Any physicists wanna throw some cold water on our hopes and dreams here? Compared to most papers with far-out results, there didn't seem to be any obvious caveats here. What's up with worldline numerics? Could there be any issues hiding in the numerical methods there? How established are those methods in the field?
Also, to be clear, is it correct that they haven't actually built such a device, this result is still just in simulation?
FTL travel implies violation of causality, no matter how you slice it. How sacred causality is to you depends of course on your personal world view, but to me it is inconceivable how causality could be violated, so I won't be getting my hopes up about this at all, even though I can't comment on the technicalities of this paper.
Causality isn't nearly as central to physics as it may be to your worldview. Lawrence Krauss and others who have commented on the matter have argued that FTL travel, would mostly require a re-evaluation of our perspectives rather than a re-evaluation of physics
Probably a pretty good analogy! Even now, it's not known whether time has directionality in any way that is meaningful in physics. FTL travel would resolve the "Arrow of Time" question (https://en.wikipedia.org/wiki/Arrow_of_time) but this wouldn't invalidate much/any of physics because the arrow is essentially non-observable at the micro level
He discusses it extensively in The Physics of Star Trek.
Also, supposed locally FTL travel for subatomic particles is pretty different from locally non-FTL but globally FTL travel a la Star Trek, Alcubierre drives, etc
>> Causality isn't nearly as central to physics as it may be to your worldview
No, but locality seems to be a sacred cow in physics. They'll latch on to just about anything to explain violation of the Bell inequalities, but nobody is willing to part with locality.
At least at quantum level there are experiments where the outcome depends on things that did _not_ happen (according to our intuitive understanding of causality). Mostly in weak measurement research.
So I'd say while causality is real, there are still some surprises to be expected.
Warp in this case I believe is referring to bending space time or traversing something similar to a wormhole, it’s not talking about Star Trek and tachyons and FTL. Hence the discussion points of exotic matter that exudes negative mass, which is what is required to stabilize mathematical models of Einstein Rosen bridges.
Doesn't matter, if you make it from here to the moon in less than a second, no matter if it's using a warp bubble or something else, then there is a frame of reference where you arrive before you leave.
You'd need negative mass either way. Bending spacetime is the most plausible implementation of FTL travel a la Star Trek; doesn't matter a whole lot if you're using the negative matter to keep the wormhole open or create an Alcubierre drive-style spacetime wave on which to surf
Not a physicist, but some friends who are almost-barely physicists have pointed out that the concept of worldline numerics comes from string theory, which itself may or may not be generally bogus depending on who you're asking.
As far as I understand the main problem of string theory is that it has been carefully constructed to fit all the physics we know about, and has not actually predicted anything we didn't already know about that we could experimentally verify. So in a practical sense string theory has been quite useless.
If indeed it is true that string theory predicts this effect, and the effect can be experimentally verified (afaik this was dubious at best) then that would be a huge boon for string theory.
> As far as I understand the main problem of string theory is that it has been carefully constructed to fit all the physics we know about.
Doesn't string theory have a lot fewer tunable parameters than the standard model?
> and has not actually predicted anything we didn't already know about that we could experimentally verify
I don't like that argument for a couple of reasons.
First, it depends on the timing of when we discover things. If the experimentalists had taken longer to discover some things a theory that we would criticize today as not predicting anything we don't already know about would be a theory that would be celebrated for its predictions if it had just been posed earlier.
I think a better thing to look at is if a theory can correctly calculate things that weren't built into the theory. I remember reading [1] that string theory correctly calculated some things concerning black holes that none of the people who had developed string theory to that point knew about.
Second, I don't like it from a philosophical point of view. It suggests that if say some pre-Newton gravity theorist had just included enough epicycles, science should have rejected Newtonian gravity because it would not have explained anything that the epicycle theory didn't.
[1] Probably either in Brian Greene's "The Elegant Universe" or Lawrence Krauss' "The Greatest Story Ever Told--So Far". Possibly Greene's "The Fabric of the Cosmos", but that seems unlikely. I distinctly remember reading it, and my copy of "The Fabric of the Cosmos" is an audiobook. The other two are Kindle books.
> I think a better thing to look at is if a theory can correctly calculate things that weren't built into the theory. I remember reading [1] that string theory correctly calculated some things concerning black holes that none of the people who had developed string theory to that point knew about.
Well if that's true, then string theory definitely isn't useless, so I'd be interested in the specifics. This prediction from string theory wasn't explained by any of the accepted physical models?
> Second, I don't like it from a philosophical point of view. It suggests that if say some pre-Newton gravity theorist had just included enough epicycles, science should have rejected Newtonian gravity because it would not have explained anything that the epicycle theory didn't.
Well yeah, but why not reject Newtonian gravity if everything observable can be predicted by the epicyclical view? The goal is not to generate pretty models, the goal is to make accurate predictions of the physical universe, ideally through the simplest model we can come up with just to guard against overfitting.
Anyway, it's not that I (or anyone, I don't have any physics authority certainly :P), am rejecting string theory, it's just that as far as I understand string theory hasn't had any real use to our physical models. I certainly don't have an alternative to string theory.
Well, string theory has actually predicted Supersymmetry, which so far seems not to exist (though it is always possible to say it exists only on some higher energy than we can detect right now).
As I understand it, supersymmetry was taken as a concept and baked into the strings concept, to come up with superstrings. So it’s not really a prediction as much as it is baked-in by the prevailing notions of the time.
It's possible to test string theory experimentally, just the amount of energy required is far too big for any foreseeable future. With a bruteforce approach, at least.
The issue seems to be that the alcubierre drive requires things like external negative energy which are 'theoretically possible' but have never been detected and probably should have been already if they existed. Also, even if they worked, the negative energy requirements is something like the mass energy of jupiter on the high end or the moon on the low end.
This is an hour long interview Dr Miguel Alcubierre who wrote the paper describing the Alcubierre drive.
> The issue seems to be that the alcubierre drive requires things like external negative energy
Yes that's traditionally been the stumbling block. But the whole point of the linked article is that they have predicted a way to meet this requirement:
> a micro/nano-scale structure has been discovered that predicts negative energy density distribution that closely matches requirements for the Alcubierre metric
Obviously it's still a very very long way from a practical application re. Alcubierre (if such a thing is possible), but it's certainly an intriguing result if correct.
From a quick flick through the paper, the above commenter seems to be correct in saying that they haven't yet completed a practical experiment to confirm. So nothing more than a simulated result at this stage.
Yes again it seems like one of those 'theoretically possible but never seen in a lab' kind of requirements, just like negative energy.
The PBS spacetime video mentions you can 'do away' with the negative energy requirements at quantum scales, but those aren't really productive scales for useful space flight. Maybe for very tiny micro exploring robots? I'm not sure how such a device would usefully communicate with us though.
Cynical prediction: a nano-scale implementation could be a step towards a cable that can transmit signals faster than light... which would only be useful for HFT
I have a drunken plan involving sending neutrinos through the earth as a form of communication. Friends inform me that it has only three problems: producing the neutrinos; modulating the signal; and detecting it at the other end. I shall continue pottering.
Atomic bombs produce large bursts of neutrinos, which should be sufficient for the Super-Kamiokande detector in Japan. Amplitude modulation is possible through Dial-a-Yield and MIRV warheads can convey multiple bytes. Environmental impact may rival Bitcoin though..
> We report on the performance of a low-rate communications link established using the NuMI beam line and the MINERvA detector at Fermilab. The link achieved a decoded data rate of 0.1 bits/sec with a bit error rate of 1% over a distance of 1.035 km, including 240 m of earth.
That’s surprisingly similar to my build-a-laser-to-traverse-the-core-and-then-beam-financial-data-through-it.
Current state of research: my remote cousins in New Zealand and I have made a “planet sandwich” by laying bread on the floor of our antipodal dwellings.
Basic loop: Price of X rises to Y at time T2, time-traveling trade packet is transmitted to T0, past-X is purchased at price W increasing demand of X and therefore increasing price to Z at T1.
If T1 == T2 and Z == Y: the loop is stable. If T1 > T2 and Z >= Y: the loop is stable and not paradoxical. Every other option produces interesting results depending on the trading algorithm.
Hypothesis: all unstable loop scenarios will converge on Z == Y == W, negating the sending of the signal altogether. Or from another perspective, the superposition-timelines where Z == Y == W does not occur destructively interfere with each other.
Reminds me of the "portals" (quantum spacial entanglement devices) in Peter F Hamilton's Salvation Sequence, which as well as people, vehicles and equipment, are used for electrical and communications cables.
There's nothing which specifically stops you from having wormholes that don't violate relativity but do allow you to bypass annoying things like solid matter, but stabilizing them is something you also need negative energy to do.
Replacing all radio communications with point to point lasers via wormhole-on-a-chip devices would be a heck of a communications revolution (probably also an answer to the Fermi paradox).
I'm curious, why is that? Because the way I understood the Fermi paradox was that highly advanced civilizations should be visible from their energy requirements alone (e.g. via Dyson Swarms), not specifically in the way they communicate.
The assumption that ET communicates via radio waves has always seemed unusually anthropocentric compared to the rest of SETI attitudes.
If it’s not sending lasers through wormholes, it will be something else – but it seems the height of arrogance to assume that an advanced civilization would communicate via radio waves just due to our own familiarity with them.
You don’t see this elsewhere – SETI is always keen to downplay “little gray men” (they might not even take physical form! Maybe we can’t conceive of them!) or “carbon based lifeforms” (maybe they’re made of silica!). But for some reason there’s less questioning of any assumptions about their communications media. I wonder if this is due to SETI betting the bank on radio waves.
Depends on how easy it is to project a wormhole endpoint elsewhere in the universe. If it can be done at >= C then sensitive radio receivers don't have much value.
I suppose an optimist would say that success, even at a tiny scale, would be a step in the right direction. But you're right, it could well be possible that the effect doesn't scale up.
I think gram-scale probes are definitely being considered -- though not with Alcubierre drives obviously lol. Breakthrough Starshot think they can transmit back from Alpha Centauri at 2.6-15 baud per watt by using their light sail as a laser reflector [0]. Pretty crazy.
Negative energy is “theoretically possible” in the same way that you can take the formula for compound interest and substitute it an imaginary or complex interest rate: it will generate results, but the whole premise is profoundly suspect and would never occur in reality.
Just need a tiny, stable black hole and some way of containing it. And then some way of scaling up the Casimir effect away from nanoscale electron microscopy.
Maybe you could create a collider scale facility and warp particles? From what I can understand, there's nothing wrong in principle, it's just that the conditions are currently absurdly beyond our reach.
There’s lots of things wrong with the naivest formulation, and plenty still wrong with the most sophisticated constructions: for example, you cannot steer your ship, as that requires violating casualty locally, and also you’d blast your destination with a shower of infinitely blue-shifted radiation.
Also, to be clear, is it correct that they haven't actually built such a device, this result is still just in simulation?