Into the Impossible With Brian Keating - The Loop Quantum Gravity War

Starting point is 00:00:01 Any sufficiently advanced technology is indistinguishable from magic. Open the pod bay doors, hell. In the 1990s, there were fierce battles, from the East Coast to the West Coast, featuring renowned physicists like Dr. Dre. And he was battling, Biggie Smalls, Tupac, Nas and the Wu-Tang Clan. Well, what would surprise you to know that there are battles in physics every bit as heated, although hopefully not as bloody as those battles that plagued the rap scene of the 1990s. Today I'm doing a reaction video to another reaction video.

Starting point is 00:00:45 How about that for meta? If you're new here, I'm Brian Keating, the Chancellor's Distinguished Professor of Physics at UC San Diego. I'm also an experimental cosmologist for decades. Been involved with some of the biggest and best experiments of all time in this field. Bicep, Bicep 2, Simon's Array, Simon's Observatory, and many, many more. I speak today as an experimentalist to my two friends, Carlo Rovelli, and Sabina Hassenfelder. As I said, I'll be reacting to a reaction,

Starting point is 00:01:10 but that reaction was provoked by an original video that I made that depicted loop quantum gravity as possibly suffering a fatal blow, thanks to new data from an experiment coming out of China. Talk about East versus West. That video was about loop quantum gravity and the so-called appearance of Lorentz-invariance

Starting point is 00:01:29 violation that seems to occur within certain models of it. There was a paper published by a Chinese team operating the lasso experiment. I contacted the paper author about the Lorenz Invariance Violation Effects in reported in his team's paper. I asked him specifically, does this mean that certain models of loop quantum gravity are dead? He replied, yes, linear loop quantum gravity models are dead. And in fact, that was the entirety of the subject of my previous video. Well, that video unleashed a whirlwind of firestorm.

Starting point is 00:01:57 First came a video made by Phil Halpern, who runs a channel called Skydive Phil. and he's done many videos with his friend, Carlo Revelli, and I don't blame him. Loop quantum gravity is fascinating, and as you know, I've done multiple videos about my hope for success of loop quantum gravity, but this most recent video saw me very much disillusioned. So when Phil of Skydye Phil fame, he contacted Carlo and said that my video was bullocks. I don't know what that really means, to be honest with you, I'm a Yank. So after Phil put out his video criticizing my video, including a five-minute commentary from 2019, about Carlo Rovelli responding to claims that loop quantum gravity should have

Starting point is 00:02:36 Lorentzance variance violation in it. Carlo wrote me and told me I should take the video down. Now Carlo and I are good friends. We've done many videos together, we've met in person many times, and he played the role of Galileo in our 22-hour-long audiobook of Galileo's dialogue. He plays the lead role, Salviati, the genius who proves the Copernican theory to be correct, and then suffers some consequences, shall we say? Needless to say, I respect Carlo greatly. He's written some of the most popular and best-written books in physics and science of all time, and I've reviewed many of them, and he will be coming on to directly rebut me to my face. Sabina recently released a video, which also comments and

Starting point is 00:03:16 seems to suggest that some of what I claimed in my video is absolutely correct. So I want to review some of the correspondence that Carlo and I had and Phil Halpern as well about my previous video where I discussed how the new findings from Lassau might impact certain models of loop quantum gravity. Yes, I did show thumbnail of Ed Witten in front of the grave site of loop quantum gravity. Maybe that was a little bit impolite of me, but that's the nature of YouTube and sometimes you need to be a little bit provocative. First, we're going to start with a quick recap of the arguments that Carlo and I have been having by email for the past several weeks about this video that I made and the claims that he makes to counter some of the claims

Starting point is 00:03:51 that I made. I think it's important. I admit I could be wrong. And in fact, in the video, I suggested that of all people on Earth, Carlo will probably be the person to prove me wrong. or say that my position is wrong. I've tried in the video and in my previous work to make a distinction between loop quantum gravity and models of it and versions of it that predict Lorentz Invariance violation. In the paper, I said specifically that Lassau results pose a significant blow to theories like loop quantum gravity that predict Lorentz invariance violation, LQ that predicts LIV, and that they do rule out a vast landscape of loop quantum gravity. Now, according to the lead author of Lassau, I'll redact his name, but show you the email,

Starting point is 00:04:29 here, he said yes, this does roll out the link. It's peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speeds. That's why I chose GoogleFi Wireless. My connections stay strong even when the hive is buzzing. Plus, unlimited plans started $35 a month. Now, that's a deal that doesn't stay. Explore GoogleFi Wireless plans today.

Starting point is 00:04:54 Plus taxes and government fees, Google FiWireless is not subject to data traffic deprioritization during times of high network usage. Now, linear Lorentz and Variant's terms you took quarrel with and you said that in your estimation, you would agree with that fact, but according to you, it applies as much to stream theory as it does to loop quantum gravity. So why didn't you make a video you said that says string theory is dead? And that's a good point, except I'm making a comment at the very start of the video that monopolies are bad, and string theory has monopoly on all of high energy particle physics.

Starting point is 00:05:26 Many of my past guests, I won't name their names again and again, have come on to decry how bad string theory is for not just high energy physics world, but for science society and maybe even the opportunity to leave planet Earth and teleport and transmute ourselves across the galaxy. I was trying to make a statement that it's good to have competitors to string theory. It's bad to have a monopoly. It's bad when you only have one cell phone carrier, one internet search engine, one cable company, or here in San Diego, only one professional. sports team. Go Padres. So I felt like the monopoly that string theory has was very pernicious. And I was hoping more than almost anybody that good, hard experimental evidence could come to slay string theory or at least challenge it. We need challenges to these ideas. And I've had on all the top proponents of all alternative theories of quantum gravity. And I won't go into

Starting point is 00:06:18 those videos. As I said, you can find them in my links down below. But it seems to me that I'll make an Italian analogy. If there is a leader of Lupinian quantum gravity, it would be you, sort of the pope of loop quantum gravity. And anybody like me who claims that loop quantum gravity has flaws or maybe could be proven wrong, you look at me as a heretic or an apostate. And that doesn't, didn't turn out so well for people like Giordano Bruno or my good friend Galileo. So I want to make sure that this is clear. I'm not trying to be non-collegial and trying to express the possibility that you could

Starting point is 00:06:50 be wrong too. And I want to collect evidence based on both the historical facts, theoretical evidence, observational evidence, and also bring in other people. It's my duty to do some due diligence to fact check and see if there are, indeed, are no theories of loop quantum gravity that have linear dependencies as they express in the lasso paper in equation one. You're absolutely right. I agree 100% that these can apply to linear string theory models, which would then be a bit

Starting point is 00:07:18 of evidence in favor of string theory in that now it has evidence that can be used to falsify it. Remember, there are whole books as I've shown, you know, What is the experimental evidence for string theory? There's a blank page. Now of course, we don't only try to find evidence for something, we find evidence against it. So therefore, it's a good thing that last such results have implications for anything that could potentially be fatal, either for string theory, loop quantum gravity, E8, GU, and even

Starting point is 00:07:43 things like the Wolfram Physics project. So I've genuinely been hoping for loop quantum gravity to thrive, potentially as a replacement for string theory. But when the facts, as I understand them, change, as John Maynard Cain said, I have, I have I changed my mind and especially based on new experimental data. Any prediction that results from equation one is now ruled out by their data. And so since you have no quarrel with that,

Starting point is 00:08:06 I can't understand why you'd also conclude that it doesn't rule out findings in loop quantum gravity, which also feature this linear effect. And the reason I said it rules out such a vast landscape is because usually the most likely term to be present in a theory are the lower energy terms or the terms that they are responsible These are small effects.

Starting point is 00:08:27 So anything that's higher than a linear power will be a much, much smaller effect. Typically, in most of these theories, and I've studied these in optical polarimetry. I refer to a 2004 paper that predicted Lorentz-invariance violation in loop quantum gravity. And you told me that it's been debunked in our email correspondence. But there are still people that are promulgating the notion that there is Lorentz-invaryance violation in loop quantum gravity. So even though you claim that it was debunked in 2004, and maybe even earlier, Still, five years after that, the Fermi Space Telescope, using gamma-ray astronomy, led to a claim published in Symmetry magazine, which I'll put a link to down below, that this was bad for certain models of loop quantum gravity.

Starting point is 00:09:08 So to me, that suggests, if you claim it was ruled on 2004, the Fermi telescope doesn't claim that it was ruled out in 2004, and even the Big Bang Theory television show, which I opened the original video with, they were still promulgating that many, many years after the so-called 2004 debunking. So either I have 100% faith in trust in you and don't question anything that you say to me, or I should investigate and do a little bit more due diligence, which I did. That's why I contacted the lead author of the paper before I even made the video. If he said, no, this has no implications for loop quantum gravity. I wouldn't have made the video. I have to be honest with you. So your beef, if anything, was with him, but now you're agreeing that, yes,

Starting point is 00:09:46 anything that has its linear dependence as in equation one, like string theory, certain models of string theory, at least, could be ruled out. So I think it's a win-win to have this discussion. Now, you said this place was steps from the water. We just haven't found the steps yet. How much did we save? Enough. Enough to get lost.

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Starting point is 00:10:23 Hilton, for the stay. Let's bring in good friend of the show, Sabina Hasenfelder, where she analyzed my video. Again, this is very meta here. We're going super above the fray. She takes a more nuanced take on the history and currency and curnsate a loop quantum gravity, concluding that effectively it's time to give up.

Starting point is 00:10:41 In fact, her title of her video is, please, no more loop quantum gravity. She's not even extending the charitable offer, if you will, to you, Carlo, that loop quantum gravity could still thrive, and survive at either higher order than linear or in some other way. She's saying it's dead. Stop talking about. Stop bothering.

Starting point is 00:10:58 She talks about our good friend and past guest, Lee Smollett, one of the founders of Luke Pun on Gravity, who positioned it early on as a contender to string theory. One of the big deals, according to Sabina's video, was that Lee and others claim that the benefit is that it is testable, and therefore testable means falsifiable in the Paparian sense. Carl Popper said a good scientific theory should not only be able to be proved right, but it should also be falsifiable being able to be proved wrong. According to Smolenskamp, Sabina said, loop quantum gravity implies the speed of light should depend on the color or energy of the field due to a supposed minimal length scale in space. And this would lead to observable delays in light

Starting point is 00:11:36 from cosmic sources. Exactly what I talked about. And those delays would be either of the entire wave packet at all frequencies or of their polarization states could arrive at different times, or their colors could arrive at different times as well. And Carlo pointed out that actually he disabused me of the notion that loop quantum gravity predicts that in an interview that we did in 2020. And he's absolutely right. He did say that. But again, do I only take one person if it's my friend, Carla Raleigh, what if I only took Lee Smollin, who's also my friend, or only took Sabina Hasenfelder's voice? What I want to do as an experimentalist is collect all the evidence and leave it, not for you to decide out there because you may not be an expert. You may be a

Starting point is 00:12:14 complete layperson, but very interested in learning more about string theory and its rivals. And this is a very interesting case in the sociology of science, which something. we never talk about. So Sabina agrees with my claims in the earlier video, and she said so on X, that these results, including Fermi and other results, as well as the recent Lassar result, constrain or maybe even rule out such Lorentz's invariance violation effects. More importantly, she highlights that most researchers in loop quantum gravity, including Carlo Rovelli, disagree with Smoland's assertion that loop quantum gravity necessarily predicts Lorentz invariance violation. Now, Carlo in his email says that he convinced that

Starting point is 00:12:51 Lee that Lee was wrong. And that might be true. And I know that Lee didn't retract exactly. He actually sort of strengthened that after the Fermi results in 2009 led to a big brouhaha, probably was what made the Big Bang Theory use that differentiation between loop crudum gravity and strength theory in the cold open of my previous video. That came out in 2009. Lee had a reaction to the Fermi results that seemed to say there could be wiggle room that it seemed to me at least loop quantum gravity could still survive. So Sabina concludes that the experimental results rule out search. models of loop quantum gravity that predict Lawrence invariance violation, but they don't

Starting point is 00:13:26 invalidate loop quantum gravity as a whole. And I said that in the video as well. I said this rules out the linear model, et cetera, and Carlo can probably prove me wrong and show how it's loop quantum gravity can still thrive. Sabina doesn't believe that we should even be troubled by loop quantum gravity ever again, a much more charitable. Carlo rightfully pointed out to me that string theory gets tons and tons more money, more attention, and there are still whole conferences and stuff devoted to this. My colleagues go to them. They go to beaches, they go skiing, they talk about it. But even to me, it seems like some people who are really positioned themselves as the definitive voice of string theory have kind of gone

Starting point is 00:13:59 away from it. Ed Witten hasn't published much on this at all. He's published things on black holes, and Juan Maldesana has published more on wormholes than he has on string theory, at least in the cursory search discussions that I've had with one. So I want to make sure that science is allowed to continue based on a diversity of thought. We should be open to the possibility that certain models within loop quantum gravity might be constrained or even rule. out while others remain viable. I don't see a problem with that. So let's move forward together. I've had many, many positive comments about that video, including some from eminent stream theorist and theorists of what's called Suzy or Super Symmetry, reacting in a very positive way.

Starting point is 00:14:35 Perhaps that's understandable because it led to the, it discussed the death of potential death, at least the thumbnail suggested that, sorry again for maybe being a little too clickbait at that point. But I believe that by acknowledging models that are in trouble have been ruled out, and focusing on those that are still consistent with experimental results, we can make real progress in our pursuit of quantum gravity. In my field, experimental cosmology, when a theory is constrained by new data, the theorists appreciate it. They rejoice. It helps refine their models and deepen their understanding. What I do and the theoreticians in my field are just as bright and just as capable as Carlo, as Lee, as Sabina, or any of the voices we've had on this channel. That's how we push

Starting point is 00:15:14 science forward. Now, I'll be having Carlo back on the show and I'll have Sabina on the show. I won't put them together because I'm afraid of what might happen. But if you enjoyed this episode, make sure you check out my most recent conversation with Sabina, my previous videos on loop quantum gravity, and my many discussions with others about alternative theories of unification of forces and fields and specifically loop quantum gravity. And don't miss the takedown of me, the reaction video of me, from Phil Hopperman on Scott Eye Phil on his YouTube channel. And stay tuned for my friendly debate with my good friend, co-author, and co-narrator, Carlo Rovelli. Let me know in the comments what you'd like me to ask him and whose side you're on?

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Into the Impossible With Brian Keating - The Loop Quantum Gravity War

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