Doc wrote:Typhoon wrote:Doc wrote:OK CS Here is what Thomas has to say about measurement. Do you have any problems with it?(I transcribed this so any typos are mine)
Let us reconsider a particle which is isolated from the rest of the universe, or has been generated as a new particle and has not yet interacted with the rest of the universe, ie., it has not yet been measured or observed. What can we say about its properties? Once again in the absence of absolutes(There is not universal unit of measure that it absolute - my insert), nature is fundamentally unable to assign absolute values to the particle. And because the particle has not yet interacted with the rest of the universe to be measured or observed, nature is unable to assign any relative values either. As discussed in the last section, all we can say about its property values is "They go up to 11", an essentially meaningless statement reflecting the fact that the particle's property values are undefined -- they have no relation to the rest of the universe. Before observation or measurement, the object must be like a blank sheet: it must be an undefined object with the potential to take up any possible property values. So before observation, the object must have a multi-valued form of reality -- as is observed in quantum mechanical behavior. It is only when the object interacts with the rest of the universe that its properties become progressively tied down to particular values.
This is what we saw in the case of environmental decoherence. It is through interaction with the rest of the universe, via the measuring apparatus,(the measuring apparatus being huge compared to the particle measured -- my insert) that the properties of a particle become fixed.
So here, rather wonderfully, we have a rational -- an explanation -- for the multi-valued nature of quantum behavior before measurement, or observation. Here are the logical steps we followed to get to this conclusion:
1) Nature has no access to absolutes, so it is always fundamentally unable to assign absolute property values to a particle.
2)Therefore, particle properties are defined by the relationship of that particle with the rest of the universe.
3)Bearing this in mind, if we consider as isolated particle, or a newly generated particle which has not yet been measured or observed, nature has fundamentally no way of assigning any form of property values -- absolute or relative to the particle.
4) The properties of the particle are therefore fundamentally undefined -- like a blank sheet. Its properties must have the potential to be any possible value
5)The object must therefore have a multi-valued form of reality before it is observed. It is only after observation -- when the object interacts with the rest of the universe -- that the properties of the object become fixed.
Anyway what do you think about this?
Not even wrong.
Let's have a look at the non-relativistic QM
Schrödinger equation which is known to describe the evolution of, for example, a single partice wave function Psi:
m is the mass of the particle. It is not ever "undefined".
Even if we set the potential V(x), which in the QM case describes the interaction of the particle with the rest of the universe, identically to zero
m is still defined.
The relativistic QM
Dirac equation for a single particle, with V(x) zero, is given by
wherein the particle now has both mass m and the matrices beta, alpha_1, alpha_2, alpha_3 which describe the electron's intrinsic spin of 1/2 [in units of hbar: Planck's constant / 2 * Pi]
These properties carry over into the QFT of the electron:
[click on the equation for the link to the details]
To sum up, if the properties of a fundamental particle, it's mass, intrinsic spin, and possible charges (electric, weak, colour) are "undefined" at some point, then we can't write down an equation for it.
Another point: mathematics is the language of the physical universe.
I don't think that one can learn physics without mathematics.
For anyone who would like to learn non-relativistic QM, the best textbooks are
Quantum Mechanics: Vol. I and II by Claude Cohen-Tannoudji and Bernard Diu
bar none.
For the sake of argument -- m is related to gravity. Gravity would be defined for any particle ir-regardless of it being otherwise defined. In the double slit experiment it is not gravity that collapses the wave function. If it were true then certainly there would be no wave function to begin with as any such experiment done on earth, the earth itself would be a measurement apparatus. The same for the electric charge of a wave/particle function The earth's magnetic field would "measure" it. That leaves intrinsic spin. Something I know little about. How do you measure intrinsic spin?
The wavefunction is |Psi>(x,y,z,t), thus it is a function of spatial position and time [switching to
Dirac bra ket notation].
It is
not a function of mass m, electric charge q, or intrinsic spin s.
<Psi|Psi>(x,y,z,t) thus gives a probability of observing a particle of mass m, charge q, and spin s at spatial position (x, y, z) within an infinitesimal volume dV at time t.
Mass m and electric charge q of a particle cannot [to-date] be calculated from first principles,
they have to be empirically measured and put in "by hand" into the wave equation
before solving for |Psi>.
[Note that the use of mathematics rather then reams of descriptive text makes this immediately obvious.]
This is one point that the author clearly gets wrong and, in doing so, misinforms and misdirects his readers.
Actually, it's a bit difficult to understand what the author is trying to say as quoted text is far from clear.
As for intrinsic spin:
Behold the vectors of the field: they toil not, what they do is spin
Doc wrote:
Thanks. Just one point of real contention
I don't think that one can learn physics without mathematics.
Einstein could not do the math for relativity when he first came up with the theory. He figured it out through mind experiments where he imagined he was traveling at the speed of light and what that would look like. His wife helped him with the math. His college instructor gave him credit for coming up with the idea that Einstein could not mathematically describe But Einstein did not know the math to prove it until later. IE is not always about the math. But unless someone that does not know the math is extremely lucky in who surrounds them at best they can look foolish at worse someone else will get credit for the ideas.
There is a lot of popular mythology about Einstein. Much of it is wrong.
Einstein excelled at mathematics.
Once Einstein had the ideas of the equivalence principle and general covariance of GR, he searched for a mathematical structure that would describe these concepts and found it in tensor calculus and Riemannian geometry. See the correspondence between Einstein and Levi-Civita.
SR and GR are two of the very rare cases in physics wherein thought experiments, as opposed to experimental observations requiring explanation, lead to a new new theory.
I'm not aware of any contribution to the theories of physics that was done without mathematics and
I did spend some time trying to recall any such example.
Of course, creativity and imagination are required, but a facility with math is apparently a prerequisite
as it does seem to be the
unreasonably effective language of the physical universe.