MadSci Network: Physics
Query:

Re: What happens to gravitional energy in matter-antimatter reaktion.

Date: Sun Jun 6 19:18:00 1999
Posted By: Steven Levin, Research Scientist, Astrophysics, Jet Propulsion Laboratory
Area of science: Physics
ID: 927617792.Ph
Message:

Hi Mattias,

The short answer is "nothing happens to the gravitational 
energy when antimatter and matter particles annihilate".  
I imagine you'd like a longer answer, though, so here's 
my attempt to explain how that works:

Looking at gravity the way Newton did, every massive 
object attracts every other massive object, and the amount 
of the attractive force (called "gravity"), is 
proportional to the masses of the two objects.  Early in 
the 20th century, Einstein suggested that this Newtonian 
theory of gravity is only an approximation, and that:

1)	Mass is a form of energy.  The conversion factor to 
figure out how many grams of mass is equal to how many 
ergs of energy is the speed of light squared, leading to 
the famous equation E = mc^2.  Since the speed of light is 
so large, a very small amount of mass is equivalent to a 
really large amount of energy.

2)	Gravity can be thought of as a distortion of space-time, 
in which the amount of the distortion is proportional to 
the amount of energy.  Since mass is a form of energy, and 
it takes a lot of energy to equal a small amount of mass, 
you can usually ignore everything but the mass, and the 
amount of gravity you calculate will come out essentially 
correct.  Thus Newton' theory still works in most situations.

(Einstein also figured out a bunch of other really 
interesting things, most of which were laid out in two 
theories, called "Special Relativity" and "General 
Relativity".  If you search the Mad Scientist archives at 
http://www.madsci.org/MS_search.html, you can find lots of 
questions and answers about Einstein's theories.)

When a a particle and its antiparticle annihilate, the 
mass gets converted into (a different form of) energy, but 
the gravity stays the same, because it depends on the 
total energy, not just the part of the energy which we 
call "mass".  Of course, the mass-energy is generally 
converted into electromagnetic radiation.  (Whether visible 
light, or gamma rays, or X-rays, it's still electromagnetic 
radiation.)  Since this electromagnetic radiation travels 
at the speed of light, the energy quickly moves away from 
where it started, and the gravitational forces all change 
accordingly.  

			-Steve Levin  
______________________________________________________
DISCLAIMER:  Just because I work for JPL/NASA/Caltech 
doesn't mean  anything I say is in any way official.  
This is just me talking, not NASA,  JPL, or Caltech.     



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