1
$\begingroup$

I read on the Arxiv blog (and elsewhere) that 'there is the hint in C. Fields’ ideas that information provides the ghostly bedrock on which the laws of physics are based. That’s an idea that has gained traction among other physicists too.'

Source of Abstract: https://arxiv.org/abs/1502.03424

Within the quantum Darwinist framework introduced by W. H. Zurek ({\em Nat. Phys.}, 5:181-188, 2009), observers obtain pointer-state information about quantum systems by interacting with a local sample of the surrounding environment, e.g. a local sample of the ambient photon field. Because the environment encodes such pointer state information uniformly and hence redundantly throughout its entire volume, the information is equally available to all observers regardless of their location. This framework is applied to the observation of stellar center-of-mass positions, which are assumed to be encoded by the ambient photon field in a way that is uniformly accessible to all possible observers.

To avoid possible confusion, Fields here refers to the author of the above: Chris Fields.

A brief account is at Cosmological constant paradox.

As a biologist, I have no clue if this is just an exotic hypothesis or it's possibly true. Also, can anyone give an intuitive explanation of how could this be the case? thanks

$\endgroup$
1
  • 2
    $\begingroup$ Please provide a link to the blog article you mention, so people don't have to search for it. $\endgroup$
    – StephenG
    Jul 16 '17 at 15:34
2
$\begingroup$

The variety of things that people mean, when they say "information" is fundamental, defies summary. It ranges from near-tautological statements that physical systems are only affected by that which affects them, to half-baked metaphysics in which Information is treated as the substance of reality itself.

In this case, the anonymous blogger at "arxiv blog" (no official relation to arxiv, by the way) is excited by a completely obscure paper that would explain the magnitude of dark energy in a small region in space, as a result of something like the degree of quantum correlation between the location of every star in the observable universe, and unspecified physical degrees of freedom within the small region.

The argument seems to be: If the center-of-mass of every star in the universe is quantum-delocalized by about 5 kilometers, and if information about the magnitude of the delocalization for each star is somehow processed or actively encoded within the same small region in space, and if we estimate that the amount of energy dissipated in order to perform this computation is the minimum allowed by Landauer's principle, then we find that it adds up to the energy density required for dark energy.

On a superficial inspection, I strongly suspect that this argument makes no sense, for multiple reasons. But I can at least say that the author is talking about interactions between specific physical entities: the dark energy is supposed to be "the free-energy cost of decoherence" resulting when "an all-pervasive classical gravitational potential energy density" decoheres the quantum information contained in an "ambient photon field".

Anyway, this paper may not provide the best introduction to information-centric physics, given that it is so obscure and probably wrong.

P.S. The skeptical questions I would ask about the paper:

Is there such a thing as the "free-energy cost of decoherence", at all?

Is it remotely possible that a star could have a center-of-mass quantum wavelength of as much as 5 kilometers?

Why and how does this density of "free energy" act like a source of negative pressure?

$\endgroup$
1
  • $\begingroup$ "free-energy cost of decoherence" does sound like someone just rammed words together like a script writer for a sci-fi show. :-) $\endgroup$
    – StephenG
    Jul 17 '17 at 0:22
1
$\begingroup$

You write you that are a biologist, looking for an intuitive picture, so I would like to attempt an answer at that level and, to be frank I lack the expertise to achieve a more detailed description. I am assuming I am writing material you are already familiar with, probably more so than I am.

From the source you quoted:

One of the biggest puzzles in science is the cosmological constant paradox. This arises when physicists attempt to calculate the energy density of the universe from first principles. Using quantum mechanics, the number they come up with is $10^{94} g/cm^3.$

And yet the observed energy density, calculated from the density of mass in the cosmos and the way the universe is expanding, is about $10^{-27} g/cm^3$. In other words, our best theory of the universe misses the mark by 120 orders of magnitude.

To me, this is clear enough, but can I refer you to Wikipedia Cosmic Cosmological Problem, and the links included there, rather than simply repeat what you have read. In fact, most of this will my personal interpretation of what Fields is getting at, so please accept this as a simple variation and synopsis of the article you read.

So how do we address this disparity, which arises from the superposition principle inherent in quantum mechanics?

There are at least eight different interpretations/explanations of how the quantum world "turns into" the classical world, each of which, to varying degrees, has a certain number of adherents. The interpretation that Fields appeals to in his argument is the decoherence argument, crudely put this involves the interaction of other objects (rather than, for example the Copenhagen Interpretation which involves us, that is humans, to initiate the process of making a photon appear in one place, as opposed to the almost infinite numbers of places it could be until it is measured).

So decoherence does not require people, but I would ask you to check my simplistic assertion by using Wikipedia where appropriate.

If you have one football, classically (and obviously). you need less information to describe its position and velocity than if you tried to keep track of 100 footballs.

To quote from the blog:

But there is an important consequence from having a specific position — there must be some information associated with this location in 3D space. If a location is unknown, then the amount of information must be small. But if it is known with precision, the information content is much higher.

And given that there are some $10^{25}$ stars in the universe, that’s a lot of information. Fields calculates that encoding the location of each star to within 10 cubic kilometres requires some $10^{93}$ bits.

That immediately leads to an entirely new way of determining the energy density of the cosmos. Back in the 1960s, the physicist Rolf Landauer suggested that every bit of information had an energy associated with it, an idea that has gained considerable traction since then.

So Fields uses Landauer’s principle to calculate the energy associated with the locations of all the stars in the universe. This turns out to be about $10^{-30}g /cm^3$ very similar to the observed energy density of the universe.

This figure is remarkably similar to the 120 orders of magnitude discrepancy between the observed energy density and that calculated using quantum mechanics. Indeed, Fields says that the discrepancy arises because the positions of the stars can be accounted for using quantum mechanics. “It seems reasonable to suggest that the discrepancy between these numbers may be due to the assumption that encoding classical information at [the Planck scale] can be considered physically meaningful.”

So, most of this "answer" depends on how persuasive you personally feel about the mechanism behind the transformation of the quantum world to the classical world. If you believe that the moon disappears when we are not looking at it, you may not be convinced.

Basically, in my opinion, this is ultimately not a physics question, and no physicist can currently definitively answer it, relying as it does on belief in the possible role of the human observer (biology and neuroscience) and philosophy (regarding the ultimate nature of reality, whatever that actually means). Also, the assertions about the role of the Planck scale cannot be experimentally tested, this to my mind is therefore not physics, in its true empirically based nature

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.