Leo Szilard: The Genius Behind the Bomb
. Source. 1992. TODO an external link to the production? Producers credited at end: Helen Weiss and Alain Jehlen. As indicated at: archive.org/details/TheGeniusBehindtheBomb it was apparently produced by WGBH, public radio station from Boston.He was a leading figure at the MIT Radiation Laboratory, and later he was head at the Columbia University laboratory that carried out the crucial Lamb-Retherford experiment and the anomalous magnetic dipole moment of the electron published at The Magnetic Moment of the Electron by Kusch and Foley (1948) using related techniques.
This is a good book. It is rather short, very direct, which is a good thing. At some points it is slightly too direct, but to a large extent it gets it right.
The main goal of the book is to basically to build the Standard Model Lagrangian from only initial symmetry considerations, notably the Poincaré group + internal symmetries.
The book doesn't really show how to extract numbers from that Lagrangian, but perhaps that can be pardoned, do one thing and do it well.
Richard Feynman's mentor at Princeton University, and notable contributor to his development of quantum electrodynamics.
Worked with Niels Bohr at one point.
Web of Stories interview (1996): www.youtube.com/playlist?list=PLVV0r6CmEsFzVlqiUh95Q881umWUPjQbB. He's a bit slow, you wonder if he's going to continute or not! One wonders if it is because of age, or he's always been like that.
Lillian Hoddeson talking about Bardeen
. Source. From Video "The Story of John Bardeen at the University of Illinois (2010)". She's actually good looking!The bald confident chilled out particle physics guy from Stanford University!
Also one can't stop thinking abot Leonard Hofstadter from The Big Bang Theory upoen hearing his name.
Leonard Susskind lecturing in 2013
. Source. Like all big names in science, she was at the right place at the right time and with the right interest and passion.
Notably, the man she married, Pierre Curie, happened to be a the world master at precisely the technique that she needed to carefully measure radioactivity: he had the most precise electrometers in the world, which allowed to detect small amounts of radioactivity via the ionization of air by radiation . These used piezoelectricity, which Pierre Curie co-discovered with his brother.
Marie Curie c. 1920
. Source. An ELF file contains the following parts:
- ELF header. Points to the position of the section header table and the program header table.
- Section header table (optional on executable). Each has
e_shnumsection headers, each pointing to the position of a section. - N sections, with
N <= e_shnum(optional on executable) - Program header table (only on executable). Each has
e_phnumprogram headers, each pointing to the position of a segment. - N segments, with
N <= e_phnum(only on executable)
The order of those parts is not fixed: the only fixed thing is the ELF header that must be the first thing on the file: Generic docs say:
In pictures: sample object file with three sections:
+-------------------+
| ELF header |---+
+---------> +-------------------+ | e_shoff
| | |<--+
| Section | Section header 0 |
| | |---+ sh_offset
| Header +-------------------+ |
| | Section header 1 |---|--+ sh_offset
| Table +-------------------+ | |
| | Section header 2 |---|--|--+
+---------> +-------------------+ | | |
| Section 0 |<--+ | |
+-------------------+ | | sh_offset
| Section 1 |<-----+ |
+-------------------+ |
| Section 2 |<--------+
+-------------------+But nothing (except sanity) prevents the following topology:
+-------------------+
| ELF header |---+ e_shoff
+-------------------+ |
| Section 1 |<--|--+
+---------> +-------------------+ | |
| | |<--+ | sh_offset
| Section | Section header 0 | |
| | |------|---------+
| Header +-------------------+ | |
| | Section header 1 |------+ |
| Table +-------------------+ |
| | Section header 2 |---+ | sh_offset
+---------> +-------------------+ | sh_offset |
| Section 2 |<--+ |
+-------------------+ |
| Section 0 |<---------------+
+-------------------+But some newbies may prefer PNGs :-)
Web of Stories 1997 interview playlist: www.youtube.com/playlist?list=PLVV0r6CmEsFxKFx-0lsQDs6oLP3SZ9BlA
The way this dude speaks. He exhales incredible intelligence!!!
In the interviews you can see that he pronounces names in all languages amazingly, making acute effort to do so, to the point of being notable. His passion for linguistics is actually mentioned on Genius: Richard Feynman and Modern Physics by James Gleick (1994).
Maybe this obsession is partly due to his name which no English speaking person knows how to pronounce from the writing.
This passion also led in part for his names to some physics terminology he worked on winning out over alternatives by his collaborators, most notably in the case of the naming of the quark.
Running:outputs:
readelf -h hello_world.oMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 64 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 7
Section header string table index: 3Running:outputs:
readelf -h hello_world.outMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x4000b0
Start of program headers: 64 (bytes into file)
Start of section headers: 272 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 2
Size of section headers: 64 (bytes)
Number of section headers: 6
Section header string table index: 3Bytes in the object file:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 01 00 3e 00 01 00 00 00 00 00 00 00 00 00 00 00 |..>.............|
00000020 00 00 00 00 00 00 00 00 40 00 00 00 00 00 00 00 |........@.......|
00000030 00 00 00 00 40 00 00 00 00 00 40 00 07 00 03 00 |....@.....@.....|Executable:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 02 00 3e 00 01 00 00 00 b0 00 40 00 00 00 00 00 |..>.......@.....|
00000020 40 00 00 00 00 00 00 00 10 01 00 00 00 00 00 00 |@...............|
00000030 00 00 00 00 40 00 38 00 02 00 40 00 06 00 03 00 |....@.8...@.....|Structure represented:
# define EI_NIDENT 16
typedef struct {
unsigned char e_ident[EI_NIDENT];
Elf64_Half e_type;
Elf64_Half e_machine;
Elf64_Word e_version;
Elf64_Addr e_entry;
Elf64_Off e_phoff;
Elf64_Off e_shoff;
Elf64_Word e_flags;
Elf64_Half e_ehsize;
Elf64_Half e_phentsize;
Elf64_Half e_phnum;
Elf64_Half e_shentsize;
Elf64_Half e_shnum;
Elf64_Half e_shstrndx;
} Elf64_Ehdr;Manual breakdown:
- 0 0:
EI_MAG=7f 45 4c 46=0x7f 'E', 'L', 'F': ELF magic number - 0 4:
EI_CLASS=02=ELFCLASS64: 64 bit elf - 0 5:
EI_DATA=01=ELFDATA2LSB: little endian data - 0 6:
EI_VERSION=01: format version - 0 7:
EI_OSABI(only in 2003 Update) =00=ELFOSABI_NONE: no extensions. - 0 8:
EI_PAD= 8x00: reserved bytes. Must be set to 0. - On the executable it is
02 00forET_EXEC.Another important possibility for the executable isET_DYNfor PIE executables and shared libraries.ET_DYNtells the Linux kernel that the code is position independent, and can loaded at a random memory location with ASLR. - 1 2:
e_machine=3e 00=62=EM_X86_64: AMD64 architecture - 1 4:
e_version=01 00 00 00: must be 1 - 1 8:
e_entry= 8x00: execution address entry point, or 0 if not applicable like for the object file since there is no entry point.On the executable, it isb0 00 40 00 00 00 00 00. The kernel puts the RIP directly on that value when executing. It can be configured by the linker script or-e. But it will segfault if you set it too low: stackoverflow.com/questions/2187484/why-is-the-elf-execution-entry-point-virtual-address-of-the-form-0x80xxxxx-and-n 40 00 00 00on the executable, i.e. it starts immediately after the ELF header.- 2 8:
e_shoff=407x00=0x40: section header table file offset, 0 if not present. The Intel386 architecture defines no flags; so this member contains zero.
- 3 4:
e_ehsize=40 00: size of this elf header. TODO why this field needed? Isn't the size fixed? 38 00on executable: it is 56 bytes long02 00on executable: there are 2 entries.- 3 A:
e_shentsizeande_shnum=40 00 07 00: section header size and number of entries - 3 E:
e_shstrndx(Section Header STRing iNDeX) =03 00: index of the.shstrtabsection.
quoteinvestigator.com/2017/09/25/progress/ on Quote Investigator says it appeared in 1948. Can't easily check, but will believe it for now.
Now that we've done one section manually, let's graduate and use the
readelf -S of the other sections: [Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 2] .text PROGBITS 0000000000000000 00000210
0000000000000027 0000000000000000 AX 0 0 16.text is executable but not writable: if we try to write to it Linux segfaults. Let's see if we really have some code there:objdump -d hello_world.ohello_world.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <_start>:
0: b8 01 00 00 00 mov $0x1,%eax
5: bf 01 00 00 00 mov $0x1,%edi
a: 48 be 00 00 00 00 00 movabs $0x0,%rsi
11: 00 00 00
14: ba 0d 00 00 00 mov $0xd,%edx
19: 0f 05 syscall
1b: b8 3c 00 00 00 mov $0x3c,%eax
20: bf 00 00 00 00 mov $0x0,%edi
25: 0f 05 syscallIf we grep
b8 01 00 00 on the hd, we see that this only occurs at 00000210, which is what the section says. And the Size is 27, which matches as well. So we must be talking about the right section.The most interesting part is line to pass the address of the string to the system call. Currently, the This modification is possible because of the data of the
a which does:movabs $0x0,%rsi0x0 is just a placeholder. After linking happens, it will be modified to contain:4000ba: 48 be d8 00 60 00 00 movabs $0x6000d8,%rsi.rela.text section. Pinned article: Introduction to the OurBigBook Project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 3. Visual Studio Code extension installation.
Figure 4. Visual Studio Code extension tree navigation.
Figure 5. Web editor. You can also edit articles on the Web editor without installing anything locally.Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.Video 4. OurBigBook Visual Studio Code extension editing and navigation demo. Source. 
- Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact