Zero-energy_universe doesnt add up

  • Thread starter granpa
  • Start date
  • #1
2,257
7
[According to Hawking] our universe can appear out of nothing because the positive energy (mass and motion) and negative energy (gravitational potential energy) cancel each other out on a large enough scale
http://en.wikipedia.org/wiki/Zero-energy_universe

Hawking is probably right, however

the energy in the gravitation field of an elliptical galaxy is approximately:
E = Gm2/r

where G = 6.67×10-11 N m2/kg2

and of course E = mc2

so using r = 1021 m (100,000 Light years) we get

Gm2/r = mc2

m = r * c2 / G

m = 1.347×1048 kg = 6.774×1017 solar masses

thats 6 * 104 times larger than the largest elliptical galaxies
Elliptical galaxies vary greatly in both size and mass, from as little as a tenth of a kiloparsec to over 100 kiloparsecs (300,000 Ly), and from 107 to nearly 1013 solar masses
So in order to break even you need 60,000 galaxies worth of mass in a region of space only 100,000 Ly across.
 
Last edited:

Answers and Replies

  • #2
Chronos
Science Advisor
Gold Member
11,408
742
Read the intro to the wiki article again. The zero energy hypothesis is derived using pseudo tensors.
 
  • #3
1,525
10
Feynman and others have long puzzled over the zero energy universe - in his "Lectures On Gravity" he comes back to it serval times in different chapters. At one point he comments that it is an exciting prospect that it costs nothing to create a mass at the center of the universe (which is everywhere) because the mc^2 energy is always balanced by the negative gravitational energy.

So perhaps the thing we call the big bang didn't create anything - it just rearranged things
 

Related Threads on Zero-energy_universe doesnt add up

  • Last Post
Replies
16
Views
2K
Replies
9
Views
1K
Replies
10
Views
1K
  • Last Post
Replies
19
Views
2K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
9
Views
741
  • Last Post
Replies
9
Views
4K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
3
Views
3K
Top