🧵⊃🧵🧵🧵...
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Nirmal Raj
@PhysicsNirmal
Theoretical physics postdoc | Writer at particlebites.com | Dark matter hunter | "excellent explainer", "delightful posts", "funniest"
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(This assumes you know the angular diameter of the Sun, which you do because the clouds part once in a while during daytime.)
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It now comes down to convincing the final few skeptics.
Take them to Niagara Falls on April 8, 2024. After lunch, tell them: "Don't panic, ladies and gents, but the light will begin to dim now. And for four minutes beginning 3.18 pm, we will be plunged into darkness."
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You should have figured out the Moon's mass and trajectory by now, especially with lots of tidal data.
Assuming rock-like density, get its radius.
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Then hypothesize that this axial precession comes from celestial bodies pulling on the Earth's equatorial bulge via gravity and producing a torque somewhat perpendicular to the spin axis.
Fit to a Moon + Sun model and see that the Moon is the major culprit.
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OK, any complementary evidence?
Note the slow drift of seasons across the calendar!
That's from the whirl of the Earth's spin axis, the "precession of the equinoxes". It takes ~13000 years to flip summer and winter, so historic records should track seasonal shifts.
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At night moonlight never reaches us. Could we ever tell if there's a Moon?
Yes, exploit gravity! Note the tides!
Measure them at multiple shores and times, and fit the data to a Moon + Sun model.
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In a recent talk in Tamil courtesy of , I introduced #darkmatter by stealing an idea from David Morrissey.
🧵
Say the Earth is under permanent, thick cloud cover. At daytime humans can tell there's some bright external source of light that filters through.
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Replying to
Indian astrology is superior to Western astrology for using the stars as background as opposed to the Sun, so that the precession of the equinoxes is taken out of the equation. Your zodiac sign aligns with your constellation.
When pseudosciencing, pseudoscience with style. 😎
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Absolutely nailed it!!
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When I teach astronomy as a Gen Ed course, I include mythology and stories from a variety of cultures and traditions, because that is part of the history of the field, and the history of the development of the scientific method. 1/ twitter.com/martinmbauer/s…
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I'm near a triple point. I know because transitions between states followed changes in temperature and pressure.
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Neat. Black hole cosmological coupling disfavoured by BHs observed in >10 Gyr old globular cluster.
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A short paper where I argue that black holes have not grown by a factor of 50 from redshift three and are not the origin of dark energy arxiv.org/abs/2302.12386
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TIL that astronomers mark time by counting days since Mon, Jan 1, 4713 BC.
And that this "Julian day number" is gotten from a calendar date using
JDN = (1461 × (Y + 4800 + (M − 14)/12))/4 +(367(M − 2 − 12((M − 14)/12)))/12 − (3((Y + 4900 + (M - 14)/12)/100))/4 + D − 32075
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Happy New Decamillenium! 
(JD 2460000)
(JD 2460000)7
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Replying to @DudeDarkmatter
I do not understand why you cherry pick on the subject. There are papers which find the Bullet Cluster to be perfectly reasonable within LCDM, for example this one arxiv.org/pdf/1410.7438.. So it is FALSE it falsifies LCDM.
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Thinking of Alex Vilenkin, working as a zookeeper in Kharkiv because he was blacklisted from university for refusing to work with the KGB, holding a clandestine physics journal club after hours at the zoo. Respect.
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There is no evidence for a Universe before the Big Bang
Like many claims made by people challenging the consensus picture of our Universe, this one not only has no evidence supporting it, but a mountain contradicting it.
Sorry, Penrose and CCC fans.
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Replying to @curiouswavefn
@PhysicsNirmal is my favorite !!
twitter.com/Kaju_Nut
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Very interesting progress on the muon (g-2) calculations this week.
New data from CMD3 (Novosibirsk) finds a larger
(e+e- -->π+π-)
cross section, and, as a result, a larger contribution to the (g-2).
This piece dominates the theoretical uncertainty.
arxiv.org/pdf/2302.08834
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Entropy & gravestones.
(1) Boltzmann: RT-ed.
(2) Hawking: black hole thermodynamics.
(3) Dorothy Parker: "Excuse my dust".
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Boltzmann's entropy equation is one of the most basic equations of the universe, relating the number of microstates of a system to its entropy. It's even more fundamental than that because it forges a relationship between entropy and probability.
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The Standard Model represented as the double simplex of must get more attention than it does.
arxiv.org/abs/hep-ph/050
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read image description
ALT
This is the optimal known packing of 17 particles into a universe, I promise
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"contemplate" shares a root with "atom" (10^-10 m),
"consider" shares a root with "sidereal" (> 10^16 m).
🤟
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One of my favorite fun facts is that "galaxy" and "lettuce" share the same etymological root word
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தமிழ்-speaking, physics-curious tweeps,
I'm giving a public talk on #darkmatter
Saturday evening IST!
twitter.com/i/spaces/1jMJg
There will be plenty of time for questions & discussion.
இங்ஙனம் தங்கள் நல்வரவை இனிதே விரும்பும் நானும்
-உம்.
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0:10
#அறிவியல்தமிழ்உரையாடல் -94
#PhyFron Team Presents
Feb 18 Sat, 6:00 PM IST
தலைப்பு: Dark matter மர்மங்கள்
உரை: @PhysicsNirmal
Spaces : twitter.com/i/spaces/1jMJg
அனைவரும் வருக
Please do share and support
Feb 18 Sat, 6:00 PM IST
தலைப்பு: Dark matter மர்மங்கள்
உரை: @PhysicsNirmal
Spaces : twitter.com/i/spaces/1jMJg
அனைவரும் வருக
Please do share and supportShow this thread
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Roses are red.
Violets are blue.
You wonder where green is,
but this is just SU(2).
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A noodle on ditto.
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A world with no weak forces.
-- a gedanken 
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Gravity, electromagnetism, strong, weak -- the beating hearts of the universe, the four fundamental forces.
But do we really need the last one for us to exist?
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Gravity, electromagnetism, strong, weak -- the beating hearts of the universe, the four fundamental forces.
But do we really need the last one for us to exist?
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A bite on the weakless universe of hep-ph/0604027.
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Do we really need the weak force, anyway? @PhysicsNirmal talks about a world without: particlebites.com/?p=9871
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Dunkle Materie is in finance today, making more dark $$ than the entire tenure committee put together.
(- different version of a story heard from Neal Weiner 9 years back)
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"...Why, that's how one is stable! No other fermion to decay to!
The whole damn thing's renormalizable, you see. Though I did have to tune the SU(2) x U(1) symmetry-breaking scale to make it work. Yeah, I had to tune it very fine. Oh, and the matter comes in 3 copies."
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"... much lighter fermion that's stable thanks to your reason. My calculations show these 2 fermions can form "atoms" and pave way for chemistry -- who knows, even life! The excess in what? Radiation density data? That's got to be from other fermions, very, very light."
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"... It's charged under a U(1) subgroup that comes from breaking the SU(2) x U(1). What's that? No, it's not cosmologically stable because it's the lightest fermion under this U(1), haha no, it's stable due to an accidental symmetry. But guess what, there's another, ..."
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"I have reason to believe there's an entire other sector of matter and radiation out there. To be precise, 5 species of matter charged variously under an SU(3) x SU(2) x U(1). The SU(3) confines -- in fact, the lightest composite makes up most of the mass excess..."
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In the dark world, Dunkle Materie goes up for tenure.
Committee: Dr Materie, nobody's seen you in a while.
DM: I've been hard at the recent excesses observed in cosmological and lensing data.
Committee: Ugh. What did you find?
Materie takes a deep breath, and goes:
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So is a dark sector ruled out? No, because we have no data to constrain it. Is there any reason to expect a dark sector of multiple stable species? Also no.
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For some reason I wanted to RT this today, my favourite tweet -- most revisited.
Then I got curious why she hadn't tweeted in a while... 😞
Hope her family finds peace.
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I am so #grateful for this life. I’ve looked at what drives me and I’ve realised that I am not driven by insecurities, nor by grudges, greed, fame, nor status. I am only driven by love, for my family, my friends, my colleagues, our students. And it’s such an amazing place to be
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- 92.9^2
=
1234567890123456789012345678901234567
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1234567890123456789012345678901243197.
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Follow up: what are some results in your field that you think nobody should ever find out? twitter.com/Kaju_Nut/statu…
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In the slow clock-transport convention one cannot remove anisotropy due to the direction of transport.
The correct time dilation factor is this here formula with kappa spanning -1 to 1.
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In either convention your measurement of the speed of light won't detect a possible anisotropy in the velocity of light.
In the Einstein convention this is obvious: the forward speed may differ from the backward.
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(ii) The "slow clock-transport convention" transports the second clock slowly to the desired point.
The slower the transport, the smaller the time-dilation-induced error.
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What to do? Live with some convention. There are at least 2.
(i) The "Einstein convention" fixes the time of the second clock by bouncing a light beam off a mirror close to it, detecting it at the place of emission, and noting the time lag.
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If the clocks are apart, you can't synchronize them without knowing the speed of light beforehand. 🤷♂️
So you want to start by synchronizing them close to each other? Well, separating them implies relative acceleration, and that introduces time dilation. Synchrony gone. 🤷♂️
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