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comment by shminux · 2021-11-11T22:26:09.144Z · LW(p) · GW(p)

the idea that physical limits are set in stone

is not what physicists believe. The actual statement is that under a wide variety of conditions the Core Theory is a very accurate description of the universe. And it precludes possibilities like FTL and time travel, among others. By the way, the FTL proposals you mentioned are not really FTL. For example the Alcubierre drive, contrary to popular views, does not enable one to travel arbitrarily far faster than light, only as far as the light propagates before the drive is "engaged" An eternal Alcubierre drive is another story, but it's not something you can control, it just is. Same thing with Krasnikov's tubes. All these, as well as traversable wormholes require negative energy sources and lead to various paradoxes. Additionally, there are theorems in general relativity that state that under a variety of conditions changing the topology of space is impossible without having singularities and/or closed timelike curves (the latter cannot be created, they are eternal). 

Some hope of further breakthroughs is at the interface of general relativity and quantum field theory, since we know they do not play well together, even in the low-energy limit, hence the black hole information paradox. 

The hope that such a breakthrough might lead to effectively FTL travel is quite dashed by the lack of astrophysical observations that would hint at anything happening superluminally, even though the energies that are achieved in many observed natural phenomena are very much higher than anything we can hope to reach in lab experiments. The main astrophysical unknowns, dark energy and dark matter, are not in any way superluminal. 

So, for anything like what you hope for (and we all hope for) would have to go beyond the core theory, and even further beyond the observed but yet unexplained macroscopic phenomena, which is a really tall order. 

Replies from: None, None
comment by [deleted] · 2021-11-14T17:18:45.823Z · LW(p) · GW(p)

The hope that such a breakthrough might lead to effectively FTL travel is quite dashed by the lack of astrophysical observations that would hint at anything happening superluminally, even though the energies that are achieved in many observed natural phenomena are very much higher than anything we can hope to reach in lab experiments.

Actually, not that much higher. The Oh-My-God particle had a center-of-mass collision energy of 750 TeV, roughly 60 times that of LHC. I seriously doubt it's a good idea to probe into energy ranges outside of naturally occurring events considering the potential benefits and existential risks.

comment by [deleted] · 2021-11-12T04:11:14.778Z · LW(p) · GW(p)
comment by interstice · 2021-11-11T22:26:07.912Z · LW(p) · GW(p)

There's a big difference between our current state of knowledge regarding physics and previous eras': we now completely understand the physics of everyday existence. In the past, there were many, blatantly obvious unknowns -- e.g. Newtonian mechanics doesn't let you understand how chemistry arises from physics. Nowadays there's a lot less room for reality to surprise us with new observations -- indeed, theoretical physics has largely stalled out in recent years due to the infeasibility of obtaining observations our theories don't already predict. More generally, this seems to be what we should expect to happen in a lawful universe: after an initial period of discovery, we eventually discover all the laws and are done. What you propose -- an endless string of new discoveries, each upending the last -- is incompatible with the universe having a finite description. It's not logically impossible that we live in such a universe, but scientific progress so far seems to support finite lawfulness.

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comment by [deleted] · 2021-11-12T04:06:03.507Z · LW(p) · GW(p)Replies from: None, interstice
comment by [deleted] · 2021-11-14T17:11:10.301Z · LW(p) · GW(p)

We don't have much data on 1 million Kelvin interactions

Neither have we tried saying magical spells in a high pitch much. Aside from the difference in literary genre, why would you expect either scenario to produce anomalies that violate the fundamental laws of physics? To be sure, new discoveries are made all the time in chemistry, biology, medicine etc. but they are all very much compliant with known physics.

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comment by [deleted] · 2021-11-15T03:59:26.104Z · LW(p) · GW(p)Replies from: None
comment by [deleted] · 2021-11-17T23:01:06.211Z · LW(p) · GW(p)

1 million Kelvin doesn't even get close to the limit of known physics, LHC generates collisions equivalent to quadrillions of Kelvin, and quantum gravity is another trillion times that. To a physicist looking for new fundamental physics in a 1 million Kelvin plasma sounds about as random a suggestion as chanting spells. In terms of observational science, only cosmology still has the potential to uncover new fundamental physics, which is way beyond this galaxy or galaxy cluster. This ain't the 17th century no more.

comment by interstice · 2021-11-12T09:05:00.405Z · LW(p) · GW(p)

Do you have reason to believe we will never collect surprising observations?

Sure, it's likely we'll get some new surprising observations before we nail down the TOE. The question is just about how surprising, and whether they will let us upend physical limits. Agreed that there's a lot of new interesting things we could observe, but for most of your examples, I don't think we have good reason to think that we'll learn new things about fundamental physics from them.

Let me rephrase my objection. I think my main issue with your post can be found in this phrase near the beginning: you speak of the "rate at which we have constantly upended our own physical theories". I don't think that progress in fundamental physics is like technological progress or other things which happen at a steady rate per unit effort. It's more like exploiting a non-renewable resource: our ignorance of physical phenomena. So 400 years ago we basically started with a huge 'reservoir' of ignorance, which has gradually been drained as our theories improved, until now there's only a few small pools left that we can see. The reason that we've seen steady progress until recently is due to our slow draining of this reservoir, so now that it's mostly gone, we no longer have a reason to expect further such steady progress. It's possible that we might find new reservoirs someday, but equally possible that we won't, so it's a reasonable assumption that many of our current theories' physical limits will continue to apply indefinitely into the future.

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comment by [deleted] · 2021-11-12T09:54:13.771Z · LW(p) · GW(p)
comment by Dagon · 2021-11-11T19:23:07.524Z · LW(p) · GW(p)

I suspect the currently-known limits are actual limits.  There may be exceptions for theoretical constructs, but the information analysis approach seems to be pretty strong.

Note that these limits aren't all that limiting.  There's a LOT of stuff in our light cone, and a LOT of behaviors and information/experiences we haven't considered, even within out currently-known constraints.

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comment by [deleted] · 2021-11-11T19:28:59.471Z · LW(p) · GW(p)Replies from: Dagon
comment by Dagon · 2021-11-11T20:17:11.694Z · LW(p) · GW(p)

https://en.wikipedia.org/wiki/Black_hole_information_paradox is a reasonable writeup of the approach for black hole physics.  There are similar information-centric views of quantum computation and tunneling.

comment by [deleted] · 2021-11-11T19:46:16.611Z · LW(p) · GW(p)