bangstrom » December 1st, 2018, 2:52 pm wrote:Einstein did away the ether theory with his special relativity but some say he restored the ether with general relativity by replacing the ether with spacetime and gravitational frame dragging. So what is the difference between the ether and spacetime?

This claim above has been circulated too many times on this forum and it is time to set the record straight on the history. This article is not an attempt to re-adjudicate Special Relativity or General Relativity as physics theoruis, but an attempt to get the history correct on the man, Albert Einstein, in relation to the development of S-R and G-R.

We will find that the above quote is woefully wrong both historically and scientifically. Some facts here may surprise the reader, and many of them I just learned myself only recently. For many (especially bangstrom) the big take-away lesson is that history is very complicated and involves a cast of colorful characters both prior and after the years where a theory was normally said to be 'established'.

History of Science

PBS Nova, other TV series and wikipedia are short synopsis histories that grossly simplify history. History is extremely complex in reality. Short sound bites are easier for people to remember and get spread very quickly because of their simplicity and punctuality. For example,

"Isaac Newton invented calculus."

"Elvis Presley invented rock-and-roll."

"Einstein invented special relativity."

"Gregor Mendel invented genetics."

All of such rough-hewn statements mask a much deeper and more complex topic. In the case of Elvis-and-rock-&-roll , the arguments can get quite heated. The development of landmark theories of physics and science are always as complicated as the thorny as the issue about "Who invented rock-&-roll?" Even relativity is. Even quantum mechanics was.

Arguments made both pro- and con- for Elvis being the inventor are both equally valid and both have "good points" to make. con- people point out that Elvis stole most or all of his music from black artists, and that rockabilly preceded him in terms of the raw stylistic sound of the music. Those are valid points. pro- people point out that Elvis was a charismatic front man gyrating and swinging a microphone stand around. That basic template of public performance would form the basis of the next 70 years of popular music. (also a good point). A room of historians will never agree about who invented rock-&-roll and the debate rages on. The point is, the question is complex and contentious.

( Newton and calculus. ) Multiple youtube videos featuring Niels deGrasse-Tyson have him just blatantly stating that Newton "invented differential and integral calculus" in what apparently seemed to be one weekend. And there are these anecdotes about how the foundational papers were later found in a desk by a maid or something. Anyways, Isaac Newton did not invent calculus. The brutally honest history is that Newton was the first person known to use calculus-based-reasoning in his mathematics. His notebooks are unreadable by modern eyes, because the notation that was beat into us in high school was only invented in the middle of the 19th century, some 170 years after Principia. The claim that calculus did not exist in 1660, and that by 1670 , presto change-o , a fully-formed mathematical discipline suddenly existed. That's absolutely wrong. Isaac Newton never referred to what he was doing as "calculus" -- and that is something the reader should keep in mind when I get to Einstein later.

( Gregor Mendel is the father of genetics. ) It turns out that Mendel's notebooks containing his data were only re-discovered in 1900 by Austrian geneticists. Mendel's scientific work only referred to various ''Principles of Independent Assortment'' that are not taught today. Mendel was the first person to have been seriously considering the expression and suppression of genes in scientific experiment. Mendel never described them as "genes", and never referred to his own work as "doing genetics".

Okay so Elvis did not invent rock-&-roll, and Newton did not invent calculus, and Mendel didn't really invent genetics. These men contributed some landmark ideas and approaches that constituted the foundational pillars of what later became rock-&-roll, calculus, and genetics. But certainly these complex and bizarre historical twists do not apply to Albert Einstein, physics genius extra-ordinaire. Right? I mean, we "all know" that Einstein invented Special Relativity in 1905, and I heard it on TV and that's that. Right?

Wrong.

Let's begin . . .

Minkowski Spacetime

4-dimensional Minkowski spacetime is central to the mathematical foundation of Special Relativity. It is, bar none, how S-R is taught in universities today in the 21st century. But Minkowski spacetime with its lightcones and all that jazz was not coined by Albert Einstein, nor did its mathematics appear in anything Einstein ever wrote.

When 4D Minkowski spacetime was shown to Einstein , he described it as quote , "superfluous erudition."

Spacetime curvature

So clearly Einstein said that space and time are curved and distorted in the presence of mass, right? I mean clearly he- ... stop right there. He did not. He didn't write it. He didn't say it.

More accurate to the complex history of G-R, it was Herman Weyl that founded the idea of spacetime curvature being the basis of gravity. https://en.wikipedia.org/wiki/Hermann_Weyl

The second loud proponent of spacetime curvature was Tullio Levi-Civita. https://en.wikipedia.org/wiki/Tullio_Levi-Civita

While I am not a professional biographer on Albert Einstein, the possibility exists that he actually rejected the idea that space was curved. Instead Einstein interpreted these curvature tensors as representing some aspect of the gravitational field itself.

It is true that Einstein derived what we now call the Field Equations. This is a differential equation containing various tensors. At the time of its derivation, Einstein did not know what the equation was saying or depicting. Only mathematicians recognized that one term in the Field Equation was something called a Riemann metric tensor. Einstein himself didn't know what "Riemann metric tensor" was, having never been trained in that mathematics. A metric tensor is the way in which distances are defined in non-euclidean geometries. Instead of using the word "distance" in those non-euclidean manifolds, they use the word "metric". This is the basis of the historical anecdote that goes :

"Only six people in Europe understand General Relativity."

{ edit : Arthur Eddington? research }

Those six people were the mathematicians trained in non-euclidean geometry. There may very well have been a whole 6 of them at some time in the early 1900s.

Relativity itself?

Wherefore Einstein went into a cave as a hermit, where he fasted and meditated daily for hours. When he emerged from the cave weeks later, he carried a large stone tablet, upon which was carved E = mc

^{2}He returned to the assembly and held the tablet above his head :

I am Albertus Einsteinius Maximus. I do declare that energy and mass are but one of the same substance!

The members of the assembly fell upon their faces before him. And they did anoint him.

Anyways..

A music critic-journalist wrote about "heavy metal falling" when trying to describe the sound of Jimi Hendrix playing a distorted guitar. Thus was coined the genre : heavy metal. Hendrix did not describe what he was doing as heavy metal. Mendel never said he was doing "genetics". Newton, while reasoning about infinitesimal quantities, did not call what he was doing "calculus".

But certainly, we can rest assured that Einstein called what he was doing in 1905 the theory of Special Relativity .. right?

Sorry. No.

Albert Einstein, the man himself, only ever referred to something he called "the principle of relativity". If we had Albert in the room with us, and we asked him what he meant by this principle, he would likely say something along the lines of "space coordinates and time coordinates are covariant". We can be sure he would say something nearly like this, as we can tell from his writing in a long article in 1950.

Unanimously, modern textbooks delineate and frame this topic as the theory of Special Relativity. Physics and engineering students in universities are not shown a "principle of relativity". Students are instead exposed to momentum 4-vectors. The tails of the vectors are on the here-and-now event, and the heads point somewhere else in Minkowski spacetime. The same Minkowski spacetime that Albert E referred to as superfluous erudition.

So what did Einstein really even contribute to physics after all this? The answer is that he contributed some key foundational ideas and insights... which later formed the foundations of a modern theory we call Special Relativity. In 1905, Albert Einstein believed he was submitting papers to the Annalen der Physik on the topic of electrodynamics (what we now call electromagnetism). Very much like the historical foundations of quantum mechanics, the very men who we popularly associate with these theories sometimes even rejected their more mainstream interpretations. Or rejected them at first, and later changed their minds, (or possibly more complex events.)

Paul Dirac's work was the key catalyst for the discovery of anti-matter. However Dirac himself couldn't see it. He may have even initially rejected the idea that positively-charged holes in a "sea of charge" could be a particle. It was in fact one of Dirac's Phd students who was the loudest proponent of the positron. That student's name : Robert Oppenheimer.

So yeah. History is a complicated and often dramatic and surprising. People change their minds, insights and ideas are formed by single people, but then groups of others seize control of them and develop them in new and unforseen directions. On the way, the personal opinions and prejudices and nuances of those people infect the theory and modify it reception within the scientific community. Sometimes even ideas are outright stolen. It's a big loud mess. Colorful characters, drama, intrigue.