Saturday, April 27, 2013

On Lee Smolin's "Time Reborn"

Below is Lee Smolin's summary of his new book Time Reborn. (See Peter Woit's critic of the book or Smolin's article in New Scientist which is included at the end of this post for those readers that don't subscribe to New Scientist.)

Smolin: "
(1) Whatever is real in our universe is real in a moment of time, which is one of a succession of moments.
(2) The past was real but is no longer real. We can, however, interpret and analyze the past, because we find evidence of past processes in the present.
(3) The future does not yet exist and is therefore open. We can reasonably infer some predictions, but we cannot predict the future completely. Indeed, the future can produce phenomena that are genuinely novel, in the sense that no knowledge of the past could have anticipated them.
(4) Nothing transcends time, not even the laws of nature. Laws are not timeless. Like everything else, they are features of the present, and they can evolve over time.

The problem with Lee Smolin's conclusions (especially conclusion #4) is that once you state that "the laws of nature transcend time," then you destroy any attempt at rationality. For example, how does one make predictions if the laws of nature transcend time? In general, I think that the argument that the laws of physics can evolve randomly is just silly because one has to explain why the laws of physics (such as gravity) haven't changed over the last billion or so years. (For example, the gravitational force didn't change from inverse squared to inverse or inverse cubed...or else the solar system wouldn't have been stable.)

It's not that hard to introduce time into the laws of just need one of the forces of nature to be time asymmetric. My personal belief is that time is intimately associated with the weak nuclear force because, by including the weak nuclear force, we now have a force of nature that is not time-reversal symmetric. In fact, there is exactly one parameter in the CKM matrix that describes this asymmetry. (Had there been two or more independent parameters in the CKM matrix that are time asymmetric, then there could have been some weird worlds with multiple axes that expand or contract.)

But Lee Smolin only discusses the weak nuclear force once in the book.

"The Standard Model of Particle Physics is almost time-reversible but not fully so. (There is one mostly inconsequential aspect of the weak nuclear interaction that does not reverse.)" (pg52)

Smolin runs around the time-reversibility of the known laws of physics by saying the the laws of physics can change in time. Time (for Smolin) is therefore just an artifact of the changing laws of physics (of course Smolin provides no evidence for time changing laws of physics.) So, Smolin is basically ignoring the most important aspect of the universe for life: the weak nuclear force is space, charge and time asymemtric. Without this crucial aspect of the world, then (1) there would have been equal numbers of particles&anti-particles, (2) there would have been no difference between left&right, and (3) there would have no difference between past and present.

I think that what we (physicists) should be focused on studying how the weak nuclear force introduces this asymmetry of space, time, and charge. We are so used to thinking in terms of time-reversible equations of motion that I think that we've become ingrained in thinking that symmetries of motion are constant, and can't increase. But what if the equations of motion (when including the weak nuclear force) can increase the symmetries of motion but can't decrease the symmetries of motion (i.e. the weal nuclear force acts as a symmetry generating machine.)

In the Earth/Sun system (treating only gravity), there are certain symmetries of motion, such as (1) a mirror symmetry about the plane of motion, (2) a time-reflection symmetry, and (3) a mirror reflection symmetry plane through the objects that rotates as the Earth/Sun orbit their center of mass. But the number of symmetries doesn't increase with stays exactly the same.

But with the weak nuclear force, we can increase the symmetries of motion. For example, with the weak nuclear force, we can generate large quantities of neutrinos. When we generate large quantities of new particles, we can increase the number of permutation symmetries between particles. This increases the symmetries of motion. For example, the maximum number of symmetries in the universe would (likely) occur when all energy is in the form of low energy photons and neutrinos. There is nothing "random" about increasing the number of permutation symmetries. Once you reach the point where all energy is in the form of low energy photons and neutrinos, you can't "randomly" go back to the Big Bang (where all of the energy is in the form of a few really heavy quarks and high energy photons.) This would require decreasing the number of symmetries (especially permutation symmetries.)

The weak nuclear force is the "weirdest" of the forces of nature because it is space (P), time (T) & charge (C) asymmetric; it is also CP asymmetric (though likely not CPT asymmetric); and it seems capable of increasing the number of permutation symmetries in the universe.

So, hopefully you all can see that there is a way out of the question of why time exists without having to resort to laws of physics that change with time. And on that note, I've posted below Lee Smolin's article in New Scientist in which he attempts to summarize his book. Note his statement in the article that the laws of physics can "evolve." In my opinion, this is pure quackery.

It's time physics recognised that time is real
We all feel the forward march of time, but the laws of physics tell us it is an illusion. A radical rethink is needed
THE aim of science is to explain all the features of the universe, from the mass of the Higgs boson to the fact that the night sky is filled with stars. Perhaps the most obvious feature of all is that time in our universe only travels in one direction: forwards. We remember the past but not the future, and most things about our world are irreversible, from a glass of spilt milk to the birth of a child.
No single feature of our universe is more in need of explanation than the forward march of time, yet physics and cosmology have so far failed to explain this basic fact of nature. It's time for a radical approach. We need a new starting point for explaining the directionality of time.
Physicists speak about arrows of time. One such arrow is visible in the light we see coming to us from distant stars: all of it comes from the past, showing us what they were once like, with none coming from the future. This is mysterious because the equations we use to describe light are unchanged if we reverse the direction of time. Consequently these equations have two solutions: waves that propagate energy and information from the past to the future, and waves that do the reverse, moving backwards in time.
But nature only seems to use the first kind. This is called the electromagnetic arrow of time. To explain it we have to impose a harsh condition on the theory of electromagnetism, which rules out most of its solutions, leaving only those that propagate from past to future. Within the big bang cosmology this amounts to imposing the condition that there were no light waves travelling freely at the first moment of time. But this drastic condition requires explanation and so far there is none.
The best known arrow is the thermodynamic arrow of time, which refers to the irreversibility of processes such as broken porcelain. To explain this we invent a quantity that increases whenever an irreversible process happens – entropy – which the second law of thermodynamics asserts can only increase. In the 19th century, Ludwig Boltzmann proposed that the second law can be understood as a consequence of the hypothesis – then unproven – that matter is made of atoms. Entropy, Boltzmann proposed, is a measure of the disorder of atoms, and its tendency to increase is a consequence of the observation that random processes are more likely to introduce disorder than order.
Boltzmann's atomic hypothesis was correct. Yet he faced critics who were quick to point out a paradox lurking in his reasoning. The laws that describe the motion of atoms are reversible in time. So how come the second law of thermodynamics isn't? The closest we can get to a time-symmetric form of the second law says that if we find a system with low entropy it is most probable that entropy will increase in the future and that it was higher in the past.
Yet this still doesn't explain why our universe has such a strong arrow of time. As physicist Roger Penrose pointed out in 1979, the only thing that can explain the thermodynamic arrow of time is that the entropy of the initial conditions of the universe was very low. But this is extremely improbable too.
So both the electromagnetic and thermodynamic arrows of time require that the initial conditions of the universe were extraordinarily special. But why is this? The only way we can explain the time asymmetry of our universe is some mathematical trickery which involves choosing special solutions to time symmetric laws. Which is to say it is not explained at all.
I would like to propose a radically different approach. In my book Time Reborn I take up Penrose's suggestion that the truly fundamental laws are time asymmetric, making time's irreversibility a fundamental condition of the universe. The laws we had thought fundamental up until now – general relativity, quantum theory and the standard model – must then be approximations of a more fundamental time-asymmetric law which would explain the otherwise improbable initial conditions.
This proposal has huge implications for the question of the nature of time. One big question is whether time is fundamental or an illusion. Many of my fellow theorists argue that it is an illusion. In accordance with this view, there are proposals for fundamental laws that don't mention time at all. Physicist Julian Barbour argued in his book The End of Time that time disappears completely from the fundamental theory that merges quantum theory with cosmology. I hold a contrary view that time is real, which means that the distinction between the past and the future must be fundamental as well. I have been developing this view in collaboration with the Brazilian philosopher Roberto Mangabeira Unger.
It might be a funny thing to say, but the idea that time is real requires a radical departure from the standard paradigm of physics. This is because the effect of 400 years of the development of physicists' conception of nature has been to devalue time and ultimately to remove it from the fundamental aspects of nature. Ever since the era of René Descartes in the 17th century, time has been represented as if it were just a dimension of space. This culminated in the "block universe" conception of general relativity in which the present moment has no meaning – all that exists is the whole history of the universe at once, timelessly. When laws of physics are represented mathematically, causal processes which are the activity of time are represented by timeless logical implications.
But the real universe has properties which are not representable by any fact about a mathematical object. One of them is that there is always a present moment. Mathematical objects, being timeless, don't have present moments, futures or pasts. However, if we embrace the reality of time and see mathematical laws as tools rather than as mystical mirrors of nature, other stubbornly inexplicable facts about the world become explicable, such as the laws themselves. If the laws are just true, timelessly, there is no way, within science, to explain why the particular set of laws we observe are the true ones. But if time is real, laws can evolve and hypotheses about the process of evolution become testable, and hence offer the basis for a scientific explanation of why the laws hold.
Can it work to reverse the standard idea in which irreversible phenomena emerge from reversible laws? In work in progress with the cosmologist Marina Cortês at the University of Edinburgh, UK, we have constructed simple models of systems governed by rules which are irreversible in time, from which emerge approximately time-symmetric behaviours. These models may be simple, but they are a first step to developing a new approach to the arrows of time.
The idea that nature consists fundamentally of atoms with immutable properties moving through unchanging space, guided by timeless laws, underlies a metaphysical view in which time is absent or diminished. This view has been the basis for centuries of progress in science, but its usefulness for fundamental physics and cosmology has come to an end due to its inability to answer key questions such as what chose the laws of nature or why the universe is so asymmetric in time. Some people have confused the reliance on timeless laws with science itself, but this is wrong.
A new scientific world view is emerging based on the principles that time is real, laws evolve and irreversibility is fundamental. It is already clear this view has the capacity to explain – in ways that are testable by experiment – basic facts about our universe that otherwise appear to be inexplicable.


Lee Smolin is a theoretical physicist at the Perimeter Institute in Waterloo, Canada, who focuses on quantum gravity. His latest book is Time reborn: From the crisis in physics to the future of the universe

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