And the fundamental physics problem is indeed interesting. If you are unfamiliar with this physics brain-teaser, I highly suggest watching this excellent video by Veritasium to introduce the topic.
I'll summarize the main points that are relevant to my further analysis on the nature of the debate. Spoiler warning for people who like to work through physics problems by themselves.
- Verdict: yes it is possible.
- This is both theoretically sound and empirically tested.
- A common objection is that it seems to violate conservation of energy. It does not; the vehicle increases its kinetic energy by extracting energy from the media it's in contact with. In this specific case the Blackbird vehicle pushes on the air behind it, so the speed of the wind behind it is ever-so-slightly lower than it otherwise would be. It's extracting kinetic energy from the air (i.e. the wind).
- While there is "Conservation of Energy", there is no such thing as "Conservation of Speed". Gear ratios and levers clearly violate any would-be "Conservation of Speed". Velocity of the input does not need to equal velocity of the output; only the total energy exchanged must be equal.
- Owing to the above, this phenomenon actually does not require any aerodynamic or fluid dynamic effects. In a later video (see below) the same principle is used to build a wheeled vehicle that moves between two solid surfaces.
- In fact, with a vehicle that has some sort of contact to two media moving relative to each other, it is theoretically possible to achieve any speed in Newtonian physics (before considering energy loss to inefficiency, and uh...relativistic limits in the real world)
- The word "media" used above is important: media here implies a part of the environment that is much bigger than the vehicle. Thus, the effects of the vehicle back on the medium is negligible. Infinite speed in the previous point shouldn't be surprising as we have an infinite source of energy in our toy model. After all, we are imagining an infinite column of air moving over an infinite stretch of ground, indefinitely. This is NOT a simple closed system.
And here is the follow-up video by Veritasium, chronicling the events after a physics professor watched that previous video and decided to bet $10,000 against the authenticity of the Blackbird claims, with Bill Nye (the Science Guy), Neil deGrasse Tyson and Sean Carroll as witnesses. You should probably watch this one too, since I'll be using some of the content in there as examples of the debate participants' psychology.
In the end, the professor conceded he was wrong.
So what went wrong for the professor? And he was but one of the many people on that side of the argument: why did so many others think the same way? These people are not the usual suspects for being wrong: just in that video alone we see the UCLA professor, Bill Nye, and the friends of Derek (the host of Veritasium) all siding against the authenticity of the Blackbird results. They are not trolls or common lay-persons who might have been too easily over-confident, though I'd say they were indeed over-confident. What made them over-confident?
For brevity, I'm going to call people who argue that "the proposed mechanics of the Blackbird are authentic" as "Believers", and the people who oppose that as "Non-believers".
I think the reason this issue is so hotly debated is because there are so many red-herrings, false lines of reasoning that may seem convincing. The presence of fluid dynamics (air in this case) seems to lead to a common pitfall where Blackbird Believers tend to look directly into aerodynamics as an explanation for the Blackbird's motion. Oftentimes this leads to the Believer actually getting aerodynamics wrong, because aerodynamics is complicated, and results in a fake explanation of the phenomenon.
Thus on the other side you'll have people debunking the mistaken explanations, thinking that it debunks the faster-than-wind vehicle. Of course, the vehicle still works regardless of the bad explanations. You can see an example of this entangled thinking in the way the UCLA professor focused on vertical wind gradient, when the focus should have been elsewhere. Thinking that the Believers didn't consider the wind gradient made the professor more confident than he should have been. He thought he identified where the Believers got tricked. But in fact that was not the reason they believed in the Blackbird.
Combined with the wind gradient, the professor also posited that there were perhaps wind-gusts. The tell-tale signs of bias are strong here. The professor presents a graph of [vehicle speed and wind speed vs time] that he literally made up, because he thought the wind-gusts must have caused the "anomaly". But in fact we have actual telemetric data from the Blackbird tests, and they disprove this (if the data is to be believed). When presented with these the professor simply did not believe that the data was authentic. I mean, yes I would also doubt data that came from sources that I thought were crackpots, but I don't know if I should trust my own made-up data any more than that. I mean at best, they are both fake numbers pulled out of nowhere. Why would mine be better? I hope a less biased person would have alarm-bells ringing in their head whenever they begin to draw made-up and totally fictional graphs for a presentation to try to convince someone.
Then the professor's bias took him even farther in the wrong direction. To explain the apparent successful treadmill tests, the professor invoked "unconscious human bias", meaning that he thought some subtle movements of the human hand holding the test vehicle could have produced the strongly observed results.
See a pattern yet? The professor is basically looking around for any possible alternate explanations for the observed result. He puts them together and makes the argument that all of these effects added up together should cumulatively be enough to explain the observations, and thus the Believers' explanation must be wrong. The idea of this is...not bad, but it would really need more testing to discriminate between the alternative hypotheses, which the professor crucially does not do! I think this is where we see that his own biases got the better of him. Merely positing an alternate hypothesis is not disproving the other hypothesis!
One should not become so confident against the original hypothesis, merely by thinking an alternate hypothesis into existence. That is bad epistemology.
And in this specific case, the degree of reality-stretching in all these alternate hypotheses should seem obviously desperate. The treadmill videos seem quite clearly to have a strong force that is not likely to come from subtle pushes of the hand. The wind-gust hypothesis also stretches disbelief, to the point where deGrasse questions the believability that no one noticed that the wind speed suddenly dropped by a factor of 3. The professor responded by invoking selection bias. But the vehicle operator testified that the Blackbird maintained the speed differential with the wind for about 30 seconds. And the big drop in wind speed would have been so obvious that all the witnesses recording the data would have to conspire to pretend not to see it. It isn't merely a matter of selection bias.
And that's one of the pitfalls of learning about cognitive biases. If you are not careful, it allows you to do Motivated Skepticism. If you only suspect others of being biased when they disagree with you, you're just setting up a bias for yourself, and worse, make yourself even more over-confident than you otherwise would have been without learning the concept of biases.
Misusing knowledge of human biases can lead to shooting yourself in the foot. And unfortunately, in this story we saw Bill Nye shoot himself in the foot when he bought the UCLA professor's argument wayyyyy too easily, and also concluded that the Blackbird Believers must have been "fooling themselves". Unfortunately Bill, the ones fooling themselves have been you and the prof, thinking that the others have been fooling themselves! This is how dangerous selective skepticism is.
So how do we cut through the biases and convince the other side to give us $10,000? Veritasium shows us how at 14:17 in the video. Also see this video which Veritasium references.
I think Veritasium's choice of demonstrating with the moving wooden-board is absolutely ingenious. It cuts through the Gordian Knot of the debate by taking all the complexities and misdirections out. Various things that people argued about, including lift, drag, pressure, human error, fluctuations in media and standing waves, suddenly all no longer mattered, because we see a vehicle with virtually no-slip contact with the ground and a moving board. And gears are intuitive enough for people to understand. They might not trust math equations, and to be fair it is likely that the equations missed a term here or there when presented by their proponents on either side, but the wheels-and-board demonstration removes that uncertainty.
Now with the benefit of hindsight, all those detailed alternate hypotheses the professor focused on earlier seem like excuses, no? Now there's no reason to suspect that the Blackbird telemetry data was fake, or that everyone present missed the big gust of wind, because even the professor says that going faster than wind is clearly possible from the equations. Now there's also no need to invoke that the human testing the model on the treadmill is somehow subconsciously pushing it forward.
In hindsight, the professor clearly put too much weight on his ability to find flaws in the Believers' experimental conditions, and not enough weight on the possibility that he had overlooked something himself. And really, I'm just using the professor as an example, because this isn't about chastising him, it's about how this pattern of thought is so pervasive in this debate and this class of debates in general. If you read some of the internet comments on this topic, you'll see that both Believers and Non-believers make many of the mistakes mentioned here. And that is exactly why this topic is so contentious. Anyone interested in seeking truth would benefit from thinking about which other debates the points raised here might apply to.