Observable Definition and 210 Threads

Let us consider the http://en.wikipedia.org/wiki/Stern-Gerlach_experiment" experiment. The inhomogenuous magnetic field produces a drift force that can separate particles according to their spin and offer a possibility for a "measurement". This (very) small magnetic interaction can be...

I've noticed recently that many posts are veering towards the question of just how much of our total Universe can we observe. So I thought a new thread could address this question. 1) What is the radius of the observable Universe? 2) What are our best guesses as to the radius of the...

Note from SpaceTiger: This discussion originated in the "what existed before the big bang?" thread. Well put marcus. I think we are on the same page [albeit you are more eloquent] - and I tend toward being brutally blunt. We reside in an OBSERVABLE universe. And, by definition, it includes...

The model that Lisa Randall and Raman Sundrum propose consists of two four dimensional (Minkowskian) branes, bounding a five dimensional bulk between them. In their initial model the branes are very close together; this is not a "large extra dimensions" model. The motivation of the model is...

Is it just black space extending forever? Or perhaps black space for a finite distance until another universe? I find it hard to believe our universe is just the only universe. I don't see how it wouldn't extend for eternity instead. What is so special about our universe and the space we are...

Certainly an horrible way of thinking and that's why I should like to get a fundamental critic about this: As I can read in some threads, the Poynting’s vector is of a great importance (e.g.: to know if a radiation is present or not) in a lot of works and theories; in mine too. One of the...

In the standard formulation of QM, time is a scalar parameter. I have seen time being treated as the 0th dimension of spacetime in a covariant Dirac equation, but is there any way of having time as an observable (i.e. associated with a Hermitian operator etc) which has a spectrum and so on?

The Law of Projection: "No matter where a particular sensory pathway is stimulated along its course to the cortex, the conscious sensation produced is referred to the location of the receptor." ('Review of Medical Physiology', 6th Edition, W.F. Ganong, p. 63) OK, the term 'projection' might...

How far away are the most distance objects we can see? What is currently the volume of space that we can study with the light that is reaching us? You might want to look at this brief Cosmology FAQ paragraph: http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN *******footnote...

Say I observe a physical phenomenon; does that mean I can necessarily mathematicize it? Does possible observation reach only a fraction of physical reality? Will mathematics ever be able to explain a unification between general relativity and quantum mechanics? If such a TOE is ever...