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I apologize if this question is posted on the wrong portion of the website, but I knew no better place to ask.

I've come to see that some effects, such as super-conduction may happen at either extremely low temperatures, or at extreme temperatures (the recent discovery of superconducting iron in the bowels of the earth, for one), and this is fascinating.

My question is: can (does?) the same principle be applied to quantum effects? Would it be applicable to, for example, say that although quantum effects happen at nano scales and below they may happen on a grand scale of say, the entire Universe (as a solitary unit)?

Can said quantum effects happen at moments of say, picoseconds after the Big Bang due to the turbulence of forces involves in such an event? Or even within the core of a dying star?

Thank you for any answers or clarification of my misinformation.

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Hi user991710, and welcome to Physics Stack Exchange! What sort of quantum effects are you asking about? –  David Z Dec 24 '11 at 4:27

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up vote 3 down vote accepted

a) Superconductivity is a macroscopic quantum manifestation. The theories that describe it are quantum theories

b)It is macroscopic because it manifests on kilometers of wire for superconducting magnets, which are used in accelerators , the LHC at CERN for example has a large number of superconducting magnets made of kilometers of superconducting wire; the detectors also.

c) If you look at the brief comment on the theory of superconductivity it is seen that it is relevant for cosmology also.

To understand a bit what is at play, one should be aware that the whole of Nature is based on Quantum Physics. It is the intrinsic behavior of the underlying stratus on which our every day materials are based.

There are two reasons why in usual materials and behaviors the underlying quantum mechanical nature is masked:

a) As you guessed the small magnitude of the numbers entering and deciding the thresholds of observation of quantum effects. These depend on the small value of h-bar, a constant which controls the scale of clear quantum behavior in interactions.

b) The second reason is coherence. A classic example of coherence/decoherence is the following: when soldiers march across an old bridge they break step. If they do not, if they keep coherently marching in step, the additive and synchronous in time vibrations induced on the bridge may destroy it by resonating with its basic resonance.

When one has a wave description, and quantum mechanics describes the probability of interactions mathematically as a wave, there are phases between waves. If the waves are in step, i.e. the phases are fixed and unchangeable, macroscopic manifestations of quantum effects can appear, as happens with superconductivity and superfluidity. Fortunately for the way we see the world usually, the smallness of h-bar assures that unless great effort is made to keep the phases, the phases are lost statistically, due to zillions of interactions at the molecular level. This is called decoherence and leads to the classical physics level we usually live with.

As far as cosmological models go, yes quantum effects are expected to manifest there:

Heisenberg's uncertainty principle predicts that during the inflationary phase there would be quantum thermal fluctuations, which would be magnified to cosmic scale. These fluctuations serve as the seeds of all current structure in the Universe. Inflation predicts that the primordial fluctuations are nearly scale invariant and Gaussian, which has been accurately confirmed by measurements of the CMB.

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Yes, if well isolated from the observer in the process. This is possible only at very low temperatures and with non-existing currently isolating equipment.

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