[00:00] Sending messages into the past just got easier.&nbsp; Or, as the headlines put it “We have figured out&nbsp;&nbsp; a new way to send messages into the past”&nbsp; and “Physicists Say It’s Possible to Send&nbsp;&nbsp;
[00:12] Messages Backward in Time”. Even more&nbsp; amazing, these headlines are based on&nbsp;&nbsp; a paper published in PRL, the top journal&nbsp; in the field. As you’ve guessed correctly,&nbsp;&nbsp; no one’s yet figured out how to actually send&nbsp; messages into the past, this is a theoretical&nbsp;&nbsp;
[00:29] study. But it’s quite interesting indeed, and no&nbsp; it does not involve a DeLorean, a time fairy, or a&nbsp;&nbsp; black hole behind a bookshelf. It just requires a&nbsp; little bit of quantum physics. Let’s have a look.
[00:42] Quantum physics has an uneasy relation&nbsp; with causality. This is because once&nbsp;&nbsp; you accept that particles can do&nbsp; multiple things at the same time,&nbsp;&nbsp; and factor in that Einstein tells us there&nbsp; is no objective way to tell what happens at&nbsp;&nbsp;
[00:57] the same time, then quantum mechanics also&nbsp; tells you that generally you can’t tell what&nbsp;&nbsp; happened in which order. Causality becomes&nbsp; as uncertain as the rest of quantum physics.&nbsp; And of course the first question you might have&nbsp; is: can I make money with it? Who wouldn’t want&nbsp;&nbsp;
[01:14] to tell their younger self to buy Nvidia stocks&nbsp; without having to grow a wormhole in the basement! The new paper is a continuation of an earlier&nbsp; work. It comes from an MIT group and the scenario&nbsp;&nbsp;
[01:27] they look at is loosely speaking this. You&nbsp; have a receiver device that you have built at&nbsp;&nbsp; some time and that is ready to receive messages&nbsp; from the future. Before you build the device,&nbsp;&nbsp; you can’t get any messages. Then you have&nbsp; a special quantum state that you prepare&nbsp;&nbsp;
[01:44] and you let it do its quantum thing. And&nbsp; once the quantum state has done its thing,&nbsp;&nbsp; there is a sender who measures the quantum&nbsp; state and that, so the idea injects&nbsp;&nbsp; information in the message receiver in the past. In the new paper they show that this still works&nbsp;&nbsp;
[02:01] if there is noise in this communication channel.&nbsp; Amazingly enough, if you want to send messages&nbsp;&nbsp; into the past, the noise is less of a problem&nbsp; than if you want to send it into the future.
[02:13] referring to a future work from 1985&nbsp; co-authored by E L Brown and M McFly. Ok, but leaving aside the noise, just what do they&nbsp; say we must do to send messages into the past?&nbsp;&nbsp;
[02:32] They are using what is called “postselection”.&nbsp; This basically means that after you have done&nbsp;&nbsp; the measurement of the quantum state,&nbsp; you only look at specific outcomes. You see, in quantum physics we cannot&nbsp; normally predict the outcome of the&nbsp;&nbsp;
[02:48] experiment. But they postulate that we&nbsp; basically live in a universe with only&nbsp;&nbsp; one outcome. And then the message that you get&nbsp; in the past is… the outcome which will happen.
[03:00] Ok, but wait, how is this not just making a&nbsp; prediction? Well, to me this is the key point&nbsp;&nbsp; of the paper: in general you can’t tell these&nbsp; two things apart. Forget the quantum stuff for&nbsp;&nbsp;
[03:14] a moment, imagine that you just sit there with&nbsp; your device that can receive messages from the&nbsp;&nbsp; future… or so you think. It has a screen and&nbsp; noise flickers on the screen most of the time,&nbsp;&nbsp; then suddenly it says “BUY NVIDIA”. You go&nbsp; buy Nvidia and a year later you’re rich.&nbsp;&nbsp;
[03:29] But did you get a message from the&nbsp; future or is your machine just good&nbsp;&nbsp; at predicting the stock market? There is&nbsp; no way to tell these two things apart. I don’t know about you, but if I had such&nbsp; a device I wouldn’t care. Physicists could&nbsp;&nbsp;
[03:43] discuss until the end of time whether&nbsp; it really does receive messages from the&nbsp;&nbsp; future or whether it’s just crazy good at making&nbsp; predictions. I'll be sitting at the pool, cheers.&nbsp; That said, in today’s reality we&nbsp; can’t predict the outcome of quantum&nbsp;&nbsp;
[03:59] measurements and post-selection isn’t&nbsp; something you can magically enforce on&nbsp;&nbsp; our universe. This means that for practical&nbsp; purposes their device works more like this: Suppose I set up an X-twitter account and post&nbsp; a hundred thousand messages predicting the next&nbsp;&nbsp;
[04:17] major LA earthquake for any possible day until&nbsp; 2100. Then, once it happens, I delete all messages&nbsp;&nbsp; but one, celebrate the correct prediction&nbsp; and claim that it was given to me by a time&nbsp;&nbsp;
[04:32] traveller. Works on X, doesn’t work in reality. So I have to give this paper a 8 out of 10 on&nbsp;&nbsp; the bullshit meter. The maths works out, but their&nbsp; interpretation is highly questionable. That said,&nbsp;&nbsp;
[04:45] the real story here isn’t that physicists have&nbsp; invented a working telephone to yesterday.&nbsp;&nbsp; The story is that physicists are slowly&nbsp; rethinking temporal relations which I&nbsp;&nbsp;
[04:57] think are much more complicated than the&nbsp; simple cause-effect idea that we’re used to. I promise I’ll have a word with my past&nbsp; self about questionable hairstyle choices.
[05:11] I am very protective of my privacy, but it's&nbsp; become incredibly difficult online when there&nbsp;&nbsp; are a dozen companies tracking you each time&nbsp; you open a website. That's why I'm signed up&nbsp;&nbsp;
[05:23] to Incogni. Incogni is a service that keeps your&nbsp; personal data out of the hands of data brokers.&nbsp;&nbsp; These are companies which collect data about you&nbsp; each time you visit a website and when you fill&nbsp;&nbsp;
[05:35] in information. Then they sell this information&nbsp; off. You can request that they remove your data,&nbsp;&nbsp; but this is incredibly time-consuming. Incogni&nbsp; automates this process. It's very simple. You&nbsp;&nbsp;
[05:48] sign up and they'll contact the big sinners,&nbsp; request that your personal details be removed.&nbsp;&nbsp; They also now have a new custom removal feature&nbsp; where you can submit specific websites. If you&nbsp;&nbsp;
[06:01] use my code SABINE or the custom link in the&nbsp; info below, you'll get 60% off of Incogni,&nbsp;&nbsp; which isn't expensive in the first&nbsp; place. That's an amazing deal. So,&nbsp;&nbsp;
[06:13] go and check this out. Thanks&nbsp; for watching. See you tomorrow.