logoalt Hacker News

btilly10/11/20241 replyview on HN

Well, if you want a simple argument from authority, John Carlos Baez's confirmation that she's right is pretty good. If you want a better one, she very rarely gets any of her facts wrong.

Now let's go point by point.

Is Carlo Rovelli fine with it not being testable, in that he is fine with research continuing even though it can not be tested with up coming experimental set ups? He is arguing for a version of the theory that can't be tested, is continuing to do research on it, and presumably thinks that he is doing science.

If Sabine was going to expose howe much money was going to these topics and where it could be better spent that would be worth watching. Discussing how these things wind up getting funded would be a very different video. And would not likely be interesting to most of her audience.

Or is Carlo Rovelli ok with the theory being unfalsifiable in the sense that that he is ok with the research not being science? Presumably he thinks that he is doing science. Sabine's opinion clearly is that this isn't really science. However she only claims her opinion as her opinion, not established fact.

Ok what percentage and total amount of founding is going to this? Again, that would be a very different video. In 10 minutes for a general audience, you have to make decisions about what you will and will not cover. It's not a valid criticism of her that she made a choice. Particularly in a video that she disclaims as a personal rant.

Arguments saying loop quantum gravity require space to be quantized, but they can not be lorentz invariant without having the quantization go to zero volume, according to Sabine, and no one has done that and extracted back out loop quantum gravity. This is not according to her, this is according to an argument that comes from Lee Smolin. A region of space that has a specific amount of area will, according to special relativity, have a smaller area according to an observer that is traveling fast enough. By having the velocity as close as you want to C, you can make the area arbitrarily small. So your choice is to violate Lorentz invariance, or have arbitrarily small areas. If you violate Lorentz invariance, the speed for light will depend on the wavelength.

As her previous video at https://www.youtube.com/watch?v=ZlHvW6k2bcM said, this prediction of Lee Smolin has been tested to extremely high precision, and the predicted effect was not seen. That version of LQG has been falsified. The alternative supported by Carlo Rovelli is that you need to average out over quantum areas in all reference frames. This is a neat idea, but in several decades, nobody has made it work. Until someone can make it work, LQG can't produce any testable predictions.

Please note that John Baez, who worked on LQG for 10 years, specifically complimented her presentation of this particular issue. Her description of where research stands is accurate.

I am experimentalist and this is not my area. I would want to see a link to a paper/book etc. Rants generally do not come with properly cited references. That said, the previous video that this refers back to is based on https://arxiv.org/abs/2402.06009?utm_source=substack&utm_med..., which is one of the experimental tests showing that Lee Smolin's prediction is false.

The analogy to the angular momentum operator comes off as a good place to start investigation/research but is treated dismissively, anologies like this often do not apply in the end but can still be useful. It was a good place to start. After 20 years of research that has failed to turn that idea into anything workable, most people would conclude that this is an analogy that will not apply in the end. But apparently Rovelli gets mad at anyone who doubts that it will work out. One of the triggers for this rant was whatever Rovelli said to her in private. Personally, I excuse her for being human here in her reaction.

Ok that does not seem like the gottcha that it is laid out to be. Interesting stuff happens where their are apparent contradictions in physics. No, it really is the gotcha it claims to be. It's directly inside of the math. This demonstration is no different than, say, proving that sqrt(2) is irrational by proving that if you start with the smallest fraction that equals it, you can find a smaller one.

The conclusion of that gotcha is exactly what she said: if there's a minimal area then you can't have Lorentz invariance. And conversely, if you have Lorentz invariance, then you can't have a minimal area. Experimentally, we have tested for the Lorentz invariance to be expected from a minimum area based on the Planck length. It does not exist. And therefore there isn't Lorentz invariance.

Why did Sabine talk about it being a mathematical contradiction if you can make the theory work, but it leads to physical phenomenon that we do not observe? Her previous video (that triggered the nasty emails)_made this point more clearly. She's saying that there is a mathematical contradiction between having minimal areas and Lorentz invariance. This forces us to choose to have one or the other. Minimal areas leads to a testable and now falsified theory. Lorentz invariance has yet to lead to a theory that doesn't blow up with unnormalizable infinities, let alone one which can produce a testable prediction.

I can not make those two arguments jive in to a cohesive whole. Not that it can not happen, but I can not from this video and that is the conclusion, or similar, I normally reach when watching Sabine's videos and why I do not watch or recommend them generally. Is that Sabine's fault, or yours? This video is much lower quality than her normal ones. And yet absolutely none of what you think are flaws, do I think is one. Every one of your objections has an answer that jives. And the conclusion is agreed with by John Baez, whose background on this specific topic is much stronger than yours.

Perhaps, rather than looking for things to complain, you should try figuring out what she actually said. In my experience it is logically internally consistent. Even though it skewers some sacred cows.


Replies

davorak10/11/2024

> Well, if you want a simple argument from authority, John Carlos Baez's confirmation that she's right is pretty good. If you want a better one, she very rarely gets any of her facts wrong.

It is not what I want. I read the linked comment by John Carlos Baez[1] and do not agree with the wording of your conclusion "that she's right". There is some alignment, but you have removed any nuance.

> Again, that would be a very different video. In 10 minutes for a general audience, you have to make decisions about what you will and will not cover. It's not a valid criticism of her that she made a choice. Particularly in a video that she disclaims as a personal rant.

My specific comments are about why I do not find value in Sabine's video not about not about a general audience. The over all arch is a point that I do not find her videos or the discussions in the comments valuable on hacker news in response to Dang's comment:

> so I think we can give this thread a second chance

[2]

So my comments are not about how she decides to reach her general audience.

I think this covers some of your pervious comments too.

> This is not according to her, this is according to an argument that comes from Lee Smolin.

"What I said in my pervious video" is what she said in her video. So this idea may not have originated from her, but my word choice is correct by saying according to her. This does no assert she came up with the idea or is 100% sure of it.

> A region of space that has a specific amount of area will, according to special relativity, ...

> ...

> Please note that John Baez, who worked on LQG for 10 years, specifically complimented her presentation of this particular issue. Her description of where research stands is accurate.

My comment about about the video and why it is not useful to me or useful seeing it on HN, not about the correctness or incorrectness of Sabine's statements which is what you seem to be addressing here.

> It was a good place to start. After 20 years of research that has failed to turn that idea into anything workable, most people would conclude that this is an analogy that will not apply in the end. But apparently Rovelli gets mad at anyone who doubts that it will work out. One of the triggers for this rant was whatever Rovelli said to her in private. Personally, I excuse her for being human here in her reaction.

You are making some assumptions here and empathizing with Sabine, which is understandable. Arrogant Physics professor gets mad when someone questions their pet theory is not unrealistic but is not headline worthy either. Does it matter if he was mad? Is this any different than any other celebrity spat? If not, that is not what I read HN for.

> Rants generally do not come with properly cited references.

I know it was a rant, I saw the labeling. That does not help make it good material for HN or lead HN commenters to interesting and curious comments though. The reverse is often true regardless of the source of the rant.

> No, it really is the gotcha it claims to be. It's directly inside of the math. This demonstration is no different than, say, proving that sqrt(2) is irrational by proving that if you start with the smallest fraction that equals it, you can find a smaller one.

Physics is not practiced like math though, so it is different. A contradiction in physics theories is not the same as saying true = false in math. Experimental evidence and observation rule the day until we find the fundamental laws of physics, after that it will be more like math(well at least some physics will).

> Her previous video (that triggered the nasty emails)_made this point more clearly. She's saying that there is a mathematical contradiction between having minimal areas and Lorentz invariance. This forces us to choose to have one or the other. Minimal areas leads to a testable and now falsified theory. Lorentz invariance has yet to lead to a theory that doesn't blow up with unnormalizable infinities, let alone one which can produce a testable prediction.

Comments like this, and much of what you said before this, lead me to think Sabine's pervious video would be less likely to cause me to write a comment like I did.

> Is that Sabine's fault, or yours?

Nothing I have said is about Sabine being at fault of something. I can stand corrected if something I wrote was too misleading though.

> This video is much lower quality than her normal ones.

This seems like it would argue against Dang giving this Sabine video an exception.

> Perhaps, rather than looking for things to complain,

That is not what happened here. My response was to Dang about giving this video a exception and the comment on "sensational style".

> you should try figuring out what she actually said.

And if I was having a conversation with Sabine or if I was corresponding with her then both people are responsible for reaching out to cover any communication gaps. That is not what this is, this was Sabine's rant as labeled by her and you.

> Even though it skewers some sacred cows.

I do not think Sabine's videos "skewer sacred cows". At least not any in the physics community at large, maybe some sub disciplines. The physic's community at large does not seem to have many if any sacred cows, that is my experience at least.

[1] https://mathstodon.xyz/@johncarlosbaez/113285631281744111

[2]

> so I think we can give this thread a second chance

https://news.ycombinator.com/item?id=41811140

show 1 reply