Since the question of the age of the Universe is coming up on Twitter, here's a brief primer on what we know and what we don't. Punch line: all current evidence indicates the Universe is 13-14 billion years old.

https://twitter.com/joerogan/status/1680665430325641224

The most precise measurement of the age of the Universe (t_0) comes through observations of its oldest light, the cosmic microwave background (CMB), from an epoch when the Universe was ~1100x smaller than today. Careful measurements of the CMB give t_0=13.8 ± 0.023 billion years.

A lot of the discourse on tenure has (rightly) emphasized its role in allowing faculty members to engage in research without external political influence. A less discussed but crucial aspect of tenure is its role in facilitating complex research with long time horizons. 1/

https://twitter.com/MBKplus/status/1649043179759366145

By its very nature, cutting edge research involves working at the frontier of the unknown. There is no guarantee of success on any specific problem and projects often end up in very different places from their initial goals.

Have questions about the high-redshift galaxies that are just popping up one after the other in #JWST data and how they relate to the expansion of the Universe, expansion speeds, etc.? Here's my take, starting with a update of my plot from last week (it's hard to keep up!). One helpful tool is a space-time diagram. The horizontal axis here shows the "comoving radial distance"; this distance is unchanging over time for galaxies that simply travel with the expansion of the Universe. The vertical axis shows time since the big bang.

A few further thoughts about Steven Weinberg. Disclaimer: I've only known Steve for ~6 years, so these will undoubtedly paint a picture from a specific era. First and foremost, Steve was a remarkable intellect. And I don't just mean a brilliant physicist, one who brilliant physicists revered. He was just an unbelievably smart person who could talk intelligently about pretty much everything, from baseball to opera to military history.

Dan Weisz (@bigticketdw) and I wrote a white paper on Near-field Cosmology for the Astro2020 decadal survey. The main point: the study of nearby galaxies on a star-by-star basis has big implications that extend far beyond the nearby Universe. arxiv.org/abs/1901.07571 For example: SED-based interpretation of faint, distant galaxies relies on calibrations within the Local Group; nearby, low-mass galaxies are currently our only probe of the matter power spectrum on small scales and can tell us about the reionization era.

Thread. Scientific research has tremendous innate value, and detector development (and training of scientists/engineers) has clear and tangible contributions to the economy. At the same time, resources are not infinite.

https://twitter.com/WKCosmo/status/1088405580857913345

There are lots of considerations here, not the least of which is that it's not possible to shelve an entire field for a decade (or longer) & expect it to pop back up when the time is right. People will move onto different careers or different applications; that loss is permanent.

OK, my people, time for the tweet storm you neither need nor deserve (nor want?), but that you’ll get anyway. It’s about the paper by T. Kelley (@UCIastro) out today on the arXiv; arxiv.org/abs/1811.12413 Once upon a time (~1999), the dark matter satellites expected to orbit around the Milky Way (MW) were missing.

Only 11 satellite galaxies were known, whereas simulations (Klypin ++, Moore ++) predicted 10-1000x more dark matter subhalos, depending on how one compared masses

Galaxies, star clusters, and the high-redshift Universe: a thread inspired by the really interesting paper by Vanzella et al. on today's arXiv. arxiv.org/abs/1809.02617 There's a lot we don't know about the earliest stages of galaxy evolution, particularly the Epoch of Reionization (redshifts ~6-10, when the Universe was < 1 billion years old)