I Need Help on Particle Spin

  • I
  • Thread starter Thread starter LarryS
  • Start date Start date
LarryS
Gold Member
Messages
357
Reaction score
33
TL;DR Summary
Why do particles spin all the time?
All elementary particles have an intrinsic spin/angular momentum. The fact that particles spin at all is due to Special Relativity. How MUCH they spin, half-integer multiples of reduced Planck's Constant, is due to Quantum Mechanics. Right?

Apparently, the reason particles spin at all is because two non-colinear Lorentz Boosts are the same as one Lorentz Boost followed by a rotation. How do you go from that to all particles spin all the time?

Thanks in advance.
 
Physics news on Phys.org
LarryS said:
All elementary particles have an intrinsic spin/angular momentum.
Except those that don't, such as the Higgs. Unless you're counting spin zero as having "intrinsic spin/angular momentum".

LarryS said:
The fact that particles spin at all is due to Special Relativity.
Why do you think this?

LarryS said:
How MUCH they spin, half-integer multiples of reduced Planck's Constant, is due to Quantum Mechanics. Right?
There is a spin-statistics connection which is believed to be due to quantum field theory, that particles with integer spin are bosons and particles with half-integer spin are fermions.

LarryS said:
Apparently, the reason particles spin at all is because two non-colinear Lorentz Boosts are the same as one Lorentz Boost followed by a rotation.
Where are you getting this from? Do you have a reference?
 
LarryS said:
TL;DR Summary: Why do particles spin all the time?

All elementary particles have an intrinsic spin/angular momentum. The fact that particles spin at all is due to Special Relativity.
In addition to #2:
Elementary particles don't spin. Many of them have non-classical degrees of freedom which are named "spin", because their quantum behavior under application of Lorentz transformations (especially spatial rotations) resembles that of angular momentum. The polarizations of light are a well known example of spin. They readily appear in the classical treatment when we regard light as EM waves. You know that a linear polarization of an EM plan-wave in vacuum doesn't "spin", right?

LarryS said:
Apparently, the reason particles spin at all is because two non-colinear Lorentz Boosts are the same as one Lorentz Boost followed by a rotation.
Could it be that you are confused between spin and Thomas Precession?
 
  • Like
Likes dextercioby and PeroK
LarryS said:
How do you go from that to all particles spin all the time?
This question looks like if you were asking for why are particles spinning, do not confuse spin (intrinsic quantum property) with spatial rotation, particles cannot rotate.
 
We often see discussions about what QM and QFT mean, but hardly anything on just how fundamental they are to much of physics. To rectify that, see the following; https://www.cambridge.org/engage/api-gateway/coe/assets/orp/resource/item/66a6a6005101a2ffa86cdd48/original/a-derivation-of-maxwell-s-equations-from-first-principles.pdf 'Somewhat magically, if one then applies local gauge invariance to the Dirac Lagrangian, a field appears, and from this field it is possible to derive Maxwell’s...
I read Hanbury Brown and Twiss's experiment is using one beam but split into two to test their correlation. It said the traditional correlation test were using two beams........ This confused me, sorry. All the correlation tests I learnt such as Stern-Gerlash are using one beam? (Sorry if I am wrong) I was also told traditional interferometers are concerning about amplitude but Hanbury Brown and Twiss were concerning about intensity? Isn't the square of amplitude is the intensity? Please...
This is still a great mystery, Einstein called it ""spooky action at a distance" But science and mathematics are full of concepts which at first cause great bafflement but in due course are just accepted. In the case of Quantum Mechanics this gave rise to the saying "Shut up and calculate". In other words, don't try to "understand it" just accept that the mathematics works. The square root of minus one is another example - it does not exist and yet electrical engineers use it to do...
Back
Top