Slashdot Mirror
Researchers Identify 'Tipping Point' Between Quantum and Classical Worlds
wjcofkc sends this report from R&D Magazine:
If we are ever to fully harness the power of light for use in optical devices, it is necessary to understand photons — the fundamental unit of light. Achieving such understanding, however, is easier said than done. That's because the physical behavior of photons — similar to electrons and other sub-atomic particles — is characterized not by classical physics, but by quantum mechanics.
Now, in a study published in Physical Review Letters (abstract), scientists from Bar-Ilan University have observed the point at which classical and quantum behavior converge. Using a fiber-based nonlinear process, the researchers were able to observe how, and under what conditions, 'classical' physical behavior emerges from the quantum world.
Now, in a study published in Physical Review Letters (abstract), scientists from Bar-Ilan University have observed the point at which classical and quantum behavior converge. Using a fiber-based nonlinear process, the researchers were able to observe how, and under what conditions, 'classical' physical behavior emerges from the quantum world.
As far as I understand it:
The problem is that it is not in any one state, until observed. Then we just see a snapshot of our particular history that led to that observation. Observation determines the state but also modifies the system forever more, too.
One hypothesis of this leads to the "many worlds" interpretation" - it's in only in one state but until we actually look (and therefore modify the system) we don't (can't) know which particular universe of possibilities we happen(ed) to be in.
Unfortunately, quantum physics gets a lot weirder, which only serves to show us how little we know of it. I get lost in it as it's maths way beyond my capability nowadays (despite a maths degree), but as far as my friends in the research fields explain stuff, you can even get things such as particles "borrowing" energy from their future selves (at least, that's one hypothesis of what they are doing) - they don't have to energy to do X, suddenly they acquire it, then they always have pay it back afterwards. It only works if you consider time as "just another dimension" or if you include other spatial dimensions they could be getting this energy from.
Though we might be able to describe a convergence between classical and quantum mathematically (at some point in the future), the outcome is always going to be the same because we're just 4-dimensional creatures. Weird stuff is going to happen.
Physics is going to get a lot harder for us long before it gets any easier. Breakthroughs are few and far between and we're only now properly confirming stuff that was discovered / hypothesised in the 20's, 30's, 40's, etc. (don't forget, technically quantum mechanics goes back as far as the late 1800's!).
'No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.'
In this case, local hidden variables refer to what you describe as it being in a single state and us just not knowing. Without faster-than-light information transfer (which we cannot have if causality is to hold within relativity), it is not possible that 'the system is in a state and we just don't know it. '. Quoting wikipedia,
In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously, so that a theory could not be Lorentz invariant.
This has been shown experimentally using Bell's equations and this work got him nominated for a Nobel prize but died before it was awarded that year.
That is not a correct description. Lower frequency radio waves are no less 'quantum' or 'classical' than higher frequency radio waves. AM radios can penetrate objects primarily because they have a wavelength on the order of 400 meters (up to around 1 MHz), whereas FM radios have a wavelength of only a few meters (through around 100 MHz). The longer wavelength of AM effectively allows the radio wave to bypass even relatively large objects such as mountains.
The same effect can be seen even within your house if you have a dual-band WIFI router. The 2.4 GHz band is able to penetrate walls and go around corners and reach the second floor far more easily than the 5 GHz band can.
-Matt
11 dimensions is M-Theory, but if you go by Loop Quantum Gravity, you can formulate it in 3 or 4 dimensions.
There's really no theory that has "won" yet, so it is far too early to say there is a minimum number of dimensions.
Like you suggest, I believe that the "magic" of quantum effects would be a lot less "magical" if the objects in question could be described in at least one more dimension. The uncertainty principle is likely uncertain because you can have almost identical looking 4-D slices in a 5-D space. It only breaks down when you realize that certain objects or processes are prone to change much more extremely in higher-numbered dimensional space. So, if you fail to take 5-D into account, you can come up with a formula which seems to have two equally probable states, but in the end, of course, there was never any doubt.
For some value of 'q' the cat is dead and for some value of 'q', the cat is alive. Our current state of science is that we have equations that work very well with objects that are less variant in the 5th dimension than photons or quantum scale objects/processes are. Just like when we assumed that stars and mountains never changed or things didn't evolve because those processes are far less variant in the time dimension than the typical human lifetime.