There's a lot of mysticism and superstition surrounding C++ exceptions. It's instructive to sit down with godbolt and examine specific scenarios in which noexcept (or exceptions generally) can affect performance. Read the machine code. Understand why the compiler does what it does. Don't want to invest at that level? You probably want to use a higher level language.
Or set the compiler flag -fno-exceptions and ban the use of exceptions. While it isn’t standard-compliant, a surprisingly large number of companies and projects follow these practices.
You won't get a sense of how bad exceptions can be by using Godbolt. A lot of the magic of exceptions is handled behind the scenes by the compiler and/or the Itanium ABI. For example one disasterous consequence of using exceptions in GCC is that there is a global application wide lock used to manage stack unwinding.
This means that only one single thread can unwind a stack at a time and the lock is held from the start of the exception being thrown until the very last destructor is called. If you have a multicore server with 100 threads, and one of those threads throws an exception, you better hope that no other thread throws an exception because even if those two threads are entirely independent of one another, one of them will block.
It's more of the same slop we've seen for decades from the social sciences. We know most traits are heritable. We know that low time preference yields higher lifetime earnings. Of course an experiment is going to show no effect when it controls for the effect! What else would you expect?
Yeah. The reality is exactly the opposite of the headline. The study is confirmed, not refuted. Low time preference is heritable no matter what you believe the mechanism might be.
Afaik, if we introduce a special frame of reference (e.g. the cosmic microwave background frame) and this special reference frame is the only frame in which FTL is permitted, FTL does not violate causality
Put another way, travelling FTL in and of itself does not mean you're travelling backwards in time. But the geometry of the universe provides a barrier between STL and FTL, yet no barrier between forwards and backwards in time except inasmuch as you need to first rotate from STL to FTL before you can rotate from forwards to backwards-
So if you invent such a barrier, then sure, FTL is fine. It's just that there's geometrically nowhere to attach that barrier, except if you make use of the CMB.
Causality is not robust, and you can prove it to yourself with three sheets of light polarizing gratings. When we figure out how to put probability hooks on things other than photons, it’s going to get rowdy.
This is a nitpick. The warp drive concept doesn't allow for FTL travel, but it could allow for you to get from point a to point b faster than light could.
The idea behind a warp drive is that it utilises expansion of space, which is not subject to speed of light restrictions. The universe has already expanded faster than light without breaking causality.
The causality violation examples I've seen in relativity all involved going back to where you started. No return trips, which includes the cosmic horizon, no causality violation.
One question I've got though: does relativity (1) remove the need for universal frame of reference, or (2) preclude the possibility of a universal frame of reference?
Because if it's the former, then (I think) FTL doesn't need to also be a time machine?
> No return trips, which includes the cosmic horizon, no causality violation.
The drawback is that if a warp drive going from A to B leaves expanded space in its wake, a return trip will take longer than light would take to make a round trip. At the same time, an observer on B looking in the direction of the ship will see a shift to blue until the ship arrives, and, then, would see a marked shift to red when observing A.
For one thing it can create paradoxes, like your future you deciding they didn’t like where they ended up and stopping yourself from setting out on a journey in the first place.
This is true if and only if we live in a universe with a time continuum that is not branching (i.e. a line). Instead, if we live in a time continuum that can branch (which will result in a directed acyclic graph) the act of traveling faster than light simply creates a new branch in which you go to the past and in that branch your past self never traveled.
This relates to the different interpretation of quantum mechanics. The one that has paradoxes is the Copenhagen interpretation and the one with the branching is the many-worlds interpretation.
There is also the pilot wave interpretation, but I am unsure how to map the example you proposed to that one.
I thought branches happened when a wavefunction 'collapsed' -- i.e. for every possible value of the wavefunction, you get a branch with a unique answer for 'value of the wavefunction'?
The wavefunction decoheres; it doesn't collapse. Collapse is a function of collapse theories like Copenhagen, but has never been observed in reality.
That said, decoherence doesn't branch time in the sort of absolute manner you might be thinking of. "How many timelines exist" is a question similar to "how long is a coastline"; it depends on how closely you're looking. At the smallest scales, 'timelines' interfere and mingle in a way that distinct universes really shouldn't. It's only once decoherence has gone well out of control that they can be said to be truly separate, and even then the interference never goes to zero, only approximately zero.
If we exist in a block universe, then all time-travel effects are "already" baked in. Just because something's path through the block isn't always "forward" doesn't mean it can change its path, or anything else's.
In a growing block universe, I think time travel would be impossible, but I also think that the growing block universe theory is cope.
Not really at the quantum level, at least not in the form that is typically understood as causality. There are all kinds of ways that you can interfere with probability and when you do, the “no taksie-backsies” rule goes out the window. You can prove this to yourself with a flashlight and 3 diffraction gratings.
That’s where probability manipulation really gets interesting.
My preferred conjecture is that all things exist, at all times, in all places, but only a fraction of all of those infinite-dimensional probability vectors will produce the act of your observation, so those are all of the vector-spaces that you can detect. We can’t observe, for example, a probability vector-space where water boils at 15c/1bar, or where e=3 because we would never have existed to observe within that environment. Perhaps other things exist and observe those places, but not carbon based biological life as we know it.
I think that the Casimir effect and especially Casimir pressure in constrained geometries, Zero point energy, the uncertainty principle and other observable phenomena point towards the possibility of a continuum of multiple overlapping observable probability fields, but obviously that could be just a convenient hand wavy explanation.
In the bandwidth of overlapping probability fields flavour of MWI there is no branching or creation of new realities, merely extant vector spaces drifting in and out of observability based on probabilistic functions. Vector spaces within observability tend to be similar, and the overall aggregate sum is what we perceive as a unified observation.
As we make changes that manipulate this probability space, new probabilities dominate our perception. The apple was very unlikely to be seen on the table until we moved it there, making it then extremely probable to be observed in that position.
There are some very interesting ramifications that appear to be observable phenomena if this line of thought is drawn out to its extrema. It’s one of my favourite possible models.
Perhaps one day I or someone else will figure out how to experimentally test the idea, but so far it seems to be unfalsifiable (which obviously doesn’t mean that it is more correct, just that it’s hard to test, like the simulation conjecture and many others)
I should have also made it clear that the probability vector-spaces that become unobservable include those where you got hit by a bus, and all of the coherent/adjacent spaces to that event. So the bandwidth of perceivable “universes” keeps shrinking to lesser infinities as you go through life.
In addition, the perceivable vector spaces where you can talk to your friend also includes only those where she also got missed by the bus, and to a lesser extent all those who are connected and perceivable through communications… the act of communication being a constraint to the infinities of perceivable vectors where the communication would be possible, making us much more constrained as a society than we would have been when distant people had little or no contact.
There are a lot of interesting implications of this conjecture that may go some distance in explaining subjective human experience.
Um, sorry, how does that experiment prove anything quantum? It's explained entirely by Malus' law of I = I0 * cos^2(alpha) which has an entirely classical, simple wave-theoretical explanation (even if Malus himself was an emissionist and derived his law by introducing transversal asymmetry in the light corpuscles).
Malus’s law does indeed describe the amplitudes of the resulting light, but it does not say “why”, only how. In the same way that Newtonian physics assumes gravity but fails to explain its existence.
For more in depth look at this there is a 1995 paper by K Wódkiewicz contrasting the corpuscular formula with the quantum explanation IIRC.
Obviously, despite its explanatory power, we know that QM is incomplete so YMMV, but I’ll take QM over light corpuscles, until something better comes along.
Having light corpuscles that have poles and can experience fits of easy transmission/reflection is not much mathematically different from having photons with spins and wave phases, to be fair.
And Malus' original justification of his law straightforwardly carries over to the photons.
I saw something recently that one explanation is that we're in a cosmic void. Sure the milky way is big, but we're still exposed to a fraction of the worlds that a non-void area would be.
Of course there are 80,000 other explanations that are also fascinating. A wonderful subject.
For me what makes most sense is that we're relatively early in cosmic history. You need enough heavy (and diverse!) elements to be able to support life/civilization and you won't get that from early stars.
Most probably yes, I mean we only have few generation of stars actually producing heavy elements enough to see what we see ie on Earth, not just some hydrogen & helium ball.
Also most probably there isnt any way to travel back in time, since we would most probably be eliminated at the seed to not compete for resources or avoid aggression. For all wonderful things mankind did and does, we are still deeply flawed and highly emotional primitive beings, and we may kill ourselves due to this.
On cosmic scales of time, theres no reason to assume spacefaring humans would remotely resemble us in any recognizable way. Imo especially their minds, they’d almost certainly have augmented and modified their thinking drastically.
And earth has been around for 1/3rd of the current age of the universe. As far as things go it's pretty old.
Add to that that we probably aren't as "normal" as we initially believed. A solar system with small rocky planets on the inside and big gas giants on the outside seems to be the exception and was very important for earth's development. Then there's the above mentioned "void" we are in, and probably other things we don't realize yet.
There's a really good case that we are among the earliest spacefaring civilizations
They haven't cited a source or their reasoning, I would guess they mean "seems to be an exception by observation"
Emphasis on "observation".
Currently we infer planets that orbit stars that are extremely distant by starlight dipping in intensity .. this is a method that works better with larger planets and that skews the results of observing distant planets.
We have observed some small rocky earth like planets IIRC but these are rare, observations perhaps due more to luck in looking than frequency of existence.
This is the crux of the problem; does the distribution of planets we observe match the distribution of planets that exist?
I hadn’t considered that angle of things before. It also brings up the opposite idea, I wonder if the over abundance of heavy elements in an old universe could reduce the likeliness of life being able to form due to the toxicity or higher levels of background radiation.
Well don't forget that Earth had it's reset button smashed 66 million years ago. Let's say another world started out at the same as we did but never encountered such a cataclysm. Even if they took an additional 65 million years to develop, they'd still be a million years older than us.
The KT boundary is hardly a "reset button smashed". Yes, it was a mass extinction event, but these things happen. The products of billions of years of evolution survived, even if megafauna had a setback. Evolution spent billions of years figuring out basic things like the genetic code, sexual reproduction, and mitochondria. All these technologies survived the KT boundary. Complex multicellular life emerged only about 560 million years ago (after single-celled life had been around for billions of years). The implication is that the early innovations in life (ribosomes, etc.) were "harder" than later ones involving eyes, brains, and so on.
A "reset button" would be more like the impact that created the moon: ramming a Mars-sized body into Earth turns Earth into a magma ocean. Nothing survives that. By comparison, the KT boundary asteroid is small potatoes.
What would be horribly unsettling is detection of ET intelligence, as it would imply either interstellar travel is impossibly difficult or that the Great Filter is in our future.
Exactly. If we set our minds to it and dedicated enough resources we could likely reach the next star within the century: 40 years travel time at 0.1c with something like nuclear pulse propulsion, and we could probably get the remaining technical challenges for achieving that out of the way in 30 years.
If I was a really advanced civilization and the universe was nearing its end, I'd embark on a project of unparalleled scale that might wind up resembling a big bang with a spark of panspermia-precursor seasoned in.
Indeed, we know so little about the nature of things that it's really a bit premature to hold our current understanding as the final word over what will happen.
For one thing, a large fraction of possibilities involves simulations. In a simulation with successful traits, some constants and elementary particles might turn out to have been misunderstood later on...
In a physically constrained system all exponential growth becomes at best a sigmoid sooner or later... it's only sad if you let it make you feel this way.
You don't need anything near light speed for single human lifetimes to navigate beyond the solar system but it will be a one way trip mostly devoid of communication. We can seed the galaxy but can't watch it bloom.
Absolutely. We want FTL in stories because it allows us to tell a sequential narrative across vast galactic distances. We want FTL in science and mathematics because humans as a species don't like hard limits to what is allowed. We want FTL in our life because few people are willing to cut all ties to their family, friends, and society to wander off into the void without hope of ever returning or being heard from again. But... some people are okay with that finality of their decision to push limits and that's how islands over the horizon get discovered and settled.
We haven't actually looked for them yet. The frequency of the theoretical gravitational waves is also beyond what our current detectors can reasonably pick up.
IIRC, a warp bubble a few km in diameter moving at <0.3c produces gravitational waves at a frequency just beyond what we can currently detect. Superluminal warp bubbles haven't been simulated, apparently that's beyond the computational resources available to this team.
Don't expect a real detection any time soon. We'll need another generation or two of development on our detectors and to actually simulate a more realistic (small and superluminal) warp field.
Personally, I think we'll find something once we build detectors good enough. I'm a firm believer that purely based on statistics there has to be someone else out there. I also choose to believe that superluminal travel is possible because the universe would be a much less interesting place otherwise.
The Dark Forest theory is fear-mongering anyway. If there's a civilization out there that wants to conquer others, it just has to send a probe to every star out there. Sufficiently advanced automation would allow this to happen without much work on their part. In theory, WE could do that right now, though very clumsily and with many failures. 3D printing, AI, harvesting materials off asteroids. Not outside of possibility, just hard at our level of tech. Now imagine the boogeyman of the Dark Forest theory - they would obviously have a greater level of tech if they're so dangerous, and it would be much easier.
Warp drives are probably a pretty terrible way to move around since they require exotic things like negative energy that probably don’t exist, and quantities of power that would destroy the destination solar system.
If anyone out there is crossing interstellar distances they’re probably doing it a different way.
Have you tried wormholes? Those are pretty promising. Let’s simulate one of those collapsing.
If you're spending at least a quadrillion dollars to build a warp drive, you better make sure it doesn't fail or fails safe. We may never see a failure, even if we make it depending on where it is.
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