What is the process of converting energy into mass?

[cdm1a23]

Hi,

I have only taken two semesters of Physics, so please keep that in mind when answering. Thanks!

OK, I have heard of fission and fusion, and I basically understand them. Smash together some mass, and the result is a little bit of missing mass which creates a ton of energy.

I have always heard about these processes, but unlike most other topics, I haven't really ever heard about what the opposite process is of each of these. How do you convert energy into mass? I have heard that a person can truly show they understand something by explaining it in simple terms, and I know this sometimes leads to an imperfect explanation, but please don't use terms like Higgs Field or Higgs Boson without a simple explanation of what that means.

Sorry if I am asking for too much, but I have asked some of my friends, and they can regurgitate the complex words and terms they have learned, but they haven't been able to really make me understand this.

Thanks very much for any help or information.

 

[cesiumfrog]

Heat a potato. It now weighs more. You just can't measure it so easily, unlike nuclear reactions where a significant fraction of the total mass-energy changes form (and escapes).

 

[cdm1a23]

Ok I weighed myself while i was holding a potato, then i heated it and ate it, and then i weighed myself, and the weight was the same.

 

[cdm1a23]

Yes... that was a joke, but I am asking a real question here. I know that energy = mass c^2, so when you add energy to something you are increasing it's mass energy or whatever, but does that mean that mass and energy are the exact same thing? I don't think so, because then a really really cold rock would weigh almost nothing?

 

[LurkingEyes]

The theory is that mass and energy are interchangeable in a sense, not that they are the SAME thing. My bit of mass can be changed into energy, but it's not mass and energy at the same time. With heat it's one mass that is containing another (the heat) energy.

One theory in string theory puts vibrating energy strings as the basis for every particle, but I don't think that's what you're asking. Or if that theory is still being used.

 

[mjsd]

Re: what process creates mass?

we simply don't know the answer to such questions very well... not yet...if we do, we could precisely calculate the masses of quarks and leptons.

 

[gabee]

This is something I've wondered for a little while about too...I've only read snippets here and there and haven't studied it because I've just now begun classical E&M in school. I've read that in high energy particle collisions, new mass can be created. I guess it is a humongous quantity of energy that creates a tiny bit of new matter? Why does this happen?

On a somewhat related note, I got into an argument with one of my chemistry teachers about why you should not weigh hot objects. She tried to reason that since density is dependent on temperature, and d = m / V, that when objects are hot their mass changes...I told her that's obviously wrong, it's the same mass but the volume has changed. I could understand the fact that perhaps a change in volume could affect the weight measurement since there would be slightly more buoyant force (since it is immersed in air) but this effect would be minimal. I proposed that it was probably just a safety precaution and that you shouldn't be fooling around with a beaker of boiling water on a scale anyway, but she didn't concede this. Can you guys shed light on that?

 

[quetzalcoatl9]

This is something I've wondered for a little while about too...I've only read snippets here and there and haven't studied it because I've just now begun classical E&M in school. I've read that in high energy particle collisions, new mass can be created. I guess it is a humongous quantity of energy that creates a tiny bit of new matter? Why does this happen?

the mechanism, as i understand it (which is not much), is that it is a consequence of the fact that both matter and radiation are fundamentally described by waves. it is also for this reason that light and matter interact at all (as in electron excitation, for example). things in the universe are made up of bosons (example: photons) and fermions (example: electrons), both of which can be described as perturbations to an underlying quantized field - this is the achievement of quantum field theory. so what we call matter ("particles") and radiation ("EM wave") are really just collective modes (i.e. stable states) of a vacuum field. these states can interchange in a time-dependent way - which would be what you are talking about, matter to radiation (i assume that is what you mean by 'energy') and vice versa. someone else on the forum, please correct me if i am wrong about any of this.

On a somewhat related note, I got into an argument with one of my chemistry teachers about why you should not weigh hot objects. She tried to reason that since density is dependent on temperature, and d = m / V, that when objects are hot their mass changes...I told her that's obviously wrong, it's the same mass but the volume has changed. I could understand the fact that perhaps a change in volume could affect the weight measurement since there would be slightly more buoyant force (since it is immersed in air) but this effect would be minimal. I proposed that it was probably just a safety precaution and that you shouldn't be fooling around with a beaker of boiling water on a scale anyway, but she didn't concede this. Can you guys shed light on that?

when i was an undergraduate, my analytical chem TA told us the same thing. he was a good researcher, so i believe it. i think your 2nd explanation was the reason behind it (that the heat winds up preferentially heating the air around it - except on the bottom where there isn't much air) causing a buoyancy effect that supposedly can be noticed on an ordinary chem lab balance. I've never actually tried this tho - altho i recall many days where i wanted to finish lab quickly so i would just weigh the hot stuff anyways :) if it made a difference, i didnt notice it..then again, an analytical chemist probably would

 

[CarlB]

No one really knows where mass comes from. Current theory puts it in by a rather involved procedure that has not been verified, and is quite arbitrary. For a book on mass that is fairly elementary, see Max Jammer's classic, available for $5 on amazon:

Concepts of Mass / In Classical and Modern Physics
https://www.amazon.com/dp/B000EYPSEU/?tag=pfamazon01-20

 

[cdm1a23]

Thanks to everyone for your answers. Some of them were very interesting. This question sprang about from a discussion on entropy that I was having with one of my friends.

 

[Gib Z]

Well yes basically, To your original question, No one really knows. If anyone says they do, their just going to spit out a fat load of words about The Higgs boson, maybe some amazing TEV particle accelerators, and Quantum Field Theory. Thats another way of them saying, they don't really know, but their trying...

 

[quetzalcoatl9]

can someone here with a PhD in physics and whom is currently doing research in modern physics, confirm that in fact "no one knows" the process of mass->radiation and radiation->mass?

i am unqualified to evaluate this, but it sounds a bit pessimistic to me.

more specifically, (a) i find it hard to believe that the standard model works so well (in terms of describing experimental observations) without an understanding of this underlying process and (b) i have noticed that in an area in which i AM qualified to evaluate, that often times people who do not understand or feel comfortable with the mathematical abstractions of something will claim that the current understanding is somehow a sham - sometimes the interpretation for the layman actually brings harm to the promethian samaritan.

 

[jtbell]

I know that energy = mass c^2, so when you add energy to something you are increasing it's mass energy or whatever, but does that mean that mass and energy are the exact same thing? I don't think so, because then a really really cold rock would weigh almost nothing?

In relativity, even a stationary particle has energy because of its mass: $E_0 = m_0 c^2$ where $m_0$ is the particle's invariant mass (which is often called "rest mass"). We call this the particle's intrinsic energy or rest energy.

This intrinsic energy can be converted into other forms of energy, for example in particle decays such as $\Lambda^0 \rightarrow p + \pi^-$. The sum of the invariant masses of the $p$ and $\pi^-$ is less than the invariant mass of the $\Lambda^0$. The difference manifests itself in the kinetic energies of the outgoing $p$ and $\pi^-$.

Some people describe this by saying that the $p$ and $\pi^-$ have larger "relativistic masses" because of their kinetic energy, so the sum of their relativistic masses equals the relativistic mass of the $\Lambda^0$. This description is equivalent to the other one using invariant mass, but particle physicists generally prefer to talk about invariant mass rather than relativistic mass. (I worked in particle physics as a graduate student, and I don't remember anyone in the field using relativistic mass.)

 

[Gib Z]

I assure you quetzalcoatl9, even if most of us here don't fit the description of PhD etc, we know enough to tell you no-one knows for sure. There have been certain theories, and there are people who think they know. But so far, nothing has been confirmed, or generally accepted by the Scientific Community.

 

[cdm1a23]

Thank you again for some of the further explanations. This is a very interesting subject to me... sometimes people say that mass and energy are the same thing, and I don't know that we really know whether that's true or not. Any additional info would be great.

 

[Elementric]

I may be talking rubbish here, but am I not correct in saying that mass cannot be created or destroyed, much like energy cannot be created or destroyed? A 'particle' cannot be simply created or destroyed, for example during nuclear fission neutrons are removed from split nuclei, but not 'destroyed', rather the it is simply an exothermic reaction in which the energy does not come from a net loss of mass, but from a smaller amount of energy contained within the particles.

 

[cesiumfrog]

I may be talking rubbish here, but am I not correct in saying that mass cannot be created or destroyed, much like energy cannot be created or destroyed?

No, unless you mean relativistic mass (which is trivially equivalent to energy).

A 'particle' cannot be simply created or destroyed,

Incorrect, for example energy can be used to create a particles (say, an electron and positron) in an accelerator lab.

for example during nuclear fission neutrons are removed from split nuclei, but not 'destroyed', rather the it is simply an exothermic reaction in which the energy does not come from a net loss of mass, but from a smaller amount of energy contained within the particles.

If you measure the weight before and after you'll see it has changed, but maybe you're onto something. Particle physicists will tell you that some of the rest mass has been converted to energy. Personally, I think it's interesting that we call the chromodynamic potential energy "rest mass", but we call the increased potential energy of a hypothetical box-of-photons (or hot potato) by the name "relativistic mass" (in a frequently disdaining manner despite that in every classical sense the box/root behaves as though it is now more massive than when empty/cold).

 

[Elementric]

Ah, so you can create a 'particle', for example an electron, form only energy and nothing else? It certainly is an interesting idea..
thanks for the clarification btw ^^

 

[Sojourner01]

Elementric; two photons of high, equal energies and perfectly opposite momentum vectors can collide and produce an electron-positron pair. A photon has no mass but it is most definitely 'something' - so it's not exactly pure energy.

 

[ZapperZ]

Elementric; two photons of high, equal energies and perfectly opposite momentum vectors can collide and produce an electron-positron pair. A photon has no mass but it is most definitely 'something' - so it's not exactly pure energy.

Please note that we still do not have a photon-photon collider. This means that this technique of generating electron-positron pair has not been experimentally demonstrated!

So of course, the most obvious question following this is, how has e-p pair been generated, especially at SLAC and the now-retired LEP? How would the position be generated at the proposed ILC? I believe this has been mentioned and explained already a few times on here.

Zz.

 

[Newbie says Hi]

Please note that we still do not have a photon-photon collider. This means that this technique of generating electron-positron pair has not been experimentally demonstrated!

So of course, the most obvious question following this is, how has e-p pair been generated, especially at SLAC and the now-retired LEP? How would the position be generated at the proposed ILC? I believe this has been mentioned and explained already a few times on here.

Zz.

Woahhh, REALLY? I don't remember my books mentioning this little tidbit. Got any relevant links to explain this?

Still, wooahh!

 

[ZapperZ]

Woahhh, REALLY? I don't remember my books mentioning this little tidbit. Got any relevant links to explain this?

Still, wooahh!

Let's put it this way. Does your book mentioned anything about such a thing in existence already?

There are proposal that with the LHC, and even the proposed ILC, that photon-photon collider, or more specifically gamma-gamma collider, might be possible as one of its by-product. Till then, we have no such thing that has been done or verified. You're welcome to scour the web or various journals to find any experimental evidence of that.

Besides, e-p production using such a technique is VERY inefficient. If I want to show an example of the production of mass out of photons, I certainly would not have used that example. Why can't the already-verified pair production being done almost routinely nowadays not used as the example, I have no idea.

Zz.

 

[Newbie says Hi]

Let's put it this way. Does your book mentioned anything about such a thing in existence already?

No, but being a student still at Griffiths' level, it was not readily apparent.

In any case, do you have any links to explain how a photon-photon collider would work (explained at Griffiths' level)?

 

[quetzalcoatl9]

No, but being a student still at Griffiths' level, it was not readily apparent.

In any case, do you have any links to explain how a photon-photon collider would work (explained at Griffiths' level)?

i think it would be exactly the reverse process of a medical PET scan...the problem is that it is much easier to detect 2 antiparallel photons than to make them that way (I believe because of the energy-time uncertainty relation?).

 

[Sojourner01]

Besides, e-p production using such a technique is VERY inefficient. If I want to show an example of the production of mass out of photons, I certainly would not have used that example. Why can't the already-verified pair production being done almost routinely nowadays not used as the example, I have no idea.

I used such an example to make absolutely clear that, according to our current understanding of particle physics, mass most definitely can come from 'no mass' - that is, from a state where there was no mass to begin with i.e. photons. This was what Elementric was asking.

 

[ZapperZ]

I used such an example to make absolutely clear that, according to our current understanding of particle physics, mass most definitely can come from 'no mass' - that is, from a state where there was no mass to begin with i.e. photons. This was what Elementric was asking.

Yes, but the pair-production that we are using nowadays for positron sources in, let's say, particle accelerators, do not use gamma-gamma collision. This, as I've said, has not been proven. Thus, can you see the problem with trying to answer this question by pointing to something that hasn't been done yet?

We have a very-well known and well-tested/demonstrated means of generating pair production via gamma going through tungsten or berilium that can generate this pair-production. Why aren't you using that as an example?

Zz.

 

[Sojourner01]

We have a very-well known and well-tested/demonstrated means of generating pair production via gamma going through tungsten or berilium that can generate this pair-production. Why aren't you using that as an example?

Because I've never heard of it. I started my first ever specific course on particle physics three weeks ago - this is the limit of my knowledge.

 

[cesar314]

thank you ZapperZ and jtbell for helping to clarify this issue.

I think the original question being posed was about simple relativistic collisions and not the Higgs mechanism, to start off. So let's begin with E=mc^2

This is a relationship between mass and energy. This means, in one way of phrasing it, that mass and energy are equavelent. Mass is a form of energy, just like kinetic energy is a form of energy or classical potential energy (at least at this level of presentation). Notice that E=mc^2 is an equation where m describes the total (or relativistic) mass of the particle. E is then the total (relativistic) energy. The minimum total energy that a particle (or system of particles) can have is its rest-mass energy, E0=m0c^2--m0 is the rest mass, or the mass measured when the particle is seen to be stationary. This means that a mass isolated from all forces and observed to be stationary will still have energy, no matter what--it is energy. But once that thing is moving, it will carry kinetic energy, as we well know. The total energy will be then be KE+E0 (in the nonrelativistic limit; relativistically E^2=(pc)^2+(mc^2)^2 ) , or the kinetic energy plus the rest mass energy. In classical (nonrelativistic) interactions, KE<<E0, and because no new particles are being created or whatever, E0 is ignored when taking into account energy exchange (you can take a Taylor expansion approximation resulting in the classical energy expression from the relativistic). Note that I am not including effects from potential energy fields, as this involves more complicated theories and mathematical constructions.

Ok, but now realize that if KE+E0=E=total mechanical energy, at least roughly speaking in the classical limit, E=mc^2 still. This means that as KE increases, m increases! So, if you really do have an extremely hot fluid (plasma), the mass of this ensemble would be significnatly increased. But then of course the temperatures are ridiculously high and you would feel these high-energy particles burning into you and your equipment, not being able to measure its mass by conventional methods. My understanding is that, in ordinary chemical reactions, the change in mass due to bond energy released from broken checmical bonds from high temperatures does alter the mass you measure, but this depends on the properties of the material and how precisely you are measuring.

All right. Now this applies to particles with mass. A photon does not have mass and so E is obviously not mc^2 because its energy is not zero. If the energy of light were zero you wouldn't have solar energy, photosynthesis, etc. E=hf according to Einstein, and this determines the energy of a photon.

So now the question is, how do relativistic collisions generate 'mass' from 'energy.' Though the specific particles I mention are not of consequence to the principle illustrated here, consider an electron and a positron (anti-electron) that are both moving very quickly relative to each other. Let us choose a center of momentum frame so that the momentum of the electron and the momentum of the positron are equal and opposite (analogous to the center-of-mass frame in Newtonian mechanics). If they are both moving at extremely high velocities they will have very large kinetic energy. But remember a large kinetic energy means a large relativistic ('total') energy, and thus a large relativistic mass. So now the two particles collide. Because of the rules of relativistic quantum mechanics (and more generally particle physics), if the sum of the relativistic energy of the two particles is large enough, it can create two more particles that are more massive (i.e. their rest masses are greater), provided that the relativistic energy is conserved. What will happen is that the resulting particles will have a lower momentum because the rest mass energy is larger than it was before the collision; E0 increases, so KE must decrease to maintain ~E0+KE=E (correctly: E^2=(pc)^2+(mc^2)^2 ). If you think in terms of relativistic mass, in fact there was really no mass generated at all during this process, because the total energy stayed the same and hence the total relativistic mass stayed the same (the two are proportional by c^2).

When you get to the quantum field theory of it, the pair annihilates to form a photon which then decays into other suitable particles, such as a muon anti-muon pair (chosen particularly to suit conditions in particle physics that I don't want to discuss). Note here that the photon is massless, which is not the case for more complicated interactions (with massive exchange particles). Then, the question is, how does the creation of a massless virtual photon change two particles with mass to something without mass, and then into two things with mass again? Recognize first of all that when these things "collide" or interact, they are on distance and time scales that are very small and due to the Heisenberg Uncertainty relation this a corresponding allowed increase in the uncertainty in the energy and momentum of the exchange particle, which really is why the exchange particle is 'virtual' in the first place. Note though, that no matter what, on large enough time scales for the Heisenberg Uncertainty Principle to be noncrucial, there is no violation of the conservation of energy, and hence there is no mass being 'destroyed' because energy and mass are equivalent. This is the main point.

Now if you want to go deeper and say, 'What do you mean, the particle pair generates a virtual photon that then sponataneously generates another particle pair with different rest mass?' This is a tough question. The way that quantum electrodynamics works as formulated today, it is a perturbative theory. When the electron and positron collide we don't know exactly what will come out. It's not like photosynthesis, where you just add light energy and you get what you want to get. There are certain probability amplitudes telling you what you are likely to get depending on how much energy you have. If you don't have enough relativistic energy to make a proton and an antiproton, you're just not going to make them (this is why we need ever-larger colliders to make ever-bigger particles). But if you do have enough energy, there's no telling whether you're going to make a proton & antiproton, muon & antimuon, quark & antiquark, etc. There are certain probabilities for each depending on various factors, but we cannot deterministically calculate what will result.

On a more fundamental level we do not even know what really 'causes' this 'generation' of mass; we do not know exactly what happens to the mass when matter and antimatter annihilate in the sense that we do not know about a specific mechanism we can use to predict and calculate what results from such 'generation' or 'destruction' of mass. But again remember, mass and energy are equivalent and energy is not destroyed. Truly, the conservation of energy-momentum is the most fundamental conservation law we have, and the day we lose that is the day we lose everything know about the way nature works.

So I think the answer to the original question was that we aren't just creating mass out of nowhere, there are certain conservation rules that must be respected, and these rules are what make creating a suitable mass-generation theory difficult and elusive.

 

[cesar314]

correction

The relativistic expression for the conservation of four-momentum should read:

E^2=(pc)^2+(m0c^2)^2

m0 is the rest mass. p is the relativistc momentum, which is gamma*m0v, gamma being

( 1-(v/c)^2 )^(-1/2)

 

[cdm1a23]

Wow, ok my head is kind of reeling after trying to "catch up" with this thread. So, a quick clarifying question if anyone understands this better than me. Do we currently know of a process that converts pure energy (not energy and mass interacting) into mass?

Also something else just came to mind. Are we sure that there is any difference between energy and mass, and if so, how do you specifically define that difference? I ask because I have heard about gravitons and the search for their existence. Would this mean that gravity is an actual physical thing if the existence of gravitons was found to be correct?

Thanks again to everybody for all the answers. This is very interesting.