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Justin C. Feng

@jcfeng

General relativity and gravitation postdoc at CEICO FZU in Prague.

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09.11.2024
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Latest posts by Justin C. Feng @jcfeng

Chris Reiss, Justin C. Feng: Redshifted civilizations, galactic empires, and the Fermi paradox https://arxiv.org/abs/2510.00377 https://arxiv.org/pdf/2510.00377 https://arxiv.org/html/2510.00377

02.10.2025 06:43 πŸ‘ 0 πŸ” 2 πŸ’¬ 0 πŸ“Œ 0
Preview
What is dark matter made of? New study bolsters case for 'primordial' black holes In the early universe, primordial black holes could acquire a "dark charge," giving them an unnaturally long lifetime, new research suggests. This makes them an interesting candidate for dark matter.
08.04.2025 09:00 πŸ‘ 0 πŸ” 1 πŸ’¬ 0 πŸ“Œ 0
Portal - 'Still Alive'
Portal - 'Still Alive' YouTube video by OTG

An appropriate song to end the week on:

m.youtube.com/watch?v=Y6lj...

28.03.2025 07:45 πŸ‘ 0 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
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Figure 1

Figure 2

Figure 2

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Figure 3

Figure 4

Figure 4

Immortality through the dark forces: Dark-charge primordial black holes as dark matter candidates. Jessica Santiago (National Taiwan University) et. al. https://arxiv.org/abs/2503.20696

27.03.2025 16:19 πŸ‘ 0 πŸ” 1 πŸ’¬ 0 πŸ“Œ 0

Miguel Duarte, Justin C. Feng, Edgar Gasper\'in, David Hilditch
An asymptotic systems approach for the good-bad-ugly model with application to general relativity
https://arxiv.org/abs/2503.17036

24.03.2025 04:19 πŸ‘ 0 πŸ” 1 πŸ’¬ 0 πŸ“Œ 0
Side eye monkey meme looking at the famous double slit experiment 

The monkey looks away from the experiment and the results suggest light is a wave

The monkey looks at the experiment and the results suggest light is a particle

Side eye monkey meme looking at the famous double slit experiment The monkey looks away from the experiment and the results suggest light is a wave The monkey looks at the experiment and the results suggest light is a particle

For me this is the best meme of all time and nothing else even comes close

26.11.2024 15:06 πŸ‘ 96 πŸ” 15 πŸ’¬ 3 πŸ“Œ 1
ORCID

Hi, I'm a general relativity/gravity postdoc at CEICO/FZU in Prague. Here's my orcid:

orcid.org/0000-0003-24...

25.11.2024 20:57 πŸ‘ 2 πŸ” 0 πŸ’¬ 1 πŸ“Œ 0
Black and white photo of Einstein standing in front of shelves of papers and journals. His messy hair is dark - not yet the famous white shock that comes to mind when you hear his name. He is wearing dark pants and a dark cardigan with light trim. Einstein is looking at the camera but not smiling.

Black and white photo of Einstein standing in front of shelves of papers and journals. His messy hair is dark - not yet the famous white shock that comes to mind when you hear his name. He is wearing dark pants and a dark cardigan with light trim. Einstein is looking at the camera but not smiling.

The intro of the paper reads (in German)

Die Feldgleichungen der Gravitation.
Von A. EiNSTEIN.
In zwei vor kurzem erschienenen Mitteilungen' habe ich gezeigt, wie man zu Feldgleichungen der Gravitation gelangen kann, die dem Postulat allgemeiner RelativitΓ€t entsprechen, d. h. die in ihrer allgemeinen Fassung beliebigen Substitutionen der Raumzeitvariabeln gegenΓΌber ko-variant sind.

The intro of the paper reads (in German) Die Feldgleichungen der Gravitation. Von A. EiNSTEIN. In zwei vor kurzem erschienenen Mitteilungen' habe ich gezeigt, wie man zu Feldgleichungen der Gravitation gelangen kann, die dem Postulat allgemeiner RelativitΓ€t entsprechen, d. h. die in ihrer allgemeinen Fassung beliebigen Substitutionen der Raumzeitvariabeln gegenΓΌber ko-variant sind.

This passage shows the final field equations  relating the Ricci tensor to the stress tensor with 1/2 of the trace removed.

This passage shows the final field equations relating the Ricci tensor to the stress tensor with 1/2 of the trace removed.

Albert Einstein submitted "The Field Equations of Gravitation" to the Prussian Academy #OTD in 1915.

After years of work culminating in a frenzied month-long race against David Hilbert, Einstein had finally obtained the correct form of the field equations for general relativity. πŸ§ͺ πŸ”­ βš›οΈ
(1/n)

25.11.2024 15:41 πŸ‘ 122 πŸ” 37 πŸ’¬ 4 πŸ“Œ 7

With many physicists arriving daily at Bluesky I’ve created a comprehensive list -which I update daily- with Cosmologists, Astrophysicists, Gravitational Wave Astronomers, Particle Physicists… Please SHARE so it reaches more people! 🀩 Warning: it may contain Mathematicians

bsky.app/profile/did:...

20.11.2024 14:57 πŸ‘ 77 πŸ” 32 πŸ’¬ 4 πŸ“Œ 6
National Taiwan University, Leung Center for Cosmology and Astroparticle Physics Full service online faculty recruitment and application management system for academic institutions worldwide. We offer unique solutions tailored for academic communities.

My previous institution is hiring:

academicjobsonline.org/ajo/jobs/29236

18.11.2024 15:42 πŸ‘ 1 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
Submission - 24th International Conference on General Relativity and Gravitation & 16th Edoardo Amaldi Conference on Gravitational Waves - SEC

I am delighted that we our hosting the joint GR & Amaldi meetings in Glasgow in July 2025

Abstract registration is now open iop.eventsair.com/gr24-amaldi1...

The conference will cover gravitation, gravitational-wave and multimessenger astronomy, cosmology and relativistic astrophysics, and more!

08.11.2024 17:12 πŸ‘ 9 πŸ” 5 πŸ’¬ 1 πŸ“Œ 0

I code in julia---does that count?

It still amazes me how straightforward it is to autodiff through numerical ODE solutions in julia.

09.11.2024 14:13 πŸ‘ 1 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
Post image

Recently moved institutions to FZU - Institute of Physics of the Czech Academy in Prague.

This is a picture of the entrance to the new Solid State building (the main building where I work is in the back).

09.11.2024 13:48 πŸ‘ 3 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
Preview
Talent vs Luck: the role of randomness in success and failure The largely dominant meritocratic paradigm of highly competitive Western cultures is rooted on the belief that success is due mainly, if not exclusively, to personal qualities such as talent, intellig...

A few years ago, I came across a paper that more or less said the same thing:
arxiv.org/abs/1802.070...

09.11.2024 13:39 πŸ‘ 2 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0