How exactly does energy become mass?

[Quantum_Grid]

How exactly does energy "become" mass?

In Einstein's equation E=mc² or more sepcifically the "inverse", m=E/c², how exactly does mass "become" energy? I [vaguely] understand how energy may be released from mass, but how would mass come about from just energy?

Maybe this question is unanswerable, or maybe I'm not asking it correctly.

If its unanswerable in a few paragraphs, any suggestion on books that may be relevant to my question would help too.

 

[DaveC426913]

When two particles fuse, such as in the heart of stars, their combined mass is greater than their separate mass.

More later.

 

[Quantum_Grid]

Thanks. My question was in relation to the theory on the origin of mass, or more specifically F. Wilzcek's description of the compromise between gluon field energy and and quark localization energy; and their resulting residual energy. How does this energy translate into mass?

 

[malawi_glenn]

Mass is one form of energy, there is no such thing as "pure" energy.

you have already asked this question in quantum forum.

 

[Quantum_Grid]

Yeah, sorry, I was hoping to get a more specific reply than I had over there. I guess I'll just try the library. Thanks for your help, though!

--edit: I'll search around the forums here for one too...

 

[malawi_glenn]

so what is wrong with the answers given by us?

(same guys in these forums, so no need for double posting)

 

[Quantum_Grid]

so what is wrong with the answers given by us?

(same guys in these forums, so no need for double posting)

Your right, won't happen again, sir! I didn't see your post describing mass as a form of energy, that does help clarify it a little.

I am starting physics as a major this semester in school, so I guess it will all come to me in time!

Thanks again for your input.

 

[JANm]

In Einstein's equation E=mc² or more sepcifically the "inverse", m=E/c², how exactly does mass "become" energy? I [vaguely] understand how energy may be released from mass, but how would mass come about from just energy?

Perhaps you should try to look into the mass velocity relation. If a mass has higher velocity then the mass equivalent of the extra energy is added to the mass.

 

[yuiop]

Mass is one form of energy, there is no such thing as "pure" energy.

you have already asked this question in quantum forum.

Given that relativistic mass is not recognised in modern textbooks and only the invariant rest mass of a particle is considered as mass, is a photon not "pure" energy?

 

[Denton]

When two particles fuse, such as in the heart of stars, their combined mass is greater than their separate mass.

More later.

You mean their separate masses are greater than their combined mass. The difference in mass is released as energy.

 

[DaveC426913]

You mean their separate masses are greater than their combined mass. The difference in mass is released as energy.

Not always, no. Depends on what the reaction is. Certainly, we prefer fusing hydrogen into helium because that releases energy, which is useful to us.

But pick the particles right and it works the other way. Fuse barium and krypton to get uranium, you will actually gain mass.

Stolen from http://en.wikipedia.org/wiki/Nuclear_fusion" for brevity:
"The fusion of two nuclei with lower mass than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy"

 

[Phrak]

Given that relativistic mass is not recognised in modern textbooks and only the invariant rest mass of a particle is considered as mass, is a photon not "pure" energy?

The OP question is about the stuff that depresses a scale; about that stuff that resists accelleration.

 

[malawi_glenn]

is a photon not "pure" energy?

why should it be? What is the definition of "pure" energy? I am a master student, but still never heard of it.

 

[DaveC426913]

why should it be? What is the definition of "pure" energy? I am a master student, but still never heard of it.

Aren't we describing electromagnetic radiation here?

 

[jambaugh]

Mass is bound energy they are (in GR and SR) exactly the same thing with different units.

If for example you could measure accurately enough, the energy stored in a compressed or stretched spring would give it slightly more weight and inertial mass than that of a relaxed spring. But also as has already been mentioned...

The net difference in energies between the components of an atom (separate electrons, protons and neutrons) and their bound atomic form all add up if you 1.) equate mass and energy with unit conversion: E=mc^2 and if you 2.) take into account the binding energies.

Note that you must account for those binding energies = masses as they are what gives say a block of carbon its weight and inertia as compared to that of the constituent protons neutrons and electrons.

 

[Naty1]

Nobody knows "exactly"...heck nobody knows "exactly" what mass or energy is..where it comes from,etc. But we can describe a lot of their characteristics.

A completely different way of looking at an answer to your question: strings! In string theory mass is one type of energy vibration, energy is simply another form of vibrating energy. And different partciles (masses) have different vibrational modes...

Regarding classical mass and energy conversion: we are really poor at converting either to the other...fission/fusion for example only releases a tiny portion of the available energy... is it maybe 1% or so mass that is converted in bombs?? Likely less in power reactors...

"We know a lot, we understand little."

 

[malawi_glenn]

Aren't we describing electromagnetic radiation here?

nope the general question was "how exactly does mass "become" energy?"

One guy claimed that photons, electromagnetic waves, are "pure" energy. But where is such definition stated and motivated?

To me, photons are one form of energy, mass is one form of energy. Energy can not be created or destroyed, only converted into different forms.

Look at the electromagnetic field, and the energy equations from SR:

E = \hbar \omega photons

E = c^2 m_0 rest-energy for massive particles

Now how does one see that photons are "pure" energy? The field is described by an angular frequency (omega). Working in units where c = 1, mass has same units as energy. Working in units where hbar = 1, omega has same units as energy.

Why do we have to work in SI units? It is just that we are used to it and take it for granted.

 

[Quantum_Grid]

Thanks a lot for all your responses guys, this is fascinating stuff! I can't wait to start studying this in college this year.

Nobody knows "exactly"...heck nobody knows "exactly" what mass or energy is..where it comes from,etc. But we can describe a lot of their characteristics.

A completely different way of looking at an answer to your question: strings! In string theory mass is one type of energy vibration, energy is simply another form of vibrating energy. And different partciles (masses) have different vibrational modes...

Regarding classical mass and energy conversion: we are really poor at converting either to the other...fission/fusion for example only releases a tiny portion of the available energy... is it maybe 1% or so mass that is converted in bombs?? Likely less in power reactors...

"We know a lot, we understand little."

Interesting, I think "we don't know", inspires me to seek out the real answers more than anything else. I'm a little wary of string theory, but I won't get off topic with that.

Thanks again for all the interesting replys!

 

[Quantum_Grid]

... To me, photons are one form of energy, mass is one form of energy. Energy can not be created or destroyed, only converted into different forms...

The "To me..." actually clarifies your original answer even more. Thanks again.

 

[malawi_glenn]

The "To me..." actually clarifies your original answer even more. Thanks again.

Well the "To me" is there just because I don't have it written in stone somewhere like "the 10 commandmends of physics". I am just trying to argue that it is ridicolous to call photons "pure" energy.

 

[JANm]

The OP question is about the stuff that depresses a scale; about that stuff that resists accelleration.

Photons do indeed not accelerate, but they travel (sometimes) vast distances almost indistructable apart from full absorption. A little bended and a little gravitationally shifted that is all. So perhaps not pure energy but indeed the purest energy we know...

 

[malawi_glenn]

Thanks a lot for all your responses guys, this is fascinating stuff! I can't wait to start studying this in college this year.



Interesting, I think "we don't know", inspires me to seek out the real answers more than anything else. I'm a little wary of string theory, but I won't get off topic with that.

Thanks again for all the interesting replys!

Aslo beware that some things we don't know since we CAN'T know them.
Studying some kind of philosophy is quite fruitful when doing fundamental physics.

 

[malawi_glenn]

Photons do indeed not accelerate, but they travel (sometimes) vast distances almost indistructable apart from full absorption. A little bended and a little gravitationally shifted that is all. So perhaps not pure energy but indeed the purest energy we know...

Define "pure" and "pureness"...

I asked one guy that question, think it was yesterday, and he said that pure energy is energy which is not attached to mass.. that was why I somewhat repeted the answer I gave him here in this thread.

 

[Quantum_Grid]

Aslo beware that some things we don't know since we CAN'T know them.

Maybe this is diverging off the topic a little, but I'll ask it anyway:

How could you possibly know that it is impossible to KNOW something like that? Couldn't it just be that we don't YET know?

Feel free to ignore that if its too off-topic, but now I'm interested, I'll post a new thread otherwise!

 

[malawi_glenn]

Well it is just basic philsophy of knowledge.

Our mind is limited.

 

[Phrak]

Photons do indeed not accelerate, but they travel (sometimes) vast distances almost indistructable apart from full absorption. A little bended and a little gravitationally shifted that is all. So perhaps not pure energy but indeed the purest energy we know...

A) How did "pure energy" get mixed up into this?

B) I'd be hard pressed to describe the angular momentum of a photon as pure energy.

C) Light propagating in anisotropic media will accelerate tangentially.

 

[JANm]

B) I'd be hard pressed to describe the angular momentum of a photon as pure energy.

C) Light propagating in anisotropic media will accelerate tangentially.

Answer/Question to B) Angular momentum not as a linear function you mean of course?

Answer/Question to C) Is that not by absorbsion and re"emission?

 

[yuiop]

nope the general question was "how exactly does mass "become" energy?"

One guy claimed that photons, electromagnetic waves, are "pure" energy. But where is such definition stated and motivated?

The title of the thread is the reverse. (How exactly does energy "become" mass?)

To answer that question we first need to define what we mean by the terms mass and energy. General we associate mass with the properties of influencing a gravitational field and with having momentum, but a photons can have both those properties and yet it is often stated that a photon is massless. The only form of mass that is officially recogised is rest mass. A single photon has no rest mass, because it can not be identified with an inertial rest frame.

Wikipedia says this:

"Matter creation is the process inverse to particle annihilation. It is the conversion of massless particles into one or more massive particles. This process is the time reversal of annihilation. Since all known massless particles are bosons and the most familiar massive particles are fermions, usually what is considered is the process which converts two bosons (e.g. photons) into two fermions (e.g., an electron-positron pair).

Photon pair production Because of momentum conservation laws, the creation of a pair of fermions (matter particles) out of a single photon cannot occur. However, matter creation is allowed by momentum conservation law when in the presence of another particle (it may be another photon or other boson, or even a fermion) which can share photon's momentum. Thus, matter can be created out of two photons, for example (this is the process inverse to annihilation)."

I think the above article is what the OP is getting at. How can photons with no rest mass be turned into particles and anti-particles with rest mass?

The article identifies photons as bosons which are defined as massless particles. If a photon is massless and yet has energy, can it not be described as pure energy?

It also defines fermions as matter particles. In other words they have a property that photons do not have. Namely, the property of having mass. Mass is in effect energy that is confined and for which a rest frame can be identified. All particles that have no mass have to travel at the speed of light and all particles that have mass, can not travel at the speed of light and that is the main distinction between pure energy and mass.

To me, photons are one form of energy, mass is one form of energy. Energy can not be created or destroyed, only converted into different forms.

While no one will argue with fact that energy can not be created or destroyed, it can also be said that rest mass can not be created or destroyed either. For example if a nuclear bomb is detonated, the rest mass of the system is the same before and after the nuclear bomb detonated, just as the total energy of the system is the same before and after the bomb detonated. What changes is the nature of individual particles. Some individual particles that had the property of rest mass before the explosion, now have the property of being able to travel at the speed of light and not having an identifiable rest frame as an individual particle. Just to make things clear as to why the rest mass of the system is the same before and after the detonation, it should be made clear that that a pair of photons going in opposite directions, can have an identifiable rest frame (and associated rest mass) as a pair, in which their total momentum is zero.

 

[yuiop]

How could you possibly know that it is impossible to KNOW something like that? Couldn't it just be that we don't YET know?

Check out Godel's incompleteness theorem if you want to investigate further.

 

[Quantum_Grid]

Thanks kev, very helpful input! I will def. check out Godel.

 

[yuiop]

I guess that malawi glenn is right, that the term "pure energy" is not a very useful term, in the context that everything, including particles with rest mass, is pure energy. In other words particles with rest mass are not a mixture of energy and "something else". A more useful term might be something like unbound energy to describe a massless particle and bound energy to describe particles with rest mass or the effective additional mass in a spring due to tension or the binding energy of inside the nucleus of an atom for example.

 

[Phrak]

"How exactly does energy become mass?"

Can this be answered exactly? There is potential energy, kinetic energy, heat energy, the energy of a particle as a function of wavelength made uncertain by it's bandwidth, gravitational potential energy, static electric potential energy, whatever it is from the weak and strong forces... Can one answer exactly cover them all?

 

[malawi_glenn]

kev: Sure the TITLE of the thread is "energy "become" mass", but look at his first post, the question is reverse:"how exactly does mass "become" energy".

Matter creation can be viewed as just an energy transformation. Recall that terms like "annihilation" is not used properly when describing physics.

My elude on "energy can not be created or destroyed", is one way to see that photons are energy, mass are energy and so on. Quantifying things like "pure" "purest" without specifying, we have not done anythink useful for science I guess the Vienna Circle would scream at us "faul!" ;-)

Godel's theorem should be standard to learn in all (not at least physics) educations.

 

[t-money]

KEV I believe you have hit the head on the nail. Bound energy vs unbound energy that is what is used in quantum mechanics to describe energy at least in the textbooks I have read. I have always thought energy is just a relationship between mass inversely related with c^2.It is what it is nothing more or less.

 

[DaveC426913]

KEV I believe you have hit the head on the nail. Bound energy vs unbound energy that is what is used in quantum mechanics to describe energy at least in the textbooks I have read. I have always thought energy is just a relationship between mass inversely related with c^2.It is what it is nothing more or less.

You're kind of missing the point though. "Relationship" is an ambiguous term. Clearly, matter and energy are two different things, in that we percieve them, measure them and treat them in definably different ways (even they are, at their core, the same thing). And they can be converted into each other. The OP simply wishes to understand the process by which energy is converted to mass.

 

[Quantum_Grid]

The OP simply wishes to understand the process by which energy is converted to mass.

Thank you, at least a FEW of you understood! ;)

 

[malawi_glenn]

But as I, and others, have argued -> talking about such "process" is synthetic and diffuse, mainly because a distinction between "mass" and "energy" must first of all be made.

Secondly arguments that mass is one FORM of energy have been made, and energy can only be converted into several forms - such a thing as "pure energy" does not exist (?)

 

[Quantum_Grid]

I think I understand what you're saying, but I feel I have to repeat DaveC -

Clearly, matter and energy are two different things, in that we percieve them, measure them and treat them in definably different ways (even [if] they are, at their core, the same thing)

I see what you are saying in that at a very "basic" level they ARE the same thing, but...
...I don't know, maybe I was just hoping for a different answer, whatever that is! Thanks again mg, you ARE helping, even if it still hard for me to grasp what you are trying to explain to me.

 

[malawi_glenn]

Maybe this helps you: Think of energy as a property of matter, not an entity itself.

 

[Naty1]

Fuse barium and krypton to get uranium, you will actually gain mass.

This can't actually be done, right? or can it?? In other words, is this a theoretical statement or a practical one as well??

 

[DaveC426913]

This can't actually be done, right? or can it?? In other words, is this a theoretical statement or a practical one as well??

I picked those two because they are the byproducts of uranium fission. So, you could reverse the process.

Can we fuse heavy elements in a lab? Maybe, maybe not. But stars sure can. That's how we got uranium in the first place! All elements heavier than H were formed by fusion.

 

[DaveC426913]

Maybe this helps you: Think of energy as a property of matter, not an entity itself.

? Are you saying you can't have energy without matter??

 

[malawi_glenn]

? Are you saying you can't have energy without matter??

No, not really exactly, but I have never encountered anything like "pure" energy.

What is "pure" energy dave?

I cannot see energy as an entity that can be separated and be observed as "pure energy".

 

[JANm]

The only form of mass that is officially recogised is rest mass. A single photon has no rest mass, because it can not be identified with an inertial rest frame.
/QUOTE]
Photons indeed have no restmass, but not for that reason. GR and ST both concur that all physics within an inertial frame are the same. They move with velocity c with respect to any such frame, so there cannot be an inertial comoving frame for photons.

Always thought that the term inertial rest frame was used for the one derived from the backgroundradiation.

 

[Naty1]

"How exactly does energy become mass?"

Can this be answered exactly? There is potential energy, kinetic energy, heat energy, the energy of a particle as a function of wavelength made uncertain by it's bandwidth, gravitational potential energy, static electric potential energy, whatever it is from the weak and strong forces... Can one answer exactly cover them all?

Yes and I might be able to do it in one word: unification! (when we get that far.)

Currently we don't know enough about matter,energy,time,space,etc,..to REALLY answer
the original question(s) ...maybe the unification of relativity and quantum theory will provide that. At the "start" it appears they are all the same entity, and the different forms of energy as well all unified, at the moment of the creation of the universe: call it the big bang or big jump or whatever you want. If we really knew about that we might know more precisely how they are all related.
But that's a tall order as it apparently came from "empty" space, maybe from nothing! a mere quantum fluctuation??

Once that extremely high energy and extremely unstable initially unified state went through inflation and a far more stable, lower energy and more slowly "dying" universe emerged (the one we live in) everything now "looks" different. Yet via mathematics we have been able to unify the strong and weak and electromagnetic forces...only gravity remains "untamed".

Alchemy was the middle ages pseudoscience of converting one material into another...we still don't know how to do that in most cases...A few light elements from the original bang are synthesized by stars to make all elements up to iron...with the collapse of larger stars supernova can then produce nearly all the heavier elements...but we can't do most of that.

and to the OP: don't dismiss string theory because it's mathematics, while largely incomplete, offers tantalizing insights...string theory mathematics can be fabricated to elicit strings (to compose bosons and fermions, etc) and in turn these strings can be formulated to emerge as space via Penrose Spin Networks...so there are fascinating elements of unification here...not just mass and energy but perhaps space as well!...come to think of it, time may be missing as a basic ingredient in string theory, unlike relativity, which provides some integration.

 

[JANm]

Some individual particles that had the property of rest mass before the explosion, now have the property of being able to travel at the speed of light and not having an identifiable rest frame as an individual particle.

Rubbish. How many rest frames do you need with this kind of physics?

 

[Nickelodeon]

Re: How exactly does energy "become" mass?

by accelerating it.

 

[JANm]

Wow, a lot of reading work to come at the end of this thread. Sometimes it is getting highly filosophical, sometimes redrawn to the main subject.
Two examples:
1) Birth of a star from/in a hydrogen cloud; gravitational potential energy is transformed in macro- and microscopic kinetic energy. I.e velocity of the molecules gets bigger and the mass velocity relation explains how much...
2) A photon is absorbed by a hydrogen atom in ground state and the hydrogen atom is in exited state; the electron gone to a higher orbit. Thus electro potential has risen. The exited state atom is heavier then the groundstate atom. How much? Del m= hf/c^2.
Two examples of how energy increases mass...

 

[Phrak]

You did ask about the mass in Einstein's mass-energy equation--rather than the particle mass. In addition, this is the Relativity Folder where mass is poderable mass--inertial mass.

It's the mass referred to in / E=mc^2

In this context, the measurable mass never goes away. Mass doesn't change into in energy, the energy changes form. Mass remains constant.

When an atomic bomb ignites it looses mass. The mass increases to where is energy is transported, and becomes heat energy. This energy increases the mass of the material that absorbed it. The mass doesn't go away. It changes local.

Where this energy from an atomic blast may be captured and stored in an organized form, it becomes potential energy, increasing the mass of the material storing the kinetic energy. The mass changes local.

This is not inconsistant with particle physics, nor energy in transit as photons. Measure the photons on a scale, they have inertial mass.

 

[feynmann]

When two particles fuse, such as in the heart of stars, their combined mass is greater than their separate mass.

More later.

Isn't that true their combined mass is Less than their separate mass. e.g. mass of helium atom is less than the sum of 2 neutrons and 2 protons.
It's called mass defect, extra mass is converted to energy