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Reposted by Shaun Hotchkiss

Sam Gregson @badboyofscience.bsky.social · Apr 5

Fantastic time discussing whether the latest blockbuster cosmology results really do show that Dark Energy is evolving!

Brilliant explanations from @clairelamman.bsky.social
, @tamarastro.bsky.social and @justshaun.bsky.social

Check it out!

Full talk: youtu.be/reNicLW2vpY?...

🧪⚛️

Is Dark Matter Evolving? Cosmologists Explain

YouTube video by Bad Boy of Science

youtu.be

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Reposted by Shaun Hotchkiss

South Pole Telescope @sptelescope.bsky.social · Mar 30

Unfortunately it was pretty cloud during #Sunset this year at the South Pole, but our winterover Sim managed to catch this picture just before the weather got bad, with the moon over SPT! #southpole #Antarctica

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Reposted by Shaun Hotchkiss

Astronomer Royal for Scotland | Catherine Heymans @astroroyalscot.bsky.social · Mar 26

🥳 It's paper day for the completed #ESO Kilo-Degree Survey. We end our journey with a consistent picture of #cosmology 😲
I've been co-leading KiDS for 12yrs & I'm so proud of what the team's achieved. If you're at the #Euclid meet, go to Angus Wright's talk @10am today!🔭

ℹ️: arxiv.org/pdf/2503.19441

$A two panel figure. The x-axis is omega_m, the fraction of matter in the Universe. The y-axis is S8 on the left and sigma_8 on the right. Both are measures of the 'clumpiness' of dark matter. The contours show that the KiDS data (two measurements using slightly different statistics, COSEBIs and Bandpowers) agree with the data from the Planck CMB survey.$

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Shaun Hotchkiss @justshaun.bsky.social · Mar 26

The Cosmology Tension Gods giveth and the Cosmology Tension Gods taketh away 🤷

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Shaun Hotchkiss @justshaun.bsky.social · Mar 26

What if I told you there is no S8 tension?

youtu.be/PIQKe-tW1xQ

KiDS Legacy - The Final Cosmology Results

YouTube video by Cosmology Talks

youtu.be

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Shaun Hotchkiss @justshaun.bsky.social · Mar 25

Haha 😅, I'll let you know if Enrique from Universe 2845b has any great insights.

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Shaun Hotchkiss @justshaun.bsky.social · Mar 25

Register now, or in another branch of the multiverse, you've surely registered in one of them! (Right?!)

Shaun Hotchkiss @justshaun.bsky.social · Mar 25

Rather appropriately, given this proliferation of "from Home" events, the next one to announce is:

Multiverse from Home!

I suspect discussion won't be hard to come by in this one 😅.

multiverse.cosmodiscussion.com

Multiverse from Home

multiverse.cosmodiscussion.com

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Shaun Hotchkiss @justshaun.bsky.social · Mar 25

"Tabletops" in space might still be necessary sometimes though 😂.

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Shaun Hotchkiss @justshaun.bsky.social · Mar 25

Another "from Home" conference has launched (complete with the *perfect* banner image)...

*Tabletop Scale Cosmology*

Register now to discuss, and hear about, how you don't need giant telescopes and colliders to learn about the cosmos!

tabletop.cosmodiscussion.com

Tabletop Scale Cosmology

tabletop.cosmodiscussion.com

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Shaun Hotchkiss @justshaun.bsky.social · Mar 21

There are certainly examples of groups revealing results too soon, before double/triple checking possible interpretations 😅.

Shaun Hotchkiss @justshaun.bsky.social · Mar 21

I think I do disagree on the scaffolding metaphor, but I'm not sure my disagreeing is interesting 😅.

I'd liken it more to halftime at a sports game, or showing partial counts on election day (In terms of how interesting people find it, not how feasible it is to do without compromising other things)

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Shaun Hotchkiss @justshaun.bsky.social · Mar 21

I don't *think* I disagree with any/most of this. Me calling it the "dream" did mean to imply it isn't necessarily feasible, partially for reasons you point out.

It can still be a dream to aspire to get *closer* to, without compromising too much on other important things of value.

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Shaun Hotchkiss @justshaun.bsky.social · Mar 21

One last thing I realised after writing everything above...

Going from ΛCDM to "wCDM", with w0 \neq -1 and wa \neq 0 doesn't, as far as I know, break any other observation (yet!)

So many other solutions to tensions/problems within ΛCDM fix one thing, only to bust something else.

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Shaun Hotchkiss @justshaun.bsky.social · Mar 20

Ah, cool!

You should polish them and make them public somewhere 😁.

Shaun Hotchkiss @justshaun.bsky.social · Mar 20

"where the dust will settle" 👀

dangerous choice of language in astronomy 😅

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Shaun Hotchkiss @justshaun.bsky.social · Mar 20

This is really cool. I'd love for something like this to be recorded and shared afterwards so that the rest of the world can re-live the excitement.

(The dream would be one day for the scientists and public to be unblinded simultaneously, with expert commentary as it unfolds!)

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Reposted by Shaun Hotchkiss

Sesh Nadathur @seshnadathur.bsky.social · Mar 20

A nice blog post by Gillian Beltz-Mohrmann about the DESI "unblinding" event last year, the excitement and the reactions:
www.desi.lbl.gov/2025/03/19/a...

At the Big Reveal: DESI’s December 2024 Unblinding Results

www.desi.lbl.gov

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Reposted by Shaun Hotchkiss

Claire Lamman @clairelamman.bsky.social · Mar 20

DESI's DR2 BAO results are out!!
TL;DR... 1/n
@desisurvey.bsky.social

A blocky lambda symbol crumbles as it is pulled apart by creatures representing Baryon Acoustic Oscillations, the Cosmic Microwave Background, and supernovae. Caption reads "something has to give..." Credit: Claire Lamman

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Reposted by Shaun Hotchkiss

Héctor Gil Marín @cosmonautico.bsky.social · Mar 20

🔊 New BAO analysis from the 3-year observations (DR2). Long story short, as follows.
1. DESI alone is consistent with LCDM. 👉 Boring
2. DESI and Planck have a 2.3 discrepancy in Ωm-H0rd plane. 👉Interesting.

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Shaun Hotchkiss @justshaun.bsky.social · Mar 19

Yeah, I agree with that framing too. It does seem to look like wo,wa though (e.g. from the binned w(z) plot).

Now that at least the yr1 data is public I'm looking forward to which a posteriori model floats to the top of the a posteriori best fit pile 😅. (Hopefully one well motivated one rises up!)

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Shaun Hotchkiss @justshaun.bsky.social · Mar 19

w0,wa is of course just a parameterisation, but it seems to be a genuinely good one for the observations we've made of this universe in 2025 🤷

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Shaun Hotchkiss @justshaun.bsky.social · Mar 19

And finally, the best fit combined value of wo,wa isn't somehow in tension with what each individual probe wants, it's more or less a consistent story of wo,wa-ness in the data 🤷

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Shaun Hotchkiss @justshaun.bsky.social · Mar 19

In ΛCDM there seems to be a genuine "Omega_m" tension between probes... in wo,wa it goes away...

(see DES Y5 vs DESI DR2 BAO)

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Shaun Hotchkiss @justshaun.bsky.social · Mar 19

Not to mention that neutrinos masses in ΛCDM with neutrinos masses looks very suspicious, because it is starting to rule out the lower bound from particles physics...

But in wo,wa it goes back to being all fine...

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