Underlying Assumptions in Physics: The Relationship Between Evidence and Theory by Emily Christine Adlam

Hi Emily and George,

I seem to be in the strange position of having to disagree with both of you. On the one hand, I agree with George that it seems a bit absurd to assume that the appearance of your essay from random fluctuations must be much more probable than were it to have been written by a conscious person. On the other hand, I agree with Emily that random fluctuations can nevertheless give rise to complex phenomena. My reason for both stances is the same: "highly improbable" is not the same thing as "impossible."

This seems to be a common trait among humans in regard to our interpretation of statistical phenomena: an event that occurs is a priori assumed to be highly likely by dint of the fact that it has occurred in the first place. In light of additional information, the event's relative likelihood may be revised downward, but the fact of the matter is that it is initially assumed to be high simply because it happened. But even highly unlikely events still happen. My neighbor has been struck by lightning. If he grew up ignorant and isolated, he might be led to conclude that *everyone* gets struck by lightning which is absurd.

In short, an equally valid interpretation is that our memories are perfectly valid and correct but that the universe simply evolved in a highly unlikely (but not impossible) way. For example, suppose there is a spectrum of *possible* universes (these would be *actual* universes in an Everettian interpretation). Even if only a single universe occurs, nothing says it absolutely must be one of the more likely candidates. That's the point of a random process.

Also, one other point I wanted to make: entropy depends on how you define it. It is entirely possible to define it in such a way that a low entropy in the early universe is not unexpected.

Regardless of my aforementioned gripes, it was a nice essay. I found it to be well-written and carefully considered.

Ian Durham

Emily,

In your abstract, you state that:

"scientific enquiry has presupposed a relatively simple relationship between our empirical evidence and the facts of reality... Such assumptions seem to be necessary... But developments ... give us specific reasons to question these assumptions."

The simple relationship between evidence and reality, need not be questioned. Physical theories merely produce numerical predictions, that either agree or disagree with observations. They do nothing else. In particular, they provide no evidence, either for or against, all the metaphysical "interpretations" that have the attached to the theories. The theories can do little more than "fit curves to data", and they can only even do that, in cases where the data has an extremely low information content - that is what makes the data "predictable", by the theory, in the first place.

Since the "interpretations of the theory" invariably have a higher information content than the theories themselves, the "interpretations" cannot possibly be contained within the theories themselves; they have simply been made-up and slapped-on. Hence, while experiments may confirm that the theory "fits" the data, they cannot provide any evidence that the "interpretation" fits the theory.

Rather than questioning the "reliability of memories", physicists need to question the "meaning" and "significance" that they have attached to them.

Thank you for your comments! It's certainly true that both the concept of entropy and the second law of thermodynamics are plagued with difficulties both in derivation and interpretation, and this essay is not intended to be a defence of either. My discussion of 'the entropy of the universe' is mainly a way of pointing to the appearance of temporal asymmetry - according to our memories and records there seems to be a kind of directedness in the way that events come about, yet that direction doesn't seem to come from the underlying microdynamics and therefore needs to be accounted for in terms of a further assumption about the initial conditions. It's convenient to frame that assumption in terms of the initial low entropy of the universe, but the argument isn't dependent on specific assumptions about the nature of entropy and/or the status of the second law.

Your statement that "we need some specification of which mathematical features of the theory are meant to correspond to particular features of our evidence" is exactly on target. It is discussed extensively in my own essay. Unfortunately, as I indicated there, making such a correspondence provides no evidence that it is correct.

The problem is that the "meaning" of a high information content signal cannot be deduced from any observation of the signal, for the simple reason that "high information content" is synonymous with the fact that the signal itself is devoid of meaning. In effect, the signal is nothing more than a "serial number", whose "meaning" can only be deduced by "looking it up" within the memory of an entity that knows, a priori, the correspondence between the serial number and its "meaning's" address in memory.

Physicists do indeed need to "stop interpreting that data quite so literally." Complex entities respond to data observations "symbolically" as well as "physically." Physical responses behavior as though data measurements are "real numbers", but symbolic responses behave as though they are "serial numbers." The entire information content of Physical behaviors can easily be represented, by short sequences of symbols, known as "equations." The vastly larger information content of the initial conditions, in the memory of a complex observer, cannot. For such observers, it is the initial conditions, not the equations, that determine all "interesting" behaviors, because that is the only thing that gives any meaning to observed "serial numbers."

Emily,

You wrote: "It's convenient to frame that assumption in terms of the initial low entropy of the universe, but the argument isn't dependent on specific assumptions about the nature of entropy and/or the status of the second law."

But "initial low entropy" already presupposes some "specific assumptions about the nature of entropy and/or the status of the second law". By the way, at the end of his paper, Uffink in fact rejects the law of entropy increase:

http://philsci-archive.pitt.edu/archive/00000313/

Jos Uffink, Bluff your Way in the Second Law of Thermodynamics, p. 94: "This summary leads to the question whether it is fruitful to see irreversibility or time-asymmetry as the essence of the second law. Is it not more straightforward, in view of the unargued statements of Kelvin, the bold claims of Clausius and the strained attempts of Planck, to give up this idea? I believe that Ehrenfest-Afanassjewa was right in her verdict that the discussion about the arrow of time as expressed in the second law of the thermodynamics is actually a RED HERRING."

Pentcho Valev pvalev@yahoo.com

I believe that the act of contemplating the possibility of past intervention in human affairs by demons (aliens, gods, God, whatever the label shall be, just as long as they evolved over a great period of time like we did) is no less scientific than the act of contemplating the possibility of the many worlds scenario.

I say this wholeheartedly, because even if one were to somehow logically disprove many worlds here, there is still the possibility that there is another world in which this logic was proven false because it was based on some incomplete information. I also say this wholeheartedly, because the simplest thoughts about the origin of life point directly to the laws of thermodynamics themselves -- life is special, but not that special.

Anyway, who knows? Perhaps one day we will be able to communicate with aliens, as well as be able to hop between the branches of the many worlds. Until then, my bet is on aliens first, and possibly last.

Dear Emily,

You write exceptionally well. You give a balanced and mature analysis that reveals a strong grasp of the issues you address, without being carried away by any particular argument. I have a few thoughts for you to consider.

1. Of course you are correct that classical microdynamics is time-symmetric, but we know beyond reasonable doubt that classical statistical mechanics is not fundamental. A general mechanism that produces time-like asymmetry across a broad range of "fundamental" physical theories is asymmetry in configuration space. My own favorite version is causal configuration space, as described in my essay:

On the Foundational Assumptions of Modern Physics

The idea is that different possible universes are related to each other in ways that make time-like asymmetry inevitable. I say "possible" here because I don't believe one has to be a committed Everettian to make use of configuration spaces and Feynman's sum over histories method. I also explain in the essay precisely what I mean by "time-like" in this context.

Julian Barbour's essay in this contest mentions a different type of configuration-space asymmetry, shape space asymmetry, which is relevant under different assumptions. He can explain his approach better than I can.

2. As you point out, there is a self-referential difficulty associated with doubting one's own memory; you mention this by remarking that your essay is "more likely" of random origin than produced by a conscious person. To your credit, the essay itself is strong evidence against this supposition, but more seriously, I believe that the pragmatic assumption you mentioned is necessary, if only as a last resort. There is no incompatibility between pragmatism and idealism in this regard, unless one is certain that one can never do better than the pragmatic assumption. You can continue to do science and seek better foundations at the same time.

3. On the subject of decoherence, I will mention that Jorge Pullin and Rodolfo Gambini have an essay in this contest that attempts to refine the decoherence approach to the measurement problem. I will also repeat that ascribing some degree of reality to the various histories in Feynman's sum doesn't necessarily imply full-blown Everettianism; in particular the relationship between observers and the configuration space admits several possible interpretations.

4. Einstein's objection to nonlocality need not have been totally wrongheaded, even if it was misapplied in the case of quantum theory. In particular, it relies on assumptions about the structure of spacetime. I discuss this point in my essay, as well.

Thanks for the great read! Take care,

Ben Dribus

Emily

You are ignoring my post.

Why?

Hello! I'm sorry that I took some time to reply, I have been busy.

I'm sorry, but I don't entirely understand your question - what do you mean by 'victimization' with regard to the second law?

Dear Emily Adlam,

Didn't they intuitively decide that frequencies have to be positive while they didn't overlook the due consequences? I can provide references that reveal what e.g. Schroedinger, Dirac, and Weyl thought.

Well, you are not reading mathematics. However, I consider the mathematical flaw related to physics.

Curious,

Eckard

Drew attention to quote from Dirac in my essay:

"It seems very likely that sometime in the future there will be an improved quantum mechanics, which will include a return to the causation and which justify the view of Einstein. But such a return to the causality may be possible only at the cost of failure of some other fundamental ideas, which we now accept undoubtedly. If we are going to restore causality, we shall have to pay for it and now we can only guess what idea must be sacrificed." P.A.M. Dirac. Directions in Physics

I mean to sacrifce second law of thermodynamics

Victimization of second law....

I agree that great care needs to be taken with the second law - in particular, I would reinforce that it shouldn't be taken as a 'fundamental' law (whatever that means!) but rather as a statistical generalisation which holds as a matter of high probability.

I invoked entropy in this essay mainly as a simple way of pointing out the asymmetry that exists between our predictions and retrodictions - the problem is that if we accept the time-symmetry of the microdynamical laws we seem to have no good reason not to believe that the 'entropy' (using this concept as a way of formalising closeness to thermal equilibrium, without presupposing any substantive claims about irreversibility or the second law) should increase in both the past and future direction. Only the past hypothesis gives us an adequate basis for retrodicting lower 'entropy' states in our past, yet our principal reason for accepting the past hypothesis is our belief that entropy was in fact lower in the past - hence we seem to have a circularity in our reasoning, and I don't think that alternative definitions of entropy or revisions of the status of the second law will do enough to make the problem go away.

Thank you very much for your comments!

1) I've read your essay and Dr Barbour's with interest - if anything, I would say that the points I've raised here give reason to take these sorts of speculations seriously, since the problems with classical statistical mechanics would make it unsatisfactory even if we didn't have other good reasons to view it as non-fundamental.

2) I certainly wouldn't advocate giving up all or even most of the pragmatic assumptions that we need to get physics started. However, I do think we should keep in mind that they are assumptions, and be willing to question them (judiciously) in circumstances where that becomes appropriate, such as our current predicament with regard to statistical mechanics and quantum mechanics.

3) Bringing in alternative interpretations of quantum mechanics certainly complicates the issue here, but I think the problem of probability remains pressing for any interpretation which ascribes reality to more than one outcome of a measurement, since it's then no longer possible to make the straightforward pragmatic assumption that the (single) course of events that actually happens is one rendered highly probable by the theory.

4) I agree - I think there's a prevailing idea that Einstein disliked nonlocality mainly because it disagreed with his own theory of relativity, and that's doing him an injustice, because he clearly had good independent philosophical reasons for opposing it. I think he's right to worry that if we were to get rid of locality altogether we'd simply end up with chaos; but what quantum mechanics demonstrates is that we can sometimes weaken underlying assumptions like locality without completely undermining the practice of physics.

Emily,

One way to resolve the Everett hypothesis is to eliminate the external timeline of events and allow the process to proceed atemporally. Sound impossible? How can you have process without time? It emerges from the process, but it's dynamic, not dimensional. It's not the past proceeding into the future, but the future becoming the past. Not the earth traveling a narrative dimension from yesterday to tomorrow, but tomorrow becoming yesterday because the earth rotates. As an effect of action, time then becomes the collapse of probabilities into actualities. Duration is not external to the present, but is the state of the present between measured events. It is only when we consider time in retrospect that it emerges as narrative. Yet that past is receding, rather then the present moving.

As an effect of action, time is similar to temperature. Time as rate of change, while temperature as level of activity. When we change the level of activity, such as in gravity fields, or at significant speed, this affects the rate of change. Which is why clock rates vary. Not because they travel alternate time vectors.

This way, the past is determined, but the future is probabilistic, since the lightcone of input is not complete until the event happens.

EA:

Very interesting and informative essay as philosophy.. As a newcomer to the FQXi community, I feel few of the "community" grade, or even look at, my essay which approaches the problem very realistically, based on an internal philosophical view.. Might you look at it, comment if so inclined, and grade it?

To Seek Unknown Shores

聽聽 http://fqxi.org/community/forum/topic/1409

Thank you

TE