois University

Despite contrary evidence, physicists are reluctant to reject certain theories of gravity. Is it ever reasonable to hold on to a falsified theory? Examining the soundness of scientific knowledge, Allori probes the hidden assumptions behind our understanding of gravity.

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Peter Morgan 3 October 2017

Should there also be a teleparallelism article? A different perspective, and all that? [To quote the "About IAI" page, "in search of alternative and better ways to hold the world".] Modify the torsion component of the parallel transport away from trivial instead of modifying the metric, and its flat torsion Christoffel parallel transport, away from flat?
From a QFT perspective, a nontrivial torsion field on a flat metric background space might be a worthwhile approach. Not a mainstream idea, of course, but even so there are many papers and books on the subject.