Path: ...!weretis.net!feeder8.news.weretis.net!pasdenom.info!from-devjntp
Message-ID: <6IzDXUAa0a3D4hY6shZ2ExTznxI@jntp>
JNTP-Route: news2.nemoweb.net
JNTP-DataType: Article
Subject: [SR] relativistic elasticities
Newsgroups: sci.physics.relativity
JNTP-HashClient: xMUEke9wQ2vz25yT2cgIF55lj_E
JNTP-ThreadID: 8-a3fgSDfJNa8INEsiMI9bNmN74
JNTP-Uri: http://news2.nemoweb.net/?DataID=6IzDXUAa0a3D4hY6shZ2ExTznxI@jntp
User-Agent: Nemo/0.999a
JNTP-OriginServer: news2.nemoweb.net
Date: Wed, 10 Jul 24 21:27:52 +0000
Organization: Nemoweb
JNTP-Browser: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
Injection-Info: news2.nemoweb.net; posting-host="e8cbf2474b472b9bb79db3dccb6a856bc1d05409"; logging-data="2024-07-10T21:27:52Z/8942482"; posting-account="4@news2.nemoweb.net"; mail-complaints-to="julien.arlandis@gmail.com"
JNTP-ProtocolVersion: 0.21.1
JNTP-Server: PhpNemoServer/0.94.5
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
X-JNTP-JsonNewsGateway: 0.96
From: Richard Hachel <r.hachel@tiscali.fr>
Bytes: 4271
Lines: 74

I am absolutely certain that if I pose a problem to physicists, they will 
be absolutely incapable of approaching the solution correctly.
The problem is however well known and if we had listened to Richard 
Hachel, it would not have posed any difficulties for a long time.
The problem is simple.
We propose to pass a rod 50 cm long through an opaque cylinder, also 50 cm 
long.

We will pass the rod from left to right, and at a speed of 240,000 km/s.
It's very fast. This is equivalent to 0.8c.

An observer placed transversely quite far from the cylinder, say thirty 
meters, observes the cylinder which therefore measures 50 cms.

When the rod reaches the cylinder, it becomes completely invisible, since 
it only measures 30 centimeters (which is true) and it is momentarily 
inside the opaque cylinder.

So far, everyone has understood.

If we could take a high-speed photo, we would only see the cylinder.

But now, we are going to place ourselves at the level of an observer who 
is in the frame of reference of the rod, and who crosses the first 
observer at the same place, and this one too, will take a photo
at the same time, and while they are married.

Breathe, breathe.

What does the great, the immense, the celestial light Richard Hachel say?

Nah, I say that to piss off Python.

Though...

The great, the immense, the brilliant Richard Hachel, he says that when 
two observers cross paths, they see exactly the same universe (but very 
spatially distorted).

N.B. The opposite would be quite absurd, it would mean that if a rocket 
passed close to the earth and photographed the universe, it would not 
collect the same photons as those captured by the terrestrial photograph.

The two observers therefore see the same thing, that is to say an 
invisible rod placed in an opaque cylinder.

We will ask ourselves the question: but in the frame of reference of the 
rod, how much does the rod measure?

The answer is obvious: 50 cm of proper length, not 30.

This is where an error in reasoning can occur, we will say that in fact 
the stem is 50 cm,
but the cylinder is only 30 and therefore we will see the rod in the other 
photo and not in the first (but we have just said that this is absurd).

No, no, we will not see the rod, and the error in reasoning comes from the 
fact that we believe that the observer placed in the frame of reference of 
the rod, sees at this moment, a rod placed transversely,
and a transverse cylinder measuring only 30 cms.

There is an alpha angle which will bring the cylinder and the rod to the 
left (Lorentz transformation) by an alpha angle such that sin alpha=Vo/c 
and if the rod measures 50 cms, the cylinder measures much more than 50 
cms (and not less).

And the rod is well inside the cylinder.

The two photos will be concordant (taken at the same place) and identical 
(but with spatial deformations well known to physicists who correctly use 
Lorentz transformations).

There is therefore neither paradox nor possible misunderstanding.

R.H.