| ▲ | ekjhgkejhgk 2 days ago |
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| ▲ | noone_important 2 days ago | parent | next [-] |
| I am not sure what you are refering to. You absolutely can break Lorentz Invariance in string theory[1]. There is a reason why even some string theory researchers call it the theory of anything. [1] https://inspirehep.net/literature/262241 |
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| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | Wellllll. Despite the title, the paper does not make a claim about string theory. The starting point is the "Witten string field theory" which is a field theory engineered to have properties like string theory. Nothing guarantees that theory is exactly like string theory. In addition, the idea is perturbative in nature, there's no guarantee that perturbative effects are in fact realized in the full quantum theory - exoteric cancellations happen often in field theories with many symmetries. This is two degrees of questionable. So A) the paper isn't actually about string theory and B) it's not clear that the claim it makes is actually correct for the field theory it supposedly applies to. | | |
| ▲ | noone_important 2 days ago | parent [-] | | Well this is just an early example of the lorentz breaking string theory niche. You can find a lot more. In the short time frame where opera had this supposedly faster than light neutrinos, a lot of papers were published in that regard. For example you can have string theories that lead to finsler spacetimes, which were used to explain the opera results. | | |
| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | I literally have no idea what our conversation has to do with opera results, or what you think that shows, but just lost all interest in continuing this conversation. | | |
| ▲ | wizzwizz4 2 days ago | parent [-] | | People are not likely to look for unphysical models, if they're trying to do physics. The connection is social. |
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| ▲ | munchler 2 days ago | parent | prev | next [-] |
| That’s just piggybacking on a prediction of special relativity itself. If string theory predicted something novel that’s testable, that would be a lot more noteworthy. |
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| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | > That’s just piggybacking on a prediction of special relativity itself. Let me stop you right now to inform you you don't understand how scientific theories are structured. Special relativity is not a prediction of special relativity. Likewise, 1+1=2 isn't a predict of arithmetic, it's the starting point. | | |
| ▲ | munchler 2 days ago | parent [-] | | If you are suggesting that string theory is somehow more fundamental or powerful than special relativity, and so SR is a mere consequence of ST, that’s a claim that probably requires more explanation or evidence. | | |
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| ▲ | jameshart 2 days ago | parent | prev | next [-] |
| Forgive my non specialist questions here, but doesn’t special relativity predict that special relativity is preserved at all scales? |
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| ▲ | ekjhgkejhgk 2 days ago | parent | next [-] | | No. Special relativity postulates that special relativity is preserved at all scales. It's an axiom. Comes from nowhere. It's assumed. This is what a theory is: assume XYZ is true, and see how much of the world you can explain. Why is XYZ? That theory doesn't explain it. Theoretical physics is: what is the smallest set of XYZ assumptions that can explain other theories. So if you can come up with a theory that's internally self-consistent that _predicts_ something which is postulated by another successful theory, that's a very convincing result. | | |
| ▲ | drdeca 2 days ago | parent [-] | | Pardon, but, huh? I very much thought that Lorentz invariance was built into the assumptions of string theory. Concluding from “A AND B” that “A”, while it does reach a conclusion that is distinct from the assumption, is not impressive. If string theory does not bake SR into its assumptions, wouldn’t that make the way it is formulated, not manifestly Lorentz invariant? Don’t physicists typically prefer that their theories be, not just Lorentz invariant, but ideally formulated in a way that is manifestly Lorentz invariant? Of course, not that it is a critical requirement, but it is very much something I thought string theory satisfied. Why wouldn’t it be? Like, just don’t combine coordinates in ways that aren’t automatically compatible with Lorentz invariance, right? If you formulate a theory in a way that is manifestly Lorentz invariant, claiming to have derived Lorentz invariance from it, seems to me a bit like saying you derived “A” from “A AND B”. If string theory isn’t manifestly Lorentz invariant, then, I have to ask: why not?? | | |
| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | Lorentz invariance is built into some descriptions of some stringy theories. For example chapter 1 of the Polchinski, you have the 26-dimensional bosonic string which is constructed to be Lorentz invariance. Obviously in this case it's not a "prediction", but then again, it's just a toy-model. Our Universe doesn't have 26 dimensions and doesn't have only bosons. | | |
| ▲ | drdeca 2 days ago | parent [-] | | Ok, so I looked into it a bit, and here’s my understanding: The Polyakov action is kinda by default manifestly Lorentz invariant, but in order to quantize it, one generally first picks the light cone gauge, where this gauge choice treats some of the coordinates differently, losing the manifest Lorentz invariance. The reason for making this gauge choice is in order to make unitarity clear (/sorta automatic). An alternative route keeps manifest Lorentz invariance, but proceeding this way, unitarity is not clear. And then, in the critical dimensions (26 or 10, as appropriate; We have fermions, so, presumably 10) it can be shown that a certain issue (chiral anomaly, I think it was) gets cancelled out, and therefore the two approaches agree. But, I guess, if one imposes the light cone gauge, if not in a space of dimensionality the critical dimension, the issue doesn’t cancel out and Lorentz invariance is violated? (Previously I was under the impression that when the dimensionality is wrong, things just diverged, and I’m not particularly confident about the “actually it implies violations of Lorentz invariance” thing I just read.) | | |
| ▲ | ekjhgkejhgk a day ago | parent [-] | | > losing the manifest Lorentz invariance. You understand that this have nothing to do with actual Lorentz invariance, yes? It sounds like you don't really understand the meaning of those terms you're using. Do you understand what "manifest Lorentz invariance" means? | | |
| ▲ | drdeca a day ago | parent [-] | | Yes? It means the Lorentz invariance is automatic from the form of the expression, does it not? | | |
| ▲ | ekjhgkejhgk a day ago | parent [-] | | Yes. But when "Lorentz invariance isn't automatic from the form of the expression" it does NOT follow that you don't have Lorentz invariance. | | |
| ▲ | drdeca 5 hours ago | parent [-] | | Of course. Did part of what I said suggest I thought otherwise? I guess the part about the “when you quantize it after fixing the gauge in a way that loses the manifestness of the Lorentz invariance, if you aren’t in the critical dimension, supposedly you don’t keep the Lorentz invariance” part could imply otherwise? If that part is wrong, my mistake, I shouldn’t have trusted the source I was reading for that part. I was viewing that part as being part of how you could be right about Lorentz invariance being something derived nontrivially from the theory. Because, the Polyakov action (and the Nambu-Goto action) are, AIUI, typically initially(at the start of the definition of the theory) formulated in a way that is not just Lorentz invariant, but manifestly Lorentz invariant, and if there is no step in the process of defining the theory that isn’t manifestly Lorentz invariant, I would think that Lorentz invariance wouldn’t be a nontrivial implication, but something baked into the definition throughout, so, for it to be a nontrivial implication of the theory, at some point after the definition of the classical action, something has to be done that, while it doesn’t break Lorentz invariance, it “could” do so, in the sense that showing that it doesn’t is non-trivial. And, I was thinking this would start with the choice of gauge making it no longer manifestly Lorentz invariant. I trust you have much more knowledge of string theory than I do, so I would appreciate any correction you might have. |
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| ▲ | drdeca 2 days ago | parent | prev [-] | | It does, but a number of alternative theories of quantum gravity do not. So, if Lorentz invariance is shown to be violated, this would favor those over string theory. |
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| ▲ | 2 days ago | parent | prev | next [-] |
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| ▲ | bsaul 2 days ago | parent | prev [-] |
| as i know really nothing about the subject, could someone explain why parent was downvoted ? is it for the tone, or the content ? Because, i , having viewed the youtubers in question, had the same opinion about string theory. |
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| ▲ | shin_lao 2 days ago | parent | next [-] | | Because String Theory hasn't delivered falsifiable predictions, yet keeps expanding to accommodate failure. | | |
| ▲ | sesm 2 days ago | parent | next [-] | | The word 'falsifiable' comes from Popper's criterion, which is central to scientific methodology. What it means: if theory predicts something, and later observations show that prediction doesn't hold, then the theory is incorrect. String theory doesn't work this way, whatever was measured will be explained as an afterthought by free parameter tuning. | |
| ▲ | ekjhgkejhgk 2 days ago | parent | prev | next [-] | | What do you mean by "falsifiable"? Do you mean that have been falsified? Of course, no standing theory delivers falsified predictions, when that happens you throw the theory in the garbage. Do you mean that can be falsified in principle? In that case String Theory has falsifiable predictions, I gave you one. In principle, we can make experiment that would falsify special relativity. In fact, we've made such experiments in the past and those experiments have never seen special relativity being violated. The test of special relativity are the most precise tests existing in science. | | |
| ▲ | drdeca 2 days ago | parent [-] | | I suspect what they mean is that there is no outcome of an experiment such that, prior to the experiment, people computed that string theory says that the experiment should have such a result, but our other theories in best standing would say something else would happen, and then upon doing the experiment, it was found that things happened the way string theory said (as far as measurements can tell). | | |
| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | But there are such experiments. String theory says that the result of such experiment is: Lorentz invariance not violated. > but our other theories This is not how scientific research is done. The way you do it is you a theory, the theory makes predictions, you make experiments, and the predictions fail, you reject that theory. The fact that you might have other theories saying other things doens't matter for that theory. So string theories said "Lorentz invariance not violated", we've made the experiments, and the prediction wasn't wrong, so you don't reject the theory. The logic is not unlike that of p-testing. You don't prove a theory correct is the experiments agree with it. Instead you prove it false if the experiments disagree with it. | | |
| ▲ | drdeca 2 days ago | parent | next [-] | | There are no such experimental results satisfying the criteria I laid out. You may be right in objecting to the criteria I laid out, but, the fact remains that it does not satisfy these (perhaps misguided) criteria. In particular, predicting something different from our best other theories in good standing, was one of the criteria I listed. And, I think it’s pretty clear that the criteria I described, whether good or not, were basically what the other person meant, and should have been what you interpreted them as saying, not as them complaining that it hadn’t been falsified. Now, when we gain more evidence that Lorentz invariance is not violated, should the probability we assign to string theory being correct, increase? Yes, somewhat. But, the ratio that is the probability it is correct divided by the probability of another theory we have which also predicts Lorentz invariance, does not increase. It does not gain relative favor. Now, you’ve mentioned a few times, youtubers giving bad arguments against string theory, and people copying those arguments. If you’re talking about Sabine, then yeah, I don’t care for her either. However, while the “a theory is tested on its own, not in comparison to other theories” approach may be principled, I’m not sure it is really a totally accurate description of how people have evaluated theories historically. And, I think, not entirely for bad reasons? | |
| ▲ | ogogmad 2 days ago | parent | prev [-] | | > But there are such experiments. String theory says that the result of such experiment is: Lorentz invariance not violated. This is not a new prediction... String theory makes no new predictions, I hear. I don't understand why you need to be told this. To your point, there exist various reformulations of physics theories, like Lagrangian mechanics and Hamiltonian mechanics, which are both reformulations of Newtonian mechanics. But these don't make new predictions. They're just better for calculating or understanding certain things. That's quite different from proposing special relativity for the first time, or thermodynamics for the first time, which do make novel predictions compared to Newton. | | |
| ▲ | ekjhgkejhgk 2 days ago | parent [-] | | > there exist various reformulations of physics theories, like Lagrangian mechanics and Hamiltonian mechanics, which are both reformulations of Newtonian mechanics You have no clue what you're talking about. Did you hear this in some youtube video and have been looking to try it on someone? | | |
| ▲ | ogogmad 2 days ago | parent [-] | | I suppose it's my bad that I've interacted with a troll that might not even be a real human being. |
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| ▲ | drdeca 2 days ago | parent | prev [-] | | It has delivered falsifiable postdictions though. Like, there are some measurable quantities which string theory says must be in a particular (though rather wide) finite range, and indeed the measured value is in that range. The value was measured to much greater precision than that range before it was shown that string theory implies the value being in that range though. Uh, iirc . I don’t remember what value specifically. Some ratio of masses or something? Idr. And I certainly don’t know the calculation. |
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| ▲ | ekjhgkejhgk 2 days ago | parent | prev [-] | | Because a lot of people felt this applied to them (this was the intention) and were hurt. Good on you for being able to articulate it. Respect. |
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