Observatory Version of Misc Musings, Ravings, and Random Thoughts

[Dmytry]

If you're completely mining apart a very small planetoid, you could shoot the projectiles in one direction to speed up the rotational velocity of the planetoid to the point where it nearly falls apart on it's own...

 

[Dmytry]

Random thought after hearing of Google's balloons: would it be possible to make a hydrogen balloon that stays afloat indefinitely, by electrolysing humidity? It could either use a thermoelectric cooler to condense humidity from the air, or use a very hydrophilic electrolyte that gets exposed to air. Not sure how much hydrogen is lost through the skin of a typical balloon. edit: using solar panels for power, of course.

 

[Dmytry]

Hellburner[/url]":1aluqs4v]Entropy/weathering, doubt there's anything usable in a balloon that will last almost any definition of "indefinitely".

I saw NASA mention that they managed to keep a balloon aloft for 55 days once.

I think the biggest limiting factor currently is hydrogen or helium getting lost, though. Everything else can be far more durable. But the gas will just plain diffuse out (which is exactly entropy he he).

 

[Dmytry]

Apteris[/url]":2kle16va]

Dac[/url]":2kle16va]Posted in the Videos etc thread, but worth posting here too, Max Tegmark's Q&A on The Mathematical Universe.

https://www.youtube.com/watch?v=jzmbSBr ... fuFKqxIAXw

I was completely fascinated by Tegmark's The Multiverse Hierarchy when I first read it; I still am. However, Scott Aaronson's criticisms of the concept and of Tegmark's The Mathematical Universe demand to be acknowledged.

If you're interested in this topic you owe it to yourself to read Scott's post, as well as the discussion between himself and Max Tegmark in the comments.

You may want to look at Marcus Hutter's page with regards to such 'theories'. The point of having a hypothesis, as opposed to not having a hypothesis, is that a hypothesis restricts possible observations (and thus can be ruled out, or be useful).

edit: also I highly recommend some of Greg Egan's fiction works, Luminous and Dark Integers if I recall correctly, where for the sake of an argument Egan describes the mathematics as a correlation between what distinct physical systems do, a correlation which doesn't even need to be immutable. We don't know if physics runs on math, Tegmark style, or not. But we do know that math we actually do runs on physics, and in principle the fact that your finger count of apples matched the count of actual apples (in the sense that you could e.g. poke each apple with a finger and then have no unpoked apples) can, and perhaps must be treated no differently from the correspondence between the fall of an apple in one place and another similar massed object (under same gravity). Sure, we do physics using math, but the math itself is just a way for us to construct analogous physical systems (e.g. some physics simulator, digital or analog) that can be used to approximately match other physical systems.

Now that we do a lot of our math on computers, it is a perfectly valid empirical question regarding physics, whenever a long chain of physical interactions involved in e.g. multiplication and division of large integers, when put into a comparison operation with the results of a presumably analogous proof, would yield the physical signal we expect.

 

[Dmytry]

The way I see it, what actually exists (when we say "math exists") is a property of the universe along the lines of e.g. if I set up two counters for apples (one involving finger counting, other involving eating them, for example) and feed counter outputs to a comparator then I'll get a zero from the comparator, which is an empirical fact about physics and needs not be true (one could come up with the alternate physics where the mere act of trying to compare the count of apples to the count of fingers would act in some bizarre manner). Not very different from how if I set up a wind tunnel it may predict how a wing will work flying through the air. There are other relations, e.g. when they simulate black hole with some sonic waves in a superfluid or whatnot. There's this set of relations between simple counting on fingers and more fancy ways of counting like binary counting, which works through application of the counting relation to the counting. The reason "math" is so useful for predicting universe is that our universe is not diverse enough or random enough for a behaviour of one system not to be approximated by the behaviours of many different systems, so for a system we want to approximate, there's a broad range of substitutions we can make repeatedly to build an approximation. For example we can replace position with a count, replace count with a binary count, replace binary count with a floating point count, and so on, when we write a simulator (We replaced comparing that our replacement methods actually match up, with 'proofs').

So the physical systems corresponding to proofs about large numbers relate to each other, that's about it. They don't really relate to any simple counter counting off that number though, i.e. don't imply existence of such a counter.

 

[Dmytry]

A study on salt intake and cardiovascular disease had been making rounds online. (With the usual sensational take: the mainstream proved wrong...)

What blows my mind is just how bad those studies are. You take a population and then either approximately measure, or, in the worst instances, get the self reported sodium intake. Then you correlate it with the mortality, and publish. Never mind that those with low sodium intake may be consuming less sodium because they have high blood pressure. Let alone the subtleties such as literally everything being different between their diets, the diet's relation to ethnicity, and so on. And this is taken seriously.

 

[Dmytry]

Random thought: can there be a fuel cell battery where the oxidizer and the fuel are both dissolved in the electrolyte (like a monopropellant for a rocket engine), reacting only on the catalyst cathode and anode?

 

[Dmytry]

PhaseShifter[/url]":3v4beqjo]

truth is life[/url]":3v4beqjo]

PhaseShifter[/url]":3v4beqjo]OK, looks like (to a first approximation) atomic number 194.

Which is absurdly high, as you'd expect.

But it's not absolutely ludicrous--half that number would actually be a known element, which makes me wonder if anyone's actually ever experimented with muons and actinide metals.

I think I recall hearing about a plan to use muonic atoms to probe some beyond Standard Model physics (probably looking for some anomalous decay event), but I don't recall anyone planning on binding muons and actinide atoms. It seems to me like it would be hard to do that measurement due to the radioactive background, but you might be able to do certain things to take care of that. An energy cut occurs to me immediately because the Michel spectrum ought to peak far above the radioactive decay spectrum (given that U-238, probably a good choice for this, has a decay energy of around 4 MeV). Positron capture and annihilation might be a problem depending on the size of the sample, too, though it'd probably be minor unless you made it fairly large.

(Dealing with backgrounds on low-background experiments is my day job)

I'm not sure atoms that heavy can actually exist for any remotely reasonable length of time, either, but I'm not a nuclear physicist (I am a particle physicist), so that's not in my wheelhouse.

Well, I'm still trying to figure out the difference between a neutron star and an obscenely heavy atomic nucleus. I've never heard an explanation that indicates there is any distinction.


That is a kinda big gap in the middle, though.

Well, the gap's your distinction... One is held together predominantly by the strong nuclear force, other by gravity. That would be a fuzzy distinction if there was no big gap between the two.

I wonder what would be the smallest possible neutron star size (not the smallest that would form but the smallest that can exist for some time). edit: apparently it is around 1/10 of the solar mass.

 

[Dmytry]

At the very outer layers, there's normal nuclei, so if we were to call the deeper part a nucleus then the whole thing is a really crazy molecule, if we expand the notion of a chemical bond to include gravity. That or a star that has an atom in the middle and stuff around it. I imagine it also transitions smoothly between the two as well.

I'd say most of the things that we consider to be distinct are a lot less distinct than a normal nucleus and a neutron star.

edit: or maybe not. Under the enormous pressure in the neutron star's crust, there would be much heavier nuclei than possible on Earth, bridging the gap. Either way, the whole neutron star is definitely not an atomic nucleus, if anything because there's a lot of nuclei, but a part of it perhaps may be (with a big stretch) called one. But this 'nucleus' can only exist when you have more or less normal nuclei piled on top of it.

 

[Dmytry]

Arbelac[/url]":2ely79xa]

shread[/url]":2ely79xa]See also http://en.wikipedia.org/wiki/Neutron_star . That article is a bit confusing. The intro says "neutron stars are composed almost entirely of neutrons." That statement seems to be at variance with the article's Structure section, but, I am a biologist!

There's some thought that neutron stars, although essentially pure neutrons at the core (depending on model), have a "crust" of other matter from cosmic infall.

They'd definitely need a crust of more or less normal matter piled on top to generate the pressures for the neutron matter.

 

[Dmytry]

Arbelac[/url]":2mxxhcsf]

Dmytry[/url]":2mxxhcsf]

Arbelac[/url]":2mxxhcsf]

shread[/url]":2mxxhcsf]See also http://en.wikipedia.org/wiki/Neutron_star . That article is a bit confusing. The intro says "neutron stars are composed almost entirely of neutrons." That statement seems to be at variance with the article's Structure section, but, I am a biologist!

There's some thought that neutron stars, although essentially pure neutrons at the core (depending on model), have a "crust" of other matter from cosmic infall.

They'd definitely need a crust of more or less normal matter piled on top to generate the pressures for the neutron matter.

What? Piled on top? No, the cosmic infall is due to gravity; the gravity of the neutrons packed together (due to a SN event usually) causes the crust; the crust doesn't cause the neutron star. The "pressure" for neutron degeneracy is first caused by the SN event, the ongoing pressure equilibrium is then due to gravity and the Pauli exclusion principle.

There can only be pressure due to gravity if there's mass for the gravity to act upon. You can't have neutron matter at the very surface of the neutron star, facing vacuum, because the pressure on the top layer of it would be zero. Starting from the surface as you get down pressure increases, until it is high enough.

 

[Dmytry]

truth is life[/url]":3e8y5ip3]

AmigaPhreak[/url]":3e8y5ip3]I'm sure there is some economic theory that describes the problem, which essentially boils down to "Why do I care how much trash I generate if it's not piling up around me?" It's an up-scaled equivalent of someone throwing wrappers out the window as they drive down the road, instead of putting it in the trash can when they get home.

It's called "externalities". Costs that you don't pay, but someone else (in this case all of society) does. It's a major problem for the environment, because impacts on the environment are easily externalized--it doesn't affect a paper plant, for instance, if the waste it's dumping in a river is killing all the fish and starving or sickening people downriver, even though it affects those people downriver quite a lot.

It's also called 'tragedy of the commons', i think.

 

[Dmytry]

Conserve[/url]":h3xrmk2x]A plastic-eating organism would be solar powered so it has that going for it. Actually, it wouldn’t be surprising if a phytoplankton adapted to do so on its own initiative.

Well, in the nature for the most part you have solar powered organisms that don't really eat organics, and non solar powered organisms that do...

 

[Dmytry]

Is there any study on the "someone wrong on the internet" phenomenon? E.g. why I (and others) feel compelled to even bother arguing with LBG's nonsense in the other thread? Is it maybe that reading something in print is associated for us (the older generation) with books and study materials and a textbook that wrong would be very bad? The behaviour pattern seem to be like "okay, I'll just ignore it... okay I'm too curious what sort of nonsense came up, I'll just look... writing a reply when I would better spend time working".

 

[Dmytry]

Keef[/url]":nkte68o5]So I'm just finding out that there are glasses that correct color-blindness.
http://enchroma.com/technology/how-it-works/

Pretty cool, I was under the impression that color information was just plain lost.

Yeah, likewise, I thought red and green curves ended up exactly identical. If those glasses worked you would think that fluorescent LCD backlights would have worked too, because those have spectral peaks in green and red. What I suggested to some people is to try using filters from the cyan/red anaglyph glasses (so you can at least tell apart colours in cables), perhaps with some training one can just wear the glasses and do that.

 

[Dmytry]

You could have time travel that only works within a machine, and you can't go to a time before the machine was built. Then you can't go anyplace that you can't move the machine from. That would be the classic time travel, i.e. with a magical cave or something. No teleportation here, especially if it say takes 1 hour subjective time to go back 1 hour (or any nonzero subjective time at all).

 

[Dmytry]

truth is life[/url]":278frz1a]

Dmytry[/url]":278frz1a]You could have time travel that only works within a machine, and you can't go to a time before the machine was built. Then you can't go anyplace that you can't move the machine from. That would be the classic time travel, i.e. with a magical cave or something. No teleportation here, especially if it say takes 1 hour subjective time to go back 1 hour (or any nonzero subjective time at all).

Sure you can. My argument still holds precisely, though a few of the details would have to be altered. So, you're an ancient Athenian, and you've found this magic cave that lets you go back in time one hour for every subjective hour you spend inside. As ancient Athenians do, you have business in, say, Rhodes. So, you sail to Rhodes, learn about the conditions there, and sail back to Athens. Say it takes a month, altogether. Then you go to your cave and stay inside a month, coming out just after you sailed for Rhodes so that you can arbitrage with your knowledge of exactly what it going on there at that very moment.

From your frame, you traveled through time, and the hard way too. From the frame of an observer who knows about your trip, you, once again, completed a round trip from Athens to Rhodes to Athens instantly--far faster than you could possibly have normally. Special relativity says that those two frames are equally valid, and there is no "correct" frame to look at it from, so saying it's teleportation is just as valid as saying it's time travel. You can always construct a frame where time travel is equivalent to teleportation.

Well, in my book teleportation implies moving from one point to the other while skipping the points in between, irrespective of the speed of said teleportation. f you gone through a path then it isn't teleportation - you could build a wall around athens and then this teleportation of yours can't be done. edit: ditto for crawling backwards while staying inside your past lightcone. If you change a frame of reference it's still inside the lightcone.

Re:FTL equivalent to time travel, not exactly so. Time travel into the past lets you interact with, say, your grandfather, giving rise to the grandfather paradox. FTL, if defined within a single frame of reference, does not (requires FTL in two moving frames of reference to get back into your past lightcone; with one FTL jump you do get outside your future light cone but you can't actually jump into your own past lightcone). So in a scifi story you can have FTL that is instantaneous in the frame of reference of the microwave background, if you wish with the handwavy explanation that it doesn't establish a truly absolute preferred frame of reference, it's just all the masses in the universe influence the travel.

I drafted scifi physics where a FTL spaceship can jump, instantaneously in it's own frame of reference, anywhere, if it been going for a while at a constant speed and is alone in space; otherwise the frame of reference where the jump is instantaneous is determined by the velocity of spacetime-nearby masses (still need to work out the formula so things like hopping around in a circle won't work either), so you can't jump ahead, turn around, jump back, and get where you started before you started, you can't use two spaceships to do that, and so on - two very nearby ships going in opposite direction and doing a FTL jump will jump instantaneously in the frame of reference of their COM. You can't set up a grandfather's paradox with FTL if you can't have two nearby FTL travels in different reference frames.

edit: back to non-teleportation timetravel, picture it like this:

The machine takes energy from an enormous energy bank, and creates Dr Timetravelson (older) and sorta anti-Dr Timetravelson ghost. Dr Timetravelson (older) leaves.

Anti-Dr Timetravelson in a chamber proceeds to act backwards, un-eats his lunch, then Dr Timetravelson (younger) with a lunchbox walks into the chamber and both he and anti-he overlap then match up exactly and disappear (and the machine recharges it's energy bank or something).

At no point anything moved faster than light; the weird bit is that the fate has it so the Dr Timetravelson (younger) and his ghost would match up with atomic exactness and disappear, and another weird bit is that inside the chamber, Dr was un-eating his lunch and everything was backwards about him (from his perspective the world was rewinding back). From the outside point of view the Dr which got to the Rhodes and back was created out of the energy stored in the time machine.

 

[Dmytry]

LordFrith[/url]":6u70wd0x]If you have an absolute reference frame, you can get away with infinite speeds without much issue.

However, you also lose a century of relativistic experiments that show there is no preferred reference frame.

The actual constraint is not that there must be an absolute, constant reference frame, it's that the reference frames affecting the FTL travel must not change too sharply, so that two nearby FTL travels never get into one's past lightcone.

The point is, when you're writing your fictional physics you could just set the "preferred reference frame" to be defined by the motions of nearby masses, in such a way that you have a reference frame that nowhere changes sharp enough to yield time travel, and which is not absolute in the sense that it depends on the nearby masses. You still don't get some absolute velocity measuring device - you run it on Earth and it just gives you velocity relatively to some combination of the velocity of the Earth, a weak contribution from the velocity of the Sun et cetera.

disclaimer: I'm making a videogame where you're flying at up to like 10 apparent lightyears per second... doing 60 jumps per second he he. Not actually going to implement any fancy timetravel evading physics though. It is much too difficult, in terms of programming, to even add a speed of light delay to a game engine not written for that sort of thing.

(Also, relativistic experiments only tell that the interactions being studied are unaffected by the choice of the reference frame. However, for angular momentum such a frame seems to exist, i.e. an object that is spinning is locally distinguishable from the object that is not spinning).

 

[Dmytry]

Given all sorts of crazy/impossible projects that get government funding (reactionless thrusters, cold fusion, directing lightning for military applications), could it be that various conspiracy theories concerning HAARP or the like have a (small) kernel of truth to them?
Along the lines that yes there were some experiments for one nefarious purpose or the other but no, the idea is completely stupid and it doesn't work. The fact that e.g. HAARP can't possibly do what ever conspiracy theorists think it does wouldn't necessarily stop someone with connections from getting a grant for trying.

 

[Dmytry]

Yeah, it seems to me as well that the main reason why it's harder to land on Mars than on the Moon is that Mars is heavier, so you need more powerful retro-rockets (but not heavy enough to have a lot of atmosphere so you wouldn't need any). Albeit I'm not even sure if that's true, as you still get some atmospheric braking on Mars.

Obviously there may be problems with the rocket engine blowing in the direction of your travel in an atmosphere, but if you have to use a rocket then it's blowing gas a lot harder than the atmospheric drag on the same area, so that shouldn't be a big issue.

 

[Dmytry]

truth is life[/url]":3nj5fud1]

Dmytry[/url]":3nj5fud1]Yeah, it seems to me as well that the main reason why it's harder to land on Mars than on the Moon is that Mars is heavier, so you need more powerful retro-rockets (but not heavy enough to have a lot of atmosphere so you wouldn't need any). Albeit I'm not even sure if that's true, as you still get some atmospheric braking on Mars.

No, that's not it at all. Mars is not all that much bigger than the Moon.

Escape velocity of Mars: 5km/s
Escape velocity of the Moon: 2.4km/s

>4x energy difference. Escape velocity is roughly how fast you're going to be falling down if you start falling in from afar.

That's a huge, huge difference with regards to the viability of retro-rockets, especially with the rocket equation. I'm pretty sure that parachutes and the heat shield would weight a lot less than a rocket of equivalent dV, thus making it easier to land on Mars than if there was no atmosphere.

 

[Dmytry]

truth is life[/url]":4zmtcr76]

Dmytry[/url]":4zmtcr76]That's a huge, huge difference with regards to the viability of retro-rockets, especially with the rocket equation. I'm pretty sure that parachutes and the heat shield would weight a lot less than a rocket of equivalent dV, thus making it easier to land on Mars than if there was no atmosphere.

You are wrong because you are not considering non-mass issues. You might save mass because of the atmosphere, but that doesn't actually make landing on Mars easier than it would be with no atmosphere, because it introduces many new complications. Now you need to have a heat shield and parachutes or other decelerator system (and Curiosity's parachute was the largest, fastest-opening supersonic parachute ever flown...in fact, there's no real scope to build bigger, better parachutes). Additionally, you cannot slow down to safe terminal velocities with just parachutes (especially if you're a large, crewed vehicle...you'll hit the ground at supersonic velocities), so you must have retrorockets anyways. Therefore, to safely land you have to arrange to jettison your heat shield, open your parachutes, jettison your parachutes, and ignite your retrorockets, all while only a few miles above a planet you're falling towards at hundreds of miles per hour. Compared to just igniting your retrorockets, this is definitely more complicated and difficult. Now you have many things that can go wrong, aside from just one (and one that you can test before you commit to landing, at that).

Well, and without the atmosphere you would need a much bigger rocket to bring enough fuel for retro-rockets that are firing for much longer and are engineered for maximum Isp. We're talking multiple times mass of the rover worth of fuel (to slow it down from 5.8 km/s), versus a small fraction of the mass of the rover in fuel to stop it after the parachuted descent. And with a fixed budget this could make the 'easier' mission impossible. I think you're focussing too much on the engineering difficulties and forgetting the sheer cost (or the engineering difficulties involved in the bigger launch vehicle).

Ultimately what you get with the atmosphere is that instead of carrying a very huge amount of extra fuel, longer burning and perhaps more powerful engines, and so on all the way to a far bigger rocket on your launch pad and far bigger budget, you can carry much lighter heat shield and parachutes to deal with the bulk of the velocity.

edit: Also, Soyuz uses retro-rockets on Earth, too.

 

[Dmytry]

Okay, here you go, for TR201-like engine for slowing your payload down from 5.8 km/s in the vacuum, using this calculator with ISP of 301s, I get 7.15 tons of fuel and spacecraft for a ton of spacecraft, and that's without counting the fuel tanks or engines.

That's seriously bad, given that Curiosity's actual descent stage weighted about as much as the rover itself. We're talking roughly, say, something like 5x the mass to get to mars, maybe worse, with the tanks and the engines, than Curiosity had to. It was launched on Atlas V, which has mass of 334 tons. You'd have to use Saturn V instead. edit: a comparison: http://en.wikipedia.org/wiki/Comparison ... ch_systems . Based on mass to LEO, you need >92500 kg to LEO, with the only candidates being:

N1 (blew up, never worked)
Energiya (retired)
SLS (in development)
Saturn V (retired)
Chinese Long March 9 (in development).

I think it's safe to say it wouldn't have launched for many years from now.

Basically if Mars had no atmosphere we'd probably not have landed anything Curiosity sized there anytime soon. Now, of course it is much easier not to do something...

If we did something with atmosphere and wouldn't have done it if there was no atmosphere, that in my book is the meaning of it being easier with atmosphere. Even if that involves more complicated engineering. People mining the resources are also doing hard work, and there would be a lot more of this hard work involved, as reflected in much higher price for the no atmosphere hypothetical. Not to mention that with all the sufficiently big rockets retired, you'd need a lot of extra engineering for large rockets.

tl;dr; rocket equation's a harsh mistress, no atmosphere on mars = no curiosity rover launch for many years from now.

 

[Dmytry]

It's probably less weight to slow down further with a rocket. The drag is proportional to velocity squared, so it's not very effective at low speeds. You need parachutes that are too large. Same applies to Soyuz capsules, albeit at a much lower speed. They use retro-rockets for the last few meters per second (the astronauts would survive without but may get injured).

 

[Dmytry]

Speaking of fission, i always loved the concept of the fission sail. Very thin membrane covered with an isotope with high spontaneous fission rate. Alpha particles would also work. Carrying bunch of genetically engineered spores or whatever scifi payload...

 

[Dmytry]

Keef[/url]":1i0z0pyo]A likely worthless idea, inspired by this and this...

• Take a supertanker, and cover the deck in solar cells to power the ship and run the conversion process. And maybe a few windmills to supplement.
• Install the hardware to run the process in a small portion under deck, leave the rest for fuel storage, batteries, etc.
• Figure out an efficient way to avoid sucking up and killing all the plankton and other tiny fauna and flora with the water used.
• After a few months out at sea you got a tanker full of synthetic fuel, and increased salinity and reduced acidity of the ocean (by a minuscule amount) to boot.

So, dumb idea?

Quite a bit more than a few months...

Say, you're getting 100W/m^2 on the average over the day (which is unrealistically high) on the top of the tanker, and your tanker is 10m deep. Fuel oil has energy density of 35.8e9 J/m^3 , meaning you have to produce 35.8e10 joules to fill up those 10 meters under the cell, which will take 35.8e8 seconds, or 113 years, at 100% electricity to oil efficiency.

 

[Dmytry]

MilleniX[/url]":2rjc3sht]

Keef[/url]":2rjc3sht]

Dmytry[/url]":2rjc3sht]Say, you're getting 100W/m^2 on the average over the day (which is unrealistically high) on the top of the tanker, and your tanker is 10m deep. Fuel oil has energy density of 35.8e9 J/m^3 , meaning you have to produce 35.8e10 joules to fill up those 10 meters under the cell, which will take 35.8e8 seconds, or 113 years, at 100% electricity to oil efficiency.

Gotcha, I guess that's why it makes more sense for the Navy to do it, with its nuclear reactors and all.

And the only thing they want the hydrocarbon fuels for is aviation, which is a tiny fraction of the overall ship's energy consumption.

That's pretty cool though, almost like nuclear powered aircraft.

 

[Dmytry]

Wouldn't you end up "supporting" them with chlorine? A-la pool sanitizer? edit: I don't know if you can get some oxygen not just chlorine if the current density is low enough, or not. Need someone who actually knows chemistry...

 

[Dmytry]

Wheels Of Confusion[/url]":3qmm6ube]Crazy thought time, inspired by all those videos on Youtube of people playing with "burning lasers" (usually with some dangerously bright green, blue, or near-violet with a rating of 500mW and up).

I understand that laser modules, especially the affordable ones, have a certain amount of divergence that spreads the beam out over distances on the order of something like a millimeter per meter. This obviously decreases the intensity of the laser beam as it travels, causing the effective "burning" power to drop for distant targets.

How practical would it be to rig up multiple laser modules to focus onto arbitrary points at greater distances to make up for the lost power of individual beams? Say, instead of a single 1W beam you had an adjustable ring of 4 1W beams converging on the same point. Maybe with (bonus!) a laser range finder to measure the distance and feed it into a microcontroller that handles the focusing mechanism automatically. Not really worth it versus buying a bigger laser? Not going to give you much more power over the same distance? Would a set of adjustable lenses in front of several parallel modules work better?

Well, to fight the divergence you could use bigger optics.

Speaking of lasers, when I have time (won't be until the end of the year probably) I want to try measuring radiation reaction force upon a laser (using a torsion pendulum). Should be a bit easier than your usual radiation pressure experiment because I can completely box up the laser with it's battery (to delay any thermal effects) and shine it through a small glass port. I would run it using IR remote control or on a timer. I can also document the nonsense that happens without a box, or try various conventional devices that fuck up the readings (ultrasonic piezo for example).

 

[Dmytry]

Technarch[/url]":37r1rlbj]

Wheels Of Confusion[/url]":37r1rlbj]
Combat shmombat, I'm just thinking of those dinky .5-1.5W lasers that are actually (reasonably) affordable. I shudder to contemplate what would happen if you pointed any of this in the general direction of a person with working eyes, or even bounced it off a light-colored wall, without laser goggles. I'm more concerned with the idea of extending the "useful" range at which it could pop balloons or scorch cardboard.

IIRC the LaWS that is currently deployed on the USS Ponce is little more than six commercial welding lasers controlled to converge on a single point on a target at a given range. So it's certainly a feasible concept.

As for the eyes/goggles comment, that's why Wicked Lasers no longer sells to US customers.

You can just get the individual laser diodes. Regulations usually apply to consumer products (a laser with a battery compartment etc), not to individual electronics components (i.e. you can't sell a microwave oven that leaks microwaves, but you can sell a magnetron, even though you can mess things up with a magnetron pretty badly).

I myself would be very much in favour of better banning >5mw laser pointers (laser with optics that can focus it at near infinity, with a battery compartment), or maybe limit pointers at 1mw green and 5mw red. It is already prohibited to sell electronics that interferes with communications, and there's simply a regulatory loophole when it comes to ensuring that visible light sources interfere less with things like "communicating where the fuck is the landing field to pilot's eyes". The laser's power circuit already needs FCC conformity certification, if it got a switching regulator.

You'd still be able to buy the laser diodes, and lenses, and you can still put together what ever you want, but there won't be a hundred thousands idiots shining increasingly bright lasers at aircraft every year, because idiots can't put anything together.

 

[Dmytry]

Decoherent[/url]":zbt8v5rt]

Should be a bit easier than your usual radiation pressure experiment because I can completely box up the laser with it's battery (to delay any thermal effects) and shine it through a small glass port. I would run it using IR remote control or on a timer. I can also document the nonsense that happens without a box, or try various conventional devices that fuck up the readings (ultrasonic piezo for example).

I don't understand- how will the cat get in?!

The cat can rub on the outside of the outer box, electrostatics will be strong enough to mess up the readings...

 

[Dmytry]

Wheels Of Confusion[/url]":vtzv8ukj]

Dmytry[/url]":vtzv8ukj]

Technarch[/url]":vtzv8ukj]As for the eyes/goggles comment, that's why Wicked Lasers no longer sells to US customers.

You can just get the individual laser diodes. Regulations usually apply to consumer products (a laser with a battery compartment etc), not to individual electronics components (i.e. you can't sell a microwave oven that leaks microwaves, but you can sell a magnetron, even though you can mess things up with a magnetron pretty badly).

It's my understanding that the only real limiting regulation in effect for the US market is that the >5mw products can't be sold or referred to as a "pointer."

I thought they also had a bullshit "interlock" (with bypass instruction straight on the website).

IMO that really needs better enforcement. If it has a battery compartment, is some variety of hand-held-able, has beam spread <x, and power >y , or is designed to be very easily modifiable to such a form (e.g. 1W laser through a dark filter that reduces it to 5mW), as determined by a common idiot being able to modify it, ban it. As the power increases and cost decreases (resulting in an increasing number of increasingly powerful lasers in increasingly more idiotic hands), someone's going to actually cause an aircraft accident and there will be some very severe over-regulation afterwards, all that can be prevented by sensible regulation now, just applying the general principle of EMI compliance regulations to light with very low beam spread. There wouldn't be millions of those things if you couldn't buy them pre-made.

 

[Dmytry]

Well, for a graphene solar sail you'd need to emit protons to neutralize the charge, or electrons will start coming back. But maybe you would pick up those from the solar wind before the charge gets huge enough.

 

[Dmytry]

Well, picture that the machine is literally blind and flagging things completely at random. So the simulated explosives pass and shorts don't, simply because the shorts got unlucky.

Improve that a little bit to where it occasionally actually detects a firearm, and that's what you have for "security". It is still almost entirely random.

The issue is that there was no widespread efficacy testing when all that got adopted in the first place, so the efficacy was entirely unnecessary (and detrimental to profitability - you charge millions for a machine but it costs you less to make a non working machine than a working one).

Besides technology, you have the people manning the machines. And they get paid irrespective of whenever they're actually doing their job or not (which guarantees that they are not doing their job)

 

[Dmytry]

Keef[/url]":3krjxppm]Also more lasers, with bonus pseudo-holograms.

https://www.youtube.com/watch?t=18&v=GNoOiXkXmYQ

I wonder what are the power requirements though, or how much noise would it make if it's drawing a lot of points.

 

[Dmytry]

Keef[/url]":w9r2jv30]

Dmytry[/url]":w9r2jv30]

Keef[/url]":w9r2jv30]Also more lasers, with bonus pseudo-holograms.

https://www.youtube.com/watch?t=18&v=GNoOiXkXmYQ

I wonder what are the power requirements though, or how much noise would it make if it's drawing a lot of points.

I'm lost on how the hell its able to ignite one little point of air like it does. As far as I can tell its using just one IR beam.

It really is very simple... if you focus an IR laser to a small enough spot, the field will exceed the air electrical breakdown strength, and the air will arc over. A video.

 

[Dmytry]

It just takes so much more mass in capacitors to store the same energy than with pressurized gas or even a spring... that is as long as you're not using super-capacitors but those are expensive and don't discharge very quickly. edit: ahh wait they said they use stored kinetic energy, i.e. something like a flywheel.

 

[Dmytry]

I only trust a few kinds of results... Clear observations that don't really leave anything to chance (e.g. observing x-rays on a fluorescent screen, with the shadow of the bones of a hand, not observing variations in the speed of light in Michelson-Morley experiment, electrons diffracting after passing through a crystal, etc). Strong consistent results well above the error floor. Conclusions from a formally defined and internally consistent theory based on the previous two.

Physics is so successful because a tiniest deviation from known laws in any obscure experiment would be in contradiction with the rest of physics (which we, fortunately, got mostly right). In psychology almost any finding is an island upon itself. Unless contradicted by an exact replication (and sometimes even then), it's going to stick around.

 

[Dmytry]

The thing is, math is hard. In an university the folks that are good at math gravitate towards STEM and people who aren't gravitate towards other fields including psychology - ironically the very fields that naturally need the most mathematical rigour (due to small sample sizes).

The thing is when >50% of studies fail to replicate, it means one is better off assuming a null hypothesis even when there's some experiments disproving it. For example this popular result about faces being more attractive in groups. You're better off assuming that to be false, because it would probably fail to replicate without you doing something dodgy.

The methodology too often seem to be to make up a hypothesis then confirm it whenever the effect exists or not - it'd be interesting to compare the replication rate of psychological findings to the rate at which people predict psychological effects by mere speculation - it is possible that actual studies as performed add too little on top of original guesses to justify the expense. (Of course that also happens in physics, e.g. see EmDrive, but fortunately so far such things are an exception)

 

[Dmytry]

bluloo[/url]":3fqt76rm]

The thing is, math is hard. In an university the folks that are good at math gravitate towards STEM and people who aren't gravitate towards other fields including psychology - ironically the very fields that naturally need the most mathematical rigour (due to small sample sizes).

Art is hard. Curiously, many people can't draw a straight line, or a relatively accurate depiction of the simple human form. The folks that are bad art tend to gravitate toward the qualitative nature of STEM fields.
Why can't so many in the STEM fields do well in something as non-rigorous as art?

Conversely, you might ask why those most uncomfortable with uncertainty, seem to gravitate toward the relative "safety" of the discrete sciences (but you probably shouldn't).

Well the other thing is that the average IQ by major is something like 130+ for physics and <115 for psychology, and that's something which is pretty easy to measure rather than someone's personal bias (yes I am aware of the irony that I'm deferring to psychology here).

I'm actually quite dubious that psychology or similar majors (other than arts) would perform better at some arts task like drawing or painting than physicists - certainly a point in case that I'm not comfortable just believing something I'd be so uncertain in. (In children at least the complexity and quality of drawings correlates positively with IQ).

If I were to make a guess I would guess physicists would be better at drawing tasks, especially from memory or by imagination (drawing requires a lot of planning what goes in front of what and how lines connect, and is not a cognitively easy task).

Assigning value judgments like "math is hard" or "people who aren't good at math gravitate toward psychology - ironically the very fields that need the most mathematical rigour" demonstrates a fairly significant bias, and a rather poor understanding of human behavior and of the underlying science.

The general answer is that individuals vary in their aptitudes, skills and abilities and, optimally, gravitate towards the disciplines that best allow them to develop and express their resulting preferences in those fields.

The thing is when >50% of studies fail to replicate, it means one is better off assuming a null hypothesis even when there's some experiments disproving it. For example this popular result about faces being more attractive in groups. You're better off assuming that to be false, because it would probably fail to replicate without you doing something dodgy.

These are rather lazy assumptions. There shouldn't be the same kind of assumptions and expectations, WRT replication or otherwise, applied to behavioral studies as in physics, chemistry or math, for example.
As you note, there's a greater certainty in the observations found in physics experiments, so replication studies aren't often necessary.

And yet there's always replication studies in physics as it is a quantitative field where new experiments improve accuracy or are necessary for practical applications.

Because life itself, and behavior, involves multiple stochastic processes (which can't be experimentally controlled to the extent as in the discrete sciences, for example) there's not the same kind of certainty in single-study experimental results.

It necessitates wider support and acceptance of replication work.
It also demonstrates the greater number of comparative difficulties the behavioral scientists must deal with.

You shouldn't expect the same sort mathematical certainty in any one, or small number of, behavioral science experiment(s). Period.

Well, of course I don't expect the same sort of certainty - instead any time I see some publicized psychology finding in the news I just think, this effect is likely false or at best much weaker than what the findings were, and the supposed mechanism is very likely wrong. (Of course, I also think that about some physics findings, whenever in contradiction with established knowledge).

The methodology too often seem to be to make up a hypothesis then confirm it whenever the effect exists or not - it'd be interesting to compare the replication rate of psychological findings to the rate at which people predict psychological effects by mere speculation - it is possible that actual studies as performed add too little on top of original guesses to justify the expense. (Of course that also happens in physics, e.g. see EmDrive, but fortunately so far such things are an exception)

While I'm not the first to comment on this (At least one working Neuroscientist has commented similarly on your Obs posts, for example), this demonstrates a rather poor understanding of human behavior, as well as a strong personal bias against the related sciences.

While some criticism is certainly valid, you may need to take better care to differentiate between the weight of your personal biases, and valid scientific criticisms.

Well, all I am saying is that there seem to be no experiment that compares confirmation rate of hypotheses made up on spot (by people sufficiently motivated to guess right) to confirmation rate of some published results. If there is you're certainly free to show me wrong.