If you have an idea for a blog post or a new forum thread, then please contact us at firstname.lastname@example.org, with a summary of the topic and its source (e.g., an academic paper, conference talk, external blog post or news item). You may also view a list of all blog entries.
FQXb (bio) By WILLIAM OREM • Mar. 23, 2014 @ 21:39 GMT
Everyone is talking this week about the dramatic confirmation of inflationary theory: those first-instant gravitational waves whose details may even point--being, if you will, quantum phenomena that went suddenly ultra-macroscopic--toward the correct way to unify QM and GR.
I myself have been musing on rather astonishing work in another field. Will you pardon the intrusion if we talk a little bit about biology?
Recently the big news there was released: an unprepossessing experiment involving a weak acid bath showed it's possible to revert mature, differentiated cells to a stem cell state, allowing for the prospect of wholesale repurposing. The surprise wasn't that reversion (or conversion from one mature type into another) can be done--genetics work in that direction took home a Nobel in 2012--but that it can be done so simply. Since FQXers are a physics crowd, you might say it's a bit like someone offhandedly noticing you can trigger a controlled fusion reaction by rewiring a microwave oven.
This is the angle most science journalists gave the discovery last month: "Outsider runs outrageous experiment, stumbles upon success." Charles Vacanti's brilliance, we were told--"outsider" because he's an anesthesiologist, without even a Ph.D.--came in trying something that anyone could have done, but nobody though to, because it was just too unlikely. There can be a virtue to not being too educated in a certain field; to get all Zen about it, "In the beginner’s mind there are many possibilities; in the adult's mind, there are few."
Alas--you knew this part was coming--it is now looking like the champagne may have been premature. There are certain "improprieties in the data," as it has been politely phrased in the weeks since. (Or, as a friend of mine--himself a Harvard neuroscientist--more trenchantly put it: "A weak acid bath? Give me a break.") One of the photographs in the article has already been confirmed to be a goof. No one is averring foul play, but whether we have a home-run or a whiff is in serious question.
Either way, though, I'm left musing.
Were I to win the Lottery tomorrow, I would immediately do two things: fund FQXi indefinitely and expand it into other fields. Imagine an FQXpb (psychobiology) or an FQXg (genetics). After all, it is not only cosmology and high energy physics that carry foundational questions. Who was it that floated the idea--wacky, but rather wonderful to contemplate--that if "junk DNA" really has no purpose, at some point we might want to mine it for communication, perhaps put there by the species that fabricated us? (In his novel Contact, Carl Sagan came up with lovely notion that pi, when you advance to the point of being able to decipher its pattern, turns out to be an instruction manual on how to operate reality from the beings who engineered this region of spacetime.)
So, in the spirit of FQX bio, let's just assume for the moment that Vacanti et. al. paper is correct. What follows? Therapies for spinal cord injury and damaged heart tissue, by all means; bring them on. But what really would be interesting would be the fact of simple cellular reversibility. This phenomenon would be telling us something completely surprising about what cells are, at a deep level--and what, by extension, we ourselves are.
As a finding, it's counterintuitive. Why should cells, already long since differentiated, be capable at all of reverting to a stem state, as if awaiting reassignment? (As Rabi said of the muon, who ordered that?)
Is this a natural propensity of all cellular life? Is mutability far more common than has been understood? Does cell reversion happen all the time in the body, and we just never noticed it? (Don't scoff; we should remember it was the 16th century before medical science understood the circulation of the blood.) Could this be a key to understanding what cancers are, at a deep level?
From Carolyn Y. Johnson's Boston Globe article of Feb. 17:
"Even normal cells appear to contain a capacity for regeneration far more powerful than anyone knew. This new idea is opening up profound, almost philosophical questions about why cells would have this capacity. [ . . . ]
'It's slowly changed how we think about life, and I know that sounds grandiose, but it's not grandiose at all,' said Dr. Richard T. Lee, a stem cell scientist at Brigham and Women's Hospital."
Life coming to know itself; not too grandiose at all, I should think.
Updated: Congratulations to FQXi's Alan Guth and Andrei Linde following the announcement of the first direct detection of B modes -- evidence of their inflation theory. Well done to those working on BICEP2, and all others who have contributed to the development of inflation theory over the years. Here's a lovely video, from Stanford University, showing Linde's reaction to the news:
Rumours have been flying since last week about a major discovery that will have implications for our understanding of the early universe. Later today—as I'm certain you will already have heard—there will be an official announcement from the BICEP2 experiment. The experiment involves a ground-based telescope at the South Pole, specifically designed to look for the "B-mode" signature of inflation (a predicted period of rapid acceleration of the universe in its infancy) in the CMB.
This is a thread to discuss what looks most likely to be the announcement of some level of discovery of such B modes, a twisted signature in the polarisation of CMB light that could only have been made by primordial gravitational waves—ripples in the fabric of space-time, set off by the rapid acceleration of space-time during inflation. Gravitational waves have been predicted to exist by general relativity, but primordial gravitational waves are considered to be evidence for inflation theory, in particular, because only period of massive expansion in the early universe could leave us with a detectable imprint of them today.
Details on where to watch the announcement and read the papers (once available) are here:
Dear friends and colleagues,
We invite you to join us tomorrow (Monday, 17 March) for a special webcast presenting the first results from the BICEP2 CMB telescope. The webcast will begin with a presentation for scientists 10:45-11:30 EDT, followed by a news conference 12:00-1:00 EDT.
For a slightly more technical description of the different types of polarisation in the CMB, what B Modes are, and how they would be left behind by the passage of gravitational waves, you can see a great slideshow by Daniel Baumann.
Anthony close his essay with a terrific set of questions, which I am just cutting and pasting here:
1. If the speed of light were much slower, so we could really experience the subjectivity of simultaneity implied by Relativity, how to you think it would change our experience of time, space, and the world?
2. If you truly believed that the past, future, and present all exist in just the same way, as in the Unitary Block view, would it change your attitude toward life -- or death, or decisions?
3. If there are aspects of the world that are unpredictable in principle, is there still a sense in which we can say that they are determined? Or do those two ideas go hand-in-hand?
4. I've suggested that part of the controversy over how to think about quantum mechanics is a controversy over whether the classical, macroscopic world emerges from the quantum world, or whether the quantum world is a particular, stripped-down limit of an essentially classical world. How do you see it? What theoretical or experimental findings might lead you to accept one view as more viable than the other?
Please do visit BQO to take part in this discussion and more.
Some of you may have noticed that I enjoy writing about the question of what happens when you fall into a black hole. At the recent FQXi meeting in Vieques, Puerto Rico, "quantum mechanic" Seth Lloyd talked through this problem and discussed a way to potentially escape a black hole, first proposed by Horowitz and Maldacena, which uses quantum teleportation to smuggle information out--but also violates some quantum laws, in return.
Here is Seth, describing it in his inimitable style. He also explaining why, if you are unlucky enough to cross an event horizon, you shouldn't try and fire up the engines of your rocket and accelerate away from the singularity…because you'll only die faster.
For more about the debate over the fate of an unfortunate astronaut heading into a black hole, here's Anil Ananthaswamy's story about Steve Giddings' research, "Black Holes: Paradox Regained." There's also a story I wrote for Nature last year on the firewall debate, based on the work of Joe Polchinski, Don Marolf, Giddings and others, which pits general relativity against quantum physics--and tries to answer whether the space traveller would be spaghettified, as traditionally thought, or burnt to a crisp at the event horizon. And a follow-up discussing Stephen Hawking's take on the whole issue.
As promised, this is a follow-up to one of the summary posts from the FQXi conference in Vieques. If you have read those, you may recall that Anthony Aguirre asked the intriguing question: is there any way for us to tell if the universe is infinite or simply really, really big? (George Musser has also blogged about this.) In this blog post I suggest one possible way in which this might be accomplished. I emphasize that much of the content of this post is entirely speculative but it does offer suggestions on how to more rigorously determine the validity of the conjecture. It relies, however, on an assumption that runs entirely counter to my own conclusion in my most recent FQXi essay: that bits (in some fashion) constitute the basic building blocks of the universe.
Consider the following string of binary digits
where, for the moment, we assume that the full string is infinite but that we only have knowledge of the sub-string shown above. Now consider the following maps:
00 —> a
11 —> a
01 —> b
10 —> b
Notice that each digit in the original string ends up getting counted twice.
Thus the original string can be mapped to
where the X and the Y are unknown given that we do not know what precedes the 0 on the left and what follows the 1 on the right. Formally, this second string is doubly-infinite meaning its cardinality is double the cardinality of the first string since every digit in the first string is counted twice (yes, there are actually levels of infinity!).
Now suppose that we have complete knowledge of the doubly-infinite string of a’s and b’s with the exception of one value. It should be relatively clear that, if we know the distribution of 0’s and 1’s in the original string (e.g. 60/40 or 30/70), then the unknown value in the second string should be immediately known unless the original distribution is 50/50 in which case we have no idea (try it!).
So now take any two locations, X and Y, on what we call the “image” string (the strings of a’s and b’s) with the caveat that there are at least two letters between them. Suppose that we have complete knowledge of the doubly-infinite string other than these two locations. From the argument in the preceding paragraph, it should be clear that the instant we know one of these two values (say X), we immediately know the other (Y). A formal proof of this appears in Section 5 of this article by Steve Shea, which is open access.
Do we really need an infinite amount of knowledge?
The way I have described the problem (courtesy of Steve Shea) would seem to imply that we need to know absolutely every value in the doubly-infinite string, i.e. we need an infinite amount of knowledge, if we are to correctly predict the value of Y given the value of X (which also assumes that the original string of 0’s and 1’s is not a 50/50 split). But this gets to the heart of Anthony’s problem: do we really need an infinite amount of knowledge or just a whole lot of knowledge? One could imagine that we could approach a very high probability of correctly predicting Y given our knowledge of X as our knowledge of the doubly-infinite string gets large (though I would like to emphasize that I am not aware of a formal proof of this as yet—Steve’s article has just been published, though he’s been working on it for several years).
Nevertheless, approaching such a high-degree of accuracy with a prediction would also seem to require that the strings really are infinite. One can imagine that if they are not infinite, there could be some sort of "edge" effect caused by the fact that the second string would be ill-defined at the ends and that such an effect could somehow propagate through the string (again, I emphasize that this is speculation at this point and that there is no formal proof of this). For example, we could interpret the mapping (and thus, to some extent, the original string) as being nothing more than a kind of production rule somewhat akin to those in formal language theories: it’s just a rule for generating the string of a’s and b’s (note that in such theories the "start" symbol need not be at the extreme left or right of a string which means it could still be infinite—if you are unfamiliar with the concept of a "start" symbol, a good read is Douglas Hofstadter’s Pulitzer Prize-winning opus Gödel, Escher, Bach). Given that (and assuming that the ratio of 0’s to 1’s in the original string is not unity, i.e. they are not a 50/50 split since, otherwise, there really is no production rule), it should be clear that the a’s and b’s are interdependent which means I could rewrite the production rule simply in terms of the a’s and b’s themselves. Inherent in the original rule, however, there is no way to deal with endpoints. Specifically, the endpoints of the string of a’s and b’s would be ill-defined based on the production rule which would make any neighboring values in the string undefined and so on such that the entire string is ill-defined (e.g. it would be as if there was no "start" symbol). Thus the string must be infinite, at least in this formal system.
I would then conjecture that while the strings themselves must be infinite, we only need a finite (though arguably large) amount of knowledge in order to predict Y given X with a high degree of accuracy. Of course this all hinges on whether or not the original string is completely random. If the original string of 0’s and 1’s is exactly 50/50, the value of Y cannot be predicted with any greater accuracy than 50% (which essentially means it cannot be predicted at all). Likewise, the requirement that the string of a’s and b’s be infinite no longer holds, i.e. it’s really a relic of the production rule.
A universe of qubits
What does any of this have to do with the universe? Let’s just suppose that John Wheeler was correct and that, at its core, the universe is built up from bits—binary digits—or, rather, qubits. Since we don’t actually see the world as 0’s and 1’s (or answers to yes/no questions) it is clear that there is some form of mapping that goes on at some deep level from these binary questions to something slightly less fundamental. Let’s take, as a first approximation, the map introduced at the beginning and suppose that the string of a’s and b’s represents the results of measurements of simple two-level quantum systems. In other words, the a’s and b’s represent our knowledge of the universe at its most fundamental level (notice that it may or may not suggest a deeper reality of 0’s and 1’s or even something else entirely). We might then imagine that the universe (or, rather, our knowledge of it) can be reduced to a sub-string of a very, very long (possibly infinite) string of outcomes of measurements on qubits. This is not so radical an idea, by the way (see Seth Lloyd’s article on this topic: arXiv:1312.4455).
One glitch in this argument, of course, is that we don’t know the order of the measurement outcomes, i.e. the string of a’s and b’s. We have small strings of correlated outcomes, but we don’t know for certain if all of these small strings are part of one larger string, i.e. if we know, for example,
is it necessarily true that
If all of the sub-strings indeed are part of one, larger string it would seem to suggest that all possible qubit measurements in the universe may be correlated in some way since, as long as there exists a production rule, we can connect even the most far-flung elements of the full string of a’s and b’s. This, also, is not such a radical idea if we take the correlations as being equivalent to quantum entanglement (see Buniy and Hsu’s article on this: arXiv:1205.1584v2).
Note that there is one question here that I have not addressed and that is whether knowledge of X necessarily implies that Y is the opposite of X. If the a’s and b’s represent measurement outcomes for entangled qubits then one would seem to expect that the outcomes of X and Y must be opposite one another. There is no requirement in the mathematics that this be the case. In addition the mathematics imply a string of somewhat looser correlations (recall they must be at least two letters apart) in between the entangled pair. It might be possible to address the latter through something like quantum teleportation, but I won’t address that here. Instead I will simply assume that the production rule is such that the sub-strings that are accessible to us appear to behave in such a way that X and Y always behave as if they are entangled.
Is the universe infinite or just really, really large?
Let’s take Buniy and Hsu’s idea as correct in which case all qubit measurements are somehow part of a single, large string. We can access different sub-strings of this larger string via entanglement measurements. Note, however, that X and Y do not necessarily need to be in the same sub-string. So, for instance, an entanglement experiment with qubits might represent the following pair of sub-strings
In other words, we are ignorant of some of the intermediary processes that connect them. Nevertheless, we do know that a determination of X immediately tells us what Y must be since this is measurable in a laboratory. This suggests that the intermediary processes, while perhaps not readily apparent to us, nevertheless exist as long as there is a production rule and as long as the full string is doubly-infinite. In fact, if Buniy and Hsu are correct (and note that their argument is based on cosmological models and thus not dependent on anything I suggest here), the mere presence of entanglement suggests that the string of all qubit measurements in the universe is infinite which would itself suggest that the universe is infinite, but only if the underlying production rule is not completely random. Recall that none of this works if the 0’s and 1’s in the original string are a 50/50 split. If they are, there is no correlation between X and Y.
I caution against rushing to judgement about these ideas. Clearly we see correlations and entanglement in the universe on some level. Does this automatically imply, then, that the universe is infinite and not entirely random at its base level? It clearly does not since we don’t know if Buniy and Hsu are correct. In other words, we have no idea of our measurements of entanglement are merely parts of one large, interconnected string of such measurements. What it does seem to tell us is that if they are correct (and it is a big "if"), then it is highly likely that the universe is both infinite and non-random. (It also would seem to suggest that Max Tegmark might be right after all about the role mathematics plays in the universe.)
Now Anthony was interested in this from the standpoint of the multiverse and one could easily modify these ideas to take that into account. I won’t do it here. I can also imagine someone taking Steve’s results without reference to Buniy and Hsu and coming up with a way to measure whether the universe is infinite or merely very large.
There are a lot of assumptions and conjectures in this post but there are also a lot of concrete starting points for further exploration. Can we definitively prove, mathematically, that these strings must be infinite for this effect to be possible? I offered a heuristic argument above as to why, but a more formal proof would be welcome. Can we really re-interpret Steve’s original mapping in a way that makes it self-referential to the string of a’s and b’s, i.e. can we find a production rule for the string of a’s and b’s such that it would exactly match what we would have obtained using the original mapping? Conversely, if we can’t, can we definitively rule out the possibility that one exists? Are Buniy and Hsu correct in suggesting that all particles in the universe are ultimately entangled and can we actually reduce everything to a set of qubit measurements? What might the results presented here say about the multiverse? Is there some other way to work with these results that might say something useful about the size of the universe?
In my mind, these are all ideas worth pursuing and so I suppose you could interpret this blog post as a challenge: let’s get some answers to these questions!
Might the Infinity of the Universe Have a Tangible... By GEORGE MUSSER
“There is a difference between whether the universe is infinite or just really really really really really really big,” Anthony Aguirre said at the recent FQXi conference in Puerto Rico. I’m pretty sure I counted six reallys. With that remark,...
Consciousness as a State of Matter--Max Tegmark's... By ZEEYA MERALI
[picture]More audio from the FQXi meeting in Vieques, this time from cosmologist Max Tegmark. As Ian has already blogged, Max has been pondering what qualities conscious matter would have that differentiates it from non-conscious matter.
Time From a Timeless World By GEORGE MUSSER
Theoretical physicists commonly say their biggest challenge is to unite general relativity with quantum theory. But at this month’s FQXi conference in Puerto Rico, Carlo Rovelli said they have an even bigger challenge: to unite general relativity...
Interesting Ways to Die (and More) By IAN DURHAM
[picture]The final full day of the conference in Vieques began with a session on quantum gravity. (Some slides and videos from the meeting are now up: here.) Seth Lloyd led off the longer talks by essentially summarizing what we know about in-falling...
The History of Astronomy with Julian Barbour and... By ZEEYA MERALI
This is a quick post to alert you to a new video project by FQXi members Julian Barbour and Flavio Mercati. Backed by FQXi, they are creating a series of films, in English and Italian, on the history of astronomy. Here is part one, in Italian, but...
String theory vs Loop Quantum Gravity: Bousso and... By ZEEYA MERALI
Depending on how familiar you are with FQXi, you may know that we like to cause a little mischief at our conferences. Knowing that we had famed string theorist Raphael Bousso and Carlo Rovelli, one of the originators of loop quantum gravity, in the...
Fluctuations, Schmucuations By GEORGE MUSSER
PUERTO RICO—One of my favorite talks at the recently concluded FQXi conference was Sean Carroll's takedown of the concept of quantum fluctuations in inflationary cosmology. Regardless of the fate of his overall argument—which my fellow FQXI...
Consciousness, Free Will--and Asking Siri Out on a... By IAN DURHAM
As I mentioned in my previous post, they keep us rather busy at this conference so I did not have the opportunity to put additional thoughts down on "paper" until just now as I sit in the Philly airport for the next few hours (it’s January and...
FQXi'ers Debate the Deep Questions of Free Will By GEORGE MUSSER
VIEQUES, PUERTO RICO—Some years ago, while visiting South Africa, I was astounded by the number of languages my friends spoke. It’s not just they knew Xhosa, Zulu, SeSotho, English, and Afrikaans, but that they moved freely among languages to...
Sean Carroll Fluctuates on Boltzmann Brains and... By ZEEYA MERALI
[picture]More audio from the FQXi meeting is now in. Those of you that read Ian Durham's summary of Day 2 will already know that cosmologist Sean Carroll, at Caltech, gave (in his own words) an "inflammatory" talk (with the deliberately boring title...