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Oct 5, 2022 11 tweets 9 min read Read on X
🧵 "Designing #ActiveMatter in Space-time"

Today's SFI Seminar by @SurajShankar92 (@Harvard), streaming now:
"I consider the Organism, or natural Machine, a machine in which each part is a machine."
- #Leibniz

🦠 Energy → Work

"Active matter *employs* control, either internally [e.g., embryogenesis] or externally [e.g., with sheepdogs]."
- @SurajShankar92
@SurajShankar92 A potent control mechanism for active matter: using #optogenetics to paint portraits and drive micro-robotic ensembles made of modified #bacteria.

"What are the rules you need to follow and the policies you need to enact?"
- @SurajShankar92 contemplates design principles:
Optimizing a balance between forces, @SurajShankar92 seeks the least work required to move a drop without changing its shape.

Size, however, is variable. "It's like a dinner party: first, you gather everyone together..."



#SurfaceTension #Physics
"You can INCLUDE shape change; once you do that the problem has to be solved numerically. Once you allow shape change you have to ask how strong are the active forces relative to the passive forces. For small capillary numbers, surface tension dominates."
- @SurajShankar92
"Perhaps cells DO use strategies that are perhaps similar, if not the same, as what we obtain from this optimization process."
On optimization in evolving systems:

"It's been shown in *several* contexts that what we see E. coli doing is the best it *can* do."
- @SurajShankar92
"You can use local excitations to carry information. You can think of this [magnetic] vortex-like structure as an entity unto itself, and think of the swirling as a bit. All of these systems are continua, and a common way of controlling them is by creating localized excitations."
"There are two key excitations in these systems: one is this trifoil-shaped structure & the other is this comet-shaped thing."

"How should we think about control in such a system? Can you design strategies and protocols for assembling these defects into configurations we like?"
"Symmetry is the key. The +1/2 defect can be described by a vector. The -1/2 defect is described by a complex number. How do we model these systems? By writing hydrodynamical equations...it couples order to flow."

"Viscosity dominates and force balance is linear."
"For constant activity, the +1/2 defect moves & the -1/2 defect stays put."

"This allows us to collapse an ∞ degrees of freedom..."

Re: +1/2, "The direction of the parabola allows you to choose the direction of the flow."

"You can build any complex trajectory that you wish."

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More from @sfiscience

Mar 10, 2023
🧵 "The Smell of Inhibition. A Code in the Nose?"

ICYMI, this week's SFI Seminar by Fractal Faculty Stuart Firestein (@Columbia) on "what started out ass a very simple-seeming problem [re: #olfaction] and turned out to be very complicated":

"Everything we know about the world comes through these little holes in our head and the skin covering our body, processed through tissue specialized to interpret it."

"The thing to notice about [sight and hearing] is that they're [processing] fairly low-dimensional stimuli."
"Even a simple smell is composed of a VARIETY of molecules, and these are high-dimensional from a chemical point of view. And it's also a somewhat discontinuous stimulus. How do we get from this bunch of molecules to this unitary perception of something like a rose?"
Read 8 tweets
Mar 10, 2023
🧵 "#Possibility Architectures: Exploring Human #Communication with Generative #AI"

Today's SFI Seminar with ExFac Simon DeDeo @LaboratoryMinds (@CarnegieMellon), streaming now:
"A key feature of this is talk is that we make sense of what each other are saying IN PART by what they say, but ALSO by what we expect of them."
"Language transmits info against a background of expectations – syntactic, semantic, and this larger cultural spectrum. It's not just the choices of make but [how] we set ourselves up to make later choices."

@LaboratoryMinds re: work led by @clairebergey:
Read 15 tweets
Mar 9, 2023
"I think what really drives [the popularity of the #multiverse in #scifi] is regret... There's a line in @allatoncemovie where #MichelleYeoh is told she's the worst version of herself."

"I don't think we should resist melting brains. I think we should just bite the bullet."
"When you measure the spin of an electron, or the position...what happened to all of the other things you could have seen? Everett's idea is that they're all real. They all become real in that measurement."
- SFI Fractal Faculty @seanmcarroll at @guardian
theguardian.com/science/audio/…
"At the level of the equations there is zero ambiguity, but the metaphors break down. The two universes it splits into aren't as big as the original universe. The thickness of the two new universes adds up to the thickness of the original universe."
Read 4 tweets
Dec 14, 2022
"Compositionality in Vector Space Models of Meaning"

Today's SFI Seminar by @marthaflinders, streaming:


Follow this 🧵 for highlights!
"Scientists gather here
Santa Fe Institute, oh so near
Inquiring minds seek truth"

#haiku about SFI c/o @marthaflinders & #ChatGPT

...but still, #AI fails at simple tasks:
"One way to represent the kind of #compositionality we want to do is with this kind of breakdown...eventually a kind of representation of a sentence. On the other hand, vector space models of #meaning or set-theoretical models put into a space have been very successful..."
Read 14 tweets
Dec 13, 2022
"Humans are prone to giving machines ambiguous or mistaken instructions, and we want them to do what we mean, not what we say. To solve this problem we must find ways to align AI with human preferences, goals & values."
- @MelMitchell1 at @QuantaMagazine:
quantamagazine.org/what-does-it-m…
“All that is needed to assure catastrophe is a highly competent machine combined with humans who have an imperfect ability to specify human preferences completely and correctly.”

- Stuart Russell (@UCBerkeley) as quoted by @MelMitchell1 in her latest @QuantaMagazine article
"It’s a familiar trope in #ScienceFiction — humanity threatened by out-of-control machines who have misinterpreted human desires. Now a not-insubstantial segment of the #AI research community is concerned about this kind of scenario playing out in real life."
- @MelMitchell1
Read 6 tweets
Dec 12, 2022
"Training Machines to Learn the Way Humans Do: an Alternative to #Backpropagation"

Today's SFI Seminar by Sanjukta Krishnagopal
(@UCBerkeley & @UCLA)

Starting now — follow this 🧵 for highlights:
Image
"When we learn something new, we look for relationships with things we know already."

"I don't just forget Calculus because I learned something else."

"We automatically know what a 'cat-dog' would look like, if it were to exist."

"We learn by training on very few examples." Image
1, 2) "[#MachineLearning] is fundamentally different from the way humans learn things."

3) Re: #FeedForward #NeuralNetworks

"You choose some loss function...maybe I'm learning the wrong weights. So I define some goal and then I want to learn these weights, these thetas." ImageImageImage
Read 13 tweets

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