Clarity in Physics

What role does "clarity" play in physics?

These are the core theses of the special theory of relativity and they are ultimately nothing more than a consequence of the failed Michelson experiment.

Does the question in this headline strike you as odd?

Yes, me too !

With this epilogue I will try to console you if one or the other detail in the history of Sagnac & Co appears completely incomprehensible

I hope you share my opinion that the mathematical ability requirements in the previous chapters have not been too high. The expressions were partly maybe a bit "bulky", - but the basic arithmetic operations, some tigonometry and the very first basic concepts from integral calculus were enough for understandingcompletely off. the tofdemands on our imagination in connection with e.g. with the propagation of light in different systems were enormous.

What was it about ?

What were the core theses of our reflections on the MIchelson and Sagnac experiment ?

1. The same laws of nature apply throughout all systems moving uniformly in relation to one another.

I think you can live with that, right?
But here it comes:

2. The speed of light is a constant in every frame of reference.

This reads quite harmless, but it is a blatant imposition on our everyday experience.

Does this thesis mean nothing else than that a ray of light always arrives at you at the same speed, regardless of whether you are moving or standing still, no matter whether it comes from the headlight of a moving car or from the flashlight of a stationary companion!

If a moving car throws stones at you, the speed of the stones is made up of the speed of the car + the speed at which the stone is thrown from the car - that's clear!

This does not apply to a light beam, whose speed remains completely unaffected by the transmitterspeed

That alone wouldn't be too surprising, because that also applies to sound, otherwise a supersonic fighter could never overtake its own sound wave, ... but also for theRecipient the speed of light is always the same whether it is moving towards the light beam, standing still or moving away.

FA-18 Supersonic Fighter overtakes its own sound wave.

Philip Lenard, 1862 - 1947,Initiator of an Aryan physics.

"Basically" means - there are also exceptions ;-)

And because it's all so unimaginable, Philip Lenard also his very own opinion - he considers everything to be nonsense that in his opinion is not "descriptive" and demands that physical models must always be descriptive.

And I think that's nonsense!
But who am I compared to a Nobel laureate?

Philipp Lenard received the Nobel Prize in 1905 for his work in the field of cathode rays - so he's not "just anybody". Since he is not alone with this opinion and still has followers today (read morehere andherearoundhere !!) you should lose a few words on the subject of "lucidity in physics".

When do we find an explanation, a theory, a thought experiment clear?

I would say - if we can combine it with an everyday experience, or (to put it a little more elegantly) - the perception refers to the sensory-receptive part of knowledge(Immanuel Kant)

And now my question to Mr. Lenard and his disciples:

Can a newly gained knowledge be vivid?

Can it be supported by everyday experience, or can it be experienced with the senses in Kant's sense?

Answer - no, she can't!

If that were the case, if it corresponded to everyday experience, then the knowledge would not be new! I would even go so far as to say that new physical knowledgebasically cannot be clear!

At the time of its discovery, the knowledge that has now become "flesh and blood" was not "descriptive".

Would you like some examples?

Nicholas Copernicus

Galileo Galilei

Martin Luther - "Inventor" of the relativity principle !

The earth revolves around the sun!

When Copernicus (1473 to 1543), Galileo (1564-1642) and some others tried to replace the geocentric world view with a heliocentric one, their contemporaries had considerable problems with it. It didn't seem "descriptive" to them, on the contrary! Couldn't you see every day how the sun rises in the east, orbits the earth and sets in the west?

Marthin Luther (1483 - 1546) writes e.g. about it : (Link to Wikipedia page):

"There is talk of a new astrologer who wishes to prove that the earth moves instead of the sky, the sun and the moon, as if one in a moving chariot or ship might think that it stands still while the earth and the trees are moving. ...." *)

First spontaneous reaction to this comment by Luther (from today's point of view):

Gosh, - but that's close to the truth!

If Luther had thought this thought through, then he might have become the father of the principle of relativity almost 100 years before Galileo and almost 150 years before Newton, because that is precisely the core statement of this principle: you really can't decide whether the "ship" or the "trees" move. For Luther and his contemporaries, however, this thought was so foreign and indescriptive (!) that they were prepared to burn the authors of these considerations at the stake!

That brings us to the next example:

Isaac Newton (1642-1727)

Alright: Galileo and Newton have not yet used the term "principle of relativity" - as far as I know!

You should really take a look at Galileo's "Dialogue"! ( Here is the link to a German translation.) It is really impressive with what amount of examples and comparisons, with compelling logic and without any mathematics, Galileo describes the behavior of bodies in moving systems.

Es existierte auch die Ansicht, dass ein Stein, der von der Mastspitze eines fahrenden Schiffes fällt - je nach Geschwindigkeit des Schiffes - mit mehr oder weniger Abstand zum Mast aufs Schiffsdeck fällt - und wenn die Erde sich bewegt, dann müßte genau dasselbe mit einem Stein passieren wenn man ihn z.B. von einem Turm herabfallen läßt !

The principle of relativity!

In his work "Philosophia Naturalis Principia Mathematica" Newton writes:

"The movements of bodies in a given space are the same among themselves, whether the space is at rest or whether it is constantly moving in a straight line." (Link to Wikipedia page.)

Einstein later put it more generally:

"The same laws of nature apply throughout all systems moving uniformly in relation to one another."

.... and from this it follows, by implication, that the uniform state of motion of a system cannot be determined, precisely because the laws of nature are exactly identical in all of these systems!

Please put yourself in the imagination of people in the 16th and 17th centuries:

There are some weirdos who claim that the earth goes around the sun - although you can see the opposite in the sky every day! - and now these smartasses come along and talk about a principle of relativity and claim you can't tell whether the ship is moving in the water or the trees on the shore! So something else is clear!

The problems people had with this principle in the 16th and 17th centuries can be wonderfully understood if you take a look atGalileo famous "Dialogue Concerning the Two Main World Systems".

According to the conception then prevailing, if the earth were actually moving at great speed (30 km/sec) around the sun, it would have to leave its atmosphere behind and a bird in the air would have to lag behind the fast-moving earth.

Galileo's sketch of the principle of relativity

This is roughly how Galileo's contemporaries imagined the fall of a stone from a tower:

If the earth moves, the stone should hit some distance from the base of the tower. But since the stone arrives right next to the base of the tower, the earth can't move either!

Now prove that this argument is wrong!

Galileo Galilei, 1564 - 1642

Precisely because the experiment could have brought about a quicker clarification in this particular case, Galileo complains about the ignorance of the "authorities" because they (quote):

"... to rely on their predecessors without ever coming across anyone who actually tried. For whoever does so will find that the result is exactly the opposite of what one reads in writing. You will come to the conclusion that the stone always falls in the same place on the ship, whether it is stationary or moving at any speed. ...! (Page 151 in "Dialogue")

In his famous example of a ship, he makes it clear that (without contact with the environment) there is no way of determining (quote) "... whether the ship is moving or standing still..."(Page 197 in "Dialogue")

Against the background of the physical understanding of his time, Galileo's achievement in abstraction in formulating the principle of relativity cannot be overestimated. Although he tried to provide tangible, "descriptive" examples in his writings - examples that seem downright trivial to us from today's point of view - he probably overtaxed the willingness (or the ability?) of his contemporaries to follow the "descriptive" arguments.

The "perception" - or should one say better: the preconceived notion - was extremely "obstructive" for the implementation of the principle of relativity!

Pierre de Fermat, 1607-1665

A ray of light always follows the shortest path in terms of time!

Pierre de Fermat's (1607-1665) famous principle for the propagation of light has - in its popular form - the charm that one believes one can "feel" or "understand" the behavior of light.

shortest time ? -
That makes sense right away.
I would do that too!
Pretty clever that beam of light!

Fermat's principle is a good example that the attempt can even mislead an obviously descriptive description, because of course the ray of light has no idea about the "shortest path" and in fact it does not follow the same path, but follows the path on which the Change (variation) in optical path length compared to adjacent paths is smallest. (This is usually the shortest!)

If you look at light as an electromagnetic wave - but Fermat had no idea about this - then this variation principle becomes understandable very quickly: Wherever the differences in the path of travel (phase difference) between neighboring light wave trains are very small or even zero, the light waves can constructively superimpose and thus strengthen. Wherever the path differences (phase differences) are large, they cancel each other out!

Tangential velocity in a rotating system.

But there are also examples from the normal "everyday mechanics" that, if you look at them critically, are not "descriptive" at all.

We had an example in the chapter"Why isn't there a Michelson effect?" already mentioned - you remember:

---> You are at the center of a rotating disk; There is a cat sitting at the edge of the disc and although you don't see any movement between you and the cat, I am sure you would agree that the cat is moving at (tangential) velocity relative to your position in the center.

... if you change your position (arrow in the center) on the disk, something like this ... then the relative speed between you and the cat has also changed! (In the sketch on the left, it has almost doubled!

You can't "see" any of it!

Even if you, as a person interested in technology or physics, know that the centrifugal forces that you feel are due to the rotation and if you are also aware that in a rotating system all points are in a relative movement against each other - but are You honestly: "see"can't you do any of this and from"vivid"can't be a question either!

Albert Einstein, 1879-1955

"Visuality" is the wrong tool for assessing a physical idea. New ideas cannot be graphic, otherwise they would not be new!

Conclusion

At the end of this brief reflection on the topic of "lucidity" in physics, I would like to quote Albert Einstein's response to Phillip Lenard's criticism of the lack of clarity in the theory of relativity:

Albert Einstein (1879 - 1955)

Einstein's answer:

"... the contents of "clearness" or "common sense" have grown historically and are changeable, so that they cannot be used as criteria for the correctness of a theory."(from Wikipedia: "Criticism of the theory of relativity")

I think that hits the nail on the head!

I'll try again with my words:

Often what appears "clear" to us is nothing more than pure habituation and what is "unillustrated" and too theoretical could be linked to a very concrete idea in a few decades! There are enough examples of this! (so.)

We are talking here about models that help us to describe the experimental results. In physics, these are usually mathematical models ....:

(Quote) However, modeling is often confused with clarity. Doesn't perception actually have something to do with seeing (hearing, feeling)? Gaining physical knowledge ultimately means setting up a physical theory, making pictures, mental concepts, models of natural phenomena and processes. .... The attempts to explain physical causes should not be confused with clarity. ...(Frank Kameier)

The history of physics consists of a constant adaptation of the models to the experimental results and even if the inventors of these models believe that they have discovered a piece of "truth" again - it is just another shadow on the wall of Plato's cave - (s.d. the parable of the cave. )