Not all supermassive black holes are actively accreting. In fact, the fraction of time their accretion disks actually output massive amounts of radiation is ~10%, on patches of ~ hundred million years timescales.

A planetary system could form outside the center of the galaxy and travel close to the galactic center. You have to keep in mind that the distances between stars are enormous when compared to distances between planets. For example, our nearest star is 270 000 earth-sun distances (4 lightyears) away, while Jupiter is only 5 earth-sun distances from the Sun. So a "stripping" of planets, due to tidal forces, is extremely small, even when it comes close to the supermassive black hole in the center of the galaxy. It is true however that for the closest orbits, such as 120 earth-sun distances for S2 (S2 reaches speeds of 5000 km/s), this effect will be important. However, I suspect that while a single, quick swing-by will alter the orbits of planets (generally increasing ellipticity), that effect leads to the immediate destruction of the entire system. Normal planetary systems are also not stable systems. Changes in the orbits, interactions between planets, etc. are common; Only when stable oscillations are reached, the orbits remain the same for a few million years. So I suspect that the planets can re-arrange into a stable system (perhaps under ejection of one of the planets).

I think the changes are better if the system is a newly born star, where planetoids are still forming in a thick disk of gas and dust. Then, the partially destroyed disk can re-arrange quickly and form planets after swing-by. That would not necessarily be a problem for "spreading of life", if this process occurs e.g. via comets.

Unfortunately, space is not Euclidean on giga-parsec scales. Here, when talking about 5000 Gpc, they refer to a "comoving scale". That is a scale where the expansion of the universe has been divided out, so that e.g. the same number of galaxies remain in this box. So if you would place the atoms of the number of swimming pools you computed in the volume, they would be twice as dense at the largest distances, where the Universe was half the current size. Also, the largest distance within a 5000 Gpc^3 is 3200 Gpc (space is not Euclidean).

What happens when you link the Antikythera mechanism with the Kythera mechanism? Fusion experts should investigate!

Yes, so what init system and service management are they going to use?
Is it meant just for servers? Then they could get away with sysvinit.

If this Debian derivative is meant for desktops too, then you want some type of the systemd solutions to service management, to dynamically change hostname, datetime, do hibernation, add/remove bluetooth/modem devices, multi-seat login, etc...

I think the options are: Upstart or OpenRC; the others are too obscure or untested.
Probably you would have to use the abandoned Consolekit to replace logind?

If you are unfamiliar, this is what (systemd-)logind does (and previously ConsoleKit did part of it):

.
        keeping track of users and sessions, their processes and their idle states,
        creating control groups for user processes,
        providing PolicyKit-based access for users to operations such as system shutdown or sleep,
        implementing a shutdown/sleep inhibition logic for applications,
        handling of power/sleep hardware keys,
        multi-seat management, session switch management, and device access management for users,
        automatic spawning of text logins (gettys) on virtual terminal (console) activation and user runtime directory management.

from https://access.redhat.com/docu...

That's not true. We know the luminosity output of GRBs very well, as well as their spectrum across the electromagnetic spectrum. For a number of exoplanets (and the planets in the solar system) we know their main atmospheric content. For each composition of atmospheres you can predict the effects of a GRB for any chosen distance in terms of photo-dissociation, heating and radiation pressure. I don't see great unknowns there.

I think it can be argued that due to the luminosity output of GRBs, that "GRB==doom" holds, within a certain radius and for typical orientations. That serves as a useful starting point. For special orientations, or special atmospheres that one could imagine, this may not hold. But then the burden is on the person dreaming up these scenarios to show that these can more happen frequently than expected due to random orientations and atmospheres representative of the gas make-up of observed stellar and star-forming systems (which is well-studied as well, the technical term is metallicity and (heavy) element abundance). Until then, I think "GRB==doom" is a suitable working hypothesis we can adopt.

Actually, it's only 17 million. A quick calculation gives me that the number of galaxies within 5 billion light-years is 170 million. Neglecting very small, dwarf galaxies, which are more numerous but have drastically fewer stars, I multiplied the stellar mass density by the comoving volume up to z=0.5.

I can not answer about the deadliness of GRBs, but I think you will find those answers in Phil Plaits book "Death from the Skies!".

Yes, insulation is a good idea. But the planet will always radiate as a black body and loose energy, which has to be re-supplied by the suns radiation. The radiation drops with the square of the distance, so rather quickly. These considerations (make-up and size of planets) go into calculations for the habitable zone.

I can also imagine that a GRB comes with considerable photon pressure and might strip the entire atmosphere off a planet, or heat it to a point where it dissipates into space.

I think the rotation of planets around their own axis (spin) is not known outside the solar system. Generally, the spin is generated from formation of planets in the rotating protostellar disk, but interactions and changing orbits may modify the spin (Venus, Uranus).

If you do not have the problem of heating and evaporation of the atmosphere I mentioned above, then yes, that is probably possible. For example if the GRB goes off from the direction of the spin axis ("below/above the solar system"). This may safe you from one GRB, but since GRBs come randomly from all directions it is not failsafe across many billion years.

Not sure. I think it is possible to come up with such scenarios as you stated, but it has to be shown that they are frequent occurrences to be relevant for changing the survival rate of complex life.

While the Universe may be infinite, the Observable Universe is not infinite (limited by the speed of light).
The Universe within a radius of a certain number of light-years (and thus of age comparable to our location) is also finite. So considering the galaxies younger than 5 billion years, the number of those galaxies that can be observed (and can contain life that could communicate/meet with us) is finite.

A quick calculation gives me that the number of galaxies is 170 million. Neglecting very small, dwarf galaxies, which are more numerous but have drastically fewer stars, I multiplied the stellar mass density by the comoving volume up to z=0.5.

Most of the instruments (e.g. electronics) have a large US contribution. CERN operates the ring, but the instruments are "clients", which are international research teams. That was the vision of CERN after the second world war -- bring leading science to Europe, and make research in Europe attractive. Particle physics was chosen back then.

You could filter out all the Higgs events and make them into a artsy OpenGL visualisation or use them in a audio piano piece.
Like here, magnetic field observations has been converted to audio: https://soundcloud.com/esaops/...

I think the way forward will be a lot of systemd forks that strip away functionality, and implement other functionality. That which will bring about the need for a common, standardized interface. And then, choice in init systems will be an option again (but timezoned, hostnamed, logind will be required).

Or why don't they put all of that time and energy into implementing an alternative to systemd.
For example, by implementing a systemd-independent logind.

Sorry, I'm not completely familiar with the US legislative system. Does this election mean it is the law now, or it is just the expression of voters that politicians now have to form into new laws?

People tried that, 15-10 years ago. It did not work.
The reason it did not work is because it required every computer user to make sure their install is working, and the website could not fix setup problems. The user got the feeling that the website did not work and unusable. Sometimes this is justified, when you do not have install rights on the computer (e.g. labs). Websites started to offer plugin/viewer downloads, which caused a lot of malware problems.
Implementing it in the browser solves this problem. Implementation in HTML/CSS/JS on each website would not be enough, because the video data has to be streamed onto the graphic card for fast enough support.

Yes, but: Nature or Nurture?