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Modern vs Classical Physics 
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#1
Apr2605, 12:35 AM

P: 37

Hoping for some input on the following:
In the development of what is now known as classical physics, there was a tacit assumption that the universe was governed by laws, which we did not know, but attempted to understand. In modern physics, most notably with Relativity and Quantum Mechanics, it seems that this philosophy changed. Instead of assuming that the universe acted in a certain way, regardless of how we observed it, we began treating the universe as acting in a way consistant with how it is measured. To more aptly illustrate my point consider the following: Werner Heisenberg proposed that we could not measure both the position and momentum of a particle simoultaneously. Classically speaking, one might say, a particle has a definite position and momentum at a given moment, but any attempt to measure one will skew the measurement of the other. Modern Physics, specifically Quantum Mechanics, seems to insist that the particle does NOT have a definite position and momentum at a given moment. Instead, the view became that a particle is actually a "likelihood of positions and momentums." In an attempt to simplify my point, I will abuse the language a bit and say: Classical View: Am I mistaking something about the interpretation of modern physics, or overlooking something in the development of classical physics? In any case, input is appreciated. 


#2
Apr2605, 01:59 PM

P: 309

In fact it seems to me you're speaking about
1) classical QM 2) modern QM I will first do just classical and quantum mechanics : a) Well I think in QM you can measure p and q simultaneously in the sense : if you measure them simultaneously, then you get an uncertainty. Interprete this as : taking the same configuration (wf in qm) if you measure position p', then momentum can have several values q' (uncertainty) in any case (there exist no wf for this is not true) b) Classically : if you take the same configuration (same initial conditions, same forces), then at a certain time at a given position you have only one p', there are no other possibility. The remarks are : 1) However if you take commutating observable in QM, you can deduce the value of one knowing the other measurement value. So that in fact the philosophical position of classical mechanics is a special case of the possibilities given by QM.... 2) the time specifically comes into classical mechanics to distinguish them. This should have something to do with the special nature of time in QM 3) I think QM gives no indication about "classical" interpretation (one measurement disturbs the other, but particle had a precise value for both before measurement). QM just affirms : generally before measurement the particle is in a superposition of states. I think there is somewhere in this forum an indication about Feynman Lectures III that gives indication about why in QM a physical quantity has no meaning considered independtly from a measurement (or something equivalent) 


#3
May105, 01:46 PM

P: 90

I think that the real difference between quantum mechanics and general relativity is that quantum mechanics is not only abstract but also deals with the interactions of absolute particles.
Also quantum mechanics rejects the existence of physical space, existing seperately from absolute matter. I think that's the physical error in relativity. Space cannot exist seperately from matter. The relative is abstract (in our head) and depends on the absolute. Still not convinced? Check this site... The contradiction is when one introduces a time dimension, the possibility of motion is automically prevented. There is no change/motion in the time axis because time is an invariant by definition. 


#4
May405, 12:35 PM

Emeritus
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PF Gold
P: 5,533

Modern vs Classical Physics



#5
May405, 01:05 PM

P: 309

GR is an equation for spacetime itself (the metric)....no prob. of find anything here. So the Graal would be : how to find an equation which governs spacetime AND the wavefunction depending on this spacetime....with of course selfinteraction possible.... 


#6
May405, 04:14 PM

P: 90

Proper time is time measured when the clock is at rest relative to the observer. [tex]d\tau = \frac{dt}{\gamma}[/tex] or [tex]d\tau = dt\sqrt{1[\frac{v(t)}{c}]^{2}}[/tex] He writes that tau is also an invariant evolution parameter that is used in physics as a calculational tool with which to describe a rate of motion or change (see time dilation). 


#7
May405, 04:28 PM

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PF Gold
P: 5,533

http://farside.ph.utexas.edu/teachin...es/node15.html 


#8
May405, 05:52 PM

P: 90

There is no evidence for the physical existence of spacetime and definitely not for motion in spacetime. Get a grip man. 


#9
May405, 05:53 PM

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PF Gold
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#10
May405, 05:55 PM

P: 90




#11
May405, 06:01 PM

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PF Gold
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Starship, you are going to find yourself banned from here very quickly if you do not stop posting bald assertions and ad hominem argumentation. Stop it. 


#12
May405, 06:18 PM

P: 90

The laws of physics (especially thermodynamics) do not even distinguish between our past, present and future. They're all abstract. 


#13
May405, 06:27 PM

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PF Gold
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Kid, you need to bring up the quality of your posts. You aren't making any sense, you are quoting obvious cranks as authorities, and you are making one strawman argument after another. It's really getting boring. 


#14
May405, 07:16 PM

P: 90

[tex]g_{\mu\nu}\eta^{\mu}\eta_{\mu} = \gamma^2 c^2 (1\frac{v^2}{c^2}) = c^2[/tex] 


#15
May405, 07:44 PM

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PF Gold
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#16
May405, 08:44 PM

P: 90

In fact, i think he was right in everything he said. There is no evidence for the physical existence of a time axis. 


#17
May505, 11:00 AM

Emeritus
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PF Gold
P: 5,533

Yes, the spacetime of SR is a mathematical construct. So is any other theoretical device used in physics. The question is, "How well does that mathematical construct map onto observable reality?" The answer is that SR maps very well onto it. 


#18
May605, 01:41 AM

P: 90




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