(July 18, 2017 at 9:22 pm)Tres Leches Wrote: Who's your avatar?

-Teresa

That's Arnold Schönberg, my favorite 20th century composer, in a portrait photograph by surrealist artist Man Ray.
p.s. the quote in my profile is from one of his string quartets which involves a poem.

(July 18, 2017 at 9:45 pm)ignoramus Wrote: When are you definitely going to to be famous?

(None of this uncertainty principle please)

(Also, now that the silly troll is gone, between you and me, can you tell me the real reason helicopters can't fly?)

If the LHC discovers that there is a certain type of remote brane with supersymmetric dark matter on it, my name might appear in the papers.

As to your second question, have you seen the things? They are basically upside down milk frothers. Of course they can't fly, it's all CGI.

(July 18, 2017 at 9:50 pm)mh.brewer Wrote: What is the least understood and/or most controversial thingy that physics is looking at?

You might expect that I mention the usual cosmological phenomena like dark matter or dark energy, but I think what's much more complicated is the behavior of complex and chaotic systems such as high temperature superconductivity. Noted physicist and Nobel laureate Robert Laughlin has written an entire book moaning about how fundamental physics is doomed because we don't understand complex systems. He is wrong about fundamental physics, but it is true that deriving properties of complex systems from the basic laws is very difficult. In the same vainvein, for most controversial, I'd vote for the claim that consciousness is tied to the effects of quantum physics, and that quantum physics plays an essential role in how consciousness arises in the brain. Legendary physicist Roger Penrose has been a famous advocate of that idea. He's wrong though.

The Everett ("many worlds") interpretation of quantum mechanics is obviously very controversial, but several very smart people such as David Deutsch and Sean Carroll swear by it, claiming that it is the only philosophically sound interpretation of QM. I also find it very compelling, but I wouldn't bet my life on there being parallel copies of myself.

(July 18, 2017 at 10:54 pm)bennyboy Wrote: Alex, I have a question concerning the dimensions in SST.  My understanding is that most of them are found at the tiniest scales.  Does this mean they are in some way fractal, and if so, could you INFER something reasonable about some kind of super-dimension despite the observational breakdown at the event horizon of the BB singularity?  In other words, is there any possibility of unifying all the dimensions under a single principle or mathematical relationship, say it's turtles all the way down, and then extend that principle upward as well?

Or am I just talking out my ass?

The role of space in Superstring Theory is interesting and sometimes controversial. In the usual approaches to superstring theory, a smooth ten-dimensional spacetime is usually assumed as a starting point because the quantum theory of supersymmetric strings demands it for consistency. (This assumption of a smooth geometry as a starting point is sometimes criticized by proponents of more audacious approaches to quantum gravity such as loop quantum gravity, in which you basically take nothing for granted, which leads to horrible technical challenges.) Closed strings are actually nothing but gravitons and hence fluctuations of spacetime itself, and so, the presence of a closed string indicates a small fuzzy deviation from flat space. If you zoom in, you will find the string having loops and holes and twists of all sorts, corresponding to arbitrarily complicated deformations of space at small scales, and this could, I suppose, look as if space was fractal. However, I have never heard it claimed by real string theorists (I have only dabbled in string theory from a field theorist's perspective) that the spacetime they formulate their theory in has anything but exactly 10 dimensions, not some weird fractal dimension. Maybe that's because there is an intrinsic string length related to the planck length, and I would venture a guess that below this length, deformations of the string, and hence of spacetime as well, are strongly dampened, smoothing out the fluctuations of space at the smallest scales and ensuring a well-defined dimensionality. But I am not sure at all.

An amusing side note: in order to get rid of infinities in quantum field theory, Nobel laureates Martinus Veltman and Gerardus 't Hooft have invented a mathematical scheme that is now universally used in calculations called dimensional regularization, in which it is assumed as a mathematical trick, that the dimensionality of spacetime is some noninteger number d. Only after all calculations are done and observable quantities are expressed in terms of other observable quantities is the limit d->4 taken, and the infinities are gone. People have entertained the thought that maybe, nature actually has a noninteger number of dimensions close to 4, and that this is more than just a mathematical trick, but that is a complete pipe dream.

In recent years, string theorists have considered scenarios which are non-geometric, i.e. the quantum structure of the additional space dimensions is so weird that it cannot be expressed in terms of usual geometry. I know next to nothing about how that works, though.

(July 18, 2017 at 11:30 pm)pool the matey Wrote: Also question for Alex, why did you leave your previous job? How flexible is your current job to balance with your family time?

You answered it yourself. My current job is perfect to balance it with family time, and being an academic nomad is hell if you have anyone else in your life. My next logical career step would have been to apply for an assistant professorship or something similar abroad, and that would have put incredible strain on my family and would have killed my wife's career.

(July 19, 2017 at 4:00 pm)Alex K Wrote: You might expect that I mention the usual cosmological phenomena like dark matter or dark energy, but I think what's much more complicated is the behavior of complex and chaotic systems such as high temperature superconductivity. Noted physicist and Nobel laureate Robert Laughlin has written an entire book moaning about how fundamental physics is doomed because we don't understand complex systems. He is wrong about fundamental physics, but it is true that deriving properties of complex systems from the basic laws is very difficult. In the same vainvein, for most controversial, I'd vote for the claim that consciousness is tied to the effects of quantum physics, and that quantum physics plays an essential role in how consciousness arises in the brain. Legendary physicist Roger Penrose has been a famous advocate of that idea. He's wrong though.

Yay! So glad to hear you say that. AI researchers generally just ignore him.

Which is related to a question I was going to ask you. Do you get annoyed with woo-ists, arm chair philosophers and new agey people justifying what they want to believe by explaining it as something to do with quantum mechanics? And is it a big problem with people with absolutely no experience or knowledge of physics thinking that they know a lot about it and arguing with experts who actually do? It certainly is a common occurrence in AI but I think that's because the field is still in its infancy and has so few successes.

Do you teach in a way that does not bore your students?

(July 19, 2017 at 4:00 pm)Alex K Wrote:

(July 18, 2017 at 9:50 pm)mh.brewer Wrote: What is the least understood and/or most controversial thingy that physics is looking at?

You might expect that I mention the usual cosmological phenomena like dark matter or dark energy, but I think what's much more complicated is the behavior of complex and chaotic systems such as high temperature superconductivity. Noted physicist and Nobel laureate Robert Laughlin has written an entire book moaning about how fundamental physics is doomed because we don't understand complex systems. He is wrong about fundamental physics, but it is true that deriving properties of complex systems from the basic laws is very difficult. In the same vainvein, for most controversial, I'd vote for the claim that consciousness is tied to the effects of quantum physics, and that quantum physics plays an essential role in how consciousness arises in the brain. Legendary physicist Roger Penrose has been a famous advocate of that idea. He's wrong though.

The Everett ("many worlds") interpretation of quantum mechanics is obviously very controversial, but several very smart people such as David Deutsch and Sean Carroll swear by it, claiming that it is the only philosophically sound interpretation of QM. I also find it very compelling, but I wouldn't bet my life on there being parallel copies of myself.

And I'm off to google. Thanks (no sarcasm, no really, seriously, camon-what do I have to say?)

(July 19, 2017 at 5:56 pm)Lutrinae Wrote: Do you teach in a way that does not bore your students?

You'll probably get different answers depending on which of them you ask. But yes, I think I accomplish that goal most of the time. I am an engaging speaker with lots of experience giving talks, my classes always and constantly involve the audience with questions and exercises, and I create an atmosphere in which students usually have no qualms to admit or complain if they don't get something. Nevertheless, individual students who are lost will perceive the class as boring, although I am always willing to go back to square one with individual students while others are working. Also, there are some problems I have to teach which even I have a hard time justifying in terms of applications. Those can be a bit boring to solve.

Do you have a TA?