The Vacuum Fluctuation Myth - Comments

In summary: The predicted spectrum of these fluctuations was calculated by Guth and...The predicted spectrum of these fluctuations was calculated by Guth and...In summary, Neumaier submitted a new PF Insights post criticizing the idea that quantum fluctuations can stabilize a gas beyond the instability threshold imposed by mean-field interactions. He cites two papers that support this idea. However, quantum fluctuations are only a heuristic for reasoning about what's possible, and in practice they don't resemble the "fluctuation" reasoning much at all.
  • #211
A. Neumaier said:
The smooth evolution of the wave function is dynamically happening while it passes a magnet. It is not the wave function but the intuitive semiclassical picture of an electron as a moving point that ''causes'' the apparent jumps.

Got it. To me, to say that the electron ia fluctuating in its position is roughly to say that it is jumping between one position and another when not measured which is clearly related to the semiclassical picture you (and vanhees) described. And which is of course false.

When I said nothing happens in the wf, I meant that. Electron isn't jumping between the spots, it literally is in a state of variance which may change over time. But it is still only a variance - nothing happens 'inside' the wf. This is a different context of happening than deterministically evolving which applies to the wf as a whole. For something to happen, you need measurement. Would you agree with this line of reasoning?
 
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  • #212
durant35 said:
This is a different context of happening than deterministically evolving which applies to the wf as a whole. For something to happen, you need measurement.
No. In more complicated contexts, a lot may happen, and this is expressed in the evolution of the state. Indeed, ''the moment of measurement'' is itself a gross simplification of a very complicated interaction that happens between the electron and the measurement device, described not by the state of the electron alone but by the state of the combined system electron+device+environment. The apparent randomness in the fate of the electron state alone is due to this additional complexity.
 
  • #213
I used to know a bit about the "toy model" ##\phi^4_2## QFT in 1+1 dimensions (Glimm & Jaffe). They rigorously construct interacting particle states with bound states and scattering. AFAIK there is nothing corresponding to vacuum fluctuations in this mathematically well defined theory. I can't think how you could even rigorously ask "are there vacuum fluctuations?" in this context.
"Vacuum fluctuations" seem to be an artifice of trying to apply perturbation theory when you don't know that the perturbed theory is mathematically well defined.
 
  • #214
Keith_McClary said:
I used to know a bit about the "toy model" ##\phi^4_2## QFT in 1+1 dimensions (Glimm & Jaffe). They rigorously construct interacting particle states with bound states and scattering. AFAIK there is nothing corresponding to vacuum fluctuations in this mathematically well defined theory. I can't think how you could even rigorously ask "are there vacuum fluctuations?" in this context.
"Vacuum fluctuations" seem to be an artifice of trying to apply perturbation theory when you don't know that the perturbed theory is mathematically well defined.
Vacuum fluctuations refer to the fact that smeared field operators have in the vacuum state a nonzero variance. This is captured by the Wightman distribution functions, hence a fact even in ##\phi^4_2## QFT in 1+1 dimensions.

On the other hand, interpreting (as in most popular accounts of quantum phenomena) these vacuum fluctuations as happenings in time is completely fictitious.
 
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  • #215
If vacuum fluctuations are fictitious, then what is the proper explanation of the Casimir effect?
 
  • #217
Fred Wright said:
If vacuum fluctuations are fictitious, then what is the proper explanation of the Casimir effect?

Its actually a manifestation of Van Der Walls forces you probably learned about in HS chemistry::
https://arxiv.org/pdf/hep-th/0503158v1.pdf
'The Casimir effect is a function of the fine structure constant and vanishes as α → 0. Explicit dependence on α is absent from eq. (3) because it is an asymptotic form, exact in the α → ∞ limit. The Casimir force is simply the (relativistic, retarded) van der Waals force between the metal plates'

See also:
https://arxiv.org/abs/1605.04143

Thanks
Bill
 
  • #218
Thank you Dr. Neumaier and Dr. Bill for taking the time to respond to my post. I have been perplexed and annoyed by the term "vacuum fluctuation" for many years. After reading the paper by Jaffe my angst has been lifted and I have a renewed appreciation for the incredible predictive power of QFT. Alhamdu lila!
Salam,
Fred
 
  • #219
A. Neumaier said:
Vacuum fluctuations refer to the fact that smeared field operators have in the vacuum state a nonzero variance. [...]

On the other hand, interpreting (as in most popular accounts of quantum phenomena) these vacuum fluctuations as happenings in time is completely fictitious.

The source of this (mis)interpretation is surely the fact that in normal English usage, the word "fluctuation" does mean "variation with respect to time." At least, that's how I always understand it in everyday language.

This is of course not the only case in people are confused by the re-purposing of everyday words into physics jargon with specific technical meaning. Consider "work", "energy", and "power", which introductory physics students often struggle with at first. Or "speed" and "velocity".
 
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  • #220
The word vacuum is also problematic when you look at the definitions from classical to quantum.
 
  • #221
Fred Wright said:
Dr. Bill

Many that post here have doctorates, including Dr. Neumaier. I however am not one. Just a guy with a degree in applied math and computing who is now retired from 30 years spent programming, so can indulge his fascination for and interest in physics.

Thanks
Bill
 
<h2>1. What is the vacuum fluctuation myth?</h2><p>The vacuum fluctuation myth is a common misconception that the vacuum of space is not completely empty, but instead contains virtual particles that constantly pop in and out of existence. This idea is often used to explain the origin of the universe or to support theories such as the multiverse hypothesis, but it is not supported by scientific evidence.</p><h2>2. Why is the vacuum fluctuation myth considered a myth?</h2><p>The vacuum fluctuation myth is considered a myth because it is based on a misunderstanding of quantum mechanics. While virtual particles do exist, they are not fluctuations in the vacuum and do not have the ability to create or influence the universe. The concept of a true vacuum, where no particles or energy exist, is a fundamental concept in physics and is well-supported by experimental evidence.</p><h2>3. Can vacuum fluctuations be observed or measured?</h2><p>No, vacuum fluctuations cannot be directly observed or measured. They are a theoretical concept used in quantum field theory to help explain certain phenomena, but they cannot be detected with current technology. However, their effects can be indirectly observed through experiments such as the Casimir effect.</p><h2>4. Why do some scientists still believe in the vacuum fluctuation myth?</h2><p>Some scientists may still believe in the vacuum fluctuation myth because it is a compelling idea that can help explain certain phenomena. Additionally, the concept of virtual particles and their effects is still an active area of research, so there may be some disagreement among scientists about the exact nature of these particles.</p><h2>5. How does the vacuum fluctuation myth impact our understanding of the universe?</h2><p>The vacuum fluctuation myth can lead to misconceptions about the origins of the universe and the nature of space. By understanding that the vacuum is not a seething sea of particles, we can better understand the true nature of the universe and how it came to be. Additionally, rejecting this myth can help prevent the spread of misinformation and promote a more accurate understanding of physics.</p>

1. What is the vacuum fluctuation myth?

The vacuum fluctuation myth is a common misconception that the vacuum of space is not completely empty, but instead contains virtual particles that constantly pop in and out of existence. This idea is often used to explain the origin of the universe or to support theories such as the multiverse hypothesis, but it is not supported by scientific evidence.

2. Why is the vacuum fluctuation myth considered a myth?

The vacuum fluctuation myth is considered a myth because it is based on a misunderstanding of quantum mechanics. While virtual particles do exist, they are not fluctuations in the vacuum and do not have the ability to create or influence the universe. The concept of a true vacuum, where no particles or energy exist, is a fundamental concept in physics and is well-supported by experimental evidence.

3. Can vacuum fluctuations be observed or measured?

No, vacuum fluctuations cannot be directly observed or measured. They are a theoretical concept used in quantum field theory to help explain certain phenomena, but they cannot be detected with current technology. However, their effects can be indirectly observed through experiments such as the Casimir effect.

4. Why do some scientists still believe in the vacuum fluctuation myth?

Some scientists may still believe in the vacuum fluctuation myth because it is a compelling idea that can help explain certain phenomena. Additionally, the concept of virtual particles and their effects is still an active area of research, so there may be some disagreement among scientists about the exact nature of these particles.

5. How does the vacuum fluctuation myth impact our understanding of the universe?

The vacuum fluctuation myth can lead to misconceptions about the origins of the universe and the nature of space. By understanding that the vacuum is not a seething sea of particles, we can better understand the true nature of the universe and how it came to be. Additionally, rejecting this myth can help prevent the spread of misinformation and promote a more accurate understanding of physics.

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