If they are successful, you can expect to have an accessible (ie, couple thousand dollars) brain-computer interface covering a tiny portion of your brain sometime in the 2030s. New knowledge would necessarily need new connections between between neurons, ie you have to grow and connect neurons in a very particular and intricate pattern. I think we're still at the "just barely trying to understand wtf is going on" stage.
If you'd like a more in-depth intro to the state of the art, Jeff Lichtman's work on connectomics is a great place to start. Here's a 3-part lecture: https://www.youtube.com/watch?v=MtTOg0mzRJc
You can skip ahead to part 3, where he describes the absolute state of the art machine they are building which will be able to map the structure of a tiny slice of brain <1mm^3 part of a brain using advanced optics, robotics and machine learning. It's quite humbling.
The easiest reply would be "They are called books", or whatever container and format for information - and already there issues and risks are more than just possible, mitigated by filters one is trained to develop. The more acquisition of information takes the aspect of an "injection", a whole world of issues open.
From "I read War and Peace in one hour: it was about Russia", to all kind of mental poison (from "bad" notions to concretions of intellectual inadequacies): information has to be digested - processed and integrated.
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So, on the point of view of feasibility: if knowledge implies diffused transformations (as opposed e.g. to installing an independent informatic file, non-integrated with its peers), that idea of injecting knowledge is absurd - it does not work that way. When you come to know that Paris is in that location, in that position on the map, you modify a number of notions: some directly related to Paris, others of all related entities - of the idea of France and its layout, of Montparnasse, of the Second World War, of the treaties there signed etc. Information needs to be digested to be productive.
On a different note, the new Matrix really failed to captivate and imagine like the old movie series did.
The best practical way to achieve your end? Reform education. We are forced to learn so much useless, outdated, opinionated information in the 20 years of mental training we call education. Let people begin apprenticeships very early on, let them try actual jobs and tasks, not just tests.
A low tech noninvasive way? Phones. If our phones downloaded all the data they needed, theoretically they could make our decisions for us. We'd never need to know things as long as the phone can communicate precisely what to do, without the costly why.
Obviously, I wouldn't sign up for the latter unless it became necessary to stay relevant. I don't like the privacy and freedom implications of a device with all the "right answers".
There will be market forces to put there more than just the intended knowledge you want. And probably it won't be so easy to debug or clean as with plain text.
Probably something that the brain does very early in life, like around infancy, is to figure out for itself a way to store knowledge and learn how to store new things that it learns in that way. If each one makes it all up for itself, then it stands to reason that they're all different in unpredictable ways. The observed fact that people vary widely in overall intelligence, what they're good and bad at learning, and how they learn it, seems to follow naturally from that.
Remember that in the Matrix story, a world in which they could download skills from the simulation and instantly become things by essentially just imagining them, so long as they stayed within its confines - was the world they were trying to escape. If you tell a 5yr old that their crayon drawing is beautiful, they become an artist, and for most people, that pattern doesn't change for the rest of their lives unless they become disillusioned and pursue their destiny as an existential hero.
Maybe there could be some neural interface that lets you transmit and replay brain activity through other bodies faster than language does now, or muscular electrostimulation that simulates say, deadlifting, but just as having a music collection doesn't make you a musician, I'm with Feynman in that I don't think we understand what we don't ourselves create.
As a start, what "data format" would that downloadable knowledge be represented in? It would have to be interpretable by your brain and able to reference knowledge and other concepts you already know about - not just explicit knowledge, but also motor memories, etc. Unfortunately, all this stuff depends heavily on the experiences and learnings you personally have made until this point - so this is probably completely unique for every brain.
We know our bodies age and die whereas sustaining a computer for 100s of years via a part replacements is quite doable.
How quickly we forget, https://www.youtube.com/watch?v=Bg21M2zwG9Q
But I have seen nothing remotely approaching this idea of being able to download into the brain.
The TL;DR is yes but its insanely hard and we're decades away from knowing how to do this (if not longer). We still lack the technologies to interface with individual neurons. We're good at reading from a handful of neurons, we very good are reading from a population of neurons.
When it comes to writing there are a number of problems that need to be solved.
First we haven't cracked the "neural code". We don't have a unified theory of how information is represented across the brain. We do have some idea of what individual brain region are doing but the codes used by each region can be wildly different. I'm not as caught up on my neuro literature as I would like but its completely possible their isn't a unified code and therefore we'll need to learn how each specific neural population encodes information. The software analogy here is we're trying to reverse engineer a system running in product without the source code and each module was written in a different programming language that we've never encountered before.
Second we do not have mechanisms to write to individual neurons at the population level. The best we can do is akin to blasting a loud speaker at a crowd of people. We can push around the population but we cannot do much more than that. Software analogy here, what we can do its more akin to Steve Balmer yelling "Developers, developers, developers" than a class room instructor teaching students python. Opto-genetics is a potential path forward here but it requires controlling the genome of an individual and really only lets you target specific neural populations rather than any neuron in the brain.
Third, we still do not understand where the memories or information live exactly. We know what brain regions are involved but we're a long ways away from truly understanding how long term information is consolidated to the cortex from the hippocampus and other structures.
Finally, lets assume we know how to do all of the above (in rodents). Translating the science to humans is going to be a Herculean task for a bunch of reasons. Some of these reasons are scientific while others are ethical. The immune system of the human brain is more aggressive than in other animals and tends to reject implants more quickly. Next finding human test subjects is akin to sending someone to Mars. You're putting their life at risk and there's not true way for them to come back. Nearly all of the human subjects in studies that required invasive brain surgery were suffering from medical conditions so severe that the risk of the condition was greater than surgery and the research was piggy-backed on top of a planned medical intervention.
As compelling as that tech would be, the risks are crazy!
As far as I'm aware, all of the current work on brain-computer interfaces are focused on output, interpreting electrical signals from the brain either to control external devices or perform some extremely simplistic form of "mind reading." I don't believe anyone is working on input.
That said, there is no reason in principle it can't be done, but there are additional challenges in that encoding knowledge in the brain involves changing neural architecture, and doing that via attached mechanical device is risky. The closest to this we've ever achieved is electroconvulsive shock therapy to try and treat certain types of psychiatric disorders, which is controversial at least. I have no idea how effective. We don't currently have the means to do this at any finer granularity level and we wouldn't know what we're doing anyway because we don't know in any general way how knowledge gets encoded in the brain (and for athletic activities like kung fu, the entire CNS, not just the brain).
I can imagine at least a line of research where we attach extremely good internal sensors to a person's entire CNS and observe what happens when they train. If it looks sufficiently similar on all test subjects, you can possibly assume what you're seeing is a pattern of electrical activity that amounts to "learning kung fu" and then try to induce that via mechanical device rather than actual training.
Even if this works, however, you're limited by a few factors. One, if you've ever done any serious athletic training, you'll know it can actually fry your CNS, not just cause muscle soreness. Your CNS does need time to recover from learning activity. So you can't just upload kung fu instantly, or in the span of hours like they do in the Matrix. The human CNS can't actually handle that level of continuous input and needs rest and recovery.
Let's grant you can still learn faster than by actually training. In The Matrix, they're only ever performing kung fu in a simulation, not in physical reality, so their level of physical fitness doesn't matter. Performing real kung fu takes more than just knowing kung fu. You need to be sufficiently physically fit, in terms of strength, endurance, aerobic capacity, flexibility, everything it takes.
I can imagine a future where, given these limitations, maybe time to mastery can be decreased from 20 years to 2 years, but I don't see it ever being possible to become a kung fu master in a matter of hours like in The Matrix. At least one major difference between brains and hard drives is brains can only have knowledge encoding gradually changed. We need repetition to learn. It isn't possible to just erase a file and write a new one. There are no files. And the rate at which it is possible to learn is inherently limited by biochemical realities. "Electrical signaling" in the brain involves ion channels opening and closing, physical molecules moving around. It's an energy consuming process and it wears down the cellular machinery that then needs to be repaired by producing and emplacing new proteins to replace broken down. These same things are true of silicon microchips, but there are major differences in that you can just keep it plugged in and give a continuing energy source. Humans need to eat, digest, excrete waste, all of which take longer. CPUs can be much more easily and quickly cooled. Some rigs just blast them with liquid nitrogen, which you definitely can't do to a brain. And they can be replaced. You don't need to rebuild them in-place at the molecular level. You can just keep a fresh stock of excess chips, and when one burns out, replace it. When a hard drive fails, you have backups of the file and write them to a fresh hard drive. You can't do that to a brain. You have to let it recover and rebuild itself in-place.