The Uncertainty Principle Is Here to Stay (I'm pretty sure)

[Ansgar Seraph]

You are mistaken. I'll eat my own bachelor thesis if you can show me that I'm wrong. If you can't, then stop playing expert.

Well, I hardly think that I'm playing expert. I haven't given my statements any more authority than a layman's knowledge. And from a layman's knowledge, quantum fluctuations in a vacuum that do not result in the destruction of the matter/anti-matter pair constitutes an apparent violation of thermodynamics (I misspoke singling out 2LoTD . . . but I'm doing five things at once today).

Now I'm more than happy to be shown how this isn't the case and the semi-popular press stuff I've read is wrong. But you've got to give me something to work with. Or just say that my layman understanding is wrong and I'll accept that — never claimed to be an expert, after all.

I think I'm gonna suggest this one as a screwball. I'm sorry, but if you know anything about thermodynamics this is just gold.

Feel free; I was fishing around for a descriptor that would separate the categories I was thinking of and almost surely picked one that was less than ideal. If it ended up being just plain stupid, it probably deserves the screwball.

Projecting much? You ignored the post I made that responded to you, and went into the meat of Seer. He's actually right on this one, and you're mistaken. Try easing your 'certainty' of this certain topic and stop being perennially opposed to any kind of learning experience.

I didn't see your post to me; the e-mail notifications haven't been timely and I've just been skimming through multiple posts when I check 'em. My frustration with seer, however, is not a product of just this thread but rather a culmination of threads where he has repeatedly resisted even acknowledging the difference between concepts like populations, species, ancestor populations and daughter populations. Our last chat ended with seer snarking about something being luck, me spending over an hour creating a graphical representation to better explain it and then nada.

My point on this thread has been to drive at the uncertainty that exists in regards to these matters. I may well be beyond my educational and/or intellectual limits here but I've never been perennially opposed to bettering my understanding of a topic.

—Sam

[Ansgar Seraph]

If the General Theory of Relativity is correct and something not too dissimilar from modern Quantum Field Theory is correct in all possible worlds, then the 2nd law holds true in all possible worlds. I think this is reasonable to suppose since, ignoring the String Landscape, a lot of multiverse speculations are based on extrapolations based on QFT and GR in mind.



False, thermodynamics makes perfect sense with quantum field theory. Energy still can't come from nothing. However if you have a field of negative energy density, which the vacuum of space seems to have, then it can cancel the positive energy density of matter and in total you have zero energy. Then you can keep on expanding the universe as much as you want as long as those two contributions cancel each-other perfectly, that was the basis for the old Steady State model of cosmology. It might still be the case, and it enjoys a weak confirmation since the large scale curvature of space-time is zero, which is exactly what you'd expect in that case.

As for the 2nd Law of Thermodynamics it simple requires that the number of ways to order things in a given closed volume must always increase. The form of the law changes for an open volume, but only in trivial way. I don't know of any inflationary cosmologies (not admittedly an expert) that violate the 2nd Law. I know Penrose postulates something akin to that in his cyclical universe model, where information about what falls into a blackhole disappears, returning the universe to a simple state by erasing all the accumulated information. Not sure if this is a violation of the second law, it seems all that is required is for the information that falls into the black hole to become permanently unavailable and it could do so in a huge number of ways. If the information is "deleted" then that would be a violation of the 2nd Law.

Found it. That explanation makes sense and I'll look into it further. Thank you.

—Sam

[Ansgar Seraph]

Apparently, "Classical Thermodynamics" was the term I was fishing for. Lesson learned.

[Ansgar Seraph]

Took a bit of reading to jog my memory regarding quantum fluctuations. So here's my (non-expert, Leonhard!) thought process:

Quantum fluctuation in a vacuum creates matter/anti-matter pairs. Hawking wrote about such phenomena being a cause of radiation surrounding black holes: when a matter/anti-matter pair fails to annihilate itself, one particle falls into the black hole and the other particle becomes "actual." This results in the black hole losing mass/energy/whatever, and the laws of thermodynamics are not violated. My understanding, and where I'd like some guidance, is that such a failure to annihilate would be an apparent violation of the laws of thermodynamics if there were no counter-effect, such as the shrinkage of a black hole. If such quantum fluctuations occur in all vacuums and some pairs experience a failure to annihilate, how is this not an apparent violation of thermodynamics, given the lack of a counter-effect? My understanding is that thermodynamics isn't violated because of the annihilation process itself.

—Sam

[Leonhard]

Won't have time to answer this tonight. I will be back tomorrow.

[OmniSkeptical]

What is Quantum Field Theory and what are its industrial uses?

[pancreasman]

What is Quantum Field Theory and what are its industrial uses?

Transporter beams.

transporter-beams.jpg

[shunyadragon]

What is Quantum Field Theory and what are its industrial uses?

The wiki article gives some insight into the practical uses of Quantum Field Theory, and other aspects of the quantum world. It functions as a model for some ways things work in the macro world.

http://en.wikipedia.org/wiki/Quantum_mechanics#Applications

A great deal of modern technological inventions operate at a scale where quantum effects are significant. Examples include the laser, the transistor (and thus the microchip), the electron microscope, and magnetic resonance imaging (MRI). The study of semiconductors led to the invention of the diode and the transistor, which are indispensable parts of modern electronics systems and devices.

. . .

While quantum mechanics primarily applies to the atomic regimes of matter and energy, some systems exhibit quantum mechanical effects on a large scale - superfluidity, the frictionless flow of a liquid at temperatures near absolute zero, is one well-known example. Quantum theory also provides accurate descriptions for many previously unexplained phenomena, such as black body radiation and the stability of the orbitals of electrons in atoms. It has also given insight into the workings of many different biological systems, including smell receptors and protein structures.[45] Recent work on photosynthesis has provided evidence that quantum correlations play an essential role in this basic fundamental process of the plant kingdom.[46] Even so, classical physics can often provide good approximations to results otherwise obtained by quantum physics, typically in circumstances with large numbers of particles or large quantum numbers.

© source where applicable

[Leonhard]

Quantum fluctuation in a vacuum creates matter/anti-matter pairs. Hawking wrote about such phenomena being a cause of radiation surrounding black holes: when a matter/]anti-matter pair fails to annihilate itself, one particle falls into the black hole and the other particle becomes "actual." This results in the black hole losing mass/energy/whatever, and the laws of thermodynamics are not violated. My understanding, and where I'd like some guidance, is that such a failure to annihilate would be an apparent violation of the laws of thermodynamics if there were no counter-effect, such as the shrinkage of a black hole. If such quantum fluctuations occur in all vacuums and some pairs experience a failure to annihilate, how is this not an apparent violation of thermodynamics, given the lack of a counter-effect? My understanding is that thermodynamics isn't violated because of the annihilation process itself.

Sorry for taking so long to respond to your questions, in particular because I gave some vague responses that I feared might give you the wrong idea. I said that something like chaotic inflation could keep on spawning mass as long there is a negative energy field that cancels out the energy contribution of the mass. This however is emphatically not at all what takes place in a virtual particle/particle process. Even if there wasn't such a weird ( even though dark energy might this, its something we can't explain yet and its not something we had predicted) field it, you could still talk about virtual particle/anti-particle pairs.

I guess I can only give a sketch of a response here, since your questions touch on a lot of issues where you'll only get a second-hand understanding if you don't know the theories themselves. I'll try to give a more adequate sketch of what's going on.

Quantum Field Theory deals unsurprisingly with a quantum mechanical description of fields. How they are 'quantized'. This is the word we use to describe that something has been described quantum mechanically. Its quite a surprise to find out that something that is so continuous (which it remains so even after being quantized) can turned into something with discrete components. However it can. Its easiest to do with EM fields. Its much harder to do with the fields that give rise to the weak force, or even the strong force (the equations are almost unsolvable on that one). It turns out that particles are related to these fields in a unique way. I wish I could show you the math on this one, because its pretty cool (if you know linear algebra and calculus, I invite you further up and further in, ask me for the appropriate litterature). Vector fields (like the EM field) are related to particles of a spin 1, scalar fields (Higgs-field for instance) are related to particles of spin 0 (yet to be confirmed for the Higgs-boson they've found). These particles have coupling strengths and interact with 'charges'. The electrons (EM force) interact with charge +-, the Z and W particles (weak force) interact with isospin, the gluons (strong force) with color charges (red, green, blue, anti-red, anti-green, anti-blue). Interesting a spin-2 particle creates a tensor-field (more components than a vector)... hmmm... Einsteinian General Relativity is a tensor-field equation... hmmm... what if we introduce a spin-2 particle, who's 'charge' is mass and who is massless (gravity waves move at the speed of light). Yup that would be quantum gravity, unfortunately the equations blow up and spit out nonsense. Sorry.

Anywho, that's a very rough ground work of what's going on. A particle is related to a field. Any situation with particles that interact with eachother, can be cast as a field in a particular configuration. Imagine a box. The situation that we would describe as 'vacuum', corresponds to a particular arrangement of the fields. To 'one particle is present' to another linear combination of those fields, and so forth. Notice that there's always fields present! From those fields you can get probabilities for various questions "If I put a detector here, what's the odds of detecting an electron?". If we place the field inside of it into any configuration, we can run the time forward and see how it behaves at any point in the future.

Relating these fields to thermodynamics is also possible. In fact in some ways this can be very straight forward and easier than with Classical physics! Back then they had to postulate the ergodic hypothesis and hope for the best, however you can actually derive most if not all of the results of thermodynamics from QM (in general and QFT in particular). Its not trivial, and I'll spare you the details. The second law comes down to information being conserved, nothing is being deleted. You can derive this result from studying 'time evolution'. Basically there's an equation that tells you how a field will change over time. From this you can find that it always changes in a way that conserves information. If you're interested the technical term you should be searching for is 'the time evolution operator is unitary'.

Now there's still some questions I'm sure, and I'm sorry that this is a very rough sketch. And without any pictures too! I don't blame you if this is so much word babble.

What about 'virtual particle/anti-particle annihiliation' doesn't those break energy conservation?

You're right that they do, however I'm not sure virtual particles are real. They aren't put into the theory, but they emerge as a sort of book-keeping utility in doing some of the calculations. I made it sound easy, but calculating how these fields change isn't trivial. You get infinite sums and a famous physicist by the name of Richard Feynman noticed that the sums could be rearranged into terms that he identified with those diagrams of particles splitting up and annihilating. I think he believed that those virtual particles were real, I'm less certain less certain myself. The trick is that a surplus of energy E can be put into the system, and will be completely undetectable, as long as its present for at most t = hbar/(2E). Its only detectable results which are what's interesting, and that we can be certain about.

Then what is meant by 'vacuum fluctuations'?

There's a lot of concepts that fit onto those two words, so I'm deeply sympathetic with your confusion. Sometimes its used to refer to virtual particle/anti-particle pairs, sometimes to space-time itself being made of something quantized which can decay into a lower state of energy, etc... it depends on what the author has in mind and the context usually makes it clearer.

Our universe can't simple be a virtual particle/anti-particle pair. It wouldn't be here for long in that case.

[Leonhard]

What is Quantum Field Theory and what are its industrial uses?

In practical terms, other than simple being the best understanding we have of how stuff works out in the real world under sufficiently extreme conditions? Hmm... Imagine that you have a source gamma radiation. Now if you're doing ordinary quantum mechanics (the kind of stuff you learn second-year in college), then you'll be able to figure out how that radiation would scatter off some particles. However that's not the whole story. There's a chance that the incoming photons, in the presence of the electrical field of the particles, would split off into (not virtual, but honest to god real detectible) an electron and anti-electron pair. If you want to calculate the scattering amplitude of those pairs, at what energy they occur and so forth, you need QFT.