Re: What would happen if all the matter in the Universe turned into energy?

Hi Joe,

Matter already is "pure energy".  Matter is one form of energy.  
Energy can take many other forms, such as electromagnetic radiation 
("light"), or gravitational potential energy, or kinetic energy of 
a moving particle.  They're all just as real and just as pure.  
Television and movie scripts sometimes talk about "pure energy", 
and usually represent it as something similar to light, but that's 
just entertainment, not reality.

Since matter is *already* a form of energy, the answer to the 
question you asked is "nothing".  Since that's not a very 
interesting answer, let's discuss a slightly different question:  
Suppose all the matter in the Universe turned into a different 
form of energy, such as electromagnetic radiation ?  What would 
happen then ?

Well, first of all, that probably can't happen.  Matter can turn 
into other forms of energy, but it can't just happen any old which 
way.  Besides conservation of energy, there are other rules which 
the Universe appears to follow.  In particular, there's something 
called "conservation of baryon number", which implies that a proton 
can't turn into light unless it meets up with an anti-proton.  
Since we think there are many more protons than anti-protons in 
the Universe, you can see that this poses a problem.  Nonetheless, 
let's suppose it happened anyway.  (Maybe there are more antiprotons 
than we think, or maybe baryon conservation doesn't always hold true, 
or something...)  In that case, all the energy in the Universe would 
be in the form of light.  Light particles ("photons") can interact 
with each other to produce matter (turning energy of electromagnetic
radiation into energy of mass) so some mass would form again, but 
certainly not as much as we started with, and the Universe would be 
a very different place.  Things would tend to spread out more, 
because energy in the form of light travels faster than energy in the 
form of matter, and as the photons spread out, they'd have less 
chance of interacting with each other, and eventually you'd just be 
left with a vast, boring expanse of more or less uniformly dim light. 
There'd be no people left, because people are made of matter.  
Doesn't sound like a fun place at all to me!  I guess it's a good 
thing there are more protons than anti-protons.

			-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.