What is Quantum Interference?

[stevendaryl]

They believed geometry for example had no objective reality - it was simply a convention we have - just a construct we adhere to.

Okay, thanks.

Geometry shows up in equations of motion through the appearance of additional velocity-dependent terms:

$m (\frac{d^2 x^\mu}{ds^2} + \Gamma^\mu_{\nu \lambda} \frac{dx^\nu}{ds} \frac{dx^\lambda}{ds}) = F^\mu$

I suppose you are free to move the terms to the other side and interpret them as velocity-dependent forces:

$m \frac{d^2 x^\mu}{ds^2} = F_{eff}(m, v)$

where $F_{eff}(m,v) = - m \Gamma^\mu_{\nu \lambda} v^\nu v^\lambda + F^\mu$

Kaluza-Klein models go the other way; they reinterpret forces (electromagnetism, in the original model) as being due to geometry. So maybe even if geometry is not completely conventional, we may not be able to empirically distinguish geometrical explanations from other types of explanations. So our observations may not uniquely determine the geometry

 

[bhobba]

Geometry shows up in equations of motion through the appearance of additional velocity-dependent terms:

That's true. But a conversationalist would counter something, gravitions maybe, simply makes flat space-time act as if its curved - it isn't really - its flat. I asked Steve Carlip about this and he said there is no way to tell the difference. Its just the way it is. Its simply convention based on simplicity that we choose curved space-time. But an actual quantum theory of gravity below the Plank scale may change that - who knows.

The same with LET and SR. Both are equally valid scientifically - we just choose SR because its simpler, more beautiful and elegant, generalizes more easily to QFT - all sorts of reasons. But LET may be true. However IMHO you would need rocks in your head to choose it - all our current knowledge supports SR over LET. I think it's rubbish, personally, to consider theories that are simply contrived for the purpose of demonstrating some philosophical position. As Einstein said - nature is subtle, but never malicious. Can I prove it - of course not.

Thanks
Bill

 

[vanhees71]

They believed geometry for example had no objective reality - it was simply a convention we have - just a construct we adhere to. Turing countered, since it is used in deigning bridges etc it must have some kind of objective truth or bridges could fall down etc. Wittgenstein, and I presume Poincare, simply said - so what. If they fall down, they fall down and we adjust our conventions.

Here is a link:
http://www.chass.utoronto.ca/~jrbrown/PhilosophyofPhysics.V.ppt

Thanks
Bill

I think, in this case both views are right but in different senses. Geometry, as a mathematical axiomatic system, is of course convention. You can invent any system of axioms you like to define a geometry. As long as you don't run into some contradictions, it's each a valid mathematical theory. As a description of physical observation it's subject to experimental/observational testing, and one has to verify how accurate the description coincides with observations, and there indeed Euclidean geometry has been found to be only a good approximation, neglecting gravity. Gravity is a very weak interaction, and thus the approximation in our everyday world is very good, because we are surrounded only by quite tiny amounts of matter (the Earth and even the Sun are pretty small masses, and it's hard to find the deviations from Euclidean geometries, like the classical tests of GR, i.e., perihelion shift of Mercury and the deflection of light by the Sun). In this sense, as a physical model of Nature geometry is not pure convention but an empirical finding.

 

[bhobba]

As a description of physical observation it's subject to experimental/observational testing,

The trouble is we have theories like LET that are experimentally indistinguishable from SR. Why would anyone but 'cranks' choose LET? Conventional scientists know it just fits better with our other knowledge like QFT. It isn't experiment that chose's it - it's some sense we have of right and wrong - maybe what Gell-Mann was getting at.

This is really my last comment. We are getting way off its purpose. Please can we simply stick to its purpose. Really - if we don't it will be shut down.

Thanks
Bill

 

[Dale]

We will go ahead and close this thread at this point. It has gone out of physics and into philosophy.