New 10 Terapixel Image of the Night Sky Contains 1B Galaxies

When I spent (a relatively small amount of) time working with one this was the main thing the director drilled into my head. Use it to solve large, parallel problems that require lots of intranode communication of intermediate results. Embarrassingly parallel problems can be solved on cheaper hardware like GPUs.

I have no sense of how much of the Galaxy it maps, but I know it's crucial for distance ladder measures because it will constrain the distance to the large Magellanic cloud better than ever before, so I think it's measuring individual stars at that range

Doing astrometry and proper motion measurements for more stars than ever before, very cool

2. Can gravitation lensing work in a daisy chain fashion by having multiple galaxies positioned ever so precisely to cause the light from our galaxy to travel in a semi-circle arc back to us?

An early version of this work with a gallery of objects that might match what the Milky Way looks like (given all the observational uncertainties) is discussed at https://www.news.pitt.edu/milkywaycolor .

A couple of the resulting scientific papers are at https://ui.adsabs.harvard.edu/abs/2015ApJ...809...96L/abstra... and https://ui.adsabs.harvard.edu/abs/2016ApJ...833..220L/abstra... and

I think the expression you might be looking for is "a contemplative state".

The basic idea is simple enough: if you have a random collection of people, and keep adding more, eventually 2 of them will have the same birthday. If you run that experiment a bunch of times, eventually you’ll get the average number of people where there’s a 50% chance of having a “collision”. The surprising part is that the number is so small: in this case, it’s 23.

This one right under it is also neat: https://viewer.legacysurvey.org/?ra=148.7892&dec=69.0730&lay...

We might in principle be able to see beyond the surface of last scattering using ultracold neutrino or ultra-low-frequency gravitational radiation astronomy some decades from now, but that just gives us a view of the universe before there were molecules (let alone stars and galaxies), and we could only surmise that what we see at such a huge redshift evolved into the sorts of things (galaxies, stars) close to here-and-now. That might justify a "as far as we know" comment like yours; for now, however, it is better to say that we really just don't know because we don't have nearly enough data yet.

Unless there is a violation of Lorentz invariance available to us very near hear-and-now, there is no hope of seeing long distances at our scale factor (which is a spacelike hypersurface in the standard cosmology's comoving frame, which means essentially that it's a collection of things all at the same "time", but that's coordinate time, and in this case the scale factor is the coordinate). Consequently we can't even be certain about highly-redshifted galaxies' fates at a(t)=1. To be sure would need to outrun the metric expansion of space, or equivalently, we would have to move much more quickly towards a cosmologically-redshifted source of the fastest known messengers than those relativistic neutrinos, photons, or gravitational waves that it emits have been moving towards us. There is an enormous amount of indirect evidence that shows that nothing observable moves like that, and plenty of direct tests of the relevant part of the equivalence principle that require Local local invariance everywhere in the universe since the electroweak epoch moments after the hot big bang.

So while most astrophysicists and physical cosmologists would bet that that there is physics like ours at great distances, including "just one metre, or just one megaparsec" (or even much further) outside our Hubble volume, there is no honest way to assign a probability of that being correct at this time. We can only say that it is consistent with the data we have on cosmic inflation (mainly from the cosmic microwave background's inhomogeneities), and it is exceptionally hard to produce a consistent theory allowing for very different physics just beyond the farthest galaxies we can see, yet still match the overwhelming majority of the data we have collected.

https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29

https://en.wikipedia.org/wiki/Particle_horizon

https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_vi...

So, the tl;dr is that wondering about what's outside the observable universe might be fun, but it's not scientific because any hypotheses one might generate can never be verified by observation, even in principle, by the very definition of "observable universe". At best we can only hope that the observable universe is bigger than we think today (e.g. by a very surprising resolution to the tensions in the cosmic-distance ladders, by the discovery of wormholes and comparable topological "defects" in the universe, or by the discovery of faster-than-light travel). I happen to hope some of that, but have no honest basis for that hope.

The Fermi paradox is just a way to have fun at parties (or over the internet, especially on HN). There are so many possible solutions to the Fermi paradox. But each solution has questions, and answers, and more questions and more answers. That's why it's so fun.

But it's not that deep.

To the point, the Dyson swarm is virtually guaranteed to not be used by any advanced civilization. Once a civilization tames nuclear fusion (and we are on the brink of doing so), then harnessing the energy produced by the local star via a bunch of solar panels becomes just a clunky way of getting energy. Controlled nuclear fusion can be many, many orders of magnitude more productive and convenient compared to solar energy. A star is indeed a massive fusion reactor, but it's a very slow one. Our Sun in particular produces about as much energy per pounds as the heat produced by the fermentation of manure. ITER is projected to produce hundreds of millions of time more. And ITER is just the beginning. Sure, the Sun contains most of the matter in the solar system, but plenty exists in the planets. We could use hydrogen stripped from Jupiter to produce trillions of times more power than a Dyson swarm could produce, and we can have that in a portable form that we could take with us in interstellar travels.

Bottom line, whoever is looking to find Dyson spheres out there in the sky, is simply wasting time.

Almost half a trillion in the case of Milky Way.

It's hard to quantify the chances of life existing anywhere else at the same time as us when we don't have any idea of how it came to exist in the first place. We might be the exception, we might not. You can't just make the connection: "billion of stars" = "we're not alone". I don't pretend to know what's "likely" on a universal scale and I don't think anyone should

Of course, nobody has specific evidence either way, this is all guesses through Bayesian reasoning (Anders Sandberg has a paper arguing the opposite to my above guess, along Bayesian lines). But no evidence is distinct from no information.

Space is big.

"Just works" for me, with no sign in.

The patterns it sees are real, and very cool.

https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy...

https://en.wikipedia.org/wiki/Galaxy_filament

with a concrete rendering at

https://en.wikipedia.org/wiki/Void_(astronomy)#/media/File:S...

and some more at

https://en.wikipedia.org/wiki/Observable_universe#Walls,_fil...

These filamentary luminous matter distributions (and the sparse, dark, cold voids between them) drive our theories of structure formation:

https://map.gsfc.nasa.gov/universe/bb_cosmo_struct.html

There are some patterns at scales of up to a few tens of megaparsecs, but beyond that matter is for all practical purposes homogeneous and isotropic: with a good enough (infrared- or radio-) telescope you will observe a galaxy or a precursor along every line of sight unobscured by objects within our own galaxy, and only the reddening and dimming from the metric expansion of space permits any darkness at all in our sky.

This is important to the standard mode of cosmology, \Lambda-CDM, which relies on Friedmann equations, which model all the matter content of the entire universe (past and present) as a perfect fluid of uniform dust. Because of the "local" nonuniformities like filaments and voids, grains of dust are thus on the order kilo- to megaparsecs. If we find that there are bigger grains, the standard "concordance cosmology" will have to be adjusted to be concordant with the new large-scale evidence.

(There is lots of looking right now, but so far everything points to smoothness at scales much smaller than gigaparsecs, kinda how a sheet of paper looks smooth in your hands, but a tiny piece of it under a light microscope looks very fibrous, and under an electron microscope one might discern the remnants of plant cells, or even see microbes!).