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4hv.org :: Forums :: General Science and Electronics
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Some random QM questions

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Bjørn
Sun Oct 14 2007, 04:26PM
Bjørn Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Box is still, not in free fall; and let's say that tunneling happens in an infinitesimal time. Only the object is affected by the force. I just took gravity as an example, any force is good to create a potential well.

So wouldn't object always tunnel to lower energy state?
5. If one particle tunnels 1 nm against gravity from time to time or if 100 atoms tunnel 10 cm agaisnt gravity once every 10^100 years it has no observable effect on the conservation of energy as a whole and would be balanced out by the opposite happening just as often. It would be just as bad to tunnel in the direction of gravity because then energy is lost. It is unknown how particles interact via gravitation so I doubt if anyone knows for sure how gravity affects the statistical properties.


Is that right or wrong? If it's right, how doesn't it directly violate conservation of momentum?
As far as I know, it applies universally and at quantum scales too.
6. It is not clear how deep the conservation of energy goes. It is complicated by many things. For example the vacuum energy latent in the universe might be a lot higher than the total energy in what we observe as reality. If it is possible to "borrow" energy from the vacuum energy it might completely break "our" conservation of energy and yet still conserve it as a whole. Since the mechanisms and topology of the universe is unknown in the details it is all just speculation.

When it comes to momentum a slow particle can borrow energy from the uncertainty and speed up enough to transfer energy to a faster moving particle. The conservation of energy should still be intact. On these scales the particles are fuzzy waves that follow their own set of complicated rules and the billiard ball thought experiments often fail to give correct answers. One possible way to imagine it is that all these countless events averages out to what we observe on a macroscopic scale.
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Marko
Sun Oct 14 2007, 08:25PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
5. If one particle tunnels 1 nm against gravity from time to time or if 100 atoms tunnel 10 cm agaisnt gravity once every 10^100 years it has no observable effect on the conservation of energy as a whole and would be balanced out by the opposite happening just as often. It would be just as bad to tunnel in the direction of gravity because then energy is lost. It is unknown how particles interact via gravitation so I doubt if anyone knows for sure how gravity affects the statistical properties.

Bjorn: Sorry, but just can't get that as right - tunneling happens all the time everywhere and with that what you're saying conservation of energy would break down, which is idea I don't like in any case. I know that from nowhere - just trying to use logic neutral

I hope this isn't misunderstanding.

Take a more familiar example of a capacitor or radioactive decay.

As I already mentioned, electron can tunnel through the dielectric without completing the circuit... so it's energy would have to go somewhere, presumably into kinetic as if barrier was removed.

Electron will not tunnel into unfavorable energy state, for example it won't tunnel to charge the same capacitor when electric field disallows it.

I just hope nothing violates conservation of energy there.

ball may tunnel through a hill, but never appear at top of it with more energy that it could ever have.

With nuclear decay: particles tunnel at random out of the strong+coulomb force potential well.

After that they leave with specific, always equal kinetic energy. This means that at possibly varying tunneling destination it already 'materialized' with the amount of kinetic energy, and then is further accelerated by coulomb force, always yielding in equal kinetic energy for all decays. AFAIK. (prove me wrong)

Just too curious,

marko




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Marko
Tue Oct 16 2007, 09:36PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi again...

I just hope I haven't confused everyone to death with this, or you just find this so archetypally boring that you avoid it? I mean everyone else, bjorn probably had enough.

I actually started derelicting my projects and school just to study this. (romanticistic pursuit).

More I learn I see how poorly is QM explained in general.

Now I'm trying to understand Feynman's lectures in physics, but that'll need a lot of re-reading.

On internet I keep running into various forum discussions like this:
Link2
Link2

Which confuse me further.


Now what is about conservation of energy after all?

From all I know, conservation of energy should not be violated for any senseful (>planck time) amount of time, im. never. I'm pretty much narrow minded about that, still.

Now; Link2


In quantum mechanics, energy is defined as proportional to the time derivative of the wave function. Lack of commutation of the time derivative operator with the time operator itself mathematically results in an uncertainty principle for time and energy: the longer the period of time, the more precisely energy can be defined (energy and time become a conjugate Fourier pair). However, quantum theory in general, and the uncertainty principle specifically, do not violate energy conservation.

I assume this is what bjorn was trying to say, as it brings things into a further level.

Quantum tunneling is actually on overall very poorly explained - nowhere I can find even as simple problems like my charged capacitor thought experiment.


The problem becomes clearer with macroscopic cases like cool-object-in-a-box where it would clearly build a perpetual motion machine of any size if it didn't follow potential well.

Can electron find itself on higher electrostatic potential than it's energy? I think not...

I assumed it should always go to lower potential than it's maximum energy could be, and convert the rest to something else. (would it?)

I thought, no matter what uncertainity in energy particle has, anywhere it tunnels it will ''later be revealed'' that it had enough energy for that.


But this still doesn't stop me from creating absurd paradoxes.


If we have a charged capacitor which is very cold, and turned upside down so electrons would need to increase their gravitational potential energy in order to tunnel.

Contradictory, as we lower the temperature the electron's kinetic energy is smaller, wavelength longer and it is easier for it to tunnel through dielectric barrier, and from other side, colder they are, less and less electrons have enough kinetic energy to jump into higher gravitational gravitational potential without violating CoE.

My answer would be that tunneling never occurs in such a capacitor, but is that true?

Would your answer be ''nobody knows'' without theory of QG?


PS. oh, and the much simpler question of relation of voltage across a capacitor with tunelling remains unsolved! Tunneling current density increases proportionally*exponentially with voltage:

J = K1*U^2*exp(-K2/U) ?

Why is that so? Is this just about higher voltage creating shallower potential well? How does it then depend on temperature?













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Bjørn
Wed Oct 17 2007, 01:29AM
Bjørn Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I just hope I haven't confused everyone to death with this, or you just find this so archetypally boring that you avoid it? I mean everyone else, bjorn probably had enough.
I just missed your post, I still find it very interesting. It is also a very difficult subject.

If we assume that tunneling only happens in the direction of gravity it implies that the wavefunction is greatly distorted by a very weak gravity field. In a really strong field it would then be extremely distorted and all sorts of observable effects would appear that no one have observed. Also as you probably suspected, devices that used tunneling does not appear to be greatly affected by how they are pointed relative to ground.

So it seems quite clear that a weak gravity field does not affect the tunelling significantly so we must ask ourselves at what level is energy conserved.

When it comes to the perpetum mobile you will never be able to extract any energy from it because the energy gained is very small compared to the neergy needed to observe it just to check if there was a gain. You would always spend billions of times more energy than it is possible to exctract. Only in a special case can you extract energy but it happens so rarely that it compares well to a compressed air drill running on air molecules that by random chance move in the same direction through it.

It is possible that you can argue that energy has been conserved but that the uncertainty of our knowledge of it has incrreased. Then we are on a slipperly slope towards questions about the nature of observations and observers. The conversion process from wavefunction to reality so we can gain knowledge of the experiment is not trivial so we might have been heading in that direction anyway.

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Marko
Wed Oct 17 2007, 09:38PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi bjorn

More I'm re-reading my post, I question the idea behind it more.

Gravity is in most cases extremely weak at scales talked about and really not something like reciprocal to electric field, so;
In a really strong field it would then be extremely distorted and all sorts of observable effects would appear that no one have observed. Also as you probably suspected, devices that used tunneling does not appear to be greatly affected by how they are pointed relative to ground.

So it seems quite clear that a weak gravity field does not affect the tunelling significantly so we must ask ourselves at what level is energy conserved.

Even at lowest achieved molecular energies (10^-31J) small particles wouldn't be affected by gravity in their tunelling. The capacitor example would in most real cases have huge potential energy in behind compared to this tiny gravitational potential.

That doesn't imply for macroscopic objects, though.

You would always spend billions of times more energy than it is possible to exctract. Only in a special case can you extract energy but it happens so rarely that it compares well to a compressed air drill running on air molecules that by random chance move in the same direction through it.

I'm not sure what you mean by this - air drill would be against second (see my other thread) but not first law, and no matter if I get 'overunity' of 0.0001% it's still violation of CoE.

If that is observable or isn't is another thing.


The general idea I got about tunneling was, that it always happens to a lower potential state.
So I thought even gravity should distort the wavefunction heavily if uncertainity is small and mass big enough like macroscopic object experiment.

I thought, sum of all interactions particle can interact by must create favorable energy state for it to tunell.

But, your last post greatly opposed that and this kept me confused.

All I wanted is to understand tunelling better, but I just generated more questions...


One most familiar thing someone from here could do:


Anyone here played with tunnel diodes?
I'm unfamiliar with them, but, when tunelling current is conducted, not a lot of electrons are allowed through the barrier, like with thermionic tubes, and the diode shows some electrical resistance, right?

One has to wonder where is really that energy (I*I*R) dissipated, diode does get hot, right?

It may appear puzzling because if we made all 'non-relevant' parts superconducting, diode would still show resistance and dissipate heat?

This would imply that electrons would need to gain in kinetic energy while passing the barrier, pretty much the same as they would in vacuum, and turn it into 'braking' heat pretty much the same way. As I think it would absolutely newed to do that to preserve CoE.

These are all just my rantings and I would greatly appreciate good source of information which would prove me wrong...

If it is possible to "borrow" energy from the vacuum energy it might completely break "our" conservation of energy and yet still conserve it as a whole. Since the mechanisms and topology of the universe is unknown in the details it is all just speculation.

Not the first time I hear phrase 'vacuum energy' - and yet I know nothing about it except that it's poorly described and that it makes excellent buzz word for overunityers and conspiracy theorists.

To define the form of energy I need particle and an interaction, which I don't know.

What kind of energy would that be in first place? Apparently it needs to be able to interact with matter, otherwise it doesn't exist.

Excuse my ignorance at this point.

Marko




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Bjørn
Thu Oct 18 2007, 12:09AM
Bjørn Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
thought, sum of all interactions particle can interact by must create favorable energy state for it to tunell.
This is correct. The problem is that the interaction of gravity is not known in detail so it is very difficult to reason how it behaves in a gravity gradient. Since there are gradients in all directions everywhere in the universe it can't tunnel in any direction without changing it's potentional energy relative to some galaxy at the other end of the universe.

My claim is that even if we can't deduce a way to account for the change in energy it will not break any laws since the laws are statistical in nature and does not apply for single random events.

Not the first time I hear phrase 'vacuum energy' - and yet I know nothing about it except that it's poorly described and that it makes excellent buzz word for overunityers and conspiracy theorists.
No one knows the nature of it. It arises from the fact that vacuum is far from empty and that theoretical work and measurements indicated that it contains energy. Here is an interesting picture and some useful links: Link2

My point was that when you have an isolated box with a particle in it, it might still not be obvious where the energy is at all times. Even if conservation of energy holds perfectly it might not be simple in all cases to account for the energy. The particles in the box is inside a bubbling quantum foam of fields.

It is not my intent to make it more complicated but to illustrate that even if energy seems to created or destroyed it is probably possible to recover it by adjusting the thought experiment so that it mirrors reality better.
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Marko
Thu Oct 18 2007, 02:25PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
The problem is that the interaction of gravity is not known in detail so it is very difficult to reason how it behaves in a gravity gradient. Since there are gradients in all directions everywhere in the universe it can't tunnel in any direction without changing it's potentional energy relative to some galaxy at the other end of the universe.

My claim is that even if we can't deduce a way to account for the change in energy it will not break any laws since the laws are statistical in nature and does not apply for single random events.


Now I think, in really most cases particles should have enough energy to move through gravity wells of distant galaxies for few um so it may not be all absurd as I thought.

It's all about whether it really works as I have conceived it...

No one knows the nature of it. It arises from the fact that vacuum is far from empty and that theoretical work and measurements indicated that it contains energy.

So what kind of energy it is? What kind of particles?
I was actually thinking about putting casimir effect into the list but I didn't know how to formulate the question well.

Without any obvious links to reality it just looks like result of an absurd equation.

In order to interact with anything it needs to fell one of four forces.

Link2 ;

The Casimir effect can be understood by the idea that the presence of conducting metals and dielectrics alter the vacuum expectation value of the energy of the second quantized electromagnetic field. Since the value of this energy depends on the shapes and positions of the conductors and dielectrics, the Casimir effect manifests itself as a force between such objects.

So vacuum energy is electromagnetic?

Sorry but I don't know how to conceive such a thing from my current understanding.

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Amateur-Scientist
Thu Oct 18 2007, 05:37PM
Amateur-Scientist Registered Member #1015 Joined: Fri Sept 21 2007, 06:43PM
Location:
Posts: 14
Marko wrote ...
So vacuum energy is electromagnetic?
It is thought to be all the forces. It is also known as "Zero-Point Energy".
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Marko
Fri Oct 19 2007, 09:36PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Now does it manifest in form of virtual particles? Then what do other virtual particles do? Like virtual photons or gravitons in static fields?

How is it linked?
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Amateur-Scientist
Sat Oct 20 2007, 01:03AM
Amateur-Scientist Registered Member #1015 Joined: Fri Sept 21 2007, 06:43PM
Location:
Posts: 14
Marko wrote ...

Now does it manifest in form of virtual particles?

Yes, virtual particles (particle/anti-particle pairs), pressure (Casimir effect) and spontaneous light emission. It is thought that the interaction of the particle pairs with other particle pairs before they anihilate each other are responsible for the four forces.
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