#5 Kathryn Johnston - The Milky Way, Dark Matter vs MOND, Gaia

In this week's episode, David is joined by Kathryn Johnston. Prof Johnston is a Professor of Astronomy at Columbia University and the Dynamics Group Leader at the Flatiron Institute. Kathryn is a world renown expert for her work on Milky Way dynamics, especially tidal streams and the dark matter components of our galaxy.
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[@paulpence8895]

You have one of the most soothing voices,,, listen to all your productions, to fall asleep,,, but it's way more than that, cant fall asleep because its all way to interesting... hahaha!!!

[@AndrewBlucher]

8:27 Ah! That's a great explanation @Katherine This is a great episode David. I trained in Physics in the early 70's and have followed Astronomy and other sciences intently ever since. This discussion with Katherine is the first time I have grasped the relative size of the Milky Way's central black hole, and also the first time I have heard in simple terms how the competing theories of gravity might be distinguished. Great work, both of you!

[@celestromel]

Gee - Kathryn is such a great “simplified” of the hopeless complicated (to the rest of us). What a great colleague! Thanks to you both. Perhaps you could invite her back - as she relaxes, her enthusiasm becomes infectious.

[@celestromel]

… “simplifier”..

[@celestromel]

… “hopelessly” … How I hate predictive text!

[@asherstribe5695]

Perhaps they should both speak out about the horrible antisemitism at their school. Columbia turned out to be a hot bed of hatred.

[@victorburns4061]

This conversation answered a lot questions; some I didn't even know I had. Very insightful.

[@152iq9]

The best podcast in the world. I listen to you at work and before I sleep.

[@grantgeorgebuffett]

I love all these deep dives into frontier astronomy. Great job!

[@mystryfine3481]

Cosmology will never be put to rest.😊

[@dougg1075]

The buildings in that window behind y’all is great. Would make a great painting as a window frame for a frame. Great conversation

[@TheArgusPlexus]

What an enchanting voice she has I'm on audio only right now. I could listen to this for hours

[@fadedparadigm]

Wow, thank you so much for hosting and sharing this talk! I hadn't really taken the time to read much about dark matter other than hearing some quick quips about it accounting for a dominant percentage of mass. It was really awesome to have you two talk in plain language about the evidence we see that's consistent with dark matter, and how it relates to our own galaxy. I had no idea our galaxy is apparently as large as it is, or that these dwarf galaxies are orbiting around in these nutty dynamical patterns based on some apparent mass distribution of dark matter that we're only just beginning to understand. Great stuff! Thank you again!

[@CoolWorldsPodcast]

So pleased you enjoyed these deeper dives!

[@EuphoricDan]

@@CoolWorldsPodcast The internet has been serving up more and more anti-dark matter physicists over the past few years. It'd be truly awesome if you could personally go over the claims someone like Pavel Kroupa (or even interview him/people like) who's claiming we've refuted the existence of Dark Matter at 5 Sigma certainty and people aren't doing serious work if they're still working there - that's a pretty bold claim and the man does have some bonafides, yuno?

[@davidb2380]

@@CoolWorldsPodcast I have enjoyed listening to your podcasts. For future podcasts, A few suggestions are Sara Seager (MIT), of whom I am sure you know, Meg Urry (Yale) who is leading expert on active galaxies and Ron Ekers (ATNF), renowned for his work in radio astronomy.

[@jimsteen911]

@@EuphoricDan yea notice no one touches Kroupa? You know the Stellar dynamics astrophysicist with the same credentials as this woman yet his are “claims?” Have you read his papers? MOND doesn’t have to be right for DM to be wrong. His points are this isn’t a simple “which is right?” Anymore… DM is proven wrong many ways. I’ll name only one for you to enter a rabbit hole. “ Chandrasekhar dynamical friction.” Whenever someone like Pavel Jroyoa shows up, DM ppl end up arguing that we need a better theory to replace ΛCDM In order to get rid of it. That’s not science. When something is blantsntly wrong, you can explain everything without it, why would you postulate dark matter? Why would you add fuzzy tiny fairy 🧚‍♀️ if you don’t need it to explain what you see? What we are witnessing is a sociological effect where some weird cognitive dissonance occurs. She implied DM explained tidal streams and mond couldnt. Here’s the paper in 2017 done perfectly. If you actually listen to what she says she does a long diatribe implying it then saying they need more than that. It was ridiculous. Watch it again. Again. Lovely woman lovely ppl, but they don’t see it yet.

[@jimsteen911]

Get Pavel Kroupa on man. If it’s not personal and it’s all about science, why not?

[@rolandsummers9179]

Your podcasts are great man! Thanks for the great content!

[@UrusaiJoe]

Discovered you lately, amazing podcast.

[@nicohocco75]

great video that made me thoughtful and curious : so we have a spiral galaxy with a massive spining black hole in it's right center (as we think all spiral galaxy have), with a symetrical perfect bar of stars around it and symetric spiral arms around (certainly spining in the same direction the black hole does and the orientation of the galactic disc would certainly follow the orientation of the spinning black hole, as our planetary system is more or less aligned on the rotation of our sun, found no information about it, if anyone know about it please tell me) BUT as we noticed the Einstein equation were false at 80 %( missing mass) at the galactic scale to describe how this galaxy works, we then invented dark matter to fill the gap and we keep going on with Einstein/Schwarzschild equations and since this time we try to find justification to existence of dark matter. Then we say that the black hole in the middle of our galaxy is too "little" to be responsible of anything gravitational we see around it. OK but how are calculated the galactic black hole properties ? With the Einstein 80% false equation of course (more precisely the Schwarzschild solution from the Einstein equations). Heuuuu ????? I m not an astrophysicist but that does not really makes any logical sense to me, so illogical that i dont see clearly how an astrophysicist can cope with that without questioning. Or im missing something due to my great lack of knowledge in astrophysics, please tell me. And also explain how dark matter would influence gravity to build this galactic shape an put a massive black hole right in its center but with no role ? So, if im not wrong, what we think today about galactic massive black holes is by definition false by 80 %. Gravity ripples made by merging somehow modest black holes (dizains of solar masses) make their way to our detectors from more a billion lightyears through space(that we also dont know ANYTHING about), but a multi millon solar mass black hole would be too weak to have any influence on gravity at a 100000 light year galactic size level !?!? Personally as a logical result i think that dark matter has 80 % chances to end up as the string theory did, even if many great scientists spent their whole career working on it. What is true today was false yesterday and will be false tomorrow ... Lets hope im wrong which i prefer to be, regarding respect i have for generation of scientist working hardly to find dark matter. So even being totally wrong i will stay thoughtful and stay curious and keep whatching your videos that i really Love ;-)

[@RichardKCollins]

Kathyrn Johnston, The vector tidal signal at a superconducting gravimeter or more modern gravimeter detector shows a nearly pure Newtonian signal. You can get the JPL time series of precise positions for the sun moon earth every second, use a WGS84 ellipsoid and station position, International Earth Rotation Service rotation rate and calculate GM/R^2 for the sun at the station minus the sun at the center of the earth, add the moon at the station minus the moon at the center of the earth, add the centrifugal acceleration from earth rotation and put that into station North East Vertical. It is nearly perfect fit with a linear regression. Two numbers for each axis will lock the station data to a global standard reference model. The broadband seismometers are just barely able to detect the "sun moon vector tidal signal" but all three time series for the three axes each only require a linear regression. So 6 numbers. The MEMS gravimeters and others like atom interferometer gravimeters will drift. But since you only need to solve for 6 parameters you can calibrate the otherwise drifting baseline to the model every hour or every day. The residual after you remove the calibrated signal is all "earth local" and mainly atmosphere, ocean surf, cars trucks and such. The raw data is archived to update models over time. It is a convenient way to set global reference gravity for low cost local gravity efforts. There are a LOT of local gravity measurement and mapping efforts. About 20 kinds of sensors. Richard Collins, The Internet Foundation

[@duggydo]

I enjoyed the discussion. This is the first for me. I will have to go back to watch the others.

[@melissanoriega5615]

Wow! I love this! Subbed! I'm so excited to see more videos

[@SnapDash]

Fascinating chat! I've heard that there have been recent estimates for the number of starless planets; suggesting that there may be a great many more than previously acknowledged. Would that in turn impact the overall gravity (and particularly dark matter) calculations, or are planet-scale objects just too small to be significant? Has there been much work yet looking into that? A starless/"rogue" planet Cool Worlds episode would be nifty- On a rather different tangent... What's the chronology for the formation of the Solar System compared to its dynamics with the other stars that were around when it formed. How should we picture the nearby interstellar environment as the planets were forming, and how does that differ from what we see now?

[@jimsteen911]

Love this podcast man

[@nias2631]

Serious question, suppose you had a device that made precision measurements of the Casimir pressure. If you put the device on a spacecraft and sent it away from Earth, taking periodic measurements when the thruster was off. What would be some possible implications for the vacuum or MOND (if any) if you saw the pressure increasing/decreasing. Also, is out assumption that the quantum vacuum is the same everywhere to general?

[@doxinator3560]

Spirograph is still available for retail purchase.

[@johnmackay3136]

Brilliant, thanks.

[@lib8884]

I know it's more time consuming but some timestamps on these would be great.

[@Inug4mi]

Since we have the visual of scooping star off the dwarf galaxies and the stars are kind of light and fluffy, would something like cotton candy be a worse visual as opposed to spaghetti? You can kind of stretch cotton candy as you’re pulling it apart? Just a random thought.

[@Inug4mi]

I think David definitely has his NPR voice developed now.

[@christophercasserly7988]

Do a Brian cox podcast please 🙏

[@CoolWorldsPodcast]

If I could get him I’d leap at the chance!!

[@jessegallagher3952]

Second that!

[@benhargaden995]

Brian Cox 🙄

[@benhargaden995]

Dr Becky is fab 👍

[@altonwilliams17]

​@CoolWorldsPodcast you are gorgeous. You're like a young version of George Michael. Wham! Intelligence is sexy and so are you biceps.....

[@EarlyRains]

Im confused about the destinction being made between motions of planets vs motions of stars at around 30min, doesnt mercury also move in a "petal"-type shape?

[@Nargle19.]

#awsome

[@bad1970muts]

Large clusters of black martier or black stars also have gravity. 1) How does this affect Einstein's theory of spacetime and its possible curvature. 2) If there is curvature or gravity, then "ordinary matter" may have been attracted by it, which these processes may have provided, even if black matter and hydrogen influence each other directly, this form of a perhaps weaker space curve may well if this occurs on a gigantic scale and can create gigantic black holes?

[@tmjmccormack]

“Galaxsehs…” wonderful listen

[@joshuagharis9017]

I was struck by a thought, its possible, depending on her choices, that Davids younger Kipping, could one day be a guest on a future Cool Worlds podcast, imagine that David, even if not, Im sure they'll make ya proud no matter where they venture 😊 perhaps its because my own daughter just turned 7.... 😅 goes by so fast

[@CoolWorldsPodcast]

That would be wild!

[@janklaas6885]

📍53:35

[@adammasuch5626]

Man I can't wait to see this. I read they proved mond to 5 sigma with Gaia

[@fredfreer2818]

Sorry, but why does everything rotates on s plane and not on a esphericall way as logical would dictate? Ty

[@user-do2eh2il6m]

THE WAY IMAGINE THE ARMS OF THE MILKY WAY ARE ENTERTWINED SIMILAR TO A BRAID OF HAIR? PEOPLE CORRECT ME....

[@peterquinn2997]

I would say clumped more like dread locks. That’s a pretty good analogy though.

[@mystryfine3481]

Halo of dark matter? We don’t understand gravity on galactic scales.

[@hypatiastanhope4716]

🤔

[@jimsteen911]

Heres the paper from 2017 MOND reproduces perfectly MW tidal streams. That’s not an argument. You must maintain multiple hypotheses collecting evidence for each in bins. I appreciate your brief sentiment after implying tidal streams are why dark matter is right then caveating saying indeed you don’t know. We all know most professionals in the US are absolutely Married to dark matter. Not to mention HUNDREDS of papers disproving it using a dozen parameters. It’s not predictive at all is it? You’ve got so many ways to fiddle the parameters in λcdm. You’re too close to it to see it. Idk if MOND is right. But theories aren’t graded on a curve. We don’t need a replacement to say something’s wrong. Many many things are wrong. You’re lovely people. But you’re bordering priests.

[@CoolWorldsPodcast]

Thanks for your thoughts, send me the tidal streams MOND paper!

[@hindsight2022]

My theory is that all of the antimatter that was present at the big bang spread out to the boundary of the physical universe . Much like a cell wall holding all the regular matter inside . This is what causes the gravitational forces we witness . I further propose that there is a density or field that keeps them separate like oil and water . A surface tension property , Like a soap bubble . To me this seems more likely than the 2 obliterating each other at the moment of creation . With an odd amount of regular matter , as that would not be symmetrical . My theory is symmetrical.

[@marktunnicliffe2495]

Most of the antimatter present at the big bang was annihilated in collisions with normal matter.

[@hindsight2022]

@@marktunnicliffe2495 I addressed that in my theory .

[@marktunnicliffe2495]

@@hindsight2022 well no, you didn't! You've made an assumption backed up by nothing more than an idea you've had. It's not a theory, it's not even a hypothesis. If you're going to claim you have revolutionized particle physics and have an actual scientific theory, which journal did you submit it to for peer review?

[@hindsight2022]

@@marktunnicliffe2495 you need to read more . Specifically , start with the definition of the word theory .

[@hindsight2022]

@@marktunnicliffe2495 also I believe there to be several lines of evidence to support my theory if you'd like to hear them let me know .b

[@wilezekiel5773]

I guess it’s just one of those things but I really couldn’t listen to this one because of her “Yeah, yeah, yeah, yeah, yes, yes, yes, yes” constantly while he was speaking, incredibly distracting to the point of annoyance unfortunately. Once I noticed it, which was very quickly, I could only hear that. Maybe I’ll check out the transcript

[@antoniologan7648]

Thats just how some people process information in conversations

[@peterquinn2997]

Dude you’re wayyy too sensitive. The yeah, yeah, and yes, yes, stuff was nothing. It’s the way she pronounces Galaxies (“galaxsehs”) that was way more annoying. 😂

[@msxciejhello]

So glad you started a podcast. I've been following your channel from the beginning. Also, get John Michael Godier on the podcast😁

[@bernardofitzpatrick5403]

Subd. 🪐💥🌏💫