Mass-Energy Conversion: Exploring the Possibilities & Limitations

[AnthreX]

can mass changed to energy
and can energy changed to mass ?
if no why ?

 

[chroot]

Yes, both are possible.

- Warren

 

[relativelyslow]

i don't understand this. i know they are two words for the same thing but i don't know how. i know fusion or fission (one of them) converts mass to energy, so would the other convert energy to mass?

 

[chroot]

Matter-antimatter reactions are the classic examples of the interconvertibility of mass and energy. If you slam a proton and an anti-proton together, you get gamma rays -- mass has been converted to radiation, which is massless but energetic. Conversely, if you put enough radiation in a small enough area, you'll provoke the creation of a pair of particles, one normal matter and one anti-matter -- energy has been converted into mass.

Nuclear reactions are another common way to see the equivalence. When energy is realeased by a nuclear reaction, you can be assured that the products have less total mass than the reactants.

- Warren

 

[relativelyslow]

cool. i still don't understand the actual physics of it but ill try to find out.

 

[sciart]

E = mc2 = E0 + ΔE = m0c2 + Δmc2 = m0c2 + (mv2)/2


http://sciart.icpcn.com/physics/relativity.html

 

[HallsofIvy]

Fusion and fission both convert matter to energy- that's why both are used for bombs! A tiny amount of matter converts to a huge amount of energy.

Conversely, a huge amount of energy converts to a tiny amount of matter. Currently the only observable examples of energy converting to matter are elementary particles.

 

[sciart]

a huge amount of energy = a huge amount of photons(Δm)
a tiny amount of matter = imply energy(m0)

 

[JohnDubYa]

I think it is incorrect to say that mass is converted to energy. Mass IS a form of energy. What happens in a fission process is that the mass energy is converted to kinetic energy.

Or maybe this is just a matter of semantics.

 

[kuenmao]

"Mass converted to energy" or "Mass energy converted to kinetic energy" is just a terminology problem. Whatever the case, mass is equivalent to energy, and we don't need to argue more about that.
A huge amount of energy is needed to produce a small amount of mass, as said in Einstein's famous equation:
E = m c2
Since c, the speed of light in vacuum, is a pretty big number(299792458 m/s), that's quite a lot of energy for a small amount of mass.

 

[Moe]

Since this is a physics forum, I feel compelled to nitpick and add that the formula you mentioned is incomplete. There are higher terms that have been left out and that incorporate such things as kinetic energy for example.

 

[Cheman]

I would argue that surely mass and energy must both be part of the same thing - not different versions of the same "mass-energy". ( ie - Energy HAS mass, not that energy can be converted into mass and vice versa.)
I've come up with a simple argument for this - imagine a football; you kick this ball converting chemical in yours muscles to kinetic energy. Hence the all moves and gets heavier since it has gained mass - the energy it gains is the SAME as the chemical energy i have lost because energy has been conserved. Now, if energy and mass were different versions of the same thing, then surely 2 things would happen instead - 1) the ball would move (since gained the energy from my chemical) but would not get heavier, because all energy has gone to energy and not mass, as it can be proved that the ball gains the same energy as I have lost, or 2) the ball would not move, just get heavier as energy goes to mass. Both are untrue - therefore energy must HAVE mass, rather than BE mass.
From this we could also conclude that photons have mass, which in a way would make sense if you think about it - after all light can not escape the gravitational field of a black hole. Therefore is must have weight. Therefore it must have mass.
What do you think? :-)

 

[chroot]

Cheman,

Do not post personal theories here. Personal theories are welcome only in the Theory Development portion of the site.

- Warren

 

[Cheman]

May I ask why?

 

[Cheman]

If there is a problem with what I said, then please just remove it. Thanks. :-)

 

[europium]

Because if it is wrong, and people unfamiliar with the forums take it as a proven theory, then it could get confusing. Whereas if it is in the theory development section, then that is well stated. Also, i am no expert physicist, but what you have said is based on a very common misunderstanding. The things in 'our' world behave a lot different to those in the quantum world ie. Spin, a component of quantum particles, is undefinable by anything that we understand in 'our' world. Thus it is probably very likely that what you have stated, does not hold up in the quantum world of elemntary particles. And could you verify why you believe photons entering a black hole, and not leaving, must have weight, and therefore mass. Because the equation for weight is: Gravitational field strength x mass = weight

Now no matter what the gravitational field strength is, if mass is 0, then weight will be 0. Relatively, if the weight is 0 then the mass is 0. Photons don't need to have weight to be unable to escape a black holes gravitational pull. It is the curving of space, which everything 'follows', that causes the gravitational effect. It is not mass that causes gravity. Therefore i cannot understand how you came to the conclusion that photons have weight.

Kyle

 

[Cheman]

That was not the main point of my argument - if you read the rest then it does appear to make sense. Also, it is a known fact that photons have momentum - it is what the De Broglie Quantum Wavelength equations are based upon. Hence, if a photon lacks mass then how can it have momentum if momentum = mass * velocity? My football argument does, to some extent, appear to make sense and would coincide with E = mc2.

 

[Cheman]

Does anyone at least consider it valid and reasonable? :-)

 

[chroot]

This is your second, and last warning, Cheman. Stop posting personal theories.

- Warren

 

[Cheman]

Chroot,
I apologise if what I have said has not been posted in the correct way or place - i do not mean to cause confusion, simply ask questions, which is surely the whole idea of science. However, I would just like to ask (if you would like to tell me by perosnal email as not to cause further confusion) what you thought of my idea?

 

[chroot]

This is not the appropriate place to post your idea, or to ask for opinions on it.

- Warren

 

[pmb_phy]

For a complete and thorough understanding of the concept of mass and energy in relativity go to http://www.geocities.com/physics_world/ and click on the URL labeled "On the concept of mass in relativity".

Pete

 

[flexten]

Beware you modem users, pmb phy's reference takes 10 minutes to load.
Now that caused me to gain some mass !

Best

 

[Cheman]

I am sorry but I don't see why my message was inappropriate. After all, the entire idea of science is to question why things happen. I thought of something, and decided to ask a question on it - why is that not appropriate on a science forum?

 

[europium]

it is... just on the theory development forum :-)

 

[chroot]

Cheman,

From this we could also conclude that photons have mass

You did not ask a question, you made an assertion which concluded that light has mass. This is contrary to all accepted physics, and thus is not welcome here, except in the Theory Development forum. If you cannot deal with our rules, please don't post at all.

- Warren

 

[Cheman]

Ok, I apologise, it shall not happen again. However, I do believe that you'll find I actually asked at the end my message "what do you think?", implying that I simply wished to know whether what I thought was correct or not. I apologise for any inconvieniance.

 

[Cheman]

Ques: Through accepted scientific theory at the moment how do we explain that photons has momentum when they do not have mass?

 

[chroot]

Because momentum in relativistic mechanics is defined more generally than in classical mechanics. In relativistic mechanics, the energy of a particle is related to its momentum via

$$E = \sqrt{p^2 c^2 + m_0^2 c^4}$$

where E is the energy, p is the momentum, $m_0$ is the rest-mass, and c is the speed of light. Energy can come in several forms: kinetic energy, rest-mass energy, and so on. Thus, a photon does not need mass to have momentum. This definition winds up being precisely the same as the classical definition when you consider particles that aren't moving very fast, so the two are not incompatible; it just happens that the relativistic version applies everywhere (as far as we currently know anyway), while the classical version has restrictions on where it can be applied.

- Warren

 

[Michael F. Dmitriyev]

Because momentum in relativistic mechanics is defined more generally than in classical mechanics. In relativistic mechanics, the energy of a particle is related to its momentum via

$$E = \sqrt{p^2 c^2 + m_0^2 c^4}$$

where E is the energy, p is the momentum, $m_0$ is the rest-mass, and c is the speed of light. Energy can come in several forms: kinetic energy, rest-mass energy, and so on. Thus, a photon does not need mass to have momentum. This definition winds up being precisely the same as the classical definition when you consider particles that aren't moving very fast, so the two are not incompatible; it just happens that the relativistic version applies everywhere (as far as we currently know anyway), while the classical version has restrictions on where it can be applied.

- Warren

Does it not means that radiation is the TWO DIMENSIONAL PRODUCT of light (c^2) and an object having mass is a FOUR DIMENSIONAL PRODUCT of light (c^4) ?

 

[chroot]

Does it not means that radiation is the TWO DIMENSIONAL PRODUCT of light (c^2) and an object having mass is a FOUR DIMENSIONAL PRODUCT of light (c^4) ?

No.

- Warren

 

[Michael F. Dmitriyev]

No.

- Warren

Why?

-Michael

 

[chroot]

Why?

-Michael

Mostly by default. The assertion that "radiation is the two dimensional product of light" doesn't even make sense. I'm going to warn you, as well, to resist the temptation to post your personal theories in parts of the site where they are unwelcome.

- Warren

 

[Cheman]

Sorry, but how was Michael F. Dmitriyev inappropriately expressing a personal theory? He asked a question ( hence the question mark at the end) - he didn't demand that he was right, just asking if he was correct. ( as I in fact was) He wasn't in flicting a confusing personal theory on anyone.

 

[pmb_phy]

You did not ask a question, you made an assertion which concluded that light has mass.
...
Because momentum in relativistic mechanics is defined more generally than in classical mechanics. In relativistic mechanics, the energy of a particle is related to its momentum via

$$E = \sqrt{p^2 c^2 + m_0^2 c^4}$$

where E is the energy, p is the momentum, $m_0$ is the rest-mass, and c is the speed of light. Energy can come in several forms: kinetic energy, rest-mass energy, and so on. Thus, a photon does not need mass to have momentum. This definition winds up being precisely the same as the classical definition when you consider particles that aren't moving very fast, so the two are not incompatible; it just happens that the relativistic version applies everywhere (as far as we currently know anyway), while the classical version has restrictions on where it can be applied.
- Warren

Cheman has \ correctly deduced that light has mass. re - he was correct when he said

Hence, if a photon lacks mass then how can it have momentum if momentum = mass * velocity?

In your comment above you posted the correct relationship between inertial energy, rest mass and momentum. You then used the term "mass" unqualfied to mean "rest mass" as you have in previous posts and threads in this forum. Cheman does not seem to be aware of the semantics of this point and that is where the disagreement is. Once more we're back to the debate of what the term "mass" means.

The statement made by Cheman is correct if the term "mass" refers to "inertial mass, aka "relativistic mass" , m, and is wrong if it refers to "rest mass", m₀. Relativistic mass, aka inertial mass, is defined as the "m" in p = mv (e.g. see French, D'Inverno, Rindler, Mould, Schutz etc.). If the particle is a tardyon (moves at v < c) then it depends on velocity, i.e. m = m(v). Rest mass aka proper mass is defined as m₀ = m(0).

Therefore cheman is speaking of relativistic mass and chroot is speaking of rest mass.

Its also incorrect to claim that people mean "rest mass" when the use the term "mass" unqualified. Differerent relativists mean different things by this term as evidenced in many new modern relativity texts etc.

Cheman - See
http://www.geocities.com/physics_world/relativistic_mass.htm
http://www.geocities.com/physics_world/sr/inertial_mass.htm
See the links at the bottom of that page under Particle Accelerator Labs for examples from Cern, Argonne National Laboratory, Lawrence Berkeley National Laboratory, and University of Wisconsin-Madison

Even the text A Short Course in General Relativity, Foster & Nightingale, Springer Verlag, (1994) discusses the photon mass in one derivation of gravitational redshift.


There was a recent artilce on relativistic mass in the American Journal of Physics

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71(9), 878, Sept. (2003).

That was an article which addressed tardyon's only.


Here is a quote you'll like Cheman. From The Evolution of Physics, Einstein & Infeld, Touchstone Pub., (1966). Commenting on the observation made by an observer inside an accelerating elevator that light is ‘weightless’ Einstein writes

But there is, fortunately, a grave fault in the reasoning of the inside observer, which saves our previous conclusion. He said: “A beam of light is weightless and, therefore, it will not be affected by the gravitational field.” This cannot be right! A beam of light carries energy and energy has mass.

Pete