- #1

No-where-man

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

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In summary, according to quantum physics, energy can exist in small pockets known as quantum or virtual particles. These particles are created in pairs and can briefly violate energy conservation laws before they are annihilated. This is known as the Heisenberg Uncertainty Principle. In quantum field theory, virtual particles are used to describe the interaction between initial and final states, but they are not a part of quantum mechanics. The concept of negative energy also arises in these theories. Hawking radiation is an example of energy creation and destruction, where one particle is absorbed by a black hole and the other is released into space to maintain momentum. This process does not violate energy conservation, as the total energy of the system remains the same.

- #1

No-where-man

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

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- #2

Kruger

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Watch in google, or wikipedia for:

Heisenberg's uncertainty prinziple

Energy-time uncertainty

virtual particles

- #3

marlon

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Kruger said: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

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Kruger

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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?

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marlon

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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.Kruger said:

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?

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

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Hawking radiation is made up of real photons.

Daniel.

Daniel.

- #7

vanesch

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No-where-man said: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.

- #8

Kruger

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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.

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El Hombre Invisible

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- #10

selfAdjoint

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El Hombre Invisible said:

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.

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Kruger

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- #12

Kruger

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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.

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El Hombre Invisible

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- #14

Chi Meson

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

- #15

vanesch

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Chi Meson said: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.

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wangyi

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vanesch said: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 [tex]\delta^4(\sum p)[/tex] 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

- #17

wangyi

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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

- #18

Rebel

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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.wangyi said:

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

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- #19

jackle

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vanesch said:...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

- #20

vanesch

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jackle said:I thought Hawkin radiation had been observed?

I'd be surprised :-)

cheers,

Patrick.

- #21

jackle

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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?

- #22

selfAdjoint

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jackle said:

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?

- #23

trinocide

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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.

- #24

No-where-man

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wangyi said:

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?

- #25

No-where-man

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jackle said:I thought Hawkin radiation had been observed?

I also thought that energy is uncertain in quantum physics forrealparticles 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?

- #26

jackle

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

- #27

marlon

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jackle said: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

- #28

Kruger

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

- #29

marlon

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Kruger said: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

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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.

- #31

Nereid

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

- #32

Kruger

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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.

- #33

marlon

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Kruger said: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

- #34

jackle

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marlon said: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

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