Hacker News Reader

Comment by antognini | Hacker News Reader

In one of my interstellar medium classes I remember learning about the physicist Geoffrey Taylor's estimate of the yield of the first atomic bomb. At the time, the energy of the atomic bomb was classified information, but photographs of the explosion like this one [1] had been published in newspapers and magazines. Crucially, this photograph was labelled with both the time after the explosion, and a scale bar. With just this information Taylor found it was fairly simple to calculate the energy of the explosion. He ended up publishing two papers about it [2] [3]. In astrophysics, his calculations are now used when modeling the effect of a supernova on the surrounding interstellar medium.

[1]: https://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Tr...

[2]: http://rspa.royalsocietypublishing.org/content/201/1065/159

[3]: http://rspa.royalsocietypublishing.org/content/201/1065/175

View on HN

Those WW2 era photos are interesting, and I like the story about Taylor's analysis, but what really spooks me from early atomic bomb tests are the Rapatronic photos by Edgerton.

He took high-speed photography to the ultimate limits, at exposure times of 10^-8 seconds, and the pictures are absolutely eerie looking. Some are like gaping skulls of pure energy, like this one:

https://upload.wikimedia.org/wikipedia/commons/e/e9/Tumbler_...

http://petapixel.com/2014/03/05/rapatronic-camera-atomic-bla...

I didn't know Edgerton name, nor how many things he shot at the time. https://www.youtube.com/watch?v=gspK_Bi0aoQ

From the article: "This is 1/100,000,000th of a second after the first photo."

A 100 millionth of a light-second is about 10 feet, the tower was 100 feet. So that couldn't have been the time between exposures, and they used multiple cameras anyway.

The Wikipedia article https://en.wikipedia.org/wiki/Rapatronic_camera says the exposure times were several microseconds.

I don't think that's the first image in the sequence, just the most famous one. They took a lot of images in sequence. Here they are edited together into a sequence (several series, presumably from multiple tests, unfortunately looks a bit incomplete): https://m.youtube.com/watch?v=KQp1ox-SdRI

I gather that some of the lumpiness is caused by imperfections in the strength and time synchronization of the implosion. Ideally, you'd see spheres. There are also bumps caused by flanges, ports, etc in the casing.

Thank you. I had known about Taylor's work from a course on scaling methods in continuum mechanics (it is also one of the introductory examples in Barenblatt's very nice book Scaling), but did not know that it has other applications.

Barenblatt looks like something I need right now -- just put it on my library list for tomorrow. Thanks!

I don't know why (perhaps the other-worldly look of the explosion at such a small amount of time after detonation), but this picture and the picture of the Howitzer delivered mushroom cloud, has always filled me with absolute dread and horror. I think for different reasons.

The former just looks so ... weird, and scary, and like anyone witnessing it would know that's the last thing they'll see. The latter because of the implications of what we have the power to do, and probably won't be able to resist actually doing.

So far, so good.

I can't figure out if that is awesome or absolutely terrifying... Imagine what is the equivalent today.

Reply on news.ycombinator.com