The devices we call "lie-detectors", are a joke. They measure only physiological signs, and are easily fooled. It is for good reason that they are not accepted as evidence in court.
But will this always be the case?
There have already been attempts to detect lies using a brain scanner, and even in its infant stages this technology has already beaten polygraph tests.
Imagine what the technology might look like in a few decades if people keep working on it: A brain scanner that is both small, accurate and cheap enough to be usable in everyday life, combined with a better understanding of how the brain works as we gain more experience, operated by people who have been steadily improving their craft for decades, and who unlike polygraph testers actually have a proper scientific basis.
Given enough time for the technology to mature, it is possible in principle to detect any kind of lie or deception. Just the simple fact that we are able to differentiate our own lies from reality means that the brain must contain some kind of pattern that activates when we lie. We don't yet know how hard it will be to detect this pattern, but it surely must exist and the technology to detect it will arise eventually.
The impact of such a technology on all aspects of life would be enormous.
Lie-detectors will likely only improve gradually in quality. Brains are complicated, so we can't expect to get everything right immediately.
Giving a timeline here would be pointless, since it depends too heavily on how much time and money is spent on research, and that might rise dramatically once powerful people catch on to how useful this technology would be to them. I expect the order of development will likely look like this, though:
Difficult to use, only sometimes reliable
We need a detailed brain scanner, which is a large machine, and experts to interpret results. The experts don't always agree with each other.
Difficult to use, always reliable
We have found a way to interpret results so that we can be sure that they are accurate. It still takes experts to perform the test and evaluate results.
Easy to use, always reliable
The brain scanner is small enough to be carried around, and the evaluation can be done automatically, without the need for expert oversight except in difficult cases.
Altering a brain is possible
This is no longer just lie-detection, but a more advanced technology based on it. By artificially exciting precisely targeted neurons, the behavior of a person can be altered. Psychological disorders can be cured, and low levels of mind control become possible. I'm not going to talk about this here, because it deserves its own article, but it's worth keeping in mind that this is a simple extension of the technology.
The early stages of developing lie detectors will have uses in specific situations, while the later ones could easily revolutionize society as we know it.
The economic impact of this technology is massive and can act as a catalyst that causes lie-detectors to be developed and adopted in other areas of life more quickly.
Imagine you are a very rich shareholder in a large company. You hire a CEO with the world's best accolades who has undergone an extensive vetting process. You pay him many millions of dollars to do his job. You can only hope that trust is not misplaced.
Imagine how much you would be willing to pay to get a truthful answer to the following questions from that CEO:
"Did you lie about any part of your interview process?"
"Are you planning to make this company great, or is this just a stepping stone for you to get richer?"
"Did you hire that friend/relative of yours because you actually believe he is the most suited for the job, or because of personal reasons?"
"Did you decide to make that business deal because you think it is best for the company, or because it will look good on your resume?"
(Note that some of these questions may not work with a lie detector because they are too abstract. In practice, you would need to find a couple dozen concrete examples for each question and ask those instead.)
Just by asking these questions, you do more to ensure effective leadership for your company than any amount of vetting and personal recommendations ever could.
Any company that employs a working lie-detector test on its employees will be highly resistant to corruption. Any time you suspect that an employee is motivated by something other than what they should be motivated by, you can simply use the lie-detector to check.
So long as lie-detectors are difficult to use and not fully reliable, this will only be worth the effort on upper management. Once the technology is more mature, it could be worth using on virtually every employee.
Companies could institute a policy that every employee has to undergo routine interrogations to verify that they are not corrupt, are not breaking the law, and that managers are not playing favorites with other employees.
Think about how much time and effort people spend every day at work not getting things done, but signalling to others that they are important, or playing politics, or just slacking off when nobody is watching. All of this could be heavily reduced by routine lie-detector tests. Imagine the boon this would be to the economy.
Would this be a gross violation of privacy? Absolutely. Would it happen anyway? I'm pretty sure it will. Capitalism is a powerful force.
Capitalism will cause this technology to be adopted by companies very quickly if it is not declared illegal. Once it has been adopted there, it is only a matter of time until the government gets involved, too.
The Legal System
As a first step, lie-detectors could become admissible as evidence in court. Why shouldn't they be, once they are proven to work?
The impact of that alone would already be massive, but it doesn't stop there:
Assuming that you really have working lie-detectors that work all the time, can't you just ask people if they have broken any laws? If a murder trial can be resolved by just asking "did you do it?" and waiting for a response, what would that do to the justice system?
Better yet, if lie-detectors become easy enough to use, couldn't you use them pre-emptively? Just ask everybody once a month if they have broken any laws.
On the one hand, if any crime can be uncovered with trivial ease, crime really does not pay and the crime rate would go down drastically.
On the other hand, many of our existing laws were designed with the expectation of only sometimes being enforced. Virtually everyone breaks minor laws as a routine occurrence every day, such as speeding or jailwalking. If you make it possible to detect each such minor transgression but don't also lower the fines for them, the end result would be catastrophic.
Politics
Imagine that it was common practice that politicians had to use a lie-detector while making campaign promises.
Politicians are infamous for lying all the time, so what would happen if you took away their ability to do so?
What if you asked every politician "are you only saying that because it sounds good, or do you actually believe it?"
What if you asked "are you doing this for personal power, or are you actually trying to make life better for the people?"
What would happen if, for the first time in human history, people were actually able to trust that their leaders genuinely do have their best interests at heart?
How would society react to all of these changes?
Many of these changes would be unequivocally good, but others are terrible.
Would adopting lie-detection technology lead to a totalitarian police-state? It very well could. But it could also lead to a stable and benevolent government instead. It can lead to either a utopia or a dystopia. The one important thing to note is that, whatever political system ends up dominant when lie-detection technology becomes widespread, that system will become almost impossible to change from the inside:
If you have an evil dictator, then that dictator can routinely ask people if they are loyal to him using a lie-detector, and execute everyone who isn't.
Likewise, if you have a utopian society with benevolent leadership, the leaders can institute a policy of asking some screening questions of any aspiring leaders. These screening questions make it impossible for any egoists and sociopaths to become powerful, thereby keeping the leadership benevolent.
Since both the utopian scenario and the dystopian scenario are stable and can't be changed from the inside, it is absolutely crucial that we deal with this technology correctly the first time, because we won't get a second chance and will be stuck with whatever political system we end up with.
The transition between our current political system and this hypothetical future system would be very complicated and full of problems.
Society essentially suffers from two problems that any political system needs to deal with: Stupidty and Misaligned Goals.
Democracy handles stupidity through elections (with mixed success) and handles Misaligned Goals through a system of checks and balances.
A society that makes thorough use of lie-detectors would handle both problems very differently, and thus the transition would be very difficult: Misaligned goals are very effectively handled by lie-detectors, while stupidity would be most efficiently handled not by elections but by expert consensus.
To give an example where the transition would be difficult: The idea that you could lose a lot of privacy through the use of this technology is terrifying to many people. Being concerned about privacy makes sense in a society where lots of powerful people could do who-knows-what with your information. However, this concern isn't very sensible in a society where lie-detectors can ensure that this data is only used for purposes that are beneficial to society.
One basic thing to take away is this: If lie-detectors become available in the future, that means you shouldn't be doing anything now that you wouldn't want people to find out then.
Once developed, the technology is going to be used sooner or later anyway. There are too many reasons why people would want to use it. Attempting to work against that would be futile. Even if we succeeded with a ban, any countries that do not ban the technology would quickly overtake us economically due to the enormous economic boosts you can get from reducing office politics and increasing trust in managers.
Instead, we should make sure to educate people on the benefits and risks and make sure that this technology gets developed in a positive way. We must think of ways to regulate its use effectively, to guide us towards the utopian vision instead of the dystopian one.