What is energy, exactly?

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Pour me a cup of energy, then. While you're at it, I'll have a cup of length as well.

I see what your saying, I do... but I feel the word ''unphysical'' is quite a drastic use of the word. Should ''unphysical'' be the word we use?

Hands up I don't know. I just think it would be hard to say energy is not when it has real effects on the physical world. Now, sure we cannot pour a cup of energy. There are some models which treat photon energy however as a gas - with a temperature, pressure and entropy. Black body radiation is said to be the equilibrium of the photon gas... and we don't think of gas as unphysical do we?

I don't know.... ''unphysical'' to me, just seems like something which shouldn't effect the physical world, but energy does so...

What led you to believe that energy is a physical thing? I'm sure that you've seen all the derivations of the various forms of energy and how nothing about them was physical. E.g. what do you think is physical about, say, potential energy. There is always a constant added to the potential which is chosen for convenience. What's physical about such an arbitrary constant?

In case you missed my post on the definition of energy you can take a gander at it at

http://home.comcast....t_is_energy.htm

This is a page in my own website. What do you think? Do you have any comments on it? Something I might add?

Hello pmb, I read your work, it is a good read for anyone who is wanting to learn this stuff... I perhaps only have one suggestion - it's a bit of a quibble.

''Notice how the energy moves back and forth from system to system yet the total energy of the universe remains constant. ''

I don't think current mainstream cosmology believes that the universe conserves energy any more.

(Here's a paper which entertains the idea that the zero point energy field is a physical manifestation http://arxiv.org/abs/hep-th/9901011 ---- I think the problem here will lye in how to persuade people to think of energy as a non-physical entity. I gave some reasons above. I could be completely wrong and you two could be completely right, certainly wouldn't be the first time I have been wrong.)

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Aetherwolf,

I don't think current mainstream cosmology believes that the universe conserves energy any more.

Yup, mass/ energy conservation in a closed system is still, as far as I know, a standard mainstream assertion with only a very few alternative-mainstream asserted exceptions

Why do you think that such assertions of the conservation of mass/ energy may not be valid in the universe as a whole?

//

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I see what your saying, I do... but I feel the word ''unphysical'' is quite a drastic use of the word. Should ''unphysical'' be the word we use?

Hands up I don't know. I just think it would be hard to say energy is not when it has real effects on the physical world. Now, sure we cannot pour a cup of energy. There are some models which treat photon energy however as a gas - with a temperature, pressure and entropy. Black body radiation is said to be the equilibrium of the photon gas... and we don't think of gas as unphysical do we?

I don't know.... ''unphysical'' to me, just seems like something which shouldn't effect the physical world, but energy does so...

Treating photons as a gas is not the same thing as treating energy as a gas. Photons represent something real, and have energy.

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Treating photons as a gas is not the same thing as treating energy as a gas. Photons represent something real, and have energy.

I'm quite sure that is meaningful, but if it was it went right over my head Swansont.

Ok... I guess the most logical question is, why can't you generalize to photon energy? When you say energy, what kind of energy did you have in mind?

Aetherwolf,

Yup, mass/ energy conservation in a closed system is still, as far as I know, a standard mainstream assertion with only a very few alternative-mainstream asserted exceptions

Why do you think that such assertions of the conservation of mass/ energy may not be valid in the universe as a whole?

//

I have good faith in them. I like it. I like the idea that a universe does not conserve energy, globally-speaking.

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I'm quite sure that is meaningful, but if it was it went right over my head Swansont.

Ok... I guess the most logical question is, why can't you generalize to photon energy? When you say energy, what kind of energy did you have in mind?

I don't have any particular form in mind. The fact that it has different forms is another indication that it's a property and not a physical substance.

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Aetherwolf,

I have good faith in them. I like it. I like the idea that a universe does not conserve energy, globally-speaking.

Faith is not a good word in science . not that faith is necessarily a bad word in general, au contraire Monsieur, . But the so called law of the conservation of mass/ energy is based upon the concept that if there is less energy in the universe at a given time there accordingly would be more matter/ mass. This is the present consensus I think. If you would, please post whatever links that you think might assert otherwise, or your own ideas, so that I and others might analyze them and express our opinion I'm not necessarily a fan of many mainstream models so you have my ear -- even though I happen to agree with this conservation principle.

//

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I don't have any particular form in mind. The fact that it has different forms is another indication that it's a property and not a physical substance.

So does mass however, mass has many forms. I don't know if saying it has many forms can preclude that energy is not physical.

Aetherwolf,

The so called law of the conservation of mass/ energy is based upon the concept that if there is less energy in the universe at a given time there accordingly would be more matter/ mass. This is the present consensus I think. If you would, please post whatever links that you think might assert otherwise, or your own ideas, so that I and others might analyze them and express our opinion I'm not necessarily a fan of many mainstream models so you have my ear -- even though I happen to agree with this conservation principle.

//

I could try and find some and I certainly have my own idea's for sure... I don't know if posting them here in this subforum would be within the rules... One quick one however, the fact that the observable universe is now receding faster than light is an indication that the universe is using energy at a rapid and accelerated rate. This may be an indication that the universe is not conserving energy.

I believe the universe might quantum leap in the future. Current mainstream seems to agree with the prediction of my own http://www.scientificamerican.com/article.cfm?id=is-the-universe-leaking-energy

As wiki explains

''In general relativity conservation of energy-momentum is expressed with the aid of a stress-energy-momentum pseudotensor. The theory of general relativity leaves open the question of whether there is a conservation of energy for the entire universe.''

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

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Aetherlwulf,

There are a number of mainstream explanations for the redshifting of EM radiation and the perceived loss of total energy in the universe. Although I agree with none of them, the mainstream explanation that I presently prefer is this: As the universe expands the Zero Point Field accordingly maintains its intensity per volume. The supposed loss of the energy of EM radiation, by this hypothesis, is conserved via the maintenance of the energy density of the ZPF. Another proposal is that what EM radiation losses to redshifts it gains in changes to dark energy.

I agree that this may be a serious mainstream problem if one wishes to maintain the conservation of energy principle in the universe as a whole And you're right, this is not the forum for personal ideas other than possibly brief mentions.

//

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Aetherlwulf,

There are a number of mainstream explanations for the redshifting of EM radiation and the perceived loss of total energy in the universe. Although I agree with none of them, the mainstream explanation that I presently prefer is this: As the universe expands the Zero Point Field accordingly maintains its intensity per volume. The supposed loss of the energy of EM radiation, by this hypothesis, is conserved via the maintenance of the energy density of the ZPF. Another proposal is that what EM radiation losses to redshifts it gains in changes to dark energy.

I agree that this may be a serious mainstream problem if one wishes to maintain the conservation of energy principle in the universe as a whole And you're right, this is not the forum for personal ideas other than possibly brief mentions.

//

Ok then, so back on topic.

Do you think energy is physical? I think it's a bit of an oxymoron to say it isn't, since energy has real effects on the physical objects of the world, from everyday life to cosmology. I will be honest, I have never thought of energy as being ''unphysical'' until I came to this forum.

When Swansont said, pour a glass of energy, the reason we can't is because it is not condensed like matter is, but is it wise to say it is not physical? If it is not physical what is energy, ethereal?

Of course, this doesn't mean that photons are completely incapable of being described that way. I believe, in superconducters, photons behave as though they have a mass. So they certainly can behave like your normal everyday by changing the medium in which they are in, which is a clue they are not really unphysical manifestations.

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When Swansont said, pour a glass of energy, the reason we can't is because it is not condensed like matter is, but is it wise to say it is not physical? If it is not physical what is energy, ethereal?

You need to take my statements in context, which was a response to the question in the OP: Is energy(joules, kilo-watt hours...or whatever) a physical thing on the subatomic quantum scale? Which I took to mean: Is there an energy particle? i.e. an exchange particle responsible for energy transfer? No, there isn't. Energy is not a physical object.

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Right... there is no one fundamental unit of energy.

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Hello pmb, I read your work, it is a good read for anyone who is wanting to learn this stuff... I perhaps only have one suggestion - it's a bit of a quibble.

The entire paper needs to be rewritten. I initially was addressing this debate on what mass is in nodern physics. I've changed my mind. I hate debates so I'll take another tact in the next version

''Notice how the energy moves back and forth from system to system yet the total energy of the universe remains constant. ''

I don't think current mainstream cosmology believes that the universe conserves energy any more.

I am familiar with that. It brings the entire meaning of energy into question. Energ has to be conserved for it to have meaning. I know that energy (outside of gravity) is conserved. With gravity in Netonian gravity, its conserved.

The T^00 component of the stress-energy-momentum (SEM) tensor is energy density. It's no different that the energies we've been talking about. E.g. in many cases its simply potential energy, em engery, kinetic energy, etc. None of which is a physical thing.

The one funny thing about T^00 is that it assigns a location for energy. Normally one doesn't assign a location to, say, kinetic energy. But the SEM tensor does this. A very odd thing for classical mechanics.

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There are cases I might be able to come to agree on that energy is physically meaningless, like for instance, the self energy of an electron.

$U_{e} = \int_{|\vec{r}| \leq R} \frac{\epsilon_0}{2}E^2 d\vec{r} = \int_{R}^{\infty} \frac{e^2}{8\pi \epsilon_0 r^2}dr$

When $R=0$ the energy of an electron is infinite. So basically all ''pointlike'' particles like electrons should have infinities energies - but they don't. This would be a case where the energy for me is defined as an ''unphysical case''.

Of course, one way to solve this is by saying there is some kind of classical electron radius $r_0 = 2R$ but you say that normally to a scientist and they may call you a psuedoscientist. We should in my opinion, believe that there is an experimental limit on particles sizes, that below a certain threshold, whether a particle is pointlike or not, there will always be experiments which show they still act like pointlike particles, which is entirely conceivable.

Back to the question of conservation for a universe, I don't quite know what you had in mind for the lack of conservation for a universe ''bringing in the meaning of energy'', but what I had in mind when you said this, I think of conserved quantities that are associated to the generators of the theory such as

$UU^{\dagger} = (1 + i \epsilon T)(1 - i \epsilon T^{\dagger})$

which gives

$i\epsilon(T-T^{\dagger})=0$

Where $T$ is the generator. This is of course is Noethers Theorem in a nutshell - a simple Noether Theorem example would be

$q_i \rightarrow \phi_i + \epsilon f_i (q)$

Which is just a transformation with a small parameter in it, neglecting it we have

$\sum_i P_i f_i (q)$

would be conserved if

$\delta L = 0$

As I am sure you know, the system doesn't change, conserves it's quantity... but if this kind of idea does not work for the universe as a whole, perhaps we need to start defining our conservation laws into two distinct set of groups, the global case and the local case. Local Conservation works well, in the Global case it seems to break apart.... the question is why? Well we don't know, but perhaps there is a striking similarity to being unable to find a Global time. Indeed, to make a symmetry transformation on the energy of the universe, you'd need a Global time. Time in GR relativity vanishes completely http://en.wikipedia....DeWitt_equation and http://arxiv.org/pdf/0909.1861v1.pdf helps to explain the vanishing time derivative of the global wave function. Now, the meaning of energy for a global description may just be the same as the description of energy on local levels except for a small tweak, we might find for instance that energy is leaking from the universe which causes the non-conservational properties, or we might find that there is some kind of intrinsic link between the accelerated expansion of the universe and the non-conservation, or even both.

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Aethelwulf,

Ok then, so back on topic.

Do you think energy is physical? I think it's a bit of an oxymoron to say it isn't, since energy has real effects on the physical objects of the world, from everyday life to cosmology. I will be honest, I have never thought of energy as being ''unphysical'' until I came to this forum.

Energy has many categories to it: EM radiation, momentum, relative motion, potential energy, Zero Point Energy, etc. Even unrealized energy, AKA potential energy, and the list goes on. My perspective is that energy is a relative condition concerning matter, but concerning EM radiation its nature can depend upon variations of theory. Energy, like dimensions, and time, are an explanation of measurement. Measurement is not physical. EM radiation, for instance, might have physical particles associated with it however.

When Swansont said, pour a glass of energy, the reason we can't is because it is not condensed like matter is, but is it wise to say it is not physical? If it is not physical what is energy, ethereal?

EM radiation, for instance, supposedly has physical constituents in the form of quanta AKA photons. There also may be background field particulates like dark matter, Higg's particles, etc. If background field particles are involved with the propagation, or being the carrier of EM radiation, for example, then I think that "etherial" might be the proper word for the propagating medium.

Of course, this doesn't mean that photons are completely incapable of being described that way. I believe, in superconducters, photons behave as though they have a mass. So they certainly can behave like your normal everyday by changing the medium in which they are in, which is a clue they are not really unphysical manifestations.

In my view there is a difference between substantive and massive. Mass, simply described, is a measurable characteristic that can be made within a gravitational field, measured in weight then converted into standard mass units such as Earth pounds or kilograms. Substance might be like a photon at rest, it could have existence but no mass. Its energy when traveling at the speed of light is what gives it a mass equivalence. When traveling far below "light speed" such as in a solid or liquid, photons can have much less linear velocity but the asserted cause of this is deflection by the medium so that much of its energy of linear motion might be lost to the medium producing heat energy via molecular vibrations, and maybe detectable in the form of increased temperature.

I think "energy," like "time," is just a man-invented concept, but a good one in my opinion Does this seem reasonable to you?

//

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Aethelwulf,

Energy has many categories to it: EM radiation, momentum, relative motion, potential energy, Zero Point Energy, etc. Even unrealized energy, AKA potential energy, and the list goes on. My perspective is that energy is a relative condition concerning matter, but concerning EM radiation its nature can depend upon variations of theory. Energy, like dimensions, and time, are an explanation of measurement. Measurement is not physical. EM radiation, for instance, might have physical particles associated with it however.

EM radiation, for instance, supposedly has physical constituents in the form of quanta AKA photons. There also may be background field particulates like dark matter, Higg's particles, etc. If background field particles are involved with the propagation, or being the carrier of EM radiation, for example, then I think that "etherial" might be the proper word for the propagating medium.

In my view there is a difference between substantive and massive. Mass, simply described, is a measurable characteristic that can be made within a gravitational field, measured in weight then converted into standard mass units. Substance might be like a photon at rest, it could have existence but no mass. Its energy when traveling at the speed of light is what gives it a mass equivalence. When traveling far below "light speed" such as in a solid or liquid, photons can have much less linear velocity but the asserted cause of this is deflection by the medium so that much of its energy of linear motion might be lost to the medium producing heat and maybe detected in the form of an increased temperature.

I think "energy," like "time," is just a man-invented concept, but a good one in my opinion Does this seem reasonable to you?

//

Yes, energy and time are indeed measurements... However, the concept of observables puts into place a difference between energy and time... for instance; A good example of an observable would be spin. Even energy particles, like a photon has a spin which is a measurable property of particles. Time is not an observable in physics.

So for this reason, I can agree that time is an invented concept. The word ''energy'' is also a concept we invented, but it surely was to describe ''a real thing'' .... whilst time is arguably something of more a book -keeping of events - like a clock measures a second pass, a clock is invented to measure that second pass. But energy is different, it has real physical effects on the world... whereas time is more like a coefficient to real events, if that makes sense at all?

Again, time is not an observable, so I completely agree from this point of view.

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Aethelwulf,

Time is not an observable in physics.

Time involves many different hypothesis, but maybe from the simplest perspective, time is an interval of change. Its observable physical motions involve matter and/or EM radiation. Its measurement is via standard measuring devices/ tools which we call clocks, which are of many different designs. Since time is an interval, the clock requires an actuated or calculated beginning and ending to it. A clock's measured intervals are a comparative measurement of change, like a ruler is to length, for instance.

The word ''energy'' is also a concept we invented, but it surely was to describe ''a real thing''....

In the concepts of Special Relativity, the energy of motion or inertia are solely from a relative perspective, and have no reality to them. The energy of EM radiation is based upon the relative speed (the speed of light) to the background gravitational field which contains it, as in General Relativity. In both cases their would be nothing physical to it. Many things are not either true or false but can involve one or more differing perspectives.

From the perspective that EM radiation is physical, one might argue that theoretically photons are considered substantive and therefore are physical. I see nothing wrong with this perspective or argument. But I think concerning relative motion, it is a condition described by changing locations rather than something physical. In the same way I consider time to be a measurement of changing conditions and locations. What say you

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Aethelwulf,

Time involves many different hypothesis, but maybe from the simplest perspective time is an interval of change. Its observable physical motions are of matter and/or EM radiation. Its measurement is via standard measuring tools which we call a clocks, which are of many different designs. Since time is an interval, the clock requires an actuated beginning and ending to it. A clock's measured intervals are a comparative measurement of change, like a ruler is to length, for instance.

In the concepts of Special Relativity, the energy of motion or inertia are solely from a relative perspective, and have no reality to them. The energy of EM radiation is based upon the relative speed (the speed of light) to the background gravitational field which contains it, as in General Relativity. In both cases their would be nothing physical to it. Many things are not either true or false but can involve one or more differing perspectives.

From the perspective that EM radiation is physical, one might argue that theoretically photons are considered substantive and therefore are physical. I see nothing wrong with this perspective or argument. But I think concerning relative motion, it is a condition described by changing locations rather than something physical. In the same way I consider time to be a measurement of changing conditions and locations. What say you

You certainly give one to have much to debate, that is what one says I will be right back.

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I said I would have been right back, but I got held up and I ended up doing something else... I will get back to this later! Promise.

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''Time involves many different hypothesis, but maybe from the simplest perspective time is an interval of change.''

Yes, perhaps, but I don't think time should mean change. Indeed, Julian Barbour has explained in his own idea's, that all there is in the universe is change, but no time. He argues that time is not an observable and all we should deal with is observables... he says ''this is the way science should work''.

''Its observable physical motions are of matter and/or EM radiation. ''

Yes, it is true that scientists often define time by radiating clocks, but you can essentially freeze an atom which is ready to give up all of its energy via the weak measurement theory. You can suspend an atom in time while ''time'' ticks on. So in a sense, I think its a mistake to think the two define each other.

''In the same way I consider time to be a measurement of changing conditions and locations. What say you''

Well, as I explained, time isn't an observable - it's only a tool we use to measure things passing. There does not seem to be any conclusive evidence that time is anything but a subjective phenomenon, which scientists often call the psychological arrow of time.

Sorry I never answered sooner, I was suffering from a bad fever recently and have not posted here as much.

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''Time involves many different hypothesis, but maybe from the simplest perspective time is an interval of change.''

Yes, perhaps, but I don't think time should mean change. Indeed, Julian Barbour has explained in his own idea's, that all there is in the universe is change, but no time. He argues that time is not an observable and all we should deal with is observables... he says ''this is the way science should work''.

"All-that-there-is in-the-universe" statements, in my opinion, are perspectives like every other description of reality from a particular point of view.

''Its observable physical motions are of matter and/or EM radiation. ''

Yes, it is true that scientists often define time by radiating clocks, but you can essentially freeze an atom which is ready to give up all of its energy via the weak measurement theory. You can suspend an atom in time while ''time'' ticks on. So in a sense, I think its a mistake to think the two define each other.

To have a condition of no motion at all within matter generally would require a temperature of absolute zero, whereby this temperature may be theoretically unobtainable. Even at absolute zero matter still has spin to it, which involves measurable change.

//

The kinetic energy of the ground state cannot be removed.

http://en.wikipedia....i/Absolute_zero

''In the same way I consider time to be a measurement of changing conditions and locations. What say you''

Well, as I explained, time isn't an observable - it's only a tool we use to measure things passing. There does not seem to be any conclusive evidence that time is anything but a subjective phenomenon, which scientists often call the psychological arrow of time.

I think the motion of the second hand on a clock can give a good sense of the rate that time passes, relative to the second. As to time being subjective, if you mean a human perspective of reality, then I would agree.

Sorry I never answered sooner, I was suffering from a bad fever recently and have not posted here as much.

Get lots of rest, inhale the appropriate meds , and talk to you soon

//

//

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''"All-that-there-is in-the-universe" statements, in my opinion, are perspectives like every other description of reality from a particular point of view. ''<br style="font-size: 13px; line-height: 16px; background-color: rgb(248, 250, 252); ">

Yes, but it's not a baseless opinion, in my opinion There are some good reasons to think he is right.

''To have a condition of no motion at all within matter generally would require a temperature of absolute zero, whereby this temperature may be theoretically unobtainable. Even at absolute zero matter still has spin to it, which involves measurable change. ''

In my case, we are not talking about the absolute freezing of a system, we are talking about freezing the evolution of the system. An atom can be frozen by making weak measurements on the system, while we still expect time to truck on - so using radiation to define time in my eyes, is a faulty premise. You may think of my example as a priori. The name this goes by is the Zeno Effect of Quantum Mechanics.

''I think the motion of the second hand on a clock can give a good sense of the rate that time passes, relative to the second. As to time being subjective, if you mean a human perspective of reality, then I would agree. ''

Yes, the clock is not an illusion, but it was constructed to mirror our ''sense of time''. There are gene regulators apparently, one for short range sense of time and one for the long sense range of time inside of the brain which can fully explain why we even have a sense of time at all.

Because of this, one must infer that time is a subjective experience and not a real component of the world around us. Again, one should not define time as a component of change - but rather a change in perception and the knowledge of the observer.

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In my case, we are not talking about the absolute freezing of a system, we are talking about freezing the evolution of the system. An atom can be frozen by making weak measurements on the system, while we still expect time to truck on - so using radiation to define time in my eyes, is a faulty premise. You may think of my example as a priori. The name this goes by is the Zeno Effect of Quantum Mechanics. [/size]

The quantum Zeno effect is not the same thing as weak measurement. Furthermore, the effect keeps the atom is a particular state; it has nothing to directly do with its motion.

Radiation is not used to define time.

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The quantum Zeno effect is not the same thing as weak measurement. Furthermore, the effect keeps the atom is a particular state; it has nothing to directly do with its motion.

Radiation is not used to define time.

It's not the same thing, I thought they were related?

As for the radiation thing, I have seen people use the rate of radiation as a definition of change and define in on equal terms as ''time''.

(I just checked it up), they are related to a number of topics:

'' weak-measurement quantum Zeno effect (WMQZE).''

http://www.millitangent.org/pubs/08_double_well_zeno.pdf

''For weak measurements, this time may be much longer than the tunnelling time. For very strong measurements, there is no Zeno effect. ''

I am sure there is more papers that can be found, these where the first two results from my search.

Here is a reference to the radiation topic

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

'' of time, the second, is defined in terms of radiation emitted by caesium atoms ...''

The cesium atoms define the unit of time.

This is just trying to define time from natural clock systems, but as I have noted, things like atoms can be suspended in time through periodic measurements.

Here's a paper showing that the zeno effect can be induced by weak measurements http://www.arimizel.com/images/PhysRevB_73_085317.pdf

Which is absolutely what I mean.

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

'' of time, the second, is defined in terms of radiation emitted by caesium atoms ...''

The cesium atoms define the unit of time.

My mistake; radiation is in the definition. As you also state, the atoms define the time. But I did not adequately state my objection: you wrote about radiating clocks. Most clocks (in particular, cesium clocks) do not measure the radiation emitted by the cesium. They are passive devices.

Here's a paper showing that the zeno effect can be induced by weak measurements http://www.arimizel.com/images/PhysRevB_73_085317.pdf

Which is absolutely what I mean.

Can be induced. They are still not the same thing. You can do weak measurement for non-Zeno effect experiments, and do Zeno-effect experiments which do not use weak measurements.

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My mistake; radiation is in the definition. As you also state, the atoms define the time. But I did not adequately state my objection: you wrote about radiating clocks. Most clocks (in particular, cesium clocks) do not measure the radiation emitted by the cesium. They are passive devices.

Can be induced. They are still not the same thing. You can do weak measurement for non-Zeno effect experiments, and do Zeno-effect experiments which do not use weak measurements.

If you can show me where I said they are the same thing (weak measurements and the zeno effect) then it will be my turn to apologize.

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