Andy Lawrence, Edinburgh astronomer by day and e-Astronomer by night, has participated in a Five Books interview at The Browser. You’ll remember that I did one where I picked five books about relativity and cosmology. Most of the other interviewees (and they have a great list) have been a bit more playful, mixing in different genres. Andy takes a judicious middle tack, including some straight-up astronomy but also some biography.
I was glad he picked Dennis Overbye’s Lonely Hearts of the Cosmos, which is one of my favorite books about science and scientists. It manages to show the human side of science in all its quirky glory, without either creating fake scandals or putting anyone on a pedestal.
Sean,
sorry if this is out of place (the relevant posts are outdated by now), but what are your thoughts on http://arxiv.org/abs/1108.3080 which claims to solve the inflationary entropy problem and argues that your recent papers have missed important aspects of the entropy?
Any thoughts would be appreciated. Thanks
“Andy Lawrence, Edinburgh astronomer by day and e-Astronomer by night”
Surely it is the other way around. 🙂
@Fred: Yes, I would like to hear Sean’s take on this as well.
From the abstract: “a given observer can reduce entropy by much more than the amount of information her brain can store.” I agree with Max here; I’ve known some women like that. 🙂
o/t but at least astronomical, this story out of the Penn State astronomy department
http://live.psu.edu/story/54646
I’ve mentioned Lonely Hearts in the Cosmos before, but Overbye describes Simon White as a sandy haired irishman!
“Secrets of the Night Sky” by Bob Berman (formerly at Discover, now at Astronomy mag) is an awesome book, it’s what inspired me to become an amateur astronomer. I’ve reccomended it to at least a dozen people, and everyone’s loved it. Great for beginners or anyone wishing to read a beautifully written book on the wonders of the universe.
A few comments by a information specialist on Tegmark’s new paper
Fred #1, please don’t be too annoyed at me for making an entry regarding your question to Sean Carroll about Max Tegmark’s new paper.[1] I hope you will view this as simply as confirming your assertion that comments on Max Tegmark’s paper from a highly competent peer of his would be a really interesting.
I would also note that since both Sean Carroll and Max Tegmark are organizers of the FQXi “Setting Time Aright” conference that starts Saturday in Bergen, Norway and Copenhagen, Denmark, they may both be pretty short on time right now. Reading a paper like that one can take a few days, at least to do it the right way, since it introduces a number of comments.
My comments are just passing remarks from someone reasonably familiar with entanglement.
1. I think Tegmark’s concept of “long-range entanglement,” [2] and his application of the idea to the cosmic inflationary problem, is a very nice innovation that has some decent potential for changing our understanding of how quantum effects interact with cosmology. I’m even a bit puzzled why someone didn’t make similar observations a lot earlier, which may just be my way of saying that I think Tegmark captured the idea clearly enough and with enough accompanying mathematical support to make it seem “obvious.” If so, that’s a good sign. Ideas that seem obvious in retrospect are usually the same ones that are hitting on something important.
Tegmark’s argument on this point is explicitly both quantum and classical, although I happen to find the entanglement part a lot more interesting due to its potential relevance to certain other quantum phenomena.[3] What Tegmark seems to be pointing out is that a rapid spatial expansion of any type produce a form of large-region uniformity — Tegmark expresses this in terms of entropy — that can be detected by sampling very miniscule parts of that region.[4] Especially as he applies it to entropy, I really think Tegmark is on to something there.
2. … More comments later, perhaps; I took longer on this than I meant too.
Cheers,
Terry Bollinger
———-
[1] Max Tegmark, How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problem. 15 Aug 2011, http://arxiv.org/PS_cache/arxiv/pdf/1108/1108.3080v1.pdf
[2] Entanglement is not complicated! It happens when you have two preconditions: (a) Some quantity that is absolutely conserved, and (b) a lack of observation, which is the defining condition that causes a system to become “quantum,” that causes that conserved the conserved quantity to spread out over time within some region or subset of ordinary xyz space.
These two preconditions are usually applied to angular momentum, which is absolutely conserved, but here’s something most of you (including physicists) may not have noticed: It also applies to other absolutely conserved quantities such as mass or linear momentum. I am working on a paper on that, but being an open source kind of person I’ll mention the main points here.
Not recognizing that entanglement happens whenever a conserved quantity is part of a quantum wave functions results in most instances of entanglement being overlooked or quantified rather oddly. The precise evolution of a quantum wave function, for example, is the result of entanglements of of both mass and linear momentum within the wave function, and also with the classical systems that is used to set up the wave function. Mass conservation caused the location of the particle to be “entangled” with xyz space, so that finding the mass in one location guarantees its “non-location” in all other regions.
However, the entanglement of linear momentum, which behaves as a bridge between classical and quantum systems, does not seem well captured, even though it guides and enables the overall evolution of the wave packet. I suspect that representing linear momentum as an entanglement effect can be used to produce a cleaner, more predictive model for understanding Mossbauer, for example.
[3] Specifically, the issue of object coherence in quantum interactions. Large bound objects with significant mass are excruciatingly sensitive to information effects, so that quite literally a single photon can knock an entire large object out of a quantum state and back into classical locality. This extreme asymmetry of effect has fascinated me for years, and is one of the hallmarks of information, which otherwise looks a lot like ordinary momentum or mass in terms of traditional physics units. Tegmark’s ideas seem to be addressing a similar idea at the cosmological level, and so may also be applicable to a much “close to home” analysis of that curious boundary between quantum and classical, which has never been well quantified. John Bell, as always, recognized that there is a significant understanding problem there, and came up with some thought problems to poke at it.
[4] Some folks may notice a similarity to the computer recognition concept of “sparse sensing,” in which very limited random sampling of a scene can produce remarkably (and unexpectedly) accurate understandings of the object content of that scene. I don’t think that is a coincidence at all. Since any object with physical coherence traces back to some sort of “origin” event that created that coherence, the originating event likely qualifies as a looser form of the classical version of Tegmark’s rapid expansion. Thus, even very limited sampling (a pixel or two) can, under the right circumstances, access the same sort of statistical assumption of uniformity that is the basis of Tegmark’s idea.
Incidentally, in the quantum entangled case the big difference is “wave collapse”: The particle or properties ceases to be locatable at any other part of the region once it is identified within even a very, very small part of that region. I was a bit amused to see “wave collapse” in quotes in Tegmark’s paper; the quotes show just how uncertain the status of this concept is in physics. Me, I happen to think wave collapse is real (for decades I did not), experimentally very accessible, and critical to any clear understanding of how time flows (see e.g. my Stephen King’s universe comments yesterday).
@ Terry Bollinger 7,
you say that no-one had make the argument earlier – the argument being that the entropy in our branch of the wavefunction is much smaller than in the total sum of the branches. But it has actually been stated much earlier, in most cases in quite crackpotty papers, such as http://www.tony5m17h.net/EntropyInflation.pdf and http://arxiv.org/pdf/gr-qc/0007006v1, which tie it all to consciousness and funny things.
@ Fred 8 said
> … you say that no one had make the argument earlier – the argument
> being that the entropy in our branch of the wavefunction is much smaller
> than in the total sum of the branches …
What I found interesting in Tegmark’s paper is that he seems to be working on representations that could be useful (I may be wrong) to modeling how information interacts with complex entities such as solid objects. That is a different and far smaller subset of everything Tegmark addressed.
I’m not very useful for addressing your questions, since I’m a hierarchical materialist.
By that I mean that I think there is solid evidence that the universe is constantly “nano-observing” itself, starting at the atomic and molecular levels and moving up. My premise is that any exchange of a particle collapses wave packets, and by doing so creates real, historical information traces — observations. For example, a stream of neutrons can be refracted by a crystal without leaving any historical traces, but other neutrons in the same stream can transmute nuclei and thereby leave detectable traces of their actions.
My view that the universe nano-observes itself has two consequences relevant to your question.
Firstly, it implies that the idea of a universal wave function idea is more illusion than reality. Instead, a classical framework dominates and provides isolation, with packets interacting in ways that are likely more entangled and a interesting than we realize. In the end, though, I think classical locality is the dominating framework, in part because classical frameworks scale up much more easily than do quantum systems.
Secondly, apart from the weak anthropic principle, intelligent observers become largely irrelevant in a universe with nano-scale self-observation. In fact, if particle exchanges really are the fundamental building blocks of observation, very few human actions would even qualify as quantum.