On 3/2/2014 3:46 PM, LizR wrote:
On 3 March 2014 11:54, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
On 3/2/2014 2:38 PM, LizR wrote:
On 3 March 2014 08:33, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
I don't think Tegmark appreciates how much the "laws of physics" depend
on our
demands that the "laws" be invariant, e.g. conservation of energy is a
consequence of requiring the lagrangian to be time-translation
invariant.
That isn't a demand, it's an observation. (Made by Emmy Noether, IIRC.)
Noether observed the connection between continuous symmetry in a lagrangian
and the
existence of a corresponding conserved quantity. But that a lagrangain (or
theory
in any form) have that character is a "demand"; or at least a strong desiderata.
Remember how the neutrino was discovered. If some process seemed to not conserve
energy, we'd just look for something new we could count as the energy
difference.
I don't want to nitpick here, but that sounds like a highly disingenuous comment to come
from someone who knows a lot about physics (either you or Vic Stenger).
IMHO it makes perfect sense to expect an unexplained phenomenon to obey conservation
laws, given their success to date. That is, given that everything in the universe that
had been studied over the previous 300 years or so appeared to obey these principles,
why would they immediately assume that they wouldn't apply to a new discovery? And as it
turned out, they were right. Neutrinos have observational consequences above and beyond
being a mere "accounting process" in beta decay, or whatever it was, such as being
directly detected, as well as having strong theoretical support (e.g. in how the sun
operates and how supernovas explode).
Of course different forms of energy were identified - but by showing something not
previously accounted for could be called 'energy' and thereby achieve conservation. I
don't think the general conservation of energy was considered a firm principle until the
mid 1800's and its violation was seriously entertained in the case of beta decay. But the
idea that the "laws of physics" should not depend on time or place goes back much further
and had broader historical support; not just empirical but also metaphysical. Notice how
outrageous Edgar's p-time appears, and he just wants a universal clock. How would it
sound to put forth a theory that reference a specific time? No one would accept it as
fundamental.
Also, some processes /do /violate symmetries, and these have been duly detected, and
scientists were duly surprised.
Sure, SR violate Galilean symmetry, CPT isn't even a continuous symmetry and so doesn't
fall under Noether's theorem. I don't claim it's an absolute requirement (notice I said
"desiderata") but it's surprising how much you can get out of symmetry principles. Did
you read Stenger's essay? My main point though was to look a little askance at Tegmark,
and others, idea that if we just get the right math, or the most elegant theory, then
we'll know what's really real. I don't think they pay enough attention to the fact that
we make up the laws of physics.
Brent
I'm kind of surprised myself to see you coming out with what seems like a postmodernist
take on how scientists operate.
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