The first gravitational wave detected (GW150914 in 2015) was from a collision 1.3 billion years away. IIRC ~5 Solar masses was converted into energy in a matter of seconds. This is a mind-bogglingly large energy event.
Yet to detect is LIGO has to be unbelievably sensitive. I've heard it described as measuring the distance to Alpha Centauri with the variation of the width of a human hair.
I still don't believe warp drives (in this case Alcubierre drive [1] isn't viable. It's an exercise in hopium. People want to live in Star Trek or Star Wars so want it to be true. It's an object lesson in not understanding the domain of a function. Warp drive concepts rely on concepts like negative mass and/or energy. I can plug negative (or even complex) numbers into quantities like velocity or acceleration but again I've just violated the function domain even though various formulas will spit out (nonsencial) values. Garbage in, garbage out.
But let's just say this is possible (which, again, IMHO it isn't), then we get to the energy budget required for any of these FTL concepts. The amount of energy to reach even our nearest stellar neighbour is mind-bogglingly large. Some estimates I've seen for various warp drive concepts involve things like 1 Solar mass of energy.
> The amount of energy to reach even our nearest stellar neighbour is mind-bogglingly large. Some estimates I've seen for various warp drive concepts involve things like 1 Solar mass of energy.
I really hate this argument because you can use it for quite literally anything to the point it mans nothing. It doesn't mean anything.
Criticisms of FTL don't come from being a naysayer. We now have more than a century of testing relativity and to date it has made no wrong predictions. So your bar for sayhing it's wrong is really high and the onus is on the advocate for FTL to ay how relativity is wrong and how that can be verified.
You plug -3+2i kg into mass, for example, and say you're not violating Einstein's field equations but you are. You've violated the domain of one or more of the quantities. Now that's fine if you have a theoretical basis for that but there isn't one. It's just hopium.
Likewise, physicists have analyzed the Alcubierre drive and come up with some real and genuine problems like the energy requirements [1].
We’ve done pretty well with quantum theory as well, but when we try to integrate that with general relativity, we get nonsense answers. So at least one of those incredibly accurate, incredibly useful theories is incomplete or wrong in some way.
Dark matter seems to make up about 25% of the universe. It seems to obey general relativity (that’s how we inferred its existence), but not quantum mechanics (we cannot seem to interact with it electromagnetically, e.g. see or feel it).
Something is making distant galaxies accelerate away from us. Taken as an amount of energy, that’s about 70% of the universe. It’s accelerating a lot of mass! Often called dark energy.
This is all to say that despite our success with the physical theories we believe in today… we still have some pretty darn big unanswered questions in front of us. It seems a little early to be definitively ruling things out.
That goes both ways here. “Why can’t we violate causality?” “Because our current theories say you can’t.” BlackBerry execs didn’t believe the iPhone was a real demo based on their extensive practical understanding of phone design and batteries at the time.
Human history if full of Rumsfeld’s “unknown unknowns”.
Agree, but I suspect at that time the opinions regarding the impossibility of flight, though popular, must have been highly uninformed. There were no violations of long established physics to achieve flight, "only" engineering challenges to make it possible.
I still don't see any point in claiming that a given thing can never be done. What does it help? Our knowledge of the universe isn't complete and I don't think people are starving because others are thinking about warp drives.
Kind of a sad reflection of society that this comment is grayed out. In that the person downvoting it was so certain it was wrong, they didn't even stop to consider they might be the one who is wrong - and they are. [1] Galaxies are already moving away from one another at speeds greater than the speed of light. So the speed of light already has at least one asterisk there. In that nothing can be perceived as moving through space at speeds faster than light, but the expansion of the universe can happily send objects drifting apart at speeds well above the speed of light, and accelerating.
It's greyed out because it's FTL by technicality. If FTL had an appropriate name, it would be clear why it doesn't count.
Take a strong laser pointer and point it at one side of the moon. Then flick your wrist to point it at the other side. The laser just "broke the speed of light" but it didn't transfer any information so it's all good.
Well, that would break causality. I believe if we ever learn how to go FTL (improbable!), it'll still force non-causality breaking. Meaning the place where you FTL'd is not your universe anymore.
> . People want to live in Star Trek or Star Wars so want it to be true.
I think it's more than just wanting it: a century of scifi has convinced people that "cheap" (in terms of energy and time dilation) FTL travel does exist and we just have to figure it out, when there's no a priori reason to think so at all. The same with most other aspects of space travel. There's no reason to believe anything recognizably human will be engaging in interstellar space travel, and if it's not human, I personally don't care. I don't feel some sort of religious mandate to invent machines or bioengineered entities to take over the universe. We've really underestimated the power of media programming.
Not even 100 years ago computers could do a few operations per second, today you can put a 100,000,000,000,000 operations per seconds computer in you pocket.
I agree though that Alcubierre drive is probably a dud, no one with serious physics education takes that as a real possibility, there are always some crackpots but seeing the math and looking at the standard model it’s very unlikely such a thing exists. Close to speed of light travel is probably good enough though, people are hung up on the idea humans will take to the stars but that’s just very unlikely. AI on the other hand seems almost plausible with our current technological basis already.
> Not even 100 years ago computers could do a few operations per second, today you can put a 100,000,000,000,000 operations per seconds computer in you pocket.
These computers still obey the same fundamentals though, in fact we’ll reach the Moore limit soon and it’ll take a breakthrough to advance further. Steady progress inside what’s possible is different than the argument of OP about the physics of WD being fundamentally flawed.
Theory of low-dimensional semiconductors and many other theories underlying modern computers were largely incomplete or non-existent 100 years ago, general relativity isn’t that old either and there are substantial gaps in the extremes (e.g. huge masses/curvatures on the quantum scale), there’s definitely stuff lurking there waiting to be discovered. Just because we kno a lot doesn’t mean we know everything, there are ridiculous gaps in our understanding e.g. mass-energy density of the universe, I expect our understanding of the world to fundamentally change again this century, maybe more than once.
Just expanding on a peer comment in a different direction, but no - modern computers are fundamentally different.
Earlier computers used relatively simple vacuum tubes for switches. Imagining billions of these fitting in your pocket, let alone being able to be powered by a tiny battery, would have seemed completely nonsensical. Modern computing required the development of entirely new technology that people had no real reason to think would ever exist. The Golden Age sci-fi got so much right, yet basically nobody predicted miniaturization on anything like the scale we achieved. Because they wanted to remain within the domain hard sci-fi, and not what would have been perceived as fantasy at the time.
I disagree with this definition of "fundamentally different", because nothing in physics stops you from building a computer out of a billion vacuum tubes.
That's very different than requiring negative energy or something never observed.
Interesting question, actually I think building a computer out of vacuum tubes that would rival say an iPhone 15 seems impossible, the waste energy alone would be prohibitive. The Eniac used around 100 W per vacuum tube, for 10^13 tubes that’s 10^15 W, and that’s two orders larger than the global electricity output, and keep in mind you need to deliver that on a small cubic area of your computer and you need to dissipate that heat somehow (a 1 megaton nuke dissipates around 1 MWh of energy, so this computer would have to dissipate the energy equivalent of one billion megaton nukes per hour). Setting off a billion megaton nukes every hour in a small area seems almost as ridiculous to me as converting the entire mass of Saturn into energy. Also signal runtimes and crosstalk would likely make this infeasible as well. So no, you would never be able to scale vacuum tube technology to the current level of semiconductor physics, not even remotely. If you told the Eniac engineers you know how to put 20 billion vacuum tubes in the area the size of a coin and make each of them switch a few billion times per second they would have been quite skeptical I think and relegated you to the realm of science fiction, because the theory of semiconductors and the “exoticly” engineered electron bandgap materials patterned on the scale of a few angstrom you need for them would’ve been largely incomprehensible to them.
You're shifting the goal posts there. We're talking about a device that fits in your pocket, powered by a tiny battery. And, by the knowledge of computing at the time. The amount of energy required to power such a device, let alone the space, would have made the concepts plainly impossible, by the limits of what was known at the time.
That's all true, but fundamentally compute has worked the same way for decades, maybe even 100 years at this point. The scales are orders of magnitude different, but the fundamentals haven't changed much. I believe that's all they were pointing out.
I think we have all plugged v > c into 1 / sqrt (1 - v^2 / c^2) and observed that the math works but aren't clear about what it means. However, I feel our understanding of the universe is not nearly complete. There may be ways to travel > c, we may discover them or we may not.
Forgive me if I get this wrong as I'm exceeding the limits of my physics knowledge here but what you're talking about sounds like what I would call a special relativity model of thinking. The general relativity model is where everything has a constant spacetime velocity vector. So time dilation just expresses that higher velocity through space necessarily lowers time "velocity".
So the special relativity view is to think of a straight line as the shortest distance between two points where the general relativity view is the longest proper time between two events in spacetime.
So if we're just going to talk about velocity through space (rather than a constant spacetime velocity), it's best to think of velocity as a value with domain [0,c] rather than an unbounded real number because that's what we're used to dealing with.
Probably worth mentioning that to date (IIRC) this is the only gravitational wave observed that correlates with an em spectrum event. Which seems super weird.
Yes, I'm suggesting LIGO might be a scam. (The pulsar timing network seems solid, though).
And would you not say that this pessimism is a recurring theme in humanity? In 1903 the NYTimes predicted that human flight would be impossible, that it's been a complete waste of resources to pursue - resources that could be put to much better and realistic use elsewhere, and that it was ultimately a childish fantasy. They had typically great timing as it was only 9 weeks later than the Wright Bros completed their inaugural flight. Then once it was completed they insisted it was pointless anyhow, because it would only ever be possible for but a handful of rich elites to actually utilize.
By 1920 they'd be back boldly claiming that human spaceflight would be impossible. This time with even more scorn, mockery, and appeal to expertise: "That [rocket pioneer Robert] Goddard… does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react — to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools." [2] Everybody with a basic knowledge of Newtonian laws knows you need something to react against to move, and there's nothing in space to react against. What imbeciles to think otherwise!
The problem we face is that it's impossible to meaningfully predict the future when there may yet remain many revolutionary or otherwise unimaginable discoveries yet to be made. In general I see room for extreme optimism because in terms of basic knowledge of the universe we knew next to nothing but a century ago. And we remain a people stranded on a single planet relying on imprecise limited instrumentation, lots of assumptions, and some math to try to figure out what's happening in the other 99.999999999% (one should add quite a few more nines there) of the universe. To assume we've just figured it all out in this century seems improbable, to put it very mildly.
All these people didn't make a prediction based on physics. Of course, it also doesn't help if you misunderstand physics.
Physics will determine a lot of what's actually possible and not possible to build, and there's a lot of things we could build even without FTL. FTL is understood as mostly impossible because it violates causality.
Right. I think many don't really appreciate the famous Einstein quotes many of us are familiar with. When Einstein referred to quantum entanglement as "spooky action at a distance" it was not in the context of describing it, but mocking it. Picture more like him making a face while adding some scare quotes to the quote.
In fact Einstein rejected, to his death, what would come to be seen as the standard/Copenhagen model of quantum mechanics precisely because he refused to accept this apparent violation of causality, to which there remains no clear explanation.
Yes, they were making their predictions based on physics, math, and experimental evidence. One thing you have to keep in mind is that in most cases science tends to follow discovery, rather than vice versa. Here [1] is a random selection of great quotes from the time. If you're not familiar with the names, feel free to Wiki them. It is about as credentialed a list of scientific experts as one might imagine possible:
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Is it not demonstrated that a true flying machine, self-raising, self-sustaining, self-propelling, is physically impossible? — Joseph LeConte, November 1888
It is apparent to me that the possibilities of the aeroplane, which two or three years ago were thought to hold the solution to the [flying machine] problem, have been exhausted, and that we must turn elsewhere. — Thomas Edison, November 1895
I can state flatly that heavier than air flying machines are impossible. — Lord Kelvin, 1895
I have not the smallest molecule of faith in aerial navigation other than ballooning, or of the expectation of good results from any of the trials we heard of. So you will understand that I would not care to be a member of the Aeronautical Society. — Lord Kelvin, 1896
The present generation will not [fly in the next century], and no practical engineer would devote himself to the problem now. — William Worby Beaumont, January 1900
There is no basis for the ardent hopes and positive statements made as to the safe and successful use of the dirigible balloon or flying machine, or both, for commercial transportation or as weapons of war. — George Melville, December 1901
The demonstration that no possible combination of known substances, known forms of machinery and known forms of force, can be united in a practical machine by which men shall fly along distances through the air, seems to the writer as complete as it is possible for the demonstration to be. — Simon Newcomb, 1900
Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible. — Simon Newcomb, 1902
It is complete nonsense to believe flying machines will ever work. — Stanley Mosley, 1905
The aeroplane will never fly. — Lord Haldane, 1907
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I'm sure one can dig up plenty more. Mathematicians and physicists simply thought it impossible. You could have asked the question on stock overflow math/physics of the time and gotten plenty of well informed and accurate (by the standards of the times) explaining exactly why it was impossible. It just so turns out that everybody was wrong, as was about to be demonstrated by a couple of high school drop-out bike shop repairmen. As the article mentions, one noteworthy thing is that the final quote is even after the Wright Bros succeeded. So absurd was the concept to many, that most people still did not believe it happened, even after it did.
Just because they thought it was impossible doesn't mean they actually well reasoned their way using the known physics of the day. All you have are quotes from people who say it's impossible or that they think the problem is too intractable that it won't be done, not actual papers on why they think it's impossible.
The Wright Brothers succeeded, but they also rely on the works of people before them, and observing nature. They were not even the first to achieve powered flight nor the first to study rigorously how the physics of flight works.
Yes, they did. For instance here is the source of the first quote from Joseph Le Conte - a paper from 1888 in Popular Science with him elaborating on why a flying machine would be physically impossible. [1] And indeed his article is in response to another trying to argue for the viability of flying machines, failing, but then holding out some "hopium" (to use the term preferred by our antagonistic poster earlier on in this thread) by appealing to the birds, which Le Conte set out to snuff.
The other quotes are likely to have similarly rich results. It was a widely discussed, debated, and trialed topic. Everybody wanted flying machines, but centuries of practice, science, research, experience, and evidence had demonstrated they were plainly impossible. Until a couple of bicycle mechanics, of no formal education of note, demonstrated otherwise.
Fine. But they are still mistaken in their understanding of physics. Ultimately, physics is what determined what is not possible and possible.
Also, your source provide a figure of 300-400 pounds to be the limit. So clearly, he didn't actually say it's impossible if someone somehow manages to get under the weight limit. The Wright Flyer actually weigh more than that, around 600 to 750 pounds depending on if you include a person, which is in the right order of magnitude. Nonetheless, the author contradict himself by saying it's impossible.
A few points here, which I'm just going to put into bullet points rather than stringing together because they're all mostly completely detached.
- You are misunderstanding their argument. They put 300-400 pounds at the bare minimum for a human flying machine + human, whereas were arguing that they max weight for flight would likely be in the ~50 pound ballpark.
- Can you point to any significant misunderstandings of physics they had? I have quickly skimmed the article multiple time sand have not noticed any.
- Physics does not say what is or is not possible in the world, the characteristics of the world do. Atmospheric pressure, material science, and other factors all have to work together favorably to enable flight. The exact same with spaceflight. If our world was just 50% larger at the same density/composition, it would be impossible for current spaceflight technology to work owing to the tyranny of the rocket equation.
- The most fundamental point here is probably that science is not the alpha and omega. It's our best guess approximation of how the world works, but science always obeys the world - and not vice versa (though good science does make surprising predictions as a means of demonstrating it's a good approximation). So for instance relativity and quantum mechanics are still extremely accurate given all we know, yet simply do not play well together at all - meaning something is definitely wrong.
It's akin to how Newtonian physics works 100% well for nearly everything, yet somehow could not explain the orbit of Mercury. For many decades people thought there was another invisible planet somewhere - heh, dark matter so to speak. Of course it turns out that that "somehow" is because Mercury was close enough to the Sun for observable relativistic factors to start kicking into play and break Newtonian mechanics. As one observes more of the world, and it's seemingly endless oddities, the science changes to keep up.
> But they are still mistaken in their understanding of physics.
So are we. We have significant gaps, and we almost certainly hold some incorrect items as factual at the present time. It's why theoretical physicists still have jobs, and likely will for quite some time.
On HN, comments meant to stimulate optimism and willpower don't tend to get encouraged. Cynicism, skepticism, figuring out how things will fail -- as they inevitably will, of course -- or how if they succeed, they're corrupt or broken in some way...that is increasingly the coin of the realm here. :)
In reality, your sentiment is correct. Sure, there are laws of physics. But they are also unknown, as the ones humans understand don't describe all observed phenomena by a long shot. There are still restrictions even so, but incredible unknowns await us. As they always have.
What engineering-minded folks frequently don't understand is the need to apply sheer old willpower, after using all that intellect. Ending with a positive, with the notion that it can be done; we just have to figure out how.
The unfortunate thing is many people seem to equate cynicism with demonstration of intelligence. While you generally need to be smart to come up with reasons why something might not work, it becomes a lazy way of thinking. Experience in life has taught me that it is far simpler to sit back and poke holes in things than to construct something new.
It also works better for people's egos. Saying and trying things that might end up being wrong means a willingness to not only accept failure, but failure that might end up making you look stupid. By contrast appeal to 'what everybody knows' in a given time and you can never be wrong. Because even when you are wrong it can easily be hand-waved away as, once again, 'well everybody thought...'
Though, thankfully for humanity - not "everybody"!
Indeed! And as a European, I find it even more curious when Americans take this more cynical stance.
I mean, what have we come to, when a European will go and take a risk, for a chance at an awesome discovery, and an American dare not? ;)
The explorers who first went sailed into the deep Atlantic, with unknown seas and lands beyond, were full of doubts too -- but they did it anyway. Because they had to. In our time, we humans have to continually rekindle our explorer spirit, no matter how settled or distraught our ambient culture becomes. We must explore, with optimism and willpower -- and yes, with plenty of intellect and skepticism too, but end with optimism -- precisely in order to solve the actual problems our world faces.
If things were so fragile that accidents could be heard from here potentially at millions of light years away, it would be the kind of feature that could uninvent itself destroying the civilizations using it and the ones close enough to them. A good enough alternative explanation of the Fermi paradox or a reason for having a dark forest universe.
Reminder that life can also make interstellar travel thinkable by slowing down - four years (or four thousand years) seem like a long time because our lifespans are short and we think fast. If we were tree-like, or immortal, our timescales would change.
Also a reminder that no time passes for a photon when it crosses the universe. i.e. to the people on a ship approaching light speed, not much time passes as they reach their destination. And less time passes the closer they get to light speed.
Yet to detect is LIGO has to be unbelievably sensitive. I've heard it described as measuring the distance to Alpha Centauri with the variation of the width of a human hair.
I still don't believe warp drives (in this case Alcubierre drive [1] isn't viable. It's an exercise in hopium. People want to live in Star Trek or Star Wars so want it to be true. It's an object lesson in not understanding the domain of a function. Warp drive concepts rely on concepts like negative mass and/or energy. I can plug negative (or even complex) numbers into quantities like velocity or acceleration but again I've just violated the function domain even though various formulas will spit out (nonsencial) values. Garbage in, garbage out.
But let's just say this is possible (which, again, IMHO it isn't), then we get to the energy budget required for any of these FTL concepts. The amount of energy to reach even our nearest stellar neighbour is mind-bogglingly large. Some estimates I've seen for various warp drive concepts involve things like 1 Solar mass of energy.
[1]: https://en.wikipedia.org/wiki/Alcubierre_drive
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