How to Spot a Psychopath

A reader writes:

Is there such a thing as food with less than no calories?

You're supposed to be able to eat lettuce or celery or something, and the energy your body uses to digest it is more than you get out of it.

(Well, I don't really know if you're "supposed" to be able to or not, but I've certainly heard people say this.)

What about eating ice? Obviously you get no nutrition at all from that, but I've never seen a Get Thin By Eating Snow diet book, so I figure it's not practical.

Nat

There are foodstuffs that have very little "food energy". They're pretty much what you'd expect, and do include a lot of green vegetables.

But digestion is good at sucking energy out of food. Your body does better than break even, even when you're eating celery. It's not easy to gain weight eating nothing but undressed salads and vitamin supplements, but it's possible.

The eating-ice thing, in contrast, sounds like a great idea. But only if you make a particular mistake, having to do with the term "calorie".

There are 540 calories in a Big Mac. But the enthalpy of fusion of water is about 80 calories per gram. And then you need another calorie to heat one gram of water by 1°C; if your ice starts out a few degrees below zero and ends up at body temperature, that adds up. And the only place this energy can come from is your body's own reserves.

So you can more than offset the entire nutritional value of your hamburger by crunching up one lousy ice cube! Right?

Sorry, no. Because the "physics" calorie, the one being used on the melting-ice side of the equation, is one thousandth of the "dietary" calorie, on the food side of the equation.

(This is noticeable when the dietary calorie is clearly indicated, as "kcal", for instance. The modern metric alternative to the two kinds of calorie is the joule and kilojoule; fortunately, there's no colloquial tendency to call both of these units "joules".)

A hundred grams of celery is about 14 kcal. To offset only that much energy value, you'd need to eat more than a hundred grams of ice. A whole tray of ice cubes would probably do it; the ice-cube trays in my fridge hold about 160 grams.

So as few as 35 trays of ice cubes might compensate for a Big Mac!

Presuming, of course, that you actually can Freeze Yourself Thin at all.

The human body runs warm as a matter of course. If the ambient temperature is below body temperature, which it is for most humans most of the time, then the body's leaking heat all the time anyway, and eating cold stuff may change where the heat goes, more than it changes how much heat is lost.

This page at livestrong.com gives a ballpark figure of only one dietary calorie burned per ounce of ice eaten. 80 small calories of enthalpy of fusion per gram of ice, plus 40 small calories of heat to take the water from a bit below freezing to body temperature, times about 28 grams to the ounce, gives 3360 small calories or 3.36 dietary ones of raw heating power. If that only adds up to one extra dietary calorie burned, the tooth wear and ice-cream headaches don't seem like much of a trade-off. Especially since you don't actually get any ice-cream.

(If you really apply yourself to slimming via low temperatures, I would not put it past your body to decide that all this shivering indicates you're now living in a cold climate, so more incoming food should be directed towards creating a nice insulating layer of fat.)

Your natural basal metabolic rate is probably closer to 2000 kcal per day than it is to 1000. Adding a couple of dozen kilocalories to that by ice-eating may actually hurt more than doing an energy-equivalent amount of exercise.

(Exercise is not really a great way of burning calories. Run ten kilometres, burn 700 kcal. As a general rule, if you're not some sort of athlete or heavy manual labourer, exercise will make you fitter and stronger, but not thinner.)

Needless to say, Wikipedia has a page about negative-calorie food. And a funnier one about the "Negative Calorie Illusion".

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:

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.