﻿PHYSICS 
  OF 
  THE 
  UNIVERSE 
  JEANS 
  173 
  

  

  When 
  this 
  particular 
  temperature 
  begins 
  to 
  be 
  approached, 
  but 
  not 
  

   before, 
  radiation 
  of 
  the 
  wave 
  length 
  in 
  question 
  becomes 
  abundant; 
  

   at 
  temperatures 
  well 
  below 
  this 
  it 
  is 
  quite 
  inappreciable. 
  

  

  We 
  have 
  seen 
  that 
  radiation 
  of 
  short 
  wave 
  length 
  is 
  needed 
  to 
  break 
  

   up 
  an 
  electric 
  structure 
  of 
  small 
  dimensions, 
  and 
  as 
  we 
  now 
  see 
  that 
  

   short 
  wave 
  lengths 
  are 
  associated 
  with 
  high 
  temperatures, 
  it 
  appears 
  

   that 
  the 
  smaller 
  a 
  structure 
  is, 
  the 
  greater 
  the 
  heat 
  needed 
  to 
  break 
  it 
  

   up. 
  On 
  combining 
  the 
  relation 
  just 
  given 
  between 
  Tand 
  X 
  with 
  that 
  

   implied 
  in 
  the 
  rough 
  law 
  of 
  the 
  "860 
  limit," 
  it 
  appears 
  that 
  a 
  structure 
  

   of 
  dimensions 
  r 
  cm. 
  will 
  begin 
  to 
  be 
  broken 
  up 
  by 
  temperature 
  radia- 
  

   tion 
  when 
  the 
  temperature 
  first 
  approaches 
  l/3000r. 
  Atoms, 
  for 
  

   example, 
  whose 
  general 
  dimensions 
  are 
  of 
  the 
  order 
  of 
  10~^ 
  cm., 
  begin 
  

   to 
  be 
  broken 
  up 
  when 
  the 
  temperature 
  approaches 
  30,000°; 
  nuclei, 
  

   whose 
  general 
  dimensions 
  are 
  of 
  the 
  order 
  of 
  10~'^ 
  cm., 
  must 
  remain 
  

   unaffected 
  until 
  the 
  temperature 
  approaches 
  3,000,000,000°. 
  

  

  To 
  take 
  a 
  more 
  precise 
  instance, 
  yellow 
  light 
  of 
  wave 
  length 
  6000A 
  

   is 
  specially 
  associated 
  with 
  the 
  temperature 
  4,800°. 
  At 
  temperatures 
  

   well 
  below 
  this 
  there 
  is 
  no 
  j^ellow 
  light 
  except 
  such 
  as 
  is 
  artificially 
  

   created. 
  Stars, 
  and 
  all 
  other 
  bodies, 
  at 
  a 
  temperature 
  of 
  about 
  

   4,800°, 
  are 
  of 
  a 
  yellowish 
  color 
  and 
  show 
  lines 
  in 
  the 
  yellow 
  region 
  of 
  

   their 
  spectrum. 
  These 
  lines 
  occur 
  because 
  yellow 
  light 
  removes 
  the 
  

   outermost 
  electron 
  from 
  the 
  atoms 
  of 
  calcium 
  and 
  similar 
  elements. 
  

   When 
  a 
  temperature 
  of 
  4,800° 
  begins 
  to 
  be 
  approached, 
  but 
  not 
  before, 
  

   rearrangements 
  of 
  the 
  electrons 
  in 
  the 
  calcium 
  atom 
  begin 
  to 
  occur. 
  

   This 
  temperature 
  is 
  not 
  approached 
  on 
  earth 
  (except 
  in 
  the 
  electric 
  

   arc 
  and 
  other 
  artificial 
  conditions) 
  so 
  that 
  terrestrial 
  calcium 
  atoms 
  in 
  

   general 
  are 
  at 
  rest 
  in 
  their 
  states 
  of 
  lowest 
  energy. 
  Einstein's 
  paper 
  

   of 
  1917 
  showed 
  it 
  to 
  be 
  a 
  necessary 
  deduction 
  from 
  Planck's 
  law 
  of 
  

   black-body 
  radiation 
  that 
  a 
  collection 
  of 
  calcium 
  atoms 
  in 
  other 
  states 
  

   would 
  behave 
  precisely 
  like 
  atoms 
  of 
  radioactive 
  substances 
  to 
  the 
  

   extent 
  of 
  spontaneously 
  slipping 
  back 
  to 
  states 
  of 
  lower 
  energy. 
  

  

  Just 
  as 
  calcium 
  atoms 
  in 
  the 
  cool 
  temperatures 
  of 
  the 
  earth 
  simulate 
  

   the 
  behavior 
  of 
  radioactive 
  atoms, 
  so 
  radioactive 
  nuclei, 
  if 
  raised 
  to 
  a 
  

   sufficiently 
  high 
  temperature, 
  would 
  simulate 
  the 
  behavior 
  of 
  calcium 
  

   atoms 
  in 
  the 
  hot 
  atmosphere 
  of 
  a 
  star. 
  The 
  shortest 
  wave 
  length 
  of 
  

   radiation 
  emitted 
  in 
  the 
  transformation 
  of 
  uranium 
  is 
  about 
  0.5 
  X 
  

   10"'" 
  cm., 
  and 
  this 
  corresponds 
  to 
  a 
  temperature 
  of 
  5,800,000,000°. 
  

   When 
  some 
  such 
  tempera 
  cure 
  begins 
  to 
  be 
  approached, 
  but 
  not 
  before, 
  

   the 
  constituents 
  of 
  the 
  radioactive 
  nuclei 
  begin 
  to 
  rearrange 
  themselves 
  

   just 
  as 
  the 
  constituents 
  of 
  the 
  calcium 
  atom 
  do 
  when 
  a 
  temperature 
  of 
  

   4,800° 
  is 
  approached. 
  

  

  We 
  must 
  probably 
  suppose 
  that 
  rearrangements 
  can 
  also 
  be 
  effected 
  

   by 
  bombarding 
  the 
  electric 
  structure 
  with 
  material 
  particles. 
  If 
  so, 
  

  

  