Eh. Suppose our current theory of relativity was wrong in some specific way or someone came up with something that sidestepped our current understanding - you could still have a logically coherent universe in those scenarios, because it'd just mean that our current understanding and theories of how the universe works were wrong.

> Suppose our current theory of relativity was wrong in some specific way

There aren't many ways in which relativity can be wrong. Relativity follows logically from the assumption that the laws of electrodynamics are independent of the observer's state of motion. The evidence that this is true is overwhelming. To overturn this part of physics would be comparable to showing that the earth is in fact flat.

I'm not saying that it is wrong - experiments and data to date seem to mostly validate our current theories etc - I'm just trying to point out that it's not inconceivable that we might not have a 100% correct theory and that that the parts that we're incorrect on could lead to possibilities that we would otherwise consider inconsistent (within our current understanding).

I'm sure that historically, scientifically minded folks who believed in whatever they thought they knew at the time considered some aspects of their "knowledge" to be incontrovertible given how overwhelmingly the evidence until then seemed to support their theories - until it didn't.

There's not a reasonable reason to expect that we have arrived at the ultimate understanding of most things such that most if not all new discoveries will only be refinements; the evidence until now has shown that that approach to science has been incorrect for basically most of history.

> I'm not saying that it is wrong

This is exactly what you said:

> Suppose our current theory of relativity was wrong

You should read this:

https://chem.tufts.edu/AnswersInScience/RelativityofWrong.ht...

I'm saying that it could be wrong (as any and all things could be), not that it currently is.

Im also aware of Asimov's essay on the topic of how wrong something can be. That being said, his point about getting less wrong really addresses one thing: theories are largely formed on predictive power and we improve over time as we collect more observations and attempt to address the inconsistencies between our theories and our observations to the contrary. As a result, since newer theories should have greater predictive power, they should be less wrong, and thus should have a higher probability of being correct. None of that, however, necessitates that the current theories should have a 100% probability of being correct.

Keeping that in mind, it is worthwhile to realize that there are questions that can be asked today given our current level of understanding and observation that are simply nonsensical to ask in a prior time frame (easy example: asking "what is the band gap voltage of InGaAs?" in 1600 AD). This means that results that seem impossible at a given time frame (real time displays that render imagined worlds) become a simple question of how to in a different time frame.

Putting this all together: we could definitely be wrong about anything. Sure, theories that seem consistent and have consistently provided good predictive power across most of not all current observations are useful, but they don't preclude new discoveries that could be even more correct and allow for things that we couldn't have previously considered possible.

> it could be wrong (as any and all things could be), not that it currently is

Unless you think the laws of physics can change over time, this is false. Unless the actual underlying laws of physics change with time, Einsteinian relativity at this moment is either correct or it is not. More to the point, the principle of relativity, i.e. that the laws of physics are the same in all reference frames, is either correct or it is not, and Maxwell's equations are either correct or they are not. My money is on all of these things being correct, which logically entails the impossibility of FTL signaling.

Yes, any of these things could be wrong. And it might be possible to violate the second law of thermodynamics, and the earth could be flat, and Bigfoot might be real. Personally I put all of these things in the same category: the odds of any of them being true are indistinguishable from zero. But if you're feeling lucky, by all means, feel free to pursue any of them. I won't stand in your way.

BTW...

> theories are largely formed on predictive power

No, scientific theories are selected according to their explanatory power, not their predictive power. Ptolemaic epicycles are a perfectly good predictive theory of planetary motion to within the margin of error of observation for several thousand years of human history. It is nonetheless absolutely without merit as a scientific theory because it purely descriptive, not explanatory.

>Ptolemaic epicycles are a perfectly good predictive theory of planetary motion to within the margin of error of observation for several thousand years of human history.

Except for Mercury. The math for Mercury's orbit didn't add up until general relativity came along and frame dragging could be taken into account[0].

This doesn't contradict your point, because Pluto's orbit was a sign of something that observable physics couldn't explain, pointing towards a more complete explanation. As far as I'm aware, there's no "hole" in physics that can only be explained by the existence of antigravity, and models in which it exists don't have the same or better explanatory power as current models.

The fallacy here lies in looking back at the advance of science and assuming that because models were inaccurate before, they must always be arbitrarily inaccurate. Rather, the more we learn, the less likely it becomes that everything we know is entirely wrong, because any new models have to explain every observable facet of reality that the current one does as well as fill in gaps.

[0]https://www.forbes.com/sites/startswithabang/2015/11/25/how-...

Edit: I meant Mercury, not Pluto, and the other relativity. Oops.

> Except for Pluto.

You mean Mercury.

> The math for Pluto's orbit didn't add up until special relativity came along and frame dragging could be taken into account[0].

You mean general relativity.

> the more we learn, the less likely it becomes that everything we know is entirely wrong

Exactly.

Yes, I meant what I meant, not what I wrote...

"The basic trouble, you see, is that people think that "right" and "wrong" are absolute; that everything that isn't perfectly and completely right is totally and equally wrong."

always a great read. this bad logic he describes is also one of the most frustrating things about politics

Does general relativity explicitly rule out causal paradoxes?

It's my understanding that causality is more of a fundamental axiom of the scientific method than a direct product of general relativity theory specifically.

That's right. The impossibility of causal paradoxes has nothing to do with relativity, it's a consequence of basic logic. ((P AND (NOT P)) IMPLIES Q) is a tautology of propositional logic, so if there were ever a physical situation in with P and (NOT P) were simultaneously true then there would remain only two possibilities: either 1) propositional logic is not an accurate model of reality or 2) no proposition is false. Either way, all of science and math instantly go poof.

I think it's certainly possible that a model built on propositional logic does not cover the whole of reality. I struggle to think of how a system of thinking built on propositional logic could completely exclude the possibility of information that it can't prove. This feels like we're getting into Godel territory.

I don't see how that would necessarily mean that all science and math go poof; if some phenomena satisfy our axioms, they would continue to satisfy analysis based on those axioms. If some phenomena do not, they would be excluded from our analysis.

We already hypothesize at least one such event: the Big Bang. Scientifically, it's nonsensical to reason about what happened "before" it to cause it; but we also seem to have a ton of evidence that it actually happened.

I'm not trying to be woo-woo new-agey here BTW. I don't think it's wrong to consider the limits of scientific analysis.

> I think it's certainly possible that a model built on propositional logic does not cover the whole of reality.

Not only is it possible, this is the normal state of affairs. Until we have a theory-of-everything, none of our models cover the whole of reality.

But all of our models rest on a foundation of certain basic assumptions. Among these are that (some) statements about reality can be classified as true or false, and that these are mutually exclusive possibilities. Not all statements can be classified as true or false (e.g. Euclid's fifth postulate) but for the ones that can, if it is true then it is not false, and if it is false then it is not true.

If you deny that, then the entire edifice of human intellectual achievement really does crumble into dust.

You're saying that, in principle, new physics could allow for FTL travel that nevertheless does not permit time travel and the grandfather paradox etc, right?

Yep! Alternatively, perhaps new physics would allow for what appears to be "time travel" but in reality is not (travel between the present here and a different "time" in a remarkably similar but parallel universe).

Closed timelike curves (i.e. causal loops) are exotic but not altogether outside of mainstream physics. The basic fact of continuity that's inherent in QM means that no logical paradox arises; consistency is always possible. FTL is more problematic for other, less directly-related reasons.

> Closed timelike curves

Those are not the same as FTL signaling. CTCs don't by themselves produce causal paradoxes. FTL signaling does.

> FTL signaling does.

Pick some example of a "causal paradox" of the sort that might introduced by FTL signaling. If the underlying system is a quantum one (hence with continuous amplitudes, albeit the reasoning also extends to simple probabilities) no logical paradox actually arises because the underlying values are continuous. This would imply that there's no difference between that and a CTC.

Of course larger-scale physics appears classical to us but that's a consequence of quantum decoherence and ultimately of the "law" of increasing entropy (2nd law of thermodynamics). Which is just as much of an obstacle to classical CTC's.

The word "signaling" necessarily implies the transfer of classical information (because of the no-cloning theorem) and that in turn implies some model of the transition between quantum and classical. Whether that transition is (meta)physically real (i.e. collapse) or just an arbitrary threshold applied to a continuous process (decoherence) doesn't matter. What matters is that FTL leads to a logical contradiction with respect to the characterization of the state with respect to whatever model you choose to apply. The underlying metaphysical reality is irrelevant.

Eh, that model might still allow you to probabilistically send information back in time, in a way that saves the universe from an outright causal paradox (a weird "chronology-protection" principle of sorts). You can't send your patent back in time and generate prior art that destroys it, but you can end up with a 50:50 probability of doing so, and that description is logically self-consistent. Probability is still "classical".

All communication is probabilistic. There is no such thing as a noiseless communications channel. But per Claude Shannon you can always tilt the odds in your favor as much as you like given enough time and energy.

Ah, it's not the laws of physics you care about! It's causal paradoxes!

In other words, you want the patent office to not only know the laws of physics (reasonable), but also have a deep knowledge including where there is future potential for change in understanding (maybe less reasonable).

I would expect someone at the patent office to be familiar with the basics of modern physics, including the "cosmic speed limit" imposed by the speed of light. I would not necessarily expect them to know why nothing can move faster than c, but I would expect them to know that nothing can and to reject a patent for something that moves faster than c on those grounds.

There is actually a specific rule for this sort of thing:

https://www.ipwatchdog.com/2011/10/11/the-patent-law-of-perp...

It is generally applied to perpetual motion machines.