Can energy be created/destroyed in quantum physics(I need experts)?

[No-where-man]

According to quantum physics energy only exists in small pockets of energy called quantum-or something like that,I personally don't know qunatum physics,that's why I need an expert.
The law of energy conservation is wrong according to quantum theory of physics?

 

[Kruger]

Yes, energy can be created from nowhere for a short amount of time cause of Heisenberg's uncertainty principle. The particle that are created are called "virtual particles" and are always created in pair because of conservation laws (charge, ...). Energy conservation can be violated for short times and this happens all the time. In the same way we can describe interactions in quantum electro dynamics. The hawking effect is based on this energy creation and destruction.

Watch in google, or wikipedia for:
Heisenberg's uncertainty prinziple
Energy-time uncertainty
virtual particles

 

[marlon]

The particle that are created are called "virtual particles" and are always created in pair because of conservation laws (charge, ...).

Actually, virtual particles are inherent to QFT not QM. When going from an initial state to a final state we describe the actual transition in terms of a sequence of virtual states. These are like a bridge between the initial and final state. These states are a consequence of perturbationtheory and are virtual because indeed they do not obey energy conservation during a short amount of time. That is why these states don't have long lifetimes. Energy conservation is respected between initial and final states but not inbetween. In field theory, the analogon of these virtual transition states are virtual particles because vibration of fields corresponds to particles. But again, that last interpretation is a QFT thing NOT a QM thing

marlon

 

[Kruger]

We have to differ from two things now.
marlon you describe the way particle exchange forces (spoken in simple language)
and I think of the particles that take there energy from "nowhere". Consider for example the "hawking radiation". You see what I mean?

 

[marlon]

We have to differ from two things now.
marlon you describe the way particle exchange forces (spoken in simple language)
and I think of the particles that take there energy from "nowhere". Consider for example the "hawking radiation". You see what I mean?

you are making two mistakes here. First of all, virtual particles only arise in QFT because of second quantization. The mere fact that a change in vibrational modes of a field (you know going from energy level 1 to level 2) corresponds to a particle of certain momentum and energy is a QFT thing.

Secondly, in QFT, virtual particles can arise in two distinct and completely different ways. You are mixing these two ways. Virtual particles can arise as the force mediators between matter particles. In this case they carry a distinct momentum value and due to HUP, they are everywhere in space (not in spacetime!). These are the analogon of what we call virtual transition states in QM, because these virtual particles also directly arise from perturbation theory in QFT. Then, you have the vacuum fluctuations or the zero point energy (ZPE). These two ways of 'generating' virtual particles are totally different in nature...That is my point

marlon

 

[dextercioby]

Hawking radiation is made up of real photons.

Daniel.

 

[vanesch]

The law of energy conservation is wrong according to quantum theory of physics?

I think it is correct to say that in quantum theory, there is strict energy conservation between the initial prepared state and the final observed state. However, in the *calculation* you can encounter intermediate ("virtual") states which do not respect energy conservation. But that's just a way to solve the time evolution problem.

cheers,
Patrick.

 

[Kruger]

Then, you have the vacuum fluctuations or the zero point energy (ZPE). These two ways of 'generating' virtual particles are totally different in nature...That is my point

I see marlon. But the vacuum fluctuation is a result of energy time uncertainty and the zero point energy is a result of momentum position uncertainty. And vacuum fluctuation is the case where virtual pair are created and these pair annihilate after a short time. The ground state field is always there.

 

[El Hombre Invisible]

Energy conservation following Hawking radiation... I think I read years ago in that bastion of semi-interested science readerships A Brief History Of Time that one of the pair is negative energy and the other is positive energy. Is this true? What the heckfire is negative energy anyhoo?

 

[selfAdjoint]

Energy conservation following Hawking radiation... I think I read years ago in that bastion of semi-interested science readerships A Brief History Of Time that one of the pair is negative energy and the other is positive energy. Is this true? What the heckfire is negative energy anyhoo?

No. One of them is a regular particle and the other is its antiparticle. They both have positive energy but their charges, if any, and spins, if any, are opposite.

 

[Kruger]

@Self Adjoint: For this negative energy question we have to look with which theory we word. According to Dirac's hole theory positrons are holes in the negative energy sea. And according to QFT or QM (I'm not sure which theory) the positron has negative energy and a negative velocity and thus a positive energy. You see what I mean?

 

[Kruger]

Sorry, I have a little problems with a something:

Is the vacuum state of the em-field (energy: E=h(bar)w/2) a product of virutal particles or is it a product of momentum-position uncertainty?

please, need help.

 

[El Hombre Invisible]

How can energy be conserved if Hawking radiation is possible? (The answers probably that my understand is so far off it ain't even funny.) If a virtual particle can break the laws of energy conservation for a short period of time, but in that time the black hole attracts one of the pair and the other is flung off to maintain momentum, and both have positive amounts of energy, then the amount of energy both in the black hole and the space outside has increased. Also, when I read it he did not seem to be talking about matter/antimatter. In fact, I thought Hawking radiation was somewhere in the x-ray dept. But then maybe my memory is just screwed.

 

[Chi Meson]

I think what Hombre is referring to is the "evaporation" of a black hole. I have also read that the drawn-in particle consists of "negative energy" which annihilates with the energy of the singularity. This way the emmitted Hawking radiation is balanced by the loss of mass/energy in the interior. (I *know* something is wrong here, I'm seeking clarification).

Is the "evaporation" of a black hole still a valid theory? (My mantra is "I graduated such a long time ago.")

 

[vanesch]

Is the "evaporation" of a black hole still a valid theory? (My mantra is "I graduated such a long time ago.")

Dunno what's in vogue, I'd think it is still the case.
But I find it rather peculiar that people jump at such hypothetic and badly understood phenomena to illustrate *quantum theory*. Hawkin radiation and black hole evaporation are educated guesses of results a future quantum gravity theory should be able to answer clearly, by mixing stuff from general relativity and quantum field theory.
Why take such examples ?
How about talking about a radiating atom ?

cheers,
Patrick.

 

[wangyi]

I think it is correct to say that in quantum theory, there is strict energy conservation between the initial prepared state and the final observed state. However, in the *calculation* you can encounter intermediate ("virtual") states which do not respect energy conservation. But that's just a way to solve the time evolution problem.

cheers,
Patrick.

in QFT there is a \delta^4(\sum p) on each vertex. i think this means conservation of energy is respected everywhere, not only the initial and final state, but also intermediate states. (on condition that you still take p^0 as energy). I think the "virtual" only indicates that it does not satisfy the E^2=p^2+m^2 relation, so the energy can be conservationally passed to other particles freely on condition that the time period is short.

But i do not have full confidence on by opinion, and waiting for your idea:)

regards
wangyi

 

[wangyi]

Say something on my view of Hawking radiation,
first, black holes do not only radiative photon, but all kinds of particles(see,eg,gr-qc/0406017).
second, the particle pair in Hawking radiation is particle and antiparticle, but also,
they are positive and negative energy ones. because their four-momentum sum is zero.
third, we can not say it do not respect energy conservation. because in our point of view, we see the black hole give out positive-energy particles, and then it gets smaller, i.e. less energy. in the point of view of person inside the black hole, they think the black hole has eaten a particle with positive energy(because the x and t changes in black hole), and the black hole gets larger. As the two people can never tells each other, they think energy is conserved(here i have a question: what if the observer outside run fast into the black hole and tells the one inside the black hole)
fourth, in GR, energy is questionable.

cheers
wangyi

 

[Rebel]

Say something on my view of Hawking radiation,
first, black holes do not only radiative photon, but all kinds of particles(see,eg,gr-qc/0406017).
second, the particle pair in Hawking radiation is particle and antiparticle, but also,
they are positive and negative energy ones. because their four-momentum sum is zero.
third, we can not say it do not respect energy conservation. because in our point of view, we see the black hole give out positive-energy particles, and then it gets smaller, i.e. less energy. in the point of view of person inside the black hole, they think the black hole has eaten a particle with positive energy(because the x and t changes in black hole), and the black hole gets larger. As the two people can never tells each other, they think energy is conserved(here i have a question: what if the observer outside run fast into the black hole and tells the one inside the black hole)
fourth, in GR, energy is questionable.

cheers
wangyi

Sorry, but I don't know how can you talk about a person " thinking " inside a black hole and the observer to " run fast into the black hole " - to tell the other one- , nor the x and t changes in the black hole, can anyone tell me if some (and wath) of this has any sense? Maybe the only intriguing question to me is really about that of the x and t changes and giving an positive amount of energy inside.

 

[jackle]

...Hawkin radiation and black hole evaporation are educated guesses...

I thought Hawkin radiation had been observed?

I also thought that energy is uncertain in quantum physics for real particles as a consequence of entanglement with time. As I remember, energy is always conserved as long as you discard unthinkably unlikely events and don't introduce unthinkably short fractions of time.

 

[vanesch]

I thought Hawkin radiation had been observed?

I'd be surprised :-)

cheers,
Patrick.

 

[jackle]

I must be wrong about H.R. having been observed.

I want to stick by my second paragraph. Energy of real particles is uncertain but energy is still conserved in QM as long as statistically implausible outcomes are ignored and we steer clear of durations that are short enough to frighten ordinary people into submission?

 

[selfAdjoint]

I must be wrong about H.R. having been observed.

I want to stick by my second paragraph. Energy of real particles is uncertain but energy is still conserved in QM as long as statistically implausible outcomes are ignored and we steer clear of durations that are short enough to frighten ordinary people into submission?

If we observe both those constraints, aren't we kissing the macroscopic classical limit?

 

[trinocide]

*****the answer*****

i thought that this forum was made to anser a question involving great simplicity's it seems to me that it has turned to an argument ...so let me anser that question now ... quantum physics is a science involving the realationships of multiple particles and energy and has only one great problem
which is toe (theory of everything) which tries to combine the electromagnetic force gravitational force the nuclear force and the weak forces together ... but since this science is clearly involving the realationships between multiple particles and energys this proves that matter is never created nor destroyed but merley moved it has always existed within the atom so therefore even in the quantum world of mechanics energy is still never created nor destroyed ....thank you and goodbye.

 

[No-where-man]

Say something on my view of Hawking radiation,
first, black holes do not only radiative photon, but all kinds of particles(see,eg,gr-qc/0406017).
second, the particle pair in Hawking radiation is particle and antiparticle, but also,
they are positive and negative energy ones. because their four-momentum sum is zero.
third, we can not say it do not respect energy conservation. because in our point of view, we see the black hole give out positive-energy particles, and then it gets smaller, i.e. less energy. in the point of view of person inside the black hole, they think the black hole has eaten a particle with positive energy(because the x and t changes in black hole), and the black hole gets larger. As the two people can never tells each other, they think energy is conserved(here i have a question: what if the observer outside run fast into the black hole and tells the one inside the black hole)
fourth, in GR, energy is questionable.

cheers
wangyi

How can any particle or anti-particle get out from the black hole if nothing travels faster than the speed of light?

 

[No-where-man]

I thought Hawkin radiation had been observed?

I also thought that energy is uncertain in quantum physics for real particles as a consequence of entanglement with time. As I remember, energy is always conserved as long as you discard unthinkably unlikely events and don't introduce unthinkably short fractions of time.

Is Hawking radiation ever proven in practice?
The only thing if energy is the ability to do a work,than what gives a work energy-maybe the dfinition of energy is totally wrong.
In practice,energy has proven to be indestructible in all levels,as far as I know,I bet equally indestructible even on quantum level-because you can't get work from nothing.
Any thoughts?

 

[jackle]

I think energy uncertainty is a problem but it could depend how you interpret this.

 

[marlon]

I think energy uncertainty is a problem but it could depend how you interpret this.

hello,

what exactly do you mean by these words ?

marlon

 

[Kruger]

Is this right: In QM energy is always conserved, In QFT energy is not always conserved.

 

[marlon]

Is this right: In QM energy is always conserved, In QFT energy is not always conserved.

no, energy is not conserved in QM as well due to the HUP ; it is this QM-idea that is adopted by QFT. Momentum-conservation is always respected in both QM and QFT. For example in QM the transition from one state to another is described in terms of virtual transition states. These are the QM analogon of virtual particles in field theory. In such a virtual state, energy is not conserved for a certain amount of time. BUT, energy is conserved when you compare the initial and final state.

marlon

 

[dextercioby]

Guys,it's simpler if u look at this this way.

QM:On stationary states (think H atom),the hamiltonian is time independent,which means it commutes with itself,which,by means of the quantum version of Noether's theorem,it (the hamiltonian) is a conserved quantity.Now,of course,the obsevable,the energy is also constant.H atomn the stationary states of the H atom,the energy is conserved=constant in time.

A quantum transition between 2 stationary states is fueled by a perturbation,which means adding a time dependent term to the original Hamiltonian.Therefore,the hamiltonian becomes time dependent,its eigenvectors are non stationary states,therefore,u cannot apply the Noether's theorem (quantum version),and so one concludes that,in between 2 stationary states,on the intermediary states,the energy is not conserved.

QFT:In and out states are eigentstates of a time independent hamiltonian.The 4-mometum in these states is fully conserved (the time-indep.Ham commutes with itself).
Inserting a perturbation (meaning adding a time-dep term to the lagrangian---->time dep term to the Hamiltonian),one finds that on all "intermediary" states,characterized by a time dependent hamiltonian,the 4-momentum is not conserved.

I used in this argument the celebrated Noether's theorem.**** HUP.One needs it not.


Daniel.

 

[Nereid]

Hawking radiation has not yet been observed; not for want of looking though

 

[Kruger]

no, energy is not conserved in QM as well due to the HUP ; it is this QM-idea that is adopted by QFT. Momentum-conservation is always respected in both QM and QFT. For example in QM the transition from one state to another is described in terms of virtual transition states.

mhh. I have a physics book here and there it says that the number of particles in QM is always conserved.

 

[marlon]

mhh. I have a physics book here and there it says that the number of particles in QM is always conserved.

that is correct, the same goes for free field theories but not for interacting quantum field theories. Besides keep in mind that you are talking about real particles. The energy conservation is valid between real particles. The violation part occurs in some period of time during the actual interaction between real matter particles;

marlon

 

[jackle]

I think energy uncertainty is a problem but it could depend how you interpret this.

what exactly do you mean by these words ?
marlon

My weak understanding is like this: to know the energy of an electron you must measure it for a suitable duration. This suggests to me that conservation of energy is unprovable for very short durations. These wouldn't be long enough in principle to measure the energy. How do we interpret this?

I have already decided that my understanding is very shakey because I can't see why the same isn't true of momentum/position. ie. Can we prove conservation of momentum in a system that we know is somewhere within an unimaginabley small space? Wouldn't that make the momenta uncertain?

You might be able to help me with this

 

[Kruger]

If I may ask: Why does every integral in the attached formula needs a factor 1/pi?

Of course it is the forumula to calculate (with euler mclaurian formula) the casimir force?

 

[James Jackson]

I don't know anything about that specific integral, but I'd imagine it's some kind of normalisation factor, or a by-product of the space you're integrating over.

 

[danAlwyn]

I was told (possibly mistakenly) that the layman's particle explanation of Hawking radiation went something like this:

"Virtual" particles are created as intermediaries to an exchange in QFT somewhere near the event horizon of a black hole. These particles would normally disappear like they do in most QFT problems, except:

The proximity to the black hole leads to a massive gravitational field. Falling into the black hole, even for that brief period in which the virtual particles exist, results in the virtual particles "absorbing" enough gravitational potential energy that they can actually be turned into real particles.

One of the new real particles falls into the Black Hole. The other one may actually have enough energy to escape.

The total consequence then, from the perspecitve of a long range observer, is that somehow the gravitational energy of a black hole has been tapped in order to create an escaping particle. Thus, the black hole has lost energy equivalent to the energy of the particle that got away, and we interpret that escaping particle as Hawking radiation. In this case we end up with global conservation of energy.

Is this view incorrect? Or is it possibly an oversimplification?

 

[James Jackson]

Sounds about right, although the particle - antiparticle pairs aren't due to an 'exchange somewhere', they're particles created out of the vacuum.

 

[danAlwyn]

Sounds about right, although the particle - antiparticle pairs aren't due to an 'exchange somewhere', they're particles created out of the vacuum.

I should have clarified, I just meant that the particle-antiparticle pairs had to be created within the region sufficiently near, but not inside, the event horizon. If they're created too far away, then the gravitational field isn't strong enough, and nothing interesting happens. I'm just being unclear today, but I agree with you.

 

[James Jackson]

I think vacuum production and annihilation is pretty interesting by itself :-)

 

[Kruger]

virtual photons can also appear from nothing. they have not to be a product of field interaction (like electrostatic force, ...).

 

[Kruger]

Does somebody know my question about the 1/pi in the integral (post with attached picture)?

 

[Kruger]

? Is there anyone?

 

[marlon]

? Is there anyone?

i cannot read this forumula clearly. Where does this integral arise ? Please give some more info.

marlon

 

[Kruger]

Sorry. It is the derivation of the Casimir force. One has to build the difference between the energy inside the walls and outside the walls. And this difference is presented in the formula above. Ground state energy is hw/4pi and with w=c|k| you can integrate over all k outside the walls and inside the walls ... I think you understand.

 

[James Jackson]

Is k a reciprocal space? If so, I would imagine the relation between k space and real space would cause the Pi.

 

[Kruger]

k is the wavevector

 

[heusdens]

According to quantum physics energy only exists in small pockets of energy called quantum-or something like that,I personally don't know qunatum physics,that's why I need an expert.
The law of energy conservation is wrong according to quantum theory of physics?

I think the short answer must be that also under consideration of quantum physics, energy is still a conserved quantity, and the violations of that law under very tiny time conditions are the exclusions which admit the energy conservation law.

 

[tom.stoer]

I don't know whether it's a good idea to step into this discussion at such a late stage.

Comments from my side:
- virtual particles are mathematical entities only (we had this discussion in numerous threads)
- looking at Feynman diagrams involving virtual particles energy-momentum is conserved at the vertices - always!
- energy in quantum field theory is defined via the Hamilton operator H defined as integral over three-space
- of course energy can only be conserved if one does not restrict the region of integration to some subset of three-space
- H is conserved in any QFT I've ever seen

In curved spacetime (GR, QFT on curved manifolds) energy cannot be defined unambiguously. The problem is that local conservation of energy-momentum density (which always holds) does no longer allow one to define a globally conserved energy; this is due to the curvature which allows this integration only in certain special cases (there must be a timelike symmetry of the spacetime manifold).

So if curvature is present one must use different "non-local" definitions of energy which is no longer possible unambiguously (several different definitions are known). The problem is that these definitions do no longer rely on the Noether theorem or any other local symmetry argument.

 

[Andrey]

Yes, energy can be created from nowhere for a short amount of time cause of Heisenberg's uncertainty principle. The particle that are created are called "virtual particles" and are always created in pair because of conservation laws (charge, ...). Energy conservation can be violated for short times and this happens all the time. In the same way we can describe interactions in quantum electro dynamics. The hawking effect is based on this energy creation and destruction.

Watch in google, or wikipedia for:
Heisenberg's uncertainty prinziple
Energy-time uncertainty
virtual particles

No that's not true. You cannot create something from nothing. Something has to exist prior to creation of something else otherwise where would the causes for new phenomena come from?