How to Spot a Psychopath

A reader writes:

What are those little LED-like, but flickery, orange lights, seen in nightlights, electric-blanket power lights, etc? I've seen them in antique radios and as indicator lights in other ancient gear, so I presume they're not actually LEDs.

Minnie

They're neon bulbs. One giveaway is the colour; a plain neon tube, just low-pressure neon in a glass envelope, glows naturally with that orange-red colour when you put enough volts across it.

("Neon lights" that aren't orange-red may still contain neon, but have a phosphor coating on the inside of the glass that turns the light another colour. White fluorescent lights are all actually mercury-vapour tubes with a phosphor coating. The amount of mercury in even a large fluorescent lamp is very small.)

For a large neon tube, the voltage from end to end has to be up in the kilovolts. But if you make a little teeny neon bulb with electrodes only a few millimetres apart, you only need a bit more than a hundred volts to get it to glow.

This makes teeny neon bulbs a natural fit for indicator-light duty in countries with 115V-ish mains power. You still need to use a current-limiting resistor in series to discourage the lamp from zipping up past the C on this graph and burning up, but that's all you need. In countries with 230V-ish mains, you just need a larger resistor value.

If you run a neon lamp directly from 50 or 60Hz AC mains power like this, the bulb flickers at twice the mains frequency, because the two electrodes light up in turn, but only when the mains waveform is giving the bulb enough voltage to light. (From DC, the lamp won't flicker, but only one electrode will light up.) The older the lamp, the more flickery it will become, until eventually it doesn't light up at all. Little neon lamps ought to last 20,000 hours or more, but many modern ones seem to be of lousier quality.

(Incandescent bulbs don't visibly flicker when run from AC, because a tungsten filament has enough thermal inertia to keep glowing at very close to full brightness even when the mains waveform is crossing the zero-volts mark. A fluorescent tube driven almost-as-directly as a neon bulb from mains power will also flicker, which a lot of people hate. Modern high-frequency electronic ballasts solve this problem, for fluorescent tubes and compact-fluorescent lamps.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

When I was visiting my mother the other day, I dropped her glass casserole baking dish... thing... (I'm not much of a cook), and it broke, and so of course I said I'd get her a new one. The old one was "Pyrex" brand, but she told me I should just buy whatever similar sized glass dish is cheapest, because, and I quote "Pyrex isn't made from Pyrex any more".

The philosophical implications of that statement aside, were Pyrex products made from special glass, and now they're not? All I know about Pyrex is that I've seen that word written on laboratory glassware.

Harry

In the olden days, the "Pyrex" brand, wherever you saw it, meant borosilicate glass. Borosilicate glass doesn't change size much in response to temperature (it has a low "coefficient of thermal expansion"), so if you heat or cool it suddenly, it's unlikely to shatter.

("Pyrex" wasn't actually the first borosilicate glass; Otto Schott invented it, and the Schott company still sells it under the "Duran" brand. But Pyrex became the genericised trademark for borosilicate glass. Lab glassware that's intended to be used on heat is pretty much all borosilicate, under one name or another.)

Ordinary "soda-lime" glass expands and contracts more with temperature. So if, for instance, you suddenly cool a hot plain-glass baking dish by putting it the sink and turning on the tap, the inside surface of the dish contracts as it cools, the outside surface stays expanded, and stress between the two encourages the glass to break.

This can also happen when a glass object is originally manufactured. After forming the object, if you don't "anneal" the glass by slowly cooling it (a special kiln for doing this to glass that's been made somewhere else is called a lehr), a brand-new glass object can break spontaneously as it cools, or be right on the edge of breaking from the slightest shock.

There are numerous tricky ways to make glass objects more sturdy, the most common of which takes advantage of soda-lime glass's thermal expansion and contraction, to "temper", or "toughen", the glass and force the outside of the glass object to be under great compressive stress, which glass tolerates very well.

The simplest way of tempering glass is by rapidly cooling the outside of molten glass, so it solidifies and contracts quickly, and is then pulled into compression when the core of the glass cools later. Now, any insult suffered by the object will have to overcome the compression built into the outer layers before it can get the glass into tension and get a crack going. And if a crack does start, the whole glass object will collapse into zillions of distinctive little lumps of glass with quite safe large-angled edges, rather than dagger-like shards.

The forces involved in tempering glass are the same as the forces that make unevenly-cooled, unannealed glassware fragile; they're just tightly marshalled to make the material more durable, in the same way that prestressing "tendons" can make concrete far stronger.

(The most extreme version of the tempering process is Prince Rupert's Drops...

...which you can make at home, while wearing suitable protective clothing, by dripping molten glass into a bucket of water. Internal tensions make the body of each drop amazingly strong, but if you snap the thread-like tail - which is also very strong, but so thin that it can easily be bent or sheared past its limits - the whole drop instantly explodes into tiny particles.)

(Oh, and again, if you'd like to have the above explained much more clearly, try J.E. Gordon's classic "The New Science of Strong Materials, or Why You Don't Fall through the Floor", which is one of my favourite books, along with "Structures, Or Why Things Don't Fall Down".)

A fancier kind of tempered glass is "Corelle", which is laminated tempered glass, but doesn't look or feel much like glass at all. This is partly because it's opaque (though I don't think there's anything about the manufacturing process that says it has to be), and partly because it's so strong that plates and bowls made from the stuff can be very thin and lightweight.

Which brings us back to Pyrex, because the Pyrex and Corelle brands are now both held by World Kitchen, LLC. World Kitchen would really like people to stop saying that Pyrex kitchenware isn't made from borosilicate glass any more, because although this statement is actually correct, it wasn't World Kitchen that changed it. World Kitchen say the change happened "more than 60 years" ago; other sources can't put an exact figure on it, but it seems pretty clear that it's not a recent development.

In any case, what World Kitchen sell today as "Pyrex" bakeware isn't plain soda-lime glass, but "heat strengthened" soda-lime, which presumably means the usual kind of tempered glass. Tempered glass resists breaking from temperature changes pretty well, and resists breaking from mechanical insults very well, so it's a good choice for bakeware, which is bumped by other bakeware much more often than it has to tolerate large temperature shocks.

Well, it's a good choice for bakeware as long as your oven doesn't get hot enough to anneal the glass, which I think it definitely doesn't.

This is despite the additives in soda-lime glass, which are there to make the stuff melt at a reasonable temperature. Silica, also known as quartz, makes up the bulk of all normal glass compositions, and could be used to do anything ordinary glass does. But quartz's melting point is way up around 1700 degrees Centigrade. This is higher than the melting point of iron, and makes quartz unreasonably difficult to use for glassware, unless you're making furnace windows or something.

To make soda-lime glass from scratch you need a furnace that burns hot enough to melt silica - which is why recycling glass is so popular - but once the ingredients are mixed, the melting point of the mixed material plummets to less than 600°C.

Annealing happens significantly below the melting point, but you still need a temperature of more than 500°C to anneal soda-lime glass, even if you're willing to wait for hours, and no household oven goes that high. Actually, I don't think any food oven goes that high. The hottest are probably coal-fired pizza ovens (the great problem of making "authentic" pizza at home is getting the oven hot enough); I think those top out at around the 1000°F/540°C mark, but they usually run rather cooler.

I'm sure there are many companies that make tempered, or toughened, glass kitchenware, and I'm also sure that other companies again make plain soda-glass kitchenware, which may not even be properly annealed, much less properly tempered. So your mum may be right that Pyrex-brand glassware is not particularly good - but you also shouldn't buy the cheapest glass casserole dish you can find, unless you've good reason to believe it's made from tempered glass. Which may or may not be clearly, or honestly, indicated on the box.

I think the best way to authoritatively tell the difference is by bopping any dish you're planning to buy with a ball-peen hammer. I leave the formulation of techniques by which one could get away with this as an exercise for the reader.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

I know that when you look up at a clear sky, the dark things you see floating around inside your eyeballs are called... "floaters". Someone worked hard on that name, huh.

But what are the much smaller pale scooty things? You know what I'm talking about, right? I'm not the only one who sees them, am I? Are they bacteria or something? Oh god, they're bacteria, aren't they?

Presuming I'm not about to die of pale-scooty-eye-thing-itis, why do I only see these things when I'm looking at the sky?

Noel

The pale scooty things are white blood cells.

The blood vessels that feed your retina are located, thanks either to the blind forces of evolution or to the carelessness of a really incompetent intelligent designer, on top of the retina, so light has to pass through the blood vessels before it can get to the retina, and the blood vessels can cast shadows on the retina.

A really big red blood cell has about the same diameter as a really small white blood cell, and white cells are roughly spherical blobs instead of the doughnut-ish shape of the red cells. The result of this is that red cells zipping through the blood vessels over your retina are invisible, but the much less numerous white cells do show up, as little pale scooty things.

(Because floaters really are floating in the goop inside your eye, they move around even when you don't move your eyes. Blood cells are - with any luck - constrained to the vessels over your retina, so the paths of the little scooty things track precisely with your eyes, no matter where you look.)

There are two reasons why you see these things when you're looking at a blue sky, or daytime fog, or a white area on an over-bright computer monitor, for that matter.

The minor reason is that floater-shadows on your retina are pretty low in contrast, and white blood cell shadows are even lower, so they're hard to see if you're looking at something rich in detail. For the same reason, it's hard to notice minor dirt-spots on a computer monitor unless the image being displayed is pretty uniform.

The major reason why floaters and zippy leucocytes show up when you look at the daytime sky, though, is that the sky is bright.

Update: As Bernard points out below, the explanation I originally had here was wrong.

Bright light causes your pupils to contract, and contracted pupils give the eye a higher f-number, and a deeper depth of field. Floaters and blood cells are far from the eye's focal distance no matter what you're focussing on, but with a smaller aperture, they become sharp enough to be noticeable, against a uniform background.

The contracted pupil, as Bernard says, is closer to a point source of light inside the eye, and casts sharper shadows of whatever's in there onto the retina.

Many photographers are familiar with this effect. There can be all sorts of dust and crud on and even in a lens, and dust on the sensor too if you've got an interchangeable-lens camera, without any obvious problems for large-aperture pictures. Faint fuzzy circles may be visible if you look really closely, especially, again, in areas of uniform colour, but even things that you'd think would be totally obvious, like raindrops on the lens, can have surprisingly little effect on a large-aperture photo.

Stop your lens down, though, and the crud-shadows will be much closer to sharply focussed, and much easier to see and obsess over.

A reader writes:

I'm getting older, which is better than the only alternative, but reading small print started to get difficult, so I bought reading glasses on eBay for $3 delivered and... problem solved!

Except now I think I may be slowly blinding myself by using $3 glasses. Especially after what you said the other day about eye damage often not being noticeable until it's really bad.

Are cheap reading glasses dangerous?

Andre

You're not blinding yourself. Cheap reading glasses are a perfectly acceptable treatment for hyperopia (longsightedness).

You won't be able to focus far away while wearing even weak reading glasses (for the same reason that adding filter-thread magnifiers or extension tubes to camera lenses prevents infinity focus), but the only danger this poses is if you decide to go driving with the reading glasses still on.

It's actually pretty much impossible to damage your eyes by wearing the wrong glasses, although you certainly can give yourself a headache. There are all sorts of folk legends about how you can damage your eyesight by sitting to close to the TV or cure your myopia by doing eye exercises or massaging your eyeballs, possibly with some gadget or other, but it's all claptrap.

(It'd be nice if you could focus close and then far away and then close and then far away at some sort of eye gym and thereby cure the optical shortcomings of your particular set of eyeballs, but there's no good evidence to suggest that this is possible. Fortunately, spectacles and contact lenses are now very mature technology, and the various forms of refractive surgery are getting better and better.)

In the olden days, mail-order spectacles were exceedingly likely to be a scam, on account of how the notion of an eyeglass prescription didn't yet exist, so it was impossible for even an honest mail-order glasses dealer to actually know what glasses you needed. This didn't, of course, stop mail-order outfits from making the usual pre-consumer-protection outrageous claims about their wonderful products, and separating countless suckers from their money.

A significant portion of the mail-order hucksters' business, though, was simple mild-magnification reading glasses optically much the same as the ones you bought on eBay, As long as the people who bought those glasses really were longsighted, many of them were probably perfectly happy with their purchase (although it's likely that they were still paying more than they needed to).

Should your need to see stuff close up move beyond "reading books" and into "working with small objects, and wanting to look as much as possible like a mad scientist while I do it", allow me to recommend the Donegan Optical Optivisor. The Optivisor works very well (it's comfortable, you can easily flip it up when you don't need it, and interchangeable lenses are available for different magnifications), it looks pretty hilarious, and it isn't very expensive.

A reader writes:

I wash my hands after going to the bathroom. I do, honest! But... maybe if I've only had a wee, I might just sort of... splash them a bit.

I know I'm being disgusting. How disgusting am I being?

Patrick

Washing your hands without soap has almost no impact on the amount of bacteria on your skin. The only reason to do it is if all you want to clean off your hands is something, like, I don't know, sand or poster paint or something, that plain water easily removes.

But if your hands are covered with, for instance, garden soil, you may be able to get them apparently clean with plain water, but plenty of bacteria from the soil will still be there.

(UPDATE: It seems that it's a bit more complicated than that. Some researchers have found that you actually can wash your hands effectively without soap! You need to rub your hands together "purposefully" for at least 20 seconds under running water, though.)

Holding, not to put too fine a point on it, your penis while you urinate, probably will make your hand (or hands; I'm making no assumptions about your technique or dimensions) significantly more bacteria-laden. And the bacteria you pick up there can be nasty ones. Coliform bacteria, including ones that can cause an unpleasant stomach upset at the very least, are all over normal human skin in the approximate area that boxer shorts cover. You can't get rid of the buggers completely without bathing in antiseptic and scrubbing yourself with a wire brush.

(This is why no amount of bathing will prevent your armpits getting smelly when you start sweating again. The smell is the metabolic products of bacteria that thrive in sweat, and those bacteria live in the pores of your skin and can't all be killed without killing, or physically removing, the skin as well.)

Washing your hands with ordinary soap does, fortunately, get rid of coliforms on the surface of the skin, which is where they'll be if you've just been handing your privates. The soap doesn't kill the bacteria, but it gets rid of the oil on the surface of the skin, and washes most of the surface bacteria away with it.

(Hand sanitiser is usually based on alcohol, which also cuts the oil on your skin and actually does kill bacteria quite effectively. Washing with soap gives you live bacteria going down the plughole; hand sanitiser without washing gives you dead bacteria still sitting on your skin.)

And yet, persons in a normal state of health who don't wash their hands at all after going to the toilet will, demonstrably, not cause themselves, and everyone else they touch, to constantly get gastroenteritis. This is because bacterial transfer and growth is a statistical sort of thing.

Harmful strains of bacteria, and viruses for that matter, only become a problem when they get into your body, and can multiply faster than your immune system can get rid of them.

Let's say you've got a normal immune system, and you go to the bathroom, wash your hands in a perfunctory manner with no soap, and later on decide to eat some chips or perform some other activity that transfers bacteria from your hands to the upper portion of your gut.

You'll probably be fine, just as you will probably also get away with driving while mildly-illegally drunk.

But doing this buys you quite a lot of tickets in the Pathogen-Disaster Lottery. If you get a big enough dose of bad enough germs into yourself, your immune system won't be able to react and shut them down before they've multiplied into too large a population to stop, and then you'll be in trouble.

Which, again to not be over-dramatic, probably won't be the kind of trouble that kills you. But may be the kind that initially makes you afraid that you will die, and later on makes you afraid that you won't.

(Going around covered with nasty microorganisms also makes you a significant hazard for people with lousy immune systems - the very young, the very old, and the otherwise infirm. You don't even need to touch them; every time you leave a germy handprint on some non-antimicrobial surface, it'll wait there for quite some time to give the microscopic gift that keeps on giving to someone else.)

Any kind of hand-washing with soap will reduce the number of tickets you buy in the lottery you don't want to win, and washing your hands thoroughly with soap makes the risk essentially zero. (To do it properly you're meant to take at least 20 seconds, which can seem a rather long time while you're staring at yourself in the bathroom mirror.)

It's not just bacteria from your own body you have to worry about, of course. There are also pets, and rubbish bins, and all of those surfaces you have to touch any time you leave the house, and other people, and of course also other people's sticky, shrieking, waste-encrusted offspring.

My partner, a while ago, got really horrible gastroenteritis, the kind that sees you in hospital being intravenously hydrated on more than one occasion. I managed to get through the experience without getting the bug myself, and I didn't wall myself up in the attic and only touch her with robotic waldoes to achieve this. You'd better believe I washed my hands often, though.

Ever since, I wash my hands properly whenever I come home, and whenever I've handled anything that could plausibly be well-loaded with bacteria and/or viruses. And I've not had any tummy bugs since - though I didn't get them frequently enough beforehand for this to have generated any statistically significant data.

You don't need to go completely Howard Hughes about all this, but you also don't need to work in a hospital for a greater than zero level of germ-consciousness to be worthwhile.

Note that unless you've got a bladder infection or something, urine itself is very close to sterile (not quite fully sterile, because even a healthy urethra can contribute a few bacteria to it). Nice and warm, too.

So if you just put a soap dish on top of the toilet, you could probably get the whole job done in one operation.

(The non-comedy version of this is the cistern-top sink, available in relatively modest and also huge expensive designer versions.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

A thought struck me while driving home one night: If relativity means the speed of light is absolute, how is it possible for there to be a Doppler shift of light?

As I understand it, Doppler occurs when a wave source is moving and the peaks/valleys of the wave get scrunched up/stretched out.

The theory of relativity states that light shining from a moving vehicle is NOT traveling c (light speed) plus the speed of the vehicle, because time slows down relative to the stationary observer.

If all the crests of the wave are traveling at c and Relativity implies that the point source can't go any faster than c, then it would seem there's no way for there to be any shortening of the frequency.

How does relativistic time dilation not cancel out the Doppler effect much like the added speed of a vehicle is canceled out?

Add in the wibbly-wobbly-timey-wimey grey area of light being both a particle AND a wave at the same time and my brain is hurting me for trying to visualize how the Doppler shift works for light.

Chris

You are, and this is not something that's often said to people coming to grips with Einstein's theories, overthinking this.

Yes, as special relativity says and as everybody who talked to Einstein about it firmly understood until the concept slithered out of their brain about ten minutes after the end of the conversation (relativity is even worse than tax brackets in this regard), the speed of light is indeed a universal constant. No matter how fast the observer, or the source of the light, are moving relative to each other or relative to anything else, everybody always sees the speed of light in a vacuum as the same 299,792,458 metres per second.

(Things get a little more complicated when the light is moving in a medium other than vacuum, but our universe, at least, is conveniently largely made of vacuum. This is a useful thing to remember if someone attempts to persuade you that the universe has been fine-tuned just for us; if this were actually the case, 99.9999-and-several-more-nines-per-cent of the universe might fairly be expected to not be instantly lethal to humans... but it is. Oh, and just to make things a little more confusing again, Einstein also came up with a theory of general relativity, which has to do with gravity and is different from special relativity.)

So, as you say, light doesn't go past you any faster if the light source is coming at you, or any slower if the light source is moving away.

But when the source of a sound is coming at you, the sound doesn't pass you any faster, either.

The speed of sound is much less constant than the speed of light. Sound travels faster the "stiffer" the material it's travelling through is, so it's zero in a vacuum, around 343 metres per second in dry air at sea level, but about 1500m/s in water. Unlike the speed of light, it is of course possible for things to travel faster than the speed of sound, especially in air. But even when a sound-emitting thing, like a jet fighter, is travelling faster than sound, the sound it emits still travels at whatever the speed of sound in that part of the atmosphere is.

(This is why you don't hear a supersonic plane, or a supersonic bullet, coming...

...until it's already gone past you. In the case of a bullet, the noise it makes is pretty much entirely the "sonic boom" created by pushing air out of the way faster than sound. The shock wave around a supersonic aircraft, bullet or explosion can travel faster than sound, but the shock wave slows as it spreads out, and soon becomes a regular sound wave.)

But, as you say, the Doppler effect clearly changes the pitch of sound made by an approaching, departing or...

...passing sound source.

The reason for this is that when a sound source is approaching you, each new oscillation of whatever sound it's making is emitted when the source is a bit closer to you than the last, which puts the compressions and rarefactions of the sound waves closer together. This is, from your point of view, exactly the same as if you were listening to a stationary sound source making a higher-pitched sound. And if the sound source is moving away, the opposite happens.

Light is, once again, a somewhat more squirrelly concept, because as you say, photons have characteristics of both particles and waves. In this case the analogy still works fine, though; once again, the source of each new particle-photon or wave-photon is closer to you, or further away from you, when each new photon is emitted, creating the same effect you'd see if the light were coming from a stationary source with a higher or lower frequency, respectively.

It's often misleading to apply observations in the everyday world of modest velocities, masses and timescales to the much greater velocities, far larger masses, and/or much longer timescales which cause Newtonian physics calculations to give you clearly wrong answers, so that Einstein's refinements become necessary. In this case, the trap lurking in the speed-of-sound to speed-of-light analogy is that if you move towards a sound source, the speed at which the sound waves pass you, in your frame of reference, really will increase.

Sound waves can also pass you faster, or slower, than the speed of sound in a given medium if that medium (air, for instance) is itself moving from your point of view (because you're standing still and the wind is blowing, for instance). If you and the sound source are both stationary and a steady wind is blowing from the source to you, you'll encounter the peculiar situation in which the sound waves are passing you faster than sound, but the pitch is staying the same!

If you assume a stationary listener, no wind and perfectly spherical and inelastic cows, though, the light-to-sound analogy works.

Time dilation is irrelevant, here. If you're in a spaceship with red headlights and you're travelling at close to the speed of light, time will pass slower for you, from the point of view of a stationary observer, and your headlights will look blue, to a stationary observer in front of you. But the time-dilation affects everything on and within your spaceship, including you, your headlights and the tiny 32,768Hz quartz tuning-fork resonator...

(Source.)

...in your wristwatch. So from your point of view, your wristwatch still counts one second per second, and your headlights are still red. (But the universe in front of you will look bluer, and the universe behind redder. The sound analogy works here, too; if you're in a car driving past a stationary car that's beeping its horn, the horn will sound higher as you approach and lower after you pass by.)

But if you assume a stationary listener, the speed-of-sound to speed-of-light analogy works OK. The sound, or light, passes you at the same speed no matter how fast the source is travelling, but the sound, or light, waves arrive closer together when the source is approaching, and further apart when it's departing.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.