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A translucent drop of pond water clings to the surface of a lily pad, motionless and serene. When placed under high magnification, however, the image is transformed and we see another world, pulsing with exotic life.
Physicists have revisited another seemingly blank domain: the vacuum. Here too, a deeper reality of teeming complexity has been revealed, through theory and experiment.
Last week, Nobel laureate and ASU Origins professor Frank Wilczek outlined the rich world of “nothingness” in a lecture titled “The Materiality of the Vacuum: Late Night Thoughts of a Physicist.” His talk was followed by a conversation with Origins Director Lawrence Krauss, which explored notions of the vacuum from antiquity to the most recent scientific insights.
Notwithstanding its somewhat daunting title, the lecture drew an enthusiastic sellout audience to the Tempe Center for the Arts. Krauss took the stage for this, the 2017 ASU Origins inaugural lecture, introducing his friend and colleague of more than 30 years and ticking off a few of Wilczek’s achievements over the course of an exceptionally creative and varied career in physics.
At the age of 21, Wilczek, then a student at Princeton, switched fields from mathematics to physics and wrote a groundbreaking thesis on a topic for which he would be awarded the Nobel Prize some 30 years later. His work unveiled a property known as asymptotic freedom, a crucial feature of quantum chromodynamics, the theory describing nuclear interactions between quarks and gluons. As Krauss noted, Wilczek has also made seminal contributions to cosmology and the physics of materials.
Indeed, Wilczek began his lecture by speaking of the profound analogy between materials and vacuum. What our naked senses perceive as empty space turns out to be a riotous environment of virtual particles fluorescing and dying away on extremely small scales of space and time, as well as fog-like fields and condensates, which permeate all space and dictate the properties of elementary particles.
To give an analogy for this perplexing new picture of reality, Wilczek asks us to imagine intelligent fish in a world surrounded by water. Such creatures would perceive the water surrounding them as their version of empty space or a vacuum. “The big idea I want to convey is simply this: We’re like those fish,” he said. What our senses perceive as empty space is better understood as a substance, a material.
Just as the water-based world of the intelligent fish can change its state to ice or steam, our own vacuum may be capable of similar phase transitions. One such transition may have given birth to our universe, some 13 billion years ago — a concept explored in great detail in Krauss’ primer on the vacuum: “A Universe From Nothing: Why There is Something Rather than Nothing” (Atria Books, 2013).
Other phase transitions from initial quantum vacuum states may give rise to alternate universes, which could sprout into existence and might possess unique and unfamiliar physical laws determined by their initial vacuum states. These candidates of what has been termed the multiverse could have physical laws that are hostile to conventional matter. Such stillborn universes would be devoid of stars, galaxies and any forms of life, yet they could nevertheless exist.
Wilczek laid out a few historical milestones on the road to the concept of the vacuum as a material entity. In 1905, Einstein brought us the revolutionary idea that light has a particle-like nature whose energy is contained in discreet packets or photons. A lesser-known, though equally critical, breakthrough was Einstein’s discovery of vibrations in crystals, known as phonons, which share a number of crucial properties with photons. Wilczek proposes that the inhabitants of a world based in silicon would identify phonons as elementary particles. By the same reasoning, our own elementary particles may be similarly understood as small excitations in the material of empty space.
You are here! This animation shows the convulsive activity of the quark-gluon field. In the current description of reality, every region of empty space seethes with such fields, which dictate the behavior of matter and, in our own case, make up the foundations of a universe conducive to stars, planets and life. To give a sense of the scale of this field, the activity represented in the animation occurs at a million billion billion frames per second within a region of space just a few million-billionths of a meter across. Created by Derek Leinweber, Centre for the Subatomic Structure of Matter (CSSM) and Department of Physics, University of Adelaide, Australia
The discussion brought Wilczek to one of the foundational questions about space, namely, the existence of a space-filling medium through which sound waves, light or elementary particles could travel. This medium, known as the ether, had existed in the philosophies of earlier thinkers like Aristotle and Descartes but was radically purged from the scene by the mechanics of Isaac Newton, whose enormous success in calculating the movements of celestial bodies seemed to settle the matter, at least for a time.
There were glaring problems, however, which Newton recognized but was unable deal with. The most vexing was how a force like gravity could reach out through empty, etherless space to affect massive objects like stars and planets and do so instantaneously. If this perplexing “action at a distance” troubled Newton, it positively obsessed Albert Einstein, whose radical solution to the problem of gravity is codified in his general theory of relativity — one of the most astonishing insights into the nature of reality ever conceived.
Even before Einstein, however, some physicists made bold efforts to reintroduce the concept of the ether. They chafed at the notion that space was an empty stage on which matter danced and performed, as Newton envisioned it.
The brilliant 19th-century Scottish physicist James Clerk Maxwell revived the concept of the ether, describing space-pervading fields to explain the behavior of electricity and magnetism. His complex model was not only aesthetically and intellectually satisfying, it held for Maxwell — a devout Protestant — religious significance as well, as it demonstrated that every scintilla of the universe was suffused with the presence of the Creator. As Maxwell wrote: “The vast interplanetary regions will no longer be regarded as waste places in the universe, which the Creator has not seen fit to fill with the symbols of His kingdom.”
Initially, Einstein disputed this idea, insisting the ether was unnecessary, though later he would admit that “more careful reflection teaches us … that the special theory of relativity does not compel us to deny the ether.” Indeed, Einstein’s concept of space-time, introduced in his general theory of relativity, may be considered the ultimate ether — a highly dynamic medium whose warps, twists and bends account for the force we identify as gravity — “an ether, if ever there was one,” as Wilczek says.
More recently, science has discovered that the material of space-time can also ring, as the world witnessed on Sept. 14, 2015, at 5:51 a.m. EDT, when a pair of instruments known as LIGO detected gravitational waves — powerful ripples in space-time, born of the merger of two black holes.
Following his lecture, Wilczek expanded on a number of central themes in a discussion with Krauss. They traded ideas about how our new understanding of the cosmos can also inspire humans to transcend passive observation and become creators of new universes, through the intelligent manipulation of material substrates.
For example, new two-dimensional materials like graphene (a single layer of carbon atoms) can give rise to unusual memory-bearing particles known as anions, which may one day find their way into quantum computers. Time crystals — bizarre entities inside of which time flows in circles — were also mentioned. Time crystals were originally theorized by Wilczek but have recently been shown to exist.
In final remarks, Krauss and Wilczek examined questions of dark matter, dark energy and the prospects for physics beyond the standard model, science’s most successful description to date of the fundamental particles and forces that are the building blocks of reality. Despite the enormous insights produced by contemporary physics, current descriptions still leave some vital questions tantalizingly out of reach. Both speakers cited the knowledge we have gained and the vast mysteries still confounding us as twin aspects of life’s inexhaustible beauty.