(Pseudo-)Riemannian Geometry
1/ Sabine Hossenfelder has done an impressive job collecting and rebutting the arguments for building a new particle accelerator. I find them partially convincing. Let me give the big reasons that no one ever mentions as they are not in her list.
Nonsense arguments for building a bigger particle collider that I am tired of hearing (The Ultimate Collection)
http://backreaction.blogspot.com/2019/03/nonsense-arguments-for-building-bigger.html
2/
I) The physics community gave us both the hydrogen bomb and the Einsteinian speed limit. Humans who acquire the Bomb never lose the ability to make them and they only get cheaper with technology. Further, the speed limit of 'c' traps us on three rocks: Earth, Moon and Mars.
3/
The combination of these twin gifts likely doom humanity over the long run unless we can, somehow, get around the speed of light 'c'. For that we will need to make physics a *top* priority unless we want to pretend we are going to become wise, colonize Titan, etc..etc..
4/
II) Theoretical physics practically created the modern economy:
Chemistry
Semiconductors/Transistors
World Wide Web
Electrification
Wireless
Nuclear Power/Weapons
Molecular Biology
These are not simply taxpayer dollars. They began as Physics Dollars. We are being absurd.
End/
III) We are at the end of this thread...but also at the end of what may be the last chapter of physics. The three main equations (Dirac, Einstein, Yang Mills) are provably, in some sense, the best possible. No one would walk out just before learning the end of our story.
I) "We gotta get FTL"
II) "Might be unexpected bonuses"
III) *appeals to emotion*
I) Not exactly FTL...but that is fair from what I wrote. I was using shorthand. Guilty.
II) No. We have obligations to this community. We don't allow them to fully participate so they have economic rights that we are abusing. This is a foreign idea to most.
III) No: Meaning.
Curious... I just reviewed the 'Dirac Sea' issue last night.
@EricRWeinstein , could you 'lightly' outline the 'provably the best possible' claim? w/o definitions for dark matter/ energy/ fluid, etc. how can we be near the end of the 'story'? thx
Briefly: A) Dirac operator actually generates K-theory.
B) Einstein theory from Hilbert Lagrangian is simplest possible Lagrangian in pseudo-riemannian geometry (just scalar curvature).
C) YangMills Lagrangian simplest in Ehresmannian geometry (just norm square of curvature).
You should answer his call because he clearly doesnât have my number. Heâs a few digits off.
@HeathHimself Shhh. Have you noticed that you are like close to the only one who caught that? Explain that!
He just made that up. And no one noticed or bothered to check. And it is ALWAYS like this and has been for 40 years. I have no explanation. Itâs completely beyond my comprehension.
Thatâs just it. I keep saying that the community is pretending. But it is actually lying.
Pretending there is no crisis.
Pretending that I am not in and out of physics departments all the time.
Pretending GU makes no predictions. Like in section 11.3 on pages 52 and 53 for example.
And we can quietly be here discussing this while Sean says he has read the draft in front of over half a million people that GU doesnât make any predictions within it. Confident that no one will actually speak out with page numbers and screen shots and say âYou do realize you are lying? Either about having read the draft or about the explicit predictions within it.â
Imagine you send a paper for peer review and you get Sean Carroll as your anonymous reviewer. He says he read it and there is nothing of interest. No Lagrangians. No predictions.
It has been *exactly* like this for 40 years. No one can believe it until they experience it. It has no explanation.
@codingquark @HeathHimself GU is both the most anti-interesting theory in history as well as the only theory that cannot be steelmanned.
Right? But it is always exactly like this.
Everything works backwards from the narrative. And the narrative is that our main job is to quantize a spin 2 field to get quantum gravity. And that our leading theory is thus String Theory / M-Theory and everything else is pointless because we are too many orders of magnitude away from the Planck Scale and there is no guarantee of UV completeness.
Which is absurd. Itâs a story. Itâs not reality.
@niederhaus17566 @HeathHimself If GU were right, that narrative would be wrong. And that narrative is the entire world to those who have devoted their lives to it for >40 years.
So GU must be madness. Which it is not.
Not that you said anything wrong, but let me advance a different perspective. Seanâs work is a an undisclosed *direct* competitor to GU. Attached in a screenshot are the first three lines of his 1990 abstract.
Let me put them in the language of GU.
âThe Chern-Simons Lagrangian has been studied previously in (2+1)-dimensional spacetime, where it is both gauge and Lorentz invariant. We the authors believe that outside of this special dimension, there is a fundamental trade off where we must either violate Ehresmannian Bundle Geometry (Gauge Theory of Particle Theory) or the pointwise Lorentz Invariance of Riemannian Geometry (Einsteinâs General theory of Relativity). It appears to the authors that the right way to construct an analogous term in 3+1 dimensions is to create a Chern Simons-like term which couples the dual electromagnetic tensor to an artificial external four-vector which has no supporting evidence or motivation and violates both Einsteinâs Special and General theories of Relativity. If we take this four-vector to be fixed, the term is gauge invariant but not Lorentz invariant throwing out one of the two pillars of modern physics. We do it anyway, because we believe the above mentioned tradeoff precludes any other approach.â
I personally knew Seanâs co-author Roman Jackiw decently well on this topic as he was at MIT. This was his perspective.
Why is Geometric Unity called Geometric Unity? Because we believe you can sacrifice neither geometry or the field will come to a standstill. Itâs right there in the name. You need to have both Riemannian and Ehressmanian geometry to combine Gravity and Particle theory respectively.
Seanâs work is the DIRECT competitor of this GU theory. And GU sacrificed neither.
Odd right? He looked into a camera and said he read a draft that has a chapter called Lagrangians and said there were no lagrangians. He saw the tables of predictions and said there were no predictions. Etc.
I meanâŠthat was incredible! There are over half a million views on that video too.
@Areness_ @HeathHimself We are in too different games:
Sean is trying to win âThe Vibeâ.
I am trying to get the physics right.
Both are in play.
And I donât initiate these fights. I just return fire when forced.
@matthiasgisslar @HeathHimself Zero accountability. But no one is really reading each others papers which is why this is possible. He wouldnât be able to do this in the world of 60 years ago. So he wouldnât try.
The Vibe is all he cares about.
@matthiasgisslar @HeathHimself BTW I am taking him at his word that he read the paper so he saw the table of contents and he read chapters 9, 10, 11 which are all about Lagrangians, Interactions and Predictions.
@HeathHimself From @grok. Not that Grok is necessarily right or wrong. But interesting none the less. https://t.co/gQ7b5KG5dB
Itâs an interesting question. For 40 years the answer has been no. Precisely, no one capable without an obvious personal ax to grind will do so in public in a collegial fashion if steelmanning is expected and criticism is constructive.
Only trolls, stalkers, non-experts and people willing to lie about factual matters will do so in public. This is a consequence of the fact that the dominant 40+ year narrative is totally contradicted by GU. They correctly know what is on the line. And who it would enrage.
@NeophyteOne @matthiasgisslar @HeathHimself Ha! Ok. Optics is king. https://t.co/lf83NyiwUv
WellâŠfirst of all:
He is quite smart.
He knows a lot.
He isnât stringy.
But his opinion isnât respected so much as he is on the front line protecting much bigger people he doesnât care to contradict.
Said differently, he is protecting his masters at all costs. And his reward is his âsituationâ. He finally has tenure. And he likely deserved it somewhere earlier. He does yeomans work and does it well. And they finally gave him something in his 50s. They treated him badly in my opinion.
Ah. It has two features that general Ehressmanian geometry generally lacks:
I) A distinguished Choice of Connection (The Levi Civita connection and the connections induced from it on associated bundles).
II) Tensor Decomposition coming from the lack of structure groups auxiliary to those of the tangent bundles.
So actually the specific sub geometry of (pseudo)-Riemannian geometry is an exchange of Gauge Symmetry and field content freedom for these two attributes.
Except in totally exotic cases. Like the one in which we oddly happen to liveâŠbut I digress.
@IsZomg @HeathHimself @seanmcarroll Or he read it! Because even 45 seconds gets you to the table of contents. Here is page 3.
This is essentially what all physics people do. And I have no explanation for how this is possible. https://t.co/1NNlu8sK6t
@Areness_ @HeathHimself *two
@Elvhammer @Areness_ @HeathHimself Itâs soâŠcheap. Drama. I hate it.
@growthesque @AISpaceIdeas @matthiasgisslar @HeathHimself That sounds so sophisticated.
Except you forget what subject we are talking about. https://t.co/d6oIfrSeR5
@growthesque @AISpaceIdeas @matthiasgisslar @HeathHimself Thanks for the clarification. But this is for the source code of the universe. Itâs not the French literature department.
@BMcGrewvy @HeathHimself He's quite smart and good at many things. He knows a lot about many different areas. He's a marvelous explainer. He has some creative ideas as well.
Making progress and being courageous and an ethical colleague are difficult for *many* people in a brutal field.
@williamhbhamill @Areness_ @HeathHimself Oh well. It was a good ride. And I would have gotten away with it tooâŠif it werenât for you meddeling kids.
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