The first nuclear weapon test completely vaporized the 100 ft steel tower it was mounted on.
I’m not doubting that the shadows exist, I’ve seen them. But Dingbang’s question is a good one. If the body vaporized instantly, why is there a shadow at all? I see two possibilities, the body DIDN’T vaporize, but lasted long enough to cast a shadow. Or, the body vaporized and somehow the radiation from the bomb threw the vapor against the wall creating the shadow. The first seems more likely to me, but I’m just guessing.
Instantaneous heat, even very high heat, doesn’t imply vaporization. A meteor entering the earth’s atmosphere (nearly) instantaneously encounters temperatures of over 2000 C, which lasts for several seconds, but apart from a thin outer layer, the meteor is ice cold when and if it reaches the ground. Yes, meteors are more durable than human bodies, but the principle is the same.
–Mark
But in the Hiroshima bomb, the nuclear fireball didn’t reach the ground.
–Mark
What temperature existed at ground level?
According to the page that Machine Elf linked to earlier in this thread, it was 3000 - 4000 C directly below the blast, and 1800 C a kilometer away. That’s a far cry from the temperature within the fireball, which is approximately 10 million degrees.
–Mark
Googling about, I found that one of the shadows on steps was created where a body was burned.
Could the blast wave have thrown bodies against a wall where they were burned?
So we’ve established a fireball with the temperature of an acetylene torch. If you took a piece of flesh the size of the tip of such a torch what is the predicted outcome?
I don’t think the body is vaporized. But even if it were, the shadow area would be exposed to less energy than the rest of the concrete. The more-exposed concrete would bleach white, the less-exposed would be less bleached (or entirely unbleached, if you doubt that the body was vaporized). But in either case the shadow area would get less energy exposure, so it ought to appear differently.
Amusingly enough there is some recent tech that may help explain things and creating very fine patterns in metal using explosives. The “masking” methods allow for resolutions in the order of 2 digits in nanometers . The time frame is within a single explosive event. So the idea that you could “etch” shadows in tiny fractions of a second is far from inconceivable.
Many of the Boston marathon bombing victims lost legs. Although that damage was done by shrapnel, not blast pressure.
Yes you can, they have several such examples which have now been moved inside into the Hiroshima Peace Memorial Museum. If you are ever in Japan, I do highly recommend going to Hiroshima and seeing the dome, the peace park and the museum. It’s really a moving experience.
The shadows did have one interesting use - they were used by both Japanese scientific teams and American teams (after the surrender) to calculate the location and height of the hypocenter. Contrary to popular belief, the hypocenter was not over the ‘Atomic Dome’ building, but about a block away over the Shima Hospital.
There are pictures of the Hiroshima shadow effect all over the internet. Most of them involve objects rather than people. The most famous one involving a person was someone sitting on the steps of a bank waiting for it to open - this image is now preserved in the Peace Memorial Museum. A woman who was working inside the same bank actually survived and made it out of the firestorm that followed, due to the heavy concrete construction of the building.
Again, 3-4000 deg Centigrade is the temperature of an acetylene torch tip. So all then energy hitting a body would have that temperature.
A pyroclastic event from a volcano will have the following effect:
The first wave hit the nearby Herculaneum with temperatures as high as 500 degrees Celsius. The searing heat was enough to boil the brains and instantly vaporise the flesh of its victims so that only blackened skeletons remained.
That’s 1/6 the temperature of ground zero beneath the fireball and it’s not like the million degree temperature within fireball ceases at the edge.
Hm, that BBC claim doesn’t jive with information about cremation.
It says here that cremation occurs at 750 C to 1000 C, and it takes 1-3 hours to reduce a body to ashes.
This one says the temperature is 750 C to 900 C and it takes 2 - 2.5 hours.
This one says 1000 C to 1100 C and it takes 1.5 - 2 hours.
These are all funeral homes who perform cremation regularly, so I would assume they know what they’re talking about.
–Mark
Yeah, pretty much it does. And you can’t compare a volcanic pyroclastic flow because a heated fluid will expose objects to much more heat than an instantaneous thermal pulse.
Having said that, I’m taking a closer look at some of the shadows, and they seem to have 3 different forms:
1: Blurry black shadow: guy sitting on the steps It appears this person was instantly cooked from solid to vapor, and the organic material absorbed enough energy to prevent it from being completely burned off the concrete.
2: Sharp black shadow: shadow of water valve. Since the object casting the shadow is still intact and did not spatter, clearly it didn’t vaporize. The object was opaque to the radiation pulse, and the backdrop behind it bleached lighter (except for the shadow).
3: Negative shadow: Stalks of grass silhouetted on wood. Clearly the wood backdrop is charred, and this fragile stalk of grass absorbed enough energy to prevent its silhouette from being discolored any, if at all.
With the organics, we’ll never know how these subjects appeared before the blast wave. The man was probably a greasy spatter much like we see it now. The grass may have stood as a charred black stalk. But clearly, some things vaporize and some things don’t, and “vaporize” doesn’t exactly mean “turned into invisible steam.”
Why are you talking about temperatures far below that of ground zero? I’m missing something. If cremation occurs at or below 1000 deg C then 3 to 4 times that is a substantially greater amount of heat. And again, the fireball is substantially hotter than that. The intense heat of a hundred million degrees doesn’t end and suddenly reduce to 3,000 degrees.
I don’t understand your argument at all.
All the water in your body would vaporize, and that would blow every part of you that didn’t vaporize into smithereens.
The weapon detonated at 1,870 feet, the fireball is documented as being 1,200 feet wide, and at about 6000C degrees at its surface. So it makes sense for the air temperature at the hypocenter to be about 3000C. But that’s like a 3000C oven. But air transfers heat slowly, so that wouldn’t cause vaporization. The thermal effects are mainly going to come from the radiation pulse. That is significant, but the concept doesn’t transfer directly to the gas torches that you want to compare them to.
I’m addressing the BBC article you quoted that claimed instant vaporization at 500 C. That’s inconsistent with the known effects of cremation.
BTW, be careful of claiming one temperature is X times another. That only makes sense on an absolute scale like Kelvin. 3000 C is not 3 times 1000 C, it’s about 2.6x. Not a big difference at these temperatures, though.
–Mark