On 12/01/2016 12:56 AM, Steven Carlip wrote:
> You've left out the context. The full talk is available at
>
http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html.
> The paragraph you're quoting is
>
> "Recapitulating, we may say that according to the general
> theory of relativity space is endowed with physical qualities;
> in this sense, therefore, there exists an ether. According to
> the general theory of relativity space without ether is unthinkable;
> for in such space there not only would be no propagation of light,
> but also no possibility of existence for standards of space and
> time (measuring-rods and clocks), nor therefore any space-time
> intervals in the physical sense. But this ether may not be thought
> of as endowed with the quality characteristic of ponderable media,
> as consisting of parts which may be tracked through time. The idea
> of motion may not be applied to it."
>
> Einstein is using "ether" as a synonym for what physicists would
> now simply call "spacetime." This is, as he says, radically different
> from what the term meant before relativity.
In fact, around that time frame, Quantum Field Theory hadn't yet been
fully developed. So he needed a placeholder term to describe what the
new actor on the stage should be called, so he fell back on the old
Aether term. By the time Quantum was more developed, by the end of that
decade, then it turned out that spacetime was the actor itself. It had
its own properties, and it was considerably more complex than the old
Aether ever could be. If he had given that same speech just 10 years
later, then he would've called it "spacetime" rather than "aether". His
own General Relativity provided the bones of spacetime, while Quantum
provided the flesh of spacetime (or maybe it's vice-versa, whatever).
I toyed with the idea of calling spacetime as a synonym for Aether
myself at one time. But really after awhile, I realized that Aether is
simply the wrong model. Call Aether an early model for spacetime, except
it wasn't space nor time, it simply existed in space & time, just like
matter and energy does. In the current model, space & time are united
and interact with matter and energy. There's no way the earlier models
of Aether could do that. So it's just wrong to call it Aether, it's the
wrong model.
Yousuf Khan