troyunrau

troyunrau , 3 months ago

The Hubble constant is an interesting one – it isn’t actually a constant, but if you reframe it as a partial differential equation, the law is very predictable. en.wikipedia.org/wiki/Hubble's_law#Time-dependenc… – so in many ways, it’s just a misnamed phenomenon, and shouldn’t be called a constant at all.

Any place in the universe beyond which we’ve directly sent probes – is assumed to be like those parts we already know. Part of the reason we make this assumption is that: main sequence stars appear to behave identically across vast reaches of space and time. Thus we assume that physics hasn’t changed significantly (at least within the period of time where main sequence stars exist). Because if the physics was different, the stars would be different (spectra, lifecycles, etc.).

I’ll present a tickler I learned in cosmology decades ago, for hand-waving.

Run the big bang backwards – imagine all of the matter and energy of the universe collapsing to a single point. Which point is at the centre? They all are. Run time forwards again and all the points expand outwards from each other, but which point was at the centre that you can use to reference the centre of the universe against? They all were. Thus, I am the centre of the universe. And so are you ;)

This made my brain melt until I learned to visualize this using lower dimensional surfaces (like Riemann spheres). Imagine a beach ball being inflated. It is a two dimensional surface. You’re an ant on the beach ball and all the other points are getting further away, but it’s happening in a uniform way. (The Hubble parameter is something like the rate at which air is added to the beach ball.) Now, run this beach ball backwards through time – it shrinks and shrinks until it becomes a single point, where all points overlap – every point is the centre of the beach ball universe. Run this forward in time again and ask: which point on the surface of the beach ball is the centre of this two-dimensional universe? And the answer is “all of them” and the universe should be uniform in its expansion properties.

It might not be, but that’s the idea.

troyunrau , 3 months ago

So, this just popped. livescience.com/…/james-webb-telescope-confirms-t… which may be relevant. Haven’t read it yet.

troyunrau , 3 months ago

For the longest time I used to shelve Rand next to Marx on my bookshelf. I’ve read both at various points (might as well learn the source material if you’re going to argue about politics…), but it tickled me as a centrist to annoy their ghosts equally.

troyunrau , 4 months ago

Piranesi – after Jonathan Strange and Mr. Norrell being a thousand page masterpiece, Clark comes out with this short thing decades later that is simultaneously completely different but also amazing in its own way. As a fan of her first book, I was initially put off due to the lack of length, assuming that meant lack of depth.

troyunrau , 4 months ago

Epic find!

troyunrau , 4 months ago

First, you’ve got to realize that you’re making several very bold assumptions given current physics: (1) that we can build O’Neill cylinders with current or future materials that resemble anything like sci fi expects (probably not – pressure vessels are hard, mkay). (2) that we have a means to accelerate something larger than a probe to a significant fraction of light speed (this is actually the least difficult problem, but I suggest you look at the energy and travel time requirements). (3) that there’s any conceivable way for this thing to stop upon arrival (much harder problem without magic engines).

If all of the above are reasonable, then, well, you bootstrap manufacturing in situ in the asteroid belt or in a planetary ring or whatever. Not a huge problem. You obviously need to target a second or third generation solar system in order to find metals and heavier elements on arrival, but that’s trivial if you’ve solved the “stopping upon arrival using the energy and mass you brought with you” problem.

If you could send very small self replicating factories that could take their time to arrive, and upon arrival built a huge laser array used to slow down your larger shipments as they were inbound, you might be able to pull it off… With a few thousand years of preplanning. ;)

troyunrau , 4 months ago

The accelation problem is easier because you can build massive infrastructure in your home system that doesn’t need to make the journey, so it doesn’t incur the tyranny of the rocket equation. Still need massive infrastructure and huge amounts of energy, but it’s much easier to imagine a dyson swarm of lasers firing at the mirror at the back of the spaceship. :)

troyunrau , 4 months ago

I didn’t say speed of light – just a significant fraction of it. Even 1% is extremely ambitious from an energy budget perspective. 10% or higher is probably achievable for small outbound probes using laser based acceleration – but they’ll just cruise by systems without any means to stop. For large “settlement” ships or similar, even getting 1% would be colossal amounts of energy (like percentages of the sun’s total output). So, yes, you’ll need to take the slow road.

troyunrau , 4 months ago

I’d like to see a pressure vessel made of fibreglass that size… Not happening. Wall thickness in pressure vessels scales

Simple calculator, assuming steel… a 24 km diameter pressure vessel at 15psi is over 13 metres thick steel wall to contain the pressure. checalc.com/calc/vesselThick.html

Just the volume of steel required would be astronomical. You might be able to do this out of a similar mass of fibreglass… But forget launching it from Earth (would have to be made in situ).

And, largely, forget the fantasy renderings of what O’Neill cylinders look like – they are anything but lightweight.

troyunrau , 4 months ago

we figured out large scale and pressure vessels already

No. This is an assumption not borne of physics or engineering. There is no magic material that will make large scale pressure vessels suddenly viable. It (and space elevators) are mathematical constructs, not real things.

Use this calculator. checalc.com/calc/vesselThick.html – punch in 15 psi for pressure, and 100F for temperature. Play with your pressure vessel. Wall thickness of large scale habitats will need to be many metres of solid steel (or equivalent material). Even if you magically mass produce carbon nanotubes or something, you still need hundreds of millions of tonnes of carbon to pull off any large scale vessel. Your talking about ingesting entire asteroids just for building materials. You don’t launch that shit on an interstellar journey.

troyunrau , 4 months ago

It’s far more than building a city the size of tokyo. It’s the mass required. If you weighed Tokyo, and then engineered a hypothetical Tokyo in space, you’d find that the mass of the equivalent materials would be orders of magnitude higher than even your worst estimates.

Back of the envelope, you put Tokyo in a cylinder with a similar surface area to actual tokyo, the volume of steel in the walls of the containing cylinder (just the pressure vessel) would be about … 60 billion cubic metres, or something like 450 billion metric tonnes of steel. As a point of comparison, tokyo tower is… 4000 tonnes.

As another point of comparison: our global annual steel production is currently around 2 billion metric tonnes per year. It would take 200+ years worth of global production to build just the pressure vessel for a tokyo in space. Unless you’re building this at your source of raw materials, it just doesn’t happen.

troyunrau , 4 months ago

Yeah, if we aren’t in a hurry, and we can set up some fusion reactors and such on them and build whole civilizations on these rogue planets in the dark, it would work. Depends on how early and often we set up shop on passing planets, but in theory we could colonize much of the galaxy in a few revolutions around the milky way. So, under a billion years. ;)

troyunrau , 4 months ago

Excellent question. From first principles: mars is about 1.5 AU from the sun. Using the intensity equation (inverse square law), Mars should receive about 1/(1.5x1.5) the amount of solar radiation, or about 44% on average.

Earth gets about 1400 W/m² hitting the top of the atmosphere, but most places on earth only see about 1000 W/m² after the column of air absorbs a bunch of it. Martian air absorbs almost nothing (being very thin), so you’d expect to see about 44% of 1400W/m² – or about 600W/m².

A quick Google search for “mars solar intensity” shows a result of 590 W/m², so that is pretty close to accurate, from first principles.

So 60% as bright, if talking pure intensity. As you say, the human eye has a pretty responsive dynamic range, and this is quite an acceptable number.

For point of comparison, this is the difference between the sun at high noon versus the sun at 4pm for most of the world. On Mars, high noon would have a solar intensity more like 4pm on earth. No where close to your darkness experience with the eclipse.

troyunrau , 4 months ago

And, that eye would still need to be attached to a human. A living one. No shortcuts just launching the eye in a jar ;)

troyunrau , 4 months ago

Effectively, yes

troyunrau , 4 months ago

Time delay would be super disorienting to livestream it into your ocular nerve or something… But sure!

troyunrau , 4 months ago

You folks are awesome 👍👍

troyunrau , 4 months ago

It’s funny. I was around from KDE 1.1 to about 4.7 and some of those decisions were things I was involved in directly… Like the branding shift towards KDE as a community (people sharing vision and development infrastructure) as opposed to KDE as a monolithic desktop environment. I haven’t been involved for ages now. I did some coding too, but not a tonne.

The KDE 4.0 release messaging was one of my core tasks. We had a release party in Mountain View – and we invited all the packagers for all the distros to the event. Linux community “luminaries” like Patrick Volkerding were there and it was a great party. But we thought that, by bringing all the packaging types there, we had the messaging problem bottled – and KDE 3.5 and 4.0 would be offered alongside each other as though they were different desktops entirely. (Like Gnome, or whatever… Just choose what to launch in your session manager.) What happened instead is that 3.5 was dropped like a hot potato and users fled 4.0. Distros didn’t want two versions of libraries installed, so running a 3.5 app in a 4.0 environment was difficult, but not all the 4.0 apps had been ported yet. Yikes! This is a huge reason for the subsequent split between version numbering of Desktop releases (later Plasma) and things like “Frameworks”.

Side note: we had even considered the idea of KDE (as a community) offering multiple desktop interface offerings, each with their own branding. So you could run Plasma, Kicker (a hypothetical KDE 3.x desktop environment ported to the current frameworks), etc. alongside applications from multiple versions of desktops. This was the reason the session management code was in KRunner rather than Plasma, for example. This would allow highly experimental user interfaces to be developed around the KDE libraries. But that never happened, as far as I can tell.

Anyway, for 4.0 – so much for Linux applications and the mantra “release early, release often.” Lesson learned. Linus, I’m so sorry for disappointing you. ;)

troyunrau , 4 months ago

Heh, that’s amusing ;)

We did do the high version numbers for alpha, beta, RC etc. leading into 4.0 as well.

You can find some of that here: 4.0 release schedule - go through the version history of that page. Fun times. (Makes me nostalgic.) You’ll note that the release date got pushed back a few times as more betas and things were inserted. You’ll also see version numbers like 3.97 for release candidates.

troyunrau , 5 months ago

Meow 😻

troyunrau , 5 months ago

Using bioelectric microcurrent waves to disturb the biological metabolic reaction and structure of bacteria that forms an impenetrable biofilm

Well, it certainly sounds like jargon designed to obfuscate the actual process. At a minimum they’re relying on scientific opacity to render a buyer “convinced because it sounds smart”.

I’m always skeptical of these things. Anything that can truly destroy the biological elements that make up plaque bacteria will also likely destroy the cells in your gums. So you’re left with either a very mild human-cells safe process that is so mild that it also does little to nothing to the other things, or you actually have a dangerous process that is also dangerous to your human cells. Like drinking bleach to cure COVID… I’d rather that, if they are doing anything at all here, it’s entirely placebo (beyond the usual brushing effects).

troyunrau , 5 months ago

This seems like a perfectly reasonable answer. OP! You could probably test this by changing the type of light you’re using. Try a red laser pointer as a control, and a black light wand (the sort they use to detect counterfiet bills), and see what happens.

troyunrau , 5 months ago

Complete tangent, but alumina, aka aluminum oxide, is usually considered the second hardest naturally occurring material. When it is found in nature, it is given the mineral name corundum and is clear. But if there are some impurities in it, you can get colours. Red corundum is called Ruby, and blue is called Sapphire. In the beauty industry, the same material (mixed with magnetite) is called emery, and lends its name to emery board, and is used in nail files. In the tech industry, it’s used to make the extremely scratch resistant coating on most modern phone screens (basically nothing but diamond will scratch it).

You have subscribed to alumina facts. I’m sorry, the cat facts guy was busy.

troyunrau , 5 months ago

You. I like you.

troyunrau , 5 months ago

So… night shift?

troyunrau , 5 months ago

Is there a machining community active somewhere on lemmy (yet)? I only dabble, but I like to sneak peaks at real folks fucking up, err, showing off their projects.

troyunrau , 5 months ago

How much water…

Plasma is so low density, so the total heat capacity will be quite low. You’d need a lot of cold plasma to chill a very small amount of liquid water through freezing.

Remember that a plasma is an ionic gas, so it doesn’t have a specific temperature associated with it. It’s just a bunch of free charges (ions, electrons, protons). Assuming the bulk charge of the plasma is effectively neutral, then you have some limits on density. If they get too close to each other, they start binding to one another. At cold temperatures, it is much easier to collide and stick than at hot temperatures, so cold plasmas tend to be even lower density than hot plasmas.

Which means, it cannot absorb much energy, because there isn’t a lot of matter in it. Sure, you could cool something with it, but it would take a lot.

troyunrau , 5 months ago

No, you can run most KDE apps on other systems, including Windows and Mac. I use Kate as my text editor on my windows work machine.

I used to be a KDE dev. We were largely volunteers, unlike a lot of other FOSS projects that had hired coders. The KDE e.V. funding largely went to server maintenance and helping students attend the annual conference (travel expenses! I benefitted from this a few times). Not sure if it’s still like that. In my era, KDE could easily get by on less.

troyunrau , 5 months ago

There used to be (in the 4.x days) a general installer which allowed pretty much who whole KDE ecosystem to be installed on windows. Does that not exist anymore? I used to use Okteta on windows this way :)

troyunrau , 6 months ago

Never tried to run it on MacOS. I use it on windows, but none of those features. Nonetheless, it’s my favourite editor and I hope you find what you need.

troyunrau , 7 months ago

In my D&D campaign, I play a time wizard. It’s fun to drop lines like this. I think my DM sometimes runs with it, making my statements self-fulfilling prophecy so that I appear to be able to foresee the future.

“The reality principle does like to disabuse us of our whims.” (No one at my table has seen Steins;Gate and it is a fantastic source of content for a time wizard haha)

troyunrau , 11 months ago

You need to socialize the isotopes with other atoms when they’re young. Otherwise they don’t learn to behave normally. Like dogs. Trust me, I’m a scientician.

troyunrau , 11 months ago

I’m out of the loop, but I used to use Slackware – largely because the distro didn’t get mad when I just installed things from source directly onto the filesystem. No dependency tracking ;)

But I had a lot of experience before that with other distros.

Good choices are probable OpenSuse (tumbleweed), Arch, or Neon. Actually, I don’t know the current state of Neon… is that still a thing?

troyunrau OP , 11 months ago

You joke - but I went to Akademy in Scotland in 2007 with about the same amount of notice, thanks to the KDE eV just deciding to fly me out. :)

No, I’m running a business now and cannot just abscond anymore like an undergrad :)

troyunrau OP , 11 months ago

Nice! Mandrake was really great when it was new – Basically redhat(clone)+KDE+Mandrake Control Center. Compared to the pain of getting KDE installed on redhat (originally), it was quite a slick system. It was my third linux distro, and I rode it up until the Mandrake+Connectiva merger.

After the aforementioned redhat pains, but prior to Mandrake, I also dabbled with Caldera. This was so slick at the time: www.linuxjournal.com/article/3563 – a pity they “enshittified” before the word was coined, because that’s exactly what happened haha. It was the first distro with a graphical install process, which just seems normal now but was quite revolutionary at the time. Plus it came with KDE preconfigured.

After the connectiva merger, I moved to slackware and stayed there until I exited KDE development. It was a great development box because the systems were so minimal and just sort of stayed out of the way. At the KDE 4.0 release event, we even managed to get Patrick Volkerding to attend – which is sort of like meeting your own personal linux hero. That was fun.

troyunrau , 11 months ago

Ditto. Except for my battery operated lawn mower and snowblower, which are Ryobi because Home Depot had good prices on their 40V line.

troyunrau , 1 year ago

Hi folks. Once upon a time I was [email protected] ;)