Difference between revisions of "Talk:TFNR - A first look"

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Da <https://www.edge.org/conversation/sabine_hossenfelder-looking-in-the-wrong-places>

LOOKING IN THE WRONG PLACES

the foundations of physics, which is, roughly speaking, composed of cosmology, the foundations of quantum mechanics, high-energy particle physics, and quantum gravity what is dark energy? What is dark matter? What are the masses of the Standard Model particles? And what’s up with the foundation of quantum mechanics? Is a theory that's fundamentally not deterministic, where we cannot predict outcomes, the last word that we have, or is there something more to it? Is there maybe another underlying structure to reality? Yes, see Evolutionary Physics as part of the more general Evolutionary Knowledge there is more, but we haven't reached the fundamental level. Maybe we will never reach it. Certainly, the theories that we have right now are not all there is. The question is, of course, if we don’t have any guidance by experiment, how do we make progress? And are we doing the right thing? Very plausibly, the main reason why we haven’t made progress is that we’re not doing the right thing. We’re looking in the wrong places. We are letting ourselves be guided by the wrong principles. It’s about time that we rethink this because, clearly, it’s not working. One of the things that I’ve spent a lot of time thinking about is what would be good principles to look at. Interestingly, in high-energy particle physics and also in cosmology, people pay a lot of attention to aesthetic criteria that they use to select theories they think are promising. And we know that paying attention to beauty is not very scientific. It’s certainly a human desire, but it’s questionable whether it will bring us anywhere. Scientists often justify their use of these criteria by claiming it’s based on experience. Experience moves us forward until it doesn’t. We’ve reached this point where we have to carefully rethink if the criteria that we’re using to select our theories are promising at all. If one looks at the history of this field in the foundations of physics, progress has usually been made by looking at questions that, at least in hindsight, were well posed, where there was an actual mathematical contradiction. For example, special relativity is incompatible with Newtonian gravity. If you try to resolve this incompatibility, you get general relativity. It’s a similar problem with the incompatibility between non-relativistic quantum mechanics and special relativity that led to the development of quantum field theory. There are various similar examples where such breakthroughs have happened because there was a real problem. There was an inconsistency and people had to resolve it. It had nothing to do with beauty. Maybe beauty was, in some cases, the personal motivation of the people to work on it. There’s certainly some truth to this, but I don’t think it’s good to turn this story around and say that if we only pay attention to this motivation that comes from ideals of beauty it will lead to progress. We should be very careful in thinking about whether we’re working on the right problems. If we don’t, that ties into the problem that we don’t have experimental evidence that could move us forward. We’re trying to develop theories that we use to find out which are good experiments to make, and these are the experiments that we build.   We build particle detectors and try to find dark matter; we build larger colliders in the hope of producing new particles; we shoot satellites into orbit and try to look back into the early universe, and we do that because we hope there’s something new to find there. We think there is because we have some idea from the theories that we’ve been working on that this would be something good to probe. If we are working with the wrong theories, we are making the wrong extrapolations, we have the wrong expectations, we make the wrong experiments, and then we don’t get any new data. We have no guidance to develop these theories. So, it’s a chicken and egg problem. We have to break the cycle. I don’t have a miracle cure to these problems. These are hard problems. It’s not clear what a good theory is to develop. I’m not any wiser than all the other 20,000 people in the field.

There is a group of people who do frontier work, people who do great work that brings us forward. But then there are 95 percent of the people who are just there because they’re productive. That’s where my interest in the mathematical structure of reality comes from. much of what goes on in quantum gravity is very detached from reality. It’s pretty much only mathematics. Yes, the mathematics is there, but I still don’t know if it’s the mathematics that describes reality.

Since there were already a lot of people working on the mathematical aspects, I dedicated my research to the question of how to find out which of these approaches describes nature. I mostly work on the question of how to find experimental evidence for the quantization of gravity, which is not as hopeless as some people think it is. There are various ways that one can approach the problem. The reason that a lot of people think it’s probably impossible to ever find evidence for the quantization of gravity is that you want to directly produce the quantum of gravity—a particle called the graviton—you need to reach energies that are so high that we will never be able to reach them in a particle collider. So, it’s pretty much hopeless. But that’s not the only way that you can probe quantum gravity. There are various reasons for why we expect effects of quantum gravity to also be accessible at much lower energies: There could be relics from quantum gravitational effects in the early universe that are imprinted in the cosmic microwave background—that’s a very simple example. People are looking for it. They are not quite there yet, but they’re looking for it.

There are other reasons to be optimistic as well. For example, a lot of people think that a theory for the quantum structure of spacetime would violate certain symmetries that are valid in a special and general relativity. That would have observational consequences that are not hidden at high energies; they could also be visible at low energies. Maybe most interesting is a fairly recent development, which is that we might be able to measure quantum super positions of gravitational fields. I have to admit that when I heard about it, it was surprising even to me. The reason is fairly simple. We’re often told that it’s hard to measure quantum gravitational effects because gravity is such a weak force, and the quantum effects of gravity are even weaker. But that’s not strictly speaking true because how strong gravitational effects are depends on the mass that gravitates. That’s the very reason why we don’t normally think of gravity as a weak force. It’s the only force that is left over on long distances, and the reason for this is that it adds up. It gets stronger the more mass you pile up. More precisely, we should say that the reason we find it so hard to measure quantum gravitational effects is that we either have a particle that has very pronounced quantum properties, like, say, a single electron or something like that, but then it’s so light that we cannot measure the gravitational field. Or we have some object that is so heavy that we can measure the gravitational field, but then it doesn’t have quantum properties. Okay, so that’s the actual problem.

It’s interesting that experimentalists have made a lot of progress in bringing heavier and heavier objects into quantum super positions. They are not yet quite at masses where we can measure the gravitational fields of these objects, but it’s not so far away. Usually when we speak about the difficulties of measuring quantum gravitational effects, we’re speaking of effects that are thirty or forty orders of magnitude beyond what we can measure. But with these experiments, we’re talking about three or four orders of magnitude. And it seems to me quite possibly that this is a gap that will be closed within the next ten or twenty years. I frequently get asked if I have an approach to quantum gravity that is my favorite, to which the answer is no. Most of the approaches, at least the larger ones, have something speaking for them. They all have their benefits and shortcomings. For me the question is, can you go and test them? Do they make some predictions that you can go and look for? This experiment that I was talking about, where you might be able to measure the gravitational field of some heavy quantum object, it does not measure the strong field limit of gravity, which is where it would be the easiest to distinguish between different approaches to quantum gravity; it measures the weak field limit. Some people are quite unexcited about this, which I find totally ridiculous. They’re like, "Oh, but this would only be the weak limit of quantum gravity." I can only respond by saying, "But it would be quantum gravity. It will be the first evidence for quantum gravity. It would make this field a real science if we could go and measure it."  It’s not uninteresting in contrast to what some people seem to believe, because in different approaches to quantum gravity this limit could look different, and we could go and measure it. The problems that I see in my own community worry me a lot. Not so much because I’m so terribly worried about quantum gravity. On a certain level, even though it’s my personal interest, I realize that for most of the people on the planet making progress in quantum gravity is not that terribly important. It worries me because I have to question how well science itself is working. The problems that I was speaking about in my own community—that people work on certain topics just because the money is there, because it’s something that is popular and that their colleagues appreciate—are problems that almost certainly exist in most scientific communities. My extrapolation from my own field would tell me that I should be very skeptical about whatever comes out of the scientific community. And that’s not good. Clearly that’s not good. I’ve been thinking for a lot of time how we could go about and try to solve these problems. It’s hard, but it’s necessary. We need science to solve the problems on this planet, problems that we have caused ourselves. For this we need science to work properly. First of all, to get this done will require that we understand better how science works. I find it ironic that we have models for how political systems work. We have voting models. We have certain understanding for how these things go about. We also have a variety of models for the economic system and for the interaction with the political system. But we pretty much know nothing about the dynamics of knowledge discovery. We don’t know how the academic system works, for how people develop their ideas, for how these ideas get selected, for how these ideas proliferate. We don’t have any good understanding of how that works. That will be necessary to solve these problems. We will also have to get this knowledge about how science works closer to the people who do the science. To work in this field, you need to have an education for how knowledge discovery works and what it takes to make it work properly. And that is currently missing.

Da <https://www.edge.org/conversation/sabine_hossenfelder-looking-in-the-wrong-places>