
Einstein, Symmetry and the Future of Physics - theafh
https://www.quantamagazine.org/einstein-symmetry-and-the-future-of-physics-20190626/
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DiogenesKynikos
"Noether showed that the symmetries of general relativity — its invariance
under transformations between different reference frames — ensure that energy
is always conserved."

This isn't quite right. Energy isn't conserved in General Relativity. There is
a conservation law involving the stress-energy tensor, but as the name
implies, it's not energy alone that's being conserved.

But more generally, Noether's theorem, which leads to this conservation law,
is probably the most beautiful theorem in physics:
[https://en.wikipedia.org/wiki/Noether%27s_theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem).
Given that, what's amazing is that Emmy Noether only worked on physics for a
relatively short time. She was asked by David Hilbert to work on the problem
of invariants in General Relativity, came up with one of the most important
theorems in physics, and then moved on to other (extremely important)
mathematical work.

~~~
Whatitat90
> She was asked by David Hilbert to work on the problem of invariants in
> General Relativity, came up with one of the most important theorems in
> physics, and then moved on to other (extremely important) mathematical work.

Interestingly I just read about this in a Lawrence M. Krauss book [0] where it
was described that David Hilbert insisted on hiring Noether by the university
but was overruled by the male majority that didn't like the idea that a female
would teach male students. Hilbert commented that "this is university, not a
bath-house!" [1].

[0]: I think it was "The Greatest Story Ever Told—So Far"

[1]: I'm writing that from memory so excuse some inaccuracies.

~~~
imglorp
It was University of Göttingen, 1915.

[https://www.famousscientists.org/emmy-
noether/](https://www.famousscientists.org/emmy-noether/)

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dghf
> Specifically, Einstein was puzzled by a difference that didn’t make a
> difference, a symmetry that didn’t make sense. It’s still astonishing to
> drop a wad of crumped paper and a set of heavy keys side by side to see that
> somehow, almost magically, they hit the ground simultaneously — as Galileo
> demonstrated (at least apocryphally) by dropping light and heavy balls off
> the tower in Pisa. If the force of gravity depends on mass, then the more
> massive an object is, the faster it should sensibly fall. Inexplicably, it
> does not.

Is this right? I haven't studied physics formally since I was 16, but I
thought that the extra gravitational force due to greater mass was effectively
cancelled out by the extra inertia also due to the same greater mass: i.e.,
more massive bodies are indeed more strongly attracted by the Earth, but
because they are more massive they are also harder to accelerate to the same
degree, with the result that everything falls at the same rate, regardless of
mass. And I also thought this was known long before Einstein: if I had to
guess, I'd credit Newton.

Or am I fundamentally misunderstanding something?

~~~
hollerith
No you are not misunderstanding. The author of the article doesn't understand
elementary physics as well as you do, which means he or she should NOT be
trying to write an article about relativity or the future of physics. Welcome
to modern journalism.

In the paragraph after your quote is another point the author almost certainly
gets wrong:

>When Einstein realized that a person falling freely would feel weightless, he
described the discovery as the happiest thought of his life.

I have read elsewhere that this "happiest thought" was that there is _no
experiment_ that someone falling freely could do that would reliably
distinguish between being stationary and falling freely, with an emphasis on
measurements of the speed of light. I am pretty sure that it was common
knowledge among physics PhDs back then that people falling freely feel
weightless. It is not like physics PhD are incapable of jumping while noticing
the sensations in their bodies when the sensations are a straightforward
consequence of Newtonian mechanics.

~~~
ChrisLomont
>The author of the article doesn't understand elementary physics as well as
you do

Don't be so quick to make such judgments:

There is ample scientific interest in the differences between inertial and
gravitational mass [1]. That they seem the same is a profound question known
to Einstein. He explicitly assumed they were the same in his equivalence
principle [2].

So their equivalence is a postulate, not derived from deeper theories. But one
day we may find it is not consistent over time. It most certainly is a deep
question in physics.

There are other theories of gravity, taken seriously, as possible future
modifications to relativity, such as Brans-Dicke theory [3], that remove this
equivalence principle, yet still agree with all observational evidence to
date.

Current experimental evidence puts them equivalent to under 1 part in 10^-15
[2], with more experiments still being done.

[1]
[https://en.wikipedia.org/wiki/Mass#Inertial_vs._gravitationa...](https://en.wikipedia.org/wiki/Mass#Inertial_vs._gravitational_mass)

[2]
[https://en.wikipedia.org/wiki/Equivalence_principle](https://en.wikipedia.org/wiki/Equivalence_principle)

[3]
[https://en.wikipedia.org/wiki/Brans%E2%80%93Dicke_theory](https://en.wikipedia.org/wiki/Brans%E2%80%93Dicke_theory)

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vincent-toups
I'm reading Weyl's book "Symmetry" now and I have to say, physics looks like
it was a lot more fun and loosey goosey back in the day. I think only the
Quantum Gravity and Interpretation of Quantum Mechanics people still have
approximately this much fun.

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gone35
As others have commented, lots of physics errors and misunderstandings in this
article. The author, K.C. Cole, has no business explicating physics she
doesn't understand to the public. Expected more from Quanta Magazine...

~~~
Simon_says
> Expected more from Quanta Magazine...

You won't if you keep reading them.

