Re: A little challenge for relativists.


"Bilge" <dubious@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> schrieb
> Ilja Schmelzer:
> >"Tom Roberts" <tjroberts@xxxxxxxxxx> schrieb
> >> Ilja Schmelzer wrote:
> >> > "Tom Roberts" <tjroberts@xxxxxxxxxx> schrieb
> >> >>I meant that _today_, Einstein's SR is a fundamental component of
> >> >>physics, and Lorentz's LET is not.
> >> >
> >> > But that's simply tradition, not physical evidence.
> >>
> >> Not, it's deeper than mere tradition.
> >
> >There was some philosophy of science which was modern at
> >that time, positivism. This philosophy has favoured SR.
> >Today this philosophy is as dead as possible for a philosophical
> >idea.
>
> >> SR has Lorentz invariance as a fundamental symmetry of the theory, and
> >> LET has it only as an "accidental" symmetry FOR OBSERVABLES.
> >
> >Yep. And for the modern approach to symmetry this distinction
> >is quite irrelevant, today we use every symmetry we can find,
> >including approximate symmetries.
>
> There is a reason for using approximate symmetries.

I know.

> >> It is the assumption that Lorentz invariance is a fundamental symmetry
> >> of nature that has permitted physicists to discover other good
theories,
> >> such as GR, QED, and the standard model.
> >
> >No. Already Poincare has proposed to modify the theory of gravity
> >to fit into the new symmetry scheme. And even startet (with a wrong
> >scalar theory, but that was the natural first step).
> >
> >Once we find a symmetry, it is always reasonable to look how far
> >it extends. And, for Ockham's razor, Popper's empirical content,
> >and simply for beauty we will always try to extend the symmetry
> >as far as possible. Nothing what has been found would have
> >been prevented.
>
> If you want philosophical reasons, the reason that symmetry has
> such a prominent position in physics, is because it is the most
> philosophically appealing.

Philosophically symmetry in itself is quite irrelevant.

More symmetry gives a theory often more simplicity, more
empirical content, more beauty, more explanatory power.

> >Instead, the postulate that this symmetry is fundamental has closen
> >a lot of directions of research. Especially the research about
> >similarities between fundamental physics and condensed matter theory.

> There, you are way off base. The almost ubiquitous examples used
> to introduce spontaneous symmetry breaking are superconductors and
> the heisenberg ferromagnet.

I know, read before responding.

> The problem is that you've turned the
> analogy on its head. You would be correct in saying that most physicists
> aren't interested in treating the universe literally as condensed matter.

If physicists would have been more interested in this direction of research,
they would have been found what we know today much earlier. And, I
guess, they would have found much more than we know today. (But that's
something I cannot prove for obvious reasons.)

> If you realized how the massless part of the approximation of a
> ``massless phonon'' is really pictured, you might be less enthusiastic
> about the condensed matter description. In condensed matter, you have
> a fermi surface and an energy gap. If the phonon has a low enough energy,
> it cannot scatter from any of the matter below the fermi surface, since
> in order to do so, it would have to change the momentum of one of those
> particles. Since all of those states are filled, that matter doesn't
> exist as far as the low energy phonon is concerned and the phonon
> doesn't interact with it.

Nice. Your point?

> >> Sure. But still, EVERY modern fundamental theory of physics contains
> >> Lorentz invariance: unbroken, exact (no approximation), and valid
> >> everywhere (no limits).
> >
> >Indeed. No wonder that we have not yet found quantum gravity.
>
> Do you know of any experiments which suggest quantum gravity will
> be better addressed by something which doesn't make any sense in
> the experiments that suggest lorentz invariance is a good symmtery?

A meaningless question. We have strong theoretical evidence that
there is no quantum theory of gravity of the type GR freaks like to have.
Thus, no experiments necessary to establish this.

Ilja


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Relevant Pages

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