Monday, February 12, 2007

Time Travel

It is sometimes said amongst physicists that we should take the predictions of our theories seriously, even when those theories predict seemingly unlikely results. For example, the wave theory of light predicted that a circular obstruction placed in front of a source of light casts a circular shadow, with a small bright spot of light at the center of the shadow. This bright spot seemed an unlikely prediction and was taken at first to indicate that the wave theory of light was false. However it wasn’t long before “Fresnel’s bright spot”, as it was called, was observed experimentally. Another well known example of an unlikely prediction was Einstein’s discovery that his gravitational field equation, when applied to the cosmos, did not admit static solutions; that is, it only allowed an either contracting or expanding universe. Einstein didn’t believe this result because it seemed to him that the universe was patently static and so he introduced a term into his equation (the cosmological term) to launder out a prediction that subsequently proved to be correct; we now believe the universe is far from static – as the well known cliché goes, the universe is expanding. It seems that once we believe we have twigged the logic behind the physical world we must follow that logic through and trace it to its many inexorable conclusions. Often we find that the results of that logic are against all expectation, but so often careful observation has shown the expectations to be wrong and the logic right.

So the moral of the story, it has been suggested, is that we should take seriously the laws we believe we have discovered. But not too seriously is my suggestion, for there is a balance to kept here. Consider, for example, Hooke’s law, a law telling us how materials deform when forces are applied. This simple law states that the deformation of materials is proportional to the magnitude of the force applied to them. Basically Hooke’s law gives us a straight-line graph of deformation against force and the validity of this graph can be experimentally tested, and lo and behold experimental plots fall more or less on the predicted straight line. If one takes something like the compression of a spring one finds that this compression obeys Hooke's law. However if we extrapolate the straight line graph of proportionality we find that it passes through the origin, which at once presents us with a problem: That is, Hooke’s law predicts that a finite force is capable of compressing the length of the spring to zero. Obviously this is wrong, and thus it is clear that Hooke’s law is a law applying only within limits. So, the moral of story is yes, let’s take the logic of our laws seriously but not too seriously, otherwise we might be in for a shock.

It may be objected here that Hooke’s law is not truly fundamental; that is, unlike the deep laws of physics which it is assumed have some kind of all-embracing applicability, Hooke’s law is clearly not fundamental. Trouble is, we can’t yet claim to have grasped what is truly fundamental. The difficulties of unifying Einstein’s theory of gravity with Quantum Theory does hint that neither theory is absolutely fundamental, but like all theories so far both have limits to their application and await an underlying theory of greater applicability. Note that I am careful to say here “of greater applicability” rather than “of all-embracing applicability” as I feel we should never be too presumptuous in our beliefs about having reached some kind of absolute fundamental level.

* * *

There is clearly a balance to keep here between seriousness and not-too-seriousness, but it seems we are passing through times when physics itself is in danger of loosing its serious status altogether, and this in part may be down to over-extrapolation-itus which leads to unlikely almost comical claims. In fact I recently dug out an old video recording of a Horizon program broadcast on BBC2 on the 18th December 2003 on the subject of time travel. The program was introduced as “.. sorting out science fiction from science fact.”.. and then “This is an unlikely tale about an unlikely quest. The attempt to find a way to travel through time. The cast is an unlikely one too. God, a man in a balaclava and a pizza with pretensions.” It then cut to a paranoiac Kurt Godel wearing his eye and mouthpiece balaclava which he may have worn because he believed there was a conspiracy against him. This was followed by a turquoise jacketed Professor Richard Gott of Princeton university who, as he waved his hand over a sliced pizza, solemnly declared “This is a tarm machine!” It was December 18th; April 1st was more than three months away, so the program wasn’t one of the BBC’s fools day broadcasts. So what was their excuse?

However, in spite of this bizarre beginning the program at first continued sanely enough with an account of the well-known Einsteinian type of time travel. You know the sort of thing; you leave Earth in a space ship and after a year traveling around the galaxy at near light speed you return to Earth and find that ten years have elapsed to your one-year. This is a well-established example of the “Rip Van-Winkle effect” and is not far removed from what happens when one experiences a period of unconsciousness and therefore is unaware of the passage of time as experienced by other people.

But backwards time travel is another matter. My own guess is that reverse time travel at will is impossible, but there are quite a few people out there who believe it is possible. So it was time to bring on the cheerful eccentrics, with their turquoise jackets, and paranoiac balaclavas. Professor Michio Kaku of the City University of New York prepared the way for us:

MICHIO: “Some people complain that we physicists keep coming up with weirder and weirder concepts, the reason is we are actually getting closer and closer to the truth. So if we physicists keep coming up with crazier and crazier ideas that’s because that’s the way the universe really is. The universe is crazier than any of us really expected.”
Ah! I get it! As Physics gets weirder and weirder we need weirder and weirder people to do physics, and you can’t get weirder than what now followed. The program then went to New Orleans and ferreted out an American writer called Patricia Rees who has written books on real life time travelers and who told Horizon that there are probably thousands of people doing time travel. She was in New Orleans to drop in on one of those thousands of time travelers who the program referred to as “a voyager in time called Aage Nost”. “Aage Nost claims to have his very own time machine,” said the narrator. Aage’s time machine had lights, wires, an electronic box of tricks, and two coils of wire - in other words all the things one expects a really serious time machine to have – at least in the movies. From what we saw of this time machine it looked a lot more plausible than Professor Gott’s pizza, but this machine is not for the fashion conscious because you had to wear it to work it - or at least you had to wear one coil on your head and hold the other in your hand. It looked a lot more fashionable than Kurt’s balaclava. Perhaps Aage should have built his coil into a balaclava and then the academic community might start taking him seriously. Anyway, by using this time traveling system Aage was able to tell us that in the fall of 2005 there would be an uprising in America and the military would install a new government. Did I miss that? I bet I'm in the wrong parallel universe. Shucks.

But the worst was yet to come, because we then moved onto the really serious scientists that, according Horizon, make Aage’s efforts look positively mundane. I was still trying to sort out science fiction from science fact when on came none other than the great Professor Frank Tippler who “by sheer coincidence” said the program, also lived in new Orleans. The reference to “sheer coincidence” was obviously sarcasm, because Horizon’s random sampling of the population of New Orleans clearly shows that it is full of serious Time Travelers, and this explains the apparent coincidence.

It became apparent that Tipler had revived an idea by the paranoiac Godel. Using Einstein’s equation Godel had shown that in a rotating universe time travel is possible. But it was pointed out by Frank that there was one problem here … wait for it … the universe isn’t rotating. Frankly I think Frank does have a point here because if the universe was rotating we would all feel rather dizzy. In fact the narrator put it quite subtly calling Godel’s idea “complete nonsense, for the universe we live in does not rotate”. Anyway, the brilliant Professor Tipler, suggested we simply use a much smaller spinning object, like a black hole or a spinning cylinder and he has done the necessary calculations to show that it is possible. My suggestion is that we use Frank’s arms, which revolve at great speed in opposite directions as he speaks. Problem solved.

The Turquoise Jacketed Professor Richard Gott of Princeton has other ideas,involving “cosmic strings” which Horizon pointed out “have never been observed in the real world, they're entirely theoretical”. But an undaunted Gott proceeded to show us how time travel is possible using these ontologically challenged entities. For this scene Gott was in pasta parlor and he was going to illustrate his point using one of the parlor dishes. Perfect I thought, if he is a string theorist he’s bound to order spaghetti. Wrong, he ordered a pizza, which goes to show that even string theorists have heard that spaghetti is not the only food on the menu. He then cut two slices out of the pizza, took a mouthful from a slice and then in thick bread muffled tones Gott explained his theory and ultimately uttered his famous line as his hand traced the circle of the pizza: “This is a Tarm machine!”. To prove the point he pulled out a fat comically proportioned toy space shuttle, which no doubt by sheer coincidence happened to be in the pocket of his renowned turquoise jacket. He demonstrated how the cuts in the pizza allowed his toy shuttle to make faster than light speed jumps in "space-tarm" which by extrapolating Einstein’s special theory of relativity for velocities greater than light leads to a violation of the normal sequencing of time and hence allows time travel. But there is one little snag here: As well as being based on entirely theoretical notions Gott also admitted. “[With] the tarm machine that I propose using cosmic strings, [if] you wanted to go back in tarm about a year, it would take half the mass of our galaxy”. No problem - At least in America where pizzas, like the one Gott was playing with, have galactic dimensions. Hey Richard, didn’t your Ma ever teach you not to play with your food? Just as well she didn’t, otherwise we wouldn’t have solved the time... sorry... tarm travel problem.

But there is one other spanner in the works. Because the time machines so far proposed work by cutting and warping space-time you cant go back to any time before the machine started to make these adjustments to space-time. Hence as Paul Davies pointed out on the program, if we want to go back in time to see the dinosaurs we would have to depend on “some friendly” alien lending us the time machine they made earlier, at least 65 million years earlier in fact. Once again, no problem! We know lots of friendly aliens out there, and Horizon reminded us of this by cutting to a scene from Dr. Who of invading daleks rasping out “Exterminate, Exterminate”. At this point I was having real trouble trying to sort out the science fiction from the science fiction.

* * *

After a show like this I was left wondering if anyone takes physics and physicists seriously anymore. Some of the physicists we met in this Horizon program came over as a set of good-natured brainy clowns, good for a laugh, but who are not operating in the real world: We needn’t listen to them accept perhaps to giggle at how these clever people have wormed their way into such a rarefied highfalutin world that the are of little relevance to our lives. Their time travel theories are no doubt an extremely clever albeit irrelevant lighthearted diversion, as clearly their ideas can not be implemented by any technology that is just round the corner. Bright beyond the ken of the average person they may be, but the compensating recourse to a simple almost child like humor in order to humanize them has the effect of making them even more remote. After all, playing with your food in a restaurant accompanied by a cutesy looking space shuttle does not come over as normal behaviour. And from my point of view with a little knowledge of physics, I can’t help feeling that we have here an example of the Hooke’s law fallacy: That is, by using a little over extrapolation all sorts of silly things can be proved as long as we can find the sufficiently brainy and silly people to prove them.

Having thoroughly lampooned physics and physicists it was now time for the Horizon program to move in and deliver the coup de grace for physics. It started quietly enough with Frank Tipler telling us about Moore’s Law of computing power, a law that states that every 18 months computer power doubles:

FRANK: “People realised that processing speed of computers was increasing exponentially, every year, every few years, every eighteen months the processing speed would double. … Imagine this occurring faster and faster. If that were to occur it would be possible to process an infinite amount of information”.

Yeah right Frank, using Hooke’s law I can predict that if I apply 100lbs of pressure on this spring here it will compress to zero and not only disappear (i.e. become invisible!) but might even assume a negative length, whatever that means. But OK Frank I’ll play the game; let’s imagine this extrapolation of Moore’s law for the sake of the argument. So where does it lead us? Prof David Deutsche from the center for quantum physics told us:

DAVID: “In the distant future simulating physical systems with very high accuracy so that they look perfectly real to the user of the virtual reality will become common place and trivial.”

And Dr Nick Bostrum of Oxford University continues the argument to its conclusion.

NICK: “So imagine an advanced civilisation and suppose that they want to visit the past it might turn out not to be possible to build a time machine and actually go back into the past, physics might simply not permit that. There is a second way in which they could get the experience of living in the past and that would be by creating a very detailed and realistic simulation of the past….. An advanced civilisation would have enough computing power that even if it devoted only a tiny fraction of one percent of that computing power for just one second in the course of its maybe thousand years long existence, that would be enough to create billions and billions of ancestor simulations. There would be a lot more simulated people like you than there would be original non-simulated ones. And then you’ve got to think, hang on, if almost everybody like me are simulated people and just a tiny minority are non-simulated ones then I am probably one of the simulated ones rather than one of the exceptional non-simulated ones. In other words you are almost certainly living in an ancestor simulation right now.”

David Deutsche gave us the implications for physics itself:

DAVID: “From the point of view of science it’s a catastrophic idea, the purpose of science is to understand reality. If we’re living in a virtual reality we are forever barred from understanding nature.”

And Paul Davies hints at the frightening philosophical specters that now haunt physics as a result:

PAUL: “The better the simulation gets the harder it would to be able to tell whether or not you were in a simulation or in the real thing, whether you live in a fake universe or a real universe and indeed the distinction between what is real and what is fake would simply evaporate away…..Our investigation of the nature of time has lead inevitably to question the nature of reality and it would be a true irony if the culmination of this great scientific story was to undermine the very existence of the whole enterprise and indeed the existence of the rational universe.”

Let me broach some of the cluster of philosophical conundrums raised by this embarrassing debacle that physics now faces.

Why should our concept of a simulated reality be applicable to the deep future? Doesn’t it rather presume that the hypothetical super beings have any need for computers? The existence of computers is partly motivated by our own mental limitations – would a super intelligence have such limitations? Or perhaps these simulating computers ARE the super intelligences of the future. But then why would they want to think of us primitives from the past? Another problem: Doesn’t chaos and the absolute randomness of Quantum Mechanics render anything other than a general knowledge of the past impossible? In that case this means that any simulated beings would in fact be arbitrary creations, just one evolutionary scenario, a mere possible history, but not necessarily the actual history. And overlying the whole of this simulation argument is the ever-unsettling question of consciousness: Namely, does consciousness consist entirely in the formal relationships between the informational tokens in a machine?

But even if we assume that the right formal mental structures are sufficient condition for conscious sentience, the problems just get deeper. If physics is a science whose remit is to describe the underlying patterns that successfully embed our observations of the universe into an integrated mathematical structure, then physics is unable to deliver on anything about the “deeper” nature of the matrix on which those experiences and mathematical relations are realized. Thus, whatever the nature of this matrix, our experiences and the associated mathematical theories that integrate them ARE physics. If we surmise that our experiences and theories are a product of a simulation, physics cannot reach beyond itself and reveal anything about its simulating context. The ostensible aspects of the surmised simulation (that is, what the simulations delivers to our perceptions) IS our reality: As Paul Davies observed, “… indeed the distinction between what is real and what is fake would simply evaporate away”. Moreover, if physics is merely the experiences and underlying mathematical patterns delivered to us by a simulation how can we then reliably extrapolate using that “fake” physics to draw any conclusions about the hypothetical “real physics” of the computational matrix on which we and our ‘fake’ physics are being realized? In fact is it even meaningful to talk about this completely unknown simulating world? As far as we are concerned the nature of that world could be beyond comprehension and the whole caboodle of our ‘fake’ physical law, with its ‘fake’ evolutionary history and what have you, may simply not apply to the outer context that hosts our ‘fake’ world. That outer realm may as well be the realm of the gods. Did I just say “gods”? Could I have meant … ssshh … God?

The root of the problem here is, I believe, a deep potential contradiction in contemporary thinking that has at last surfaced. If the impersonal elementa of physics (spaces, particles, strings, laws and what have you) are conceived to be the ultimate/primary reality, then this philosophy, (a philosophy I refer to as elemental materialism) conceals a contradiction. For it imposes primary and ultimate reality on physical elementa and these stripped down entities carry no logical guarantee as to the correctness and completeness of human perceptions. Consequently there is no reason, on this view, why physical scenarios should not exist where human perceptions as to the real state of affairs are wholly misleading, thus calling into question our access to real physics. Hence, a contradictory self referential loop develops as follows: The philosophy of elemental materialism interprets physics to mean that material elementa are primary, but this in turn has lead us to the conclusion that our conception of physics could well be misleading. But if that is true how can we be so sure that our conception of physics, which has lead us to this very conclusion, is itself correct?

There is one way of breaking this unstable conceptual feedback cycle. In my youthful idealistic days I was very attracted to positivism. It seemed to me a pure and unadulterated form of thinking because it doesn’t allow one to go beyond one’s observations and any associated integrating mathematical structures; it was a pristine philosophy uncontaminated by the exotic and arbitrary elaborations of metaphysics. For example, a simulated reality conveying a wholly misleading picture of reality cannot be constructed because in positivism reality is the sum of our observations and the mental interpretive structures in which we embed them - there is nothing beyond these other than speculative metaphysics. However, strict positivism is counterintuitive in the encounter with other minds, history, and even one’s own historical experiences. In any case those “interpretative structures”, as do the principles of positivism, look themselves rather metaphysical. Hence, I reluctantly abandoned positivism in its raw form. Moreover the positivism of Hume subtly subverts itself as a consequence of the centrality of the sentient observer in its scheme; if there is one observer, (namely one’s self) then clearly there may be other unobserved observers and perhaps even that ultimate observer, God Himself. Whatever the deficiencies of positivism I was nevertheless left with a feeling that somehow sentient agents of observation and their ability to interpret those observations have a primary cosmic role; for without them I just couldn’t make sense of the elementa of physics as these are abstractions and as such can only be hosted in the minds of the sentient beings that use them to make sense of experience. This in turn lead me into a kind of idealism where the elementa of science are seen as meaningless if isolated from a-priori thinking cognitive agents in whose minds they are constructed. In consequence, a complex mind of some all embracing kind is the a-priori feature that must be assumed to give elementa a full-blown cosmic existence. Reality demands the primacy of an up and running complex sentience in order to make sense of and underwrite the existence of its most simple parts; particles, spaces, fields etc – these are the small fish that swim in the rarefied ocean of mind. This philosophy, for me, ultimately leads into a self-affirming theism rather than a self-contradictory elemental materialism.

The popular mind is beginning to perceive that physics has lost its way: University physics departments are closing in step with the public’s perception of physics as the playground for brainy offbeat eccentrics. My own feeling is that physics has little chance of finding its way whilst it is cut adrift from theism, and science in general has become a victim of nihilism. The negative attitude toward science, which underlies this nihilism, is not really new. As H. G. Wells once wrote:

"Science is a match that man has just got alight. He thought he was in a room - in moments of devotion, a temple - and that this light would be reflected from and display walls inscribed with wonderful secrets and pillars carved with philosophical systems wrought into harmony. It is a curious sensation, now that the preliminary splutter is over and the flame burns up clear, to see his hands lit and just a glimpse of himself and the patch he stands on visible, and around him, in place of all that human comfort and beauty he anticipated - darkness still."

Wells tragically lost his faith and with it his hope and expectation: He no longer believed the Universe to be a Temple on the grandest of scales, but rather a place like Hell, a Morlockian underworld with walls of impenetrable blackness. In that blackness Lovecraftian monsters may lurk. Nightmares and waking life became inextricably mixed. And in this cognitive debacle science could not be trusted to reveal secrets or to be on our side. The seeds of postmodern pessimism go a long way back.

But we now have the final irony. The concluding words of the Horizon narrator were:

"Now we’re told we may not even be real. Instead we may merely be part of a computer program, our free will as Newton suggested is probably an illusion. And just to rub it in, we are being controlled by a super intelligent superior being, who is after all the master of time."

The notions that we are being simulated in the mind of some super intelligence, that a naïve concept of free will is illusory, that we can know nothing of this simulating sentience unless that super intelligence should deign to break in and reveal itself are all somehow very familiar old themes:

“….indeed He is not far from each of us, for in Him we live and move and have our being…” (Acts 17:27-28)

My frame was not hidden from You when I was made in the secret place. When I was woven together in the depths of the earth., Your eyes saw my unformed body. All the days ordained for me were written in Your book before one of them came to be” (Ps 139:15&16)

“…no one knows the Father except the Son and those to whom the Son chooses to reveal Him.” (Mat 11:27)

Have those harmless but brainy eccentric scientists brought us back to God? If they have, then in a weird religious sort of way they have sacrificed the absolute status of physics in the process.

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