Podcast
Ologies with Alie Ward
Expert
Duration
1 hour, 25 minutes
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Physics etc.
Tags
Dark MatterReality
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Notes
First, thank you to Ologies host Alie Ward for warning us fragile, mortal listeners about the existential-dread-inducing questions we’re about to explore. As she says, “It gets spooky.” Onward!
Guest: Dr. Flip Tanedo (he/him)
- Theoretical physicist and dark-matter expert (aka “Scotohylologist” as coined in this episode)
- Tenured Professor of Particle Physics at UC Riverside
- Studied mathematics and physics at Stanford and Cambridge
- Earned a PhD at Cornell
- Is a straight-up sweetheart
Some tone-setting questions:
- What is the universe made of?
- How do stars die?
- Why are we colliding particles underground?
- Who first noticed dark matter?
- What is the best vintage insult?
- Are there space ghosts?!
What do you call the study of dark matter?
- Current literature says things like “dark matter cosmology” or “dark cosmology”
- Alie has brainstormed new ideas ahead of time:
- Non-baryonic hylology
- Hylology is the study of matter
- ‘Baryonic’ refers to everything made of normal atomic matter, so dark matter could be called non-baryonic
- Flip says that while theoretical dark matter might be a researcher’s main focus, they’re generally doing a lot of particle physics and looking at quantum fields
- They work on things that are essentially invisible, not necessarily dark, but we can’t make this man call himself an invisibleologist
- Flip mentions a senior theoretical physicist at UC Riverside, Ernest Ma, who once wrote a paper that included the word “scoto” — the greek word for dark!
- Alie mixes the best of both worlds and comes up with scotohylology. My inner linguist is fawning, fangirling, flipping out.
What are theoretical fields? What are you studying?
- The fundamental building blocks of matter
- We know about atoms, but then there’s a huge rabbit hole beyond that
- The idea is that there’s some unit of stuff, and as Einstein taught us, it can’t just be stuff — there’s some unit of energy
- In quantum mechanics, the word ‘quantum’ refers to quantizing (identifying the discrete levels of energy or number of possible states for that stuff)
- You can’t give someone 1.5 cents, you can either give them 1 penny or 2 pennies — energy behaves like that in certain systems
- Theoretical physics is meant to answer the question of: “What are the fundamental things that, if you understood them, could explain slightly bigger things?” And those then describe even bigger things, and so on
Did you set out to become a dark matter expert? How did you end up in this field?
- Dr. Flip Tanedo wanted to be an author. My heart!!!
- He loved Reading Rainbow and learned a lot from Levar Burton, who was also on a little show called Star Trek
- He watched Star Trek a little bit, but when he picked up a booked called “The Physics of Star Trek” by Lawrence Krauss and Stephen Hawking, it was the first time he saw science as something where there are big, exciting open questions with imaginative ways to explore
- He got very into the idea that the black holes in the show are actually real and posed fundamental questions! You and me both, Flip!
- He would eventually like to revisit writing — please, I beg!
When it comes to matter and dark matter: how much of the universe is made up of the stuff we can see/feel/touch?
- Five percent. Yes, that’s 5% with a single digit.
- That leaves 95% of the universe’s mass and energy a total mystery to us
So then what the heck is everything else?!
- We’ve known about dark matter, directly or indirectly, for over 100 years, but we’re just now saying “we should really figure out what all of this is”
- 25% of the universe is made of dark matter while 5% is made of the stuff we’re familiar with — so there’s 5x more dark matter than “ordinary stuff”
- The entire galaxy we live in, all of the matter and intelligent life inside of it is only here because it’s swimming in dark matter. It only formed because of dark matter
- We’re like fish discovering there’s something out there called water and setting out to investigate what it is
Is the other 70% dark energy?
- Yes!
- This quote is so good I have to write it down as accurately as possible:
“I’m excited that I have no idea what dark matter is and there are great things to do in that field; I have no idea what it is. Dark energy — I have no f***ing idea, and I’m terrified, and there’s a reason why I don’t work on it!” - Dr. Flip Tanedo
When and how did we first realize something wasn’t adding up?
- About 100 years ago
- It started with observations from astronomers
- People looked at galaxies, observed how fast stars were moving in those galaxies, and figured out that the stars were going a little bit faster than physics would predict
- Astronomy left it at “Huh! That’s curious,” for 50 or 60 years
- Evidence kept mounting that this couldn’t have been due to miscounting the number of stars
- Instruments and methods became more advanced, but the numbers weren’t coming any closer to making sense. There was way too much extra gravity, and we weren’t coming up with any answers for it
- What we know now: not only is there stuff we haven’t accounted for, it cannot be the same stuff we are made of
“This whole time we thought that we were a cookies & cream milkshake — but we’re just the oreo bits. And we’re surrounded by an invisible milkshake that can seep through us.” – Alie Ward
- Dark matter doesn’t interact with light or electromagnetic forces, so we can’t see or feel it
- Vera Rubin hypothesized that dark matter was exerting gravity, and without it, galaxies would fling themselves apart because their “normal” (or baryonic) matter could not produce enough gravity to keep everything pulled together on its own
- She figured that out in 1978 — practically yesterday, in the grand scheme of things!
- Rubin did her calculations at an observatory that did not have a restroom for women. She used her own paper to cut out the silhouette of a dress and tape it to the door of a men’s room, then went back to figuring out what might explain the nature of the entire universe and everything in it
- Later, elementary particle physicists realized they had spent decades trying to create a fundamental periodic table of elements that accounted for everything in nature. Oops, there’s a lot missing!
[20:05]
How is the Higgs-Boson related to dark matter?
- In the 80s and 90s, there was a big question mark in particle physics. It was about a theoretical particle called the Higgs-Boson
- The Higgs-Boson was later discovered in 2012 at CERN
- It’s been inaccurately called the God particle, a misinterpretation that stems from a very frustrated scientist referring to it as “the goddamn particle”
- Those earlier researchers were confident that the Higgs-Boson existed, but even if it did, something still wasn’t quite right with the theory
- Even if the theoretical Higgs had the mass and properties it would need to solve the gravity issue, somehow it still wasn’t right
- We now know that the Higgs weighs about 125x the mass of a proton
- That’s huge, but our predictions would have expected it to be much, much heavier
- “It’s like balancing a pencil on its tip. The quantum corrections to its mass would make the Higgs heavier than it is”
⚠️ I’m getting lost here. Luckily, Alie provides a helpful aside:
- Higgs particles make up the Higgs field, which is a big cloud of bosons (or particles). So, matter started out zipping around like photons, unencumbered by mass — but interaction with the Higgs field is what makes matter interact with gravity, creating mass which makes things gravitationally attracted to each other.
- But Higgs-Boson is very hard to find; you have to get, like, a Large Hadron Collider, let’s say. Maybe 27 kilometers under Geneva. And then you’ve gotta race protons at each other, explode ‘em, and measure what’s left (a.k.a. a ‘decay signature’). If you’re looking through all those pieces and you find remnants of what could have been a Higgs-Boson that existed for a fraction of a millisecond, then that’s a little sliver of proof.
Okay, back to my new best friend Flip Tanedo:
- Flip says it was like putting an ice cube in an oven, turning the oven on, and trying to figure out how the ice cube is still there
- It was the reason that our entire Standard Model of particle physics couldn’t be complete
- The Standard Model of particle physics involves a uniform framework for understanding electromagnetic, weak, and strong interactions
- They called it the Hierarchy problem with a capital H
- The Hierarchy problem refers to the discrepancy between the way a weak force (one which allows protons to become neutrons and vice-versa) is actually not very weak at all: at short distances, it’s 10^24x stronger than gravity
- People started coming up with all kinds of theories: super-symmetry, extra dimensions, etc. ‘Twas a heyday
- During this heyday, scientists also realized that in order for the Standard Model of particle physics to work—in order for protons not to decay too quickly, in order for the universe to actually look the way it does—we need to tweak it
- We end up with new particles that stick around forever and do not decay
- Flip imagines that an astronomer overheard a physicist talking about these hot, new, eternal particles and said “Excuse me, did I hear you have particles that just sit around and contribute mass forever? Have you heard about this galaxy anomaly we have?”
- Physicists essentially said, “Hey astronomers, we have discovered the answer to your dark matter problem. Give us 15 years to fire up this collider and we’ll tell you exactly what’s in those galaxies you’ve been looking at for 100 years.”
- When Flip turned in his final thesis and graduated in 2013, the Higgs-Boson had just been discovered, and it was clear that none of the theories he explored would ever be confirmed
- We had discovered the “most boring” version of the Higgs-Boson and none of the predictions around the overarching theory explained why it was there. We got stuck.
- Now, there’s revived interest in the theory of dark matter. It’s still out there!
So, what are we working on now?
- Several people are still working on understanding the Higgs-Boson
- Many others have turned to working on dark matter, but with fresh eyes and more open-ended questions rather than set theories that would explain it if proven
Did you all expect to flip a switch on the collider, hear some pew-pew-pew noises, and suddenly see that a lot of calculations were right? Or suddenly it’s quantum leap and we’re in a different dimension? How does this work?
- In general, physics is split between theorists and experimentalists
- Theorists work on the “mathematical superstructure”
- Experimentalists test the theories and actually perform the scientific method
- So theorists direct experimentalists where to look, and experimentalists do the looking
- Flip jokes that he and his fellow theorists really did imagine it would be as simple as turning the machine on and getting a result, but now they understand that colliders are huge, cavernous, intricate machines looking for invisible stuff
- The Large Hadron Collider at CERN was “turned on” in 2008, and it wasn’t until four years later in 2012 that researchers were confident that had found the Higgs-Boson
- LHC was successful because it finally had the “juice” required to produce and detect the decay signature of a Higgs particle. It was able to smack photons together hard enough, trillions of times, and collect data on all of the remains
- The discovery earned a Nobel Prize in 2013 for “the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles...”
Do you ever hear theories that say we shifted into another dimension as soon as the LHC was turned on?
- Yes, those theories are out there. Flip calls it “a bit wonky” because he is nice
What about the names ‘dark matter’ and ‘dark energy’? Who decided to call them that?
- It may have been the late Fritz Zwicky, a “famously cantankerous physicist” (FLIP!!!) in the early 20th century (most active in the field between the 1930s-1960s, died in 1974)
- Zwicky worked at Caltech and Alie confirms he was known for “old-timey verbal abuse” among other claims and feuds
- He referred to his coworkers as “spherical bastards” because “they are bastards no matter which way you look at them”
- When he called it “dark” matter, what he meant was that it didn’t interact with light
- Things that are dark actually absorb light, which is basically the maximal way of interacting with it… so… 🤔
- But if you’re an astronomer, “dark” just means you aren’t seeing any photons from it
- Dark energy came later. Whoever named it was probably drawing a similarity to dark matter (i.e., “Just like dark matter, we don’t know what this is!”)
- With dark matter, we at least know it’s stuff/particles — maybe even just one particle
- Dark energy behaves differently and is “a much weirder thing”
- Later around 45:42, Flip says that discoverability within his lifetime is a major difference between dark matter and dark energy
- We don’t know what either of them are. But with dark matter, we’re at the point of being able to experiment with it and we know enough about it that there’s a real chance we will know something about it during our lifetimes
Do you drive around in traffic and think about this stuff? Can you ever escape theorizing about this?
[Me, quietly, to myself: c a n y o u e v e r e s c a p e t h e o r i z i n g a b o u t t h i s]
- Flip’s imposter syndrome says “yeah, I escape it way too much!” 💔
- He usually finds himself thinking about physics while swimming
- That kind of problem-solving requires the creative spark that comes from being out walking around or relaxing with tea rather than calculating at a desk
Do theoretical physicists get together to have brain dumps and try to spark ideas, too?
- That’s the secret of theoretical physics
- Two of the main institutions in the US are:
- The Aspen Center for Physics in Aspen, Colorado
- The Kavli Institute for Theoretical Physics in Santa Barbara, CA
- These places are like summer camp for theoretical physicists
- It helps them all become fluent in the particular language, analogies, intuitions that they like to use to understand and explain the mathematics
- Sparks happen when everyone is in the same place with no distractions
- They can ask each other “What are you working on? And how do you think about that?”
- You can spend two weeks there and then spend the rest of the year working out those ideas and updating each other. It builds the momentum of the field
Be honest: how many astrophysicists think dark matter might be ghosts? What if it’s all ghosts?!
- Flip recalls researcher Nima Arkani-Hamed’s famous quote from a NY Times article written before the LHC was turned on:
- He pointed out that because of the dice-throwing nature of quantum physics, there was some probability of almost anything happening. There is some minuscule probability, he said, “the Large Hadron Collider might make dragons that might eat us up.”
- There’s something to be said about the idea that dark matter could be something much more exciting than just particles
- There are theories that dark matters (plural) could form dark atoms that we can’t see, but can see each other
- Those dark atoms could have dark chemistry, that dark chemistry could form dark life, etc.
- Maybe there’s an entire sentient civilization living in our dark-matter halo and we just can’t see it
- But, because there is 5x more of them compared to us, we would be the ghosts — we’re the weird thing 😳
[I thought we were friends, Flip!!! You were supposed to say “ha ha what a funny question” or basically anything but this!!!]
[36:45]
Do you still look to science fiction for inspiration, or do you pick sci-fi apart?
- UC Riverside has a fantastic creative writing department, might have to pitch the “dark matter ghosts” idea to Nalo Hopkinson
- He loves seeing how creative people play with physical ideas
- You could say he likes “hard sci-fi”
- Favorite sci fi author right now is Ted Chiang, who wrote the short story that inspired the movie Arrival
- Most people think Arrival is about linguistics, but to Flip, it’s about a particular interpretation of quantum mechanics
- It felt immediately clear that Ted Chiang had taken some quantum mechanics class or read a textbook, understood it incredibly well, and decided to create a world using those exact physical laws with one small tweak and see how that plays out
- Flip draws tons of inspiration from that kind of work because it’s exactly what he does
What was the tweak that Ted Chiang made?
- In “Story of Your Life” the main character could view her entire timeline
- In quantum mechanics, the Principle of Least Action says that to get from Point A to Point B (the universe right now to the universe right… now) we actually went through every single possible evolution on that path
- “Maybe I was sitting in this chair, maybe we were in different chairs, maybe I moved over there and then came back. All of those things “literally happened”; and the path that we took—the most likely path, quantum mechanically—is the one that minimizes some function. Some people call it the “sum over histories” interpretation of quantum mechanics.”
- Ted Chiang said, “Let’s say this character can see that entire history.”
You’ve mentioned dark atoms and dark chemistry — you’re trying to make sense of dark matter using a tool that applies to everything else. Is it possible that there’s a dark math?
- *gasp* Oh, oh boy… okay…
- In a completely non-condescending way, that might be a question for the philosophy department
- Math is logical rigor. This has to be true. Flip can’t think about a different reality with different laws of math
- He can imagine a universe where some of our fundamental constants are a little bit different, or there are more or fewer particles, but that is very different than imagining math itself being different
[41:36]
Is there a dark matter myth you’d love to bust? What does the public think they know about it that they really don’t?
- It’s not antimatter!
- If we’re swimming in a sea of dark matter, and it was really antimatter, it would constantly be mutually-annihilating with ordinary matter and producing massive amounts of light
- It’s probably also not black holes*
- *[I’m putting a pin in this one until Matt O’Dowd chimes in]
- There has been new speculation about tiny black holes formed in the early universe that would behave like (and therefore account for) dark matter
- People used to worry that the LHC would create lots of little black holes that would eat the Earth, but that hasn’t happened and we’re pretty sure tiny black holes would evaporate
[43:22]
Do you think dark matter could be extra dimensions?
- The people who work on extra dimensions don’t literally believe they could step into a parallel universe with the right equation
- The mathematics just show that if you can write a theory that works in 3 dimensions of space and 1 dimension of time, you can write a theory in 4 dimensions of space and 1 dimension of time. Or 5, or whatever. Keep adding. It’s easy to play with.
- In the 1990s, there was a big revelation:
- Particular types of theories with extra dimensions end up giving mathematically-equivalent predictions for a type of quantum theory that’s really difficult to calculate
- In physics this is called a duality. It means you could calculate something in your wonky theory of extra dimensions, and that calculation would actually mean something in an “ordinary” theory (ordinary meaning our 3 dimensions of space and 1 dimension of time) that is highly quantum mechanical but perfectly plausible
- It’s a type of theory we didn’t really know how to deal with until machines like the LHC came along
- We can make and play with predictions that we couldn’t make 20 years ago. We could use those to explore cool theories of dark matter — ones that could explain why we haven’t discovered it yet or could motivate different interesting searches, because that’s where we are right now
[46:07]
Do you have a google alert set for dark matter just in case there’s some news that breaks?
- He has RSS feed and follows some social media accounts for breaking news
- There are special notification networks in physics to get all hands on deck when big astrophysical events are detected, like a supernova explosion
- Thanks to these networks, the next supernova will be the most exciting research opportunity in decades
⚠️ Another helpful aside from Alie:
- A supernova is a giant explosion caused by a star running out of fuel and collapsing in on itself
- Imagine a star with 1,000,000x more mass than Earth collapsing in a matter of 15 seconds
- What’s left is a cloud of gasses called a nebula
- Or, if the star is really big (10x the size of our sun or bigger) you might end up with a black hole instead!
- A supernova can also happen when a white dwarf (a small star, the size of Earth) runs out of fuel, gets too close to another star, begins siphoning off some of its matter, and causes an explosion
- In our galaxy, supernovae only occur a few times every century
- So when they do happen, it’s a huge deal for physicists!
Back to Flip:
- Supernova 1987A taught us a lot about neutrinos
- Now that we know gravitational waves exist and we have lots of astrophysical tools, satellites, and observatories, there’s a network to communicate with all of them quickly
- As soon as someone realizes there’s a supernova, all of those telescopes and detectors will drop whatever they’re doing and point at that part of the sky to collect as much data as possible
[54:30]
Time for questions from listeners!
Is dark matter the absence of matter, or something measurable?
- It’s absolutely measurable stuff!
- We may not know what it is, but it’s fairly ordinary — it’s a thing, it’s stuff, it’s matter
What is a hidden valley? CERN mentions it on their web page about dark matter. Is there potentially a parallel universe occupying the same space we inhabit?
- “Hidden Valleys” are a class of theories developed by Kathryn Zurek and Matt Strassler at Caltech around 2006
- They’re related to some of the extra-dimensional signatures mentioned earlier
- Coincidentally, Flip was just reading the Hidden Valley paper recently for some research he’s working on
- In anticipation of the LHC, everyone had their favorite theories (super symmetry, extra dimensions, etc.) and the Hidden Valley authors were thinking, “What are more exotic things that could come up through the LHC?”
- As he said earlier, theorists (unlike experimentalists) really did sorta imagine that turning on the LHC would mean you could just see the particles clearly all of a sudden
- Of course they also wondered, what if it’s not so easy? What if these new particles don’t really behave like ordinary particles, or they have really different signatures?
- The “Hidden Valleys” were a type of theory that was constructed to show other physicists how unique these new signatures could potentially be
If you consider the theory of multiple universes, could another universe be made entirely of dark matter and dark energy? What’s the difference between multiverses and dimensions — or are they used interchangeably?
- “It becomes a question of where we start agreeing on what words mean”
- What is a universe?
- Let’s assume a universe is a self-consistent (perhaps imaginary) “everything”
- It has some number of dimensions of space and time (caveat: if it has more than one time dimension, we have no idea how to make sense of it)
- It has some kind of governing physical theory — some equation that tells you what the particles are, how they can move, etc.
- A ‘multiverse’ would be a collection of different universes that really should not be able to interact at all
- Whether or not “the multiverse” is real is a weird question
- Not because “if it’s real, something crazy will happen”
- It’s because if a multiverse is real, those other universes by definition have nothing to do with us
- You can’t traverse them, can’t pass through them
- They would have different laws of physics
- If you characterize our universe by some list of numbers—the mass of an electron, the strength of an electric coupling, the strength of gravity, whatever numbers—and you push them into your theory, a different universe would be one with totally a different list of numbers
- The Marvel Cinematic Universe has given us the idea that if there’s a multiverse, you can somehow go between them to harvest things and bring them back (infinity stones, naturally) but that’s just not how it works
What about Everything Everywhere All At Once?
- Flip, a man of taste, loves that movie as a work of fiction
- It’s not scientifically accurate
Time travel: yes, no, or maybe?
- “Oooh… we are definitely traveling in time,” (he’s laughing, but in a way that makes me think he’s about to hurt my brain)
- That fact by itself is interesting. We know that if you’re moving faster, you perceive time differently, so ordinary time travel in the forward direction is already pretty fascinating
- He doesn’t think any Dr. Who-style time travel is possible, certainly not within our existing theories
- Part of that is because our existing theories make causality really important
- Causality is the idea that you can’t have so-called “grandfather paradoxes,” where you could go back in time and kill your grandfather
What would the universe look like if there was no dark matter? What would happen if it suddenly disappeared?
- If there were no dark matter, there would be no “us”
- A good benchmark is the quantum fluctuations of dark matter in the early universe
- The universe was hot, small, and things were blipping into and out of existence
- Sometimes there would be a little bit more blipping into existence in one area compared to another
- That over-density of stuff—dark stuff—would gravitate and pull more stuff in, creating what we call a dark matter halo
- The big dark matter halos were so gravitationally strong—they had so much mass—that they would draw in little tiny specks of dust of ordinary matter
- Slowly, those little specks of dust would collect and turn into our galaxy
- If all the dark matter suddenly disappeared… he’s not sure what would happen! He hasn’t done the calculation to see whether our galaxy might remain or if the smaller galaxies around us would cause everything to scatter
- This question is similar to something he asks freshman physics majors: If the sun disappeared, what would happen to everything in our solar system?
- Eventually everything would just fly away because the gravitational pull that was holding them together would be gone
Is there anti-dark matter to correspond to dark matter?
- Almost certainly yes!
- The laws of physics that we understand seem to imply that everything has an anti-particle
- …with the caveat that sometimes, a particle is its own anti-particle (help help help help I need an adult)
- Photons are their own anti-particle. There is no anti-photon. (This episode will be my cause of death)
- So dark matter exists, it’s a particle, and you can define an operation that turns dark matter into anti-dark matter. It’s just an open question whether that anti-dark matter particle is the same thing as the dark matter particle
- The same question applies to neutrinos, the other invisible particle. We can detect them, and we’ve studied them, but we still do not know whether neutrinos are their own anti-particle
- The original paper about neutrinos says “you could explain this if there were some weakly-interacting, nearly-massless particle—but I’m sorry to have predicted a particle that has no chance of ever being detected”
- But we did detect it! Yay for us
⚠️ Alie saves the day with a quick overview of neutrinos:
- A neutrino is the tiniest little darling particle: they have no charge, nearly no mass, and they’re all over the universe. Millions of ‘em
- They come from exploding stars and the nuclear fusion within our sun
- They zip around at almost the speed of light, going straight through things like your own body every day
- They were discovered in the 1950s, but it took 40 years for their discovery to earn a Nobel Prize
Back to more questions:
What would happen if I had 10 pounds of dark matter in my hand? How much dark matter is in the room right now? How much dark matter is in us?
- Omg, we actually know this!
- Rule of thumb: where we’re sitting in our galaxy, there is about 1 gram of dark matter in your coffee cup
- You can use that to do a conversion and find out how much dark matter is in a room
- Caveat: That 1 gram of dark matter in your coffee cup? We don’t know how many particles that includes
- It could be one single dark matter particle that weighs a gram or 1,000 dark matter particles that each weigh 1 milligram, or anything in between
- We know the mass density of dark matter, but not the number density
- We can’t measure that mass on a scale that normally measure grams because that would be using gravity, right? So we would need a completely different scale to measure that?
- Yes, this is info we’ve inferred from the motion of stars in our galaxy—not terrestrial measurements
Does it change the way you live your life at all, knowing we’re surrounded by such mystery? Do you just take more chances or say “screw it, I’m gonna live for today” and get the whipped cream on your iced blended frappe?
- Flip is in a science book club that read “The End of Everything” by last yearKatie Mack
- There was definitely a week where he thought, “It doesn’t matter how bad things are, the universe is going to end eventually”
- Alie was just reading that book recently and thought, “This is a little depressing but oddly liberating! It’s a great book.”
- There is a two-part Ologies episode with Katie Mack and it’s a certified banger. Notes to come:
Cosmology (THE UNIVERSE) with Katie Mack, Part 1
Cosmology Part 2 with Katie Mack
[1:06:45]
What is the best music to listen to while researching dark matter?
- Currently there’s a 90s Indie Rock channel playing on his laptop, but that’s for class prep
- For research he likes lofi hip-hop playlists without lyrics. You want background music with no vocals
- Bonus: He also makes tea and pulls up a website that generates cafe sounds to create a little ambience while working alone at his desk
- He doesn’t mention which website he uses, but my favorite is imissmycafe.com
[1:07:36]
Alie says she would totally sign up for Life Tips From an Astrophysicist (me too!).
Flip is into it but kindly clarifies that he’s not technically an astrophysicist, he’s a theoretical particle physicist:
What’s the difference between an astrophysicist and a theoretical particle physicist?
- If you’re talking to a department chair, the difference is that an astrophysicist can get money from NASA while a theoretical physicist gets funding from the National Science Foundation
- The two fields are actually blending because there are topics where you really can’t distinguish whose jurisdiction it falls under
- Flip collaborates with theoretical astrophysicists on dark matter
- A particle physicist’s toolkit includes quantum field theory and the tradition of how we think about fundamental particles
- Astrophysicists have a slightly different toolkit that tacks on observational astronomy, cosmology, and a different scale to look at things and ask “what are the interesting problems here?”
[1:06:40]
I know we can’t observe it, but after working on it for years, you must get some weird imaginary images in your head when you think about it. What does dark matter look like in your head?
- He does have [mental] pictures, but the pictures are never of the dark matter itself. The pictures are of his toolkit for understanding dark matter
- If he’s thinking about dark matter as something that could be described with extra dimensions—not saying there are extra dimensions, just that mathematically he can do a calculation with an extra dimension and have it actually mean something—he then thinks about a literal extra dimension and imagines/draws tons of pictures with his grad students:
- What does the wave function looks like? Does it ripple?
- What does it look like at the boundary?
- Does it interact with other things?
- Is it wiggly?
- Is it exponentially increasing or exponentially decreasing?
- It isn’t a picture of the invisible quantum field—that’s not really a tangible thing
- He also thinks of Feynman diagrams, which are tinker toy type things used to describe “quantum scattering” in a visual way
- It’s important to be able to think of these things in analogies and pictures. Without that visual part of our brain getting involved, pages and pages of calculations are too abstract
[1:10:14]
Does dark matter have a sound?
- There are lots of great answers to this question
- A colleague at Notre Dame named Yuhsin Tsai has done work around “dark acoustic oscillations”
- Acoustic oscillations are about sound waves in the early universe
- Those early dark matter halos we discussed earlier? When they encountered a shock, they formed sound waves — ripples in the dark matter substrate
- So yes, they literally form sounds
- It’s cool but also totally mundane; the exact same thing as sound waves traveling through water or wood or the ground, it’s just going through dark matter instead
- We can’t hear it because that dark matter substrate doesn’t interact with the matter we’re made up of
Could we somehow create something that could capture [the sound of dark matter]?
- If dark matter has some motion to it, does that help us get a new handle on detecting it? It’s an interesting question
[1:11:20]
Can you imagine if one day there were just 3D-style glasses that let you see dark matter?
- ~Dr. Tanedo is audibly leaping out of his seat~
- We can actually do that with gravitational lensing!
- Several years ago scientists started using astrophysical data to map out where the dark matter is
- The dark matter distribution looks like filaments! Just like a network of neurons
- There are dark matter halos and they’re all connected by these filaments of other dark matter
⚠️ Alie puts gravitational lensing into layman’s terms:
- It’s the way mass bends a light source
- It means that a shift/bend in light is a clue that something with lots of mass nearby is affecting it
So we think that’s how they’re forming and existing? The strings of this big webby network? That’s kind of a huge way of visualizing it, right?
- Yep! Star Trek Discovery actually used a similar network/filament idea as an avenue for interstellar travel — Flip is bummed they didn’t just use dark matter
[1:13:08]
What’s the hardest thing about being a scotohylologist?
- The pace of experimental discovery compared to theoretical creativity
- The timeline for coming up with a new idea and playing with it mathematically is relatively short
- To actually test something requires convincing a lot of people and organizations to invest resources, and then it takes years to run the actual experiment
- A joke from one of Flip’s mentors:
- There’s a brilliant theorist who writes down a theory that’s so beautiful, she says, “This is it. The most elegant theory possible. This has to be it.”
- She goes to her experimental colleague and says “I have a theory and it’s predictive: I predict these 3 things, and I think your lab should be able to do it.”
- The experimentalist is excited and says, “Okay! I’ll go apply for grants.” He spends the next quarter writing grants. Eventually, he’s able to recruit new grad students and hire some post-docs.
- Over the course of the next 3 years they decide to build a new experimental apparatus that involves contracting out new equipment that’s never been made before and creating their own new technology.
- And then they’re off! Running these experiments can take 10 years, so grad students graduate, post-docs move onto new jobs, new undergrads join the experiment, etc.
- 10 years later, everyone has gray hair. The experimentalist pulls a sheet of paper fresh from the printer and reads the final outcome.
- He walks up the stairs to the theorist’s office and says “I’m really sorry. Null result. The theory isn’t proven.”
- The theorist slams her fists on the desk and says “Can you believe that? It took two whole weeks of my life to write that paper!”
Do you feel like you have more theories than you’ll ever be able to write up?
- No, he wishes it was like that
- For him, it’s more about taking a few core ideas and running with them
- Some of those core ideas are his, some are from colleagues and friends. They collaborate and cross-pollinate (love this analogy here)
- Usually it’s very slow and incremental, even on the theoretical side
Do you have any life advice as someone who studies the universe, what we are, and what all this is?
- He thinks of the “Wear Sunscreen” advice often attributed to Baz Luhrmann and Kurt Vonnegut
- It was actually an essay written by Mary Schmich for the Chicago Tribune in 1997
- Flip’s version of that advice is: Do your homework.
- When you’re doing dark matter research, or any type of research, or anything in your life as an adult, there are no solutions in the back of the book
- If you’re doing anything exciting, there’s no way to know if you’re doing it right
- All you have is the intuition you’ve built up to know when you’re going in the right direction
- He tells first-year physics students that he hates homework, he hated doing homework, he hates giving homework, he hates grading homework — but he gives it as a service to them
- It’s his way of saying “If you want to get good at this, here’s something you should do. I know what the right answer is. I’ll help you get to the right answer. And if you get the wrong answer, that’s great because we can work together and figure out what needs to be adjusted so that you build the intuition to get to the right answer.”
- It builds the intuition of “I’ve gotten this wrong before, but now I’m wiser for it and I can sense that now.”
- A lot of the work we do is conjectural. We work it out and then someone points out where we went wrong or what we overlooked.
- But then you can say “okay, now I know this type of theory needs this type of tweak”
- It becomes a toolkit that you could have only built from making the mistakes
- People who are outside of science in general are so afraid to fail, but there’s so much failure in learning! It’s the only way we learn anything
- There’s a joke among theorists: “When I die, if any of my research papers have any element of actually being true, I’d be ecstatic.” But a lot of the speculative work is “I think this is the way things work,” and even when it all works out exactly right, the universe might just not be that way. But there’s value in going through the process of 1: being creative, and 2: learning why the universe is not that way.
[1:19:43]
What’s your favorite thing about what you do?
- On any given day there are new things to learn
- It might be a new experimental result that he wants to understand
- Other times it’s something from a related field that he didn’t have a chance to learn about as a student, but might teach him a new way of understanding dark matter
Visit Alie’s webiste for more links from this episode and a delightful photo of the people who just sent you into an existential crisis:
