I thought there was no pure energy becuase Absolute Zero has never
been reached....until I read this:

" If a positron and an electron collide at low speed (so there is very
little kinetic energy) they both disappear in a flash of
electromagnetic radiation. This can be detected and its energy
measured. It turns out to be 2m0c2 where m0 is the mass of the
electron (and the positron).

Thus particles can "vaporize" into pure energy, that is,
electromagnetic radiation. The energy m0c2 of a particle at rest is
called its "rest energy". Note, however, that an electron can only be
vaporized by meeting with a positron, and there are very few positrons
around normally, for obvious reasons-they just don't get far". 

This quote is a a cut and paste from
http://galileo.phys.virginia.edu/classes/252/mass_and_energy.html.

So, is electromagnetic radiation 'pure energy', or does it contain at
least some Mass?

David

---

Request for Question Clarification by hedgie-ga on 07 Mar 2005 20:01 PST

idetal1234-ga 
 
  we did cover 'annihilation of e- and e+' into emg and agreed that
  emg is closest thing to 'pure energy', but still has a 'relativistic mass'
  in answer 1, did we not?
  
  So, in your series on 'pure' energy:

 

Nature of Energy and Matter 15 Feb 2005    5 comments  $10.00 

E=MC2 simplified            20 Feb 2005    20 comments $5.00 

Pure Energy...Yes or No?    02 Mar 2005    4 comments  $5.00 

your comment in question 2,


 http://answers.google.com/answers/threadview?id=477866
 
 This seems terribly important to me. I understood from it
that we cannot (yet) explain exactly *how* one form (eg: E) converts
into another form (M), but all we understand is that it does, and does
so at C2

and even more question 3, seems a bit like a regression (step back).

  It all reminds me quote attributed to Einstein:
  
    "Everything should be as simple as possible, but not more simple"
    
 So far, we all did sin by trying to make it 'more simple', I think.
 To grok the answer to understand the m*c*c and that ..
 in does not require to study math for ten years, but it requires more than
 one $5 paragraph. It requires understanding the concepts
 
 1) Physical quantity  (motion)
 2) Frame of reference  (relativity)
 3) amalgamation of quantities (as e.g. electro-statics plus
magneto-statics => emg)
 
 each would require at least a page of explanation and some Socratic
dialog - I would guess
 each would be a $200 ga answer. Ideally, on would recommend a book -
and that perhaps would
 be a $10 ga search to find a best textbook for this. Question is how
much time, effort and expense
 you want to expend to reach what level of understanding.
  
Hedgie

Yes, electromagnetic radiation is pure energy.  Electromagnetic
radiation is made out of photons, which are massless.

Thanks v. much biophysicist. 

Is there also 'pure mass'? 

Also, I thought that light was made of photons. If it is, and photons
have no mass, then why light bent by the sun? Does gravity affect
'pure energy'?

thanks again.

David

Good questions!
  Photons are massless only when they are at rest (not moving, zero
rest mass).  Photons move at the speed of light of the medium they are
in.  Photons transfer energy and must have some energy.  They can be
though of as pure energy, or carriers of pure energy.
  When electrons and positrons (anti-electrons) annihilate, they
produce pure energy which is release by the creation of two photons
(gamma rays of about .5 Million electron volts of energy each).  They
travel in opposite directions, so there is not net momentum created.
  This matter-antimatter annihilation is the most pure way that matter
can be converted into energy and just energy.  The reason that the
quotation mentioned the low temperature (low kinetic energy, means
moving very slowly) is that they were illustrating that mass, alone,
can be converted into pure energy.
  If the electron and positron were moving before the energy of their
motion, the kinetic energy, is also carried away by the created
photons and adds to the photons energy.  They would then have the
energy from their kinetic energy included with the energy from their
rest mass.
  In a nuclear reactor, on a small fraction of the mass is converted
into energy.  The uranium atoms break apart into parts that have less
mass than the original atoms; this lost mass is released as energy. 
In fact, the released energy is the energy required to hold the atom
together.  So, matter-antimatter annihlation is the most pure and
simple illustration of the conversion of mass into energy, or E=mc^2.
  About the light bending around objects with mass:  They do have a
mass using the same relationship E=mc^2.  So they are affected by
gravity!  However, the best way to think of it is from Einstein's
Theory of General Relativity which described the photons path as being
"straight:, but that space is warped by the presence of the massive
object.  I'd have a bit of trouble explaining that much more.

The question is not whether pure energy can exist, but rather what is
mass? Energy is the fundamental quantity that does exist, while mass
is just a concentration of energy. (E=mc^2).

Gravity therefore does not actually act between masses, but between
energy. Photons do not have mass, but they do carry energy and hence
can be attracted by gravity. Any particle that has mass can not move
at the speed of light, hence photons have no mass, whether they are at
rest or not.

As for absolute zero, it can never be reached because it is impossible
for the fundamental particles to become completely motionless. Heat is
the energy caused by motion of individual particles. It is impossible
to precisely know both the position and momentum of a given particle,
and if it stops at one point we would be able to measure both.

Funnily, if "a" photon has enough energy (about 1022MeV = 2x 511 MeV,
that is the "mass" of one electron/positron) it can break up into an
electron/positron pair without any reason.

By the way, "pure" ist a poor word. Mass ist eqaul to enery.

Hello,

A particle/anti-particle pair may anihilate, resulting in a burst of
massless photons, but it's not really accurate to say that the photons
are 'pure' energy, any more than were the original pair of massive
particles. It is, generally, a 'parameter' of a particle, which
characterises, places constraints upon, how it will interact with
another particle. A particle 'has' energy. It isn't energy itself.

I'll illustrate this with the way energy is related to momentum in
special relativity. In SR a particle traces what is called its
'worldline' through space-time. In a simple two dimensional space-time
there are two axes, (x,t), with x being space, t being time. Each
point on the t axis is a tick of the clock, so to speak. If a particle
in this system is traveling at some speed through space, then for each
value of t, the particle occupies a different value of x, a different
place in space. If it's traveling at the speed of light, c, then it
changes one unit of x for each unit of t, and so it traces a straight
path at 45 degrees to both axes. If it's at less than c, then the path
makes a smaller angle with t. As the particle's speed approaches zero,
its angle with t also approaches zero. At zero speed it's not moving
through space- but interestingly enough, it's still tracing through
the t dimension.

Energy is related to the way things change in time, and momentum to
the way they change in space, e.g.: A wave has both frequency &
wavelength. In quantum mechanics, a particle has an associated wave.
The frequency is a function of the particle's energy, the wavelength
of its momentum.

In SR, energy corresponds to the t component of a particle's
space-time path. Momentum is the x component. It's clear to see then
that even for a particle with zero speed(zero 'kinetic' energy, zero
momentum), it still has energy, because it still has an umambiguous t
component in space-time. A particle has energy because it exists. It
isn't 'made of' energy.

Hedgie

This is getting clearer for me. In layman's (ok: lay person's) terms,
there is a ball rolling down the hill. We - us people - see this and
we call the ball Mass, and we call the 'moving' Energy. But the ball
is just a unity, a one-thing, which does not know from E and M, far
less that E=M!

Put another way, we create abstractions, and then look at the
abstractions. It is the same as me looking in a mirror and mistaking
the reflection of reality for reality itself.

E and M (along with C^2) are abstractions; reflections in the mirror.
We are tempted to treat them as real (we certainly see them - in the
word-idea-mirror) but although we distinguish them in our minds, they
do not exist as distinct things in reality.

Another way of saying this is "E and M are two manifestations of the
same thing", to quote Einstien directly, or, mathemetically, E=M by a
factor of a Very Big Number (such as speed of light times itself).

At least, that is my current take on all this. It is nice to have this
verified insofar as I have yet to read any incontravertable (read:
'simple') proof that E does exist 'just by itself' independent of
Mass. This tells me, at least, that these are 'reflections in the
mirror of the mind' rather than actual realities in their own right.

yeah?!?! 
onwards...!
David

David

    I am happy that it is becoming more clear and I do see some signs of that.

     We have agreed that emg (=electromagnetic radiation) is close to the
 un-exact, common language expression, "pure energy". Then come other bosons,
 such as mesons and neutrinos, which can be considered more 'pure'
then fermions such as electron and positron.

So, I disagree with qed100-ga who says

"  ..photons are NOT 'pure' energy, any more than were the original
pair of massive particles.."

In some sense they are. But I am sorry that I have to say 'NO' to your 
' yeah?!?! '.

It is not like that. As I outlined in RFC, it is more complex than that.
 
If you want more explanation from me, you need to respond to the RFC, knowing
that it is not a yes/no issue. Some concepts are needed in order to undestand
E=m*c*c.  Energy and mass are two different quantities, according to
one theory. They are two ways of talking about the same quantity
acording to another theory. The two theories (Newton's vs Einstein's
mechanics) are both useful - and so - both valid in their realms. I
suggest, if you really want to understand this, that you ask for a
book suggestion, indicating how much time and effort you want to give
it, as well what level of math you can tolerate.

Hedgie

Hello hedgie-ga,

I also have to kindly disagree that Bosons are more 'pure' energy than
are Fermions. Even if one were to propose that Bosons are more
elementary as particles than Fermions(which, at least within the
Standard Model, they aren't), being a more primitive particle wouldn't
make them 'be energy'. Yes, work must be done on a field in order to
pop out a stable particle/anti-particle pair, i.e., it takes an
expenditure of energy to make matter. But the particles are a symptom
of the energy(or rather, a resultant of a mode of interaction), not
the energy itself.

qed (Quantum Electro Dynamics)?

 You certainly are entitled to your opinion (since we agree that 'pure' is
 a word with no exact definition - both views are just an opinion).

But I wonder if you have read the beginning of the saga:
http://answers.google.com/answers/threadview?id=475235

where we (David and I) agreed on one possible meaning of the word pure:

" Other way to interpret the question is in terms of current
  elementary particle theory.

  e.g. :  there are photons - particles of light - which are hard to
          put into a test-tube (less impossible, lately) but hard.
        
 and there are things made of atoms,like  water and air, which go well
into the test tube..."

 Bosons are not 'more elementary' (whatever that means) but fact remains that
 electrons are source of the (emg) field and not the other way around.

 So there is some 'ordering' in the sense of
http://mathworld.wolfram.com/Poset.html
 

Respectfuly

Hedgie