What do mean by "pure energy", other than photons? Right after the big bang, photon-photon collisions led to the creation of matter-antimatter pairs.
The nuclei of many atoms routinely emit electrons or positrons which are not present in the nucleus, and are created from the excess energy of the nucleus. However, that energy is initially stored as mass-increase in the nucleus, so is not usually thought of as creating mass from energy, though it is. Likewise, we routinely make negative protons from kinetic energy for feeding into the Fermilab ring.
Those photons must have been really energetic! Pure energy is electromagnetic as well as heat energy, and I think there is one more that I can't recall. Yes, it would seem that all particles are created through vacuum fluctuations, but somehow they have no mass. And there are scenarios where certain particles are prevented from forming, as is the case with the casimir force. I know next to nothing about nuclear physics so allow me to ask a few questions. What accounts for the mass increase that supplies the energy for electrons? How is charge conserved?
REPLY: Is a photon considered a particle ? I always thought of it as a unit of energy with no mass. If it had mass it could not travel at the speed of light, so how can it be a particle of any sort ? ...traveler
"pure energy" is a fuzzy concept in particle physics. There really aren't those types you mentions, i.e. electromagnetic, heat etc, there are more large scale concepts. The only enery that really exists at that level is the kinetic and potential energy of the particle fields. Potential energy still confuses me a little when I try and think about what it "is", but the particle kinetic energy is clear enough. So when you say "created from pure energy", this doesn't really have any meaning. Particles are only created or destroyed during particle interactions. Energy conservation and all that. Where did the original energy and particles come from? I think some things can be said about energy coming from the expansion of space, I believe energy conservation gets a bit screwed in an expanding spacetime, but I don't really know much about that side of things. A shorter answer is that every particle can be created from pure energy. If you have high enough energy photons they will transform into any particle they have sufficient energy to create on occasion. Of course smacking other particles together is the usual method. If you do it hard enough you can create anything, in some small amount. Walters explanation of nuclear physics was a bit confusing. I will make a more general statement: mass is a form of potential energy, kinetic energy of particles can be stored as mass, and mass can be transformed into the kinetic energy of partices. There are rules about how this can happen though. I am talking about rest mass btw. Charge conservation is one such rules that needs to be obeyed in these interactions, i.e. a charged particle can only be created from neutral ingredients if an oppositely charge particle is created too. I'm not really sure what walter was talking about, but if you have a radioactive nucleus it can release an electron or positron as part of it's decay to another element/isotope. Charge is conserved here because a proton is transformed into a neutron or vice versa. The energy for the creation of the particle comes from the binding energy of the nucleus; the new nucleus has less binding energy that the original (part of why the decay occurs) and the extra energy goes into creating the new particle. The binding energy is a particular example of the potential energy I was talking about above, although more complex since there are a whole mess of particles (mesons) being exchanged in the nucleus to hold it together. Yes, a photon is a perfectly good particle. Having mass isn't a requirement, in fact in the early universe, before electroweak symmetry breaking occurred (via the Higgs mechanism (probably)), no particles had mass (or so the standard model goes). I'm not sure what your concern is really. It is a boson, not a fermion, which makes it less of a "matter" particle than most other fundamental particles, but it is still a particle just the same.
Yes, quite correct. But the "binding energy" is manifested in the nucleus as mass. We usually say the protons and neutrons have a little higher mass when in the bound state. Certainly, the mass is manifested when they are 'weighed' by any conventional means. Thus, the mass of the positron or electron that is emitted is subtracted out of the mass of the original nucleus, so the new nucleus (after the radioactive decay) has slightly less mass. That is why I said that it is a form of pure energy conversion into mass, in which the binding energy is converted into the mass of an electron or positron. But this also involves the conversion of a neutron into a proton plus electron (or proton into neutron plus positron), and protons and neutrons also have slightly different rest masses, so it is more involved than that. The rest mass of the neutron is slightly heavier than that of the proton, so it can be readily seen that for a proton to convert into a neutron plus positron requires the energy to come from somewhere other than rest-mass alone.
You seem to be referring to things which have no rest mass. The photon and the gluon have zero rest mass but all particles can be made from 'pure energy'. A fluctuation in the photon field can produce an electron/positron pair or a W+/W- pair or any other matter/antimatter pairing.
REPLY: EVERY TIME I try to understand this STUFF, I end up more confused. I will not say more than that. ...traveler
If all these fluctuations have mass, how come we don't feel their pull? Hmmmm? Oh, I thought maybe this would be a case of C violation but I was wrong. It makes sense that a neutron could turn into a proton and an electron since there is this difference in mass. Yes, I suppose so. I am mainly looking for momentum, and things without mass have rather poor momentum. Well this is a disappointment. I am trying to turn heat [from radioactive decay] into thrust in a space setting. Photons, as a result of thermal radiation, can provide thrust. However, the efficiency is 1/c which is abysmal to say the least. When you say anything, does this include gold?
Well, no, not really, I was referring to fundamental particles rather than composite particles. There would be some chance of creating all the particles needed to make a gold nucleus, but there is almost no chance they would happen to arrange themselves in the right places to bind into a nucleus. Needless to say, it is a seriously uneconomical and impractical way to make gold Please Register or Log in to view the hidden image!. If you really want to make it you're much better off slamming protons or neutrons into some element a little lighter than gold and hoping some of them bind into the nucleus. There are seriously bad statistics involved with that kind of process too though so I'm not suggesting anyone try it Please Register or Log in to view the hidden image!.
We do. The vacuum energy contributes to the cosmological constant which is known to be small but non zero. Also, virtual particle loops that contribute to the vacuum energy are "off shell," meaning they don't satisfy \(E^2 = p^2 + m^2\). The important property is the energy, not the mass.
Not true. Any object satisfies \(E^{2} = m^{2} + |p|^{2}\) and just because m=0 for massless objects doesn't mean there is some bound on their momentum.
Yes, light-speed photons possess momentum, but not mass. Their 'pure energy' can be converted into mass, as referenced above. Let's let someone else discuss how kinetic energy (a 'pure energy') is converted into mass, as for example when we make negatively charged protons 'from scratch' and circulate them at Fermilab to collide with positively charged protons (derived from Hydrogen gas).
I have a question. Your use of the phrase 'pure energy' implies that some energy is impure. What is it about KE that makes it pure and what is impure energy?
I'm simply going with the phrase used in the opening post. I presume it to mean energy in the form of kinetics, or potentials; as opposed to energy that is a mix of those plus mass-energy, which would be 'not pure' energy; (though not 'impure energy' as you suggest). This is based on the original post having mass-particles as not being "pure energy".
Well, thats one theory. There are other theories that point to a 'catastrophe' where the universe should have mass something like 1e100 times larger than it does if all quantum fluctuations have their real world mass. Maybe I'm missing a portion of the argument but this is supposedly one of those 'mysteries in physics', at least according to the wiki. Right, but photons have the lowest momentum : energy ratio of any particle, I believe. Pure energy is just something I read on a wiki and I liked the sound of it. This is once again going back to my plan of making some kind of thruster that works in conjecture with thermal radiation. I did some work on it today and it seems conservation of momentum is fairly solid .
For a photon \(E = p[tex] so [tex]\frac{p}{E} = 1\). For particles with mass it would be \(\frac{p}{E} = \frac{p}{\sqrt{p^{2}+m^{2}}}\). This is smaller for larger m. And what does the ratio matter? For a photon its constant so can't be zero but for a particle with mass you can have p=0. Thank god we have you to check. Please Register or Log in to view the hidden image!
