I know it'll sound sarcastic, but it's a good illustration of the point:

Go build a racecar, personally, right now. No, you can't practice making a simpler one first. Straight to trophy winning.

Well, what's the problem? Racecars already exist, so it's not even like you need to develop new technologies. Go, do it. Then also make a profit, because no one's giving you free money here. Chop chop.

In this analogy, the only difference between you and them is that the current chip makers know how to make a moped.

Making stuff from scratch isn't easy, and these guys are working literally at the edge of what's physically possible. It's not even completely sure if you can go even smaller than currently available.

For comparison, you can't make a 0.01 nm chip because that's less than half the size of a hydrogen atom.

And to even do the current work, you need to come up with and build whole new tools and machines, which cost billions, because they're literally manipulating atoms at this point.

That is incorrect. The light does actually slow down without getting absorbed or bouncing.

What is important to understand is that a photon is the oscillation of the EM field, not just a particle. Charges (like an electron) interact with the the EM field both eays, they are acted upon and act on it. Oscillations cause charges to move, but moving charges cause oscillations in the field. These effects interact with eachother in such a way that it causes the oscillation (a photon) to propagate slower in that medium than the maximum speed (speed of light) even without being absorbed.

The way you're describing it, transparency would be impossible, everything would be translucent or opaque. Like, say, the core of the sun that you mentioned.

Not any more than it already does. We can't shoot people into space from a canon, the acceleration will kill them. Once you get past that idea, g forces aren't really the issue that needs solving. A rocket launch is about 3g's for the astronauts, something a healthy human (hence the rigorous health screenings) can withstand just fine, and that's pretty much the maximum they'll be subjected to (unless there's a crash).

The one difference in the same sharpness of turn between space and earth is that there's already 1g of acceleration always acting on you towards the earth.

So, say, a rocket liftoff always has 1g more acting on you than the pure acceleration of the rocket would suggest. Acceleration towards the ground would have you feel 1 less.

Any side-to-side will always point slightly towards the ground on earth (the earth's g and the side acceleration forming a triangle), while it would be a pure centrifugal effect in empty space. So technically on earth, you'd experience a slightly higher g force, but not by a full g (same as the hypothenuse of a traingle isn't the simple sum of the sides).

"G forces" is only a common term for people being squished against stuff by inertia ("certrifigal force"). No gravity necessary.

The only connection to gravity is that it's measured in multiples of gravitation acceleration at the earth's surface, aka "g". Because it's something we're familiar with and it's easy to translate into effects on the human body.

If you've ever saw a professional make pizza bases by throwing them in the air, spinning, it's more or less like that.

More specifically, gravity is attractive in all directions. When the gas cloud the solar system firmed out of started spinning along a specific axis (because of how it was contracting), there was an outward force (the centrifugal force) counteracting gravity in one plane, but nothing perpendicular to that plane. So all the matter started falling into the centre, except where it couldn't, because the centrifugal force kept it in orbit around the forming sun. Repeat the process on smaller scale for planets, and that's why most of them rotate the same way too.

So a nuclide is just a technical term for "(specific) atomic nucleus but without any electrons"?

This sounds like a reasonable ELI5 explanation, why not put that as the top level comment?

Yeah, exactly, you're just listing stuff, you're not even trying to actually say which ones matter for what.

Why do some cars have an engine in the front and others in the back? Why do some planes have straight wings and some swept? Why are missiles pointy but torpedoes round?

bEcAuSe ReAsOnS LOL

Big planes have multiple big engines. It makes sense to mount big engines on the wings, because that's where you have lots of physical space for them, and that's where the lift is generated, so they're lifted by the wing directly. Trying to mount them to the fuselage would require heavy support structures to mount the heavy engines, increasing overall weight beyond the engines themselves, putting more stress on the connection between the wings and the fuselage. It also makes the maintenance much easier, because the engines are close to the ground, rather than high up. The downside is having engines close to the cabin. This is true both for jet and old piston engines.

A small plane has smaller engines, but also very little ground clearance. So it's pretty impractical to try to put them under the wing, and it'd complicate maintenance to put them inside the wing. At the same time, because of the size difference as compared to the airliner, mounting them on the body doesn't require as much reinforcing, so you don't suffer the same weight penalties. It has an added bonus of making the cabin quieter, which for a luxury jet is certainly a factor.

>Why doesn't every car look the same, have the same engine, and use the same tire size?

Well... Why? What design requirements dictate the specific design choices?

This is a complete non-answer.

Pretty sure OP meant something like a business jet, with the two engines on the tail, compared to a big airliner with under wing engines. Not the old 3 engine liners.

The difference in what they're waves OF.

Light can get completely reflected of or absorbed by sufficiently thick stuff (how thick is "sufficient" depends) because it can be blocked by atoms from travelling.

Sound, on the other hand, is a mechanical wave. It's atoms moving around. So you need atoms to have sound, and anything made of atoms can transmit sound.

A wall is made of atoms. Atoms in a wall can block light. But atoms in a wall can transmit sound. Hell, solids are better at transmitting some sounds better than air, it's why the old-timey technique of putting your ear to the ground works, because the low rumbling of solid wheels or hoofbeats would travel through ground better than air.

Alright, nevermind then

Yeah, that's why I'm checking what they mean. I already know of muon catalysation, but who knows, maybe someone figured out how to use Pi- mesons intead of electrons

Just to check, did you mean muons or did you actually mean bosons, in which case please elaborate or link something that talks about it, because I've never heard of that one

...yeah, I know, that's literally what I've been saying. It's actual bootlegged alcohol. Like, you know, traditional moonshine, not Moonshine™

Because that was the original point. That moonshine, until circa 2010 apparently, was the colloquial term (slong with hooch) for bootlegged alcohol.

>Not knowing about a thing doesn't mean it's not a thing.

I believe you that it's a thing now, but it's just funny how offended you are when you just said it's literally only a ten year old thing, considering "moonshine" has been a thing for well over a 150.

So yes, I didn't know a bunch of corporations appropriated a pre-existing term about the same time the first Avatar came out. My bad, lol.

>And whatever you had was probably not made by a commercial distiller

Wow, how did you know!?

>Because I did have alcohol from an amateur still, fermented from whatever was available

Oh, right

I wasn't aware that Moonshine has become a "brand", made to a particular recipe, like raki or rum.

Because I did have alcohol from an amateur still, fermented from whatever was available (mushy fruit and potato peels, probably). You know, like something a moonshiner would have made back in the day. It just tasted like shit vodka.

Moonshine is literally just illegally distilled alcohol, not a flavour. It's called that because it was done secretly, often out in the middle of the woods or somewhere... In the light of the moon, if you will.

I mean, it can have SOME flavour, I suppose, if it wasn't properly distilled. Which isn't unreasonable if it was done in a slap dash setup in the woods.

>So, $300 is like… low end for a good quality one?

Yes, essentially. If it's for a child, I suppose you can go a bit lower still, but keeping within the respected brands (Skywatcher, Celestron, Meade, Explorer Scientific), like this

https://www.highpointscientific.com/celestron-firstscope-76-mm-f-3-95-dobsonian-reflecting-telescope-21024

Nothing to write home about but nice and sturdy, you can mount a phone to it. It wouldn't really do planet that well (because of it's low F-ratio it's better for deep sky), but otherwise hassle free viewing. Good for young kids for when you don't know if they're really into it.

The Astromaster I've recommended is a genuinely a good telescope in your price bracket and a quite a bit more versatile than the above (would do planets while being better overall). Again, EQ mounts require a bit of learning, but they're worth it in the end.

For a complete begginer in the $300 limit I really want to recommend this

https://www.highpointscientific.com/sky-watcher-heritage-130-tabletop-dobsonian-s11705

But the struts flex too much to reliably mount even a phone, IIRC. If you can find an equivalent from the brands I mentioned earlier but with a solid tube. Then you'd just have a choice of "large and simple, but cumbersome" or "small and versatile but more complex". Because a larger tube means better viewing, but at the cost of a dead simple and heavy mount.

Just beware of anything that says "OTA" when looking to buy, because that's just the tube, no mount. So you'll get a better tube for the price but they're not something you freehand, lol.

>Do you recommend any specific brand of camera that pairs well with telescopes?

If you don't already have one, don't worry about it. You can take nice photos with a smartphone. Astrophotography with a camera is an advanced art for when a) you're really into it yourself, willing to put in the time and money and b) already have a good grasp of photography. And conversely, likely already have a camera.

Have fun snapping phone photos, see how you like it, research the subject seriously, ONLY then ask on dedicated astrophoto boards about specific cameras. I don't know enough about cameras to make good recommendations myself.

>Also, if $300 is cheap crap, what should I expect to spend on one I actually am going to enjoy with the kids?

Nah, you only need to go higher if you decide you're really into it and want more capability. The ones I've shown will be good enough for kids. But at that point you'll hopefully have be experienced enough in the topic to be able to make informed choices, or at least ask specific questions for research. Because a setup for photographing nebulas or galaxies is fairly significantly different (and more expensive) than trying to view/photograph Mars.

Quite frankly, if/when you're looking to spend more money, I'd look to get a sturdier mount for the astromaster. It's good enough for a begginer with no expectations or goals, casual viewing and the casual phone photo snap, but you can start to find it's too flimsy once you want solid results (say Saturn photos good enough for stacking). The tube is decent but stability really makes a difference. That's why I put the Dobsonians as an option there. But again, that's when you actually have a good idea of what you want out of your telescope. Because good sturdy EQ mounts cost as much as the tube.

As long as it's not crap quality, you can take as good pictures as the camera allows through any telescope, but the mount matters (will it shake). It's more important what you're taking pictures with. You can absolutely take pictures with a phone in a mount, but a proper camera is better. But if it's a chunky old DSLR, a cheap telescope ($300 is cheap for a "real" telescope) might have trouble physically supporting it.

For general viewing at that price, I would probably go with this

https://www.highpointscientific.com/celestron-astromaster-114-eq-4-5-equatorial-reflector-telescope-31042

It requires some learning how to use the EQ mount and maintenance of the tube, and it's not the sturdiest (so no big DSLR) but it'll do the job. I believe it's also possible to buy a simple motor to drive the equatorial axis (it tracks with the rotation of the earth). That would allow for some basic astrophoto of something that isn't just planets or the moon.

If you're more interested in planets and really cannot be bothered to learn how to properly use the above in the slightest, this could be an alternative

https://www.highpointscientific.com/celestron-inspire-80az-refractor-telescope-22402

It's smaller and not suited for deep sky, and the mount won't track (no photographing nebulas with that), but still good for planets and stars, and it's really dead simple, a tube on a pintle. Minimum maintenance (don't break it and it works) and almost zero learning.

The one that best suits your needs (what you're viewing, astrophotography or eyeball mk1), budget and restrictions (transport, storage etc).

It seriously is a question of the same caliber as "what's the best car to buy".

I'm catiously optimistic

There is a short answer to your title question: "nobody knows and currently have no way of knowing". Any contradictions come from comparing ideas that aren't meant to go together because they're parts of different models.

We don't know if the universe is infinite. We don't know what was happening at the earliest moments of the universe. Was it a single point? Maybe, although that's a very unpopular idea among physicists, just like the singularity in black holes. It contradicts quantum mechanics. There's currently not a better model, but they're pretty certain infinite density should be false.

We simply do not have the maths or technology to answer those questions. It would require the "Theory of Everything", with quantum gravity and all that. And the tech to test it.

To the followup questions.

It's absolutely possible for infinite space to have infinite matter and still be relatively "empty". There's just more space than matter. Just repeat what you can see in the sky infinitely in all directions. There's no contradiction.

Expansion can be weird to think about, but that's why the baloon/rubber band imagery is helpful. If every point in space stretches the same amount, something 1 "unit" away will stretch to 2, but 2 will stretch to 4. So distance matters. "Our local area" is the few neighbouring galaxies that are gravitationally bound, so any expansion of space (at observed rates) that close wouldn't be significant.

Also, expansion isn't actually uniform, gravity does counteract it. There is no expansion within a galaxy, or even within clusters (as far as I understand). The concentration of mass counteracts expansion.

BTW, our immediate vicinity being fairly empty actually IS weird. Our galaxy is actually in a void, imaginatively called the Local Void. The galactic neighbourhoods are usually more busy.

As for CMB and flatness, I only have a rough idea based on what I've read, but essentially is goes like this: "flatness" of soacetime is all about parallel lines being parallel and angles in a triangle adding up to 180 degrees. So geometry you'd do on a sheet of paper. For example, on the surface of the earth which is NOT flat, you can draw three lines (along the great circles) which will meet at 90 degrees and yet form a triangle. That's non-euclidian geometry.

Where the CMB comes in is the fact that it represents the very early universe. But it directly corresponds to today's universe, but everything has grown since then. So depending on the curvature of the universe, the patterns in the CMB should have specific shapes, corresponding to the massive structures in the visible universe. So astronomers made the observations, made the modelling, and the shape of the CMBs patters corresponds to the model where spacetime is flat.