Monday, October 21, 2013

"Time Reborn" by Lee Smolin

Einstein removed the idea of Time from physics, rendering it an artifact of our conscious. Professor Smolin proposes a different approach to the definition of reality with Time as a real thing, and Space is an artifact.

Science depends on predictions and repeatable, testable, falsifiable results. When assembling a theory that encompasses the entire universe you have a problem with repeatability—a single universe limits your sample size. In addition, any “lab” experiment we do will only be on an “isolated system”, while the real world is an “open system”. So those experiments test only approximations.

The two predominant current theories in Physics are String Theory and Quantum Mechanics. Are they enough to explain the universe? That is, can they “scale up” to become Theories of Everything?

From String Theory it can be derived that for a finite number of universes (around 10500) the cosmological constant is positive. In our universe the cosmological constant is positive, so we could exist in any one of those universes with some random probability. This result is pretty much what we expect from String Theory: useless confirmation of what we already know, with no prediction and no chance of falsification. However, a few years ago it was also derived from String Theory that when you figure out how many universes would have a negative cosmological constant, the number is infinite. Simply by random chance a universe would have an infinitely greater chance of a negative constant. So either we are extremely lucky, or String Theory is wrong.

Quantum Mechanics is basically a method of conducting experiments—the choices the experimenter makes influences the reality of the system being studied. But at the cosmological scale, who is the observer?

We get three clues about nature from Quantum Physics: incompatible questions (i.e., simultaneously measure position and momentum), entanglement (pairs of quantum systems can share properties while each system remains individually indefinite – you can ask a question about the pair that has an answer but the related question to one of them does not), and nonlocality (as long as neither “half” of an entangled system interacts with another system, each can separate and move a great distance apart).

Both of these are “approximate theories” in the sense that they “truncate” how “accurate” they are. For example, Newtonian Mechanics is an approximate theory and as far as it went, an “effective” theory.

What must be true for a Cosmological Theory:
·         Any new theory must contain what we already know about nature
·         The new theory must be scientific (testable, etc)
·         The new theory should answer they “Why these laws” question. In particular, the values of fundamental constants
·         The new theory should answer the “Why these initial conditions” question. That is, why our universe has its properties rather than those of an alternate universe
·         The new theory should not have to assume symmetries nor conservation laws
·         Principle of explanatory closure – no chain of explanation points outside the universe
·         Principle of sufficient reason – there should be an answer to any reasonable question we ask – does the new theory increase the number of questions we can answer
·         Principle of reciprocal action – nothing in the universe acts on other things without itself being acted upon
·         Principle of No Isolated Systems – there’s no such thing as a system in nature that’s isolated from influence by the rest of the Universe
·         Identity of the indiscernibles – two things that have the same relationships with everything else in the universe must actually be the same thing – this implies there can be no symmetries
·         Physical variables should describe evolving relationships between dynamical entities. There should be no fixed-background structures (including fixed “laws of nature”)
·         We can create (from entanglement) novel properties in nature
·         Principle of Precedence – the future (that is, the way the universe is expected to behave) resembles the past (i.e., physics is case-law)
·         Conway/Kochen theory of quantum “free-will”– for entangled, then separated systems that are then tested by experimenters who can “pick” their measurements, the “response” of those systems is also “free”
·         Principle of maximal freedom – quantum mechanics describes a universe in which you can make probabilistic predictions, but those systems have the maximal freedom as would be expected with probabilistic predictions
·         Principle of before and after – if you make a prediction and then test it, implicitly time exists to distinguish between before the experiment/test and after

Time is real
The artifacts of Quantum Mechanics, entanglement and non-locality, indicate it is a truncation applicable to small, isolated systems. Restoring the reality of time makes a new formulation of Quantum Mechanics possible.

We cannot locate an object at a point unless we have some way to specify that place. If there were two identical objects then there must be two identical places in the universe. Similarly there can not be two events in spacetime that have exactly the same observable properties. Thus every moment of time, and every place at every moment, is uniquely distinguishable.

Different “kinds” of time:
·         Cosmological arrow of time – universe is expanding
·         Thermodynamic arrow of time – left to their own, things become more disordered
·         Biological arrow of time – living things are born, grow up, and die
·         Electromagnetic arrow of time – what we “see” is the world from “the past” (light is “old” when it gets to us)
·         Gravitational arrow of time – gravity waves move to their effects take time to propagate
·         Black-hole arrow of time – absence of black holes in the early universe
What if “local space” is not what you can walk to next door, but what is “on the other end of your phone”? This is the idea of Disordered Locality and the Non-local link, in which Space is an emergent phenomenon, as seen in non-locality and entanglement.
At the fundamental level of description, at which instead of “space” there is a network of interactions with everything potentially connected to everything else, then quantum theory and space emerge together.

Summary of differences:
Space is Real
Time is Real
Time is an illusion. Truth and reality are timeless
Time is the most real aspect of our perception of the word. Everything that is true and real is such in a moment that is one of a succession of moments
Space and geometry are real
Space is emergent and approximate
Laws of nature are timeless and inexplicable, apart from selection by the anthropic principle
Laws of nature evolve in time and may be explained by their history
The future is determined by the laws of physics acting on the initial conditions of the universe
The future is not totally predictable, hence partly open
The history of the universe is, in all its aspects, identical to some mathematical object
Many regularities in nature can be modeled by mathematical theories. But not every property of nature has a mirror in mathematics
The universe is spatially infinity. Probabilistic predictions are problematic, because they come down to taking the ratio of two infinite quantities
The universe is spatially finite. Probabilities are ordinary relative frequencies
The initial singularity is the beginning of time (when “time” is defined at all) and is inexplicable
The Big Bang is actually a “bounce” which is to be explained by the history of the universe before it
Our observable universe is one of an infinite collection of simultaneously existing of unobservable universes
Our universe is a stage in a succession of eras of the universe. Fossils, or remnants, of previous eras may be observed in cosmological data
Equilibrium is the natural state and inevitable fate of the universe
Only small subsystems of our universe come to uniform equilibria; gravitationally bound systems evolve to heterogeneous structured configurations
The observed complexity and order of the universe is a random accident due to a rare statistical fluctuation
The universe naturally self-organizes to increasing levels of complexity, driven by gravitation
Quantum mechanics is the final theory and right interpretation is that there are an infinity of actually existing alternative histories
Quantum mechanics is an approximation of an unknown cosmological theory

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