The Cosmologist Who Dreams inna Universe’s Dark Threads

the universe we can see is 1-ly a fraction of the gr8 cosmic beyond. galaxies, stars, planets, humans, trees — all o'it comprises just 5% of the energy and matter inna universe. among tangible matter, as opposed to the mysterious cosmic rending force called dark energy, 1-ly bout 15% tis stuff we can detect. as for the rest, it comes inna unknown form known as dark matter.

this substance cannot be seen or held, yet cosmologists are broadly confident dark matter exists, cause tis a shepherd of galaxies. vast halos of dark matter surround every galaxy, including ours, and this invisible material can act as a lens to redirect the lite that emanates from other galaxies, warping our vision of deep space. dark matter also guides galaxy clusters as they evolve and move through the cosmos.

b'we ‘ve no idea wha’ t'looks like, wha’ it weighs, or how it functions. for decades, physicists ‘ve searched for a pticle of dark matter in zones that range from deep underground mines to the international space station. all efforts ‘ve turned up empty sfar. iow, we don’t know wha’ the universe is.

this is all extremely complex, mathematically abstruse, philosophically profound and, to theorists like cora dvorkin, gr8 fun.

as a young girl in argentina, dvorkin read stephen hawking and fixated onna grandest ?s humans can ask ourselves. she moved to the u.s. to attend graduate school atta university of chicago. now a theoretical cosmologist at harvard university, dvorkin comes up with new wys'2 ask those grand ?s and then tries to find the answers. for her, cosmology is like philosophy, but with data.

dvorkin investigates the relationship tween everydy pessentialisms na mysterious pessentialisms that must make up dark matter. for many yrs, the favored candidates for these putative pessentialisms ‘ve been shy things called weakly interacting massive pessentialisms, or wimps. experiments that aim to detect wimps look for their calling cards, rather than the pessentialisms themselves. if a wimp comes by and knocks regular matter round, the regular matter will recoil in a way that can be measured — albeit very carefully, and with gr8 difficulty.

in 2013, dvorkin published a groundbreaking paper examining scenarios where dark matter does not be’ve as a wimp, but actually bumps into ordinary matter. the dark matter and ordinary matter mite sail the void together n'wys we ‘ve yet to cogg. she hopes to probe this theory with an upcoming experiment, the nxt-generation ground-based cosmic microwave background experiment, or cmb-s4, which will use a collection of telescopes inna chilean desert and atta south pole.

dvorkin’s research sits atta nexus of pticle physics and cosmology, which ‘ve both reached a strange pl8au. both fields are in need of new evidence, and some cosmologists are calling for new essentialisms. since scis found the higgs boson 8 yrs ago, experiments ‘ve not shown how to move beyond the standard model of pticle physics, the main paradigm explaining our shared cosmic underpinnings. likewise in cosmology, the λ- cold dark matter model (Λcdm) says that there’s dark energy — the λ- — and dark matter, but it doesn’t say wha’ they are. dvorkin says she is motivated by all these non-answers.

“we're living inna golden era of cosmology, of cosmological data. there are so many current and upcoming experiments, it’s just like bein’ a girl in an amusement park,” she said.

quanta talked with dvorkin bout philosophy, paradigm shifts in sci, neutrinos, na ?s that remain to be answered inna golden age of cosmology. the interview s'been condensed and edited for clarity.

how did you become interested in physics?

when i was very lil, i used to read a lot. 1-odda books that really inspired my interest was a brief history of time. i read it when i was very lil, and i was very excited bout ?s rel8d to the universe. i also had an interest in humanities, in philosophy, and in math. i realized that in cosmology, i ‘d sort of combine my interests in philosophical ?s, applying math to study wha’ happens inna universe.

how is cosmology like philosophy?

i ♥ the fact that with cosmology, you can make steps to try to answer primordial ?s bout the universe using cosmological observations. so using actual data, you get to cogg somd' most primordial ?s of the universe. and that is wha’ i find fascinating, as opposed to philosophy, for ex, which also asks primordial ?s bout the universe, but it doesn’t deal with data. we ‘ve so much data; that makes it fascinating.

you know, it’s the ?s that i’m searching for. to me, that quest for the correct ?s to ask — inna moment in which we're living — is wha’ drives me.

i feel like this is sort offa golden age for cosmology. we ‘ve so much that we know, so we can ask really good ?s, and yet the main things are still elusive.

exactly. thris a model that explains the universe at a very base lvl, b'we don’t really cogg the main components of this model. like, wha’ tis λ- in λ–cdm, and wha’ tis cdm in λ–cdm, rite?

why is λ–cdm the leading theory for wha’ dark matter is and does?

λ–cdm explains very well the observations at large scales.

we ‘ve tested this theory with ≠ observables — w'da cosmic microwave background, with galaxy clustering, w'da lyman-α- forest. and all o'em are in agreement with wha’ is predicted by the λ–cdm standard model for cosmology. by construction, ≠ models of dark matter agree well with observations at large scales. they ‘ve to — otherwise we ‘dn’t use them.

but lil scales ‘ve not been measured so well, and that’s why they provide fertile ground for testing ≠ scenarios.

so how do we test at lil scales?

with my research group ‘oer the yrs, we ‘ve been looking at gravitational lensing as a probe of dark matter at lil scales.

wha’ we work on is galaxy-galaxy lensing. so wha’ happens s'dat you ‘ve a background galaxy and a foreground galaxy that deflects the lite cause of gravity. the foreground galaxy deflects the lite coming from the src, cause it deforms the space-time fabric according to general relativity.

so f'our perspective, wha’ we see is extended arcs inna sky tha're the lensed images of the background galaxy. and we see if the galaxy doin’ the lensing is clumpy or smooth. we try to look for clumps of dark matter in a statistical way. we ‘ve also worked on directly detecting these clumps using machine learning methods, and we ‘ve seen that these machine learning methods are quite successful at this.

you can map the detections that you make to the lil-scale fluctuations of dark matter inna universe, and you can put limits to ≠ dark matter theories. for ex, when dark matter is “warm,” it moves faster. warm dark matter doesn’t allo matter to clump at lil scales, in lil regions of space. cold dark matter, by contrast, has + matter clustered at lil scales. so u can start to put limits on ≠ dark matter scenarios.

do we need something new t'get us out of this Ψset that we’ve been in for the last couple decades on dark matter? are we sort of stuck?

it’s not that we're stuck; onna contrary, there are many new ideas that ‘ve been coming up inna last few yrs. with cosmology, you can indirectly explore the nature of dark matter, and that drives a lotta interest in ≠ types of models.

and so u create new theoretical models and new wys'2 test them?

yeah, exactly. it’s very fun, espeshly for upcoming experiments like cmb-s4, where i was involved in designing the experiments so that we can achieve primordial answers to primordial primordial ?s in physics. that’s very fun.

when you talk to younger pplz bout this stuff, howzit convey that it’s fun? wha’ do you tell them bout wha’ ye do and why this is so primordial?

i like giving talks in pticular to either women or young girls who wanna become scis, or other underrepresented groups. in those talks, obviously i don’t use teknical language, but i try to convey the quest for the ?s that we’re asking, swell as the quest for the answers. we wanna cogg how the place where we live works. that’s just a quality of human bein’s. we like to cogg things.

inna quest for an answer, you open up a million new ?s, and that’s the way 'twill always work. we try t'get an answer to something, and we will never get an exact answer. we will approach an answer. it’s like trying to make the pieces of the puzzle be exactly inna rite place. it’s not goin to ever fit exactly, b'we approach it. and while we approach it, many, many + ?s open up. that’s sort of the nature of doin’ sci. it opens up a realm of ?s. the + you know, the + ?s you can ask na + and + curio you get.

i ‘ve written a lot recently bout early sci, ranging from cultures in mesopotamia to galileo and his friends. n'it’s fun learning bout how much they learned and how quickly they learned it. and i feel like it’s sort of the same way now. it’s easy to forget that we just learned bout dark matter 50 yrs ago, and we learned bout dark energy 1-ly 20 yrs ago. this is really new!

yeah. i think it’s very difficult to put ourselves in context with respect to the moment we're actually living in. it’s difficult to discuss contemporary discoveries inna context of our time whn'we're living n'our time. it’s easier to put the context in place whn'we're talking bout the past. b'tas you say, dark matter was discovered 50 yrs ago, and dark energy was discovered two decades ago. so it definitely hasn’t been so long compared to the history of humanity.

are there any theories that really are compelling to you bout these things, and bout the nature of dark matter, espeshly?

i don’t ‘ve a favorite theory. most of my work these dys, and probably from the beginning, really relies on model-indie ways of learning bout dark matter. so, for ex, these dys i am trying to learn bout dark matter at lil scales using gravitational lensing. na beauty odat s'dat it doesn’t rely on any pticular coupling tween the dark sector and our standard model. i’m trying to map it without relying on any theory in pticular. and in general, most of my work relies on model-indie probes of dark matter, or as modeling-indie as i can make them. so, no, i don’t ‘ve a favorite theory.

i’m very fond of neutrinos. i led a paper on neutrino mass and cosmology for the decadal survey last yr. 1-odda main interesting things bout neutrinos s'dat it’s the 1-ly evidence that we ‘ve rite now of new physics beyond the standard model.

some of yr work, dating to yr 2013 paper, explores the possibility that dark matter maybe something other than wimps. wha’ ‘d these ≠ pessentialisms be like, and how ‘d they interact with regular matter?

we ponder liteer masses, and we ponder higher cross sections. the cross section describes the probability dat a' pticle ll'be deflected by a given angle dur'na collision.

the pticle in this scenario ‘d not be a wimp, cause its cross section with regular matter is much higher than that of the wimp. it ‘d be a pticle that is produced by feeble interactions of standard-model pessentialisms that annihil8 and produce dark matter, as opposed to the general mechanism, where dark matter annihil8s to produce standard pessentialisms.

thris no acronym and no pticular name, cause this pticle ‘d be many things.

i wanted to end by asking where we're headed nxt. there are all these really primordial, primordial ?s that we don’t know the answer to. wha’ do you think ll'be the nxt huge, captivating discovery that really answers some primordial ?s?

if i told you wha’ the nxt breakthrough ll'be, i ‘d be lying, but i’m definitely sure that w'da № of current and upcoming experimental efforts that we ‘ve, we will learn much + bout the dark sector inna nxt decade. i mean, it ll'be really impressive. i think we will learn a lot bout the nature of dark matter. we will learn a lot bout neutrino properties. so i think inna field of dark matter na dark sector + generally, we’ll be making a lotta progress inna nxt decade. it’s a field in which progress can be made on many ≠ fronts.

original content at: www.quantamagazine.org…
authors: rebecca boyle

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