How exactly does energy become 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

 

[lightarrow]

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

What do you mean with inertial mass of a photon?

 

[Dmitry67]

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

Yes, the missing mass is carried away by the photons (goes away with their mass)
If for some reason it is not possible the helium, created in fusion is so hot, so nuclei are moving so fast that they are heavier. In any case total mass is conserved.

 

[Phrak]

What do you mean with inertial mass of a photon?

You've heard of light sails, right? Photons have inertia. They exert a force on the sail. I turn, the sail changes the momentum of the photon. Bounce enough light off a scale, it will measure an applied force.

 

[lightarrow]

You've heard of light sails, right? Photons have inertia. They exert a force on the sail. I turn, the sail changes the momentum of the photon. Bounce enough light off a scale, it will measure an applied force.

This has to do with momentum, not mass.

 

[Phrak]

This has to do with momentum, not mass.

No. The OP asked about energy and mass as defined in this: $$E=mc^2$$.

Physis is an experimental science. How do you measure this mass, m

$$m=\frac{E}{c^2}$$​

?

 

[lightarrow]

This has to do with momentum, not mass.

No. The OP asked about energy and mass as defined in this: $$E=mc^2$$.

But it doesn't interest me, I answered to your claim that a light sail works because of photons inertial mass. Photons don't have mass.

Physis is an experimental science. How do you measure this mass, m

$$m=\frac{E}{c^2}$$​

?

That equation doesn't apply to photons...

 

[Dmitry67]

What the ... ?

http://en.wikipedia.org/wiki/Photon

E=mc**2 is still applicable to photons,
as E=hv then M=hv/c**2

Photons are 'massless' because they do not have rest mass, but the do carry mass when threy move.

 

[DrGreg]

I think it's necessary to remind some participants that there is more than one definition of "mass" in relativity.

- invariant mass, or rest mass, or proper mass, which excludes the kinetic energy of the object's centre of momentum
- relativistic mass, sometimes called inertial mass, which includes the kinetic energy of the object's centre of momentum.

Be sure you know which sort of mass is being talked about.

Most modern physicists use "mass" to mean "invariant mass" but some people use "mass" to mean "relativistic mass".

Photons have zero invariant mass, but non-zero relativistic mass. The quoted Wikipedia article on the photon refers only to invariant mass, which is described simply as "mass", consistent with modern usage.

Whichever definition you choose, mass is a form of energy, like other forms such as kinetic energy, potential energy, heat energy, sound energy, etc. So mass doesn't get converted into energy, but it can be transformed from mass-energy to some other form of energy. The total energy from all sources (as measured by a single observer) remains constant.

 

[lightarrow]

What the ... ?

http://en.wikipedia.org/wiki/Photon

E=mc**2 is still applicable to photons,

No, because a photon's mass is zero, but its energy is not, so that equation is wrong. The correct one (always valid, in a flat spacetime) is:

E^2 = (mc^2)^2 + (cp)^2

p = momentum. For a photon m = 0, so E = cp.

Photons are 'massless' because they do not have rest mass, but the do carry mass when threy move.

What you call rest mass is better called invariant mass and this is the only meaningful concept of mass in SR.

 

[Dmitry67]

lightarrow, again, depending on what you call a mass.

I have 1kg of matter and 1kg of antimatter.
I annihilate them and get a huge flash of light.
There is no hardronic matter left.
(lets forget about the neutrino) do you agree that the total mass of light flash is 2kg?

 

[Dale]

Regarding "pure energy". I don't think it is important, but I would say that mass at rest is "pure energy", not light. If you look at the four-momentum you see that energy is the timelike component and momentum is the spacelike component. So mass at rest is (m₀c,0) which is purely energy, while a photon is (p,p) which is energy that is "maximally contaminated" with momentum.

 

[lightarrow]

lightarrow, again, depending on what you call a mass.

I have 1kg of matter and 1kg of antimatter.
I annihilate them and get a huge flash of light.
There is no hardronic matter left.
(lets forget about the neutrino) do you agree that the total mass of light flash is 2kg?

Yes, but only because in this case p = 0 (or you can always find a ref. frame where it's 0). For a *single* photon that's false and the mass is exactly zero.

 

[Phrak]

Apples and Oranges

Tomatoes and Potatoes

$$E^{2} = m_{p}\!^{2} c^{4} + c^{2}p^{2}$$
$$E = m_{i}c^2$$

$$m_{i}$$
and
$$m_{p}$$
are not the same vegetable.

 

[lightarrow]

Tomatoes and Potatoes

$$E^{2} = m_{p}\!^{2} c^{4} + c^{2}p^{2}$$
$$E = m_{i}c^2$$

$$m_{i}$$
and
$$m_{p}$$
are not the same vegetable.

There is only one kind of mass in SR.

 

[cesiumfrog]

There is only one kind of mass in SR.

lol. And I suppose you wish to assert that it is the "rest" kind, rather than the "relativistic" kind?

 

[lightarrow]

lol. And I suppose you wish to assert that it is the "rest" kind, rather than the "relativistic" kind?

just a few posts before (n.59) I said it's better called "invariant" mass.
You are one of those who still talk about relativistic mass?

 

[cesiumfrog]

I said ..

You said it, but that doesn't make it so.

I think rest mass is a good clear term because it describes what you would measure (the mass of the thing when it is at rest) and the manner in which it is distinguished from its natural alternative (the resistance of the thing to any applied forces, i.e., inertial mass dp/adt). I don't object to you calling it invariant mass but don't find it better since, as well as that term being less common in the literature, it strikes me as inelegant since invariant mass (of a potato say) does vary - with temperature (for example).

Personally, I still like the concept of inertial (frequently called relativistic) mass because it:

• retains the classical meaning (inertia)
• sums additively (as is familiar).
• admits an elegant explanation of the most important equation in popular culture (identification of mass and energy as opposed to "no, stuupid, that equation needs to rewritten more complicated, with more squares and a momentum term..")
• was convenient in introducing SR (the transformation of the mass concept is the same as for time and length, and the dilation intuitively refutes acceleration past light-speed)
• is the charge corresponding to space-time symmetry (another link to momentum, of which we also have a classical notion).

Granted, my arguments are pedagogical/theoretical (why use the term rest-"mass" for something that behaves more differently from the classical notion of mass?) and there don't seem to be many practical applications where relativistic mass is more convenient (whereas rest mass is obviously appropriate for cataloguing fundamental properties in particle physics and so I accept that it is the one most frequently abbreviated as just "mass") but, given reality, it is ignoble to say mass has "only one kind" of meaning.

 

[bernhard.rothenstein]

I think it's necessary to remind some participants that there is more than one definition of "mass" in relativity.

- invariant mass, or rest mass, or proper mass, which excludes the kinetic energy of the object's centre of momentum
- relativistic mass, sometimes called inertial mass, which includes the kinetic energy of the object's centre of momentum.

Be sure you know which sort of mass is being talked about.

Most modern physicists use "mass" to mean "invariant mass" but some people use "mass" to mean "relativistic mass".

Photons have zero invariant mass, but non-zero relativistic mass. The quoted Wikipedia article on the photon refers only to invariant mass, which is described simply as "mass", consistent with modern usage.

Whichever definition you choose, mass is a form of energy, like other forms such as kinetic energy, potential energy, heat energy, sound energy, etc. So mass doesn't get converted into energy, but it can be transformed from mass-energy to some other form of energy. The total energy from all sources (as measured by a single observer) remains constant.

I think that each physicist has his own problems with mass, energy and momentum in special relativity theory. Because I have no physicists next room to me, please consider my own problem. Equation m=gm(0) (1) (m relativistic mass, m(0) rest mass, g Lorentz factor) is derived in many textbooks and papers but we can consider that it is the equations that fits best experimental results. Multiply both its sides by c in order to obtain
cm=cgm(0) (2).
Even if cm and cm(0) have the physical dimensions of momentum they have no physical meaning because tardyons could never reach the speed c.
Multiply both its sides’ by cc in order to obtain
ccm=ccgm(0 ). (3)
ccm and ccm(0) have the physical meaning of energy. Introducing the notation E=ccm for relativistic energy and E(0)=ccm(0) for rest energy (3) becomes
E=gE(0) (4)
Equations (3) and (4) tell us that mass and energy have the same physical properties in special relativity theory among others they conserve.
Consider a high sensitivity balance. Put on its pans identical bodies the balance being in a state of equilibrium. Irradiate with electromagnetic energy one of the two bodies for a given time interval. Stop the irradiation after a given time interval and you will see that the balance is inclined at the side where the irradiated body is located. Using usual terminology we could say that the irradiated body has received energy from the radiation and that its mass has increased. But we could also say that that the body has received energy and its energy has increased or that the electromagnetic energy gave up mass which contributed to the increase of the mass of the irradiated body.
Please tell me if I have interpreted correctly your point of view.

 

[jostpuur]

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

What do you mean with inertial mass of a photon?

You've heard of light sails, right? Photons have inertia. They exert a force on the sail. I turn, the sail changes the momentum of the photon. Bounce enough light off a scale, it will measure an applied force.

The response to lightarrow should have been, that the comment was about inertial mass of several photons, not of a single photon.

Or was the comment about inertial mass of several photons? At least I interpreted it like that. On the other hand I was trying to interpret it so that it is right. An appropriate approach IMO, compared to the opposite one, in which interpretable claims are interpreted so that they are wrong.

 

[lightarrow]

The response to lightarrow should have been, that the comment was about inertial mass of several photons, not of a single photon.

Yes, several photons and *not traveling in the same direction*. If he talks about light sails, it's more about photons traveling in the same direction than the other way round.