Time Reborn

By James Gleick
The New York Review of Books, June 6, 2013

Edited by Andy Ross

Lee Smolin aims to convince us that time is real: "Not only is time real, but nothing we know or experience gets closer to the heart of nature than the reality of time."

Thus he contradicts Einstein. The past is gone and the future is open. Things change, and time is our name for the reference frame in which we organize our sense that one thing comes before another.

Clocks measure time. In fact you can define time as what clocks measure. For Newton, the cosmic clock ticks invisibly and inexorably, everywhere the same. He needed absolute time and space to define his terms and express his laws. With them he built an entire cosmology.

Newton reified time. When a scientist records the position of the Moon, the result is a table of numbers representing both space and time. Representing the orbit of the Moon in Cartesian coordinates makes it a curve in space and time, a mathematical object in a timeless configuration space.

Smolin: "The method of freezing time has worked so well that most physicists are unaware that a trick has been played on their understanding of nature."

We have inherited the idea of timeless truths from Plato. A leaf fades from green to brown, but greenness and brownness are immutable. Here in the sublunary world everything is subject to change and nothing is perfect. But in the mathematical world, truth exists outside of time.

Smolin: "Whatever we most admire and look up to — God, the truths of mathematics, the laws of nature — is endowed with an existence that transcends time."

We reenter time when we accept uncertainty. The prototype for thinking in time is Darwinian evolution. Natural processes lead to genuinely new organisms, new structures, new complexity, and new laws of nature. All is subject to change. Laws are not timeless.

The faith in timeless laws of nature is part of the appeal of the scientific enterprise. It is a vision of transcendence akin to the belief in eternity that draws people to religion. The explanations for our world lie in another, more perfect world. But perhaps timeless laws of nature are no more real than perfect circles.

The cosmic clock of Newton (or God) ticks no more. Einstein broke it. He did this by pointing out that every observer has a reference frame, and each reference frame includes its own clock. Simultaneity is not meaningful. Now is relative. No observer has access to the now of any other observer. Everything that reaches our senses comes from the past.

Thus space and time are wedded. One cannot be measured independently of the other. Spacetime becomes indispensable. Time is frozen into the 4D block. Only to the gaze of my consciousness, crawling upward along the world line of my body, does a section of the world come to life as a fleeting spatial image that continuously changes in time.

Smolin: "Everything we experience, every thought, impression, action, intention, is part of a moment. The world is presented to us as a series of moments. We have no choice about this. No choice about which moment we inhabit now, no choice about whether to go forward or back in time. No choice to jump ahead. No choice about the rate of flow of the moments. In this way, time is completely unlike space."

For space, the deeper reality is a network of relationships. Things are related to other things. They are connected, and the relationships define space. Smolin believes that time is fundamental but space an illusion. The real relationships that form the world are a dynamical network. The network can and must evolve over time.

Time runs one way. The universe grows ever more structured and complex, in apparent contradiction to the second law of thermodynamics. Smolin says the second law of thermodynamics applies to any isolated system within the universe but not to the universe as a whole. In a universe where time is real and fundamental, complexity evolves and systems become more organized.

By declaring space to be secondary, Smolin avoids contradicting general relativity. If size and location are relative, then time doesn't need to be. A preferred global time extends throughout the universe and defines a boundary between past and future. Now need not be the same to different observers, but it retains its meaning for the cosmos.

Smolin: "The world remains, always, a bundle of processes evolving in time."

AR This view of time is strongly reminiscent of that I developed in my 2006 paper "About time" (chapter 13 of my book Mindworlds).
In fact I sent a copy of the paper to Smolin, but he didn't reply. Perhaps this new position is the result.
 

Physics: The Limits 1

By David J. Gross
Wired, June 2013

Edited by Andy Ross

When I was a graduate student in California, experimentalists were constantly discovering new atomic particles and quantum field theory was failing to explain them. For quantum mechanical theories to be consistent with the constraints of special relativity, we picture the interactions between charged particles as flowing through a quantum mechanical field, a spatial field. Ripples in the field can be treated as electromagnetic waves or radiation or light. And these ripples can also be described as particles that transmit the forces of nature through space.

When I was at Berkeley, the framework of quantum field theory could calculate the dynamics of electromagnetism. It could roughly describe the motion of the weak nuclear force, radiation. But it hit a brick wall with the strong interaction, the binding force. The experimenters were banging protons, hoping to find direct evidence of quarks. Protons are bags of quarks, but there is no such thing as an individual quark. We glimpse them only indirectly, by measuring the energies and momentums emerging from proton collisions.

Using quantum field theory, my colleagues and I predicted certain patterns in the proton collision detritus. To our surprise, the calculations showed that the invisible quarks are not purely mathematical abstractions, but particles that can move about freely inside the proton when they are close together. And we learned that as the distance between the quarks increases, the force binding them together also increases. It was the only explanation of the strong force that could be calculated. The Standard Model is a very precise, reductionist theory.

Physics explains the world around us with incredible precision and breadth. But further explanation is highly constrained by what we already know. String theory is a model, a framework, part of quantum field theory. And there are frustrating theoretical problems in quantum field theory that demand solutions. Our model of spacetime might be a derived concept. It seems to emerge from a more fundamental physical process that informs the mathematical pictures drawn by string theory and quantum field theory.
 

Physics: The Limits 2

By Margaret Wertheim
Aeon, June 2013

Edited by Andy Ross

Things at the subatomic level are simultaneously particles and waves. They appear to us as two different categories of being. Physics itself is riven by the competing frameworks of quantum theory and general relativity, whose differing descriptions of our world mirror the wave-particle tension. Where quantum theory describes the subatomic realm as a domain of individual quanta, all jitters and jumps, general relativity depicts happenings on the cosmological scale as a stately flow of smooth spacetime.

Relativity and quantum theory each pose philosophical problems. Are space and time fundamental qualities of the universe, as general relativity suggests, or are they byproducts of something even more basic, something that might arise from a quantum process? Looking at quantum mechanics, huge debates swirl around the simplest situations. The dilemma posed by wave-particle duality is the tip of an epistemological iceberg on which many ships have been broken and wrecked.

The many-worlds interpretation of quantum theory proposes that every time a subatomic action takes place the universe splits into multiple copies, with each new world representing one of the possible outcomes. The equations are taken to be the fundamental reality. The fact that the mathematics allows for gazillions of variations is seen to be evidence for gazillions of worlds.

This kind of reification of equations strikes some humanities scholars as childishly naive. At least it raises questions about the relationship between our mathematical models and reality. Many important discoveries have emerged from revelations within equations, but it is hard not to feel skeptical about the idea that the only way forward now is to accept an infinite cosmic landscape of universes that embrace every conceivable version of world history.

The late British anthropologist Mary Douglas studied taboo rituals that deal with the unclean. All languages parse the world into categories, and all category systems contain liminal confusions, and she proposed that such ambiguity is the essence of what is seen to be impure or unclean.

Cultures can be categorized in terms of how well they deal with linguistic ambiguity. Some cultures accept the limits of their language by understanding that there will always be things that cannot be cleanly parsed. Others become obsessed with ever finer levels of categorization. Perhaps what we are encountering here is not so much the edge of reality, but the limits of the physicists’ category system.

According to Galileo Galilei and others, nature was a book written by God, who had used the language of mathematics because it was transcendent and timeless. But to articulate a more nuanced conception of what physics is, we need to abandon the loaded metaphor of the cosmic book and focus on the creation of physics as a science.

Much of physics involves finding ways to measure physical phenomena. Physics is an ever more sophisticated process of quantification that multiplies and diversifies the ways we extract numbers from the world, thus giving us the raw material for our quest for patterns or laws.

To a large degree, progress in physics has been made by slowly extending the range of phenomena we can measure. The discovery of electromagnetic waves was a triumph of quantification. James Clerk Maxwell showed that magnetic and electric fields were linked by a precise set of equations that enabled him to predict the existence of radio waves. The quantification of these fields has led to the whole world of modern telecommunications.

Light acts like a wave, yet experiments show that under many conditions it behaves like a stream of particles. And particles of matter can sometimes behave like waves. Electrons are clearly particles, yet in orbiting around atoms they behave like waves. Wave-particle duality is a core feature of our mathematical descriptions of our world, but the universe remains whole.

Returning to quantum theory and relativity, subatomic particles can be entangled. Once particles are entangled, what we do to one immediately affects the other, contradicting a basic premise of special relativity. Entanglement suggests that either quantum theory or special relativity, or both, will have to be rethought. We are in a mire of contradiction and need some new physics.

Subjective experience might not be amenable to mathematical law. Many paradoxes relating to relativity and quantum theory focus on the issue of time, and our mathematical descriptions of time conflict with our lived experience of time. Lee Smolin says we must change them.
 

Space-Time Divorce?

By Anil Ananthaswamy
New Scientist, June 2013

Edited by Andy Ross

Relativity and quantum mechanics differ radically in form and content. Sean Carroll: "One of the tensions comes from the fact that the relation between space and time is very, very different in general relativity than it is in quantum mechanics."

In 1905, Einstein wove space and time into the 4D fabric of spacetime. Here and now mean different things to people moving at different speeds. In 1916, he said massive objects curve spacetime, and measurements of lengths and times depend on the strength of the prevailing gravitational field.

In quantum mechanics, an object's state is described by a wave function in an abstract Hilbert space that encompasses all the possible states of the object. The Schrödinger equation tells us how the wave function evolves in time, moving from one state in its Hilbert space to another. Time is not part of the Hilbert space. We measure the evolution of a quantum state to the beat of an external clock.

The status of space depends on what you measure. The wave function of an electron orbiting the atomic nucleus has the spatial property of distance from the nucleus. But the wave function describing the quantum spin of an isolated electron has no mention of space. Abhay Ashtekar: "This is one sense in which there are attributes of physical systems which don't refer to space, but which change in time. One could say that for those attributes, time is more fundamental than space."

Relativity says space and time together form the fabric of reality. Quantum mechanics treats time and space differently, with time occasionally seeming more fundamental.

String theory needs at least 10 spacetime dimensions to be mathematically consistent. But according to Juan Maldacena's "anti-de Sitter/conformal field theory correspondence" (AdS/CFT), you can sometimes swap the 10D representations of string theory that include gravity for a more tractable 4D representation that dispenses with gravity.

The time dimension seems unchanged, but space is transformed: a point in the 4D world translates to multiple points within the 10D world. Carroll: "In this example it seems perfectly clear that space is not fundamental. It is very, very different depending on what description of the world you are using."

Joe Polchinski has doubts. The AdS/CFT correspondence is only valid for a negatively curved spacetime with hyperbolic geometry. No one has yet worked out an AdS/CFT-like correspondence for our spacetime. Also, if you want to let information escape from a black hole, quantum theory says a "firewall" of high-energy radiation appears just inside the event horizon.

General relativity says anything going past a black hole's event horizon should encounter nothing but gently curved spacetime. If you want to keep quantum mechanics intact and avoid a firewall too, something else must give, such as the limiting speed of light. Steve Giddings: "This does point to the fact that we may be missing something in our conceptual description."

Polchinski's team turned to Maldacena's conjecture. They put a black hole into a volume of negatively curved spacetime. There the 4D physics of an observer on the surface of the volume should be able to account for the physics of an observer deep inside the 10D bulk of a black hole. Instead, what the two observers see is described by two different quantum theories. Polchinski: "I want to shake people's faith in AdS/CFT."

But string theory is just one approach. Loop quantum gravity arose when Ashtekar rewrote Einstein's equations of general relativity using a quantum mechanical framework. Working with Lee Smolin and Carlo Rovelli, he arrived at a picture in which spacetime is smooth down to the Planck scale, where you see loops of gravitational field lines.

Loop quantum gravity provides a different perspective on space and time. Chunks of space, one Planck length to a side, appear first in the theory, while time pops up only later as an expression of the relationships between other observable physical properties. Ashtekar: "Somehow space might emerge first, and time is born by observing relations between various physical subsystems."

Giddings has been trying to describe a black hole using a network of interconnected Hilbert spaces that do not presuppose the existence of space or time. He showed last year how time can emerge relationally. A concept of space also emerges from his calculations.

Polchinski: "The direction that light rays travel in is neither space nor time. We call it null. It's on the edge between space and time. A lot of people have this intuition that in some sense the existence of these null directions might be more fundamental than space or time."