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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.arch
Subject: Re: Is Intel exceptionally unsuccessful as an architecture designer?
Date: Mon, 23 Sep 2024 05:44:30 -0700
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Michael S <already5chosen@yahoo.com> writes:

> On Sun, 22 Sep 2024 12:58:36 +0200
> David Brown <david.brown@hesbynett.no> wrote:
>
>> On 22/09/2024 10:48, Michael S wrote:
>>
>>> On Sat, 21 Sep 2024 20:30:40 +0200
>>> David Brown <david.brown@hesbynett.no> wrote:
>>>
>>>> Actual physicists know that quantum mechanics is not complete - it
>>>> is not a "theory of everything", and does not explain everything.
>>>> It is, like Newtonian gravity and general relativity, a
>>>> simplification that gives an accurate model of reality within
>>>> certain limitations, and hopefully it will one day be superseded
>>>> by a new theory that models reality more accurately and over a
>>>> wider range of circumstances.  That is how science works.
>>>>
>>>> As things stand today, no such better theory has been developed.
>>>
>>> Actually, such theory (QED) was proposed by Paul Dirac back in
>>> 1920s and further developed by many others bright minds.
>>> The trouble with it (according to my not too educated
>>> understanding) is that unlike Schrodinger equation, approximate
>>> solutions for QED equations can't be calculated numerically by
>>> means of Green's function.  Because of that QED is rarely used
>>> outside of field of high-energy particles and such.
>>>
>>> But then, I am almost 40 years out of date.  Things could have
>>> changed.
>>
>> I don't claim to be an expert on this field in any way, and could
>> easily be muddled on the details.
>>
>> I thought QED only covered special relativity, not general relativity
>> - i.e., it describes particles travelling near the speed of light,
>> but does not handle gravity or the curvature of space-time.
>
> That sounds correct, at least for Dirac's form of QED.  May be it was
> amended later.

No one does this because the gravitational effects are way beyond
negligible.  It would be like, when doing an experiment on a
sunny day, wanting to take into account the effects of a star ten
quadrillion light years away.  To say the effects are down in the
noise is a vast understatement.  (The distance of ten quadrillion
light years reflects the relative strength of gravity compared to
the electromagnetic force.)

> But that was not my point.
> My point was that the QED is well known to be better approximation of
> reality than Heisenberg's Matrix Mechanic or Schrodinger's equivalent
> of it.  Despite that in practice a "worse" approximation is used far
> more often.

I would say simpler approximation, and simpler approximations are
usually used then they suffice.  If for example we want to
calculate how much speed is needed to pass a moving car, we don't
need to take into account how distances change due to special
relativity.  When we want to set a timer to cook something on the
stove, we don't worry about whether we are at sea level or up in
the mountains, even though we know that the difference in gravity
changes how fast the timer will run (and even can be measured).
There are situations where QED is needed to get an accurate
numerical result, as for example if we want to know the magnetic
moment of the electron, and accurately enough to compare against
very sensitive experiments.  But until and unless we are
confronted with circumstances where those tiny corrections are
necessary, which is to say that the differences have measurable
consequences, generally it's better to just ignore them.