The flash from a hydrogen bomb works pretty well

A reader writes:

Why can't you see the bones in your finger/hand when you shine a bright light through it? Veins show up well, but bones are practically invisible. Are live bones as see-through as live flesh?


Bones, alive or dead, are pretty much opaque to visible light. If your flesh were for some reason perfectly transparent but your bones stayed as they are, you'd be a lovely Ray Harryhausen walking skeleton. (Or, more accurately, a Fritz Leiber ghoul.)

Your flesh isn't transparent, though; it's translucent, and diffuses light that enters it. So instead of your hand-bones being as visible as a fish in an aquarium, they're as invisible as a fish that is for some reason attempting to survive in a tank full of milk.

If that fish in its milk-tank comes close to the side of the tank, you'll be able to see it, just as you can see the little dark veins that're close to the surface on the palm side of your fingers when you shine a flashlight through your hand. Just the few millimetres of flesh on either side of the bones, though, diffuses the light so much that it's hard to tell that there's a bone there at all.

Psycho Science, as I have brilliantly decided to call it, is a new 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.

2 Responses to “The flash from a hydrogen bomb works pretty well”

  1. Malcolm Says:

    If your light source is bright enough (see post title) and/or your sensor is sensitive enough, you can see the bones in your hand using (near) visible light.

    The trick is to only look at the photons that come through first by the direct, non-scattered path:

    • Anne Says:

      Actually, what you need is a flash that increases in brightness sharply enough. If it's very bright but gets there gradually, you won't be able to tell which photons are direct and which are delayed from an earlier time. In the interest of retaining the flesh on your bones, you probably want a flash that is very short, so that you can have both a high peak brightness (so your sensor has some unscattered photons to work with) and a fast rise time but a modest total energy (since much of that will go into heating your flesh). The flash from a hydrogen bomb is actually a double flash: an initial pulse of around a millisecond, coming from a (tiny but extremely hot) fireball caused by direct X-ray heating of the air, then a darkening as the very dense but cooler shock wave hides the fireball, then a much longer (~second) pulse as the shock wave expands and the hot shocked region grows. Since in air a nanosecond is about 30 cm, you need pulses with rise times less than a nanosecond, and I'm pretty sure a hydrogen bomb doesn't provide that; if nothing else in the Teller-Ulam design the X-rays have time to thermalize in the hohlraum, which is on that size scale. So: picosecond laser pulses are the way to go. Or, conceivably, terahertz-modulated continuous-wave lasers.

Leave a Reply