This is not a presentation format that inspires confidence that this is not crackpottery
(critique of the individual cited, not you)
[1] https://www.wired.com/2014/07/fantastically-wrong-hollow-ear...
[2] https://wireofinformation.wordpress.com/tag/einstein-forewor...
Edit: the opposite being, "Being wrong about one thing doesn't make you wrong about everything"
Of course, that doesn't mean that the rest of us are obligated to listen to any of it until that success has been realized.
It's a fundamental breaking of symmetry in our universe, also known as: luck is blind, but curse has 10/10 eyesight.
and
"being wrong about one thing makes you wrong about everything."
are logically equivalent :)
First, saying that spacetime, considered as a 4-d hypersurface, has "two sides with two metrics" won't work. The metric of one side fully determines the metric of the other side since both sides belong to the same surface. That's why spacetime in standard Einstein GR only has one metric (which, btw, does not mean that spacetime in standard GR has only one "side", as the article claims). Two different metrics would have to describe two different, disjoint surfaces, which would have no connection to each other, which would mean the second one, being unobservable, would be scraped right off the model by Occam's razor.
Second, saying that negative mass would induce "opposite curvatures" as compared to positive mass, in the same spacetime, won't work. One spacetime can only have one curvature at any given ponit. Considering the simpler example of a 2-d surface should make this intuitively obvious--the same surface can't have two different curvatures at the same point.
> Two different metrics would have to describe two different, disjoint surfaces, which would have no connection to each other, which would mean the second one, being unobservable, would be scraped right off the model by Occam's razor.
The theory states that the two surfaces are not disjoint:
> What is important to note however, is that the two field equations are coupled, i.e. a mass always creates a positive curvature in spacetime according to its own metric (where the mass appears visible), and it also always induces a negative curvature in the conjugate metric (where the mass appears invisible).
I do find it confusing why this would be called two metrics, however, since it seems to be describing a unified spacetime "surface".
As for your second critique:
> One spacetime can only have one curvature at any given ponit. Considering the simpler example of a 2-d surface should make this intuitively obvious--the same surface can't have two different curvatures at the same point.
But if the surface has two sides, can it not? Consider the classic "gravity well" demonstration of a heavy ball placed on an elastic membrane. It forms a concave surface. Now turn your head upside down and look at the membrane from underneath. You'll see a convex surface. Same membrane, different curvatures.
Anyhow, I'm certainly not equipped to analyse this theory, but I do like that it attempts to make falsifiable predictions. I guess it's an attempt to explain dark energy? It would appear to leave problems of dark matter unaddressed, however.
You're thinking of this as someone who can look at the surface from the outside, in which case it makes sense to consider convex and concave curvatures to be different. But if you're restricted to moving within the surface, there's no way to tell the difference.
Within the surface, you can only measure the distances traveled along certain paths. For these distances, it doesn't matter whether you're walking across a hill or a valley of the opposite shape. The metrics of these surfaces are exactly the same.
That doesn't mean that negative curvature is impossible, just that it isn't as simple as inverting convex and concave. A negatively curved two-dimensional surface curves simultaneously in opposite directions, like a saddle point. But there's no way to have two surfaces with inverted curvatures at corresponding points, since curvature is determined by the arrangement of points, which means that inverting curvature obliterates the whole concept of "corresponding points" by arranging them differently.
Yes, but that just underscores my point that one surface can only have one metric.
> But if the surface has two sides, can it not?
No. You can describe the one curvature in two different ways, depending on which side you choose as your viewpoint. But it's still just one surface and one curvature, not two.
If that's the case, I apologize for my own noise.
EDIT: Even so, that The Fine Article is (potentially) directed at an inappropriate audience doesn't tell me much about its "crackpottery", except in a mildly Bayesian kind of way.
I like to pay attention to the discussions on physics articles that cross the HN front page because I more often than not learn something by reading the conversations between the people who understand the material better than I do. That remains the kind of discussion I want to see.
The usual reason for someone doing that is that they know their model won't be accepted by scientists. That's what I'm betting on here.
See the bottom of this page: http://www.januscosmologicalmodel.com/.
Some of his latest papers have been published in Astrophysics and Space Science, Modern Physics Letters A & Progress in Physics [1]
[1] https://scholar.google.fr/scholar?hl=fr&as_sdt=0%2C5&q=JP+Pe...
There's a huge difference between a paper about a model being published, and the model being accepted as a true fact.
So it's not like this model is totally isolated from what is being done in physics, although he has developed it on his own. He's into bimetric models of gravity like many other people in his field, and as far as I can tell, this is Occam's bush growing we are seeing here. Let's not hasten to use the razzor.
[1] https://arxiv.org/pdf/0807.2838.pdf [2] https://news.ycombinator.com/item?id=18609375 [3] https://cerncourier.com/does-antimatter-fall-up/
I'm not saying his theory is right, or that the presentation doesn't smell a bit of crackpottery (it does), but at least he's referencing some real science he's done and that has apparently been accepted.
His main grief is not that his genius theory is not understood , but that he cannot discuss it with his colleagues for the reason above.
People have set up a petition [1] so that he present his ideas during a seminary (he's indeed quite popular with videos on youtube frequently reaching more than 100k views).
To give you a more concrete example, he stumbled upon a paper by physicist Sabine Hossenfelder [2] which presents a very similar approach to the Janus model but with a broader, more abstract framework Petit is not able to understand. He reached out to her and was accused of plagiarism ! He tried to play it cool, saying she would be remembered as the 21st century's Einstein (her paper predates his by a decade), telling her she should invest energy into this (she published that paper in 2008 and did not follow this track further) offering her to collaborate as friends on the subject. Result: she declined because of his background.
Now, what background are we talking about ? IIRC he published a paper in the 90s where he thanked M. Bazoof. What you have to know is that Petit has been personally involved in the UMMO affaire [3]. Along with several people, mostly from Spain, he received letters and phone calls by people that claimed to be from another planet. These letters were full of scientific content and he's written multiple books about it (the latest, from last year, is jokingly subtilted "How far can we think to far ?"). Back to M Bazoof: "What ? He is citing an alien ? Is he kidding us ?" => that's Petit that imitates his colleagues' reaction back in the days, and then he burst in laughter. Serious again: "But that's the truth, alien or trickster, I received UMMO messages without which I would not have thought of the Janus model. A stuff life this, this is is insane, you have no idea. It brings you into a life-long adventure. It's like my life is the script to a Spielberg movie. And I suppose I'm Doc from back to the future ! laughs".
"If it's not fun, it's not really serious" is one of the maxims he lives by.
[1] https://www.mesopinions.com/petition/sante/droit-debat-nouve...
[2] https://arxiv.org/pdf/0807.2838.pdf
[3] https://en.wikipedia.org/wiki/Planetary_objects_proposed_in_...
Sabine Hossenfelder is an open-minded researcher, as far as I can tell. Sad that the author could not follow up with her, but there must be reasons for that.
Very interesting, thank you for the comment. I like math and computer science academia more than physics for these reasons -- people are less cut-throat, and generally more fun than in physics.